Many signal processing applications pose optimization problems with multimodal and nonsmooth cost functions. Gradient methods are ineffective in these situations. The adaptive simulated annealing (ASA) offers a viable optimization tool for tackling these difficult nonlinear optimization problems. Three applications, maximum likelihood (ML) joint channel and data estimation, infinite-impulse-response (IIR) filter design and evaluation of minimum symbol-error-rate (MSER) decision feedback equalizer (DFE), are used to demonstrate the effectiveness of the ASA. Keywords. Simulated annealing, global optimization, blind equalization, IIR filter, decision feedback equalizer. 1 Introduction Optimization problems with multimodal and/or nonsmooth cost functions are commonly encountered in signal processing applications. Conventional gradient-based algorithms are ineffective in these applications due to the problem of local minima or the difficulty in calculating gradients. Optimization method...

Recently, code division multiple access (CDMA) has found wide-spread applications in various applications such as advanced wireless technologies and digital cellular communications. In this paper, we consider the error rate performance of asynchronous direct-sequence CDMA in a wireless radio communications environment that is characterized by Rayleigh multipath fading channels. Because of the system complexity, the performance of CDMA systems in such an environment is difficult to assess analytically without making restrictive assumptions. Monte Carlo simulations can offer an alternative performance evaluation tool. Unfortunately, in practice such an alternative is often limited by an excessive computational burden. Importance sampling is a variance reduction technique which can significantly reduce the computational cost required by Monte Carlo simulations. This paper will describe the basic principles behind this powerful technique. In particular, it will illustrate its use as a comp...

: Estimating the bit error rate (BER) of complex digital communication systems has often been realised by using the Monte Carlo method. For very low BER, this method requires a high computational effort. Therefore, a lot of developments in theory and application of importance sampling (IS) techniques have been done especially for AWGN channels (additive white gaussian noise) or time-varying uniformly distributed channels. In this paper we discuss the applicability of several IS techniques for the simulation of Rayleigh fading mobile radio channels. By using the system threshold characteristic (STC) we first make an analytical statement of the IS efficiency for an AWGN and a frequency-nonselective Rayleigh fading channel. It is shown that due to the Rayleigh distribution the efficiency is reduced. Furthermore, the so called overbiasing effect is graphically explained and simulation results illustrate that the theoretically possible efficiencies cannot be reached in practice because of t...

An importance sampling simulation technique is used to estimate the bit-error rate (BER) of a symbol-by-symbol trelliscoded modulation (TCM) decoder/equalizer proposed for digital microwave radio applications. To evaluate the performance at a BER smaller than 10 6 , we investigate a randomized bias technique previously developed by the authors. To properly select the bias vectors, the asymptotic (infinite signal-to-noise ratio) decision boundary is first determined. The simulation technique is then extended to the one-shot symbol-by-symbol TCM decoding/equalization algorithm which is equivalent to the recursive symbol-bysymbol detection algorithm of Abend and Fritchman. By using this novel importance sampling technique, we can speed up the simulation and efficiently evaluate the BER performance of the TCM decoder/equalizer.

Abstract—This paper describes the MATLAB simulation of multiuser detection in code division multiple access (CDMA). To reach low bit error rate (BER) levels within reasonable computation times, the method of importance sampling is utilized. Our design is based on the step by step practical implementation of matched filter (MF) detection, has therefore the flexibility of variations in all parameters of interest which are otherwise difficult to accommodate in a theoretical model. Our initial findings are compared and verified against theoretical predictions and against those available in the literature. Keywords—MATLAB simulation, CDMA, multiuser detection I.