Non-coherent receivers for zero-feedback distributed beamforming in connectivity-constrained wireless sensor networks (WSNs)

Abstract

Power-constrained wireless sensor networks (WSNs) suffer from network partitioning problems. In many cases, each node among a network subset, cannot reliably communicate with a distant receiver even when transmitting at maximum power. Thus, a collaborative beamforming scheme among the distributed adjacent terminals is needed in terms of power addition. Prior art on distributed beamforming has mainly focused on feedback messages for channel estimation (CSI) or physical layer carrier phase adjustments. In sharp constrast, this thesis assumes commodity radios and studies the low signal to-noise-ratio (SNR) regime, where accurate channel estimation is not feasible and no reliable feedback exists. The main idea is to exploit recently proposed zero-feedback distributed beamforming and design specific non-coherent receivers. Towards that goal, three concrete non-coherent receivers are presented for zero-feedback distributed beamforming (ZF-DBF); one based on energy detection, one based on maximum-likelihood for a specific condition (i.e., full correlation among the received samples), and finally, one non-coherent receiver for all other cases. A non-coherent receiver for energy harvesting through time division multiple access (TDMA) is also provided for comparison purposes. Analytical and numerical bit-error-rate results are presented. It is shown that the ZF-DBF receiver outperforms the energy harvesting one at the low-SNR regime and overcomes connectivity adversities by exploiting signal alignment from the distributed terminals, at the expense of total (network) power transmission.