Transmission of digital speech in highway microcells

Digital transmission of speech over highway microcellular channels is investigated and theoretical results of bit error rate (BER) as a function of channel SNR and co-channel interference are presented. MSK modulation is used and the co-channel interferer has both a carrier phase difference and data stream time offset from the wanted signal. Transmissions over Rayleigh fading and AWGN channels are studied, and the theoretical and simulation results are in close agreement. Simulations were also performed using log-PCM, ADPCM and SBC speech. It was found that for toll quality speech it was necessary to operate with a channel SNR and co-channel SIR that both exceeded 30 dB for a BER of 5 × 10¿4. No channel coding or equalization was used. For free flowing vehicular traffic conditions where the average vehicular speed was 112 km/h, a three-cell cluster yielded a cell length of 2·13 km, assuming an allotted duplex bandwidth of 10 MHz, a channel spacing of 25 kHz and 133 mobile users per microcell. The spectral efficiency for 2% and 10% blocking was found to be 36·1 and 42·1 erlang/MHz/base station, while the corresponding erlang/MHz/km2 for a cell length of 2·13 km was 807·1 and 941·2.