Field experiments on low-rate turbo coding and soft-decision decoding for broadband packet DS-CDMA wireless access in reverse link

This paper investigates the practical effects of low-rate turbo coding and its soft-decision decoding considering the influence of path timing detection, channel estimation, and pre-decoder level adjustment for broadband packet DS-CDMA in the reverse link in a real multipath Rayleigh fading channel. Field experiments are conducted in an urban environment using the implemented broadband DS-CDMA transceiver at the average vehicular speed of approximately 30 km/h. The experimental results elucidate that accurate path timing detection and channel estimation of each packet frame are achieved by taking advantage of the dedicated pilot channel for the use of low-rate turbo coding (i.e., actual spreading factor value of data channel is nearly one). We clarify that by employing turbo coding with the coding rate of R = 1/8, the required average received signal energy per bit-to-interference plus background noise power spectrum density ratio (E_b/I_o) at the average packet error rate (PER) of 10´2 is decreased by approximately 1.0 to 1.5 dB compared to that with R = 1/2. Furthermore, we show that the additional improvements by reducing R to 1/16 are small assuming the same chip rate and employing two-branch antenna diversity reception associated with coherent Rake combining for broadband DS-CDMA with a 40-MHz bandwidth.