1. GSM and EDGE Transmission

2. What is
?
• Global System for Mobile (GSM) is a second
generation cellular standard developed to cater voice
services and data delivery using digital modulation.
• It is a digital, circuit-switched network optimized
for full duplex voice telephony.
• Most 2G GSM networks operate in the 900 MHz or
1800 MHz bands.

3. Block diagram

4. Channel encoder
• Single GSM data block uses 260 random bits
• The purpose of the channel encoder is to
provide the GSM receiver with the ability to
detect transmission errors and eventually
correct some of these.

5. Input : 260 bits
Output : 456 bits
Most significant
information bits
Channel encoding in GSM. A total of 196 redundant bits are added

6. Convolution encoder
• The convolution encoder takes a block of ‘k’
bits as input and returns a block of ‘n’ bits as
output.
• The rate of the encoder, defined as the ratio
k/n, is in the GSM system specified to be 1/2

7. Interleaving
• The interleaver shuffles the bits contained in
the data blocks output from the channel
encoder, and distributes them over a number
of bursts.
• The purpose of this procedure is to ensure
that the errors that appear in a received data
block are uncorrelated.

8. Idea behind interleaving

9. Multiplexing
• Multiplexer takes data from the interleaver,
and place it appropriately in a frame structure.
• The implemented burst, referred to as a GSM
normal burst, has the structure displayed as
(Interleaved output bits)/(burst’s) =456/4 = 114 data bits/burst

10. GMSK-Modulation
• Differential encoding
– The sequence of {0,1} is first mapped from the RTZ
(Return To Zero) signal representation to a NRZ
representation {-1,1}.
• GMSK modulation
– Gaussian minimum-shift keying
– We get {I,Q} components as output

11. Advantages of GSM over Analog system
• Reduced RF transmission power and longer
battery life.
• International roaming capability. Encryption
capability for information security and privacy.
Applications of GSM
• Mobile telephony
• SMS (Short messaging service)
• Value added services

12. Evolution of GSM
• 2nd Generation
 GSM -9.6 Kbps (data rate)
• 2.5 Generation
 GPRS (General Packet Radio service)
 Data rate: 14.4 - 115.2 Kbps
 EDGE (Enhanced data rate for GSM Evolution)
 Data rate: 547.2 Kbps (max)
• 3rd Generation
 WCDMA(Wide band CDMA)
 Data rate : 0.348 – 2.0 Mbps

13. EDGE
• Enhanced Data rates for GSM Evolution (EDGE) is a
digital mobile phone technology that allows improved
data transmission rates as a backwardcompatible extension of GSM.
• Threefold increase in capacity and performance
compared with an ordinary GSM/GPRS connection
• EDGE increased the bandwidth of GSM from 144 Kbps
to 384 Kbps.

14. Implementation of EDGE
•
No hardware or software changes to be made in GSM core
networks, only base stations must be modified.
•
EDGE compatible transceiver units must be installed in Base
Station Subsystem hardware.
•
Software upgrades to the Base Station Controller (BSCs) and Base
Stations (BS). EDGE is just an “add-on” to the BSS.
•
A new modulation scheme “8-PSK” is introduced to provide high
data rate and high spectral efficiency.

15. EDGE Modulation
• EDGE produces a 3-bit word for every change
in carrier phase. This effectively triples the
gross data rate offered by GSM.

16. EDGE Channel Coding and Frame Structure
Burst N
464 bits
1 data block
Convolution
Coding
Rate = 1/3
Length = 7
Puncture
1392 bits
Interleave
Burst N+1
1392 bits
Burst N+2
8PSK
Modulate
156.25 symbols/slot
Burst
Format
468.75 bits
Burst N+3
348 bits
20 msec frame with 4 time-slots for each of 8 bearers
8 Time Slots
0
1
2
3
4
5
6
7
1 Time Slot = 576.92 µs
Tail
symbols
3
Data
symbols
58
Training
symbols
26
Data
symbols
58
Modulation: 8PSK, 3 bits/symbol
Symbol rate: 270.833 ksps
Payload/burst: 348 bits
Gross bit rate/time slot: 69.6 kbps - overhead = 59.2 kbps user data
Tail
symbols
3
Guard
symbols
8.25
348 bits/
burst

17. Advantages of EDGE
 User Benefits
1. Speed
2. An “always-on” connection
3. Coverage
 Operator Benefits
1. Spectrally efficient and flexible
2. Ease of upgrade
3. Backward compatibility
4. Cost-efficiency

18. Applications of EDGE
• EDGE enables operators to introduce 3G data
applications into existing GSM networks and
thereby increase the speed of packet oriented
transmission three-fold.
– Mobile Internet access
– Wireless access to databases
– e-Commerce
– Video telephony
– MMS

19. Matlab implementation
1.
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9.
Generate random data of length 260
Separate input in classes 1a,1b,2
Parity encoding of most important 50 bits (1a)
Convolution encoding
Interleaving
Multiplexing
Differential encoding
GMSK modulation
Transmit {I,Q} components