Levels Of Error Protection Research Articles

Service-Aware Retransmission Control in Cellular Networks

This paper proposes a service-aware cross-layer approach between application/transport layers on the mobile terminal and link layer on the wireless base station to enable dynamic control on the level of per-packet error protection for multimedia data streams. Specifically, in the context of cellular networks, the proposed scheme enables the mobile terminal to specify to the base station the desired level of Hybrid ARQ (HARQ) protection by using an in-band control feedback channel. Such protection is dynamically adapted on a per-packet basis and depends on the perceptual importance of different packets as well as on the reception history of the flow. Experimental results demonstrate the potential benefits deriving from the proposed strategy either for audio and video real-time streams as well as for TCP-based data transfers.

A Robust Resolution-Enhancement Scheme for Video Transmission Over Mobile Ad-Hoc Networks

Historically, Error-Resilient (ER) video transmission and Super-Resolution (SR) image reconstruction techniques have evolved separately. In this paper, we propose a coordinated application of ER and SR to enhance the resolution of image transmitted over mobile ad-hoc networks. In order to combat error propagation, a flexible multiple description coding method based on shifted 3-D SPIHT (3-D Set Partitioning In Hierarchical Trees) algorithm is presented to generate variable independent descriptions (substreams) according to the network condition. And then, a novel unequal error protection strategy based on the priority level is provided to assign a higher level of error protection to more important parts of bitstream. Moreover, a robust SR algorithm is proposed in the presence of different kinds of packet loss rate to enhance the image resolution. Experimental results indicate that the proposed robust resolution-enhancement scheme outperforms the competing methods from the aspects of PSNR (Peak-Signal-to-Noise Ratio) and visual quality under different packet loss rates.

Design of unequal error protection for MIMO-OFDM systems with hierarchical signal constellations

In multimedia communication systems, efficient trans- mission system design should incorporate the use of matching unequal error protection (UEP), since source coders exhibit unequal bit error sensitivity. In this paper, we present UEP schemes which exploit differences in bit error protection levels in orthogonal frequency division multiplexing (OFDM) systems over frequency selective fading channels. We introduce an UEP scheme which improves the link performance with multiple transmit and receive antennas. Especially, we propose a new receiver structure based on two stage Maximum Likelihood detection (MLD) schemes which can approach the performance of a full search MLD receiver with much reduced computational complexity. In the performance analysis, we derive a generalized pairwise error probability expression for the proposed UEP schemes. Simulation results show that the proposed schemes achieve a significant performance gain over the conventional equal error protection (EEP) scheme.

Optimal 3GPP packet-switched streaming service (PSS) over GPRS networks

3GPP packet-switched streaming service (PSS) is a standardized packet-based mobile streaming service, which is based on IETF RTSP/SDP standards. PSS can be implemented over GPRS networks; however these cannot usually guarantee any data rates or delay bounds, but allow sufficient bandwidth for mobile streaming. GPRS cell reselections pose additional challenges for streaming, since several seconds of data transmission breaks may occur, and data may even be lost. The level of error protection of GPRS is good enough for mobile streaming, if the correct quality of service (QoS) profile is configured. In this paper, we study the effect of different QoS parameters configurations to find optimal values for PSS over GPRS. The paper shows also a method for optimizing cell reselection management at the application layer, in order to provide seamless mobility. Results show that despite all the limitations of a GPRS environment, PSS is feasible with a decent quality of service.

Content-Adaptive Packetization and Streaming of Wavelet Video over IP Networks

This paper presents a framework of content-adaptive packetization scheme for streaming of 3D wavelet-based video content over lossy IP networks. The tradeoff between rate and distortion is controlled by jointly adapting scalable source coding rate and level of forward error correction (FEC) protection. A content dependent packetization mechanism with data-interleaving and Reed-Solomon protection for wavelet-based video codecs is proposed to provide unequal error protection. This paper also tries to answer an important question for scalable video streaming systems: given extra bandwidth, should one increase the level of channel protection for the most important packets, or transmit more scalable source data? Experimental results show that the proposed framework achieves good balance between quality of the received video and level of error protection under bandwidth-varying lossy IP networks.

On Unequal Error Protection LDPC Codes Based on Plotkin-Type Constructions

We introduce a new family of unequal error protection (UEP) codes, based on low-density parity-check (LDPC) component codes and Plotkin-type constructions. The codes are decoded iteratively in multiple stages, and the order of decoding determines the level of error protection. The level of UEP among the code bits is also influenced by the choice of the LDPC component codes and by some new reliability features incorporated into the decoding process. The proposed scheme offers a very good tradeoff between code performance on one side and encoding/decoding and storage complexity on the other side. The novel approach to UEP also allows for finding simple approximations for the achievable degrees of UEP, which can be used to govern practical code design implementations

QoS management with dynamic bearer selection schemes

This paper presents an evaluation of a radio level QoS management scheme developed to ensure the maintenance of QoS contracts. The concept of QoS contract is defined as the specification of the quality requirement for various types of services. According to the contracted QoS, a dynamic bearer selection is performed to adapt the link to the channel quality variations. Terrestrial Trunked Radio system (TETRA) presents itself as a suitable platform for illustrating the concept of QoS contract. This arises from its feature-rich bearer services that support data and voice with varying levels of error protection. The generic QoS management scheme presented in this paper has been applied to a private mobile radio system but it also represents an appropriate platform for multi-vendor, multi-technology and multimedia environments such as those found with 3G systems.

On unequal error protection using convolutional codes

This paper demonstrates the inherent unequal error protection (UEP) nature of punctured convolutional codes to develop two UEP schemes. In both schemes, the UEP level of error protection is better than the original error-control coding and modulation scheme employed. The first scheme is based on utilizing the inherent UEP capability within the columns of the puncturing matrix, without a reduction in information throughput. The second scheme reduces the effective code rate b/ v of a punctured convolutional code created from an original rate 1/ v o code. Such a UEP scheme may be of use in a communication system where it is beneficial to briefly reduce the information throughput for a much improved error protection. It is shown that the performance of a simple rate 1/2, constraint length K=3 code, when transformed to an effective rate 1/3 code, provides a coding gain of approximately 5.2 dB with the use of eight level soft-decision decoding over uncoded BPSK. In general, this UEP technique provides a coding gain of slightly greater than 10 log 10(bv o /v) dB over the performance of the original rate 1/ v o code using hard-decision Viterbi decoding. A further coding gain of approximately 1.5 dB can be expected with the use of soft-decision decoding.

Concatenated Reed-Muller codes for unequal error protection

We present a new coding scheme that combines the advantages of a product-like concatenation of Reed-Muller codes with so-called iterative "turbo" decoding and provides powerful unequal error protection abilities. It is shown that various levels of error protection can be realized using a sophisticated encoding scheme for Reed-Muller codes. A discussion of this code construction, the resulting distance profile between the different levels and the iterative decoding scheme is given. The results are very promising and impressively confirm the unequal error protection capabilities of the presented coding scheme.

Embedding channel coding in arithmetic coding

An arithmetic coding algorithm that incorporates channel coding is presented. For a source alphabet with m symbols, the selected m code points over the [0-1) interval have a desired minimum Hamming distance d/sub min/ between them. The decoder utilises this d/sub min/ in conjunction with the self-synchronisation property of arithmetic coding and knowledge of the source statistics to recover the original sequence of symbols, in the presence of channel errors, without the use of known channel coding techniques. The selected d/sub min/ provides a desired error protection level. The introduced scheme is suitable for bandwidth-limited binary symmetric channels (BSCs) with moderate to high error rates.

Investigations on bit error performance for video over DAB

The digital audio broadcasting (DAB) system which was originally designed for high quality audio transmission to mobile receivers is investigated for transmission of compressed digital video and multimedia signals. The bit error performance is considered using various levels of error protection provided by the DAB system. As a result, a net bit rate of about 1.5 Mbit/s can be achieved. With additional error correction coding, a bit error ratio (BER) of less than 10/sup -10/ can be realized. This is the requirement for compressed video signals. The SNR per bit is below 16 dB. The results are demonstrated and compared using computer simulations of the complete system.

Error protection for progressive image transmission over memoryless and fading channels

Product channel codes are proposed to protect progressively compressed and packetized images for noisy channels. Within packets, the product code uses the concatenation of a rate-compatible punctured convolutional code and an error detecting parity check code. Across packets, Reed-Solomon codes are used. Benefits include flexible choice of delay, adaptability of error protection level (i.e., unequal error protection), and scalable decoding complexity. The system outperforms the best known image coders for memoryless channels and performs well on fading channels.

Rate compatible turbo codes

Turbo codes can easily be used when two error protection levels are needed. The same encoder and decoder is used to achieve this unequal error protection. This will allow turbo codes to be used for channels where some information bits are more sensitive to errors than others, and at the same time where powerful codes are required (e.g. a mobile satellite channel).

Multilevel codes for unequal error protection

Two combined unequal error protection (UEP) coding and modulation schemes are proposed. The first method multiplexes different coded signal constellations, with each coded constellation providing a different level of error protection. In this method, a codeword specifies the multiplexing rule and the choice of the codeword from a fixed codebook is used to convey additional important information. The decoder determines the multiplexing rule before decoding the rest of the data. The second method is based on partitioning a signal constellation into disjoint subsets in which the most important data sequence is encoded, using most of the available redundancy, to specify a sequence of subsets. The partitioning and code construction is done to maximize the minimum Euclidean distance between two different valid subset sequences. This leads to ways of partitioning the signal constellations into subsets. The less important data selects a sequence of signal points to be transmitted from the subsets. A side benefit of the proposed set partitioning procedure is a reduction in the number of nearest neighbors, sometimes even over the uncoded signal constellation. >

Multilevel trellis coded modulations for the Rayleigh fading channel

The authors present coded 8-phase-shift-keyed (8-PSK) modulations for the Rayleigh fading channel. The schemes are based on multilevel trellis-coded-modulation constructions and utilize maximum free Hamming distance binary convolutional codes as building blocks. A suboptimal multistage decoder that utilizes interstage interleaving and iterative decoding is proposed and evaluated. Examples are constructed to show that the proposed schemes outperform the best modified codes of the Ungerboeck type due to significantly higher implicit time diversity, yielding seven branches of built-in time diversity, whereas the Ungerboeck code yields four branches of time diversity for a 64-state system. The transmission delay is higher, however. The new schemes can provide three levels of unequal error protection when 8-PSK or 8-differential-phase-shift-keying (8-DPSK) modulations are used. They provide 10-14-dB channel signal-to-noise ratio gain over uncoded 4-DPSK at a bit error rate of 10/sup -3/ for a modest decoding complexity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The performance of rate-compatible punctured convolutional codes for digital mobile radio

The unequal error protection capabilities of convolutional codes belonging to the family of rate-compatible punctured convolutional codes (RCPC codes) are studied. The performance of these codes is analyzed and simulated for the first fading Rice and Rayleigh channels with differentially coherent four-phase modulation (4-DPSK). To mitigate the effect of fading, interleavers are designed for these unequal error protection codes, with the interleaving performed over one or two blocks of 256 channel bits. These codes are decoded by means of the Viterbi algorithm using both soft symbol decisions and channel state information. For reference, the performance of these codes on a Gaussian channel with coherent binary phase-shift keying (2-CPSK) is presented. A number of examples are provided to show that it is possible to accommodate widely different error protection levels within short information blocks. Unequal error protection codes for a subband speech coder are studied in detail. A detailed study of the effect of the code and channel parameters such as the encoder memory, the code rate, interleaver depth, fading bandwidth, and the contrasting performance of hard and soft decisions on the received symbols is provided. >

A study of vector quantization for noisy channels

Several issues related to vector quantization for noisy channels are discussed. An algorithm based on simulated annealing is developed for assigning binary codewords to the vector quantizer code-vectors. It is shown that this algorithm could result in dramatic performance improvements as compared to randomly selected codewords. A modification of the simulated annealing algorithm for binary codeword assignment is developed for the case where the bits in the codeword are subjected to unequal error probabilities (resulting from unequal levels of error protection). An algorithm for the design of an optimal vector quantizer for a noisy channel is briefly discussed, and its robustness under channel mismatch conditions is studied. Numerical results for a stationary first-order Gauss-Markov source and a binary symmetric channel are provided. It is concluded that the channel-optimized vector quantizer design algorithm, if used carefully, can result in a fairly robust system with no additional delay. The case in which the communication channel is nonstationary (as in mobile radio channels) is studied, and some preliminary ideas for quantizer design are presented. >

New Concept for Independent GPS Integrity Monitoring

Monitoring of the GPS signals-in-space status for integrity, with a fast response time, is essential if the system is to be used by civil aviation for nonprecision approach guidance. One alternative for providing such a monitoring function is to employ an independent monitoring system with a few ground-based signal monitors to cover a region and a satellite-based integrity broadcast channel to provide realtime GPS signal status. This paper introduces a new decision concept for accepting or rejecting a GPS signal for navigation in the independent monitoring system. Performance of the new concept is evaluated in terms of the probability of alarms against position error protection level, which are two important parameters for any integrity method.

Linear unequal error-protection array codes

It is useful to have codes in which some information digits are protected against a greater number of errors than other information digits. Masnick and Wolf (1967) were the first to introduce such unequal error-protection (UEP) codes. The authors present some new parameters to describe the performance of UEP codes and a new class of UEP array codes which have simple structure and many adjustable error-protection levels. >

On linear unequal error protection codes

The class of codes discussed in this paper has the property that its error-correction capability is described in terms of correcting errors in specific digits of a code word even though other digits in the code may be decoded incorrectly. To each digit of the code words is assigned an error protection level f_{i} . Then, if f errors occur in the reception of a code word, all digits which have protection f_{i} greater than or equal to f will be decoded correctly even though the entire code word may not be decoded correctly. Methods for synthesizing these codes are described and illustrated by examples. One method of synthesis involves combining the parity check matrices of two or more ordinary random error-correcting codes to form the parity check matrix of the new code. A decoding algorithm based upon the decoding algorithms of the component codes is presented. A second method of code generation is described which follows from the observation that for a linear code, the columns of the parity check matrix corresponding to the check positions must span the column space of the matrix. Upper and lower bounds are derived for the number of check digits required for such codes. The lower bound is based upon counting the number of unique syndromes required for a specified error-correction capability. The upper bound is the result of a constructive procedure for forming the parity check matrices of these codes. Tables of numerical values for the upper and lower bounds are presented.