Investigation of Adaptive Beamforming Algorithm for Smart Antenna system to Improve the Effect of Angle Separation

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Addis Ababa University


As the growing demand for wireless communications is constantly increasing, the need for better coverage, improved capacity, and higher transmission quality rises. Thus, a more efficient use of the radio spectrum is required. A smart antenna system is capable of efficiently utilizing the radio spectrum and is a promise for an effective solution to the present wireless system problems. Smart antennas combine the antenna array with signal processing to optimize automatically the beam pattern in response to the received signal. Beam forming is the method used to create the radiation pattern of the antenna arrays by adding constructively the phase of the signals in the direction of desired targets and Nulling the pattern of undesired targets. One of the central motivations for this work comes from the observed performance degradation due to angle separation between the desired and interferer signals. This is one of the challenges that face workers in the smart antenna system. In fact, the main objective of this work is to study and recommend Antenna parameters and adaptive algorithm which can reduce the effect of angle separation. In addition effect of angle separation on the Bore sight and Nulling, comparison of Adaptive Beamfoming algorithms: LMS, SMI and RLS based on angle difference presented herein. Furthermore, the paper presents array parameters and algorithms to combat the effects of angle separation on the overall system. Adaptive Beamforming algorithms such as: LMS, DMI and RLS are studied based on angle separation for different combination of array parameters. All the three algorithms performance degrades when the separation becomes narrow. Increasing number of array and spacing between array elements alleviate these problems but it increase computational complexity and introduce grating lobes. Among these algorithms LMS algorithm has low computational complexity and less grating lobes, so LMS algorithm which works based on angle separation is an excellent solution to this performance degradation.



Angle Separation, Adaptive Beamforming