A Scalable Architecture for Distributed Receive Beamforming: Analysis and Experimental Demonstration

Abstract

We propose, analyze and demonstrate an architecture for scalable cooperative reception. In a cluster of N + 1 receive nodes, one node is designated as the final receiver, and the N other nodes act as amplify-and-forward relays which adapt their phases such that the relayed signals add up constructively at the designated receiver. This yields received SNR scaling linearly with N , while avoiding the linear increase in overhead incurred by a direct approach in which received signals are separately quantized and transmitted for centralized processing. By transforming the task of long-distance distributed receive beamforming into one of local distributed transmit beamforming, we can leverage a scalable one-bit feedback algorithm for phase synchronization. We show that time division between the long-distance and local links eliminates the need for explicit frequency synchronization. We provide an analytical framework, whose results closely match Monte Carlo simulations, to evaluate the impact of phase noise due to relaying delay on the performance of the one-bit feedback algorithm. Experimental results from our prototype implementation on software-defined radios demonstrate the expected gains in received signal strength despite significant oscillator drift, and are consistent with results from our analytical framework. Index Termsdistributed MIMO, beamforming, cooperative reception, synchronization F. Quitin is with the School of Electrical and Electronic Engineering, Nanyang Technological University (NTU), Singapore (fquitin@ntu.edu.sg). A.T. Irish and U. Madhow are with the

Software Defined Radio Implementation of Carrier and Timing Synchronization for Distributed Arrays

“…These results are comparable to performance that can be obtained using a GPSDO as was mentioned in Section 6, without the added cost of the GPSDO module or the limitations of GPS signals. By using an EKF over a periodic preamble, we get higher accuracy than what is achievable without the EKF as calculated from the CRLB (14). The achievable accuracy in frequency adapted to retain robustness and ahieve the requirements of a specific waveform in a multipath environment.…”

“…From the Cramér-Rao lower bound perspective, the variance of CFO estimation and STO estimation are var(∆f ) ≥ CRLB(∆f ) = 3 2π 2 T 2 est SNR sync (14) var(∆τ ) ≥ CRLB(∆τ ) = 12πT s 3 T est SNR sync (15) where T est = M N zc T s is the observation duration [25], [26]. Consider a setting with T s = 1 µs and M = 10 repetitions of ZC sequence, i.e., T est = 0.63 ms, and 20 dB SNR.…”

“…Recently, a number of softwaredefined-radio (SDR) proof-of-concept implementations have been reported. Works [13,14] present a novel system for transmitter or receiver beamforming where slave radios estimate a continuous wave (CW) signal from the master node and use this to estimate the carrier frequency offset and adjust the phases of baseband samples to reach synchronization. In [15,16] an SDR implementation of sample timing is developed while using perfectly synchronized carriers with 10 MHz references.…”

A Distributed Relay Beamforming-Enhanced TDMA System

“…In [4], [5], authors design a system where an AF relay cluster (consisting of N single-antenna nodes) receives data from a distant node and forwards it via distributed transmit beamforming to a processing center in order to achieve over-the-air distributed receive beamforming at the processing center. [6] considers opportunistic collaborative beamforming where a designated receiver node sends a single bit of feedback to each relay in order to dictate whether or not it should participate in beamforming process.…”

Effects of differential oscillator phase noise in precoding performance

“…A considerable amount of literature introducing new synchronization methods has been published [6]. Besides, other works have analyzed the effects of phase errors on signal coherence [7], [8]. Specifically, authors in [8] consider errors resulting from imperfect clock alignment and platform spatial measurements in an open-loop system.…”