Transmission of Digitally Encoded Speech at 1.2 Kbaud for PCN

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Description/Abstract

The transmission of digitally encoded speech at 1.2 Kbaud for mobile personal communication networks (PCN) is investigated both analytically and by computer simulations. Speech was encoded at 4.8 Kbit/s using a low complexity transform binary pulse excited LPC codec. A 64-level QAM modem was used having 3 sub channels that operated with different BERs. The sensitivity of the encoded speech bits to transmission errors was identified, and the bits classified into 3 groups. Each group was then individually coded by BCH codec of differing power. The output of the BCH coders were grey coded onto 3 QAM channels. By this arrangement the protection given to the speech bits was dependent on their vulnerability. The 6 bit QAM symbols were transmitted at 1.2 Kbaud over Rayleigh fading channels with pedestrian mobiles travelling upto 4 mile/h. For microcells using a propoagation frequency of 1.9 GHz and operating with channel SNRs in excess 26 dB we achieved good communication quality speech when second-order diversity and AGC were used.