Error performance of turbo TCM in wideband CDMA vehicular channels

This paper presents the error performance of turbo coded TCM (TTCM) when applied to wideband code division multiple access (WCDMA) vehicular channels. The IMT2000 standard for third generation (3G) mobile systems proposes rate 1/3 turbo coding for data rates above 32 kb/s. Data rates up to 384 kb/s in vehicular environments and up to 2 Mb/s in indoor environments can be achieved either by reducing the spreading factor (SF) or by multicode operation (or by a combination of both). Multicode operation, however, increases the cochannel interference, which necessitates the use of complex multiuser interference cancellers in 3G systems. In this paper, we examine a turbo TCM scheme, which has the potential to offer much higher spectral efficiency when used in WCDMA systems. The proposed scheme is based on a punctured turbo TCM mapped to 8 PSK constellation. The error performance of such a scheme is examined in WCDMA channels using appropriate channel impulse response models for vehicular environments and the simulation results reported. Results show that the error performance of the scheme considered by us is 1.8-2.1 dB inferior to that of the rate-1/3 turbo coding scheme, however, the spectral efficiency is increased threefold, which is quite attractive for transmission at higher data rates