Satheesh Bojja Venkatakrishnan

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.

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

Multi-band multi-beam performance evaluation of on-site coding digital beamformer using ultra-wideband antenna array

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

Challenges in Clock Synchronization for 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

Cognitive and software defined radios require ultrawideband (UWB) antennas with digital beamforming. Recently, a novel on-site coding receiver (OSCR) architecture was proposed to significantly reduce hardware requirement for digital beamforming. At the receiver side, we propose to code several antenna outputs in the analog domain prior to digitizing them using a single analog-to-digital converter (ADC). Decoding will be done using field programmable gate arrays (FPGA) in the digital domain to perform beamforming. Doing so, hardware requirements are drastically reduced. In this paper, we demonstrate the validation of the OSCR concept by building and testing a multi-band multi-beam receiver. Measurements are performed in an anechoic chamber using an UWB antenna array operating from 200MHz–2.5 GHz, for two transmit signals modulated at f1 and f2, and incident on the receiver from various angles. Results show an accurate estimate of the angle of arrival, proving that on-site coding can perform with minimal or no degradation in signal-to-noise ratio (SNR) in a multi-beam and multi-band environment.

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

Typical radio frequency (RF) digital beamformers can be highly complex. In addition to a suitable antenna array, they require numerous receiver chains, demodulators, data converter arrays, and digital signal processors. To recover and reconstruct the received signal, synchronization is required since the analog-to-digital converters (ADCs), digital-to-analog converters (DACs), field programmable gate arrays (FPGAs), and local oscillators are all clocked at different frequencies. In this article, we present a clock synchronization topology for a multichannel on-site coding receiver (OSCR) using the FPGA as a master clock to drive all RF blocks. This approach reduces synchronization errors by a factor of 8, when compared to conventional digital beamformer.

Realization of a novel on-site coding digital beamformer using FPGAs

Ultra-wideband (UWB) systems combined with the advances in digital signal processing and data handling have drastically reduced the complexity of cognitive and software defined radios. Therefore, techniques such as monopulsing, multiple beams, among others, can be implemented for phased arrays and Multiple Input Multiple Output (MIMO) systems. A major drawback in MIMO systems is hardware redundancy after each antenna element. This implies challenges in high power, cost, and area requirements. To this end, a number of hardware reduction techniques at handling the RF front-end have been proposed. They include spatial multiplexing (SM), time-division multiplexing (TDM), and frequency division multiplexing (FDM). But these techniques are based on time slots or bandwidth sharing making them inadequate in terms of resource utilization.

Multiband and Multibeam Direction of Arrival Estimation Using On-Site Coding Digital Beamformer

Ultra-Wideband (UWB) systems are essential to realizing software defined and cognitive radios. Concurrently advancements in digital hardware and signal processing technologies have drastically reduced the realization complexity for such systems. Recently, a novel on-site coding receiver (OSCR) architecture was proposed to significantly reduce the intense hardware requirement for digital beamforming. Specifically, code division multiplexing (CDM) was implemented at the analog front-end implying a single analog to digital converter (ADC) for a group of elements. In this paper, we present a 2-channel OSCR implementation. Specifically, four measurements were performed in the anechoic chamber using UWB arrays to estimate direction of arrival (namely, θS = 0°, 15°, 30° and 45°) of incoming signals and perform beamforming. The estimated angle of arrival measurements provided verification of the new OSCR system.