A Self-Mixing Receiver for Wireless Frequency Synchronization in Coherent Distributed Arrays

Abstract

A self-mixing receiver support distributed frequency locking in coherent distributed antenna arrays is presented. Coherent distributed antenna arrays require accurate phase, frequency, and time alignment. However, each node in the distributed array generates its frequency using independent oscillators, and thus without appropriate frequency synchronization the emitted signals will not appropriately cohere. In this paper, we present a one-way frequency transfer approach that uses a self-mixing circuit architecture in a master-slave synchronization architecture. The master node transmits a multi-tone signal that consists of two tones separated by a 10 MHz frequency reference. The self-mixing circuit receives and demodulates this signal by splitting it and then passing it to the radio-frequency (RF) and local oscillator (LO) terminals of a mixer. The resulting signal is filtered to retain only the 10 MHz modulation, which is used to discipline the oscillator on the slave node. We present experimental results using software-defined radio, showing wireless synchronization via a cabled distributed beamforming experiment at 1.5 GHz.