A. Noncoherent Orthogonal Modulation

Scheme. For a binary signaling scheme that involves the use of two signals

Tttsts ≤≤0),(),( 21

which are orthogonal with equal energy,

let Tttgtg ≤≤0),(),( 21

denote the phase-shifted version of , res. , which remain orthogonal and of equal energy. This scheme is referred to as noncoherent orthogonal modulation.

)(),( 21 tsts

3. Noncoherent Binary Modulation Techniques3. Noncoherent Binary Modulation Techniques

A digital communication receiver with no provision make for carrier phase recovery is said to be noncoherent.

@G. Gong 2

At the receiver, the received signal x(t) can be expressed as follows

⎩⎨⎧

≤≤+≤≤+

=TttstntgTttstntg

tx0 sent, )( ),()(

0 sent, )( ),()()(

22

11

The receiver tries to discriminate between s1(t) and s2(t), regardless of the carrier phase. This goal can be achieved by the following receiver structure:

)(tx Comparisondevice

1l

⎪⎪⎩

⎪⎪⎨

⎧

<

>

)( choose If

)( choose If

2

21

1

21

tsll

tsll

Figure 1. Binary receiver for noncoherent orthogonal modulation

Matchedto φ1(t)

Envelopedetector

2lMatchedto φ2(t)

Envelopedetector

Sample at t = T

Sample at t = T

An noncoherent matched filter may be viewed as being equivalent to a quadrature receiver, as illustrated below. The quadrature receiver itself has two channel (recall that QPSK receiver).

)(tx

×

)(tiφ

∫T

dt0

× ∫T

dt0

+ Squarerooter

2il

Let φ1(t) and φ2(t) be the orthonormal set of s1(t) and s2(t) and be the version of that results from shifting the carrier phase by -90 degrees . The quadrature receiver is shown in Figure 2 where i = 1, 2.

In-phase channel

Qradrature channel

)(~ tiφ

)(tiφ

Square-law

device

Square-law

device

2Iix

2Qix

Figure 2)(~ tiφ

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Remark. The average probability of error for the noncoherent receiver, Figure 1, or equivalently Figure 2, is given by a simple formula

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

02exp

21

NEPe

where E is the signal energy per symbol and N0/2 is the noise spectral density. We list this result here without proof. The proof can be found the text book.

(1)

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B. Noncoherent BFSK

For the binary FSK case, the transmitted signal is

2,1 0 ),2cos(2)( =≤≤= iTttfTEts bib

bi π 2,1 ,integer , ==

+= in

Tinf c

b

ci

i.e.,22

11

frequency using)(0 frequency using )(1

ftsfts

↔↔

Thus the noncoherent binary FSK is a special case of noncoherentorthogonal modulation with and , where Tb is the bit duration and Eb is the signal energy per bit. From (1), we have the average probability of error (bit error rate) for noncoherent BFSK is

bTT = bEE =

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

02exp

21

NEP b

e

)(txComparison

device

1l

⎪⎪⎩

⎪⎪⎨

⎧

<

>

0 choose If

1 choose If

21

21

ll

ll

Figure 3. Noncoherent receiver for BFSK

Matched to Envelopedetector

2lEnvelopedetector

Sample at t = Tb

Sample at t = Tb

tfTb 12cos/2 π

bTt ≤≤0

Remark. When comparing the error performance of noncoherent FSK with coherent PSK, it is seen that for the same Pe, noncoherent FSK requires approximately 1 dB more Eb/N0 than does BFSK (for ) , because coherent reference signals need not be generated. Therefore, almost all FSK receivers use noncoherent detection. In the following, we will see that the same phenomenon occurs for noncoherent DPSK and PSK.

410−≤eP

Matched to tfTb 22cos/2 π

bTt ≤≤0

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C. Differential Phase-shift Keying (DPSK)

Transmitter’s two operations: (1) differential encoding of the input binary sequence and(2) phase-shift keying

Generation of DPSK:

For an input binary sequence , a differential encoded sequence is determined by

kkk bdd ⊕= −1 or kkk bdd ⊕= −1

where ⊕ denotes the modulo 2 operation and the overbardenotes complement.

}{ kb}{ kd

}{ kb 1 1 0 1 0 1 1 0 0 1

Table 1. Illustrating the generation of DPSK signal

index k: 0 1 2 3 4 5 6 7 8 9 10

Differentially encoded sequence

}{ kd ref. bit 1 1 1 0 0 1 1 1 0 1 1 kkk bdd ⊕= −1

Corresponding phase shift

)}({ kθ π π 0 0 π π π 0 π π

Remark. DPSK is an another example of noncoherent orthogonal modulation, when it is considered over two bit intervals. In this case, from (1) we get the average probability of error for DPSK is

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

0

exp21

NEP b

e

since T = 2Tb and E = 2Eb.

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Remark. When comparing the error performance of (2) with that of coherent PSK, it is seen that for the same Pe, DPSK requires approximately 1 dB more Eb/N0 than does BPSK (for ). It is easier to implement a DPSK system than a PSK system, since the DPSK receiver does not need phase synchronization.

410−≤eP

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Error Probability of M-ary Digital PAM SignalsSignal Representation of M-ary PSKSignal Representation of M-ary FSK

4. M-ary Modulation Techniques4. M-ary Modulation Techniques

Quaternary case:

,)2/3()(1 ats −= ,)2/1()(2 ats −=

,)2/1()(3 ats = ,)2/3()( and 4 ats =

Tt ≤≤0for

)(1 tφZ3

Z1 Z4Z2

Tas23

11 −= Tas21

21 −= Tas21

31= Tas23

41=

Ta− Ta0

m1 = 00 m2 = 01 m3 = 11 m4 = 10

Signal Constellation of Quaternary Signaling Scheme under Gray Code

⎟⎟⎠

⎞⎜⎜⎝

⎛=

0243

NTaerfcPe

where is the minimum distance of the polar quaternary signal constellation.

⎟⎟⎠

⎞⎜⎜⎝

⎛=

0243

Nderfc

Tad =

A. Error Probability of M-ary Digital PAM Signals

)(1 tφ

Z1

000

ds27

11 −=

Tad =

ds21

51 = ds23

61 =

d0

⎟⎟⎠

⎞⎜⎜⎝

⎛==

0221)111()000(

NderfcPP ee

Try for M = 8, which has the signal constellation as below (Gray code). Show that

Z2

001

Z3

011

Z4

010

Z5

110

Z6

111

Z7

101

Z8

100

(1) (2)⎟⎟⎠

⎞⎜⎜⎝

⎛==

02)011()001(

NderfcPP ee

ds25

21 −= ds23

31 −= ds21

41 −= ds25

71 = ds27

81 =0

d2−d3− d− d2 d3

where which is the minimum distance of the above signal constellation.

In general, for M-ary PAM, if the signal points are

then

12111 ,,, Msss L

dMdddddM2

1,,23,

21,

21,

23,,

21 −

−−−

− LL

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

021

Nderfc

MMPe

@G. Gong 13

Tnf cc /=

Tt,...,MiM

itfTE

ts ci ≤≤=−

+= 0 ,1 ),)12(2cos(2

)( ππ

B. M-ary PSK Scheme:

The phase of carrier takes on one of M possible values, namely,

MiMii ,...,1 ,/)12( =−= πθ

A M-ary signal set is represented as

where T is the symbol duration and E is the signal energy per symbol. The carrier frequency where nc is a fixed integer.

@G. Gong 14

Thus, the signal constellation of M-ary PSK is two-dimensional. The M messages are equally spaced one circle of radius and center at the origin, see Figure 1 for an example of octa-PSK.

Figure 1. Signal Constellation for octa-PSK (M = 8). The decision boundaries are shown as dashed lines.

Similar as we did for QPSK, each signal si(t) can be represented by the following two orthogonal functions with unit energy:

)2sin(2)( and )2cos(2)( 21 tfT

ttfT

t cc πφπφ ==

M/π

M/π

is

Remark. The probability of correct reception is to integrate the shaded area. This probability can be bounded by some bound. Therefore, for large values of E/N0, the probability of symbol error is approximately given by

4

,sin20

,

≥

⎟⎟⎠

⎞⎜⎜⎝

⎛≈−

M

MNEQP PSKMe

π

The coordinates of the received signal given si(t) was transmitted is

where nI and nQ are Gaussian random variables with zero mean and variance N0/2 (why ?).

,)12(cos II nM

iEx +⎟⎠⎞

⎜⎝⎛ −

=π Min

MiEx QQ ,...,1 ,)12(cos =+⎟

⎠⎞

⎜⎝⎛ −

−=π

(A)

C. M-ary FSK

In an M-ary FSK scheme, the transmitted signals are defined by

MiTttfifTEtsi ,..,1,0 ,])1([2cos2)( 0 =≤≤Δ−+= π

where is taken as an integer for convenience and is the minimum frequency spacing such that adjacent signals are orthogonal (recall this result form MSK).

Tf0 )2/(1)( min Tf =Δ

For coherent M-ary FSK, the optimum receiver consists of a bank of M correlations or matched filters. At the sampling times t = kT, the receiver makes decisions based on the largest matched filter output. The probability of symbol error can be upper bounded by

⎟⎟⎠

⎞⎜⎜⎝

⎛−≤−

0, )1(

NEQMP FSKMe

where is the energy per symbol and M is the size of the symbol set.

)(log2 MEE b=

(B)

@G. Gong 17

5. Multi-carrier Modulation and OFDM5. Multi-carrier Modulation and OFDM

Applications of M-ary FSK: multicarrier modulation and OFDMGoal: for combating ISI

Multicarrier modulation is a way to transmit digital data through bandlimited channel. Design of a bandwidth-efficient communication system in the presence of channel distortion or equivalently ISI, is to divide the available channel bandwidth into a number of equal-bandwidth subchannels, where the bandwidth of each channel is sufficiently narrow so that the frequency response characteristics of the subchannels are nearly equal. Such a division of the overall bandwidth into smaller subchannels is illustrated in Figure 1.

@G. Gong 18

@G. Gong 19

Number of Subchannels: Then data symbol is transmitted by frequency-division multiplexing (FDM). This is known as a multicarriermodulation system. Orthogonality: Each subchannel is associated a carrier fi, where

which is the mid-frequency in the ith subchannel. If the subcarriers are orthogonal over the symbol duration T, then it is referred to as orthogonal frequency-division multiplexing (OFDM). Thus OFDM is a special case of multicarrier modulation.

Nififfi ,,1 ,)1(0 L=Δ−+=

Description:

fWN Δ= /

@G. Gong 20

ISI Reduction: the subcarriers are spaced by 1/Ts Hz, where Ts is the symbol duration of the subcarriers, then Tofdm, the symbol duration of the OFDM system is related by

By selecting N to be sufficiently large, the symbol interval Ts of the subcarriers can be made significantly larger than the time duration of the channel-time dispersion. Hence, ISI can be made arbitrarily small by selection of N. In other words, each subchannel appears to have a fixed frequency response C(fk), k = 0, 1, … , N - 1.

Description (Cont.):

ofdms NTT =

@G. Gong 21

@G. Gong 22

@G. Gong 23

@G. Gong 24

OFDM Implemented by IDFT and DFT

@G. Gong 25

Disadvantage: A major problem with the multicarrier modulation in general and OFDM system in particular is the high peak-to-averagepower ratio (PAR) that is inherent in the transmitted signal.

Applications: High-speed transmission over telephone lines, such as digital subcarrier lines. This type of OFDM modulator has also been called discrete multitone (DMT) modulator. OFDM is also used indigital audio broadcasting in Europe and other parts of the worldand in digital cellular communication systems.

@G. Gong 26

A. Bit Error Probabilities from Symbol Error Probabilities

There are two approaches to define an equivalent bit error probability, Pb, or bit error rate (BER), from a symbol error probability, Ps. It depends on

(1) structure of the signal space, and(2) the mapping of the signal space points into equivalent

bit sequences.

6. Comparison of Digital Modulation Systems6. Comparison of Digital Modulation Systems

@G. Gong 27

Definition 1. We assume that in going from one signal point to an adjacent signal point, only one bit in the binary word representing the signal changes. In this case,

MPP s

b2log

=

Remark. M-ary PSK, if a Gray code is employed and M-ary QAM are of the case.

In the following, we will give an explicit formula for Pb. Notice that

Definition 2. Denote . We assume that all symbol errors are equally likely. We define as theratio of A, the average number of bit errors per n-bit symbols to n, number of bits per symbol.

bP

Mn 2log=

)1( −MP s

- Each symbol is in error in an M-ary system with probability

)1(1

1 −⎟⎟⎠

⎞⎜⎜⎝

⎛== ∑

= MP

kn

knn

AP sn

kb

- For a given symbol error, suppose that k bits are in error.

There are ways that this can happen, which results⎟⎟⎠

⎞⎜⎜⎝

⎛kn

sPM

M)1(2 −

= 2/sP→

for large M.

Remark. M-ary FSK is of this case.

B. Bandwidth Efficiencies of M-ary Digital Comm. Systems (DCS)

Goal: Consider the bandwidth efficiencies in terms of bits per second per hertz (bps/Hz) of bandwidth of various digital modulation schemes.

For a M-ary DCS, let Rb denote the bit rate and Rs symbol rate. Then

sb RMR )(log 2=

For a M-ary PSK, QAM, DPSK, the null to null bandwidth is

MRB b

XM2

, log2

= (bps/Hz) )(log5.0 2,

MB

R

XM

b ==⇒ ρ

@G. Gong 30

For a M-ary FSK, consider the spacing between frequency is minimum. Then the bandwidth is

MRMB b

MFSKcoh2

, log2)3( +

=

Table 1. Bandwidth Efficiencies of M-ary Signals

M 2 4 8 16 32 64

2.5 3

.1875.3125

ρ: PSKDPSKQAM

0.5 1 1.5 2

ρ : FSK 1 1 .75 .5

(bps/Hz) 3

log2 2

, +==⇒

MM

BR

MFSKcoh

bρ

Remark:

(1) M-ary PSK and M-ary QAM have 2-dimensional signal space and they are both bandwidth efficient (or called spectral efficient).

(2) MFSK has M-dimensional signal space and it is bandwidth inefficient.

Note. The other parameter used in comparing performance (power efficiencies) of different schemes is E/N0, the ratio of symbol energy to noise power spectral density. In other words, it is to make comparisons between different DSCs on the basis of the relative signal power needed to support a given received information rate assuming identical noise environment.

510 −=eP

)dB(/ 0NE b

R = C

2

4

8

16

8 0-.1-1.6 6 12 1 24 3-2

M-PSK

4

16

2

WR b /=ρ

16 M-QAM

1

1/2

M=24

816

M-FSK

Power limited region

Bandwidth limited region

R < CR > C

Figure 1. Band Width Efficiency Plane

C = W log2(1 + P/WN0)bits/s

Shannon’s system capacity C of an AWGN channel:

@G. Gong 33

7. Synchronization7. Synchronization

Synchronization at three levels:

A. Carrier synchronization (or called carrier recovery): for estimation of carrier phase and frequency.

When the coherent detection is used, the knowledge of both the frequency and phase of the carrier is necessary. In other words, there has to be phase concurrence between the incoming carrier and a replica of it in the receiver. This is achieved by employing a phase-locked loop (PLL). The following figure shows a block diagram for carrier synchronization for M-ary PSK.

Received M-ary PSKsignal

Mthpower-law BPF × LPF

VCO

Frequency divide by M

Phase-locked loop

To data demodulator/detector

If M = 2, this loop is called a squaring loop.

Figure 1. Mth Power Loop

@G. Gong 35

B. Symbol Synchronization (or called clock recovery)

The receiver has to know the instant of time at which the modulation can change its state., i.e., the starting and finishing times of the individual symbols, so that it may determine when to sample and when to quench the product integrator. The estimation of these times is called symbol synchronization or clock recovery.

Note. There are typically a very large number of carrier cycles per symbol period, this second level of synchronization is much coarser than phase synchronization (PS), and is usually done with different circuitry than that used for PS.

@G. Gong 36

One of methods that can achieve this goal is to employ a closed-loop symbol synchronizer. Among the class of closed-loop symbol synchronizers, the early/late-gate synchronizer is the most popular one which shown in Figure 3.

TT 0Δ−

(a) Rectangular pulse g(t)

t

g(t)

a

0 T T TT 0Δ+ 2T0

Ta2

(b) Output of filter matched to g(t)

Figure 2.

∫T

ddt

+

Absolutevalue

∫−dT

dt0

Absolutevalue

VCO F(ω)

|| 1y

|| 2y

|||| 12 yye −=

1y

2y

Loopfilter

Late gate

Early gate

timing

Td 0Δ=

Figure 3. Early/late-gate data synchronizer

@G. Gong 38

C. Frame Synchronization

Almost all digital data steams have some sort of frame structure. This is to say that the data stream is organized into uniformly sized groups of bits.

For a receiver to make sense of the incoming data stream, the receive needs to be synchronized with the data streams’frame structure. This is called frame synchronization. This is usually accomplished with the aid of some special signaling procedure from the transmitter.

The simplest frame synchronization aid is the frame marker, for example, in T1 system, for a total of 193 bit, one bit is to used as the frame marker.

@G. Gong 39

The frame marker could be a single bit, or a short pattern of bits that the transmitter injects periodically into the data stream. The receiver must know the pattern and the injection interval. See Figure 4.

@G. Gong 40

n bits

…

n bits

…

K bits K bits

Data stream

n bits K bits n bits K bits

Receiver generated frame marker replica

Figure 4. Frame marker illustration

@G. Gong 41

The receiver, having achieved symbol synchronization, correlated the known pattern with the incoming data stream at the known injection interval. If the receiver is not in synchronization with the framing pattern, the accumulated correlation will be low, otherwise, it should be nearly perfect, blemished only by an occasional detection error.

A good synchronization codeword is one that has the property that the absolute value of its “correlation sidelobes” is small. The bit sequences with the property that their largest sidelobe has a magnitude of unity are known as Barker sequences. Unfortunately, the Barker sequences only exist for the length less than 13.

8. Applications to Digital Cellular Communication Systems

In this section, we will present an overview of two types of digital cellular communications systems that are currently in use. One is the GSM ( Global System for Mobile Communication) systems that is widely used in Europe and other parts of the world. It employs time-division multiple access (TDMA) to accommodate multiple users. The second is the CDMA system based on Interim Standard 95 (IS-95) that is widely used in North America and some countries in the Far East.

Remark. The extended versions of GSM and IS-95 are UMTS (Universal Mobile Telecommunications Systems, 1998 or W-CDMA) and CDMA 2000, respectively.

@G. Gong 43

Generation 1G 2G 2.5G 3G 4/5G

Time Frame 1980s 1990s Late 1990s 2000s(2010 full deployment)

2010s

Signal Type Analog Digital Digital Digital Digital

Multiple Access

FDMA/FDD TDMA/FDDCDMA/FDD

EDGE, GPRS CDMA, W-CDMA, TD-SCDMA

MC-CDMA, OFDM

Frequency spectrum

824-894 MHz890-960 MHz1850-1990 MHz (PCS)

1800-2400 MHz (varies country to country)

Higher-frequency bands 2-8 GHz

Bandwidth 5-20 MHz ≥ 100 MHz

Antenna Optimized antenna, multiband adapter

Smarter antenna, Multiband and wide-band support

FEC Convolutionalrate, 1/2, 1/3

Concatenated coding scheme

Media type Voice Mostly voiceLow-speed data services via modem (10-70 kbps)

Mostly voiceHigher-speed data (10-384 kbps)

Voice High-speed data (144kbps-2Mbps)

Converged voice/data/mutimediaover IP; Ultra-high-speed data (2-100 Mbps)

Evolution of Mobile Communications Systems

@G. Gong 44

Generation 1G 2G 2.5G 3G 4/5G

Network type

Celluar Celluar Celluar WWANCell based

Integrated WWAN, WMAN, WLAN (Wi-Fi, Bluetooth) and WPAN (Bluetooth)

Structure Infrastructure based

Infrastructure based

Infrastructure based

Infrastructure based network

Hybrid of Infrastructure based and ad hoc network

Switching Circuit switched

Circuit switched Circuit switched

Circuit switchedAnd packet switched

Packet switched

IP support N/A N/A N/A Use several air link protocols, including IP5.0

All IP based (IP6.0)

New applications

Emails, maps/directions, News, shopping, e-commerce, interactive gaming, etc.

Ubiquitous computing with location intelligence

Security M-sequences for voice enc

A5, m-sequences in CDMA, authentication symmetric crypto

A5, m-seq. auth.

Stream cipher, block cipher, symmetric key auth

Public key crypto

Ex system AMPS, NMT, TACS

GSM, DCS1900, IS-95,CdmaOne

GPRS, EDGE

UMTS, IMT200, CDMA2000, WCDMA

×

RPE-LPC

speech coder

analogspeech

13 kbpsChannel

coder

Blockinter-leaver

22.8kbps

Burstassembler

andencryption

TDMAmultiplexer

GMSKmodulator

Frequencyhopping

synthesizer

Channelmeasurement

bits

7 otherusers

…270.8kbps To

transmitter

(a) Modulator PN codegenerator

Frequencysynthesizer

Receivedsignal

PN codegenerator

LPF and A/O

converterBuffer Matched

filterChannelequalizer

Decryptionand

deinterleavingChanneldecoder

Speechsynthesis

(b) Demodulator

Functional block diagram of modulator and demodulator for GSM

@G. Gong 46

Summary of Parameters in GSM System

System Parameters Specification

Uplink frequency band 890-915 MHz

Downlink frequency band 935-960 MHz

Number of carriers/band 125

Multiple-access method TDMA

Number of users/carrier 8

Date rate/carrier 270.8 Kbps

Speech-coding rate 13 KHz

Speech encoder RPE-LPC

Coded-speech rate 22.8 kbps

Modulation GMSK with BT = 0.30

Interleaver Block

Frequency-hopping rate 217 hops/sec

Multiple Access Methods

The CDMA Cocktail Party

This is great stuff

Where is she

How long will this take

You know thatWhere is the meeting

Who called

Can I go home?How can I get there

Where is the office

Who knows

@G. Gong 49

Multiple users share a common channel simultaneously by using different codesNarrowband user information is spread into a much wider spectrumby the spreading codeThe signal from other users will be seen as a background noise: multiple access interference (MAI)The limit of the maximum number of users in the system is determined by interference due to multiple access and multipathfading: Adding one user to CDMA system will only cause graceful degradation of quality

Theoretically, no fixed maximum number of users !

Code Division Multiplexing Access (CDMA)Code Division Multiplexing Access (CDMA)

@G. Gong 50

Despread signal PSD for user 1

Bandwidth

Received signal PSD

Bandwidthuser 1 user 2 user 3 user 4

user M

user 2 user 3 user 4

user M

user 1

signal power

Interferencepower

CDMA is an interference-limitedmultiple access scheme

Despreading

The signal from other users will be seen as a background noise: Multiple access interference (MAI)

Code Division Multiplexing Access (CDMA) (Cont.)Code Division Multiplexing Access (CDMA) (Cont.)

CDMA System Design

VOCODER

1 0 1 0 0 1 CODEC

Voice Coding

Voice Coding

Power Control

9600 bps 4800 bps 2400 bps 1200 bps

Convolutional Encoder and Repetition

Block Interleaver

Wt

1.2288 Mcps

I PN

QPN

1.2288 Mcps

Decimator

MU

X

DecimatorLong

Code PN Generator

User Address Mask (ESN)

19.2 ksps

19.2 ksps

800 Hz

4

Power Control

BitR = 1/2

Forward Link Generation

1 0 1 0 0 1 CODEC

9600 bps 4800 bps 2400 bps 1200 bps

User Address Mask

Convolutional Encoder and Repetition

Block Interleaver

Long Code PN Generator

28.8 ksps

28.8 ksps Walsh

Cover

307.2 kHz

R = 1/3

Data Burst Randomizer

1.2288 Mcps

I PN

QPN

1/2 PN Chip Dela

D1.2288 Mcps

Mobile

Cell

Reverse Link Generation

The CDMA Rate FamiliesIS-95 defines the 9600 bps family of rates (Rate Set 1)

9600, 4800, 2400, and 1200 bpsCan select one of the four rates every 20 ms frame

14400 bps family of rates (Rate Set 2)14400, 7200, 3600, and 1800 bpsCan select one of the four rates every 20 ms frame

Extended rates (extended Rate Set 1)Adds 19200, 38400, and 76800 bpsAt most four rates can be activeCan select one of the four active rates every 20 ms frame

Variable-Rate Vocoder

Encoder

Decoder

64 kbps

PCM

Full Rate

1/2 Rate

1/4 Rate

1/8 Rate

4 kbps

2 kbps

0.8 kbps

8.55 kbps

Encoder

Decoder64 kbps

PCM

20 ms Packets

Link Waveform

CDMA Forward Link WaveformPilot ChannelSync ChannelPaging ChannelTraffic Channel

CDMA REVERSE Link WaveformAccess ChannelTraffic Channel

QTSO

QTSO

@G. Gong 55

Rate ½, L = 9

Convolutionencoder

withrepetition

Data

9.6 kbps 4.8 kbps2.4 kbps1.2 kbps

Blockinter-leaver × × ×

× + ×Basebandshaping

filter

× + ×Basebandshaping

filter

-90 deg.

Carriergenerator

To

transmitter

PN codegeneratorQ channel

PN codegeneratorI channel

Long codegenerator Decimator

Hadamard(Walsh)sequence

Mask

Block diagram of IS-95 forward link

Pilot channeland othertrafficchannels insame cell

Pilot channeland othertrafficchannels insame cell

Reverse CDMA Channel

AccessCh 1

TrafficCh 1

TrafficCh m

• • • AccessCh n

REVERSE CDMA CHANNEL(1.23 MHz channel received by

base station)

• • • • • • • • • • • • • • • • • • • • • • • •

Addressed by Long Code PNs

Reverse Traffic Channel Structure for Rate Set 1

9.6 kbps 4.8 kbps 2.4 kbps 1.2 kbps

Convolutional Encoder

r=1/3, K=9

Reverse Traffic Channel

Information Bits

(172, 80, 40, or 16 bits/frame)

Code Symbol

Code Symbol

28.8 ksps

Add 8 bit Encoder Tail

Add Frame Quality Indica- tors (12, 8, 0,

or 0 bits/frame)8.6 kbps 4.0 kbps 2.0 kbps 0.8 kbps

1/2 PN chip Delay = 406.9 ns

D Q(t)

I(t)Baseband Filter

Baseband Filter

Data Burst Randomizer

I-channel Sequence 1.2288 Mcps

Q-channel Sequence 1.2288 Mcps

I

Q

Long Code

Generator

PN chip 1.2288 Mcps

Long Code Mask

Frame Data Rate

s(t)Σ

28.8 ksps 14.4 ksps 7.2 ksps 3.6 ksps

28.8 ksps

64-ary Orthogonal Modulator

Modulation Symbol

(Walsh chip)

4.8 ksps (307.2 kcps)

Block Interleaver

Symbol Repetition

Code Symbol

cos(2πfct)

sin(2πfct)

Summary of Parameters in IS-95 System

System Parameters Specification

Uplink frequency band 824-849 MHz

Downlink frequency band 869-894 MHz

Number of carriers/band 20

Multiple-access method CDMA

Number of users/carrier 60

Chip rate 1.2288 Mbps

Speech coder Variable rate, CELP

Speech rate 9600, 4800, 240, 1200

Interleaver Block

Channel encoder R=1/2,L=9(D), R=1/2, L=9(U)

Modulation BPSK with QPSK spreading (D)64-ary orthogonal with QPSK spreading (U)

Signature sequences Hadamard (Walsh) of length 64

PN sequence 242-1 (long code), 215 (spreading codes)