Temporal Reference Algorithms versus Spatial Reference Algorithms forSmart Antennas

Abstract

This paper compares algorithms from three different classes of adaptation schemes for smart antennas – the switched beam approach, a Temporal-Reference (TR) technique based on Direct Matrix Inversion or Least Squares adaptation, and a Spatial-Reference (SR) technique with direction finding by Unitary ESPRIT. The simulations are based on a channel model including directions of arrival (DOA) and flat Rayleigh fading. The fading signal is spread out in angle over several degrees dependent on the distance of the mobile from the base station. The results indicate that, in the uplink, TR algorithms and SR algorithms perform equally well, given perfect synchronization and successful user identification (for SR algorithms). TR algorithms are the most robust against close-by interference. For a Uniform Linear Array (ULA) with M=8 elements and an element spacing ofd equal to half a wavelength, they are able to separate two co-channel users that are as close as 5 degrees in angle. For an angular threshold as low as 10° an 8-element ULA is also sufficient to obtain nearly the same BER performance as for a single user. As concerns SR algorithms, we demonstrate their applicability to situations where no discrete DOAs exist, as it is the case in mobile communications. Mutual coupling of individual antenna elements increases the BER by an order of magnitude for the switched beam approach and for SR algorithms, in contrast to TR algorithms, where the influence of mutual coupling on the BER is negligible.