Presence Of Bit Errors Research Articles

Parameter Estimation of Convolutional and Helical Interleavers in a Noisy Environment

Forward error correction (FEC) codes followed by an interleaver play a significant role in improving the error performance of the digital systems by counteracting random and burst errors. In most of the applications, interleaver and FEC code parameters are known at the receiver to successfully de-interleave and decode the information bits. However, in certain non-cooperative applications, only partial information about the code and interleaver parameters is known. Furthermore, in cognitive radio applications, an intelligent receiver should adapt itself to the transmission parameters. Hence, there is a need to blindly estimate the FEC code and interleaver parameters in the mentioned applications from the received data stream with the availability of partial knowledge about the transmission parameters at the receiver. In this paper, a blind recognition of convolutional and helical interleaver parameters is carried out using innovative algorithms for unsynchronized, convolutionally encoded data in the presence of bit errors. In addition, the proposed algorithms also estimate the starting bit position for achieving proper synchronization. In a nutshell, it has been observed from the numerical results that the interleaver parameters have been estimated successfully over erroneous channel conditions from the proposed algorithms. Finally, the performances of the proposed algorithms for both the interleavers considering various bit error rate values have also been analyzed.

Parameter estimation of block and helical scan interleavers in the presence of bit errors

In data communication and digital storage applications, interleaver, which rearranges the encoded data stream, follows the channel encoder to prevent burst errors. In general, forward error correction (FEC) codes provide protection against randomly distributed errors, whereas interleaver provides protection against error bursts. To de-interleave the interleaved data, accurate information about the interleaver parameters is required at the receiver. However, in non-cooperative context, the parameters are either not known or only partially known at the receiver. Therefore, blind/semi-blind estimation of interleaver parameters is mandatory at the receiver in order to successfully de-interleave the interleaved data. In this context, this paper proposes innovative algorithms for the estimation of interleaver parameters such as interleaver period (or size of the interleaver matrix), number of rows and columns of the interleaver matrix, and helical array step size in the presence of bit errors provided the knowledge of type of interleaver is known at the receiver. In addition, it has been assumed that the block and helical scan interleavers follow a convolutional encoder.

OBEX Over IrDA: Performance Analysis and Optimization by Considering Multiple Applications

OBEX (Object Exchange Protocol) is a session protocol designed to exchange all kind of objects between portable devices using different ad hoc wireless links including IrDA and Bluetooth. This paper develops a mathematical model for OBEX over the IrDA protocol stack by considering multiple applications and presence of bit errors. The model is also verified by simulation results. We derive throughput equations and carry out an optimization study focusing on four major parameters: OBEX packet size, TinyTP (IrDA transport layer) buffer size, IrLAP (IrDA link layer) frame and window size. Equations are derived for the optimum IrLAP window and frame sizes. Numerical results show significant improvement on OBEX performance using the optimized parameters. The major contribution of this work is the modelling of OBEX including the low layer protocols and optimization of the overall throughput by appropriate parameter selection

IrBurst Modelling and Performance Analysis in the Presence of Transmission Errors

IrBurst is a session/presentation layer protocol dedicated for high speed large volume information transfer over IrDA links. The protocol is developed by IrDA in order to complement the existing protocol OBEX which is best suited for small files. This paper presents a mathematical model for IrBurst over the IrDA protocol stacks taking into account the presence of bit errors and multiple simultaneously applications. The performance of IrBurst is examined considering TinyTP buffer sizes and the number of IrBurst application connections as parameters. The contribution of this work is to develop a mathematical model for IrBurst, investigate the compatibility of IrBurst to low layer protocols, as well as providing suitable design guidelines for IrDA devices for high performance of IrBurst.

Modelling and Optimising TinyTP over IrDA Stacks

TinyTP is the IrDA transport layer protocol for indoor infrared communications. For the first time, this paper presents a mathematical model for TinyTP over the IrDA protocol stacks taking into account the presence of bit errors. Based on this model, we carry out a comprehensive optimisation study to improve system performance at the transport layer. Four major parameters are optimised for maximum throughput including TinyTP receiver window, IrLAP window and frame size, as well as IrLAP turnaround time. Equations are derived for the optimum IrLAP window and frame sizes. Numerical results show that the system throughput is significantly improved by implementing the optimised parameters. The major contribution of this work is the modelling of TinyTP including the low-layer protocols and optimisation of the overall throughput by appropriate parameter selection.

A novel delineation mechanism for the ATM adaptation layer 2 over wireless ATM networks

AbstractThe ATM adaptation layer 2 (AAL2) has been standardized by the ITU‐T for the support of low data rate and delay‐sensitive applications, such as voice, over ATM networks. One of the main characteristics of the AAL2 standard is the support for multiplexing information at the expense of introducing a new frame structure inside the payload of the ATM cells. The AAL2 standard introduces a mechanism for the delineation of the AAL2 packets and it has been found that the delineation mechanism reduces the performance of AAL2 in the presence of channels with high bit error rates. In this paper, a novel delineation mechanism is proposed for AAL2 to be used over highly error‐prone channels, such as wireless links. The proposed mechanism improves the performance (i.e. reduces packet loss) of the AAL2 standard in the presence of bit errors and in some cases reduces the overhead required for the delineation of the AAL2 packets. Copyright © 2002 John Wiley & Sons, Ltd.

Error Detection and Concealment with an Unsupervised MPEG2 Video Decoder

MPEG2 is an international video coding standard for broad applications ranging from video conferencing to HDTV. In this paper we study the performance of an unsupervised MPEG2 decoder in the presence of bit errors and cell loss, where errors are detected by the decoder solely without requesting any error information from external devices. The technology behind the MPEG2 standard is described briefly. Differences between the MPEG1 and MPEG2 standards are addressed. Schemes to detect errors, based on decoding errors and standard semantics violations, are proposed. Implementation details of the unsupervised MPEG2 decoder are described as necessary to facilitate discussions of these schemes. Computer simulations are conducted for two video sequences with a variety of motions and scene contents to study the visual degradations caused by header information error, random bit error, and cell loss. It is shown that a simple error concealment scheme gives an overall visual quality acceptable to general viewers even under severe transmission error environments.

A noise resistant synchronization scheme for HDTV images

A method that increases the error resistance of the HDTV system and offers graceful picture degradation in the presence of bit errors, is presented. Due to the nature of the presently proposed compression schemes for HDTV systems, an error in a data bit does not only affect the block the bit belongs to, but unfortunately the effects of this error may perpetuate to the following blocks. This is because a bit error may cause loss of synchronization between the data bits and the picture blocks they represent. Our method restricts the effects of a bit error to a picture block whose size is significantly smaller than those used by the HDTV systems. We achieve synchronization by transmitting a header-word for each such synchronization block. Each header-word contains the number of data bits representing the compressed block. This header-word is protected by two levels of FEC code. To decrease the number of extra bits needed by the header-words, two different synchronization block sizes are used, a relatively small block size for the reference frames and a larger size for the inter-frames. The resulting method improves the quality of the picture in the presence of errors and defers the SNR at which the HDTV picture suddenly deteriorates by 2.5 to 3 dB. It also allows operation at higher order modulation transmission schemes, e.g., 32-QAM instead of 16-QAM, without the requirement of increased signal power.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance study of stochastic speech coders

Four speech coders in the CELP (Code Excited Linear Predictive) family are described. By replacing the long term prediction with a self excitation sequence (adaptive codebook) as well as substituting a stochastic multipulse, or sparse codebook for the commonly used codebook of Gaussian noise, the speech quality is improved. The coders are fully quantised at 7.0 and 5.0 kbit/s, interesting bit-rates for such possible applications as the half rate GSM system and the INMARSAT-M service. The performance of the coding schemes are evaluated by a formal listening test and presented by their Mean Opinion Scores (MOS). For the coder with maximum performance with respect to quality and complexity, a set of tolerable bit error rates (BER) are given. It is shown that the presence of acoustic background noise does not influence the coder quality, and that bit errors in this case will be partially masked by the background noise giving the coder a high degree of robustness. Considering the performance in the presence of bit errors and background noise, the coder seems to be suitable for use in a mobile communication system using satellite links.

Step-Size Transmitting Differential Coders for Mobile Telephony

In using digital speech for mobile radio, we encounter the problem of severe bit-error bursts. Error clustering occurs because the bit duration is typically much smaller than that of a signal “fade,” and average bit-error probabilities greater than 1 percent are not uncommon. For speech communication over such channels, this paper proposes variable step-size differential coders based on explicit (and error-protected) transmission of quantizer step size. Specifically, we discuss delta and dpcm coders to be referred to as dm-aqf and dpcm-aqf, where aqf stands for adaptive quantization with forward estimation (and transmission) of step size. (Backward estimation, based on quantized-signal history, has the nice feature that the step-size information does not have to be explicitly transmitted. Furthermore, obtaining this information does not entail any encoding delay. However, due to the dependence of step size on reconstructed signal history, backward estimation is often less reliable in the presence of bit errors than a scheme based on aqf.) The studies reported in this paper cover the problem of step-size determination in aqf, the design of time-invariant first-order predictors for dpcm-aqf, and the performances of aqf encoders with and without burst-error-protecting ploys such as redundant time-diversity coding and bit scrambling. Judging from snr figures and informal listening tests, interesting results are obtained with the following 48-kb/s coders: three-bit dpcm-aqf with redundant error protection, and dm-aqf using bit scrambling.