Showing papers on "Forward error correction published in 2001"

Error control coding

Abstract: The basic goal in digital communications is to transport bits of information without losing too much information along the way. The level of information loss that is tolerable/acceptable varies for different applications. The loss is measured in terms of the bit error rate, or BER. An interesting application that employs error control coding is a system with a storage medium such as a hard disk drive or a compact disc (CD). We can think of the channel as a block that causes errors to occur when a signal passes through it. Regardless of the error source, we can describe the problem as follows: when the transmitted signal arrives at the receiver after passing through the channel, the received data will have some bits that are in error. The system designer would like to incorporate ways to detect and correct these errors. The field that covers such digital processing techniques is known as error control coding.

Performance analysis and code optimization of low density parity-check codes on Rayleigh fading channels

Abstract: A numerical method has been presented to determine the noise thresholds of low density parity-check (LDPC) codes that employ the message passing decoding algorithm on the additive white Gaussian noise (AWGN) channel. In this paper, we apply the technique to the uncorrelated flat Rayleigh fading channel. Using a nonlinear code optimization technique, we optimize irregular LDPC codes for such a channel. The thresholds of the optimized irregular LDPC codes are very close to the Shannon limit for this channel. For example, at rate one-half, the optimized irregular LDPC code has a threshold only 0.07 dB away from the capacity of the channel. Furthermore, we compare simulated performance of the optimized irregular LDPC codes and turbo codes on a land mobile channel, and the results indicate that at a block size of 3072, irregular LDPC codes can outperform turbo codes over a wide range of mobile speeds.

Video multicast using layered FEC and scalable compression

Abstract: The use of scalable video with layered multicast has been shown to be an effective method to achieve rate control in heterogeneous networks. We propose the use of layered forward error correction (FEC) as an error-control mechanism in a layered multicast framework. By organizing FEC into multiple layers, receivers can obtain different levels of protection commensurate with their respective channel conditions. Efficient network utilization is achieved as FEC streams are multicast, and only to receivers that need them. Furthermore, FEC is used without overall rate expansion by selectively dropping data layers to make room for FEC layers. Effects of bursty losses are amortized by staggering the FEC streams in time, giving rise to a tradeoff between delay and quality. For rate control at the receivers, we propose an equation-based approach that computes network usage as a function of measured network characteristics. We show that equation-based rate control achieves more fair bandwidth sharing amongst competing sessions as compared to existing multicast rate control schemes such as RLM and RLC. Fairness is achieved since competing sessions sharing a path will measure similar network characteristics. Simulations and actual MBONE experiments are performed using error-resilient, scalable video compression. We find that video quality is significantly improved at the same communication rate when layered FEC is used.

Coding for the Slepian-Wolf problem with turbo codes

Abstract: This paper proposes a practical coding scheme for the Slepian-Wolf problem of separate encoding of correlated sources. Finite-state machine (FSM) encoders, concatenated in parallel, are used at the transmit side and an iterative turbo decoder is applied at the receiver. Simulation results of system performance are presented for binary sources with different amounts of correlation. Obtained results show that the proposed technique outperforms by far both an equivalent uncoded system and a system coded with traditional (non-concatenated) FSM coding.

Interleaver design for turbo codes

Abstract: The performance of a turbo code with short block length depends critically on the interleaver design. There are two major criteria in the design of an interleaver: the distance spectrum of the code and the correlation between the information input data and the soft output of each decoder corresponding to its parity bits. This paper describes a new interleaver design for turbo codes with short block length based on these two criteria. A deterministic interleaver suitable for turbo codes is also described. Simulation results compare the new interleaver design to different existing interleavers.

Forward error correction in speech coding

Abstract: An improved forward error correction (FEC) technique for coding speech data provides an encoder module which primary-encodes an input speech signal using a primary synthesis model to produce primary-encoded data, and redundant-encodes the input speech signal using a redundant synthesis model to produce redundant-encoded data. A packetizer combines the primary-encoded data and the redundant-encoded data into a series of packets and transmits the packets over a packet-based network, such as an Internet Protocol (IP) network. A decoding module primary-decodes the packets using the primary synthesis model, and redundant-decodes the packets using the redundant synthesis model. The technique provides interaction between the primary synthesis model and the redundant synthesis model during and after decoding to improve the quality of a synthesized output speech signal. Such "interaction," for instance, may take the form of updating states in one model using the other model.

Differential modulation using space-time block codes

Abstract: We consider a space-time differential modulation scheme where neither the transmitter nor the receiver has to know the channel. Our scheme is based on the theory of unitary space-time block codes. Compared to the existing differential modulation schemes for multiple antennas our scheme has a much smaller computational complexity. Moreover, our codes have a higher coding gain and lower bit error rate than the codes proposed by other researchers.

Transmitter, receiver, and coding scheme to increase data rate and decrease bit error rate of an optical data link

Abstract: Transmitters, receivers, and coding schemes to increase data rate and decrease bit error rate of an optical data link are disclosed. Data is transmitted across the link with a less than nominal bit error rate (BER), by encoding the data using a forward error correction (FEC) code or by requesting retransmission of transmitted packets in error. Data is transmitted at a speed that introduces errors at a rate that is in excess of the nominal BER but that may be corrected using the FEC code or retransmission so that the data may be received with less than the nominal BER. The data rate is increased as the link operating speed is increased beyond the overhead required by the FEC codes or retransmission. High speed FEC encoders and decoders facilitating such transmission are disclosed.

FEC performance in multimedia streaming

Abstract: The performance of packet-level media-independent forward error correction (FEC) schemes are computed in terms of both packet loss ratio and average burst length of multimedia data after error recovery The set of equations leading to the analytical formulation of both parameters are first given for a renewal error process Finally, the FEC performance parameters are computed for a Gilbert (1960) model loss process and compared to various experimental data

Full rate space-time turbo codes

Abstract: This paper proposes a class of full space diversity full rate space-time turbo codes. Both parallel concatenated and serially concatenated codes are designed. A rank theory proposed by the authors earlier is employed to check the full space diversity of the codes. The simulations show that the space-time turbo codes can take full advantage of space diversity and time diversity if they are available in the channels. We also study the robustness of performance of both turbo codes and trellis codes in space-time correlated fading channels.

Space-time turbo codes with full antenna diversity

Abstract: In attempting to find a spectrally and power efficient channel code which is able to exploit maximum diversity from a wireless channel whenever available, we investigate the possibility of constructing a full antenna diversity space-time turbo code. As a result, both three-antenna and two-antenna (punctured) constructions are shown to be possible and very easy to find. To check the decodability and performance of the proposed codes, we derive non-binary soft-decoding algorithms. The performance of these codes are then simulated and compared with two existing space-time convolutional codes (one has minimum worst-case symbol-error probability; the other has maximal minimum free distance) having similar decoding complexity. As the simulation results show, the proposed space-time turbo codes give similar or slightly better performance than the convolutional codes under extremely slow fading. When fading is fast, the better distance spectra of the turbo codes help seize the temporal diversity. Thus, the performance advantage of the turbo codes becomes evident. In particular, 10/sup -5/ bit-error rate and 10/sup -3/ frame-error rate can be achieved at less than 6-dB E/sub b//N/sub 0/ with 1 b/s/Hz and binary phase-shift keying modulation. The practical issue of obtaining the critical channel state information (CSI) is also considered by applying an iteratively filtered pilot symbol-assisted modulation technique. The penalty when the CSI is not given a priori is about 2-3 dB.

Video communication method and system employing multiple state encoding and path diversity

Abstract: Video communication over lossy packet networks such as the Internet is hampered by limited bandwidth and packet loss. The present invention provides a system for providing reliable video communication over these networks, where the system includes at least two jointly designed subsystems: (1) multiple state video coding system and (2) path diversity transmission system. Multiple state video coding combats the problem of error propagation that results from packet loss by coding the video into multiple independently decodable streams, each with its own prediction process and state. If one stream is lost the other streams can still be decoded to produce usable video, and furthermore, the correctly received streams provide bidirectional (i.e., previous and future) information that enables improved state recovery for the corrupted stream. The path diversity transmission system explicitly sends different subsets of packets over different paths, as opposed to the prior art approaches where the packets proceed along a single path. By explicitly sending different subsets of packets over different paths, the path diversity transmission system enables the end-to-end video application to effectively see an average path behavior, which is referred to herein as path diversity. Generally, seeing this average path behavior provides better performance than seeing the behavior of any individual random path. The resulting path diversity provides the multiple state video decoder with an appropriate virtual channel to assist in recovering from lost packets, and can also simplify system design (e.g., forward error correction design).

Code construction and decoding of parallel concatenated tail-biting codes

Abstract: Based on the two-dimensional (2-D) weight distribution of tail-biting codes we give guidelines on how to choose tail biting component codes that are especially suited for parallel concatenated coding schemes. Employing these guidelines, we tabulate tail-biting codes of different rate, length, and complexity. The performance of parallel concatenated block codes (PCBCs) using iterative (turbo) decoding is evaluated by simulation and bounds are calculated in order to study their asymptotic performance.

Hybrid arq for packet data transmission

Abstract: The invention relates to a hybrid ARQ scheme with incremental data packet combining. In an example embodiment, the hybrid ARQ scheme with incremental data packet combining employs three feedback signaling commands: ACK, NACK, and LOST. Using these three feedback commands, the hybrid ARQ scheme with incremental data packet combining is provides both robustness and good performance. The invention is particularly advantageous in communication systems with unreliable communication channels, e.g., a fading radio channel, where forward error correction (FEC) codes are used, some of the code symbols being more important than other code symbols. The benefits of the invention are increased throughput and decreased delay of the packet data communication.

Parallel decoding architectures for low density parity check codes

Abstract: A parallel architecture for decoding low density parity check (LDPC) codes is proposed that achieves high coding gain together with extremely low power dissipation, and high throughput. The feasibility of this architecture is demonstrated through the design and implementation of a 1024 bit, rate-1/2, soft decision parallel LDPC decoder.

Product code based forward error correction system

Abstract: A multidimensional forward error correction system. Transmitted data is encoded by an encoder in multiple dimensions. The decoding of received data by a decoder is performed in multiple passes, with corrected data rewritten into memory. The encoder in one embodiment comprises a parallel column decoder and multiple row encoders encoding a (255, 239) BCH code.

Joint iterative decoding of serially concatenated error control coded CDMA

Abstract: Joint iterative decoding of multiple forward error control (FEC) encoded data streams is studied for linear multiple access channels, such as code-division multiple access (CDMA). It is shown that such systems can be viewed as serially concatenated coding systems, and that iterative soft-decision decoding can be performed successfully To improve power efficiency, powerful FEC codes are used. These FEC codes are themselves serially concatenated. The overall transmission system can be viewed as the concatenation of two error control codes with the linear multiple access channel, and soft-decision decoders are used at each stage. A variance transfer function approach applied to the analysis of this system captures the role of the component decoders in an overall iterative decoding system. We show that this approach forms a methodology to study the effects of the component codes as well as that of the iteration schedule. Analysis and simulation examples are presented for transmission systems that operate close to the Shannon limit and illustrate the accuracy of the analysis.

VLSI implementation-oriented (3, k)-regular low-density parity-check codes

Abstract: In the past few years, Gallager's low-density parity-check (LDPC) codes received a lot of attention and many efforts have been devoted to analyzing and improving their error-correcting performance. However, little consideration has been given to the LDPC decoder VLSI implementation. The straightforward fully parallel decoder architecture usually incurs too high complexity for many practical purposes and should be transformed to a partly parallel realization. Unfortunately, due to the randomness of LDPC codes, it is nearly impossible to develop an effective transformation for an arbitrarily given LDPC code. We propose a joint code and decoder design approach to construct a class of (3, k)-regular LDPC codes which exactly fit a partly parallel decoder implementation and have a very good performance. Moreover, for such LDPC codes, we propose a systematic, efficient encoding scheme by effectively exploiting the sparseness of its parity check matrix.

A class of adaptive hybrid ARQ schemes for wireless links

Abstract: Wireless links are known to suffer location-dependent, time-varying, and bursty errors. This paper considers a class of adaptive error-control schemes in the data link layer for reliable communication over wireless links in which the error-control code and the frame length are chosen adaptively, based on the estimated channel state/condition. Three error-control schemes are considered according to: (1) the number of Reed Solomon code segments a packet is divided into and (2) the way a lost packet is retransmitted. Through throughput performance and computation complexity analyses, these three schemes are compared, and then one of them is claimed to be the most attractive in terms of computation complexity and practicality even though its throughput performance is not the best. The simulation results also verify that this scheme works well over a time-varying fading channel. Error control for the medium access control (MAC) header and its effect on the performance of each error-control scheme are also considered since, without proper error protection for the header, it would be futile to exercise error control on the user data.

Channel estimation for space-time orthogonal block codes

Abstract: Space-time coding is an efficient technique to exploit transmitting and receiving diversities for wireless channels. One of the key components in the design of receivers for space-time codes is channel estimation. For the block codes based on orthogonal design proposed by Alamouti and Tarokh (see IEEE Trans. on Information Theory, vol45, no.5, p.1456-67, 1999), a new class of pilot assisted channel estimation schemes are presented where pilot symbols are superimposed on the data symbols. Placement strategies are examined for their efficiency in channel estimation and data transmission.

Apparatus and method for providing optimal adaptive forward error correction in data communications

Abstract: An adaptive and dynamic forward error correction scheme for a communication channel is disclosed. The method and apparatus calculates (206) the actual bit error rate for comparison (207) with a target bit error rate. When a channel is performing better than required by the performance specification, the forward error correction power can be reduced (214) to provide greater throughput. If the calculated actual bit error rate is greater than the target bit error rate, then the forward error correction power is increased (219) in an attempt to lower the calculated bit error rate. A feedback loop is employed to continually calculate received bit error rates as the forward error correction power is increased or decreased.

Method and apparatus for enhanced forward error correction in a network

Abstract: A method and apparatus to perform error correction is described. A stream of data is encoded using concatenated error correcting codes. The encoded data is communicated over a long-haul transmission system. The encoded data is decoded using the codes.

Systems and methods for LDPC coded modulation

Abstract: Typical forward error correction methods employ Trellis Code Modulation. By substituting low density parity check coding in place of the convolution code as part of a combined modulation and encoding procedure, low density parity check coding and modulation can be performed. The low density parity check codes have no error floor, no cycles, an equal bit error rate for the information bits and the parity bits, and timely construction of both a parity check matrix with variable codeword size and a generator matrix is possible.

Construction of low-density parity-check codes from Kirkman triple systems

Abstract: Gallager introduced low-density parity-check (LDPC) codes in 1962, presenting a construction method to randomly allocate bits in the parity-check matrix subject to certain structural constraints. Since then improvements have been made to Gallager's construction method and some analytic constructions for LDPC codes have been presented. However analytically constructed LDPC codes comprise only a very small subset of possible codes and as a result LDPC codes are still, for the most part, constructed randomly. This paper extends the class of LDPC codes that can be systematically generated by presenting a construction method for regular LDPC codes based on combinatorial designs known as Kirkman triple systems. That is, we construct (3, /spl rho/)-regular codes whose Tanner (1981) graph is free of 4-cycles for any integer /spl rho/.

FEC techniques in submarine transmission systems

Abstract: Describes different concatenated coding schemes for submarine transmission system. Simulation results demonstrate a net coding gain of about 8 dB for hard decoding strategy and up to 10 dB when using iterative soft decoding. The impact of the FEC net coding gain margin in a transoceanic submarine system is discussed.

System and method for error-control for multicast video distribution

Abstract: An embodiment of the invention includes an efficient error-control system and method for recovering packet losses, especially losses in distributing multicast video over broadband residential networks Preferably, unlike most existing error-control algorithms designed for Internet multicast, the system and method does not employ substantial feedback suppression Preferably, the system and method does not employ substantial multicasted retransmission Preferably, the system and method does not employ substantial parity retransmission Preferably, the system and method does not employ substantial local loss recovery The system and method integrates two existing classes of error-control algorithms: Automatic Repeat Request (ARQ) and Forward Error Correction (FEC), to reduce traffic overhead and achieve scalability

Frequency domain direct sequence spread spectrum with flexible time frequency code

Abstract: A spread spectrum radio frequency communication system includes a Forward Error Correction (FEC) algorithm to encode digital data to provide a plurality of symbol groups, the FEC algorithm using a Reed Solomon FEC code, an interleaving algorithm to map each one of the plurality of symbol groups into a corresponding one of a plurality of coherent subbands, and a Walsh encoder to encode each one of the plurality of symbol groups.

Use of turbo-like codes for QAM modulation using independent I and Q decoding techniques and applications to xDSL systems

Abstract: A transmitter produces a modulated signal with forward error correction from an information bit stream in a QAM transmitter. The transmitter produces parity bit streams that correspond to an inputted information bit stream using first and second concatenated coders interconnected by an interleaver. Subsets of the first and second parity bit streams are selected in accordance with a puncturing pattern. A variety of novel puncturing patterns providing various coding rates for various constellations are disclosed. The transmitter combines the selected subsets of said first and second parity bit streams with said information bit stream. A QAM symbol stream is produced by mapping a first subset of the combined bit streams to an I dimension and mapping a second subset of the combined bit streams to a Q dimension. The QAM symbol stream is modulated to produce a modulated signal that is transmitted over a communication link. A complementary receiver is also disclosed. The puncturing pattern used in the transmitter may be adapted based on a performance metric determined in the receiver.

Forward error correction

Abstract: A forward correction system using a linked low density parity check (LDPC) code. The linked LDPC code is formed by extending a portion of an original LDPC matrix such that the LDPC code becomes a periodic repeating code.

Method and apparatus for transmitter power control

Abstract: The invention includes a device and method for improving the responsiveness of the transmitter power control function so that the transmission power is more quickly and accurately controlled over a wider range of dynamic power adjustment during transmission. The present invention is directed to a dynamic transmission power control device and methodology having improved power control loop bandwidth and low power control loop variance. The invention is particularly useful for wireless communications, and more particularly to wireless digital devices having signals with large information frame size and low target frame error rate (FER). The dynamic transmission power control methodology includes a receiver including multiple power control loops for dynamically determining the amount of adjustment to make to the incoming transmission signal to achieve a desired level of signal quality at the lowest possible transmission power. For example, two power control adjustment loops, for example an outer loop and an outer - outer loop, may be provided for determining a target signal to noise ratio (SNR). The receiver may also include an inner loop. In one preferred embodiment, the transmitter may use turbo coding decoded using an iterative decoder for forward error correction. In one variation, the turbo coding is used on the forward supplemental channel (F-SCH).