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

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

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

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