The growth in wireless communications necessitates more efficient utilization of spectrum. The increased sharing of spectrum translates into a higher likelihood of users interfering with one another. Interference rejection techniques allow a high capacity of users within the available spectrum. This overview comprises a literature review of published papers pertaining to single-channel adaptive interference rejection in digital wireless dating primarily from 1980 to the present. Though previous overviews are referenced and summarized, the focus is on advances not covered by previous overviews (consequently, some papers are included that predate 1980 because they are not covered in previous overviews). An organizational chart (divided into spread spectrum and nonspread spectrum techniques) is shown which outlines the types of techniques covered. Interference rejection is important for several reasons. Cellular capacity is inherently interference limited, particularly by co-channel interference (CCI) and adjacent-channel interference (ACI). One solution to combat CCI and ACI is to split cells and decrease the power, but cell-splitting is expensive. Interference-rejection techniques often represent a less expensive alternative to cell-splitting. In addition, as newer communication technologies supersede older technologies, interference-rejection techniques are important in helping to facilitate compatibility during transitions between the old and new technologies.

Interference rejection in digital wireless communications

Adaptive Wireless Transceivers provides the reader with a broad overview of near-instantaneously adaptive transceivers in the context of TDMA, CDMA and OFDM systems The adaptive transceivers examined employ powerful turbo codecs, turbo equalisers and space-time codecs, equipping the reader with a future-proof technological road map It demonstrates that adaptive transceivers are capable of mitigating the channel quality fluctuations of the wireless channel as a lower-complexity alternative to space-time coding By contrast, if the higher complexity of multiple transmitters and multiple receiver-assisted systems is deemed acceptable, the advantages of adaptability erode • Provides an in-depth introduction to channel equalisers and Kalman filtering and discusses the associated complexity versus performance trade-offs • Introduces wideband near-instantaneously adaptive transceivers and studies their performance both with and without turbo channel coding • Describes how to optimise adaptive modulation mode switching and highlights a range of practical considerations • Introduces neural network based channel equalisers and discusses Radial Basis Function (RBF) assisted equalisers embedded into adaptive modems supported by turbo channel coding and turbo channel equalisation • Employs the above adaptive principles also in the context of CDMA and OFDM transceivers and discusses the pros and cons of space-time coding versus adaptive modulation Researchers, advanced students and practising development engineers working in wireless communications will all find this valuable text an informative read

Adaptive Wireless Transceivers: Turbo-Coded, Turbo-Equalized and Space-Time Coded TDMA, CDMA and OFDM Systems

Application of artificial neural networks (ANN's) to adaptive channel equalization in a digital communication system with 4-QAM signal constellation is reported in this paper. A novel computationally efficient single layer functional link ANN (FLANN) is proposed for this purpose. This network has a simple structure in which the nonlinearity is introduced by functional expansion of the input pattern by trigonometric polynomials. Because of input pattern enhancement, the FLANN is capable of forming arbitrarily nonlinear decision boundaries and can perform complex pattern classification tasks. Considering channel equalization as a nonlinear classification problem, the FLANN has been utilized for nonlinear channel equalization. The performance of the FLANN is compared with two other ANN structures [a multilayer perceptron (MLP) and a polynomial perceptron network (PPN)] along with a conventional linear LMS-based equalizer for different linear and nonlinear channel models. The effect of eigenvalue ratio (EVR) of input correlation matrix on the equalizer performance has been studied. The comparison of computational complexity involved for the three ANN structures is also provided.

Nonlinear channel equalization for QAM signal constellation using artificial neural networks

In the case of three-dimensional (3-D) scattering, which is appropriate to the calculation of signal statistics for personal communications, it is shown that the basic Doppler spectrum of the received signal is uniform over the full range of Doppler frequencies centered on the carrier. The corresponding temporal and spatial autocorrelations are, therefore, sine functions.

3-D mobile radio channel statistics

This paper presents a method for overcoming time-varying co-channel interference (CCI) using type-2 fuzzy adaptive filters (FAF). The type-2 FAF is realized using an unnormalized type-2 Takagi-Sugeno-Kang fuzzy logic system. A clustering method is used to adaptively design the parameters of the FAF. We use transversal equalizer and decision feedback equalizer structures to eliminate the CCI. Simulation results show that the equalizers based on type-2 FAFs perform better than the nearest neighbor classifiers or the equalizers based on type-1 FAFs when the number of co-channels is much large than 1.

http://sipi.usc.edu/~mendel/publications/Liang%26Mendel%20C%26S%2012-00.pdf

Overcoming time-varying co-channel interference using type-2 fuzzy adaptive filters

This paper investigates the behaviors of polynomial perceptrons and introduces a fractionally spaced recursive polynomial perceptron with low complexity and fast convergence rate. The nonlinear mapping ability of the polynomial perceptron is analyzed. It is shown that a polynomial perceptron with degree L(/spl ges/4) satisfies the Stone-Weierstrass theorem and can approximate any continuous function to within a specified accuracy. Moreover, the nonlinear mapping ability of a polynomial perceptron with degree L is similar to that of the three-layer perceptron with one hidden layer for time same number of neurons in the input layer. The nonlinear mapping ability of the fractionally spaced recursive polynomial perceptron is also presented. Applications of polynomial perceptrons for fading channel equalization and co-channel interference suppression in a 16-level quadrature amplitude modulation receiver system are considered. Computer simulations are used to evaluate and compare the performance of polynomial perceptron (PP) and fractionally spaced bilinear perceptron (FSBLP) with that of the synchronous decision feedback multilayer perceptron (SDFMLP), fractionally spaced decision feedback multilayer perceptron (FSDFMLP), and the conventional decision feedback equalizer (DFE). The results show that the performance of the fractionally spaced bilinear perceptron is clearly superior to that of the other structures. >

Polynomial perceptrons and their applications to fading channel equalization and co-channel interference suppression

The paper investigates the behaviours of polynomial perceptrons (PP) introduces a fractionally spaced recursive polynomial perceptron (FSRPP) with low complexity and fast convergence rate. The nonlinear mapping abilities of PP and FSRPP are analyzed. Applications of PP for fading channel equalization and co-channel interference (CCI) suppression in a 16-level quadrature amplitude modulation receiver system are considered. Computer simulations are used to evaluate and compare the performance of PP and fractionally spaced bilinear perceptron (FSBLP) with that of the synchronous decision feedback multilayer perceptron (SDFMLP), fractionally spaced decision feedback multilayer perceptron (FSDFMLP), and the conventional decision feedback equalizer (DFE). The results show that the performance of FSBLP is clearly superior to that of the other structures.

Zeng-Jun Xiang

Papers

Polynomial perceptrons and their applications to fading channel equalization and co-channel interference suppression

Polynomial perceptrons and their applications to fading channel equalization and co-channel interference suppression