Abe A. Akhiyat

Phase Error Evaluation in a Two-Path Receiver Front-End With On-Site Coding

Recently, we proposed a code-modulated multipath receiver front-end to reduce the number of analog-to-digital converters (ADCs) behind antenna elements and realize significant area, cost, and power reduction. More specifically, code division multiplexing was implemented at the analog front-end for path combining into a single ADC. At the digital baseband, the reverse process was applied to recover signals pertaining to each path. Such front-ends are suitable for spatial diversity and multiplexing and for beamforming. For the latter, it is important to accurately predict the angle of arrival. That is, it is important to faithfully recover the phase difference between adjacent signal paths at the digital baseband. In this paper, the impact of on-site coding on phase error is examined for a two-path receiver using orthogonal Walsh-Hadamard codes of length 8. Simulations show that the relative phase difference, Δφ, between signal paths can be faithfully recovered at the digital baseband. Hardware implementation of a two-path receiver with on-site coding was realized and three different phase measurements were conducted, namely, Δφ = 27°, 40°, and 45°. These measurements confirmed that upon signal and code synchronization, the phases were faithfully recovered with minimal degradation.

Code Optimization for a Code-Modulated RF Front End

Recently, a novel class of on-site coding receivers was proposed. The architecture is suitable for digital beamforming in addition to offering multiple-input multiple-output capabilities. Essential to its realization is a code division multiplexing technique aggregating multiple signal paths at the analog front end into a single analog-to-digital converter. As a result, a significant hardware reduction and a higher power efficiency are achieved when compared with the conventional digital beamforming techniques. In this paper, we examine the systems performance with different types of spreading codes, both orthogonal and nonorthogonal, namely Walsh-Hadamard and Gold codes. Bit error rate calculations show that Walsh-Hadamard codes outperform Gold codes in achieving higher dynamic range with less signal-to-noise ratio degradation, assuming a perfectly synchronous system.

Low cost, power efficient, on-site coding receiver (OSCR) for ultra-wideband digital beamforming

We propose an experimental validation of a novel hardware-reduced digital beamformer. The novelty of this receiver is a coding technique so that a single analog-to-digital converter serves all antenna array elements. We present a two-channel component implementation (with COTS components) of this receiver using Walsh-Hadamard codes of length 8. The main purpose of this implementation is to establish a proof of concept and show that we can recover the input signal and beam direction. Measurements results show signal recovery with minimal SNR degradation.

Simultaneous transmit and receive system architecture with four stages of cancellation

Simultaneous transmit and receive systems (STAR) are proposed to double the spectral efficiency and enhance spectrum utilization in the traditional microwave band. A major problem is high power self-interference (SI) due to the proximity of the transmit and receive antennas. In this paper, we propose to significantly improve system-level performance using a novel high isolation RF front-end based on collocated Tx/Rx antenna pair(s). Among our improvements, we propose a novel architecture for a STAR system incorporating four stages of self-interference cancellation across the propagation, analog, and digital domains. We aim to attain at least 120dB of total SI cancellation over a >100MHz bandwidth.

Dual-band validation of on-site coding receiver using ultra-wideband antenna array at C, X and Ku-bands

Ultra-wideband (UWB) transceivers with digital beamforming are essential for realizing cognitive and software defined radios. Concurrently, advances in digital technology and signal processing have drastically reduced digital beamforming complexity. For example, a new on-site coding receiver (OSCR) architecture was proposed to significantly reduce hardware requirement for digital beamforming using code division multiplexing (CDM). As a result, a single analog-to-digital converter (ADC) can be used for a group of antenna elements. Initial design and verification of the OSCR was done at L-band. But its functionality can be extended at higher frequency, including C, X and Ku-bands. In this paper, we present a 4-channel high frequency dual-band OSCR implementation and validation. Specifically, measurements are performed in the anechoic chamber using an UWB array operating at 4-18 GHz, to estimate the phase of incoming signals and for direction finding. It is verified that on-site coding has minimal or no phase error and degradation in signal-to-noise ratio (SNR).

Experimental Validation of On-Site Coding Digital Beamformer With Ultra-Wideband Antenna Arrays

Digital beamformers combined with ultra-wideband (UWB) antennas are essential for realizing cognitive and software defined radios. Concurrently, advances in digital technology and signal processing have drastically reduced digital beamforming complexity. Recently, a novel on-site coding receiver (OSCR) architecture was proposed to significantly reduce hardware requirement for digital beamforming. Using OSCR, the signal from each antenna element is encoded, then several of these signals are grouped and digitized using a single analog-to-digital converter. Doing so, hardware requirements are drastically reduced. At the digital back-end, field programmable gate arrays are used to decorrelate and recover the signals associated with each array element for beamforming. In this paper, we demonstrate the effectiveness of the OSCR concept by building and testing a multichannel receiver using commercial-off-the-shelf components. Various test bench measurements are performed in an anechoic chamber using an UWB antenna array operating from 200 MHz–2.5 GHz, and data were collected at multiple frequencies. Results show an accurate estimate of the angle of arrival for incidence angles of

Passive, on chip and in situ detection of neuropotentials

\theta _{s} = 0^{\circ }

Phase characterization of a 2-path on-site coding digital beamformer

, 15°, 30°, and 45° away from broadside. It is verified that on-site coding has minimal or no degradation in signal-to-noise ratio.

Phase characterization of an 8-channel on-site coding receiver for digital beamforming

A fully-passive, on chip wireless system is proposed for in situ detection of neuropotentials. The system aims to replace conventional wired brain-sensing technologies, thus enhancing patient mobility and preserving safety. It consists of an implanted neurosensor that comprises an implanted antenna and mixer, and an exterior RF interrogator. Link budget issues are discussed, highlighting the challenges of detecting human brain neuropotentials as small as 10s of μVpp.

Angle of arrival estimation across a 10∶1 bandwidth architecture using on-site coding receiver

Recently, a novel receiver architecture with on-site coding was proposed to reduce the number of analog-to-digital converters behind antenna array elements. To realize digital beamforming using this receiver, it is important to faithfully recover the phase difference between adjacent signal paths at the digital baseband. In this paper, the impact of on-site coding on the phase error is examined for a 2-path receiver. Simulations showed that the relative phase difference between signal paths can be recovered at the digital baseband and that any phase error is due to the channel noise.