Pathway to Coherent Phase Acquisition in Multi-Channel USRP SDRs for Direction of Arrival Estimation.

This paper sheds lights onto the challenging problem of achieving coherent phase reception between the RF channels of existing multi-channel software-defined radios (SDR). This is a key problem that must be solved, for instance, in applications dealing with 5G positioning and integrated sensing and communications (ISAC) when direction of arrival estimation is needed. Despite being a fundamental problem, it is far from being straightforward to implement in practice with existing SDR devices. In this regard, the present paper provides a set of golden guidelines in order to succeed in this endeavor, and thus to leverage the full potential that multi-channel SDR devices have to offer. Apart from phase coherence, practical recommendations are provided as well to achieve the highest possible data throughput between the SDR and the controlling computer. Finally, a comparison among the most relevant features of different models of Universal Software Radio Peripheral (USRP) SDR devices is discussed, including an analysis of their performance in terms of phase differences between RF channels.