general packet radio service gprs
TRANSCRIPT
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PROJECT: GPRS WIRELESS SYSTEMS (TSKS03)
Name : Susmita Saha Pnr : 910619-T282
Email : [email protected]
Assignment
2016
Wireless Systems (ISY)
Linköping University (Li.U), SE-581 83
Linköping, Sweden
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Table of Contents Acronyms ................................................................................................................................................ 3
1. Introduction .................................................................................................................................... 4
2. History of GPRS ............................................................................................................................... 4
3. GPRS Characteristics ....................................................................................................................... 4
4. GSM Architecture ............................................................................................................................ 4
5. GPRS Description ............................................................................................................................ 6
6. GPRS Architecture ........................................................................................................................... 6
7. GPRS modulation ............................................................................................................................ 8
8. GPRS performance categories ........................................................................................................ 8
9. Error correction and coding scheme ............................................................................................... 9
10. Services offered by GPRS .......................................................................................................... 10
11. Advantages ................................................................................................................................ 11
12. Drawbacks ................................................................................................................................. 11
13. Conclusion ................................................................................................................................. 11
14. References ................................................................................................................................ 12
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Acronyms GPRS- General Packet Radio Service.
GSM- Global systems for mobile communications.
SGSN- Serving GPRS Support Node.
GGSN- Gateway GPRS support node.
MS- Mobile station.
PDP- Packet data protocol.
BSS- Base Station subsystem.
NSS- Network station subsystem.
RSS- Radio station subsystem.
GSS- Gateway subsystem.
BTS- Base transceiver station.
BSC- Base station controller.
MSC- Mobile switching centre.
HLR- Home location register.
VLR- Visitor location register.
EIR- Equipment identity register.
AUC- Authentication centre.
PCU- Packet control unit.
BG- Border gateway.
CG- Charging gateway.
DNS- Domain name server.
PSTN- Public switch telephone network.
PLMN- Public land mobile network.
CKSN- Cipher key sequence number.
PDN- Packet data network.
IN- Intelligent Network.
GMSC- Gateway mobile switching centre.
SMSC- Short message service centre.
ETSI- European Telecommunications standards institute.
SIM- Subscriber identity module.
NMS- Network management system.
OSS- Operation station subsystem.
OMC- Operation and maintenance centre.
OMCR- Operation and maintenance centre for radio.
OMCS- Operation and maintenance centre for switch.
ETSI- European Telecommunications Standards Institute.
3GPP- 3rd Generation Partnership Project.
TDMA- Time division multiple access.
CDMA- Code division multiple access.
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1. Introduction
The report is about the General Packet Radio Service (GPRS) which is a packet oriented technology for
GSM (Global systems for mobile communications) mobile communication network. GPRS is
mentioned as 2.5G because it offers the services which are the middle of 2G (second generation) and
3G (third generation). For providing the end-to-end packet switched services the GPRS reuses the
existing GSM infrastructure. GPRS makes sending and receiving small bus of data possible through a
mobile phone. GPRS technology allows for higher data rates compared to the GSM cellular network.
This technology allows the user to check their mail and download the large volume of data on a mobile
phone. GPRS standards were established by the ETSI (European Telecommunications Standards
Institute), but now it is controlled by the 3GPP (3rd Generation Partnership Project).
2. History of GPRS
In 1994, ETSI was initiated for GPRS standardization. In 1997, GPRS specifications were certified by
ETSI and was completed in 1999. In 1999, cellular network started GPRS technology into their
configuration but it became available in 2001.
3. GPRS Characteristics
The characteristics of GPRS are given below [5]:
GPRS uses packet-switched network.
GPRS uses GSM architecture and GPRS support nodes.
GPRS enables voice and data flow through the network.
GPRS has dynamic time slot allocation.
GPRS is faster than GSM and Code division multiple access (CDMA).
4. GSM Architecture
The full form of GSM is Global systems for mobile communications, which is the voice technology
under second generation (2G). For GSM architecture first entity is required as MS (mobile station).
The next part as per the GSM architecture requires is BSS (Base Station subsystem); the BSS part is
required to be attached with NSS (Network station subsystem). Both the BSS and NSS part are
managed by the entity called NMS (Network management system), which is also known as OSS
(operation station subsystem) or OMC (Operation and maintenance centre). So, GSM architecture
requires four basic entities.
The first entity MS is connected with BSS. The BSS consists of BTS (Base transceiver station)
and BSC (Base station controller). BTS is controlled by BSC. GSM architecture requires NSS as well. The
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main unit of NSS part is MSC (Mobile switching centre), which works as a controller of BSC. MSC has a
part which is known as SMSC (Short message service centre) and databases are HLR (Home location
register), VLR (Visitor location register), EIR (Equipment identity register), AUC (Authentication
centre), IN (Intelligent network), other connectivity is PSTN (Public switch telephone network) and
MSC is connected with GMSC (Gateway mobile switching centre) also. OMC is divided into two parts,
which are OMCR (Operation and maintenance centre for radio) and OMCS (Operation and
maintenance centre for switch). OMCR manages the radio part known as BSS part and NSS part is
managed by OMCS. OMC is worked as network management and operation station subsystem.
Figure 1: GSM architecture [8]
The MS is required to attach the BSS part with the air interface (Um). It means antennas receive
signals and forward those signals to the BTS. The full form of BTS is Base transceiver station; that
means a unit that can transmit as well as receive. BTS manages or controls all the calls from the MS to
BTS and BTS forwards these calls to BSC. The mobile station signals are received by BTS. All BTS in a
particular area is managed by BSC. All the signals of BSC forwards to MSC. Switching part is managed
by MSC unit. All the switching functionalities, the authentication, verification as well as security
purpose are managed by mobile switching part. HLR has a functionality that stores the permanent
location of the users. Handover or changing location are saved in VLR. EIR has divided in three lists
users: white list users, grey list users and black list users. White list users are the normal users- those
who are communicating. Grey list users are the service denied users. Black list is the total number of
users, who are blocked by the networks. So, EIR checks the list whether the users are available in white
list, grey list or black list. In SIM (Subscriber identity module) there exists a key store and same key
store is also in the AUC database. If the SIM wants to communicate with the network, AUC matches
the key. If key matches then only the user can call. IN is worked as billing section for the prepaid
connection. Post-paid bills are generated by MSC. GMSC is required to connect number of MSCs
(Mobile switching centres) together. GMSC is used for international calls. SMSC (Short message service
centre) basically deals with short messages. Every messages is stored first in SMSC databases and then
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it is forwarded to the receiver. If users require to call then it passes through the MSC and if users
require to message then it needs to pass through the SMSC. PSTN (Public switch telephone network)
stands for landline connectivity. It connects MS to landline.
5. GPRS Description
GPRS packet technology means transmission of packets through air and this packet contains two kinds
of data. They are: Data Information and Control information. Control information provides source and
destination address to pass the data. Control information chooses the route from source to
destination address and data information contains the data which must be decrypted at the
destination address. Control information also contains error correction bits to control the errors.
A GPRS packet can be divided into three parts- the first part in header, last part is trailer, the
middle part is payload. Header represents the start of the packet, trailer represents the end of the
packet, in between there is a payload with data which can be transmitted. Header contains the sender
or source address, trailer contains the destination address. Packet has a constant length which
correspond to GSM time slot. Data transmission and time slot allocation are dynamic or random in
nature. It is totally based on first-in-first-out (FIFO).
6. GPRS Architecture
The full form of GPRS is General Packet Radio Service. The architecture of GPRS is combined with GSM
architecture (as shown in fig.2). GSM (Global systems for mobile communications) architecture has
BSS (Base station subsystem) and NSS (Network station subsystem). This MS is connected with BTS
(Base transceiver station) and BTSs are controlled by BSC (Base station controller). This BSC (Base
station controller) is controlled by MSC (Mobile switching centre) and MSC has databases like HLR
(Home location register), VLR (Visitor location register), EIR (Equipment identity register), AUC
(Authentication centre) and PSTN (Public switch telephone network).
GPRS has MS that can carry both data and voice. For enabling of data the GPRS architecture
has PCU (Packet control unit). The BSC is connected with NSS (Network station subsystem) part with
the first entity SGSN (Serving GPRS Support Node); this will be IP network and then it has GGSN
(Gateway GPRS support node). This is the NSS part and this is connected with firewall and external
network. SGSN is connected with BG (Border gateway), CG (Charging gateway) and DNS (Domain name
server). For GPRS architecture, addition of new entities in the NSS part are required. The NSS part
requires data connectivity with data centre. So, there are external networks like google servers etc.
The BSC which is having the PCU, requires to conduct SGSN for data.
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Figure 2: GPRS architecture [12]
If the user has to call, it will flow through BTS and then BSC and then it will forward to MSC. If the MS
has to access data, then data will take the GPRS route. It has to access data from the external networks.
It means the MS, which has only the voice or call, will follow the GSM path and the MS, which has both
voice and data, will follow the GPRS path.
There are two types of support node in GPRS: Serving GPRS Support Node (SGSN) and Gateway GPRS
support node (GGSN). Their working roles are mentioned below.
1. Serving GPRS Support Node (SGSN): It has the following main purposes.
Routing data to and from the MS.
Verification and charging of calls.
Location and mobility tracking administration.
Storages for user’s location and users profile.
2. Gateway GPRS support node (GGSN): It has the following main purposes.
Data conversion from SGSN to PDP format.
Reserve the present SGSN address.
Reserve the user’s location in the location register.
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GPRS has some subsystems. They are:
I. Base Station System (BSS): The mobile station can communicate with the radio part.
In the radio part we have a controller and that part of a radio network that is known
as BSS. BSS consists of BTS and BSC.
II. Network station subsystem (NSS): The core network or manager of the GSM network
is called as NSS. It assists in verification, operation and maintenance of subsystems.
NSS consists of SGSN and MSC.
III. Radio Station Subsystem (RSS): Consists of MS, BTS and BSC. MS having GPRS
capability and reserve the cipher key sequence number (CKSN).
IV. Gateway Subsystem (GSS): Consists of SGSN and GGSN.
GPRS has some network interfaces. They are given below:
Air interface: Connects MS and BTS. It’s also called as Um interface.
Abis interface: Connects BTS and BSC.
Gb interface: Connects BSC with the SGSN.
Gn interface: Connects SGSN and GGSN.
Gp interface: User profile with the signalling information between SGSN and GGSN of other
area.
Gr interface: Connects SGSN and HLR. Exchange the user information between SGSN and HLR.
Gc interface: Connects GGSN and HLR. Exchange the location information between GGSN and
HLR.
Gs interface: Connects the SGSN with VLR.
Gf interface: Connects SGSN with EIR. It is used to register the MS in the network.
Ga interface: Connects SGSN/GGSN with CG.
Gi interface: Connects GGSN with external PDN (Packet data network).
7. GPRS modulation
GPRS uses the basic GSM structure. It uses the same channel bandwidths-200 kHz. GPRS is used the
modulation technique called GMSK (Gaussian minimum shift-keying). GSM also uses the same
modulation scheme. GMSK is a modulation scheme in which the phase of the carrier is varied by the
modulating signal. GMSK modulation improves power and bandwidth efficiency. The receiver usually
has low cost and complexity. There are low values of the carrier-to-interference ratio when GMSK is
used. Additionally, GMSK has a greater traffic carrying capability.
8. GPRS performance categories
All types of GPRS mobiles are not designed to offer the same level of services. That is why, they are
divided into three basic types according to their abilities in terms of the ability to connect to GSM and
GPRS services:
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I. Class A: It can be connected simultaneously to GSM and GPRS. It means that, it transmits voice
and data at the same time.
II. Class B: It can be attached to both GPRS and GSM services. However, they can be used at only
one service at a time. During a GPRS connection, these mobiles can make or receive a voice
call, or send or receive a SMS.
III. Class C: These types of mobiles cannot be connected simultaneously to GSM and GPRS.
9. Error correction and coding scheme
GPRS basically uses the free time slots of GSM radio interface. GSM radio interface has the channel
bandwidth of 200 kHz and uses a GMSK modulation scheme. Both GPRS and GSM time slots occupy
the same TDMA frame. According to requirement and opportunity the BSC allocates slots to GPRS
dynamically. GPRS data channel is referred as PDCH (Packet Data Channel). The BSC allocates a PDCH
to a specific TDMA frame. However, since it contains a large packet data, the channel will often turn
to be inactive and can be used for connection control purposes. A channel data rate will be dependent
on the distance between the MS and the BTS to a large extent. When the device is near the base
station, there is a smaller amount of interference, and as a consequence a reduced likelihood of error
containing the received data. As the mobile device travels further away from the base station, surely
there will be more disturbances. Therefore, more error correction code must be implemented within
each packet sent. GPRS network devices can automatically adjust the level of correction. There are
four coding schemes of GPRS; each of them incorporates a different level of error correction which
are related on the nature of the data and the degree of signal interference.
These coding schemes are explained below:
i. CS-1: This GPRS coding scheme takes care of the highest level of error detection and
correction. When signal strength is low or interference is high, it is used. By using high levels
of detection and correction, it prevents the data to be resent too often. For each of 12 data
transmission, an extra 12 error correction code bits are provided. It essentially means that,
half of the data transferred is user data and the rest is error correction code.
ii. CS-2: For somewhat better channels this coding scheme can be used. The user data makes up
23⁄ of the payload of each packet.
iii. CS-3: If the channel is good enough, the error rate correction is further reduced. The user data
makes up 3 4⁄ of the payload of each packet.
iv. CS-4: When there is good signal strength with a small interference, this coding scheme is can
be used. Error correction code is not involved in the data.
Table 1: GPRS coding schemes [14]
Coding Scheme Data rate
CS-1 9.05 kbps
CS-2 13.4 kbps
CS-3 15.6 kbps
CS-4 21.4 kbps
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When MS connects to the GSM/GPRS and builds a connection, it is assigned a pair of data channels –
one is uplink and another is downlink. As GPRS is a packet-switched network, it means that eight
different users can share the same uplink and downlink channels. Each channel with a single Time
division multiple access (TDMA) frame, which is divided into eight discrete time slots. Assuming
mobile unit, the maximum data rate depends in part on how many time slots are actually available for
use at a given period of time, and partly in the number of time slots used for both uplink and downlink
channel. MS are divided on the basis of how many slots they can use in either direction. The maximum
potential rates of upstream and downstream data, as a consequence, rely on the GPRS device class.
Twenty-nine different kinds of GPRS device exist. Class 1 devices are capable to transmit and receive
data by means of only one slot in each of two direction. On the other hand, class 29 devices can
transmit and receive data by means of all eight slots. But, the network provides priority to voice
communications; data transmission speed will be low if the network is busy. Most commonly used
GPRS classes are indicated in the following table [14].
Table 2: Common GPRS Device Classes [14]
GPRS class Slots used Max upload (kbps) Max download (kbps)
2 3 8-12 16-24
4 4 8-12 24-36
6 4 24-36 24-36
8 5 8-12 32-40
10 5 16-24 32-48
12 5 32-48 32-48
10. Services offered by GPRS
Applications of GPRS are given below:
Sending and receiving E-mail, short message service (sms), multimedia message
(mms), fax etc.
Internet access and video conference.
Serves the connection with PC’s and other devices.
Serves location based services.
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11. Advantages
GPRS technology provides some benefits. They are given below:
Speed: GPRS technology offers much higher data rate than GSM technology. GPRS provides
speed limit up to 171kbps and offers throughput up to 40Kbps.
Packet switched: GPRS technology offers packet switching while GSM technique was a circuit
switched system. Circuit switching and packet switching can be used in parallel.
Always on capability: GPRS provides an “Always On” capability.
Spectral efficiency: Because of the shared use of radio channels, GPRS provides a better traffic
management and it has service access to a greater number of users.
Packet transmission: Generally, GPRS works more efficiently for long data packet transmission
compared to short ones.
12. Drawbacks
GPRS technology has some disadvantages as well. They are given below:
Since GPRS utilizes the GSM band to transfer data, calls and other network-related functions
cannot be used when a connection is active.
Depending on the individual service provider, GPRS is usually to be paid per megabyte or
kilobyte. But, this has been modified in various places, where there are no longer charge for
per usage of GPRS downloads. Instead GPRS downloads are rather unlimited with a flat fee to
be paid every month.
13. Conclusion
In existing cellular systems, GPRS technology provides a significant improvement of data transfer
capacity. GPRS technology announces the beginning of new generation of cellular communication.
This technology is much faster than GSM and CDMA. GSM can support only the voice or call. But, GPRS
supports both voice and data.
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