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Wireless Communications Solutions

General Packet Radio Service (GPRS)

Overview  |  Reverse/Forward Process  |  Library Components

 

    GPRS - Overview

GPRS, a 2.5G system, is poised to take off this year in popularity. Building on the GSM network, it will provide the much needed packet data services to most areas of the world. Nuntius can help make this a reality with its GPRS solutions. Nuntius has expertise in the mobile handset technologies such as RF interfaces, Physical Link Layer (PLL), Media Access Control (MAC), Radio Link Control (RLC), Link Layer Control (LLC), Subnetwork Dependent Convergence Protocol (SNDCP), and Radio Resource Management (RRM). Below is a list of some of the basic characteristics of GPRS. For more information, contact Nuntius Systems, Inc.

Data rate:     Maximum of 171.2 kbps

Channel coding
Outer block coding
Inner Convolutional coding
Interleaving scheme for error bursts
Modulation
Gaussian Minimum Shift Keying GMSK
Multiple Access
Combination of TDMA & FDMA
Transmit Frequency bands
Mobile station    
Base station
Uplink
Downlink    
Reverse ch. 890 - 915 MHz
Forward ch. 935 - 960 MHz    

Duplex seperation     45 MHz

RF carrier spacing     200 kHz

Total number of RF Duplex channels     124

Number of TDMA slots on each carrier     8

Channel allocation     1 to 8 time slots per TDMA
One time slot (Physical channel)     0.577 ms
Frame Interval:     4.615 ms
Asymmetric data traffic     different time slots for Uplink and downlink

Frequency Hopping:     217 hops/s (slow)

Equalizer:     16 Ás time dispersion

Connectivity:     Packet switched data networks such as IP and X.25

Extra nodes:
Gateway GPRS Support Node (GGSN) and
Serving GPRS Support Node (SGSN)

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    GPRS - Reverse Link / Forward Link Process
Composed of
Packet data traffic channels
Packet common control channels
Packet dedicated control channels
Packet data broadcast control channel (only for forward link)
 
Transmission
Channel coder
Block encoder
Precoding of Uplink Status Flag (USF)
Add Tail bits
Convolutional encoder
Puncturing

Channel coding schemes

Scheme
Peak Rate per slot (kbps)
RLC Block size Code
rate
CS-1
CS-2
CS-3
CS-4
9.05
13.4
15.6
21.4
181
268
312
428
.5
.66
.75
1.0

Reception
GMSK Demodulator
Viterbi equaliser
Deinterleaver
Viterbi decoding

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    GPRS - Standard Library Functions

The following is a list of the standard library functions to perform the various aspects of GPRS. These functions can be implemented in a DSP or the ARM RISC architecture. In general, the layer 1 functions are usually implemented in the DSP while upper layer protocols such as SNDCP are implemented in the ARM RISC. The channel models are used for simulating the channel operating environment and are not a function that would be implemented in a mobile handset or base station.

Channel coders
Block encoder
Fire coder
Precoding of uplink status flags
Convolutional coder (1/2, 2/3 and 3/4)
Puncturing
Interleaver / deinterleaver
Interleaver of depth 4 / deinterleaver
Channel models
Rayleigh distribution
Rice distribution
Propogation models for urban and rural areas
Modulator / demodulator
GMSK modulation / demodulation
Channel decoder
Viterbi decoder

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