Design of a Transport Triggered Architecture Processor for Flexible Iterative Turbo Decoder

In order to meet the requirement of high data rates for the next generation wireless systems, the efficient implementation of receiver algorithms is essential. On the other hand, the rapid development of technology motivates the investigation of programmable implementations. This paper summarizes the design of a programmable turbo decoder as an applicationspecific instruction-set processor (ASIP) using Transport Triggered Architecture (TTA). The processor architecture is designed in such manner that it can be programmed to support other receiver algorithms, for example, decoding based on the Viterbi algorithm. Different suboptimal maximum a posteriori (MAP) algorithms are used and compared to one another for the softinput soft-output (SISO) component decoders in a single TTA processor. The max-log-MAP algorithm outperforms the other suboptimal algorithms in terms of latency. The design enables the designer to change the suboptimal algorithms according to the bit error rate (BER) performance requirement. Unlike many other programmable turbo decoder implementations, quadratic polynomial permutation (QPP) interleaver is used in this work for contention-free memory access and to make the processor 3GPP LTE compliant. Several optimization techniques to enable real time processing on programmable platforms are introduced. Using our method, with a single iteration 31.32 Mbps throughput is achieved for the max-log-MAP algorithm for a clock frequency of 200 MHz.