Compress-and-Forward Relaying: Prototyping and Experimental Evaluation using SDRs

This paper presents a prototype implementation and experimental performance evaluation of compress-and-forward (CF) relaying using software-defined radios. Under QPSK transmissions from all nodes, the relay demodulates the received signal before applying distributed joint source-channel coding (DJSCC) implemented with the help of an off-the-shelf convolutional code. The destination employs two stages of standard BCJR decoding; a DJSCC decoding stage for the relay's demodulated data followed by another to recover the source's message. Under varying channel conditions, we propose and implement an opportunistic Decode-or-Compress-and-Forward (DoCF) relaying strategy in which the relay forwards the decoded packet if a cyclic redundancy check (CRC) is satisfied, and uses CF relaying otherwise. The prototype implementation of DoCF is carried out using National Instruments USRP 2921 devices. Over-the-air experiments in an indoor office environment indicate that the proposed DoCF strategy can achieve up to ten times smaller bit-error-rate than a standard DF implementation. To the best of our knowledge, this work is the first in the literature to carry out an experimental study of CF relaying.