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GPRS and EDGE Introduction
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What is GPRS?
GPRS－ General Packet Radio Service Packet switch is most efficient way of using frequency
in data application.
GPRS = mobile + IP, which is the integration of GSM
radio access technique and internet packet switchtechnique.
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What is EDGE?
EDGE－ Enhanced Data Rate for GSM Evolution Improve the data transmission rate through radio
connections in GSM.
Including EGPRS and ECSD, it can be used to transmit
PS and CS data. It can fully make use of existing GSM resources.
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Technical Features of GPRS
Seamless Connection to IP Network High Transmission
Always Online and Traffic Accounting
Provides existing mature GSM technologies anddata service deployment schemes.
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R
R
BSS
MSC
PSTN
SS7 Network
EIR
HLR/AUC
SMS-GMSC
Firewall
Firewall
Firewall
Router
Router
Server
Server
SGSN
Inter-PLMNnetwork
PTM-SC
GGSN
Border
GatewayGPRS
Backbone
IP based
GPRS
Infrastructure
Data Network
(Internet)
Data Network
X.25
UmR/S
PCU
Network Structure of GPRS and EDGE
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Transmission Protocol Platform of GPRS and EDGE
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Signaling Protocol Platform of GPRS and EDGE(2)
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Content
Review of GPRS and EDGE Technologies
Channel Combination and Frame Structure
Comparison of GPRS and EDGE
Data Transferring Process
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52 Multiframe Structure
PDCH frame organization One 52 multi-frame includes 12 radio blocks
In circuit domain, one TDMA frame is divided into 8 TSL
TSL assigned to GPRS is PDCH
Multiple TSL can constitute one PDCH group, each including 8 TSL
at most.
Basic unit of radio resource allocation and radio transferring is
BLOCK.
One BLOCK includes 4 TDMA frame which is the smallest unit of
user occupancy.
Surplus 4 burst is used for measuring and reporting TA
Multiple users scramble for these blocks, in this way the goal of
packet share is achieved.
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Packet Logical Channel to Physical Channel
Mapping
Combination of logical channels Mode 1：PBCCH＋PCCCH＋PDTCH＋PACCH＋
PTCCH
Mode 2：PCCCH＋PDTCH＋PACCH＋PTCCH
Mode 3：PDTCH＋PACCH＋PTCCH
PCCCH = PPCH + PRACH + PAGCH + PNCH Service Volume
When GPRS traffic is not intense, GPRS and circuittraffic generally share BCCH and CCCH in cells. In thiscase, mode 3 is needed.
With the accumulation of traffic Packet common channel is needed to be configured in
the cell. Channel combination is either mode 1 or mode2.
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EDGE Channel Coding
EDGE Coding Schemes MCS-1 to MCS-9
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EDGE Channel Coding
Coding Family Family A: The payload of family A code has 37 bytes. It
corresponds to MCS-3, MCS-6 or MCS-9 coding
scheme.
Family A padding: The payload of family A paddingcode has 34 bytes. It corresponds to MCS-3, MCS-6,or
MCS-8 coding schemes.
Family B: The payload of family B code has 28 bytes. It
corresponds to MCS-2, MCS-5 or MCS-7 codingscheme.
Family C: The payload of family C code has 22 bytes. It
corresponds to MCS-1 or MCS-4 coding scheme.
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Comparison of Physical Layer: GMSK and 8-PSK
GPRS uses Gaussian Minimum Shift Keying(GMSK) as the modulation mode.
In addition to GMSK (MCS1~MCS-4), EGPRS
also uses 8-PSK modulation mode
(MCS5~MCS9).
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Link Quality Control
In GPRS, it only supports adaptive link mode. In EDGE, it not only supports adaptive link mode
(mixed ARQ type 1), but also supports incremental
redundancy (mixed ARQ type 2).
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Channel Quality Report
In GPRS, two measurements can be done up towithin 240 ms.
In EDGE, measurement can be done on the basis
of each pulse.
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Content
Review of GPRS and EDGE Technologies Channel Combination and Frame Structure
Comparison of GPRS and EDGE
Data Transferring Process
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UL TBF Access
TBF establishment process on the following channels CCCH
PCCCH
PACCH
Access Mode
ONE PHASE
means network assigns adequate resource one time upon network
receiving channel request.
TWO PHASE
means network assigns single RLC & MAC block the first time andassign corresponding RR upon MS’s specific request.
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MS Network Packet Channel Request
Packet Immediate Assignment Packet Resource Request
Packet Resource Assignment
PRACH or RACH
PAGCH or AGCH PACCH PACCH
Uplink Data PDTCH Uplink Data
PDTCH
CCCH Two-phase Access
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Packet Uplink Ack/Nack
Data Block (last)
Access and Assignment
MS BSS
PACCH
PDTCH
Packet Uplink Assignment PACCH
PACCH
Data Block PDTCH
Data Block PDTCH
Data Block (last in send window) PDTCH
Data Block PDTCH
Data Block PDTCH
Data Block
final Packet Ack/Nack PACCH
LLC PDU
SGSN
GPRS UL Data Transfer
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Obtain TA in GPRS Data Transferring
TA Initialization Initial TA value isn’t contained in Immediate Assignment
message, indicating UL data transmission will not be
conducted before TA value is gotten from TA update
System sends Packet Polling Message requesting MSto send access burst for computing of initial TA value
Use default TA value as initial TA for cell radius is not
great.
Continuous TA update Update once every 8x52multi-frame (1920ms,
approximately 2 second)
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Continously TA Update Process
For UL & DL data transferring, TAI will be gotten
upon getting PDCH. TAI is from 0 to 15 and
indicates 16 idle frame location of constant 8*52
multi-frame.
On UL channel, MS sends access burst on Idle
frame assigned by specified TAI. On DL,
corresponding idle frame sends TA Message.
TAI
TA message 4
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
TA message 3TA message 2TA message 1
26 TDMA frames
416 TDMA frames
Downlink:
Uplink:
Idle frame
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