| In a coded CDMA system, a natural question is how to allocate bandwidth expansion to channel coding and direct-sequence spreading. Consequently, coding-spreading tradeoff in a DS-CDMA system is first analyzed, we find that the best code rate for the minimum-mean square-error (MMSE) receivers depends on system load and the target bit error rate (BER). When the system load increases, or the target BER becomes more stringent, more bandwidth expansion is suggested to allocate to spreading. By applying different coding codes, we find that the best code rate for MMSE receivers depends on the steepness of the slope of their performance curves. We further claim that there is no coding-spreading tradeoff for the conventional matched-filter (MF) receivers. The obtained results are then applied to Reed-Solomon (RS)/convolutional concatenated coding systems. Next, hybrid type-I ARQ is incorporated into the analysis. The best compromise between error detection and error correction capabilities of the RS codes is studied. It is suggested that the decoding sphere radius for error-only decoding, and the effective decoding diameter for error-and-erasure decoding, is 1 or 2 smaller than the maximum possible value, depending on the target codeword error rate. The obtained results are helpful in designing highly reliable data transmission systems.; Adaptive coding is studied first in a slowly fading channel. An enhanced Incremental Redundancy (IR) protocol is proposed to reduce the number of transmissions. The improvement over the conventional IR protocol is to adaptively adjust the starting code rate for the initial transmission. Simulation results show that the number of transmissions can be greatly reduced, especially when the signal-to-noise ratio is low. It is also shown that the proposed approaches can closely track the average effective code rate of the conventional IR in a fading environment. In Chapter 8, adaptive closed-loop power control over Rayleigh fading channel is investigated. MMSE receivers are used instead of the conventional MF receivers. The target power and the filter coefficients are iteratively updated taking into consideration the variations of the multiple access interference. (Abstract shortened by UMI.)... |
