A Survey on LDPC Codes and Decoders for OFDM-based UWB Systems

Abstract

Current UWB systems apply convolutional codes as their channel coding scheme. For next generation systems LDPC codes are in discussion due to their outstanding communications performance. LDPC codes are already utilized in the new WiMax and WiFi standards. Thus it is reasonable to investigate these codes as candidate LDPC codes for UWB. In this paper the authors present an implementation complexity and performance comparison of LDPC decoders. We will show that it is of great advantage to design new LDPC codes which are tailored to the special latency and throughput constraints of upcoming UWB systems. This new class of LDPC codes is named Ultra-Sparse LDPC codes. Synthesis results of WiMax, WiFi, and U-S LDPC decoders are presented based on an enhanced 65 nm CMOS process. We show that the implementation complexity of the new U-S LDPC decoders is 55% smaller, utilizing only 0.2 mm 2 instead of over 0.4 mm 2 , while the communications performance of all observed LDPC codes are almost identical under all the considered UWB simulation conditions.

A design methodology for optimally folded, pipelined architectures in VLSI applications using projective space lattices

“…For the proof, see [25]. The computations that can be covered using this design scheme are mostly applicable to the popular class of iterative decoding algorithms for error correcting codes, like Lowdensity Parity-check (LDPC) [3], polar [2] or expander codes [27]. A representation of such computation is generally available as a bipartite graph, though it may go by some other domain-specific name such as Tanner Graph.…”

“…No processing unit is ever idle in a machine cycle. 3. A schedule can be generated which ensures that there are no memory access conflicts between logical processing units, for each (logical ) memory unit.…”

Early detection of successful decoding for dual-diagonal block-based LDPC codes

“…The z equations in (7) can be used to replace the standard parity-check equations to detect successful decoding with all data blocks and only one parity block participating in the check. All parity bits corresponding to degree-2 nodes in the Tanner graph (equivalently, weight-2 columns in H) are excluded from the equations.…”

“…The proposed method requires a slightly lower number of shifting and XOR operations than the original parity-check equations to declare successful decoding. The mechanism can be applied to irregular repeat accumulate (IRA) codes, such as codes in the DVB-S2 standard [5] or OFDM-based UWB systems [7].…”

A synthesizable IP core for WiMedia 1.5 UWB LDPC code decoding

“…Investigations have shown the superiority of LDPC codes over the previously used convolutional codes in the context of OFDM-based UWB systems [3] [4]. In comparison they showed a high coding gain of up to 3 dB.…”