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A new discrete-domain method is proposed for the beamforming of temporally broad-band bandpass plane waves (PWs) using a real-coefficient 2-D spatio-temporal (ST) finite-impulse response (FIR) filter having a novel rectangularly symmetric double-trapezoidal-shaped passband. The arriving temporally broad-band-bandpass ST PWs are received by a 1-D uniformly distributed sensor array. The sensor signals are pre-filtered, down-shifted to the intermediate frequency (IF) band, low-pass filtered and synchronously sampled by the real IF tri-stage temporal sampler array, resulting in a real-valued 2-D sampled sequence. The beamforming operation is then carried out on this 2-D sampled sequence using the real-coefficient 2-D FIR double-trapezoidal filter. Arithmetic complexity in the hardware implementation of the 2-D FIR double-trapezoidal filter is significantly reduced by using an array of real-coefficient polyphase 1-D FIR filters. Experimental results have confirmed that this method is capable of enhancing the desired temporally broad-band-bandpass ST PWs according to their directions of arrival under severe co-channel interference.Index Terms-2-D filter, beamforming, broad-band bandpass signals, double-trapezoidal-shaped passband, finite-impulse response (FIR), polyphase, spatio-temporal (ST) plane waves (PWs).

A novel design method is proposed for an adaptive discrete-domain beamformer for the beamforming of temporally broadband-bandpass signals in cognitive radio (CR) systems. The method is based on a complex-coefficient 2D finite impulse response (FIR) filter having a trapezoidal-shaped passband. The temporally broadband-bandpass signals are received by a 1D uniformly distributed antenna array (1D UDAA), where the outputs of the antennas are complex-quadrature sampled by the front end of the CR system. This CR system is based on a software defined radio (SDR) architecture and can be instantly reconfigured by the control system to select the appropriate frequency band and the required sampling rate. The subsequent beamforming enhances the spectral components of the desired temporally broadbandbandpass signals by arranging for the asymmetric trapezoidal-shaped passband of the 2D filter transfer function to closely enclose the region of support (ROS) of the spectrum of the desired signal, whereas the ROSs of the spectral components of the interfering signals are enclosed by the stopband. The proposed novel closed-form design method facilitates instant adaptation of the shape and orientation of the passband of the beamforming 2D FIR trapezoidal filter in order to match the time-varying frequency band and the time-varying bandwidth of the signal, as well as to track and enhance received signals with time-varying directions of arrival (DOAs). Simulated results confirm that, compared with previously reported methods, the proposed method achieves the best overall tradeoff with respect to the instantaneous adaptations of the operating frequency band, the bandwidth, and the time-varying DOAs, the distortion of the desired passband signal, and the stopband attenuation of interfering signals.

SUMMARYA systolic architecture has recently been proposed for implementing two-dimensional infinite impulse response (IIR) space-time beam plane-wave filters at a throughput of one-frame-per-clock-cycle for such applications as real-time broadband smart antennas. A novel polyphase systolic architecture is proposed here that further increases the throughput of these IIR beam filters, by a factor of M, to M-frames-per-clockcycle, where M is the number of polyphases. The proposed method combines the polyphase approach, along with pipelining and look-ahead optimization methods, to achieve frame sample frequencies that are several times higher than the clock-cycle limit of the very large-scale integration (VLSI) technology, thereby potentially allowing multi-GHz frame sample frequencies using current custom VLSI circuits. The implementation of a field programmable gate array-based real-time prototype is described, tested and verified for the two-phase case (M = 2) at a technology-limited clock frequency of 50 MHz which corresponds to a throughput of 100 million-frames-per-clock-cycle.

A new method is proposed for broadband beamforming of two-dimensional (2D) spatio-temporal (ST) bandpass plane waves (PWs) using a complex 2D FIR filter structure having a trapezoidal-shaped passband at baseband and achieves the minimum possible temporal sampling rate for a given bandwidth. Experimental results show that this method is capable of enhancing 2D broadband bandpass ST PWs according to their directions of arrival (DOAs) in the presence of severe cochannel interference.