Abstract-This paper discusses the impact of flexibility when designing a Viterbi decoder for both convolutional and TCM codes. Different trade-offs have to be considered in choosing the right architecture for the processing blocks and the resulting hardware penalty is evaluated. We study the impact of symbol quantization that degrades performance and affects the wordlength of the rateflexible trellis datapath. A radix-2-based architecture for this datapath relaxes the hardware requirements on the branch metric and survivor path blocks substantially. The cost of flexibility in terms of cell area and power consumption is explored by an investigation of synthesized designs that provide different transmission rates. Two designs are fabricated in a digital 0.13-m CMOS process. Based on post-layout simulations, a symbol baud rate of 168 Mbaud/s is achieved in TCM mode, equivalent to a maximum throughput of 840 Mbit/s using a 64-QAM constellation.

Abstract-This brief proposes a new class of hybrid VLSI architectures for survivor path processing to be used in Viterbi decoders. The architecture combines the benefits of register exchange and traceforward algorithms, that is, low storage requirement and latency versus implementation efficiency. Based on a structural comparison, it becomes evident that the architecture can be efficiently applied to codes with a larger number of states where traceback-based architectures, which increase latency, are usually dominant.Index Terms-Convolutional codes, register exchange (RE), survivor path, traceback (TB), traceforward (TF), Viterbi decoder, VLSI.

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Successive interference cancellation (SIC) is a wellknown technique for mitigating interference. For multiple-layer reception, hard-decision SIC with perfect per-layer rate control has been proven to be a capacity-achieving scheme. In practice, however, due to imperfect rate control and signaling constraints, there is a potential for certain variants of SIC techniques to achieve better performance than the conventional harddecision SIC approach. In this paper, the benefits of various SIC techniques are studied. We show that a soft SIC scheme that passes information iteratively between equalizer, demodulator, and decoder enhances MIMO reception in downlink LTE.

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