Hybrid Full-Duplex/Half-Duplex Relaying with Transmit Power Adaptation

• Published in: IEEE transactions on wireless communications Vol. 10; no. 9; pp. 3074 - 3085
• Main Authors: Riihonen, T., Werner, S., Wichman, R.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.09.2011; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Access methods and protocols, osi model; Amplification; Antennas; Applied sciences; Cancellation; Detection, estimation, filtering, equalization, prediction; Exact sciences and technology; Full duplex; half duplex; High definition video; Information, signal and communications theory; infrastructure relays; Interference; power control; Protocols; Radiocommunications; Relaying; Relays; self-interference; Signal and communications theory; Signal to noise ratio; Signal, noise; Spectra; spectral efficiency; Strontium; Switches; Symbols; Systems design; Telecommunications; Telecommunications and information theory; Teleprocessing networks. Isdn; Tradeoffs; Performance evaluation; Relaying; Relay; infrastructure relays; Mode selection; Noise reduction; Transmission protocol; Downlink; System design; half duplex; Coverage; Modeling; self-interference; Duplex process; Interference suppression; Transmitting antenna; Power control; spectral efficiency; Signal processing; Full duplex; Routing protocols; Receiving antenna; Uplink
• ISSN: 1536-1276; 1558-2248
• DOI: 10.1109/TWC.2011.071411.102266

Focusing on two-antenna infrastructure relays employed for coverage extension, we develop hybrid techniques that switch opportunistically between full-duplex and half-duplex relaying modes. To rationalize the system design, the classic three-node full-duplex relay link is first amended by explicitly modeling residual relay self-interference, i.e., a loopback signal from the transmit antenna to the receive antenna remaining after cancellation. The motivation for opportunistic mode selection stems then from the fundamental trade-off determining the spectral efficiency: The half-duplex mode avoids inherently the self-interference at the cost of halving the end-to-end symbol rate while the full-duplex mode achieves full symbol rate but, in practice, suffers from residual interference even after cancellation. We propose the combination of opportunistic mode selection and transmit power adaptation for maximizing instantaneous and average spectral efficiency after noting that the trade-off favors alternately the modes during operation. The analysis covers both common relaying protocols (amplify-and-forward and decode-and-forward) as well as reflects the difference of downlink and uplink systems. The results show that opportunistic mode selection offers significant performance gain over system design that is confined to either mode without rationalization.