Implementation of channel decoding and other bit rate processing algorithms for 3rd generation W-CDMA mobile terminals

3rd Generation systems promise to revolutionise mobile communications by offering high rate and extremely flexible channels. An important part of this power and flexibility comes from the advanced bit rate processing operations. In this paper we detail these bit rate processing operations, and describe their real-time implementation in both software and hardware. UbiNetics is the leading supplier of 3G test mobiles to infrastructure manufacturers. These mobiles allow users to test high rate (up to 384 kbits/s) channels in real deployment scenarios. In such high rate mobiles the complexity of the bit and chip rate operations is similar. The main component of the bit rate processing at the receiver is the channel decoding, and both convolutional and turbo codes are specified by 3GPP and 3GPP2. We describe the issues involved in the fixed-point implementation of turbo and Viterbi (1967) decoders, and the other bit rate processing operations on both fixed point DSPs and in hardware. These issues include both the complexity and memory requirements of the decoding operations. Comparisons of results from our workstation based floating point simulations and those achieved on the fixed-point target platforms are presented. We also describe novel techniques for reducing the complexity of the decoders.