Decoder Parameters Research Articles

Performance of Reed–Solomon codes using the Guruswami–Sudan algorithm with improved interpolation efficiency

List decoding is a novel method for decoding Reed-Solomon (RS) codes that generates a list of candidate transmitted messages instead of one unique message as with conventional algebraic decoding, making it possible to correct more errors. The Guruswami-Sudan (GS) algorithm is the most efficient list decoding algorithm for RS codes. Until recently only a few papers in the literature suggested practical methods to implement the key steps (interpolation and factorisation) of the GS algorithm that make the list decoding of RS codes feasible. However, the algorithm's high decoding complexity is unsolved and a novel complexity-reduced modification to improve its efficiency is presented. A detailed explanation of the GS algorithm with the complexity-reduced modification is given with simulation results of RS codes for different list decoding parameters over the AWGN and Rayleigh fading channels. A complexity analysis is presented comparing the GS algorithm with our modified GS algorithm, showing the modification can reduce complexity significantly in low error weight situations. Simulation results using the modified GS algorithm show larger coding gains for RS codes with lower code rates, with more significant gains being achieved over the Rayleigh fading channels.

A novel turbo decoder architecture for hand-held communication devices

Mobile communication systems, such as IMT-2000, adopt turbo codes because they provide reliable, bandwidth-efficient communication over AWGN channels. The BER of turbo codes is close to the Shannon limits. As a mobile communication device can use only a limited power supply, use of low power design techniques is essential for successful device implementation. This paper proposes an architecture for the turbo decoder which adopts a fast decoding structure by initial threshold setting such that the number of decoding iterations can be reduced without BER performance degradation. The proposed decoding structure can be easily modified for other MAP decoders by employing a simple decision module. The initial iteration threshold has been decided via simulations by varying decoder parameters (mean/normalized-variance of the log-likelihood ratio; BER of the decoder outputs). Performance validations for the proposed decoder have been performed under the IMT-2000 high-speed data transmission testbed with the channel characteristic being set to BER=10/sup -6/. Simulation results show 55%-90% reductions in the number of decoding iterations when compared with conventional turbo decoders with a fixed number of iterations.

Application and standardization of turbo codes in third-generation high-speed wireless data services

This paper addresses the application of turbo codes for third-generation wireless services. It describes the specific characteristics of high-rate data applications in third-generation wide-band code-division multiple-access (CDMA) systems that make turbo codes superior to convolutional codes. In particular, it shows the positive effect of fast power control employed in these systems on the relative performance of turbo codes with respect to convolutional codes. It also shows how turbo and convolutional codes behave differently when the figure of merit is changed to frame error rate from bit error rate for high-speed data services. Furthermore, it describes in detail how and why the standardized turbo code has been selected in the presence of other candidates, which were also based on iterative decoding. Details of turbo interleaving and trellis termination as specified in the standards are explained. Performance of turbo codes under wide-band CDMA operating conditions are presented. The suitability of turbo codes for low-rate data applications is discussed. Finally it is shown that the performance loss as a result of internal decoder parameter quantization is negligible.

Knowledge-based parameter estimation for identification and equalization of storage channels

The emerging sampling detectors in digital magnetic recording require precise filtering of the readback signal. In this paper, we propose a technique for fast estimation of the channel response from which the filter coefficients are calculated. Utilizing the a priori knowledge about the general shape of the transition response in magnetic recording, the channel identification problem is reduced to estimation of one or more parameters. Specifically, the pulse width at half of the transition response peak magnitude is first estimated. The algorithm is then extended to include more practical cases. It is shown that this simplified approach has much faster convergence rate than the direct least-mean-square channel identification method. Once the algorithm converges, the estimates can be used to select or compute an appropriate set of equalizer coefficients or to modify the decoder parameters. We will describe methods for recursive filter design based on the estimated channel for partial response as well as decision feedback systems.

An evaluation of the systolic stack sequential decoder

The performance of a sequential stack decoder based on a new systolic priority queue is evaluated using extensive simulations over both memoryless Gaussian channels and Rayleigh fading channels. The results are used to determine interrelations between the decoder parameters, providing a simple way to design a systolic stack sequential decoder with an overall erasure probability approximately equal to the probability of a correct path overflow, while keeping the bit error rate of the decoder almost as low as that of the code. It is shown that this decoder circumvents some of the limitations inherent to usual stack decoders, while offering an increased decoding speed and being well suited for vlsi implementation.

Performance of radial basis functions in decoding a recently proposed chaotic modulation strategy

The use of radial basis functions for decoding a recently proposed modulation strategy is investigated. A range of data signals are considered and practical aspects are discussed when predicting, what in practice would be, a multitude of mapping and decoding parameters. The authors show that radial basis functions do not predict the next unmodulated chaotic sample with the degree of accuracy required to accurately decode a modulating signal. The authors therefore conclude that the proposed modulation technique, together with many other desirable features, results in secure transmission.

Packet-based embedded encoding for transmission of low-bit-rate-encoded speech in packet networks

Missing packets due to network congestion can seriously degrade the quality of received speech in packet voice communication. A variety of techniques exist that attempt to reconstruct the missing speech segments but these methods cannot be directly applied to low-bit-rate-encoded speech, such as ADPCM, where the decoded output depends not only on current transmitted codewords but also on the past history of the decoder. In this case, decoder parameters at the receiver lose track of encoder parameters after a missing packet leading to propagation of the decoding error into the following packet. A novel packet-based embedded encoding scheme is described that mitigates the effects of parameter mistracking caused by packet loss. The method may be applied to any low-bit-rate encoder that uses past information to decode current samples but specific results are given for its application to the CCITT 32 kbit/s ADPCM encoding standard. It is shown that packet-based embedded encoding of speech can double the maximum tolerable missing packet rate.

A generalized user interface for applications programs

A general method for using disk files (instead of a more conventional parameter-passing mechanism) to transfer control information from a user interface to a set of related applications programs is described. This technique effectively moves much of the user interface, including command decoding and limited parameter checking, from the applications programs to a table-driven executive.

Coding and decoding pictures in nuclear medicine

Optical simulations of coded aperture imaging of planar objects using the Annulus and Twin Annulus in a wholly non-coherent correlative processing system is described. The autocorrelation of the coded apertures is taken as a useful guide to the SNR capabilities of the codes. Results of planar objects occupying ∼50% of the field and a continuous-tone thyroid phantom are presented. A summary of optimum coding and decoding parameters is given.

Temperature profiles derived through the inversion of a system of first order differential equations

Generation of vertical temperature profiles from remotely sensed atmospheric radiance data is described as an analogous communications system. The radiative transport characteristics of the atmosphere encodes the continuous temperature profile into an “ n” element vector where “ n” is the number of channels in the satellite instrument. The temperature profile is a message transmitted from station A to station B and the link is the satellite instrument. At station B the decoder reproduces a continuous function which is the best estimate of the message encoded at station A. It is shown that the decoder must operate in a tuned mode where the parameters used in the encoder precisely determine the decoder parameters, and that the characteristics of the total message block must be given by a set of decoder constraints.

Simulation of Sequential Decoding with Phase-Locked Demodulation

Convolutional encoding with biphase modulation is an attractive combination of modulation/coding for the Gaussian channel, but a means of tracking carrier phase must be provided. The performance of combined sequential decoding and suppressed carrier (Costas loop) tracking in the receiver is difficult to analyze but can be obtained by computer simulations. Results of such simulations are presented in the form of a Pareto fit to the computation distributions for various tracking loop bandwidths and demodulator quantization (soft decisions). These distributions are applied to predict probability of error performance for typical decoder parameters (buffer size, speed factor). The anticipated advantage of quantized demodulation is observed. However, narrow tracking bandwidths are required, with sufficient interleaving to overcome effects of correlated phase perturbations due to noise.