Nattakan Puttarak

EXIT Chart Analysis of Nonbinary Protograph LDPC Codes for Partial Response Channels

Low-density parity-check (LDPC) codes over finite fields GF(q) provide an error correction in the noisy partial response (PR) channels. The extrinsic information transfer (EXIT) chart can be used to predict the threshold decoding of protograph LDPC codes, however, previous works only consider the binary protograph LDPC codes in the PR channels. In this paper, we propose to perform the EXIT chart analysis on the nonbinary protograph LDPC codes for the PR channels. Unlike prior works, the actual extrinsic information of the channel detector is measured, then the extrinsic information to the variable nodes is generated with the measured statistics. Moreover, since the mutual information of the variable nodes depends on GF(q), we use the Monte Carlo method to approximate the mutual information. The analysis on the regular (2,4) code, regular (3,6) code, RA code, and AR3A code on the PR channels reveal that, for the PR! channel, the RA code outperforms the others for q = 2, 4, and 8, but the regular (2,4) code is the best for q = 16 and 32. For the PR2 channel, the RA code is the best code for q = 2 and 4, but the regular (2,4) code is the best code for q > 4. The simulation of the codes for q = 4 and 16 are then used to confirm the theoretical results.

The Adaptive Network Coding-Routing (ANCR) Based on Graph Minors for Multicast Networks

The multicast wireless network, where a source needs to deliver packets of data to a set of destination through a group of relays over a network topology, is degraded by a limited bandwidth and capacity regime. Network throughput can be improved using network coding. However, the network coding might or might not be helpful to increase throughput due to an unpredictable network topology. In this paper, we propose an adaptive network coding-routing (ANCR) algorithm to automatically select whether a packet can construct a network code at a relay node before forwarding to destination or not based on the minor of network graphs. If there is no an appropriate packet, the relay will forward a data packet using routing protocol. The results show that this technique can significantly improve both throughput and timeslot usage. The throughput gain at a bottleneck relay node is increased by 35%, while the timeslot usage is decreased for more than 30%.

A study on Ka-band site switching using advanced prediction for rain-induced attenuation

High frequency satellite communications suffers from rain-induced attenuations, which may cause service discontinuity during high-intensity rain events. To combat this, we propose a novel site switching technique that anticipates signal attenuations using a linear dynamical system response model and performs site switching in advance. Using only the rainfall data measured at a ground station for attenuation prediction, we demonstrate that our method is able to lessen signal attenuation while maintaining link availability.

An implementation of low-density MDS array codes for data protection in distributed network data storage system

We present an implementation of disk arrays(RAIDs) in distributed networked data storage environment by applying an error-correcting to accommodate fault tolerance feature. Any of the current state-of-the-art distributed file systems, such as MooseFS [1], can be used as an underlying data space where low density-MDS (Maximum distance separable-Low density parity check) array codes [3] is used as a logical protection layer implemented through FUSE interface (File System In User Space). The redundancy/parity scheme is based on graph structures leading to an MDS code, then can be simply implemented in a parity matrix (H matrix) of an LDPC code. The ability of error correction and data recovery is shown as the bit-error rate (BER) has been investigated. It achieves the same trend compared to the simulation results in [3]. The low-density MDS array code can mitigate hardware failure at higher disk space efficiency comparing to the repetition code.

Latency-reduced retransmission in multicast network using systematic network code

The reliability of multicast network where source delivers many frames of data to multiple receivers over a large scale network is degraded by delay of retransmissions after some data frame has been lost. This paper proposes a coding technique applying on network layer to combat this problem by using systematic network code with overheard retransmission technique. Latency of retransmission and throughput will be measured to represent the performance of this algorithm. The results show that this technique can improve reliability and performance of multicast network by decreasing a delay of retransmission for 40-70 % and yet increasing throughput for more than 8-19% compared with a conventional method.

LDPC Decoder Using Pattern-Dependent Modified LLR for the Bit Patterned Media Storage With Written-In Errors

The written-in errors in bit patterned media recording (BPMR) system cause the erroneous bits during the writing process leading to the performance degradation. In this work, we propose the pattern-dependent modified log-likelihood ratio (LLR) usage in low-density parity check (LDPC) decoder to reduce the written-in errors and also improve the write margin. Unlike the existing works, LLR computed based on the input data patterns is used at the LDPC decoder for the cascaded written-in error channel (WEC) with the additive white Gaussian noise (AWGN) channel. The proposed LDPC decoder outperforms the one with conventional LLR in terms of both the write margin, when the SNR is fixed at 5.5 dB, and the performance of LDPC decoder. The SNR gain is about 0.2 dB at the BER of 10- 6.