A residue number system based parallel communication scheme using orthogonal signaling. II. Multipath fading channels

A novel signaling scheme is presented, where a set of orthogonal signals is transmitted in parallel, which are selected according to the so-called residue number system (RNS). Hence the system is essentially a multiple code parallel communication scheme using high modulation alphabets. It is demonstrated that the system performance can be substantially improved by exploiting a number of advantageous properties of the RNS arithmetic. The model treated in Part I of the paper is extended here to account for the effects of the multipath Rayleigh fading channel, when using noncoherent demodulation. Diversity reception techniques with equal gain combining or selection combining are concerned and the related performance is evaluated for both non-redundant and redundant RNS based orthogonal signaling. Interleaving and forward error correction (FEC) techniques are introduced for enhancing the system’s bit error rate (BER) performance. The concept of concatenated coding with a Reed-Solomon (RS) code as the outer code and an RRNS code as the inner code is presented, and the performance of the proposed concatenated code is evaluated. Expressions of the error probability for the above mentioned scenarios are presented and the associated BER performance is evaluated numerically with respect to specific system parameters. Without concatenated coding, coding gains up to 8.5dB or 11dB are achieved at a BER of 10−6 using the ‘lowest-reliability dropping’ technique of Part I and one or two redundant moduli, respectively, which is substantially higher than that over the AWGN channel reported in Part I. With RS-coding an additional 7.5dB coding gain is achieved. Indexing Terms-M -ary orthogonal signaling, residue number system, redundant residue number system, joint demodulation/decoding, forward error correction, concatenated coding, CDMA SUBMITTED TO IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, MAY 1999 2