1. GSM Speech Coding
To send a voice across a radio network, we have to turn our voice into a digital signal. GSM uses a method called RPE-LPC (Regular Pulse Excited - Linear Predictive Coder with a Long Term Predictor Loop) to turn our analog voice into a compressed digital equivalent .
SP_2_Coding_1of2

2. Speech Encoding
The GSM speech codec that transforms the analog signal (voice) into a digital representation, must meet the following criteria:
Maintain speech quality.
Reduce redundancy in voice utterances.
Adopt low complexity speech codec to reduce production costs
This reduction is essential due to transmission capacity limitation on the data channel.
SP_2_Coding_1of2

3. GSM TRANSMISSION PROCESS
STAGE 1: ANALOG TO DIGITAL (A/D)CONVERSION
STAGE 2: SEGMENTATION
STAGE 3: SPEECH CODING
STAGE 4: CHANNEL CODING
STAGE 5: INTERLEAVING
STAGE 6: CIPHERING/ENCRYPTION
STAGE 7: BURST FORMATTING
STAGE 8: MODULATION & TRANSMISSION
SP_2_Coding_1of2

4. Speech Encoding
A block diagram detailing how an analog voice is digitized and encoded to produce a digital voice signal :
SP_2_Coding_1of2