Notes on GSM

Network Overview

From a customer perpective, there are really only 2 parts to the GSM network, a cell phone and the "other end". The GSM standard defines much more than that. The high level description of the network is as follows, starting from your end.

1. Mobile Station - Your phone. It's a wireless telephone and a data terminal which can send and recieve messages from the network.

2. Base Transceiver Station (BTS) - the stuff that interfaces directly with your phone. This consists of fixed location transmitters and recievers for the cell which it is in charge of. Different radio types are used for different things, such as subscriber-to-network and network-to-subscriber, different data types, and signaling. This is "the tower" in your backyard.

3. Base Station Controller (BSC) - handles 1 or more BTS. Gateways to the network.

4. Mobile Switching Centers (MSC) connect the GSM network to the public switched telephone networks. Also provide a way to access the databases for who's where and who can do what.

5. Home Locator Register (HLR) and Authentication Center (AUC) - the databases. These things have stuff for users on the network, guests/visitors on the network, subscriber information - particularly profile.

Permananent user info is in the KLR, and the VLR stores temporary info about a mobile phone.

6. PSTN/ISDN - The switched network backbones.

Signals and RF Stuff

Overview

GSM uses Frequency Division Multiplexing AND Time Division Multiplexing. FDMA divides the frequency ranges for GSM, which are 890-915, 935-960 and some others that the book didn't have. Each is divided into 200kHz wide channels. As far as TDMA goes, each time slot is 577 micro seconds long, 8 time slices is a frame, lasting for a grand total of 4.615ms. A multiframe consists of 51 frames, 51 multiframes make up a Superframe, and 2048 Superframes make a Hyperframe which is 2715648 frames.

RF Specifics

Parameter ValueDownstream Frequencies 935-960MHz, 1805-1880MHzUpstream Frequency 890-915MHz, 1710-1785MHzChannel Spacing 200kHzDuplex Spacing 45MHzRadio Power 13-39dBm, 2dB stepsData Rise/Fall Time 28 microsecondsEmissions < -36dBmPhase Error 5 deg RMSFreq Error 95HzRecv Sensitivity 104dBmCo-channel Rejection 96dBm below signalIntermodulation Rejection 100dBm below signalSignal Blocking Level 100dBm

Packets and data

During a single time slot is your phone transmitting, and the contents of the time slot is called a packet. Packets are made of bits, and bits are made of magic.

A packet can be 4 different things: random access burst - shorter than the normal burst. synchronization burst - same length as the normal

burst but a different structure normal burst - carries speech or data information. lasts

approximately 0.577 ms and has a length of 156.25 bits

frequency correction burst - same length as the normal burst but a different structure

Each type has a different packet structure, and is visible here:

The Network Subsystem

The main component here is the MSC. The MSC contains the Home Locator Register (HLR), Visitor Locator Register (VLR), and Authentication Center (AUC). These are the most interesting non-RF related parts of the system back end.

HLR

The HLR contains a lot of interesting information. The HLR is responsible for subscription details, and supplementary services. It also maintains information on the last know location and status of a particular phone.Since a user can use any phone with his or her SIM card, there's a protocol necessary to manage accessing the network. Information contained on the SIM card is transmitted to the HLR to verify the identity of the subscriber. Location and status are continually updated in the HLR based on the base station reports and cell phone status. Any messages to be sent to the subscriber are queued in the HLR. All call setup queries ask the HLR for information before doing anything else.

VLR

Like the HLR, the VLR keeps track of users but only within the area thet the VLR is assigned. The VLR communicates with the HLR to figure out where to route calls, and to keep track of peple as they move around.

AUC

The AUC is basically just a database full onf confidential subscriber information attached to the back of the HLR. Its

located in a "secure place" and the data is stored in "coded" form (sounds like encryption to me). The AUC is responsible for controlling the rights of usage of the network services, i.e. phone calls, data, internet, etc... The AUC allows the Network Operator (Cingular, AT&T) to know "unambiguiusly" who is on the network for billing purposes. The AUC also protects the user from fraud (somehow ...) and contains the secret information necessary to handle authentication and encryption.

Authentication with the network

Authentication on the network works as follows. First the mobile terminal is asked to perform a computation on a random number supplied by the system using a secret key stored on the SIM card. The system does this calculation internally, and compares the outputs. Both the algorithm and key are stored in secure formats.More detailed authentication ... When a terminal connects to the network, a RNG gives it a number N which is encrypted with a secret personal key Kp. The resulting number is encrypted with an algorithm called A3 and transmitted back to the network and compared. The subscriber then generates a session key for encrpytion using the algorithm A8. The encryption algorithm A5 is used to encrypt each packet.After the subscriber is verified, the encryption of radio packets is handled by a different algorithm, called A5 (A3 is used during subscriber verification). The encryption key is supplied during authentication, using some key agreement scheme and each packet is also encrypted using

a changing IV of some variety, which appears to be a packet number. I do not think either of these algorithms are officially public (LINKS?).

Encryption and Security

There are 3 main algorithms used in GSM. Each of these algorithms is a trade secret and only released to people who the GSM committee determines has a need-to-know.Name Use BasicsA3 Authentication None

A5Encryption/Decryption Algorithm for packet encryption

3 Sparsely loopedback LFSRs in the original version, lots of variants

A8 Cipher Key GeneratorBasically a one way function

A5 is a stream algorithm and is reset for each packet with the orignal key plus some key frame number. Ross Anderson in [1] suggests that A5/1 has about an equivalent key strength of about 40 bits. Code-

typedef struct { unsigned long rl,r2,r3;} a5 ctx;static int threshold(rl, r2, r3)unsigned int rl;unsigned int r2.unsigned int r

{int total; total = (((r1 >> 9) & 0x1) == 1) + (((r2 >> 11) & 0x1) == 1) + (((r3 >> 11) & 0x1) == 1); if (total > 1) return (0); else return (1):}unsigned long clock_r1(ctl, r1)int ctlunsigned lonq r1:{unsigned long feedback; ctl ^= ((rl >> 9) & Oxl); if (ctl) { feedback = (r1 >> 18) ^ (r1 >> 17) ^ (r1 >> 16) ^ (r1 >> 13); r1 = (r1 << 1) & Ox7ffff; if (feedback & 0x01) r1 ^= 0x01: } return (r1);}unsigned long clock_r2(ctl, r2)int ctl;unsigned long r2;{unsigned long feedback;

ctl ^= ((r2 >> 11) & 0x1); if (ctl) { feedback = (r2 >> 21) ^ (r2 >> 20) ^ (r2 >> 16) ^ (r2 >> 12); r2 = (r2 << 1) & 0x3fffff; if (feedback & 0x01) r2 ^= 0x01; } return (r2):}unsigned long clock_r3(ctl, r3)int ctlunsigned long r3;{unsigned long feedback; ctl ^= ((r3 >> 11) & 0x1, if (ctl) { feedback = (r3 >> 22) ^ (r3 >> 21) ^ (r3 >> 18) ^ (r3 >> 17); r3 = (r3 << 1) & 0x7fffff; if (feedback & 0x01) r3 ^= 0x01: } return (r3);} int keystream(key, frame, alice, bob) unsigned char *key; /* 64 bit session key */ unsigned long frame; /* 22 bit frame

sequence number */ unsigned char *alice; /* 114 bit Alice to Bob key stream */ unsigned char *bob; /* 114 bit Bob to Alice key stream */ { unsigned long rl; /* 19 bit shift register */ unsigned long r2; /* 22 bit shift register */ unsigned long r3; /* 23 bit shift register */ int i; /* counter for loops */ int clock_ctl; /* xored with clock enable on each shift register unsigned char *ptr; /* current position in keystream */ unsigned char byte; /* byte of keystream being assembled */ unsigned int bits; /* number of bits of keystream in byte */ unsigned int bit; /* bit output from keystream generator */ /* Initialise shift registers from session key */ r1 = (key[0] I (key[1] << 8) 1 (key[2] << 16) ) & 0x7ffff; r2 = ((key[2] >> 3) 1 (key[3] << 5) 1 (key[4] << 13) 1 (key[5] << 21)) & 0x3fffff;

r3 = ((key[5] >> 1) 1 (key[6] << 7) 1 (key[7] << 15) ) & 0x7fffff; /* Merge frame sequence number into shift register state, by xor'ing it * into the feedback path */ for (i=0;i<22;i++) { clock_ctl = threshold(r1, r2, r2); r1 = clock r1(clock_ctl, r1); r2 = clock_r2(clock_ctl, r2); r3 = clock_r3(clock_ctl, r3); if (frame & 1) { r1 ^= 1; r2 ^= 1; r3 ^= 1; frame = frame >> 1; } /* Run shift registers for 100 clock ticks to allow frame number to * be diffused into all the bits of the shift registers */ for (i=0;i<100;i++) { clock_ctl = threshold(r1, r2, r2); r1 = clock r1(clock_ctl, r1); r2 = clock_r2(clock ctl, r2); r3 = clock r3(clock_ctl, r3); }

/* Produce 114 bits of Alice->Bob key stream */ ptr = alice; bits = 0; byte = 0; for (i=0;i<114;i++) { clock_ctl = threshold(r1, r2, r2); r1 = clock rl(clock_ctl, r1); r2 = clock_r2(clock ctl, r2); r3 = clock_r3(clock_ctl, r3); bit = ((rl >> 18) ^ (r2 >> 21) ^ (r3 >> 22)) & 0x01; byte = (byte << 1) | bit; bits++; if (bits == 8) { *ptr = byte; ptr++; bits = 0; byte = 0; }}if (bits) *ptr = byte;/* Run shift registers for another 100 bits to hide relationship between * Alice->Bob key stream and Bob->Alice key stream.for (i=0;i<100;i++){

clock_ctl = threshold(r1, r2, r2); r1 = clock_r1(clock_ctl, r1); r2 = clock r2(clock_ctl, r2); r3 = clock r3(clock ctl, r3);}/* Produce 114 bits of Bob->Alice key streamptr = bob;bits = 0:byte = 0;for (i=U;i<114;i++){ clock_ctl = threshold(r1, r2, r2); r1 = clock r1(clock_ctl, r1); r2 = clock_r2(clock ctl, r2); r3 = clock_r3(clock ctl, r3); bit = ((r1 >> 18) ^ (r2 >> 21) ^ (r3 >> 22)) & 0x01; byte = (byte << 1) | bit; bits++; if (bits == 8) { *ptr = byte; ptr++ bits = 0; byte = 0; }} if (bits) *ptr = byte; return (0);

}void a5_key(a5_ctx *c, char *k)( c->rl = k[0]<<11|k[1]<<3 | k[2]>>5 ; /* 19 */ c->r2 = k[2]<<17|k[3]<<9 | k[4]<<1 I k[5]>>7; /* 22 */ c->r3 = k[5]<<15|k[6]<<8 | k[7] ; /* 23 */}/* Step one bit in A5, return 0 or 1 as output bit. */int a5_step(a5 ctx *c){ int control; control = threshold(c->r1,c->r2,c->r3); c->r1 = clock_r1(control,c->r1); c->r2 = clock_r2(control,c->r2); c->r3 = clock_r3(control,c->r3); return( (c->r1^c >r2^c->r3)&1);}/* Encrypts a buffer of len bytes. */void a5_encrypt(a5_ctx *c, char *data, int len)l int i,j; char t; for(i=0:i<len i++) for(j=0;j<8;j++) t = t<<1 | a5_step(c) data[i]^=t; }}

void a5_decrypt(a5_ctx *c, char *data, int len){ a5_encrypt(c,data,len);}void main(void){ a5_ctx c; char data[100]; char key[] = {1,2,3,4,5,6,7,8}; int i,flag; for(i=0;i<100;i++) data[i] = i; a5_key(&c,key); a5_encrypt(&c,data,100); a5_key(&c,key); a5_decrypt(&c,data,1); a5_decrypt(&c,data+1,99); flag = 0; for(i=0;i<100;i++) if(data[i]!=i)flag = 1; if(flag)printf("Decrypt failed\n"); else printf("Decrypt succeeded\n");}

Unique User Identification

Each mobile radio has a couple security features to keept it from being stolen. Each phone is built with a International Mobile Equipment Identity (IMEI), and this is done in the factory beofore the phone is even activated. Each time the mobile radio is used, the network checks the IMEI against some list of authorized and banned numbers to verify that the phone is allowed to be on the network.

Code division multiple access (CDMA)

It is a channel access method utilized by various radio communication technologies. It should not be confused with the mobile phone standards called cdma One and CDMA2000 (which are often referred to as simply "CDMA"), this uses CDMA as an underlying channel access method.

One of the basic concepts in data communication is the idea of allowing several transmitters to send information simultaneously over a single communication channel. This allows several users to share a bandwidth of frequencies. This concept is called multiplexing. CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time division multiple access (TDMA) divides access by time, while frequency-division multiple access (FDMA) divides it by frequency. CDMA is a form of "spread-spectrum" signaling, since the modulated coded signal has a much higher data bandwidth than the data being communicated.

An analogy to the problem of multiple access is a room (channel) in which people wish to communicate with each other. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different languages (code division). CDMA is analogous to the last example where people speaking the same language can understand each other, but not other people. Similarly, in radio CDMA, each group of

users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can understand each other.

Uses

One of the early applications for code division multiplexing—predating, and distinct from cdmaOne—is in GPS.

The Qualcomm standard IS-95, marketed as cdmaOne.

The Qualcomm standard IS-2000, known as CDMA2000. This standard is used by several mobile phone companies, including the Globalstar satellite phone network.

CDMA has been used in the OmniTRACS satellite system for transportation logistics.

Technical details

CDMA is a spread spectrum multiple access technique. In CDMA a locally generated code runs at a much higher rate than the data to be transmitted. Data for transmission is simply logically XOR (exclusive OR) added with the faster code. The figure shows how spread spectrum signal is generated. The data signal with pulse duration of Tb is XOR added with the code signal with pulse duration of Tc. (Note: bandwidth is proportional to 1 / T where T = bit time) Therefore, the bandwidth of the data signal is 1 / Tb and the

bandwidth of the spread spectrum signal is 1 / Tc. Since Tc is much smaller than Tb, the bandwidth of the spread spectrum signal is much larger than the bandwidth of the original signal.

Each user in a CDMA system uses a different code to modulate their signal. Choosing the codes used to modulate the signal is very important in the performance of CDMA systems. The best performance will occur when there is good separation between the signal of a desired user and the signals of other users. The separation of the signals is made by correlating the received signal with the locally generated code of the desired user. If the signal matches the desired user's code then the correlation function will be high and the system can extract that signal. If the desired user's code has nothing in common with the signal the correlation should be as close to zero as possible (thus eliminating the signal); this is referred to as cross correlation. If the code is correlated with the signal at any time offset other than zero, the

correlation should be as close to zero as possible. This is referred to as auto-correlation and is used to reject multi-path interference.

In general, CDMA belongs to two basic categories: synchronous (orthogonal codes) and asynchronous (pseudorandom codes).

Code Division Multiplexing (Synchronous CDMA)

Synchronous CDMA exploits mathematical properties of orthogonality between vectors representing the data strings. For example, binary string "1011" is represented by the vector (1, 0, 1, 1). Vectors can be multiplied by taking their dot product, by summing the products of their respective components. If the dot product is zero, the two vectors are said to be orthogonal to each other. (Note: If u=(a,b) and v=(c,d), the dot product u.v = a*c + b*d) Some properties of the dot product help to understand how W-CDMA works. If vectors a and b are orthogonal, then

Each user in synchronous CDMA uses an orthogonal codes to modulate their signal. An example of four mutually orthogonal digital signals is shown in the figure. Orthogonal codes have a cross-correlation equal to zero; in other words, they do not interfere with each other. In the case of IS-95 64 bit Walsh codes are used to encode the

signal to separate different users. Since each of the 64 Walsh codes are orthogonal to one another, the signals are channelized into 64 orthogonal signals. The following example demonstrates how each users signal can be encoded and decoded.

Example

Start with a set of vectors that are mutually orthogonal. (Although mutual orthogonality is the only condition, these vectors are usually constructed for ease of decoding, for example columns or rows from Walsh matrices.) An example of orthogonal functions is shown in the picture on the left. These vectors will be assigned to individual users and are called the "code", "chipping code" or "chip code". In the interest of brevity, the rest of this example uses codes (v) with only 2 digits.

An example of four mutually orthogonal digital signals.

Each user is associated with a different code, say v. If the data to be transmitted is a digital zero, then the actual bits transmitted will be –v, and if the data to be transmitted is a digital one, then the actual bits transmitted will be v. For example, if v=(1,–1), and the data that the user wishes to transmit is (1, 0, 1, 1) this would correspond to (v, –v, v, v) which is then constructed in binary as ((1,–1),(–1,1),(1,–1),(1,–1)). For the purposes of this article, we call this constructed vector the transmitted vector.

Each sender has a different, unique vector v chosen from that set, but the construction method of the transmitted vector is identical.

Now, due to physical properties of interference, if two signals at a point are in phase, they add to give twice the amplitude of each signal, but if they are out of phase, they "subtract" and give a signal that is the difference of the amplitudes. Digitally, this behaviour can be modelled by the addition of the transmission vectors, component by component.

If sender0 has code (1,–1) and data (1,0,1,1), and sender1 has code (1,1) and data (0,0,1,1), and both senders transmit simultaneously, then this table describes the coding steps:

Step Encode sender0 Encode sender1

0vector0=(1,–1), data0=(1,0,1,1)=(1,–1,1,1)

vector1=(1,1), data1=(0,0,1,1)=(–1,–1,1,1)

1 encode0=vector0.data0 encode1=vector1.data12 encode0=(1,–1).(1,–1,1,1) encode1=(1,1).(–1,–1,1,1)

3encode0=((1,–1),(–1,1),(1,–1),(1,–1))

encode1=((–1,–1),(–1,–1),(1,1),(1,1))

4signal0=(1,–1,–1,1,1,–1,1,–1)

signal1=(–1,–1,–1,–1,1,1,1,1)

Because signal0 and signal1 are transmitted at the same time into the air, they add to produce the raw signal:(1,–1,–1,1,1,–1,1,–1) + (–1,–1,–1,–1,1,1,1,1) = (0,–2,–2,0,2,0,2,0)

This raw signal is called an interference pattern. The receiver then extracts an intelligible signal for any known sender by combining the sender's code with the interference pattern, the receiver combines it with the codes of the senders. The following table explains how this works and shows that the signals do not interfer with one another:

Step Decode sender0 Decode sender1

0vector0=(1,–1), pattern=(0,–2,–2,0,2,0,2,0)

vector1=(1,1), pattern=(0,–2,–2,0,2,0,2,0)

1 decode0=pattern.vector0 decode1=pattern.vector1

2decode0=((0,–2),(–2,0),(2,0),(2,0)).(1,–1)

decode1=((0,–2),(–2,0),(2,0),(2,0)).(1,1)

3decode0=((0+2),(–2+0),(2+0),(2+0))

decode1=((0–2),(–2+0),(2+0),(2+0))

4 data0=(2,–2,2,2)=(1,0,1,1) data1=(–2,–

2,2,2)=(0,0,1,1)

Further, after decoding, all values greater than 0 are interpreted as 1 while all values less than zero are interpreted as 0. For example, after decoding, data0 is (2,–2,2,2), but the receiver interprets this as (1,0,1,1).

We can also consider what would happen if a receiver tries to decode a signal when the user has not sent any information. Assume signal0=(1,-1,-1,1,1,-1,1,-1) is transmitted alone. The following table shows the decode at the receiver:

Step Decode sender0 Decode sender1

0vector0=(1,–1), pattern=(1,-1,-1,1,1,-1,1,-1)

vector1=(1,1), pattern=(1,-1,-1,1,1,-1,1,-1)

1 decode0=pattern.vector0 decode1=pattern.vector1

2decode0=((1,–1),(–1,1),(1,-1),(1,-1)).(1,–1)

decode1=((1,–1),(–1,1),(1,-1),(1,-1)).(1,1)

3decode0=((1+1),(–1-1),(1+1),(1+1))

decode1=((1–1),(–1+1),(1-1),(1-1))

4 data0=(2,–2,2,2)=(1,0,1,1) data1=(0,0,0,0)

When the receiver attempts to decode the signal using sender1’s code, the data is all zeros, therefore the cross correlation is equal to zero and it is clear that sender1 did not transmit any data.

Asynchronous CDMA

The previous example of orthogonal Walsh sequences describes how 2 users can be multiplexed together in a synchronous system, a technique that is commonly referred to as Code Division Multiplexing (CDM). The set of 4 Walsh sequences shown in the figure will afford up to 4 users, and in general, an NxN Walsh matrix can be used to multiplex N users. Multiplexing requires all of the users to be coordinated so that each transmits their assigned sequence v (or the complement, -v) starting at exactly the same time. Thus, this technique finds use in base-to-mobile links, where all of the transmissions originate from the same transmitter and can be perfectly coordinated.

On the other hand, the mobile-to-base links cannot be precisely coordinated, particularly due to the mobility of the handsets, and require a somewhat different approach. Since it is not mathematically possible to create signature sequences that are orthogonal for arbitrarily random starting points, unique "pseudo-random" or "pseudo-noise" (PN) sequences are used in Asynchronous CDMA systems. A PN code is a binary sequence that appears random but can be reproduced in a deterministic manner by intended receivers. These PN codes are used to encode and decode a users signal in Asynchronous CDMA in the same manner as the orthogonal codes in synchrous CDMA (shown in the

example above). These PN sequences are statistically uncorrelated, and the sum of a large number of PN sequences results in Multiple Access Interference (MAI) that is approximated by a Gaussian noise process (following the "central limit theorem" in statistics). If all of the users are received with the same power level, then the variance (e.g., the noise power) of the MAI increases in direct proportion to the number of users. In other words, unlike synchronous CDMA, the signals of other users will appear as noise to the signal of interest and interfere slightly with the desired signal in proportion to number of users.

All forms of CDMA use spread spectrum process gain to allow receivers to partially discriminate against unwanted signals. Signals encoded with the specified PN sequence (code) are received, while signals with different codes (or the same code but a different timing offset) appear as wideband noise reduced by the process gain.

Since each user generates MAI, controlling the signal strength is an important issue with CDMA transmitters. A CDM (Synchronous CDMA), TDMA or FDMA receiver can in theory completely reject arbitrarily strong signals using different codes, time slots or frequency channels due to the orthogonality of these systems. This is not true for Asynchronous CDMA; rejection of unwanted signals is only partial. If any or all of the unwanted signals are much stronger than the desired signal, they will overwhelm it. This leads to a general requirement in any Asynchronous CDMA system to approximately match the various signal

power levels as seen at the receiver. In CDMA cellular, the base station uses a fast closed-loop power control scheme to tightly control each mobile's transmit power. See Near-far problem for further information on this problem.

Advantages of Asynchronous CDMA over other techniques

Asynchronous CDMA's main advantage over CDM (Synchronous CDMA), TDMA and FDMA is that it can use the spectrum more efficiently in mobile telephony applications. (In theory, CDMA, TDMA and FDMA have exactly the same spectral efficiency but practically, each has its own challenges - power control in the case of CDMA, timing in the case of TDMA, and frequency generation/filtering in the case of FDMA.) TDMA systems must carefully synchronize the transmission times of all the users to ensure that they are received in the correct timeslot and do not cause interference. Since this cannot be perfectly controlled in a mobile environment, each timeslot must have a guard-time, which reduces the probability that users will interfere, but decreases the spectral efficiency. Similarly, FDMA systems must use a guard-band between adjacent channels, due to the random doppler shift of the signal spectrum which occurs due to the user's mobility. The guard-bands will reduce the probability that adjacent channels will interfere, but decrease the utilization of the spectrum.

Most importantly, Asynchronous CDMA offers a key advantage in the flexible allocation of resources. There are a fixed number of orthogonal codes, timeslots or frequency

bands that can be allocated for CDM, TDMA and FDMA systems, which remain underutilized due to the bursty nature of telephony and packetized data transmissions. There is no strict limit to the number of users that can be supported in an Asynchronous CDMA system, only a practical limit governed by the desired bit error probability, since the SIR (Signal to Interference Ratio) varies inversely with the number of users. In a bursty traffic environment like mobile telephony, the advantage afforded by Asynchronous CDMA is that the performance (bit error rate) is allowed to fluctuate randomly, with an average value determined by the number of users times the percentage of utilization. Suppose there are 2N users that only talk half of the time, then 2N users can be accommodated with the same average bit error probability as N users that talk all of the time. The key difference here is that the bit error probability for N users talking all of the time is constant, whereas it is a random quantity (with the same mean) for 2N users talking half of the time.

In other words, Asynchronous CDMA is ideally suited to a mobile network where large numbers of transmitters each generate a relatively small amount of traffic at irregular intervals. CDM (Synchronous CDMA), TDMA and FDMA systems cannot recover the underutilized resources inherent to bursty traffic due to the fixed number of orthogonal codes, time slots or frequency channels that can be assigned to individual transmitters. For instance, if there are N time slots in a TDMA system and 2N users that talk half of the time, then half of the time there will be more than N users needing to use more than N timeslots. Furthermore, it

would require significant overhead to continually allocate and deallocate the orthogonal code, time-slot or frequency channel resources. By comparison, Asynchronous CDMA transmitters simply send when they have something to say, and go off the air when they don't, keeping the same PN signature sequence as long as they are connected to the system.

Spread Spectrum Characteristics of CDMA

Most modulation schemes try to minimize the bandwidth of this signal since bandwidth is a limited resource. However, spread spectrum techniques use a transmission bandwidth that is several orders of magnitude greater then the minimum required signal bandwidth. One of the initial reasons for doing this was military applications including guidance and communication systems. These systems were designed using spread spectrum because of its security and resistance to jamming. Asynchronous CDMA has some level of privacy built in because the signal is spread using a pseudorandom code; this code makes the spread spectrum signals appear random or have noise-like properties. A receiver cannot demodulate this transmission without knowledge of the pseudorandom sequence used to encode the data. CDMA is also resistant to jamming. A jamming signal only has a finite amount of power available to jam the signal. The jammer can either spread its energy over the entire bandwidth of the signal or jam only part of the entire signal. [3]

CDMA can also effectively reject narrowband interference. Since narrowband interference affects only a small portion

of the spread spectrum signal, it can easily be removed through notch filtering without much loss of information. Convolution encoding and interleaving can be used to assist in recovering this lost data. CDMA signals are also resistant to multipath fading. Since the spread spectrum signal occupies a large bandwidth only a small portion of this will undergo fading due to multipath at any given time. Like the narrowband interference this will result in only a small loss of data and can be overcome.

Another reason CDMA is resistant to multipath interference is because the delayed versions of the transmitted pseudorandom codes will have poor correlation with the original pseudorandom code, and will thus appear as another user, which is ignored at the receiver. In other words, as long as the multipath channel induces at least one chip of delay, the multipath signals will arrive at the receiver such that they are shifted in time by at least one chip from the intended signal. The correlation properties of the pseudorandom codes are such that this slight delay causes the multipath to appear uncorrelated with the intended signal, and it is thus ignored.

Some CDMA devices use a rake receiver, which exploits multipath delay components to improve the performance of the system. A rake receiver combines the information from several correlators, each one tuned to a different path delay, producing a stronger version of the signal than a simple receiver with a single correlator tuned to the path delay of the strongest signal.

Frequency reuse is the ability to reuse the same radio channel frequency at other cell sites within a cellular system. In the FDMA and TDMA systems frequency planning is an important consideration. The frequencies used in different cells need to be planned carefully in order to ensure that the signals from different cells do not interfere with each other. In a CDMA system the same frequency can be used in every cell because channelization is done using the pseudorandom codes. Reusing the same frequency in every cell eliminates the need for frequency planning in a CDMA system; however, planning of the different pseudorandom sequences must be done to ensure that the received signal from one cell does not correlate with the signal from a nearby cell.

Since adjacent cells use the same frequencies, CDMA systems have the ability to perform soft handoffs. Soft handoffs allow the mobile telephone to communicate simultaneously with two or more cells. The best signal quality is selected until the handoff is complete. This is different than hard handoffs utilized in other cellular systems. In a hard handoff situation, as the mobile telephone approaches a handoff, signal strength may vary abruptly. In contrast, CDMA systems use the soft handoff, which is undetectable and provides a more reliable and higher quality signal.

Universal Mobile Telecommunications System (UMTS

Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G) cell phone technologies, which is also being developed into a 4G technology. Currently, the most common form of UMTS uses W-CDMA as the underlying air interface. It is standardized by the 3GPP, and is the European answer to the ITU IMT-2000 requirements for 3G cellular radio systems.

To differentiate UMTS from competing network technologies, UMTS is sometimes marketed as 3GSM, emphasizing the combination of the 3G nature of the technology and the GSM standard .

Features

UMTS, using W-CDMA, supports up to 21 Mbit/s data transfer rates in theory[1] (with HSDPA), although at the moment users in deployed networks can expect a transfer rate of up to 384 kbit/s for R99 handsets, and 7.2 Mbit/s for HSDPA handsets in the downlink connection. This is still much greater than the 9.6 kbit/s of a single GSM error-corrected circuit switched data channel or multiple 9.6 kbit/s channels in HSCSD (14.4 kbit/s for CDMAOne), and—in competition to other network technologies such as CDMA2000, PHS or WLAN—offers access to the World Wide Web and other data services on mobile devices.

Precursors to 3G are 2G mobile telephony systems, such as GSM, IS-95, PDC, CDMA PHS and other 2G technologies deployed in different countries. In the case of GSM, there is an evolution path from 2G, to GPRS, also known as 2.5G. GPRS supports a much better data rate (up to a theoretical maximum of 140.8 kbit/s, though typical rates are closer to 56 kbit/s) and is packet switched rather than connection oriented (circuit switched). It is deployed in many places where GSM is used. E-GPRS, or EDGE, is a further evolution of GPRS and is based on more modern coding schemes. With EDGE the actual packet data rates can reach around 180 kbit/s (effective). EDGE systems are often referred as "2.75G Systems".

Since 2006, UMTS networks in many countries have been or are in the process of being upgraded with High Speed Downlink Packet Access (HSDPA), sometimes known as 3.5G. Currently, HSDPA enables downlink transfer speeds of up to 21 Mbit/s. Work is also progressing on improving

the uplink transfer speed with the High-Speed Uplink Packet Access (HSUPA). Longer term, the 3GPP Long Term Evolution project plans to move UMTS to 4G speeds of 100 Mbit/s down and 50 Mbit/s up, using a next generation air interface technology based upon Orthogonal frequency-division multiplexing.

The first national consumer UMTS networks launched in 2002 with a heavy emphasis on telco-provided mobile applications such as mobile TV and video calling. The high data speeds of UMTS are now most often utilised for Internet access: experience in Japan and elsewhere has shown that user demand for video calls is not high, and telco-provided audio/video content has declined in popularity in favour of high-speed access to the World Wide Web - either directly on a handset or connected to a computer via Wi-Fi, Bluetooth, Infrared or USB.

Technology

UMTS combines the W-CDMA, TD-CDMA, or TD-SCDMA air interfaces, GSM's Mobile Application Part (MAP) core, and the GSM family of speech codecs. In the most popular cellular mobile telephone variant of UMTS, W-CDMA is currently used. Note that other wireless standards use W-CDMA as their air interface, including FOMA.

UMTS over W-CDMA

UMTS over W-CDMA uses a pair of 5 MHz channels. In contrast, the competing CDMA2000 system uses one or

more arbitrary 1.25 MHz channels for each direction of communication. UMTS and other W-CDMA systems are widely criticized for their large spectrum usage, which has delayed deployment in countries that acted relatively slowly in allocating new frequencies specifically for 3G services (such as the United States).

The specific frequency bands originally defined by the UMTS standard are 1885–2025 MHz for the mobile-to-base (uplink) and 2110–2200 MHz for the base-to-mobile (downlink). In the US, 1710–1755 MHz and 2110–2155 MHz will be used instead, as the 1900 MHz band was already utilized.[2] While UMTS2100 is the most widely-deployed UMTS band, some countries' UMTS operators use the 850 MHz and/or 1900 MHz bands (independently, meaning uplink and downlink are within the same band), notably in the US by AT&T Mobility, and in Australia by Telstra on the Next G network.

For existing GSM operators, it is a simple but costly migration path to UMTS: much of the infrastructure is shared with GSM, but the cost of obtaining new spectrum licenses and overlaying UMTS at existing towers is high.

UMTS is an alternative Radio Access Network (RAN) to GERAN (which is the 2G GSM air interface including GSM/EDGE). UMTS and GERAN can share a Core Network (CN), allowing (mostly) transparent switching between the RANs according to available coverage and service needs. The CN can be connected to various backbone networks like the Internet, ISDN. UMTS (and GERAN) include the three lowest layers of OSI model. The

network layer (OSI 3) includes the Radio Resource Management protocol (RRM) that manages the bearer channels between the mobile terminals and the fixed network, including the handovers.

UMTS 3G handsets and modems

All of the major 2G phone manufacturers (that are still in business) are now manufacturers of 3G phones. The early 3G handsets and modems were specific to the frequencies required in their country, which meant they could only roam to other countries on the same 3G frequency (though they can fall back to the older GSM standard). Canada and USA have a common share of frequencies, as do most European countries. The article UMTS frequency bands is an overview of UMTS network frequencies around the world.

There are almost no 3G phones or modems available supporting all 3G frequencies (UMTS850/900/1700/1900/2100MHz). However, many phones are offering more than one band which still enables extensive roaming. For example, a tri-band chipset operating on 850/1900/2100MHz, such as that found in Apple's iPhone, allows usage in the majority of countries where UMTS is deployed.

PDAs and smartphones

Symbian: 65% market share. Nokia owns Symbian and licenses it to other phone vendors including Sony Ericsson, LG, Samsung, & Sanyo. There is a lot of

SymbianOS software available but often only applicable to specific phones. Furthermore, development of Symbian applications has been hindered by a certification process imposed by Symbian on developers. Market observers anticipate that Nokia will make adjustments to lure 3rd party developers by adopting a more "open" approach and reduce the barriers to application deployment (These adjustments would be in response to Google's Android & Apple's iPhone efforts which take a much more "open" approach).

Windows Mobile: with 12% of the current market. Windows Mobile 6.1 offers a range of features for UMTS. Tethering is available using USB, bluetooth, or Wifi (with WMWifiRouter: convert your Windows Mobile unit into a router)[3] Windows Mobile is used by many manufacturers including Sony, Samsung, Palm, Motorola, and several manufacturers familiar with the PC market.

RIM OS: with 11% of the market (mostly in the USA). Most BlackBerry smartphones are not currently 3G capable, with the exception of certain models such as model 8707v, EVDO capable models and the upcoming BlackBerry 9000 series. One reason is that BlackBerry, typically known for long battery life, would have shorter battery life with 3G. The emergence of greatly improved multimedia and tethering capabilities on recent BlackBerry models, is

currently pressuring RIM to include 3G in future BlackBerry models.

Mac OS X-like iPhone OS: with 7% of the market (and growing quickly). Apple's first generation iPhone did not support 3G and is restricted to using the EDGE standard. Apple stated this was to maintain a reasonable battery life on the telephone. As power consumption of 3G chipsets improved, Apple released a UMTS (3G) iPhone on July 11, 2008.

Palm OS (also known as "Garnet OS") was initially developed by Palm Computing, Inc. for personal digital assistants (PDAs) in 1996 and was later also used on some mobile phones. It is provided with a suite of basic applications for personal information management. Palm OS has been used in Sony Clié handsets (Sony now uses Windows Mobile & Symbian) and by Samsung (which now use Windows Mobile). Palm used to be a dominant OS for smart phones but is being increasingly marginalized by other operating systems.

Android is a software platform and operating system for mobile devices based on the Linux operating system and developed by Google and the Open Handset Alliance.[4] It allows developers to write managed code in a Java-like language that utilizes Google-developed Java libraries,[5] but does not support programs developed in native code. When released in 2008, most of the Android platform was made available under the Apache free-software and

open-source license.[6] The first phone to use the Android platform is the HTC Dream.

External modems

Using a cellular router, PCMCIA or USB card, customers are able to access 3G broadband services, regardless of their choice of computer (such as a tablet PC or a PDA). Some software installs itself from the modem, so that in some cases absolutely no knowledge of technology is required to get online in moments.

Using a phone that supports 3G and Bluetooth 2.0, multiple Bluetooth-capable laptops can be connected to the Internet. The phone acts as gateway and router, but via Bluetooth rather than wireless networking (802.11) or a USB connection.

Interoperability and global roaming

UMTS phones (and data cards) are highly portable—they have been designed to roam easily onto other UMTS networks (assuming your provider has a roaming agreement). In addition, almost all UMTS phones (except in Japan) are UMTS/GSM dual-mode devices, so if a UMTS phone travels outside of UMTS coverage during a call the call may be transparently handed off to available GSM coverage. Roaming charges are usually significantly higher than regular usage charges.

Most UMTS licensees consider ubiquitous, transparent global roaming an important issue. To enable a high degree of interoperability, UMTS phones usually support several

different frequencies in addition to their GSM fallback. Different countries support different UMTS frequency bands – Europe initially used 2100MHz while the most carriers in the USA use 850Mhz and 1900Mhz. T-mobile has plans to launch their upcoming network at 1700Mhz. A UMTS phone and network must support a common frequency to work together. Because of the frequencies used, early models of UMTS phones designated for the United States will likely not be operable elsewhere and vice versa. There are now 11 different frequency combinations used around the world—including frequencies formerly used solely for 2G services.

UMTS phones can use a Universal Subscriber Identity Module, USIM (based on GSM's SIM) and also work (including UMTS services) with GSM SIM cards. This is a global standard of identification, and enables a network to identify and authenticate the phone user (actually only the (U)SIM, not the user is authenticated). Roaming agreements between networks allow for calls to a customer to be redirected to them while roaming and determine the services (and prices) available to the user. In addition to user subscriber information and authentication information, the (U)SIM provides storage space for phone book contact. Handsets can store their data on their own memory or on the (U)SIM card (which is usually more limited in its phone book contact information). A (U)SIM can be moved to another UMTS or GSM phone, and the phone will take on the user details of the (U)SIM, meaning it is the (U)SIM (not the phone) which determines the phone number of the phone and the billing for calls made from the phone.

Japan was the first country to adopt 3G technologies, and since they had not used GSM previously they had no need to build GSM compatibility into their handsets and their 3G handsets were smaller than those available elsewhere. In 2002, NTT DoCoMo's FOMA 3G network was the first commercial W-CDMA network—it was initially incompatible with the UMTS standard at the radio level but used standard USIM cards, meaning USIM card based roaming was possible (transferring the USIM card into a UMTS or GSM phone when travelling). Both NTT and SoftBank Mobile (which launched 3G in December 2002) now use the standard UMTS, and their PDC 2G networks run in parallel.

Spectrum allocation

Main article: UMTS frequency bands

Over 130 licenses have already been awarded to operators worldwide (as of December 2004), specifying W-CDMA radio access technology that builds on GSM. In Europe, the license process occurred at the tail end of the technology bubble, and the auction mechanisms for allocation set up in some countries resulted in some extremely high prices being paid for the original 2100 MHz licenses, notably in the UK and Germany. In Germany, bidders paid a total €50.8 billion for six licenses, two of which were subsequently abandoned and written off by their purchasers (Mobilcom and the Sonera/Telefonica consortium). It has been suggested that these huge license fees have the character of a very large tax paid on future income expected many years down the road. In any event, the high

prices paid put some European telecom operators close to bankruptcy (most notably KPN). Over the last few years some operators have written off some or all of the license costs. More recently, a carrier in Finland has begun using 900 MHz UMTS in a shared arrangement with its surrounding 2G GSM base stations, a trend that is expected to expand over Europe in the next 1–3 years.

The 2100 MHz UMTS spectrum allocated in Europe is already used in North America. The 1900 MHz range is used for 2G (PCS) services, and 2100 MHz range is used for satellite communications. Regulators have, however, freed up some of the 2100 MHz range for 3G services, together with the 1700 MHz for the uplink. UMTS operators in North America who want to implement a European style 2100/1900 MHz system will have to share spectrum with existing 2G services in the 1900 MHz band.

AT&T Wireless launched UMTS services in the United States by the end of 2004 strictly using the existing 1900 MHz spectrum allocated for 2G PCS services. Cingular acquired AT&T Wireless in 2004 and has since then launched UMTS in select US cities. Cingular renamed itself AT&T and is rolling out some cities with a UMTS network at 850 MHz to enhance its existing UMTS network at 1900 MHz and now offers subscribers a number of UMTS 850/1900 phones.

T-Mobile's rollout of UMTS in the US will focus on the 2100/1700 MHz bands, whereas UMTS coverage in Canada is being provided on the 850 MHz band of the Rogers Wirless network. In 2008, Australian telco Telstra

replaced its existing CDMA network with a national 3G network, branded as NextG, operating in the 850 MHz band. Telstra currently provides UMTS service on this network, and also on the 2100 MHz UMTS network, through a co-ownership of the owning and administrating company 3GIS. This company is also co-owned by Hutchison 3G Australia, and this is the primary network used by their customers. Optus is currently rolling out a 3G network operating on the 2100 MHz band in cities and most large towns, and the 900 MHz band in regional areas. Vodafone is also building a 3G network using the 900 MHz band. The 850 MHz and 900 MHz bands provide greater coverage compared to equivalent 1700/1900/2100 MHz networks, and are best suited to regional areas where greater distances separate subscriber and base station.

Carriers in South America are now also rolling out 850 MHz networks.

[edit] Other competing standards

There are other competing 3G standards, such as CDMA2000 and TD-SCDMA, though UMTS can use the latter's air interface standard.

On the Internet access side, competing systems include WiMAX and Flash-OFDM. Different variants of UMTS compete with different standards. While this article has largely discussed UMTS-FDD, a form oriented for use in conventional cellular-type spectrum, UMTS-TDD, a system based upon a TD-CDMA air interface, is used to provide UMTS service where the uplink and downlink

share the same spectrum, and is very efficient at providing asymmetric access. It provides more direct competition with WiMAX and similar Internet-access oriented systems than conventional UMTS.

Both the CDMA2000 and W-CDMA air interface systems are accepted by ITU as part of the IMT-2000 family of 3G standards, in addition to UMTS-TDD's TD-CDMA, Enhanced Data Rates for GSM Evolution (EDGE) and China's own 3G standard, TD-SCDMA.

CDMA2000's narrower bandwidth requirements make it easier than UMTS to deploy in existing spectrum along with legacy standards. In some, but not all, cases, existing GSM operators only have enough spectrum to implement either UMTS or GSM, not both. For example, in the US D, E, and F PCS spectrum blocks, the amount of spectrum available is 5 MHz in each direction. A standard UMTS system would saturate that spectrum.

In many markets however, the co-existence issue is of little relevance, as legislative hurdles exist to co-deploying two standards in the same licensed slice of spectrum.

Most GSM operators in North America as well as others around the world have accepted EDGE as a temporary 3G solution. AT&T Wireless launched EDGE nationwide in 2003, AT&T launched EDGE in most markets and T-Mobile USA has launched EDGE nationwide as of October 2005. Rogers Wireless launched nation-wide EDGE service in late 2003 for the Canadian market. Bitė Lietuva (Lithuania) was one of the first operators in Europe to

launch EDGE in December 2003. TIM (Italy) launched EDGE in 2004. The benefit of EDGE is that it leverages existing GSM spectrums and is compatible with existing GSM handsets. It is also much easier, quicker, and considerably cheaper for wireless carriers to "bolt-on" EDGE functionality by upgrading their existing GSM transmission hardware to support EDGE than having to install almost all brand-new equipment to deliver UMTS. EDGE provides a short-term upgrade path for GSM operators and directly competes with CDMA2000.

[edit] Problems and issues

Some countries, including the United States and Japan, have allocated spectrum differently from the ITU recommendations, so that the standard bands most commonly used for UMTS (UMTS-2100) have not been available. In those countries, alternative bands are used, preventing the interoperability of existing UMTS-2100 equipment, and requiring the design and manufacture of different equipment for the use in these markets. As is the case with GSM900 today, standard UMTS 2100 MHz equipment will not work in those markets. However, it appears as though UMTS is not suffering as much from handset band compatibility issues as GSM did, as many UMTS handsets are multi-band in both UMTS and GSM modes. Quad-band GSM (850, 900, 1800, and 1900 MHz bands) and tri-band UMTS (850, 1900, and 2100 MHz bands) handsets are becoming more commonplace.

The early days of UMTS saw rollout hitches in many countries. Overweight handsets with poor battery life were

first to arrive on a market highly sensitive to weight and form factor. The Motorola A830, a debut handset on Hutchison's 3 network, weighed more than 200 grams and even featured a detachable camera to reduce handset weight. Another significant issue involved call reliability, related to problems with handover from UMTS to GSM. Customers found their connections being dropped as handovers were possible only in one direction (UMTS → GSM), with the handset only changing back to UMTS after hanging up. In most networks around the world this is no longer an issue.

Compared to GSM, UMTS networks initially required a higher base station density. For fully-fledged UMTS incorporating video on demand features, one base station needed to be set up every 1–1.5 km (0.62–0.93 mi). This was the case when only the 2100 MHz band was being used, however with the growing use of lower-frequency bands (such as 850 and 900 MHz) this is no longer so. This has led to increasing rollout of the lower-band networks by operators since 2006.

Even with current technologies and low-band UMTS, telephony and data over UMTS is still more power intensive than on comparable GSM networks. Apple, Inc. cited[7] UMTS power consumption as the reason that the first generation iPhone only supported EDGE. Their release of the iPhone 3G quotes talk time on UMTS as half that available when the handset is set to use GSM. As battery and network technology improves, this issue is lessening in severity.

Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G) cell phone technologies, which is also being developed into a 4G technology. Currently, the most common form of UMTS uses W-CDMA as the underlying air interface. It is standardized by the 3GPP, and is the European answer to the ITU IMT-2000 requirements for 3G cellular radio systems.

To differentiate UMTS from competing network technologies, UMTS is sometimes marketed as 3GSM, emphasizing the combination of the 3G nature of the technology and the GSM standard which it was designed to succeed.

Contents

[hide] 1 Preface 2 Features 3 Deployment 4 Technology 5 UMTS 3G handsets and modems

o 5.1 PDAs and smartphoneso 5.2 External modems

6 Interoperability and global roaming 7 Spectrum allocation 8 Other competing standards 9 Problems and issues 10 See also 11 Literature 12 References

13 External links

[edit] Preface

This article discusses the technology, business, usage and other aspects encompassing and surrounding UMTS, the 3G successor to GSM which utilizes the W-CDMA air interface and GSM infrastructures. Any issues relating strictly to the W-CDMA interface itself may be better described in the W-CDMA page.

[edit] Features

UMTS, using W-CDMA, supports up to 21 Mbit/s data transfer rates in theory[1] (with HSDPA), although at the moment users in deployed networks can expect a transfer rate of up to 384 kbit/s for R99 handsets, and 7.2 Mbit/s for HSDPA handsets in the downlink connection. This is still much greater than the 9.6 kbit/s of a single GSM error-corrected circuit switched data channel or multiple 9.6 kbit/s channels in HSCSD (14.4 kbit/s for CDMAOne), and—in competition to other network technologies such as CDMA2000, PHS or WLAN—offers access to the World Wide Web and other data services on mobile devices.

Precursors to 3G are 2G mobile telephony systems, such as GSM, IS-95, PDC, CDMA PHS and other 2G technologies deployed in different countries. In the case of GSM, there is an evolution path from 2G, to GPRS, also known as 2.5G. GPRS supports a much better data rate (up to a theoretical maximum of 140.8 kbit/s, though typical rates are closer to 56 kbit/s) and is packet switched rather than connection oriented (circuit switched). It is deployed in many places where GSM is used. E-GPRS, or EDGE, is a further

evolution of GPRS and is based on more modern coding schemes. With EDGE the actual packet data rates can reach around 180 kbit/s (effective). EDGE systems are often referred as "2.75G Systems".

Since 2006, UMTS networks in many countries have been or are in the process of being upgraded with High Speed Downlink Packet Access (HSDPA), sometimes known as 3.5G. Currently, HSDPA enables downlink transfer speeds of up to 21 Mbit/s. Work is also progressing on improving the uplink transfer speed with the High-Speed Uplink Packet Access (HSUPA). Longer term, the 3GPP Long Term Evolution project plans to move UMTS to 4G speeds of 100 Mbit/s down and 50 Mbit/s up, using a next generation air interface technology based upon Orthogonal frequency-division multiplexing.

The first national consumer UMTS networks launched in 2002 with a heavy emphasis on telco-provided mobile applications such as mobile TV and video calling. The high data speeds of UMTS are now most often utilised for Internet access: experience in Japan and elsewhere has shown that user demand for video calls is not high, and telco-provided audio/video content has declined in popularity in favour of high-speed access to the World Wide Web - either directly on a handset or connected to a computer via Wi-Fi, Bluetooth, Infrared or USB.

[edit] Deployment

See also: List of Deployed UMTS networks

[edit] Technology

UMTS combines the W-CDMA, TD-CDMA, or TD-SCDMA air interfaces, GSM's Mobile Application Part (MAP) core, and the GSM family of speech codecs. In the most popular cellular mobile telephone variant of UMTS, W-CDMA is currently used. Note that other wireless standards use W-CDMA as their air interface, including FOMA.

UMTS over W-CDMA uses a pair of 5 MHz channels. In contrast, the competing CDMA2000 system uses one or more arbitrary 1.25 MHz channels for each direction of communication. UMTS and other W-CDMA systems are widely criticized for their large spectrum usage, which has delayed deployment in countries that acted relatively slowly in allocating new frequencies specifically for 3G services (such as the United States).

The specific frequency bands originally defined by the UMTS standard are 1885–2025 MHz for the mobile-to-base (uplink) and 2110–2200 MHz for the base-to-mobile (downlink). In the US, 1710–1755 MHz and 2110–2155 MHz will be used instead, as the 1900 MHz band was already utilized.[2] While UMTS2100 is the most widely-deployed UMTS band, some countries' UMTS operators use the 850 MHz and/or 1900 MHz bands (independently, meaning uplink and downlink are within the same band), notably in the US by AT&T Mobility, and in Australia by Telstra on the Next G network.

For existing GSM operators, it is a simple but costly migration path to UMTS: much of the infrastructure is shared with GSM, but the cost of obtaining new spectrum licenses and overlaying UMTS at existing towers is high.

UMTS is an alternative Radio Access Network (RAN) to GERAN (which is the 2G GSM air interface including GSM/EDGE). UMTS and GERAN can share a Core Network (CN), allowing (mostly) transparent switching between the RANs according to available coverage and service needs. The CN can be connected to various backbone networks like the Internet, ISDN. UMTS (and GERAN) include the three lowest layers of OSI model. The network layer (OSI 3) includes the Radio Resource Management protocol (RRM) that manages the bearer channels between the mobile terminals and the fixed network, including the handovers.

[edit] UMTS 3G handsets and modems

All of the major 2G phone manufacturers (that are still in business) are now manufacturers of 3G phones. The early 3G handsets and modems were specific to the frequencies required in their country, which meant they could only roam to other countries on the same 3G frequency (though they can fall back to the older GSM standard). Canada and USA have a common share of frequencies, as do most European countries. The article UMTS frequency bands is an overview of UMTS network frequencies around the world.

There are almost no 3G phones or modems available supporting all 3G frequencies (UMTS850/900/1700/1900/2100MHz). However, many phones are offering more than one band which still enables extensive roaming. For example, a tri-band chipset operating on 850/1900/2100MHz, such as that found in Apple's iPhone, allows usage in the majority of countries where UMTS is deployed.

[edit] PDAs and smartphones

Symbian: 65% market share. Nokia owns Symbian and licenses it to other phone vendors including Sony Ericsson, LG, Samsung, & Sanyo. There is a lot of SymbianOS software available but often only applicable to specific phones. Furthermore, development of Symbian applications has been hindered by a certification process imposed by Symbian on developers. Market observers anticipate that Nokia will make adjustments to lure 3rd party developers by adopting a more "open" approach and reduce the barriers to application deployment (These adjustments would be in response to Google's Android & Apple's iPhone efforts which take a much more "open" approach).

Windows Mobile: with 12% of the current market. Windows Mobile 6.1 offers a range of features for UMTS. Tethering is available using USB, bluetooth, or Wifi (with WMWifiRouter: convert your Windows Mobile unit into a router)[3] Windows Mobile is used by many manufacturers including Sony, Samsung,

Palm, Motorola, and several manufacturers familiar with the PC market.

RIM OS: with 11% of the market (mostly in the USA). Most BlackBerry smartphones are not currently 3G capable, with the exception of certain models such as model 8707v, EVDO capable models and the upcoming BlackBerry 9000 series. One reason is that BlackBerry, typically known for long battery life, would have shorter battery life with 3G. The emergence of greatly improved multimedia and tethering capabilities on recent BlackBerry models, is currently pressuring RIM to include 3G in future BlackBerry models.

Mac OS X-like iPhone OS: with 7% of the market (and growing quickly). Apple's first generation iPhone did not support 3G and is restricted to using the EDGE standard. Apple stated this was to maintain a reasonable battery life on the telephone. As power consumption of 3G chipsets improved, Apple released a UMTS (3G) iPhone on July 11, 2008.

Palm OS (also known as "Garnet OS") was initially developed by Palm Computing, Inc. for personal digital assistants (PDAs) in 1996 and was later also used on some mobile phones. It is provided with a suite of basic applications for personal information management. Palm OS has been used in Sony Clié handsets (Sony now uses Windows Mobile & Symbian) and by Samsung (which now use Windows Mobile). Palm used to be a dominant OS for smart

phones but is being increasingly marginalized by other operating systems.

Android is a software platform and operating system for mobile devices based on the Linux operating system and developed by Google and the Open Handset Alliance.[4] It allows developers to write managed code in a Java-like language that utilizes Google-developed Java libraries,[5] but does not support programs developed in native code. When released in 2008, most of the Android platform was made available under the Apache free-software and open-source license.[6] The first phone to use the Android platform is the HTC Dream.

External modems

Using a cellular router, PCMCIA or USB card, customers are able to access 3G broadband services, regardless of their choice of computer (such as a tablet PC or a PDA). Some software installs itself from the modem, so that in some cases absolutely no knowledge of technology is required to get online in moments.

Using a phone that supports 3G and Bluetooth 2.0, multiple Bluetooth-capable laptops can be connected to the Internet. The phone acts as gateway and router, but via Bluetooth rather than wireless networking (802.11) or a USB connection.

Interoperability and global roaming

UMTS phones (and data cards) are highly portable—they have been designed to roam easily onto other UMTS networks (assuming your provider has a roaming agreement). In addition, almost all UMTS phones (except in Japan) are UMTS/GSM dual-mode devices, so if a UMTS phone travels outside of UMTS coverage during a call the call may be transparently handed off to available GSM coverage. Roaming charges are usually significantly higher than regular usage charges.

Most UMTS licensees consider ubiquitous, transparent global roaming an important issue. To enable a high degree of interoperability, UMTS phones usually support several different frequencies in addition to their GSM fallback. Different countries support different UMTS frequency bands – Europe initially used 2100MHz while the most carriers in the USA use 850Mhz and 1900Mhz. T-mobile has plans to launch their upcoming network at 1700Mhz. A UMTS phone and network must support a common frequency to work together. Because of the frequencies used, early models of UMTS phones designated for the United States will likely not be operable elsewhere and vice versa. There are now 11 different frequency combinations used around the world—including frequencies formerly used solely for 2G services.

UMTS phones can use a Universal Subscriber Identity Module, USIM (based on GSM's SIM) and also work (including UMTS services) with GSM SIM cards. This is a global standard of identification, and enables a network to identify and authenticate the phone user (actually only the

(U)SIM, not the user is authenticated). Roaming agreements between networks allow for calls to a customer to be redirected to them while roaming and determine the services (and prices) available to the user. In addition to user subscriber information and authentication information, the (U)SIM provides storage space for phone book contact. Handsets can store their data on their own memory or on the (U)SIM card (which is usually more limited in its phone book contact information). A (U)SIM can be moved to another UMTS or GSM phone, and the phone will take on the user details of the (U)SIM, meaning it is the (U)SIM (not the phone) which determines the phone number of the phone and the billing for calls made from the phone.

Japan was the first country to adopt 3G technologies, and since they had not used GSM previously they had no need to build GSM compatibility into their handsets and their 3G handsets were smaller than those available elsewhere. In 2002, NTT DoCoMo's FOMA 3G network was the first commercial W-CDMA network—it was initially incompatible with the UMTS standard at the radio level but used standard USIM cards, meaning USIM card based roaming was possible (transferring the USIM card into a UMTS or GSM phone when travelling). Both NTT and SoftBank Mobile (which launched 3G in December 2002) now use the standard UMTS, and their PDC 2G networks run in parallel.

Spectrum allocation

Main article: UMTS frequency bands

Over 130 licenses have already been awarded to operators worldwide (as of December 2004), specifying W-CDMA radio access technology that builds on GSM. In Europe, the license process occurred at the tail end of the technology bubble, and the auction mechanisms for allocation set up in some countries resulted in some extremely high prices being paid for the original 2100 MHz licenses, notably in the UK and Germany. In Germany, bidders paid a total €50.8 billion for six licenses, two of which were subsequently abandoned and written off by their purchasers (Mobilcom and the Sonera/Telefonica consortium). It has been suggested that these huge license fees have the character of a very large tax paid on future income expected many years down the road. In any event, the high prices paid put some European telecom operators close to bankruptcy (most notably KPN). Over the last few years some operators have written off some or all of the license costs. More recently, a carrier in Finland has begun using 900 MHz UMTS in a shared arrangement with its surrounding 2G GSM base stations, a trend that is expected to expand over Europe in the next 1–3 years.

The 2100 MHz UMTS spectrum allocated in Europe is already used in North America. The 1900 MHz range is used for 2G (PCS) services, and 2100 MHz range is used for satellite communications. Regulators have, however, freed up some of the 2100 MHz range for 3G services, together with the 1700 MHz for the uplink. UMTS operators in North America who want to implement a European style 2100/1900 MHz system will have to share spectrum with existing 2G services in the 1900 MHz band.

AT&T Wireless launched UMTS services in the United States by the end of 2004 strictly using the existing 1900 MHz spectrum allocated for 2G PCS services. Cingular acquired AT&T Wireless in 2004 and has since then launched UMTS in select US cities. Cingular renamed itself AT&T and is rolling out some cities with a UMTS network at 850 MHz to enhance its existing UMTS network at 1900 MHz and now offers subscribers a number of UMTS 850/1900 phones.

T-Mobile's rollout of UMTS in the US will focus on the 2100/1700 MHz bands, whereas UMTS coverage in Canada is being provided on the 850 MHz band of the Rogers Wirless network. In 2008, Australian telco Telstra replaced its existing CDMA network with a national 3G network, branded as NextG, operating in the 850 MHz band. Telstra currently provides UMTS service on this network, and also on the 2100 MHz UMTS network, through a co-ownership of the owning and administrating company 3GIS. This company is also co-owned by Hutchison 3G Australia, and this is the primary network used by their customers. Optus is currently rolling out a 3G network operating on the 2100 MHz band in cities and most large towns, and the 900 MHz band in regional areas. Vodafone is also building a 3G network using the 900 MHz band. The 850 MHz and 900 MHz bands provide greater coverage compared to equivalent 1700/1900/2100 MHz networks, and are best suited to regional areas where greater distances separate subscriber and base station.

Carriers in South America are now also rolling out 850 MHz networks.

Other competing standards

There are other competing 3G standards, such as CDMA2000 and TD-SCDMA, though UMTS can use the latter's air interface standard.

On the Internet access side, competing systems include WiMAX and Flash-OFDM. Different variants of UMTS compete with different standards. While this article has largely discussed UMTS-FDD, a form oriented for use in conventional cellular-type spectrum, UMTS-TDD, a system based upon a TD-CDMA air interface, is used to provide UMTS service where the uplink and downlink share the same spectrum, and is very efficient at providing asymmetric access. It provides more direct competition with WiMAX and similar Internet-access oriented systems than conventional UMTS.

Both the CDMA2000 and W-CDMA air interface systems are accepted by ITU as part of the IMT-2000 family of 3G standards, in addition to UMTS-TDD's TD-CDMA, Enhanced Data Rates for GSM Evolution (EDGE) and China's own 3G standard, TD-SCDMA.

CDMA2000's narrower bandwidth requirements make it easier than UMTS to deploy in existing spectrum along with legacy standards. In some, but not all, cases, existing

GSM operators only have enough spectrum to implement either UMTS or GSM, not both. For example, in the US D, E, and F PCS spectrum blocks, the amount of spectrum available is 5 MHz in each direction. A standard UMTS system would saturate that spectrum.

In many markets however, the co-existence issue is of little relevance, as legislative hurdles exist to co-deploying two standards in the same licensed slice of spectrum.

Most GSM operators in North America as well as others around the world have accepted EDGE as a temporary 3G solution. AT&T Wireless launched EDGE nationwide in 2003, AT&T launched EDGE in most markets and T-Mobile USA has launched EDGE nationwide as of October 2005. Rogers Wireless launched nation-wide EDGE service in late 2003 for the Canadian market. Bitė Lietuva (Lithuania) was one of the first operators in Europe to launch EDGE in December 2003. TIM (Italy) launched EDGE in 2004. The benefit of EDGE is that it leverages existing GSM spectrums and is compatible with existing GSM handsets. It is also much easier, quicker, and considerably cheaper for wireless carriers to "bolt-on" EDGE functionality by upgrading their existing GSM transmission hardware to support EDGE than having to install almost all brand-new equipment to deliver UMTS. EDGE provides a short-term upgrade path for GSM operators and directly competes with CDMA2000.

[edit] Problems and issues

Some countries, including the United States and Japan, have allocated spectrum differently from the ITU recommendations, so that the standard bands most commonly used for UMTS (UMTS-2100) have not been available. In those countries, alternative bands are used, preventing the interoperability of existing UMTS-2100 equipment, and requiring the design and manufacture of different equipment for the use in these markets. As is the case with GSM900 today, standard UMTS 2100 MHz equipment will not work in those markets. However, it appears as though UMTS is not suffering as much from handset band compatibility issues as GSM did, as many UMTS handsets are multi-band in both UMTS and GSM modes. Quad-band GSM (850, 900, 1800, and 1900 MHz bands) and tri-band UMTS (850, 1900, and 2100 MHz bands) handsets are becoming more commonplace.

The early days of UMTS saw rollout hitches in many countries. Overweight handsets with poor battery life were first to arrive on a market highly sensitive to weight and form factor. The Motorola A830, a debut handset on Hutchison's 3 network, weighed more than 200 grams and even featured a detachable camera to reduce handset weight. Another significant issue involved call reliability, related to problems with handover from UMTS to GSM. Customers found their connections being dropped as handovers were possible only in one direction (UMTS → GSM), with the handset only changing back to UMTS after hanging up. In most networks around the world this is no longer an issue.

Compared to GSM, UMTS networks initially required a higher base station density. For fully-fledged UMTS incorporating video on demand features, one base station needed to be set up every 1–1.5 km (0.62–0.93 mi). This was the case when only the 2100 MHz band was being used, however with the growing use of lower-frequency bands (such as 850 and 900 MHz) this is no longer so. This has led to increasing rollout of the lower-band networks by operators since 2006.

Even with current technologies and low-band UMTS, telephony and data over UMTS is still more power intensive than on comparable GSM networks. Apple, Inc. cited[7] UMTS power consumption as the reason that the first generation iPhone only supported EDGE. Their release of the iPhone 3G quotes talk time on UMTS as half that available when the handset is set to use GSM. As battery and network technology improves, this issue is lessening in severity.

[edit] See also

(disambiguation).

4G (also known as Beyond 3G), an abbreviation for Fourth-Generation, is a term used to describe the next complete evolution in wireless communications. A 4G system will be able to provide a comprehensive IP solution where voice, data and streamed multimedia can be given to users on an "Anytime, Anywhere" basis, and at higher data rates than previous generations.

As the second generation was a total replacement of the first generation networks and handsets, and the third generation was a total replacement of second generation networks and handsets, so too the fourth generation cannot be an incremental evolution of current 3G technologies, but rather the total replacement of the current 3G networks and handsets. The international telecommunications regulatory and standardization bodies are working for commercial deployment of 4G networks roughly in the 2012-2015 time scale. At that point it is predicted that even with current evolutions of third generation 3G networks, these will tend to be congested.

There is no formal definition for what 4G is; however, there are certain objectives that are projected for 4G. These objectives include: that 4G will be a fully IP-based

integrated system. 4G will be capable of providing between 100 Mbit/s and 1 Gbit/s speeds both indoors and outdoors, with premium quality and high security. [1]

Many companies have taken self-serving definitions and distortions about 4G to suggest they have 4G already in existence today, such as several early trials and launches of WiMAX. Other companies have made prototype systems calling those 4G. While it is possible that some currently demonstrated technologies may become part of 4G, until the 4G standard or standards have been defined, it is impossible for any company currently to provide with any certainty wireless solutions that could be called 4G cellular networks that would conform to the eventual international standards for 4G. These confusing statements around "existing" 4G have served to confuse investors and analysts about the wireless industry.

Objective and approach

Objectives

4G is being developed to accommodate the quality of service (QoS) and rate requirements set by forthcoming applications like wireless broadband access, Multimedia Messaging Service (MMS), video chat, mobile TV, HDTV content, Digital Video Broadcasting (DVB), minimal service like voice and data, and other streaming services for "anytime-anywhere". The 4G working group has defined the following as objectives of the 4G wireless communication standard:

A spectrally efficient system (in bits/s/Hz and bits/s/Hz/site),[2]

High network capacity: more simultaneous users per cell,[3]

A nominal data rate of 100 Mbit/s while the client physically moves at high speeds relative to the station, and 1 Gbit/s while client and station are in relatively fixed positions as defined by the ITU-R,[1]

A data rate of at least 100 Mbit/s between any two points in the world,[1]

Smooth handoff across heterogeneous networks,[4]

Seamless connectivity and global roaming across multiple networks,[5]

High quality of service for next generation multimedia support (real time audio, high speed data, HDTV video content, mobile TV, etc)[5]

Interoperability with existing wireless standards,[6] and An all IP, packet switched network.[5]

In summary, the 4G system should dynamically share and utilise network resources to meet the minimal requirements of all the 4G enabled users.

Approaches

As described in 4G consortia including WINNER, WINNER - Towards Ubiquitous Wireless Access, and WWRF, a key technology based approach is summarized as follows, where Wireless-World-Initiative-New-Radio (WINNER) is a consortium to enhance mobile communication systems.[7][8]

[edit] Consideration points

Coverage, radio environment, spectrum, services, business models and deployment types, users

[edit] Principal technologies

Baseband techniques[9] o OFDM: To exploit the frequency selective

channel propertyo MIMO: To attain ultra high spectral efficiencyo Turbo principle: To minimize the required SNR

at the reception side Adaptive radio interface Modulation, spatial processing including multi-

antenna and multi-user MIMO Relaying, including fixed relay networks (FRNs), and

the cooperative relaying concept, known as multi-mode protocol

[edit] 4G features

According to the 4G working groups, the infrastructure and the terminals of 4G will have almost all the standards from 2G to 4G implemented. Although legacy systems are in place to adopt existing users, the infrastructure for 4G will be only packet-based (all-IP). Some proposals suggest having an open platform where the new innovations and evolutions can fit. The technologies considered to be "pre-4G" include Flash-OFDM, WiMax, WiBro, iBurst, and 3GPP Long Term Evolution. One of the first technology really fulfilling the 4G requirements as set by the ITU-R

will be LTE Advanced as currently standardized by 3GPP. LTE Advanced will be an evolution of the 3GPP Long Term Evolution. Higher data rates are for instance achieved by the aggregation of multiple LTE carriers that are currently limited to 20MHz bandwidth[10].

[edit] Components

[edit] Access schemes

As the wireless standards evolved, the access techniques used also exhibited increase in efficiency, capacity and scalability. The first generation wireless standards used plain TDMA and FDMA. In the wireless channels, TDMA proved to be less efficient in handling the high data rate channels as it requires large guard periods to alleviate the multipath impact. Similarly, FDMA consumed more bandwidth for guard to avoid inter carrier interference. So in second generation systems, one set of standard used the combination of FDMA and TDMA and the other set introduced a new access scheme called CDMA. Usage of CDMA increased the system capacity and also placed a soft limit on it rather than the hard limit. Data rate is also increased as this access scheme is efficient enough to handle the multipath channel. This enabled the third generation systems to used CDMA as the access scheme IS-2000, UMTS, HSXPA, 1xEV-DO, TD-CDMA and TD-SCDMA. The only issue with CDMA is that it suffers from poor spectrum flexibility and scalability.

Recently, new access schemes like Orthogonal FDMA (OFDMA), Single Carrier FDMA (SC-FDMA), Interleaved

FDMA and Multi-carrier code division multiple access (MC-CDMA) are gaining more importance for the next generation systems. WiMax is using OFDMA in the downlink and in the uplink. For the next generation UMTS, OFDMA is being considered for the downlink. By contrast, IFDMA is being considered for the uplink since OFDMA contributes more to the PAPR related issues and results in nonlinear operation of amplifiers. IFDMA provides less power fluctuation and thus avoids amplifier issues. Similarly, MC-CDMA is in the proposal for the IEEE 802.20 standard. These access schemes offer the same efficiencies as older technologies like CDMA. Apart from this, scalability and higher data rates can be achieved.

The other important advantage of the above mentioned access techniques is that they require less complexity for equalization at the receiver. This is an added advantage especially in the MIMO environments since the spatial multiplexing transmission of MIMO systems inherently requires high complexity equalization at the receiver.

In addition to improvements in these multiplexing systems, improved modulation techniques are being used. Whereas earlier standards largely used Phase-shift keying, more efficient systems such as 64QAM are being proposed for use with the 3GPP Long Term Evolution standards.

IPv6

Main articles: Network layer, Internet protocol, and IPv6

Unlike 3G, which is based on two parallel infrastructures consisting of circuit switched and packet switched network nodes respectively, 4G will be based on packet switching only. This will require low-latency data transmission.

By the time that 4G is deployed, the process of IPv4 address exhaustion is expected to be in its final stages. Therefore, in the context of 4G, IPv6 support is essential in order to support a large number of wireless-enabled devices. By increasing the number of IP addresses, IPv6 removes the need for Network Address Translation (NAT), a method of sharing a limited number of addresses among a larger group of devices.

In the context of 4G, IPv6 also enables a number of applications with better multicast, security, and route optimization capabilities. With the available address space and number of addressing bits in IPv6, many innovative coding schemes can be developed for 4G devices and applications that could aid deployment of 4G networks and services.

[edit] Advanced Antenna Systems

Main articles: MIMO and MU-MIMO

The performance of radio communications obviously depends on the advances of an antenna system, refer to smart or intelligent antenna. Recently, multiple antenna technologies are emerging to achieve the goal of 4G systems such as high rate, high reliability, and long range communications. In the early 90s, to cater the growing data

rate needs of data communication, many transmission schemes were proposed. One technology, spatial multiplexing, gained importance for its bandwidth conservation and power efficiency. Spatial multiplexing involves deploying multiple antennas at the transmitter and at the receiver. Independent streams can then be transmitted simultaneously from all the antennas. This increases the data rate into multiple folds with the number equal to minimum of the number of transmit and receive antennas. This is called MIMO (as a branch of intelligent antenna). Apart from this, the reliability in transmitting high speed data in the fading channel can be improved by using more antennas at the transmitter or at the receiver. This is called transmit or receive diversity. Both transmit/receive diversity and transmit spatial multiplexing are categorized into the space-time coding techniques, which does not necessarily require the channel knowledge at the transmit. The other category is closed-loop multiple antenna technologies which use the channel knowledge at the transmitter.

[edit] Software-Defined Radio (SDR)

SDR is one form of open wireless architecture (OWA). Since 4G is a collection of wireless standards, the final form of a 4G device will constitute various standards. This can be efficiently realized using SDR technology, which is categorized to the area of the radio convergence.

[edit] Developments

The Japanese company NTT DoCoMo has been testing a 4G communication system prototype with 4x4 MIMO called VSF-OFCDM at 100 Mbit/s while moving, and 1 Gbit/s while stationary. In February 2007, NTT DoCoMo completed a trial in which they reached a maximum packet transmission rate of approximately 5 Gbit/s in the downlink with 12x12 MIMO using a 100MHz frequency bandwidth while moving at 10 km/h,[11] and is planning on releasing the first commercial network in 2010.

Digiweb, an Irish fixed and wireless broadband company, has announced that they have received a mobile communications license from the Irish Telecoms regulator, ComReg. This service will be issued the mobile code 088 in Ireland and will be used for the provision of 4G Mobile communications.[12][13]. Digiweb launched a mobile broadband network using FLASH-OFDM technology at 872 MHz.

Pervasive networks are an amorphous and at present entirely hypothetical concept where the user can be simultaneously connected to several wireless access technologies and can seamlessly move between them (See handover, IEEE 802.21). These access technologies can be Wi-Fi, UMTS, EDGE, or any other future access technology. Included in this concept is also smart-radio (also known as cognitive radio technology) to efficiently manage spectrum use and transmission power as well as the use of mesh routing protocols to create a pervasive network.

Sprint plans to launch 4G services in trial markets by the end of 2007 with plans to deploy a network that reaches as many as 100 million people in 2008 and has also announced WiMax service called Xohm. Tested in Chicago, this speed was clocked at 100 Mbit/s.

Verizon Wireless announced on September 20, 2007 that it plans a joint effort with the Vodafone Group to transition its networks to the 4G standard LTE. The time of this transition has yet to be announced.

Canadian Wireless Provider TELUS announced that they will be cooperating with BELL CANADA to the next step in its evolution towards building a fourth generation (4G) wireless broadband network, the most advanced mobile broadband network in Canada. This new wireless network, based on the latest generation of High Speed Packet Access (HSPA) technology, will enable TELUS to easily transition to long term evolution (LTE) technology, the emerging worldwide LTE technology standard. The new network will 'futureproof' our technology and position TELUS for an easy transition to LTE/4G technology. Building will begin immediately and is expected to be complete by early 2010. When up and running, it will be one of the leading networks in the world.[14]

Applications

At the present rates of 15-30 Mbit/s, 4G is capable of providing users with streaming high-definition television, but the typical cellphone's or smartphone's 2" to 3" screen is a far cry from the big-screen televisions and video

monitors that got high-definition resolutions first and which suffer from noticeable pixelation much more than the typical 2" to 3" screen. A cellphone may transmit video to a larger monitor, however. At rates of 100 Mbit/s, the content of a DVD-5 (for example a movie), can be downloaded within about 5 minutes for offline access.

4G wireless standards

3GPP is currently standardizing LTE Advanced as future 4G standard. A first set of 3GPP requiremens on LTE Advanced has been approved in June 2008[15]. The working groups are currently evaluating various proposals for standardization. LTE Advanced will be standardized as part of the Release 10 of the 3GPP specification.

General Packet Radio Service (GPRS) is a packet oriented Mobile Data Service available to users of the 2G cellular communication systems Global System for Mobile Communications (GSM), as well as in the 3G systems. In the 2G systems, GPRS provides data rates from 56 up to 114 kbit/s.

GPRS data transfer is typically charged per megabyte of traffic transferred, while data communication via traditional circuit switching is billed per minute of connection time, independent of whether the user actually is using the capacity or is in an idle state. GPRS is a best-effort packet switched service, as opposed to circuit switching, where a certain Quality of Service (QoS) is guaranteed during the connection for non-mobile users.

2G cellular systems combined with GPRS are often described as "2.5G", that is, a technology between the second (2G) and third (3G) generations of mobile telephony. It provides moderate speed data transfer, by using unused Time division multiple access (TDMA) channels in, for example, the GSM system. Originally there was some thought to extend GPRS to cover other standards, but instead those networks are being converted to use the GSM standard, so that GSM is the only kind of network where GPRS is in use. GPRS is integrated into GSM Release 97 and newer releases. It was originally standardized by European Telecommunications Standards Institute (ETSI), but now by the 3rd Generation Partnership Project (3GPP).

A GPRS connection is established by reference to its Access Point Name (APN). The APN defines the services such as Wireless Application Protocol (WAP) access, Short Message Service (SMS), Multimedia Messaging Service (MMS), and for Internet communication services such as email and World Wide Web access.

Basics

The multiple access methods used in GSM with GPRS are based on frequency division duplex (FDD) and TDMA. During a session, a user is assigned to one pair of up-link and down-link frequency channels. This is combined with time domain statistical multiplexing, i.e. packet mode communication, which makes it possible for several users

to share the same frequency channel. The packets have constant length, corresponding to a GSM time slot. The down-link uses first-come first-served packet scheduling, while the up-link uses a scheme very similar to reservation ALOHA. This means that slotted Aloha (S-ALOHA) is used for reservation inquiries during a contention phase, and then the actual data is transferred using dynamic TDMA with first-come first-served scheduling.

GPRS originally supported (in theory) Internet Protocol (IP), Point-to-Point Protocol (PPP) and X.25 connections. The last has been typically used for applications like wireless payment terminals, although it has been removed from the standard. X.25 can still be supported over PPP, or even over IP, but doing this requires either a router to perform encapsulation or intelligence built in to the end-device/terminal e.g. UE(User Equipment). In practice, the mobile built-in browser uses IPv4. In this mode PPP is often not supported by the mobile phone operator, while IPv6 is not yet popular. But if the mobile is used as a modem to the connected computer, PPP is used to tunnel IP to the phone. This allows DHCP to assign an IP Address and then the use of IPv4 since IP addresses used by mobile equipment tend to be dynamic.

Class A Can be connected to GPRS service and GSM service (voice, SMS), using both at the same time. Such devices are known to be available today.

Class B 

Can be connected to GPRS service and GSM service (voice, SMS), but using only one or the other at a given time. During GSM service (voice call or SMS), GPRS service is suspended, and then resumed automatically after the GSM service (voice call or SMS) has concluded. Most GPRS mobile devices are Class B.

Class C Are connected to either GPRS service or GSM service (voice, SMS). Must be switched manually between one or the other service.

A true Class A device may be required to transmit on two different frequencies at the same time, and thus will need two radios. To get around this expensive requirement, a GPRS mobile may implement the dual transfer mode (DTM) feature. A DTM-capable mobile may use simultaneous voice and packet data, with the network coordinating to ensure that it is not required to transmit on two different frequencies at the same time. Such mobiles are considered pseudo-Class A, sometimes referred to as "simple class A". Some networks are expected to support DTM in 2007.

GPRS is new technology in which speed is a direct function of the number of TDMA time slots assigned, which is the lesser of (a) what the particular cell supports and (b) the maximum capability of the mobile device expressed as a GPRS Multislot Class

[edit] Coding scheme

 Coding scheme

 Speed (kbit/s)

CS-1 8.0CS-2 12.0CS-3 14.4CS-4 20.0

Transfer speed depends also on the channel encoding used. The least robust, but fastest, coding scheme (CS-4) is available near a base transceiver station (BTS), while the most robust coding scheme (CS-1) is used when the mobile station (MS) is further away from a BTS.

Using the CS-4 it is possible to achieve a user speed of 20.0 kbit/s per time slot. However, using this scheme the cell coverage is 25% of normal. CS-1 can achieve a user speed of only 8.0 kbit/s per time slot, but has 98% of normal coverage. Newer network equipment can adapt the transfer speed automatically depending on the mobile location.

Like CSD, HSCSD establishes a circuit and is usually billed per minute. For an application such as downloading, HSCSD may be preferred, since circuit-switched data are usually given priority over packet-switched data on a mobile network, and there are relatively few seconds when no data are being transferred.

 Technology  Download

(kbit/s)  Upload (kbit/s) 

 Configuration 

CSD 9.6 9.6 1+1HSCSD 28.8 14.4 2+1HSCSD 43.2 14.4 3+1

GPRS 80.020.0 (Class 8 & 10 and

CS-4)4+1

GPRS 60.040.0 (Class 10 and CS-

4)3+2

EGPRS (EDGE)

236.859.2 (Class 8, 10 and MCS-9)

4+1

EGPRS (EDGE)

177.6

118.4 (Class 10 and MCS-

9)

3+2

GPRS is packet based. When TCP/IP is used, each phone can have one or more IP addresses allocated. GPRS will store and forward the IP packets to the phone during cell handover (when you move from one cell to another). A radio noise induced pause can be interpreted by TCP as packet loss, and cause a temporary throttling in transmission speed.

Services and hardware

GPRS upgrades GSM data services providing:

Multimedia Messaging Service (MMS) Push to talk over Cellular PoC / PTT Instant Messaging and Presence -- Wireless Village Internet Applications for Smart Devices through

Wireless Application Protocol (WAP)

Point-to-point (PTP) service: internetworking with the Internet (IP protocols)

Short Message Service (SMS) Future enhancements: flexible to add new functions,

such as more capacity, more users, new accesses, new protocols, new radio networks.

SMS

GPRS can be used as the bearer of SMS. If SMS over GPRS is used, an SMS transmission speed of about 30 SMS messages per minute may be achieved. This is much faster than using the ordinary SMS over GSM, whose SMS transmission speed is about 6 to 10 SMS messages per minute

Availability

In many areas, such as France, telephone operators have priced GPRS relatively cheaply (compared to older GSM data transfer, CSD and HSCSD). Some mobile phone operators offer flat rate access to the Internet, while others charge based on data transferred, usually rounded up to 100 kilobytes.

During the heyday of GPRS in the developed countries, around 2005, typical prices varied from EUR €0,24 per megabyte to over €20 per megabyte. In developing countries, prices vary widely, and change. Some operators gave free access while they decided pricing, for example in Togocel.tg in Togo, West Africa, others were over-priced, such as Tigo of Ghana at one US dollar per megabyte or Indonesia at $3 per megabyte. AirTel of India charges $0.025 per megabyte. As of 2008, data access in Canada is still prohibitively expensive. For example, Fido charges $0.05 per kilobyte, or roughly $50 per megabyte.[1]. In Venezuela, Digitel charges about $20 per 100 Mb or $25 for unlimited access.

Pre-Paid SIM Cards allow travelers to buy short term internet access. The maximum speed of a GPRS connection offered in 2003 was similar to a modem connection in an analog wire telephone network, about 32 to 40 kbit/s, depending on the phone used. Latency is very high; a round-trip ping is typically about 600 to 700 ms and often reaches 1s. GPRS is typically prioritized lower than speech, and thus the quality of connection varies greatly.

In order to set up a GPRS connection for a wireless modem, a user must specify an access point name (APN), optionally a user name and password, and very rarely an IP address, all provided by the network operator.

Devices with latency/RTT improvements (via e.g. the extended UL TBF mode feature) are generally available. Also, network upgrades of features are available with certain operators. With these enhancements the active

round-trip time can be reduced, resulting in significant increase in application-level throughput speeds.

2G (or 2-G) is short for second-generation wireless telephone technology.

Second generation 2G cellular telecom networks were commercially launched on the GSM standard in Finland by Radiolinja (now part of Elisa Oyj) in 1991. Three primary benefits of 2G networks over their predecessors were that phone conversations were digitally encrypted, 2G systems were significantly more efficient on the spectrum allowing for far greater mobile phone penetration levels; and 2G introduced data services for mobile, starting with SMS text messages.

After 2G was launched, the previous mobile telephone systems were retrospectively dubbed 1G. While radio signals on 1G networks are analog, and on 2G networks are digital, both systems use digital signaling to connect the radio towers (which listen to the handsets) to the rest of the telephone system.

o

[edit] 2G technologies

2G technologies can be divided into TDMA-based and CDMA-based standards depending on the type of multiplexing used. The main 2G standards are:

GSM (TDMA-based), originally from Europe but used in almost all countries on all six inhabited continents (Time Division Multiple Access). Today accounts for over 80% of all subscribers around the world.

IS-95 aka cdmaOne, (CDMA-based, commonly referred as simply CDMA in the US), used in the Americas and parts of Asia. Today accounts for about 17% of all subscribers globally. Over a dozen CDMA operators have migrated to GSM including operators in Mexico, India, Australia and South Korea.

PDC (TDMA-based), used exclusively in Japan iDEN (TDMA-based), proprietary network used by

Nextel in the United States and Telus Mobility in Canada

IS-136 aka D-AMPS, (TDMA-based, commonly referred as simply TDMA in the US), was once prevalent in the Americas but most have migrated to GSM.

2G services are frequently referred as Personal Communications Service, or PCS, in the United States.

2.5G services enable high-speed data transfer over upgraded existing 2G networks. Beyond 2G, there's 3G,

with higher data speeds, and even evolutions beyond 3G, often called 3.5G. Sprint deployed the first 4G network in USA in Baltimore.

[edit] Capacities, advantages, and disadvantages

[edit] Capacity

Using digital signals between the handsets and the towers increases system capacity in two key ways:

Digital voice data can be compressed and multiplexed much more effectively than analog voice encodings through the use of various codecs, allowing more calls to be packed into the same amount of radio bandwidth.

The digital systems were designed to emit less radio power from the handsets. This meant that cells could be smaller, so more cells could be placed in the same amount of space. This was also made possible by cell towers and related equipment getting less expensive.

[edit] Advantages

Digital systems were embraced by consumers for several reasons.

The lower powered radio signals require less battery power, so phones last much longer between charges, and batteries can be smaller.

The digital voice encoding allowed digital error checking which could increase sound quality by reducing dynamic and lowering the noise floor.

The lower power emissions helped address health concerns.

Going all-digital allowed for the introduction of digital data services, such as SMS and email.

Greatly reduced fraud. With analog systems it was possible to have two or more "cloned" handsets that had the same phone number.

Enhanced privacy. A key digital advantage not often mentioned is that digital cellular calls are much harder to eavesdrop on by use of radio scanners. While the security algorithms used have proved not to be as secure as initially advertised, 2G phones are immensely more private than 1G phones, which have no protection against eavesdropping.

[edit] Disadvantages

The downsides of 2G systems, not often well publicized, are:

In less populous areas, the weaker digital signal may not be sufficient to reach a cell tower. This tends to be a particular problem on 2G systems deployed on higher frequencies, but is mostly not a problem on 2G systems deployed on lower frequencies. National regulations differ greatly among countries which dictate where 2G can be deployed.

Analog has a smooth decay curve, digital a jagged steppy one. This can be both an advantage and a disadvantage. Under good conditions, digital will sound better. Under slightly worse conditions, analog will experience static, while digital has occasional

dropouts. As conditions worsen, though, digital will start to completely fail, by dropping calls or being unintelligible, while analog slowly gets worse, generally holding a call longer and allowing at least a few words to get through.

While digital calls tend to be free of static and background noise, the lossy compression used by the codecs takes a toll; the range of sound that they convey is reduced. You'll hear less of the tonality of someone's voice talking on a digital cellphone, but you will hear it more clearly.

1G (or 1-G) is short for first-generation wireless telephone technology, cellphones. These are the analog cellphone standards that were introduced in the 1980s and continued until being replaced by 2G digital cellphones. The main difference between two succeeding mobile telephone systems, 1G and 2G, is that the radio signals that 1G networks use are analog, while 2G networks are digital.

Although both systems use digital signaling to connect the radio towers (which listen to the handsets) to the rest of the telephone system, the voice itself during a call is encoded to digital signals in 2G whereas 1G is only modulated to higher frequency, typically 150MHz and up.

One such standard is NMT (Nordic Mobile Telephone), used in Nordic countries, Switzerland, Netherlands, Eastern Europe and Russia. Others include AMPS (Advanced Mobile Phone System) used in the United States and

Australia[1], TACS (Total Access Communications System) in the United Kingdom, C-450 in West Germany, Portugal and South Africa, Radiocom 2000 in France, and RTMI in Italy. In Japan there were multiple systems. Three standards, TZ-801, TZ-802, and TZ-803 were developed by NTT, while a competing system operated by DDI used the JTACS (Japan Total Access Communications System) standard.