Effects of transmitter, receiver and channel impairments on the performance of the enhanced IS-136 digital cellular system for transmission of high-quality speech

Abstract

An enhanced version of the IS-136 American digital cellular system is studied, which is designed to handle low delay high-quality 16 kb/s encoded speech for low-speed mobility indoor wireless communications. Physical layer modifications which are implemented include replacing the /spl pi//4 DQPSK modulation with the /spl pi//8-DSPSK modulation, changing the channel encoding approach as well as requiring the antenna diversity in the receiver. Much of the IS-136 slot and frame structure is preserved. The effects of channel, transmitter and receiver impairments on the performance of the system are studied through simulations. An incoherent differential detector and a coherent detector with differential decoding are evaluated. Simulation results show that slot error rates of 1% are achievable for SNRs around 25 dB for the worst considered case of Rayleigh fading with 10 Hz Doppler, 5 degrees of RMS phase noise in the transmitter and receiver each, and for two antenna preselection diversity when the difference in antenna signal strengths is equal to 3 dB. For 1 Hz Doppler and smaller RMS values of phase noise, the same slot error rate is achievable for close to 20 dB SNR.