Adaptive Complex-Coefficient 2D FIR Trapezoidal Filters for Broadband Beamforming in Cognitive Radio Systems

Abstract

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.

Wide‐band aperture array using a four‐channel manifold‐type planar multiplexer and digital 2‐D IIR filterbank

“…Such 2-D FIR filters achieve highly directional selective improvement of bandlimited spatio-temporal planar waves but are of elevated order [60], therefore leading to relatively high-circuit complexity when compared with SBP 2-D IIR filters. The 2-D IIR digital beam filters encompass desired trapezoidal passbands of the plane waves, which are centered on ω x = ± ω Δ as illustrated in Figure 3 …”

Synthesis and Array Processor Realization of a 2-D IIR Beam Filter for Wireless Applications

“…We show that the proposed filters have lower computational complexity compared to the conventional delay-and-sum beamformers (approximately 70% less number of multipliers for similar performance [30], [31]) and are also of lower circuit complexity compared to 2-D FIR beamformers such as fan and trapezoidal filters [29], [32]- [34]. The lower computational complexity, closed-form design approach, broadband performance, electronic steerability, and availability of rapidly reconfigurable programming logic realizations make these emerging 2-D ST digital filters attractive and promising for cognitive radio applications [5]- [8].…”

“…We propose a second-order 2-D IIR digital filter for the directional enhancement of temporally-broadband bandpass ST PWs [5], [29] (see Fig. 1).…”

“…U LTRA-WIDEBAND (UWB) wireless communications [1]- [4], cognitive radio [5]- [8], cooperative wireless sensor networks [9], [10] require highly directional and electronically steerable smart antenna arrays capable of broadband plane-wave (PW) filtering at RFs to improve the bit-error rate (BER) caused due to interference from multiple users and multipath fading. These antenna arrays typically employ beamforming using analog delay-and-sum networks, fractional delay based delay-and-sum digital networks [1], digital phased array feeds (PAFs) [11]- [13] and multi-dimensional finite-impule response/infinte impulse response (FIR/IIR) digital filters [5], [14].…”

“…These antenna arrays typically employ beamforming using analog delay-and-sum networks, fractional delay based delay-and-sum digital networks [1], digital phased array feeds (PAFs) [11]- [13] and multi-dimensional finite-impule response/infinte impulse response (FIR/IIR) digital filters [5], [14]. Digital signal processing (DSP)-based broadband smart antenna arrays have potential applications in UWB wireless communications [1], [2], [15], cognitive radio [5]- [8], software-defined radio [16], microwave imaging [17], space science and radio astronomy [18]- [21], remote-sensing and navigation [22], [23].…”