Showing papers on "Forward error correction published in 2006"

DVB-S2: The Second Generation Standard for Satellite Broad-Band Services

Abstract: DVB-S2 is the second-generation specification for satellite broad-band applications, developed by the Digital Video Broadcasting (DVB) Project in 2003. The system is structured as a toolkit to allow the implementation of the following satellite applications: TV and sound broadcasting, interactivity (i.e., Internet access), and professional services, such as TV contribution links and digital satellite news gathering. It has been specified around three concepts: best transmission performance approaching the Shannon limit, total flexibility, and reasonable receiver complexity. Channel coding and modulation are based on more recent developments by the scientific community: low density parity check codes are adopted, combined with QPSK, 8PSK, 16APSK, and 32APSK modulations for the system to work properly on the nonlinear satellite channel. The framing structure allows for maximum flexibility in a versatile system and also synchronization in worst case configurations (low signal-to-noise ratios). Adaptive coding and modulation, when used in one-to-one links, then allows optimization of the transmission parameters for each individual user,dependant on path conditions. Backward-compatible modes are also available,allowing existing DVB-S integrated receivers-decoders to continue working during the transitional period. The paper provides a tutorial overview of the DVB-S2 system, describing its main features and performance in various scenarios and applications.

Network Error Correction, I: Basic Concepts and Upper Bounds

Abstract: Error correction in existing point-to-point communication networks is done on a link-by-link basis, which is referred to in this paper as classical error correction. Inspired by network coding, we introduce in this two-part paper a new paradigm called network error correction .T he theory thus developed subsumes classical algebraic coding theory as a special case. In Part I, we discuss the basic concepts and prove the network generalizations of the Hamming bound and the Singleton bound in classical algebraic coding theory. By studying a few elementary examples, the relation between network error correction and classical error correction is investigated.

Joint Network-Channel Coding for the Multiple-Access Relay Channel

Abstract: We propose to use joint network-channel coding based on turbo codes for the multiple-access relay channel. Such a system can be used for the cooperative uplink for two mobile stations to a base station with the help of a relay. We compare the proposed system with a distributed turbo code for the relay channel and with a system which uses separate network-channel coding for the multiple-access relay channel. Simulation results confirm that the systems with network coding for the multiple-access relay channel gain cooperative diversity compared to the system with the distributed turbo code for the relay channel. Moreover, the results show that joint network-channel coding outperforms separate network-channel coding. The reason for this is that the redundancy which is contained in the transmission of the relay can be exploited more efficiently with joint network-channel coding

Wireless Communications over Mimo Channels: Applications to Cdma And Multiple Antenna Systems

Abstract: Preface Acknowledgements List of Abbreviations List of Symbols 1 Introduction to Digital Communications 11 Basic System Model 12 Characteristics of Mobile Radio Channels 13 Signal Detection 131 Optimal Decision Criteria 14 Digital Linear Modulation 15 Diversity 16 Summary 2 Information Theory 21 Basic Definitions 22 Channel Coding Theorem for SISO Channels 23 Channel Capacity of MIMO Systems 24 Channel Capacity for Multi-User Communications 25 Summary 3 Forward Error Correction Coding 31 Introduction 32 Linear Block Codes 33 Convolutional Codes 34 Soft-Output Decoding of Binary Codes 35 Performance Evaluation of Linear Codes 36 Concatenated Codes 37 Low Density Parity Check (LDPC) Codes 38 Summary 4 Code Division Multiple Access 41 Fundamentals 42 OFDM-CDMA 43 Low Rate Channel Coding in CDMA Systems 44 Uplink Capacity of CDMA Systems 45 Summary 5 Multi-User Detection in CDMA Systems 51 Optimum Detection 52 Linear Multi-User Detection 53 Nonlinear Iterative Multi-User Detection 54 Combining Linear MUD and Nonlinear SIC 55 Summary 6 Multiple Antenna Systems 61 Introduction 62 Spatial Diversity Concepts 63 Multi-Layer Transmission 64 Linear Dispersion Codes 65 Information Theoretic Analysis 66 Summary Appendix A: Channel Models A1 Equivalent Baseband Representation A2 Typical Propagation Profiles for Outdoor Mobile Radio Channels A3 Moment Generating Function for Ricean Fading Appendix B: Derivations for Information Theory B1 Chain Rule for Entropies B2 Chain Rule for Information B3 Data Processing Theorem Appendix C: Linear Algebra C1 Selected Basics C2 Householder Reflections and Givens Rotation C3 LLL Lattice-Reduction Bibliography Index

Recent progress in forward error correction and its interplay with transmission impairments

Abstract: Recent progress in forward error correction (FEC) for optical communications is reviewed. The various types of FEC are classified as belonging to one of three generations. A third-generation FEC, based on a block turbo code, has been fully integrated in very large scale integration, and thanks to the use of 3-bit soft decision, a net coding gain of 10.1 dB was demonstrated experimentally. That has brought a number of positive impacts to existing systems. The Shannon limit is discussed for hard and soft decision decoding. The interplay between FEC and error bursts is discussed. Fast polarization scrambling with FEC has been effective in mitigating polarization mode dispersion (PMD). The error count function has proved useful for the adaptive equalization of both chromatic dispersion and PMD

Raptor codes for reliable download delivery in wireless broadcast systems

Abstract: In this work we address reliablefile delivery over mobile broadcast networks, concentrating on the Raptor codes as specified for Multimedia Broadcast/Multicast Services (MBMS) within 3GPP. We start by describing Luby-Transform (LT) codes, which are the first practical fountain codes. Then, using a natural and easy to understand linear algebra notation, we describe Raptor codes as a powerful extension of LT codes. We provide some insight into the Raptor code structure and some guidelines for implementation of encoders and decoders. Finally, some selected simulations verify the good performance of file distribution with Raptor codes as specified in 3GPP. References to a complete set of simulation results are also provided. I. INTRODUCTION

Performance of Amplify-and-Forward and Decode-and-Forward Relaying in Rayleigh Fading with Turbo Codes

Abstract: Cooperative transmission, in which a source and relay cooperate to send a message to a destination, can provide spatial diversity against fading in wireless networks. We derive analytical expressions for the error probability of amplify-and-forward (AF), decode-and-forward (DF), and a new hybrid AF/DF relaying protocol, for systems using strong forward error correction in quasi-static Rayleigh fading channels, and these expressions are shown to compare favorably with simulation results using turbo codes. Analytical results include an exact expression for the distribution of the SNR in AF transmission. For the protocols that achieve diversity (AF, adaptive DF, and hybrid AF/DF), the optimum position of the relay is midway between the source and destination, implying that mutual relaying (or partnering) to a common destination is suboptimal

Cyclic delay diversity with bit-interleaved coded modulation in orthogonal frequency division multiple access

Abstract: We consider cyclic delay diversity in OFDMA. Cyclic delay diversity is an elegant way to obtain spatial diversity in an FEC coded OFDM system without exceeding the guard interval. We first address the problem of choosing the cyclic delays and propose a new robust design rule which enables to pick up the full spatial and frequency diversity which is inherent in a frequency-selective MIMO channel. Our choice of cyclic delays has consequences for the interleaving and multiple access scheme since the spatial diversity appears to be transformed into frequency diversity between neighbouring subcarriers. Therefore, a system with a conventional block frequency interleaver will fail to exploit the spatial diversity. We propose an interleaving and multiple access strategy which guarantees that all users obtain the maximum possible diversity advantage using FEC codes with a limited constraint length. Furthermore, we provide a performance comparison to transmit diversity from orthogonal designs

Error Floors of LDPC Codes on the Binary Symmetric Channel

Abstract: In this paper, we propose a semi-analytical method to compute error floors of LDPC codes on the binary symmetric channel decoded iteratively using the Gallager B algorithm. The error events of the decoder are characterized using combinatorial objects called trapping sets, originally defined by Richardson. In general, trapping sets are characteristic of the graphical representation of a code. We study the structure of trapping sets and explore their relation to graph parameters such as girth and vertex degrees. Using the proposed method, we compute error floors of regular structured and random LDPC codes with column weight three.

A Synthesizable IP Core for WIMAX 802.16E LDPC Code Decoding

Abstract: The upcoming IEEE WiMax 802.16e standard, also referred to as WirelessMAN (2005), is the next step toward very high throughput wireless backbone architectures, supporting up to 500 Mbps. It features as an advanced channel coding scheme low-density parity-check codes. The decoding of LDPC codes is an iterative process, hence many data have to be exchanged between processing units within each iteration. The variety of the specified codes and the envision of different decoding schedules for different codes pose significant challenges to an LDPC decoder hardware realization. In this paper, we present to the best of our knowledge the first published LDPC decoder architecture capable to process all specified WiMax LDPC codes. Detailed synthesis and communications performance results are shown in addition

Analysis and optimization of CDMA systems with chip-level interleavers

Abstract: In this paper, we present an unequal power allocation technique to increase the throughput of code-division multiple-access (CDMA) systems with chip-level interleavers. Performance is optimized, respectively, based on received and transmitted power allocation. Linear programming and power matching techniques are developed to provide solutions to systems with a very large number of users. Various numerical results are provided to demonstrate the efficiency of the proposed techniques and to examine the impact of system parameters, such as iteration number and interleaver length. We also show that with some very simple forward error correction codes, such as repetition codes or convolutional codes, the proposed scheme can achieve throughput reasonably close to that predicted by theoretical limit in multiple access channels.

Adaptive information delivery system using fec feedback

Abstract: A method and apparatus for optimizing the data transfer rate over a transport layer (i.e., communication link) such as the Internet is provided. Initially the data is prepared for transmission by a transfer rate controller, then the data is encoded by a Forward Error Correction (FEC) encoder. After the data has been transferred over the transport layer, the quality of the data transfer link is assessed by an FEC decoder that determines if any errors occurred during data transfer and if errors are detected, the magnitude of the errors (i.e., FEC-correctable packets, FEC-uncorrectable packets). This information is used to generate a feedback message which is used by the transfer rate controller to adjust and optimize the data transfer rate for the link quality as determined a that point in time. By continually monitoring and assessing link quality and providing feedback to the transfer rate controller, the transfer rate can be continually adapted to the varying link quality. In addition to generating feedback used by the transfer rate controller to optimize data transfer rate, the FEC decoder can generate feedback that is used by the FEC encoder to optimize the FEC algorithm. If desired, feedback from the FEC decoders within the link layer demodulator and/or feedback from the receiver can be used to augment the feedback generated by the FEC decoder.

Punctured vs Rateless Codes for Hybrid ARQ

Abstract: Two incremental redundancy hybrid ARQ (IR-HARQ) schemes are compared: one is based on LDPC code ensembles with random transmission assignments, the other is based on recently introduced Raptor codes. A number of important issues, such as rate and power control, and error rate performance after each transmission on time varying binary-input, symmetric-output channels are addressed by analyzing performance of LDPC and Raptor codes on parallel channels. The theoretical results obtained for random code ensembles are tested on several practical code examples by simulation. Both theoretical and simulation results show that both LDPC and Raptor codes are suitable for HARQ schemes. Which codes would make a better choice depends mainly on the width of the signal-to-noise operating range of the HARQ scheme, prior knowledge of that range, and other design parameters and constraints dictated by standards.

Rate-distortion optimized hybrid error control for real-time packetized video transmission

Abstract: The problem of application-layer error control for real-time video transmission over packet lossy networks is commonly addressed via joint source-channel coding (JSCC), where source coding and forward error correction (FEC) are jointly designed to compensate for packet losses. In this paper, we consider hybrid application-layer error correction consisting of FEC and retransmissions. The study is carried out in an integrated joint source-channel coding (IJSCC) framework, where error resilient source coding, channel coding, and error concealment are jointly considered in order to achieve the best video delivery quality. We first show the advantage of the proposed IJSCC framework as compared to a sequential JSCC approach, where error resilient source coding and channel coding are not fully integrated. In the IJSCC framework, we also study the performance of different error control scenarios, such as pure FEC, pure retransmission, and their combination. Pure FEC and application layer retransmissions are shown to each achieve optimal results depending on the packet loss rates and the round-trip time. A hybrid of FEC and retransmissions is shown to outperform each component individually due to its greater flexibility.

Nested Codes with Multiple Interpretations

Abstract: This paper proposes a new approach to channel code design for wireless network applications. The resulting nested codes can be decoded at different effective rates by different receivers ? rates that depend on the prior knowledge possessed by each receiver; we say these codes have multiple interpretations. We have identified several applications in wireless networks where this property is useful. Specific nested code constructions as well as efficient soft and hard decision decoding algorithms are described. The concept of a nested code with multiple interpretations provides flexibility in the design of error protection schemes for multi-terminal wireless networks.

Cross-Layer Analysis of Error Control in Wireless Sensor Networks

Abstract: Severe energy constraints and hence the low power communication requirements amplify the significance of the energy efficient and preferably cross-layer error control mechanisms in wireless sensor networks (WSN). In this paper, a cross-layer methodology for the analysis of error control schemes in WSNs is presented such that the effects of multi-hop routing and the broadcast nature of the wireless channel are investigated. More specifically, the cross-layer effects of routing, medium access and physical layers are considered. This analysis enables a comprehensive comparison of forward error correction (FEC) and automatic repeat request (ARQ) in WSNs. FEC schemes improve the error resiliency compared to ARQ. In a multi-hop network, this improvement can be exploited by reducing the transmit power (transmit power control) or by constructing longer hops (hop length extension), which can be achieved through channel-aware routing protocols. The results of our analysis reveal that for certain FEC codes, the hop length extension decreases both the energy consumption and the end-to-end latency subject to a target PER compared to ARQ. Thus, FEC codes can be regarded as an important candidate for delay sensitive traffic in WSNs. On the other hand, transmit power control results in significant savings in energy consumption at the cost of increased latency. Moreover, the cases where ARQ outperforms FEC codes are indicated for various end-to-end distance and target PER values

SVC-based multisource streaming for robust video transmission in mobile ad hoc networks

Abstract: Emerging noninfrastructure-based network types like mobile ad-hoc networks (MANETs) are becoming suitable platforms for exchanging/sharing real-time video streams, because of recent progress in routing algorithms, throughput and transmission bit-rate. MANETs are characterized by highly dynamic behavior of the transmission routes and path outage probabilities. In this article a multisource streaming approach is presented to increase the robustness of real-time video transmission in MANETs. For that, video coding as well as channel coding techniques on the application layer are introduced, exploiting the multisource representation of the transferred media. Source coding is based on the scalable video coding (SVC) extension of H.264/MPEG4-AVC with different layers for assigning importance for transmission. Channel coding is based on a novel unequal packet loss protection (UPLP) scheme, which is based on Raptor forward error correction (FEC) codes. While in the presented approach, the reception of a single stream guarantees base quality only, the combined reception enables playback of video at full quality and/or lower error rates. Furthermore, an application layer protocol is introduced for supporting peer-to-peer based multisource streaming in MANETs

GOP-based channel rate allocation using genetic algorithm for scalable video streaming over error-prone networks

Abstract: In this paper, we address the problem of unequal error protection (UEP) for scalable video transmission over wireless packet-erasure channel. Unequal amounts of protection are allocated to the different frames (I- or P-frame) of a group-of-pictures (GOP), and in each frame, unequal amounts of protection are allocated to the progressive bit-stream of scalable video to provide a graceful degradation of video quality as packet loss rate varies. We use a genetic algorithm (GA) to quickly get the allocation pattern, which is hard to get with other conventional methods, like hill-climbing method. Theoretical analysis and experimental results both demonstrate the advantage of the proposed algorithm.

Network Error Correction Coding in Packetized Networks

Abstract: This paper, we studies basic properties of network error correction codes, their construction, and correction capability for various kinds of errors. Our discussion is confined to the single source multicast case. We define the minimum rank of a network error correction code. This plays the same role that minimum distance has played in classical coding theory. We prove the existence of codes that can correct errors up to the full error correction capability in singleton bound. Even when the rank of the error is higher than the error correction capability, we show that the error can be corrected with very high probability under reasonable assumptions

Method of improving wireless communication QoS by means of automatic packet sizing and forward error correcting based on the dynamic error rate forecast

Abstract: A method to meet the adequate QoS of wireless network by automatically sizing the packet length and/or by adding appropriate FEC (Forward Error Correction) based on the error rate forecast that is derived from the past behavior of the wireless communication channel.

Structured LDPC codes for high-density recording: large girth and low error floor

Abstract: High-rate low-density parity-check (LDPC) codes are the focus of intense research in magnetic recording because, when decoded by the iterative sum-product algorithm, they show decoding performance close to the Shannon capacity. However, cycles, especially short cycles, are harmful to LDPC codes. The paper describes the partition-and-shift LDPC (PS-LDPC) codes, a new class of regular, structured LDPC codes that can be designed with large girth and arbitrary large minimum distance. Large girth leads to more efficient iterative decoding and codes with better error-floor properties than random LDPC codes. PS-LDPC codes can be designed for any desired column weight and with flexible code rates. The paper details the girth and distance properties of the codes and their systematic construction and presents analytical and simulation performance results that show that, in the high signal-to-noise ratio region, PS-LDPC codes outperform random codes, alleviating the error floor phenomenon.

Dynamic, adaptive power control for a half-duplex wireless communication system

Abstract: The power of a signal transmitted from a mobile terminal of a half-duplex TDMA communication system to a base station is controlled by collecting data relating to bit errors in the transmitted signal received on an inbound channel, generating a time-varying statistic of the data. If the time varying statistic indicates that the power should be adjusted, a power control command is embedded in one or more time slots of an outbound channel to the mobile terminal to change the power of the signal. The data may be the bit error rate (BER) reported by a forward error correction decoder and/or returned signal strength information (RSSI). The time varying statistic may be the moving average and standard deviation of the data.

An Analysis of Finite-Memory Random Linear Coding on Packet Streams

Abstract: We consider the following packet coding scheme: The coding node has a fixed, finite memory in which it stores packets formed from an incoming packet stream, and it sends packets formed from random linear combinations of its memory contents. We analyze the scheme in two settings: as a self-contained component in a network providing reliability on a single link, and as a component employed at intermediate nodes in a block-coded end-to-end connection. We believe that the scheme is a good alternative to automatic repeat request when feedback is too slow, too unreliable, or too difficult to implement.

Code construction and FPGA implementation of a low-error-floor multi-rate low-density Parity-check code decoder

Abstract: With the superior error correction capability, low-density parity-check (LDPC) codes have initiated wide scale interests in satellite communication, wireless communication, and storage fields. In the past, various structures of single code-rate LDPC decoders have been reported. However, to cover a wide range of service requirements and diverse interference conditions in wireless applications, LDPC decoders that can operate at both high and low code rates are desirable. In this paper, a 9-k code length multi-rate LDPC decoder architecture is presented and implemented on a Xilinx field-programmable gate array device. Using pin selection, three operating modes, namely, the irregular 1/2 code mode, the regular 5/8 code mode, and the regular 7/8 code mode, are supported. Furthermore, to suppress the error floor level, a characterization on the conditions for short cycles in a LDPC code matrix expanded from a small base matrix is presented, and a cycle elimination algorithm is developed to detect and break such short cycles. The effectiveness of the cycle elimination algorithm has been verified by both simulation and hardware measurements, which show that the error floor is suppressed to a much lower level without incurring any performance penalty. The implemented decoder is tested in an experimental LDPC orthogonal frequency division multiplexing system and achieves the superior measured performance of block error rate below 10/sup -7/ at signal-to-noise ratio of 1.8 dB.

Configurable, High Throughput, Irregular LDPC Decoder Architecture: Tradeoff Analysis and Implementation

Abstract: Low Density Parity Check (LDPC) codes are one of the best error correcting codes that enable the future generations of wireless devices to achieve higher data rates. This paper presents a novel flexible decoder architecture for irregular LDPC codes that supports twelve combinations of code lengths -648, 1296, 1944 bits- and code rates- 1/2, 2/3, 3/4, 5/6- based on the IEEE 802.11n standard. All the codes correspond to a block-structured parity check matrix, in which the sub-blocks are either a shifted identity matrix or a zero matrix. A prototype of the LDPC decoder has been implemented and tested on a Xilinx FPGA and has been synthesized for ASIC.

IEEE 802.11 MAC-Level FEC scheme with retransmission combining

Abstract: In this paper, we evaluate and enhance the performance of a Forward Error Correction (FEC) scheme for IEEE 802.11 Medium Access Control (MAC). A novel retransmission combining technique is proposed to enhance the performance of the MAC-level FEC scheme.,We also identify the problem with the IEEE 802.11a physical (PHY) layer when it is used with the MAC-level FEC. A new PHY frame format, backward compatible with the original format, is proposed to resolve the problem. Finally, we analytically evaluate the error performance of the MAC-level FEC, and its enhanced performance via retransmission combining and new 802.11a PHY frame format in AWGN environment. Additionally, we present and discuss the results from simulations using TCP/UDP traffic in more realistic channel environments.

Analysis and Design of Moderate Length Regular LDPC Codes with Low Error Floors

Abstract: The traditional method to estimate code performance in the higher SNR region is to use a sum of the contributions of the most dominant error events to the probability of error. If an ML decoder is used, these events will be minimum distance codewords; the traditional decoder used in LDPC codes, some variant of the message passing algorithm, will introduce non-codeword error events known as trapping sets. For long LDPC codes it is difficult to enumerate all of these dominant error events. A procedure to efficiently find dominant error events by using the regular low-density structure of an LDPC code is presented here. The search method can be adapted to work with LDPC codes of various regular and irregular degree distributions, but is especially suited to a very practical subset of LDPC known as regular {3, 6} codes of moderate block length. We also show how codes with very low error floors can be created by utilizing this search method.

Design of Low power & Reliable Networks on Chip through joint crosstalk avoidance and forward error correction coding

Abstract: With the ever-increasing degrees of integration, design of communication architectures for big Systems on Chip (SoCs) is a challenge. The communication requirements of these large Multi Processor SoCs (MP-SoCs) are convened by the emerging network-on-a-chip (NoC) paradigm. To become a viable alternative IC design methodology, the NoC paradigm must address system-level reliability issues, which are among the dominant concerns for SoC design. The basic operations of NoCs are governed by on-chip packet switched networks. On the other hand, incorporation of different coding schemes in SoC design is being investigated as a means to increase system reliability. As NoCs are built on packet-switching, it is very natural to modify the data packets by adding extra bits of coded information to protect against any transient malfunction. By incorporating joint crosstalk avoidance coding (CAC) and forward error correction (FEC) schemes in the NoC data stream we are able to enhance the system reliability and at the same time reduce communication energy.