Khoirul Anwar

Accumulator-Assisted Distributed Turbo Codes for Relay Systems Exploiting Source-Relay Correlation

In relay systems, the probability of errors occurring in the source-relay (S-R) link can be viewed as representing correlation between the source and the relay. This letter proposes a very simple iterative decoding technique, accumulator-assisted distributed turbo code (ACC-DTC) using 2-state (memory-1) convolutional codes (CC), where the correlation knowledge between the source and the relay is estimated and exploited at the destination.

Estimation of Observation Error Probability in Wireless Sensor Networks

In this letter, we first of all propose for a parallel wireless sensor network (WSN) a decoding technique that well exploits the correlation knowledge of the sensing data to be transmitted from each sensor to the fusion center (FC). This letter then derives an algorithm to estimate the observation error probabilities, representing the correlation, of the links between the sensing object and sensors. The convergence of the algorithm is also evaluated. Furthermore, the comparison of bit-error-rate (BER) performance between two cases, one uses estimated observation error probabilities, the other assumes the full knowledge of the observation error probabilities, is made. The simulation results show that the difference is only around 0.3-0.5 dB in per-link signal-to-noise power ratio (SNR), depending on the number of sensors.

Very Simple BICM-ID Using Repetition Code and Extended Mapping with Doped Accumulator

This paper proposes very simple bit-interleaved coded modulation with iterative detection (BICM-ID) as a spectrally efficient signal transmission scheme, where irregular repetition code and extended mapping with rate-1 doped accumulator (ACC) are combined to achieve a clear turbo-cliff. Doped ACC is used for close matching of the demapper and decoder’s extrinsic information transfer curves. Although the proposed BICM-ID system is very simple, it can achieve excellent performances and completely eliminate bit-error-rate floor. An exemplifying result for extended non-Gray mapped 4-quadrature amplitude modulation symbol shows that with 0.916 bits/channel use, turbo-cliff happens at 1.27 dB away from the Shannon limit.

Spatially Concatenated Codes With Turbo Equalization for Correlated Sources

This paper proposes for single carrier signaling a simple structure that combines turbo equalization and decoding of correlated sources in multipath-rich multiuser Rayleigh fading multiple access channels (MAC), where the correlation between the sources is exploited by vertical iterations (VI) between the decoders. The bit-flipping model with a flipping probability pe is used to express the correlation ρ between the sources as ρ = 1-2pe. The proposed simple structure, spatially concatenated codes (SpCC), can achieve turbo-like performance over MAC channels suffering from severe inter-symbol interference (ISI), even though it uses short memory convolutional codes. First of all, to achieve turbo-like performance we introduce VIs to exploit the knowledge about the source correlation by exchanging extrinsic log-likelihood ratio (LLR) between the two decoders. We then add a rate-1 doped accumulator (D-ACC) to flexibly adapt for the variation of correlations between the sources. The results of computer simulations and extrinsic information transfer (EXIT) analysis confirm that in multipath-rich environments the proposed structure can achieve excellent performances, 1.02-1.28 dB away from the Slepian-Wolf-Shannon limit, at 1% outage probability for 0 <; ρ ≤ 1.

Massive uncoordinated multiway relay networks with simultaneous detections

In this paper, we consider multiway relay networks with massive number of users. In this situation a fixed transmission scheduling is difficult to apply. We propose uncoordinated communications using the concept of coded slotted ALOHA (CSA), where simultaneous transmitted signals are detected using iterative demapping (IDM) algorithm to improve the success rate probability. We allow each user to transmit the information via any random time slots (during the contention period) to the network. We show the bound of the proposed system and confirm an achievable point using practical coding. We also evaluate the bit-error-rate (BER) performance of the proposed technique via computer simulations. The results indicate that even though with the offered traffic of 1.11 packets/slot, reliable communications is achievable. It is also validated that the proposed system works very well even in relatively low signal-to-noise ratio (SNR) environments. Moreover, the packet-loss-rate (PLR) evaluation shows that the proposed technique outperforms the conventional CSA without simultaneous detection algorithm.

Outage probability of a relay strategy allowing intra-link errors utilizing Slepian-Wolf theorem

In conventional decode-and-forward (DF) one-way relay systems, a data block received at the relay node is discarded, if the information part is found to have errors after decoding. Such errors are referred to as intra-link errors in this article. However, in a setup where the relay forwards data blocks despite possible intra-link errors, the two data blocks, one from the source node and the other from the relay node, are highly correlated because they were transmitted from the same source. In this article, we focus on the outage probability analysis of such a relay transmission system, where source-destination and relay-destination links, Link 1 and Link 2, respectively, are assumed to suffer from the correlated fading variation due to block Rayleigh fading. The intra-link is assumed to be represented by a simple bit-flipping model, where some of the information bits recovered at the relay node are the flipped version of their corresponding original information bits at the source. The correlated bit streams are encoded separately by the source and relay nodes, and transmitted block-by-block to a common destination using different time slots, where the information sequence transmitted over Link 2 may be a noise-corrupted interleaved version of the original sequence. The joint decoding takes place at the destination by exploiting the correlation knowledge of the intra-link (source-relay link). It is shown that the outage probability of the proposed transmission technique can be expressed by a set of double integrals over the admissible rate range, given by the Slepian-Wolf theorem, with respect to the probability density function (pdf) of the instantaneous signal-to-noise power ratios (SNR) of Link 1 and Link 2. It is found that, with the Slepian-Wolf relay technique, so far as the correlation ρ of the complex fading variation is |ρ|<1, the 2nd order diversity can be achieved only if the two bit streams are fully correlated. This indicates that the diversity order exhibited in the outage curve converges to 1 when the bit streams are not fully correlated. Moreover, the Slepian-Wolf outage probability is proved to be smaller than that of the 2nd order maximum ratio combining (MRC) diversity, if the average SNRs of the two independent links are the same. Exact as well as asymptotic expressions of the outage probability are theoretically derived in the article. In addition, the theoretical outage results are compared with the frame-error-rate (FER) curves, obtained by a series of simulations for the Slepian-Wolf relay system based on bit-interleaved coded modulation with iterative detection (BICM-ID). It is shown that the FER curves exhibit the same tendency as the theoretical results.

PAPR reduction of OFDM signals using iterative processing and carrier interferometry codes

Generally peak-to-average power ratio (PAPR) reduction imposes transmission performance degradation or system capacity reduction. This paper proposes a method for reducing the PAPR of OFDM signals by combining carrier interferometry (CI) spreading code and iterative processing (IP). The proposed method is capable of reducing the PAPR significantly while minimizing the bit error rate (BER) performance degradation. Computer simulation results prove the effectiveness of the proposed method. Further, the proposed method does not introduce out-of-band interference, which requires filtering whose complexity depends on the filtering requirement.

Graph-Based Decoding for High-Dense Vehicular Multiway Multirelay Networks

Densely deployed wireless networks is one of the most important solutions for spectrum shortage expected by 2020 with a huge economic impact. This paper proposes decoding schemes for high- dense vehicular multiway multirelaying (HDV-MWMR) systems comprising multiple multiway relays to serve huge number of users or devices. Due to the nature of huge number, instead of using perfect scheduling, we consider coded random access schemes, where all users transmit their messages uncoordinatedly. Although the transmission is random, the network structures still can be seen as codes-on-the-graph, resembling Low Density Parity Check (LDPC) codes structure, expected to provide an additional gain. The theoretical network capacity bound for HDV-MWMR systems exploiting multiple multiway relays is derived and confirmed via extrinsic information transfer (EXIT) chart analysis and computer simulations. To achieve the network capacity bound, we propose simple decoding schemes based on successive interference cancellation over a sparse graph involving multiple multiway relays. Suitable degree distributions for Rayleigh fading channels are investigated. The results confirm that multiple relays help both on (i) improving the throughput performances, and (ii) capturing the network diversity, which are highly required for future wireless networks.

Massive Multiway Relay Networks Applying Coded Random Access

This paper considers full data exchange for massive uncoordinated multiway relay networks (mu-mRN) applying coded random access for flexible topology changes and capable of serving massive number of users. We aim to maximize the normalized throughput of the mu-mRN using the multiuser detection (MUD) technique with MUD capability of K > 1. Specifically, our goal is multiple times improvement, i.e., ten times improvement, from the maximum normalized throughput of the mu-mRN applying slotted ALOHA (SA). First, we present a network capacity bound of the mu-mRN with general K. Then, we optimize many degree distributions for the MUD-based mu-mRN. However, as K increases, the distributions are no longer optimal to achieve the network capacity bound. We propose doubly irregular coded SA (dir-CSA) to solve the problem. Asymptotically, the mu-mRN applying dir-CSA with K = 4 can achieve the ten times throughput improvement. However, for finite number of time slots, we propose to exploit side information (SI) from neighboring users to improve the normalized throughput of the mu-mRN. The results show that the mu-mRN applying dir-CSA with SI and having optimal physical encoding can achieve ten times throughput improvement, compared with the conventional SA scheme.

Joint Adaptive Network–Channel Coding for Energy-Efficient Multiple-Access Relaying

An energy-efficient orthogonal multiple-access relay channel (MARC) system is developed, where accumulator and differential detection (DD) are used at the source and relay nodes, respectively. However, the weak decoding capability of DD degrades the frame error rate (FER) performance of the orthogonal MARC system if the conventional decode-and-forward relaying strategy is applied. In this paper, a novel joint adaptive network-channel coding (JANCC) technique is proposed to support DD by making efficient use of the erroneous estimates output from DD. In the JANCC technique, the destination constructs a vector identifying the indexes of the source nodes whose information parts contain errors and sends it to the relay to request a retransmission. The relay performs network coding by taking the exclusive-or (xor)-operation only over the stored estimates specified by the identifier vector, which aims to avoid unnecessary erroneous estimates being coded. In addition, a bit-flipping probability pnc is obtained between the two sequences; one is the network-coded sequence sent from the relay, and the other is their corresponding xor-ed information sequence. The decoding algorithm of JANCC exploits probability pnc at the destination to update the log-likelihood ratio during the iterative decoding process. Hence, the information sequences received at the destination are able to be recovered, although the redundancy forwarded from the relay is generated from the erroneous estimates. Compared with the system where iterative decoding is performed at the relay, the utilization of DD significantly reduces the computational complexity, which leads to meaningful power savings with only a small loss in FER performance.