Performance of turbo TCM in wideband CDMA indoor mobile applications

This paper presents the error performance of turbo coded TCM (TTCM) in WCDMA channels. Turbo coding has been proposed as one of the coding options, for high data rates above 32 kb/s, in the IMT2000 standard. High data rates up to 2 Mb/s are proposed to be achieved using a combination of spreading factor and multicode operation that uses multiple channels with additional spreading codes. This increases the cochannel interference, which necessitates the use of complex multiuser interference cancellers in 3G systems. We examine a turbo TCM scheme, which has potential to offer much higher spectral efficiency when used in WCDMA system thereby reducing the need for multicode operation and hence results in reduced cochannel interference. The proposed system utilizes a turbo TCM mapped to 8-PSK constellation that offers a spectral efficiency of 2 b/s/Hz which is thrice that of a rate-1/3 turbo coded QPSK scheme, albeit an E_b/N₀ degradation of 1.8 dB. The three times gain in the spectral efficiency when traded with this degradation is quite significant and attractive for transmission at higher data rates