An improved construction of block‐coded modulation

Abstract

The traditional block‐coded modulation scheme is based on set partitioning of a two‐dimensional signal constellation. In this paper, we propose an improved design of the block‐coded modulation scheme which is based on set partitioning of a block modulation code at some coding levels. With no inferior error performance, the proposed scheme is far superior as regards its reduced decoding complexity.     

Classified vector quantization of LPC parameters

Abstract

To achieve high coding efficiency, modern speech coders adopt hybrid coding approaches, which utilize different coding mechanisms for various classified speech segments. With known voiced/unvoiced detection, in this paper, a classified LPC quantization (CLPQ) scheme is presented to effectively encode line spectral frequencies (LSF). The proposed CLPQ scheme improves the performance of the classified LSF vector quantizer, which adopts two LSF codebooks derived separately from voiced and unvoiced speech frames. With an objective spectral distortion measure, the CLPQ scheme successfully reduces the bit rate by about 1 bit/frame. Many classified LSF quantizers with different codebook structures and bit rates were evaluated. It would be helpful to design a classified LSF quantizer, which arrives at a compromise between distortion, bit rate and computational complexity.     

A modified floating‐point code for voice coding and its applications

Abstract

A new modified normalized floating‐point code is proposed for the use in voice coding. It has about the same signal‐to‐quantizing noise ratio and dynamic range as the A‐87.6 code. Arithmetic operations encountered in digital signal processing are easier to implement with this code. Furthermore, simple procedures, which are easier to understand, exist for converting between this code and a linear code. According to the similar algorithm of this new code, the A‐87.6 and μ‐255 codes are derived again. The comparisons and other possible modified normalized floating‐point codes are also offered. The structure of a multiplier/accumulator implemented with the VLSI technology or the gate array for this new code is proposed.     

Application of genetic algorithm to the observer‐based controller design for neutral systems

Abstract

In this paper, the dynamic observer‐based controller design for a class of neutral systems with known and uncertain time delays is considered. Delay‐dependent and delay‐independent stabilizability criteria are proposed to guarantee the stability for the feedback control systems. Linear matrix inequality (LMI) and genetic algorithm (GA) are used to design the observer‐based control. Design procedure for the observer‐based control is provided. A numerical example is given to illustrate our results.     

Using a genetic algorithm to generate D‐optimal designs for mixture‐process variable experiments

This article presents and develops a genetic algorithm (GA) to generate D‐efficient designs for mixture‐process variable experiments. It is assumed the levels of a process variable are controlled during the process. The GA approach searches design points from a set of possible points over a continuous region and works without having a finite user‐defined candidate set. We compare the performance of designs generated by the GA with designs generated by two exchange algorithms (DETMAX and k‐exchange) in terms of D‐efficiencies and fraction of design space (FDS) plots which are used to evaluate a design's prediction variance properties. To illustrate the methodology, examples involving three and four mixture components and one process variable are proposed for creating the optimal designs. The results show that GA designs have superior prediction variance properties in comparison with the DETMAX and k‐exchange algorithm designs when the design space is the simplex or is a highly‐constrained subspace of the simplex.     

Multilayered linear dispersion codes for flat fading multiple-input multiple-output channels

The authors investigate the design of linear dispersion (LD) codes, aiming at flexible encoding schemes that allow various rate-performance tradeoffs under a common coding structure. First, the capacity of LD codes is studied. It is shown that the maximum attainable multiplexing gain of a linear dispersion code is the number of symbols per channel use of the code (i.e. coding rate in symbols). In addition, conditions on the construction of linear dispersion matrices for various multiplexing gains are established. A general multilayered linear dispersion coding scheme that allows various multiplexing gains is then proposed. In the proposed scheme, coding rate can be adapted by employing different numbers of dispersion matrices. Furthermore, phase shifting among input symbols is applied to optimise the error performance without loss of multiplexing gain. The construction of dispersion matrices and the optimisation of the phase shifts together constitute a structured approach for the design of linear dispersion codes. Simulation results demonstrate that the new codes outperform conventional LD codes at various data rates.     

Grand alliance MPEG-2-based video decoder with parallel processing architecture

A practical and unique hardware architecture for video bitstream source decoding and video postprocessing of a Moving Pictures Expert Group (MPEG-2)-based high-definition television (HDTV) compressed bitstream has been implemented to impose minimal limitations on the video source coding algorithm. The Grand Alliance (GA) MPEG-2-based HDTV codec achieves a high degree of source and channel coding efficiency while preserving the delivery of high-resoultion picture quality in a variety of video input and output formats in bandwidth-limited channels. The video source decoder hardware architecture necessary to achieve the data decoding and ensuing video postprocessing poses numerous technologic challenges to the system designer, who must tradeoff minimizing codec constraints with the eventual commercialization of a video decoder for a consumer television receiver product. The powerful and flexible coding algorithm necessary to satisfy the HDTV picture quality and transmission channel bandwidth limitation requirements results in an encoder-output bitstream that necessitates high throughout decoding. Although the transmitted bitstream is of constant rate due to rate buffering, bistreams internal to the codec are both peaky and bursty. An intelligent distributive parallel processing decoding architecture has been developed to dynamically partition the MPEG-2 bitstream into a number of decodable subset bitstreams, while placing minimal constraints on the encoding algorithm. This architecture allows for high-speed, efficient decoding of the bitstream, and can be a prelude to the development of a cost-effective consumer product. Further architecture refinements can be explored, including implementation in VLSI.     

A regional genetic algorithm for the discrete optimal design of truss structures

A regional genetic algorithm (R‐GA) is used for the discrete optimal design of truss structures. The chromosomes are selected from a sub‐region centred on the continuous optimum. This approach replaces genetic rebirth as previously proposed by other authors, thereby significantly reducing computational costs. As a pure discrete method, the R‐GA method does not require heuristic arguments or approximations. This makes the algorithm highly effective when buckling and slenderness constraints with scatter in the data are introduced. A large set of numerical test examples is used to illustrate the capabilities of the method. The algorithm is shown to be effective and robust, making it suitable for the optimal design of very large truss structures. Copyright © 1999 John Wiley & Sons, Ltd.     

Design of Intra‐BS handoff in multi‐hop IEEE 802.16 broadband wireless networks

Abstract

In IEEE 802.16‐based multi‐hop networks, transmissions using a multi‐hop high‐rate relay path can potentially achieve better throughput and delay than using a single‐hop low‐rate direct path. The establishment of relay or direct connection and the handoffs between different connections for mobile subscribers are thus key design issues. This paper studies connection setup and Intra‐BS handoff operations in IEEE 802.16‐based multi‐hop networks, where each connection employs adaptive modulation and coding scheme at the physical layer against wireless fading channel. Both centralized and decentralized designs are considered. In the centralized design, the base station coordinates connection establishments and handoffs for multi‐hop IEEE 802.16‐based subscribers. In the decentralized design, the MMR‐enhanced relay stations and mobile subscribers are required to participate in the connection and handoff management. Simulation results show that the two designs can significantly improve the good put, the packet transmission delay and network throughput. The results also highlight that the centralized design outperforms decentralized design in terms of throughput and delay.     

An effective codebook search algorithm for vector quantization

Abstract

A new scheme that aims to cut down on the computational cost of the vector quantization (VQ) encoding procedure is proposed in this paper. In this scheme, the correlation between the codewords in the codebook is exploited and three test conditions are designed to filter out the impossible codewords in the codebook. The design of test conditions is based on the concept of integral projection.

From the experimental results, it is shown that the new scheme outperforms all the other schemes proposed so far in speeding up the VQ encoding procedure. When the codebook of 1024 codewords is used in the proposed scheme, the execution time it consumes is less than 2 per cent of that needed by the full search algorithm. The average time reduction rate is approximately 97.7 per cent compared to the execution time for the full search algorithm. In other words, the proposed scheme indeed provides an effective approach to speed up the VQ encoding procedure.     

一个基于FPGA的低复杂度水声直扩系统设计

基于现场可编程门阵列(FPGA),设计并实现了一个低复杂度的支持码分多址接入(CDMA)机制的水声直接序列扩频(UDSSS)通信系统--UADSSS/CDMA,给出了系统的整体设计和信道编码电路、信号捕获电路的详细设计.信道编码采用规则重复累积(RA)码,解码迭代算法采用低复杂度的最小和算法,给出了一种快速运算的电路设计;信号捕获电路采用延迟相关捕获算法,给出了一种低复杂度的基于流水线结构的电路设计.进行了水声试验平台测试、湖试、海试等性能测试,结果表明,系统在抑制多径干扰和支持多用户通信方面具有良好的性能:试验平台测试显示,单用户通信的误码率为10-4数量级,存在两个用户干扰的误码率为10-3数量级;湖试显示,零误码的数据包为74.8%;海试显示,零误码的数据包为34.4%.     

Selective receiver switching scheme for space time block coding with full code rate and non-orthogonal design

It is desirable to construct a transmission matrix with full code rate as well as full transmit diversity in the design of space time block coding (STBC). For an arbitrary complex constellation, only full rate and full diversity signal matrix with size 2 by 2 is possible, said as Alamouti Code. For a real signal matrix with a size above 8 by 8, it is also impossible to acquire full code rate and full transmit diversity simultaneously. An efficient selective receiver switching scheme is proposed for STBC with the full code rate and non-orthogonal design. In the proposed scheme with the aid of beamforming, the authors divide the received signals into two groups according to the encoded matrix. By this way, the authors can eliminate the interference from the neighbouring signals almost by half. The simulation results with the example of matrix demonstrate that the proposed scheme can provide the improved performance and more under imperfect channel estimation.     

New concatenated coding and space?time modulation scheme for MIMO wireless communications

Zheng and Tse have demonstrated that there exists an optimal trade-off between diversity gain and multiplexing gain. To realise the predicted optimal trade-off, we propose a new multiple-input multiple-output transmission scheme for a concatenated coding and space-time (ST) modulation system aimed at applications that require flexible trade-off between performance and data rate. The proposed scheme is multi-layered with linear ST modulation to allow various multiplexing gain. Through a judicious design of the inner ST modulation, the optimisation of spatial multiplexing is made simple. Moreover, a joint iterative receiver based on MMSE criterion with a priori information is developed to reduce computational complexity. Simulation results are provided to demonstrate the merits of the new design.     

Experimental demonstration of gray-scale sparse modulation codes in volume holographic storage

We discuss experimental results of a versatile nonbinary modulation and channel code appropriatefor two-dimentional page-oriented holographic memories. An enumerative permutation code is used to provide a modulation code that permits a simple maximum-likelihood detection scheme. Experimental results from the IBM Demon testbed are used to characterize the performance and feasibility of the proposed modulation and channel codes. A reverse coding technique is introduced to combat the effects of error propagation on the modulation-code performance. We find experimentally that level-3 pixels achieve the beet practical result, offering an 11-35% improvement in capacity and a 12% increase in readout rate as compared with local binary thresholding techniques.     

An experiment in genetic optimization in lens design

Abstract

A genetic algorithm and its application in lens design is studied. A combined algorithm is also presented which includes both a genetic algorithm (GA) and a damped least squares (DLS) method. The convergence property of a GA in lens design is demonstrated: first of all, a GA-generated design is obtained without artificial intervention, then, the aberration correction is completed by DLS, and the result is close to the GA-generated design.     

Dynamic selective information hiding based on search order coding with low bit rate

Abstract

A low bit rate information hiding scheme is important for efficient communication. According to our observation, in a search order coding based (SOC based) hiding method, the case distribution generated from different images and from different secret strings is different. Based on this characteristic, we designed a dynamic selective, SOC based, information hiding scheme to achieve a desirable compression effect. That is, depending on different case distributions, we used different coding modes to reduce the bit rate more effectively. The main concept of our design is to let the two cases that occur most frequently use one-bit indicators and to let the remaining two cases use four-bit indicators to indicate the following coding types. The experimental results showed that the proposed scheme has a lower bit rate than other SOC based information hiding schemes. As a result, the proposed information hiding scheme is more practical for real world applications.     

Subspace‐based techniques for 2‐d DOA estimation with uniform circular array under local scattering

Abstract

In mobile communication systems, local scatterers in the vicinity of the sources cause angular spreading of radiating signals as seen from a base station antenna array. Thus, the base station antenna array is typically situated on the roof of a high building away from potential multipath reflectors. The uniform circular array (UCA) geometry provides 360° azimuthal coverage and also provides information on source elevation angles. We consider the problem of two‐dimensional (azimuth and elevation) direction‐of‐arrival (DOA) estimation with UCA. In the multipath scenario, the base station antenna can receive many coherent signals that cause the array manifold to be different from the conventional array manifold model. Herein, parameters of the spatial signature in the presence of local scattering are presented which apply to UCA. Then, we present a fast searching technique to improve the efficiency of the MUSIC algorithm for two‐dimensional DOA estimation. The fast signal subspace‐based estimation method utilizes the ESPRIT algorithm and then adopts sequential one‐dimensional searching to save computational cost. Several simulation results are included for illustration and comparison.     

Colour image coding scheme using absolute moment block truncation coding and block prediction technique

Abstract

A predictive colour image compression scheme based on absolute moment block truncation coding is proposed. In this scheme, the high correlations among neighbouring image blocks are exploited by using the similar block prediction technique. In addition, the bit plane omission technique and the coding of quantisation levels are used to cut down the storage cost of smooth blocks and complex blocks respectively. According to the experimental results, the proposed scheme provides better performance than the comparative schemes based on block truncation coding. It provides better image qualities of compressed images at low bit rates. Meanwhile, it consumes very little computational cost. In other words, the proposed scheme is quite suitable for real time multimedia applications.     

A robust scheme for concurrent error diagnosis of MINs

Abstract

Two similar schemes for detecting and correcting errors as well as locating both permanent and temporary faults in multistage interconnection networks for multiprocessor systems are proposed. Depending on the design purpose, two systematic SEC‐DED‐AUED (single error correction‐double error detection‐all unidirectional errors detection) codes are chosen to meet the need of detecting all unidirectional errors which are prevalent in VLSI and to correct all single errors and some multiple errors. The results of encoding and error correcting may be checked by totally self‐checking checkers for Berger code if desired, and thus ensure the robust functioning of the encoder and corrector at the expense of more hardware redundancy. Locating the faulty spots can be done by analyzing the source and destination tags in the corrected packets. The result shows that the two proposed schemes improve the previous schemes at the expense of about 14% and 11% lower information rate for 64‐bit information.     

Robust network coding against path failures

In this study, an approach for robust network coding is introduced for multicast in a directed acyclic network in the presence of network edge failures. The proposed designs aim at combating the resulting path failures, which result in interestingly scalable solutions. A robust network coding scheme (RNC1) is proposed that, devising a rate-path diversity trade-off for the receivers, attains the post-failure capacity of the network with high probability. The scheme is receiver based and can also be applied for correcting random erasures. Next, a rate-guaranteed robust network coding scheme (RNC2) is proposed. The code guarantees the maximum rate for a predetermined number of path failures. The scheme, of course, attains the refined Singleton bound for the edge failure model. A path failure may not necessarily reduce the network capacity, as the remaining intact edges within the network may still facilitate backup paths from the source to the sinks. We introduce RNC3 to employ such backup paths in addition to the original paths and guarantee multicast at a certain rate in the presence of all edge/path failure patterns that do not reduce the capacity below this rate. All the three proposed schemes for multicast are robust to a number of edge failures that may, in general, exceed the refined Singleton bound. Our analyses indicate that the design complexities and the required field sizes grow as a function of the number of network paths, as opposed to the number of network edges because of prior schemes.