Performance of very low rate channel coding in W-CDMA reverse link

This paper investigates the packet error rate (PER) and the throughput performance employing code spreading (CS), in which a very low-rate channel coding is used instead of spreading by the Walsh-Hadamard channelization code, associated with Type-l Hybrid ARQ with packet combing (i.e., Chase combining) in the W-CDMA reverse link. Simulation results elucidate that the required average received signal energy per bit-to-background noise power spectrum density ratio (E_b/N₀) at the average PER of 1% employing CS-CDMA coupled with turbo coding using the coding rate of R = 1/15 and with convolutional coding using R = 1/16 is decreased by approximately 0.5 to 1.0 dB compared to that employing the DS-CDMA scheme with R = 1/2 in a 2-path Rayleigh fading channel. We also clarify that the achievable throughput employing CS-CDMA using turbo coding coupled with Chase combining and with two-branch antenna diversity reception is increased by approximately 10 to 20% compared to that with DS-CDMA. Consequently, we conclude that the code spreading associated with turbo coding is a very promising technique in the reverse-link of broadband packet wireless access beyond IMT-2000 as well as of W-CDMA packet access because a higher channel coding gain is expected thanks to the frequency (path) diversity effect.