Distributed Turbo Code Research Articles

Performance Analysis of Turbo Codes and Distributed Turbo Codes in Buffer-Aided Relay Systems

In this paper, we investigate the performance of a relay selection scheme in a buffer-aided multi-relay network with coded transmissions. We consider: (1) two different coding schemes, i.e., Turbo codes and distributed Turbo codes (DTC) and (2) quasi-static Rayleigh fading channels, where all the links are independent but asymmetric. For each of the aforementioned schemes, we analyze the performance of the system in terms of the average throughput and average delay. In addition, simple and explicit approximations of the asymptotic throughput for infinite buffer size and the high signal-to-noise ratio (SNR) regime are obtained. Our analysis of the asymptotic throughput provides the maximum achievable diversity gain of the system, and the accuracy of the derived analytical framework is assessed when compared to the Monte-Carlo simulations.

A Trellis Error Modeling Approach to Decoding Distributed Turbo Codes

In this paper, we re-examine the decoding problem of a distributed turbo code (DTC) over the three-node one-way relay channel based on the decode-and-forward protocol. In the traditional DTC scheme, the decoder at the destination assumes the error-free Viterbi decoding at the relay. However, the error propagation effect resulting from unsuccessful decoding at the relay may cause significant performance loss in some practical scenarios. Improved decoders reported in the literature typically assume a certain memoryless error model, which ignores the fact that relay decoding errors are correlated and bursty. In this paper, we propose a novel trellis error model (TEM) to accurately represent the statistics of relay decoding errors and construct two TEM-based iterative decoders (TEM-IDs) with two and three components, respectively. The TEM-ID with three components has a lower complexity than that of the TEM-ID with two components at the cost of minor performance loss. We also derive a new BER bound for the near maximum likelihood decoding of the DTC using a uniform interleaver. In addition, the extrinsic information transfer chart analysis is applied to estimate the threshold performance of the TEM-ID for large code lengths. Extensive simulation results verify that the new decoders can perform close to the derived BER bound and outperform existing decoders. Finally, we show that the TEM-ID can be extended for general distributed concatenated coding systems.

Performance Analysis of Coded Cooperation Based on Distributed Turbo Codes with Multiple Relays

Performance Analysis of Coded Cooperation Based on Distributed Turbo Codes with Multiple Relays

NTC-HARQ: Network–Turbo-Coding Based HARQ Protocol for Wireless Broadcasting System

Wireless broadcasting systems employ multiple retransmissions to guarantee the correct reception of each packet. The traditional hybrid automatic retransmission request (HARQ) protocol retransmits one packet per slot. Hence, a large amount of retransmissions is required to correctly receive all the packets, which leads to low spectrum efficiency. In this paper, we propose a Network-coding-and-distributed-Turbo-Coding-based type-III HARQ (NTC-HARQ) protocol, including an xoring Network Coding Combined (XNCC) retransmission strategy at the access node (AN) and a joint network-turbo decoding (JNTD) strategy at the user equipment (UE). Specifically, to reduce the overall number of retransmissions, lost packets of different UEs are network coding (NC) combined at the AN by utilizing the XNCC strategy. The soft information of the lost packet at each UE can be recovered from the received network-coded retransmission packet by using the proposed xoring soft network decoder. The recovered soft information of the UE's lost packet is combined with the local undecodable soft information of the same packet to form a distributed turbo code. A Chase-combining-based distributed turbo decoder is proposed to perform turbo decoding, which introduces coding gain and improves packet-error-rate (PER) performance. Theoretical analyses and simulation results show that the average-number-of-transmission performance of the proposed NTC-HARQ protocol outperforms that of the XNCC-based type-I HARQ protocol, the traditional NC-based HARQ protocol, and the JNTD-based protocol.

Interleaving Gains for Receive Diversity Schemes of Distributed Turbo Codes in Wireless Half–Duplex Relay Channels

This paper proposes the interleaving gain in two different distributed turbo-coding schemes: Distributed Turbo Codes (DTC) and Distributed Multiple Turbo Codes (DMTC) for half-duplex relay system as an extension of our previous work on turbo coding interleaver design for direct communication channel. For these schemes with half-duplex constraint, the source node transmits its infor- mation with the parity bit sequence(s) to both the relay and the destination nodes during the first phase. The relay received the data from the source and process it by using decode and forward protocol. For the second transmission period, the decoded systematic data at relay is interleaved and re-encoded by a Recursive Systematic Convolutional (RSC) encoder and forwarded to the destination. At desti- nation node, signals received from the source and relay nodes are processed by using turbo log-MAP iterative decoding for retrieving the original information bits. We demonstrate via simulations that the interleaving gain has a large effect with DTC scheme when we use only one RSC encoder at both the source and relay with best performance when using Modified Matched S-Random (MMSR) inter- leaver. Furthermore, by designing a Chaotic Pseudo Ran- dom Interleaver (CPRI) as an outer interleaver at the source node instead of classical interleavers, our scheme can add more secure channel conditions.

Performance analysis of distributed turbo coded scheme with two ordered best relays

In this study, the authors propose a distributed turbo coded (DTC) scheme utilising two best relays selected among multi-relays. In this scheme, the considered turbo encoder is a rate 1/3 parallel concatenated code composed of two recursive systematic convolutional codes. The systematic information sequence is transmitted directly to a destination, whereas the two parity sequences, one of which is interleaved, are transmitted through the two selected best relays. The authors derive a union bound for the frame error rate including an upper bounded closed form expression for the pairwise error probability of the DTC scheme with two ordered best relays (DTC-TBR) by utilising order of statistic, then the authors verify the analytical expression by simulations. Numerical results show that the proposed scheme outperforms the DTC scheme with a single best relay (DTC-SBR) because of the more selection gain of the DTC-TBR compared with those of DTC-SBR with the rise of number of relays.

Turbo Codes with Modified Code Matched Interleaver for Coded-Cooperation in Half-Duplex Wireless Relay Networks

AbstractThe parallel encoding and decoding structure of turbo codes makes them natural candidate for coded-cooperative scenarios. In this paper, we focus on one of the key components of turbo codes i.e., interleaver, and analyze its effect on the performance of coded-cooperative communication. The impact of an interleaver on the overall performance of cooperative systems depends on the type of an interleaver and its location in the cooperative encoding scheme. We consider code matched interleaver (CMI) as an optimum choice and present its role in a coded-cooperation scenario. The search and convergence of CMI for long interleaver sizes is an issue; therefore, a modification in the search conditions is included without any compromise on the performance of CMI. We also present analytical method to determine maximum S-constraint length for a CMI design. Further, we analyze the performance of two different encoding schemes of turbo codes, i.e., distributed turbo code (DTC) and distributed multiple turbo code (DMTC) after inclusion of CMI. Monte Carlo simulations show that CMI increases the diversity gain relative to other conventional interleavers such as uniform random interleaver. The channel is assumed to be Rayleigh fading among all communication nodes.

Distributed Turbo Coding Schemes for Receive Diversity: A Modified Matched S-Random Interleaver for Half-Duplex Wireless Relay Channels

It is known that one of the essential building blocks of distributed turbo codes is the interleaver and its design uses random, semi-random (S-Random) and deterministic permutations. In this paper, a new modified matched S-random interleaver for turbo code is proposed. Then we extend the effect of this new interleaver to the relay channel to evaluate the interleaving gain in two different distributed turbo-coding schemes: distributed turbo codes and distributed multiple turbo codes for half-duplex relay system. For these schemes with half- duplex constraint, the source node transmits its information with the parity bit sequence(s) to both the relay and the destination nodes during the first phase. The relay receives the data from the source and processes it by using decode and forward protocol. For the second transmission period, the decoded systematic data at relay is interleaved and re-encoded by a recursive systematic convolutional encoder and forwarded to the destination. At destination node, the signals which are received from the source and relay nodes are processed by using turbo log-MAP iterative decoding for retrieving the original information bits. We demonstrate via simulations that the new interleaving gain has a large effect with distributed turbo coding scheme when we use only one recursive systematic convolutional encoder at both the source and relay. Index Terms—Distributed turbo codes, interleaver, semi- random, relay channel

Network‐turbo‐coding‐based cooperation with distributed space‐time block codes

AbstractIn this paper, we propose a scheme to improve the performance of turbo‐coded two‐user cooperative uplink transmission. In the proposed scheme, each user transmits its partner's second parity frame in addition to its own, using a network‐coded combination, which is further protected by a space‐time block code. The proposed system is simulated in slow and fast fading environments. Numerical simulation results indicate that for slow fading, the proposed scheme can yield up to 20% increase in data throughput compared to the traditional distributed turbo coding, while simultaneously providing a gain of 0.7 dB in bit error rate. This latter gain rises to approximately 2.5 dB when a fast fading environment is considered. Furthermore, an outage probability analysis is conducted, which corroborates the simulated performance results.Copyright © 2014 John Wiley & Sons, Ltd.

Quasi-Synchronous Cooperative Networks: A Practical Cooperative Transmission Protocol

In this article, we propose a cooperative space-time coding (STC) protocol, amalgamating the concepts of asynchronous cooperation, noncoherent detection, as well as distributed turbo coding (DTC), where neither symbol-level time synchronization nor channel-state information (CSI) estimation is required at any of the cooperating nodes, while attaining high performance even at low signal-to-noise ratios (SNRs). More specifically assuming the system configuration of a single source node, multiple relay nodes, and a single destination node, each having a single antenna element (AE)a practical cooperative differential space-time spreading (CDSTS) scheme is designed using interference rejection spreading codes, to eliminate the effect of synchronization errors between the relay nodes without the assistance of channel estimation or equalization.

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.

양방향 중계 채널에서 네트워크 코딩을 이용한 분산 터보 부호 기법과 전력 할당의 성능 분석

A two-way relay channel is a bidirectional cooperative communication channel between two nodes using a relay. In many cooperative communication schemes, a relay transmits its data to each node using separate channels. However, in the two-way relay channel, a relay can broadcast the network-coded signal to both nodes in a same time slot, which can increase the system throughput. In this paper, a new cooperative network error correcting scheme using distributed turbo code in a two-way relay channel is proposed. The proposed scheme not only increases the system throughput using network code but also improves the performance by utilizing the LLR information from relay node and other user node through distributed turbo code. Also, a power allocation scheme is investigated for various channel conditions to improve the system performance.

Distributed Turbo Coding and Decoding for Wireless Sensor Networks

In this article a distributed turbo coding and iterative decoding scheme is introduced. The proposed scheme with low complexity is suitable for wireless sensor networks applications where many sensors sense similar sources resulting in correlated data sampling. Encoders reside in these sensor nodes which are close to the source, while decoders reside in another group of nodes acting as distributed decoder and relay. The decoder structure is presented using a simple suboptimal solution derived from the maximum a posteriori probability decision rule. Simulation results demonstrates a marked bit error performance at high signal to noise ratios.

M-Ary Soft Information Relaying of Distributed Turbo Codes

In this letter, an M-ary extension to the soft information relaying (SIR) scheme is derived for distributed turbo codes (DTCs) to enable higher data rate wireless communications with extended ranges. The M-ary based SIR design for DTCs is based on constructing a revised mapping constellation of the signals for calculating metrics from the soft mapping symbols. The numerical results show that DTCs using the proposed M-ary SIR with gray mapped quadrature phase shift keying (QPSK) provides a significant 5 dB performance gain over hard information relaying (HIR) DTCs at the 10 ―3 bit error rate (BER) level.

Threshold-Based Relaying in Coded Cooperative Networks

In cooperative communications, error propagation at the relay nodes degrades the diversity order of the system. To combat that effect, we present a novel technique to control error propagation at the relays, which is implemented in the context of a distributed turbo code. In the presented technique, the relay calculates the log-likelihood ratio (LLR) values for the bits sent from the source. These values are subjected to a threshold to distinguish the reliable bits from the unreliable bits. The relay then forwards the bits that are deemed reliable and discards the bits that are not, resulting in fewer errors propagating to the destination. The assumption here is that the destination does not know the location of the discarded bits. We develop upper bounds on the end-to-end bit error rate, enabling us to optimize the threshold in terms of the minimum end-to-end bit error rate. We compare our technique with existing techniques that have been proposed to control error propagation, including using only a cyclic redundancy code check at the relay, forwarding analog LLR values, and by employing no error control at the relay at all. We demonstrate, through several numerical examples, that the proposed scheme outperforms all existing schemes.

Combined Distributed Turbo Coding and Space Frequency Block Coding Techniques

The distributed space-time (frequency) coding and distributed channel turbo coding used independently represent two cooperative techniques that can provide increased throughput and spectral efficiency at an imposed maximum Bit Error Rate (BER) and delay required from the new generation of cellular networks. This paper proposes two cooperative algorithms that employ jointly the two types of techniques, analyzes their BER and spectral efficiency performances versus the qualities of the channels involved, and presents some conclusions regarding the adaptive employment of these algorithms.

Bit error probability of distributed Turbo coded relay systems over quasi-static Rayleigh fading channels

As is known, distributed Turbo coding (DTC) performs close to the theoretic outage probability bound of a relay channel when correct decoding is assumed at the relay. However, decoding error is inevitable in practical fading channels due to the error-prone feature of radio channels, and the decoding error propagation in DTC scheme will severely degrade the error performance of the relay system. As a result, it is necessary to evaluate the error performance of the DTC scheme in multi-hop relaying wireless systems in practical fading channels. Moreover, the theoretical method of analysis provides an effective tool for obtaining the error performance besides lengthy simulations. In this article, the concept of equivalent signal-to-noise ratio (SNR) of the two-hop relay channel and the method of computing equivalent SNR are developed, and then the upper bound on the bit error probability (BEP) of DTC relay systems is analyzed by use of Turbo code's distance spectrum, the concept of uniform interleaver, the limit-before-averaging technique, and the union bound method. Both theoretical analysis and numerical simulation are implemented for relay systems with DTC scheme over quasi-static Rayleigh fading channels. The results show that the upper bound approaches the simulation results in the medium to high SNR region.

Maximum-Throughput Irregular Distributed Space-Time Code for Near-Capacity Cooperative Communications

This paper presents an irregular distributed space-time (Ir-DST) coding scheme designed for near-capacity cooperative communications where the system's effective throughput is also maximized with the aid of a joint source-and-relay mode design procedure. At the source node, a serially concatenated scheme comprising an IRregular Convolutional Code (IRCC), a recursive unity-rate code (URC), and a space-time block code (STBC) was designed for the sake of approaching the corresponding source-to-relay link capacity, where the IRCC was optimized with the aid of EXtrinsic Information Transfer (EXIT) charts. At the relay node, another IRCC is serially concatenated with an identical STBC. Before transmitting the relayed information, the relay's IRCC is reoptimized based on EXIT chart analysis for the sake of approaching the relay channel's capacity and to maximize the relay's coding rate, which results in a maximized effective throughput. We will demonstrate that the topology of the Ir-DST system coincides with that of a distributed turbo code (DTC). At the destination node, a novel three-stage iterative decoding scheme is constructed to achieve decoding convergence to an infinitesimally low bit-error ratio (BER). Finally, our numerical results show the proficiency of our joint source-and-relay mode design procedure, demonstrating that the proposed Ir-DST coding scheme is capable of near-capacity cooperative communications and of maximizing the effective throughput.

Cooperative Signaling with Soft Information Combining

We propose a Decode‐and‐Forward (DF) scheme using distributed Turbo code (DTC) for a three‐node (source, relay, and destination) wireless cooperative communication system. The relay decodes, then interleaves, and reencodes the decoded data. It then forwards the reencoded packet and its instantaneous receive SNR to the destination. The performances using both ideal and quantized SNR are studied. The destination uses a modified metric within a Turbo decoding algorithm to scale the soft information calculated for the relay code. The proposed scheme is simple to implement and performs well.

Joint network‐channel coding for the multiple‐access relay channel based on turbo codes

AbstractWe consider the time‐division multiple‐access relay channel (MARC) with block‐fading channels and Gaussian noise, where two sources communicate with one destination with the help of one relay. Such a system can be used for the cooperative uplink of two mobile stations to a base station with the help of a relay. We propose a joint network‐channel code design based on turbo codes for the MARC. We compare the proposed system with a distributed turbo code for the time‐division relay channel and with a system which uses separate network‐channel coding for the MARC. Our results show that the proposed code can gain diversity compared to the system for the time‐division relay channel and allows to more efficiently exploit the redundancy in the transmission of the relay than separate network‐channel coding. Copyright © 2009 John Wiley & Sons, Ltd.