Performance Of Adaptive Antenna Arrays Research Articles

Effect of polarized signals on the performance of adaptive antenna arrays

Effect of polarized signals on the performance of adaptive antenna arrays

The effects of mutual coupling and polarization on the performance of steered-beam adaptive arrays

The polarization of the electromagnetic waves impinging on adaptive antenna arrays has a significant impact on their performance. The effects of desired and undesired polarized signals and mutual coupling on the performance of adaptive antenna arrays with an electronically steerable beam are studied based on the ratio of the output signal to the interference plus noise. The performance of adaptive antenna arrays composed of single- versus cross-dipole antenna elements is studied to illustrate the effect of signal polarization. The experimental and simulation results show that, for randomly polarized signals, adaptive antenna arrays using cross-dipole elements provide better performance compared with those using single dipoles. However, if the desired signal polarization is well known, single-dipole antenna arrays offer better performance.

Signal processing by adaptive antenna arrays

This article outlines the basic theory of adaptive antenna arrays. The basic elements of an adaptive antenna array such as a diagramforming device and an adaptive processor are presented. The task of the adaptive processor is to control the diagram forming device, which provides the required processing of the input observation based on the available a priori information on the signal-interference environment. When such information is insufficient, the adaptive processor must have the ability to automatically adjust to the receiving conditions. In other words, the adaptive processor must implement some adaptation algorithm based on the initial data bank and the signal processing efficiency criterion. To quantitatively evaluate the performance of adaptive antenna arrays when receiving a useful signal, one of the ways of quality indicator has been considered: the RMS value of the deviation of the useful signal from the reference.

Effect of Polarization on the Performance of Adaptive Antenna Arrays

The polarized electromagnetic waves impinging on adaptive antenna arrays have significant impact on their performance. In this paper we investigate the effect of polarized desired and undesired signals on the performance of electronically steered beam adaptive antenna arrays in terms of their output SINR’s (Signal to Interference plus Noise Ratios). To achieve this goal, we compare the performances of adaptive antenna arrays composed of single dipole antenna elements with those composed of cross-dipole antenna elements to illustrate the effect of polarized signals on their performance. Based on the experimental and simulation results, it will be shown that the adaptive antenna arrays using cross-dipole antennas provide better performance compared to those using single-dipoles, in presence of randomly polarized signals. However, if the desired signal polarization is well known, single-dipole antenna arrays exhibit better performance.

Using adaptive arrays for collision resolution in Slotted ALOHA packet radio systems

This paper discusses a general framework for evaluating the throughput performance of adaptive antenna arrays when the Slotted ALOHA protocol is employed as the random access mechanism for wireless packet transmission. A novel blind adaptive algorithm is presented and its performance is assessed by comparison with the minimum mean squared error (MMSE). Two propagation scenarios are considered: line of sight and Rayleigh fading. The results are obtained through a mix of analysis and simulation and it is shown that the proposed algorithm allows the antenna array to attain a high fraction of the optimal MMSE gains without resorting to training sequences.

SMI adaptive antenna arrays for weak interfering signals

The performance of adaptive antenna arrays in the presence of weak interfering signals (below thermal noise) is studied. It is shown that conventional adaptive antenna arrays sample matrix inversion (SMI) algorithm is used are unable to suppress such interfering signals. To overcome this problem, the SMI algorithm is modified. In the modified algorithm, the covariance matrix is redefined such that the effect of thermal noise on the weights of adaptive arrays is reduced. Thus, the weights are dictated by relatively weak signals. It is shown that the modified algorithm provides the desired interference protection.

Adaptive antenna arrays for weak interfering signals

The performance of adaptive antenna arrays in the presence of weak interfering signals (below noise level) is studied. It is shown that conventional adaptive arrays are unable to suppress such interfering signals. To overcome this problem, the feedback loops controlling the array weights are modified. In the modified feedback loops, the noise level in the feedback loops is reduced by reducing the correlation between the noise components of the two inputs to the loop correlator. Two techniques to decorrelate these noise components are discussed. It is shown that adaptive arrays with the modified feedback loops provide the desired interference suppression. An expression is given for the amount of noise decorrelation required to achieve a specified interference suppression.