Cornelius T. Healy

Design of LDPC Codes Based on Progressive Edge Growth Techniques for Block Fading Channels

A novel algorithm to design Root-Check LDPC codes based on Progressive Edge Growth (PEG) techniques for block-fading channels is proposed. The performance of the new codes is investigated in terms of the Frame Error Rate (FER) and the Bit Error Rate (BER). Numerical results show that the codes constructed by the proposed algorithm outperform codes constructed by the existing methods by 0.5dB.

Decoder-Optimised Progressive Edge Growth Algorithms for the Design of LDPC Codes with Low Error Floors

A novel construction for irregular low-density parity-check (LDPC) codes based on a modification of the Progressive Edge Growth (PEG) algorithm is presented. Edge placement of the PEG algorithm is enhanced by use of the Sum-Product algorithm in the design of the parity-check matrix. The proposed algorithm is highly flexible in block length and rate. The codes constructed by the proposed methods are tested in the AWGN channel and significant performance improvements are achieved. The flexibility of the proposed decoder optimisation operation is then shown by its use in modifying the Improved PEG (IPEG) algorithm to achieve further performance gains.

Generalised Quasi-Cyclic LDPC codes based on Progressive Edge Growth Techniques for block fading channels

Generalised Quasi-Cyclic Root-Check LDPC codes based on Progressive Edge Growth (PEG) techniques for block-fading channels are proposed. The proposed Root-Check LDPC codes are suitable for channels under F= 3, 4 independent fadings per codeword which is a scenario that has not been previously considered. A generalised Quasi-Cyclic Root-Check structure is devised for F= 3, 4 independent fadings. The proposed PEG-based algorithm for generalised Quasi-Cyclic Root-Check LDPC codes takes into account the specific structure, and designs a parity-check matrix with a reduced number of cycles. The performance of the new codes is investigated in terms of the Frame Error Rate (FER). Numerical results show that the codes constructed by the proposed algorithm perform about 0.5dB from the theoretical limit.

LDPC codes based on Progressive Edge Growth techniques for block fading channels

We propose an algorithm to design Root-Check LDPC codes based on Progressive Edge Growth (PEG) techniques for block-fading channels. The proposed algorithm imposes some restrictions on the traditional PEG algorithm to ensure that the LDPC code generated is Root-Check with the largest possible girth. The performance is investigated by means of the outage probability. By doing so, the codes generated by our proposed algorithm are shown to outperform the existing methods for generating Root-Check LDPC codes.

Iterative Detection and Decoding Algorithms for MIMO Systems in Block-Fading Channels Using LDPC Codes

We propose iterative detection and decoding (IDD) algorith ms with Low-Density Parity-Check (LDPC) codes for Multiple Input Multiple Output (MIMO) systems ope rating in block-fading and fast Rayleigh fading channels. Soft-input soft-output minimum mean-squ are error receivers with successive interference cancellation are considered. In particular, we devise a nov el strategy to improve the bit error rate (BER) performance of IDD schemes, which takes into account the sof t a posteriori output of the decoder in a block-fading channel when Root-Check LDPC codes are use d. A MIMO IDD receiver with soft information processing that exploits the code structure an d the behavior of the log likelihood ratios is also developed. Moreover, we present a scheduling algorith m for decoding LDPC codes in block-fading channels. Simulations show that the proposed techniques re sult in significant gains in terms of BER for both block-fading and fast-fading channels.We propose iterative detection and decoding (IDD) algorithms with low-density parity-check (LDPC) codes for multiple-input multiple-output (MIMO) systems operating in block-fading and fast Rayleigh fading channels. Soft-input-soft-output minimum-mean-square-error (MMSE) receivers with successive interference cancellation are considered. In particular, we devise a novel strategy to improve the bit error rate (BER) performance of IDD schemes, which takes into account the soft a posteriori output of the decoder in a block-fading channel when root-check LDPC codes are used. A MIMO IDD receiver with soft information processing that exploits the code structure and the behavior of the log-likelihood ratios is also developed. Moreover, we present a scheduling algorithm for decoding LDPC codes in block-fading channels. Simulations show that the proposed techniques result in significant gains in terms of BER for both block-fading and fast-fading channels.

Decoder Optimised Progressive Edge Growth Algorithm

A novel construction for irregular low density parity check (LDPC) codes based on a modification of the Progressive Edge Growth (PEG) algorithm is presented. The edge placement procedure of the PEG algorithm is enhanced by the use of the Sum-Product decoder in the design of the parity-check matrix. The proposed algorithm, like the PEG algorithm, is highly flexible in block length and rate. The codes constructed by the methods presented are tested in the AWGN channel and significant performance improvements are achieved. The flexibility of the proposed decoder optimisation operation in its application to PEG-based construction methods is then demonstrated by its use in modifying the Improved PEG (IPEG) extension to the PEG algorithm to achieve further performance gains.

Design of LDPC Codes Based on Multipath EMD Strategies for Progressive Edge Growth

Low-density parity-check (LDPC) codes are capable of achieving excellent performance and provide a useful alternative for the high-performance applications. However, at medium to high signal-to-noise ratios, an observable error floor arises from the loss of independence of messages passed under iterative graph-based decoding. In this paper, the error floor performance of the short block length codes is improved by the use of a novel candidate selection metric in code graph construction. The proposed multipath extrinsic message degree (EMD) approach avoids harmful structures in the graph by evaluating certain properties of the cycles introduced in each edge placement. We present multipath EMD-based designs for several structured LDPC codes, including quasi-cyclic and the irregular repeat accumulate codes. In addition, an extended class of the diversity-achieving codes on the challenging block fading channel is proposed and considered with the multipath EMD design. This combined approach is demonstrated to provide the gains in decoder convergence and error rate performance. A simulation study evaluates the performance of the proposed and existing state-of-the-art methods.

Knowledge-aided informed dynamic scheduling for LDPC decoding

Low-density parity-check (LDPC) codes offer excellent performance at competitive levels of complexity. Short block length LDPC codes avoid the large processing latency incurred by the large block lengths classically considered for this class of codes, making them a potential candidate for next generation wireless communications systems. In this paper, a novel informed dynamic scheduling (IDS) approach for decoding LDPC codes is developed based on the use of the current message reliabilities and the residuals of the potential updates to select the messages passed in the graph during iterative Sum Product decoding. An alternative measure of the iteration of the IDS schemes is also proposed which highlights the high cost of those algorithms in terms of processing complexity and motivates the development of the proposed approach. The proposed Rel.-RBP decoding algorithm offers very fast convergence at reduced complexity and gains in error rate performance when compared to the previous schemes.

Iterative detection and decoding algorithms for block-fading channels using LDPC codes

We propose an Iterative Detection and Decoding (IDD) scheme with Low Density Parity Check (LDPC) codes for Multiple Input Multiple Output (MIMO) systems in block-fading receivers and fast fading Rayleigh channels. An IDD receiver with soft information processing that exploits the code structure and the behaviour of the log likelihood ratios (LLR)s is developed. Minimum Mean Square Error (MMSE) receivers with Successive Interference Cancellation (SIC) and with Parallel Interference Cancellation (PIC) schemes are considered. The soft a posteriori output of the decoder in a block-fading channel with Root-Check LDPC codes has allowed us to create a new strategy to improve the Bit Error Rate (BER) of a MIMO IDD scheme. The proposed strategy has resulted in up to 3dB of gain in terms of BER for block-fading channels and up to 1dB in fast fading channels.

Serial-inspired diffusion based on message passing for distributed estimation in adaptive networks

Distributed estimation and processing in networks modeled by graphs have received a great deal of interest recently, due to the benefits of decentralised processing in terms of performance and robustness to communications link failure between nodes of the network. Diffusion-based algorithms have been demonstrated to be among the most effective for distributed signal processing problems, through the combination of local node estimate updates and sharing of information with neighbour nodes through diffusion. In this work, we develop a serial-inspired approach based on message-passing strategies that provides a significant improvement in performance over prior art. The concept of serial processing in the graph has been successfully applied in sum-product based algorithms and here provides inspiration for an algorithm which makes use of the most up-to-date information in the graph in combination with the diffusion approach to offer improved performance.