Vlsi Architectures For Multi Gbps Low Density Parity Check Decoders

Near-capacity performance and parallelizable decoding algorithms have made Low-Density Parity Check (LDPC) codes a powerful competitor to previous generations of codes, such as Turbo and Reed Solomon codes, for reliable high-speed digital communications. As a result, they have been adopted in several emerging standards. This thesis investigates VLSI architectures for multi-Gbps power and area-efficient LDPC decoders. To reduce the node-to-node communication complexity, a decoding scheme is proposed in which messages are transferred and computed bit-serially. Also, a broadcasting scheme is proposed in which the traditional computations required in the sum-product and min-sum decoding algorithms are repartitioned between the check and variable node units. To increase decoding throughput, a block interlacing scheme is investigated which is particularly advantageous in fully-parallel LDPC decoders. To increase decoder energy efficiency, an efficient early termination scheme is proposed. In addition, an analysis is given of how increased hardware parallelism coupled with a reduced supply voltage is a particularly effective approach to reduce the power consumption of LDPC decoders. These architectures and circuits are demonstrated in two hardware implementations. Specifically, a 610-Mbps bit-serial fully-parallel (480, 355) LDPC decoder on a single Altera Stratix EP1S80 device is presented. To our knowledge, this is the fastest FPGA-based LDPC decoder reported in the literature. A fabricated 0.13-mum CMOS bit-serial (660, 484) LDPC decoder is also presented. The decoder has a 300 MHz maximum clock frequency and a 3.3 Gbps throughput with a nominal 1.2-V supply and performs within 3 dB of the Shannon limit at a BER of 10-5. With more than 60% power saving gained by early termination, the decoder consumes 10.4 pJ/bit/iteration at Eb=N0=4dB. Coupling early termination with supply voltage scaling results in an even lower energy consumption of 2.7 pJ/bit/iteration with 648 Mbps decoding throughput. The proposed techniques demonstrate that the bit-serial fully-parallel architecture is preferred to memory-based partially-parallel architectures, both in terms of throughput and energy efficiency, for applications such as 10GBase-T which use medium-size LDPC code (e.g., 2048 bit) and require multi-Gbps decoding throughput.