Rate-compatible Punctured Convolutional Research Articles

On the performance of truncated type III hybrid ARQ scheme with code combining

AbstractThe hybrid automatic repeats request (ARQ) scheme, together with code combining, is an effective way to provide reliable transmission of data packets over noisy channel. In this paper, it is shown that the application of rate‐compatible punctured convolutional (RCPC) codes in truncated type III hybrid ARQ scheme leads to the so‐called composite code combining. In order to illuminate the effect of the involved composite code combining, a new concept, i.e. combined puncturing pattern, is introduced. By state‐diagram analysis, it is revealed that the overall performance of the truncated type III hybrid ARQ with code combining is dependent on both the maximum transmission number and the residual error probability after code combining. By extending the analysis to the convolutional codes whose symbols exhibit different effective signal‐to‐noise ratio owing to the composite code combining, a closed form of the residual error probability of the combined RCPC codes is derived. Based on the combined puncturing patterns, upper and lower bounds on the error performance are derived, together with an approximation method which is shown to be quite satisfactory by numerical and simulation results. Copyright © 2003 John Wiley & Sons, Ltd.

Foveation-Based Error Resilience and Unequal Error Protection over Mobile Networks

By exploiting new human-machine interface techniques, such as visual eyetrackers, it should be possible to develop more efficient visual multimedia services associated with low bandwidth, dynamic channel adaptation and robust visual data transmission. In this paper, we introduce foveation-based error resilience and unequal error protection techniques over highly error-prone mobile networks. Each frame is spatially divided into foveated and background layers according to perceptual importance. Perceptual importance is determined either through an eye tracker or by manually selecting a region of interest. We attempt to improve reconstructed visual quality by maintaining the high visual source throughput of the foveated layer using foveation-based error resilience and error correction using a combination of turbo codes and ARQ (automatic reQuest). In order to alleviate the degradation of visual quality, a foveation based bitstream partitioning is developed. In an effort to increase the source throughput of the foveated layer, we develop unequal delay-constrained ARQ (automatic reQuest) and rate compatible punctured turbo codes where the punctual pattern of RCPC (rate compatible punctured convolutional) codes in H.223 Annex C is used. In the simulation, the visual quality is significantly increased in the area of interest using foveation-based error resilience and unequal error protections (as much as 3 dB FPSNR (foveal peak signal to noise ratio) improvement) at 40% packet error rate. Over real-fading statistics measured in the downtown area of Austin, Texas, the visual quality is increased up to 1.5 dB in PSNR and 1.8 dB in FPSNR at a channel SNR of 5 dB.

Joint source-channel coding for motion-compensated DCT-based SNR scalable video

In this paper, we develop an approach toward joint source-channel coding for motion-compensated DCT-based scalable video coding and transmission. A framework for the optimal selection of the source and channel coding rates over all scalable layers is presented such that the overall distortion is minimized. The algorithm utilizes universal rate distortion characteristics which are obtained experimentally and show the sensitivity of the source encoder and decoder to channel errors. The proposed algorithm allocates the available bit rate between scalable layers and, within each layer, between source and channel coding. We present the results of this rate allocation algorithm for video transmission over a wireless channel using the H.263 Version 2 signal-to-noise ratio (SNR) scalable codec for source coding and rate-compatible punctured convolutional (RCPC) codes for channel coding. We discuss the performance of the algorithm with respect to the channel conditions, coding methodologies, layer rates, and number of layers.

Multiple Hierarchical Image Transmission over Wireless Channels

In this paper, we present a multiple hierarchical image coding and transmission scheme in which both the fragile structure of the set partitioning in hierarchical trees (SPIHT) source coding and unequal bit error sensitivity in the coded bitstreams have been taken into account. Multiple subsampling is applied to split the wavelet coefficients of the source image into multiple subsources so that each subsource is a crude representation of the original image. Therefore, the sequential dependence in the coded bitstream is broken and the error propagation is limited to a single subsource. Each subsource is coded using the SPIHT algorithm to achieve the high source coding performance. Cyclic redundancy code and rate compatible punctured convolutional (RCPC) code have been employed as the channel coding method to offer unequal error protection to the source coded bits. In each substream, all the bits in the same bit-layer are protected with the same channel coding rate. The higher the bit-layer, the more the channel coding protection is provided. Experimental results show that the proposed scheme has an excellent error resilient performance for image transmission over wireless channels with time varying and bursty error characteristics. In particular, the basic image structure is preserved even in highly noisy channels.

Performance of RCPC codes with soft-decision decoding over Nakagami-m fading channels

The analytical upper bounds on the pairwise error probability of rate compatible punctured convolutional (RCPC) codes, using coherent BPSK signals over slow frequency nonselective Nakagami-m fading channels with AWGN, are evaluated. With perfect channel state information (CSI) assumption, we use a direct integral with the Nakagami-m probability density function to obtain a closed form upper bound. For the case without CSI, we find an approximated upper bound for the high SNR cases and the approximation can be justified for signal to noise ratio (SNR) E/sub s//N/sub 0/ /spl Gt/ 1.5 dB.

Analysis of an adaptive rate convolutionally coded multicarrier DS/CDMA system

The analysis of an adaptive rate convolutionally coded multicarrier direct sequence code division multiple-access (DS/CDMA) system is considered. In order to accommodate a number of coding rates easily and make the encoder and decoder structure simple, we use the rate-compatible punctured convolutional (RCPC) code. We obtain data throughputs at several coding rates, and choose the coding rate that has the highest data throughput in the signal-to-interference and noise ratio (SINR) sense. To achieve maximum data throughput, a rate adaptive system is proposed based on the channel state information (the SINR estimate). The SINR estimate is obtained by the soft decision Viterbi decoding metric. We show that the proposed rate adaptive convolutionally coded multicarrier DS/CDMA system can enhance the spectral efficiency and provide frequency diversity.

Rate‐adaptive indoor infrared wireless communication systems using punctured convolutional codes and adaptive PPM

AbstractIn this paper, we propose rate‐adaptive indoor infrared wireless communication systems using punctured convolutional codes and adaptive pulse‐position modulation (PPM) to achieve high bit rates under various channel conditions with reasonable transmitter power. The proposed system varies the code rate of the rate compatible punctured convolutional (RCPC) codes and the modulation order of PPM adaptively according to the channel condition. When the channel condition is good, low‐order PPM and suitable code rates are selected, while high‐order PPM and suitable code rates are selected when the channel condition is bad. We analyze the performance of the proposed system on hybrid line‐of‐sight (LOS) channels. Our results show that the proposed system can achieve high bit rates by varying the code rate of the RCPC codes and the modulation order of PPM adaptively according to the channel conditions. Moreover, our results show that the proposed system can achieve longer horizontal separation between the transmitter and the receiver than that of conventional systems with repetition codes. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(8): 31–39, 2001

Error resilient transmission of SPIHT coded images over fading channels

The paper introduces a method of transmitting error resilient SPIHT coded images over highly error prone Rayleigh fading channels. First, the source significance of the SPIHT coded output is obtained. Based on the significance of the bits, the channel coding is varied accordingly. Channel coding consists of a mixture of rate compatible punctured convolutional (RCPC) codes and interleaving to combat the burst errors produced by the fading channel. An additional error concealment technique is also introduced into the SPIHT decoder to improve its results in cases where errors cause the corruption of the average luminance level during decoding. Comparison with using RS block codes at a total transmission rate of 1.0 bits/pixel is carried out over fading channels with very high error rates to show the superiority of this method over methods using burst error codes.

Rate-compatible convolutional codes for multirate DS-CDMA systems

New rate-compatible convolutional (RCC) codes with high constraint lengths and a wide range of code rates are presented. These new codes originate from rate 1/4 optimum distance spectrum (ODS) convolutional parent encoders with constraint lengths 7-10. Low rate encoders (rates 115 down to 1/10) are found by a nested search, and high rate encoders (rates above 1/4) are found by rate-compatible puncturing. The new codes form rate-compatible code families more powerful and flexible than those previously presented. It is shown that these codes are almost as good as the existing optimum convolutional codes of the same fates. The effects of varying the design parameters of the rate-compatible punctured convolutional (RCPC) codes, i.e., the parent encoder rate, the puncturing period, and the constraint length, are also examined. The new codes are then applied to a multicode direct-sequence code-division multiple-access (DS-CDMA) system and are shown to provide good performance and rate-matching capabilities. The results, which are evaluated in terms of the efficiency for Gaussian and Rayleigh fading channels, show that the system efficiency increases with decreasing code rate.

Hybrid ARQ with selective combining for fading channels

We propose and analyze a hybrid automatic repeat request (ARQ) with a selective combining scheme using rate-compatible punctured convolutional (RCPC) codes for fading channels. A finite-state Markov channel model is used to represent the Rayleigh fading channels. We show that the hybrid ARQ with selective combining yields better performance than the generalized type-II ARQ scheme for fading channels. Furthermore, simulation results of real-time video time division multiple access (TDMA) transmission system are given. Better video quality can be obtained by our proposed scheme, with a bounded delay. Analytical results of throughput and packet error rate (PER) are compared to the simulated results. Our analysis based on a finite-state Markov channel model, is shown to give good agreement with simulations.

Operational rate-distortion performance for joint source and channel coding of images

This paper describes a methodology for evaluating the operational rate-distortion behavior of combined source and channel coding schemes with particular application to images. In particular, we demonstrate use of the operational rate-distortion function to obtain the optimum tradeoff between source coding accuracy and channel error protection under the constraint of a fixed transmission bandwidth for the investigated transmission schemes. Furthermore, we develop information-theoretic bounds on performance for specific source and channel coding systems and demonstrate that our combined source-channel coding methodology applied to different schemes results in operational rate-distortion performance which closely approach these theoretical limits. We concentrate specifically on a wavelet-based subband source coding scheme and the use of binary rate-compatible punctured convolutional (RCPC) codes for transmission over the additive white Gaussian noise (AWGN) channel. Explicit results for real-world images demonstrate the efficacy of this approach.

Joint design of fixed-rate source codes and multiresolution channel codes

We propose three new design algorithms for jointly optimizing source and channel codes. Our optimality criterion is to minimize the average end-to-end distortion. For a given channel SNR and transmission rate, our joint source and channel code designs achieve an optimal allocation of bits between the source and channel coders. Our three techniques include a source-optimized channel code, a channel-optimized source code, and an iterative descent technique combining the design strategies of the other two codes. The joint designs use channel-optimized vector quantization (COVQ) for the source code and rate compatible punctured convolutional (RCPC) coding for the channel code. The optimal bit allocation reduces distortion by up to 6 dB over suboptimal allocations and by up to 4 dB relative to standard COVQ for the source data set considered. We find that all three code designs have roughly the same performance when their bit allocations are optimized. This result follows from the fact that at the optimal bit allocation the channel code removes most of the channel errors, in which case the three design techniques are roughly equivalent. We also compare the robustness of the three techniques to channel mismatch. We conclude the paper by relaxing the fixed transmission rate constraint and jointly optimizing the transmission rate, source code, and channel code.

Very low variable-rate convolutional codes for unequal error protection in DS-CDMA systems

Convolutional codes based on Hadamard sequences can achieve both orthogonality and variable rate. In contrast with other convolutional coding techniques, these codes incur no processing gain penalty in direct-sequence code-division multiple-access (DS-CDMA) systems. We describe a class of such codes called "telescopic protection codes". These codes enable variable-rate error protection in the manner of rate-compatible punctured-convolutional (RCPC) codes, but preserve the Hadamard orthogonality properties necessary to maintain processing gain that RCPC codes lack.

Performance of H.263 video transmission over wireless channels using hybrid ARQ

This paper proposes a hybrid ARQ error control scheme based on the concatenation of a Reed-Solomon (RS) code and a rate compatible punctured convolutional (RCPC) code for low-bit-rate video transmission over wireless channels. The concatenated hybrid ARQ scheme we propose combines the advantages of both type-I and type-II hybrid ARQ schemes. Certain error correction capability is provided in each (re)transmitted packet, and the information can be recovered from each transmission or retransmission alone if the errors are within the error correction capability (similar to type-I hybrid ARQ). The retransmitted packet contains redundancy bits which, when combined with the previous transmission, result in a more powerful RS/convolutional concatenated code to recover information if error correction fails for the individual transmissions (similar to type-II hybrid ARQ). Bit-error rate (BER) or signal-to-noise ratio (SNR) of a radio channel changes over time due to mobile movement and fading. The channel quality at any instant depends on the previous channel conditions. For the accurate analysis of the performance of the hybrid ARQ scheme, we use a multistate Markov chain (MSMC) to model the radio channel at the data packet level. We propose a method to partition the range of the received SNR into a set of states for constructing the model so that the difference between the error rate of the real radio channel and that of the MSMC model is minimized. Based on the model, we analyze the performance of the concatenated hybrid ARQ scheme. The results give valuable insight into the effects of the error protection capability in each packet, the mobile speed, and the number of retransmissions. Finally, the transmission of H.263 coded video over a wireless channel with error protection provided by the concatenated hybrid ARQ scheme is studied by means of simulations.

List Viterbi decoding algorithms with applications

A list Viterbi decoding algorithm (LVA) produces a rank ordered list of the L globally best candidates after a trellis search. The authors present two such algorithms, (i) a parallel LVA that simultaneously produces the L best candidates and (ii) a serial LVA that iteratively produces the k/sup th/ best candidate based on knowledge of the previously found k-1 best paths. The application of LVA to a concatenated communication system consisting of an inner convolutional code and an outer error detecting code is considered in detail. Analysis as well as simulation results show that significant improvement in error performance is obtained when the inner decoder, which is conventionally based on the Viterbi algorithm (VA), is replaced by the LVA. An improvement of up to 3 dB is obtained for the additive white Gaussian noise (AWGN) channel due to an increase in the minimum Euclidean distance. Ever larger gains are obtained for the Rayleigh fading channel due to an increase in the time diversity. It is also shown that a 10% improvement in throughput is obtained along with significantly reduced probability of a decoding failure for a hybrid FEC/ARQ scheme with the inner code being a rate compatible punctured convolutional (RCPC) code. >

Combined speech and channel coding for mobile radio communications

We present a combined speech and channel coding scheme for digital mobile communications. The speech coding algorithm is based on code-excited linear prediction (CELP) and it provides good communication quality speech at a rate of 4 kbps. For the channel code, both rate-compatible punctured convolutional (RCPC) codes and punctured Reed-Solomon (PRS) codes are considered. In the case of RCPC codes, soft decision decoding is considered, in addition to the simpler hard decision decoding. The modulation format chosen in our study is /spl pi//4-DQPSK with differential detection. Unequal error protection is used based on the bit error sensitivities of the different speech parameters. The performance of the combined speech and channel codec is studied under different mobile channel conditions, such as fade rates, signal-to-noise ratios, and interleaving delays. The results indicate that, with no interleaving delay and a large channel signal-to-noise ratio, PRS codes and RCPC codes with soft decision decoding have similar performance, given in terms of the segmental signal-to-noise ratio (SSNR) of the reconstructed speech. At low channel SNR, RCPC codes with soft decision decoding are significantly better than PRS codes. Informal listening tests were also conducted and the results indicate that the difference between the quality of the reconstructed speech in an error-free channel and that in a Rayleigh fading channel is imperceptible at channel SNRs larger than 20 dB for both the RCPC and the PRS-based codecs.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

New rate-compatible punctured convolutional codes for Viterbi decoding

New good rate-P/(P+/spl delta/) rate-compatible punctured convolutional (RCPC) codes for 2/spl les/P/spl les/7 and 1/spl les//spl delta//spl les/(n-1)P were found and tabulated, These codes have been determined by iterative search based upon a criterion of maximizing the free distance and were generated by periodically puncturing their rate-1/n mother codes of memory 2/spl les/M/spl les/6 and n=2. These codes are expected to find their applications in unequal error protection schemes employing Viterbi decoding.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Selective repeat type‐II hybrid fec/arq systems using concatenated codes

AbstractHybrid forward error correction/automatic‐repeat request (FEC/ARQ) systems achieve greater throughput than ARQ systems by combining forward error correction with automatic‐repeat requests. A type‐II hybrid FEC/ARQ system is capable of adapting error‐correction capacity according to varying channel conditions. Although a high throughput can be achieved in such systems by using conventional convolutional or rate compatible punctured convolutional (RCPC) codes, when the channel signal‐to‐noise ratio (SNR) Es/N0 is low, resulting throughput efficiency and mean block delay performances are unsatisfactory.In this paper, selective repeat type‐II hybrid FEC/ARQ systems using concatenated codes are proposed to improve the throughput efficiency and mean block delay performances on channels with low SNRs. Systems using concatenated Reed‐Solomon outer codes and either rate one‐half convolutional or rate compatible convolutional (RCPC) inner codes are evaluated. The throughput efficiency and mean packet waiting and block delay times of these two types of concatenated coding systems are evaluated. A theoretical analysis and computer simulation of throughput efficiency of the proposed systems show increased performance for a wide range of Es/N0 over previous systems that use either stand‐alone rate one‐half convolutional or RCPC codes. It is also shown that the transmitter mean packet queueing delay and mean block delay times are reduced. In particular, by computer simulation, it is shown that when the traffic density is high, mean block delay times are greatly reduced by the use of RCPC inner codes.

Estimation of unreliable packets in subband coding of speech

A robust speech communications system over a digital mobile radio channel is considered. We examine a system using 12 Kbit/s embedded subband coding of speech and rate compatible punctured convolutional (RCPC) codes with generalised Viterbi decoding for combined error detection and correction. System performance is improved by exploiting the frame-toframe redundancy in the subband energy profile used for adaptive bit allocation in the subband coder. Unreliable subband side information about the energy profile is identified through a two-stage process comprising the channel error detector and a source-based subband energy profile error detector. The subband side information deemed unreliable is replaced with the estimates based on frame-to-frame redundancy. This improved error detection capability in the subband side information allows a judicious reassignment of channel error protection bits to the subband main information, leading to an overall improvement in system performance. Using a realistic simulation model of a digital mobile radio communication system, an improvement of up to 4.4 dB in recovered speech segmental SNR is obtained at a channel SNR of 6 dB, compared with a system with only channel error protection.