Beamforming of Ultra wideband signals in an IEEE 802.15.3a channel environment

Abstract

This paper explains a methodology for beamforming of an ultrawideband signal (UWB). Tapped delay line (TDL) has been chosen as the beamformer structure and the channel environment considered is multipath and non line of sight in nature, compliant to IEEE 802.15.3a standards. The entire procedure for beamforming was done in the frequency domain owing to the nanosecond duration of ultrawideband pulses, which makes analysis in the time domain tedious. The direction of arrival (DOA) of the signal is known apriori. Least squares minimization approach has been adopted to calculate the weights needed for the tapped delay line structure. While calculating the weights, the cost function to be minimized has been subjected to several constraints like multipath and desired direction of focus. This beamforming technique mainly aims at achieving weight coefficients that are invariant to the range of wideband frequencies and immune to the multipath versions of the desired signal. The weight coefficients adapt themselves as per the varying nature of the channel and interference. This constrained least squares minimization method proves to be robust and at the same time less complex, thereby making it the perfect choice for real time positioning applications that use ultra wideband signals.