Reducing the Multiplier-Complexity of Massively Parallel Polyphase 2D IIR Broadband Beam Filters

Abstract

The superior broadband performance of 2D IIR frequency-planar beam filters, relative to conventional 2D FIR true-time-delay beamforming, has recently been reported using computational electromagnetics and real-time emulations on an antenna test range, resulting in significant improvements of bit-error-rates (BERs) in the presence of broadband interference. Further, massively parallel systolic VLSI circuit polyphase architectures have also been reported (Madanayake et al. in Int. J. Circuit Theory Appl. 2010) for the case of the direct-form signal flow graph (SFG) architecture, operating at a maximum throughput of M-(antenna)-frames-per-clock-cycle (MFPCC). The superior broadband performance of 2D IIR frequency-planar beam filters is extended here from the direct-form signal flow graph (SFG) architecture (Madanayake et al. in Int. J. Circuit Theory Appl. 2010) to the novel differential-form SFG architecture in order to reduce overall complexity. The proposed method employs a differential-form polyphase 2D IIR frequency-planar beam SFG, and a corresponding circuit architecture, to implement the required input-output 2D space-time difference equation. The resultant digital hardware has the significant advantage of much-reduced multiplier complexity, relative to the direct-form structure. For example, when look-ahead pipelining is not employed and for polyphase architectures having two, three, and four phases, the corresponding reductions in multiplier complexity are 20%, 28.6% and 33.3%, respectively. A proof-of-concept prototype circuit is designed and implemented on a Xilinx Sx35 FPGA device for the two-phase case, operating at a frame-rate of 132 million linear frames per second on the uniform linear array (ULA), corresponding to 2-frames-per-clock-cycle at a circuit clock frequency of 66 MHz. The circuit is optimized for low critical path delays (CPDs) using look-ahead pipelining of order three. For ultra-wideband (UWB) radio-frequency (RF) implementations, in such fields as radio astronomy, radar and wireless communications, custom VLSI versions of the proposed circuits are required.