Fully wireless implementation of distributed beamforming on a software-defined radio platform

Abstract

We describe the key ideas behind our implementation of distributed beamforming on a GNU-radio based softwaredefined radio platform. Distributed beamforming is a cooperative transmission scheme whereby a number of nodes in a wireless network organize themselves into a virtual antenna array and focus their transmission in the direction of the intended receiver, potentially achieving orders of magnitude improvements in energy efficiency. This technique has been extensively studied over the past decade and its practical feasibility has been demonstrated in multiple experimental prototypes. Our contributions in the work reported in this paper are three-fold: (a) the first ever all-wireless implementation of distributed beamforming without any secondary wired channels for clock distribution or channel feedback, (b) a novel digital baseband approach to synchronization of high frequency RF signals that requires no hardware modifications, and (c) an implementation of distributed beamforming on a standard, open platform that allows easy reuse and extension. We describe the design of our system in detail, present some initial results and discuss future directions for this work.

Scalable Synchronization and Reciprocity Calibration for Distributed Multiuser MIMO

“…Both synchronization of multiple transmitters and TDD reciprocity calibration have been treated to some extent in the existing literature. The synchronization of multiple transmitters for multiple-input singleoutput (MISO) cooperative beamforming is considered in [18], [19], and software-defined radio (SDR) implementations of such ideas are presented in [20]- [22]. SDR implementations of MU-MIMO have been recently presented by a few research teams (including our own) in [23]- [25], where the feasibility of overthe-air synchronization with enough accuracy to guarantee near-ideal multiuser interference suppression is demonstrated.…”

“…, P . Also let ∇ (δµ) denote the derivative of ∇(δµ) with respect to δµ, whose p-th column has only two non-zero elements equal to 20…”

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

“…In [9,26,27], distributed transmit beamforming prototypes using wired feedback channels were presented for both RF and millimeter wave frequencies. A first fully wireless setup was presented in [28], but this setup still used analog signaling for the feedback channel. A D-Tx beamforming prototype using full digital signaling and an extended Kalman filter for frequency synchronization was presented in [29][30][31][32].…”

“…In the next cycle, the whole process is repeated. It has been proven theoretically [10] and with numerous prototypes [9,28,31] that with this algorithm, the RSS quickly converges to its maximum value.…”

TDOA, Frequency and Phase Offsets Estimation Taking Into Account Carrier Phase of Arrival

“…This paper focuses on the analysis of effects of taking into account the carrier phase term exp(−jω c D) on the performance of time difference of arrival (TDOA) and frequency and phase offsets estimation in a distributed dual-channel receiving system whose receivers are time-synchronized, but have independent local oscillators. The estimation accuracy improvement by using the carrier phases has not been systematically studied in the state-of-the-art literature, although it could be beneficial to Distributed Beamforming (DB) and Distributed Multiuser Multiple-Input Multiple-Output systems (DM MIMO) applications, [1][2][3][4][5].…”