TCM on Frequency Selective Land-Mobile Fading Channels
Peter Adam Hoeher · elib (German Aerospace Center) · 1992
A power and bandwidth efficient concatenated coding system for reliable data transmission on time- and frequency--selective mobile fading channels is considered. Multi--tone signaling with spectrally overlapping pulses is achieved by orthogonal frequency--division multiplexing (OFDM). The inner coding/modulation system is trellis--coded modulation (TCM) consisting of two binary convolutional codes, outputting 16QAM symbols. This class of codes was found to be optimum in sense of complexity and performance on Rayleigh/Rician fading channels. A soft--output (Viterbi) decoding algorithm accepts channel state information, and even delivers reliability information to an outer decoder. The outer code is a rate--compatible punctured convolutional (RCPC) code providing unequal error protection (UEP). Concatenated coding in conjunction with double interleaving and slow frequency hopping (SFH) provides efficient dual diversity. A two-- dimensional pilot sequence multiplexed into the time and frequency sequence according to the sampling theorem allows a robust, truly coherent carrier synchronization, which can be realised, e.g., by a two--dimensional Wiener filter. Emphasis here is on sophisticated, yet reduced complexity channel estimation (CE) making use of the multi--tone structure and a--priori channel knowledge. The use of a guard interval circumvents the implementation of explicit equalization even under severe multipath distortions. Results (BER und power/bandwidth diagram) are presented on basis of a hilly--terrain land--mobile fading channel with f Dmax =200 Hz one--sided maximum Doppler frequency, max 64 s maximum echo delay, and system parameters (2 \\Delta 128 kbit/s data rate, bit sensitivity classes ranging from 5 \\Delta 10