Full-Duplex Infrastructure Nodes: Achieving Long Range with Half-duplex Mobiles

One of the primary sources of inefficiency in today's wireless networks is the half-duplex constraint - the assumption that nodes cannot transmit and receive simultaneously in the same band. The reason for this constraint and the hurdle to full-duplex operation is self-interference: a node's transmit signal appears at its own receiver with very high power, desensitizing the receiver electronics and precluding the reception of a packet from a distant node. Recent research has demonstrated that full-duplex can indeed be feasible by employing a combination of analog and digital self-interference cancellation mechanisms. However, two glaring limitations remain. The first is that the full-duplex state-of-the-art requires at least two antennas and extra RF resources that space-constrained mobile devices may not be able to accommodate. The second limitation is range: current full-duplex demonstrations have been for ranges less than 10~m. At longer distances nodes must transmit with higher power to overcome path loss, and the power differential between the self-interference and the signal-of-interest becomes more that the current cancellation mechanisms can handle. We therefore present engineering solutions for answering the following driving questions: (a) can we leverage full-duplex in a network consisting mostly of half-duplex mobiles? and (b) can we extend the range of full-duplex by achieving self-interference suppression sufficient for full-duplex to outperform half-duplex at ranges exceeding 100 m? In answer to the first question, we propose moving the burden of full-duplexing solely to access points (APs), enabling the AP to boost network throughput by receiving an uplink signal from one half-duplex mobile, while simultaneously transmitting a downlink signal to another half-duplex mobile in the same band. In answer to the second question we propose an AP antenna architecture that uses a careful combination of three mechanisms for passive suppression of self-interference: directional isolation, absorptive shielding, and cross-polarization. Results from a 20 MHz OFDM prototype demonstrate that the proposed AP architecture can achieve 90+ dB total self-interference suppression, enabling >50% uplink rate gains over half-duplex for ranges up to 150 m.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

Masters

Discipline thesis:degree_discipline

Engineering

Grantor

Rice University

Year dc:date.issued

2012

Author dc:creator

• Everett, Evan

Advisor dc:contributor.advisor

• Sabharwal, Ashutosh

Committee members dc:contributor.committeemember

• Knightly, Edward W.
• Aazhang, Behnaam

• Full-duplex
• Wireless communication
• Antennas
• Polarization
• WiFi
• 802.11

Statement dc:rights

• Copyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/1911/64704

OAI identifier oai:identifier

oai:repository.rice.edu:1911/64704