Department Publications

Multiple antenna techniques that allow energy beamforming have been looked upon as a possible candidate for increasing the transfer efficiency between the energy transmitter (ET) and the energy receiver in wireless power transfer. This paper introduces a novel scheme that facilitates energy beamforming by utilizing received signal strength indicator (RSSI) values to estimate the channel. First, in the training stage, the ET will transmit using each beamforming vector in a codebook, which is predefined using a Cramer-Rao lower bound analysis. RSSI value corresponding to each beamforming vector is fed back to the ET, and these values are used to estimate the channel through a maximum likelihood analysis. The results that are obtained are remarkably simple, requires minimal processing, and can be easily implemented. The paper also validates the analytical results numerically, as well as experimentally, and …

A low-complexity 2-D FIR trapezoidal filter is proposed for enhancing broadband plane waves. Motivated by the design technique of 1-D interpolated FIR filters, the proposed filter is realized by cascading a low-complexity spatiallyupsampled 2-D FIR filter having a trapezoidal passband and a low-complexity 2-D FIR masking filter having a parallelogram passband. Experimental results confirm that the proposed filter provides 74% reduction of the computational-complexity compared to conventional 2-D FIR fan and conventional 2-D FIR trapezoidal filters without deteriorating the performance in enhancing 2-D broadband plane waves distorted by strong interference and noise signals.

Multiple antenna techniques, that allow energy beamforming, have been looked upon as a possible candidate for increasing the efficiency of the transfer process between the energy transmitter (ET) and the energy receiver (ER) in wireless energy transfer. This paper introduces a novel scheme that facilitates energy beamforming by utilizing Received Signal Strength Indicator (RSSI) values to estimate the channel. Firstly, in the training stage, the ET will transmit sequentially using each beamforming vector in a codebook, which is pre-defined using a Cramer-Rao lower bound analysis. The RSSI value corresponding to each beamforming vector is fed back to the ET, and these values are used to estimate the channel through a maximum likelihood analysis. The results that are obtained are remarkably simple, requires minimal processing, and can be easily implemented. Also, the results are general and hold for all …

A multibeam filter bank (MBFB) is proposed for recovering the broadband far-field signals received from multiple directions while rejecting interfering signals and noise. The MBFB consists of two sections. The first section employs variable fractional delays and independently steers the directions of the multiple beams. It achieves low complexity by using the Farrow structure. The second section achieves low complexity by maximal decimation methods and by exploiting the spatial symmetry of a 3-D double-frustum-shaped passband. Superior performance and lower complexity compared with previous methods are numerically confirmed for a typical narrow-angle broadband multibeam beamformer of the type that could be used in radio astronomy.

In this thesis, multidimensional signal processing techniques to mitigate disturbances in synthetic aperture systems such as radio telescopes are investigated. Here, two computationally efficient three-dimensional (3D) spatio-temporal (ST) finite impulse response (FIR) cone filter bank structures are proposed. Furthermore, a strategy is proposed to design 3D ST FIR frustum filter banks, having double-frustum-shaped passbands oriented along the temporal axis, derived from appropriate 3D ST FIR cone filter banks. Both types of cone and frustum filter banks are almost alias free and provide near-perfect reconstruction. In the proposed cone and frustum filter banks, both temporal and spatial filtering operations can be carried out at a significantly lower rate compared to previously reported 3D ST FIR cone filter banks implying lower power consumption. Furthermore, the proposed cone and frustum filter banks require a significantly lower computational complexity than previously reported 3D ST FIR cone and frustum filter banks. Importantly, this is achieved without deteriorating the improvement in signal-to-interference-plus-noise ratio. A theoretical analysis of brightness distribution (BD) errors caused by parameter perturbations and mismatches among the transfer functions of receivers employed in synthetic aperture systems is presented. First, the BD errors caused by perturbations in the transfer functions of low noise amplifiers (LNAs) and anti-aliasing filters (AAFs) are considered, and the characteristics of the additive BD error and its effects on synthesized BDs are thoroughly analyzed. Second, the conditions that should be satisfied by the transfer …

It is shown that, by employing 2D FIR spatial filters and under-decimation, the computational time of 3D space-time polyphase cone filter banks may be significantly reduced. The resultant input-output 3D transfer function is almost alias-free and, further it is shown that the proposed cone filters can be used to effectively attenuate such stopband signals as radio frequency interference in radio astronomy applications.

The next generation of radio telescopes requires unprecedented levels of sensitivity, resolution, and field of view (FOV) that cannot be achieved with current radio telescopes. Radio astronomers and scientist are working on the development of next generation telescope designs, such as the square kilometre array (SKA)[1]. Depending on the observations, the signals of interest (SOIs) in the next generation of radio telescopes, such as the SKA, may span at least a decade of temporal frequency and are therefore broadband (BB). Moreover, the requirement of unprecedented levels of sensitivity makes radio frequency interference (RFI) a major problem. In achieving the science specifications, two emerging synthetic aperture applications of dense phased arrays are being considered [2],[3] for the so-called mid-frequency range from about 0.3-2 GHz: they are, rectangular dense aperture arrays (DAAs)(as in Fig. 1 (a)) and/or focal plane arrays (FPAs) in the focal plane of paraboloidal dishes (as in Fig. 1 (b)). Previously reported works on the mitigation of RFIs are based on temporal blanking techniques which are mostly suitable for intermittent RFI [2], on spatial filtering techniques which use subspace-projection methods [3]-[5], on cancellation techniques which use a reference signal approach [6], and on post-correlation cancellation and anti-coincidence techniques [7]. Such methods are mostly being investigated in the context of narrowband applications. However, for next generation synthetic aperture systems, such as the SKA, the SOIs are inherently BB and therefore it is an interesting possibility to consider a suitable BB approach capable for …

Real-time scanned-array direct-form-I hardware implementations of two-dimensional (2D) infinite impulse response (IIR) frequency-planar beam plane-wave (PW) filters have potentially wide applications in the directional enhancement of spatio-temporal broadband PWs based on their directions of arrival (DOAs). The proposed prototypes consist of a microphone sensor array, low-noise-amplifiers (LNAs), multiplexers (MUXs), a programmable gain amplifier (PGA), an analog to digital converter (ADC), a digital to analog converter (DAC), and a field programmable gate array (FPGA) circuit based 2D IIR spatio-temporal beam filter implemented on a single Xilinx Virtex2P xc2vp30-7ff896 FPGA chip. Starting from published 1 st -order designs, novel FPGA architectures for highly-selective 2 nd - and 3 rd -order beam PW filters are proposed, simulated, implemented on FPGA, and verified on-chip.

Beamforming, in brief, is a signal processing technique which has potential applications in the areas such as sonar, ultrasound, seismic, microwave imaging, radio astronomy and communications. In this report we are presenting a prototype that filters audio signals of interest, based on their direction of arrival (DOA). The prototype described in this report consists of both hardware and software. A microphone sensor array, low-noise-amplifiers, multiplexer, adjustable gain controller, FPGA development board and speakers constitute the hardware. FPGA processor is embedded with a 2D IIR beam filter. The hardware take the audio inputs, multiplex them, digitize them and finally fed them in to FPGA processor. The digital filter, filters the asynchronously sampled broadband spatio-temporal plane-wave signals based on DOA and yields a processed signal as the output. Further the report describes the synthesis of 2D IIR …