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

Evan Everett[[BR]]
MS Thesis[[BR]]
Rice University Department of Electrical and Computer Engineering[[BR]]
Defended & Submitted April 2012

== Abstract ==
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. 


== Thesis ==
[http://warp.rice.edu/trac/raw-attachment/wiki/EverettMSThesis/Everett2012MSThesis.pdf Full-Duplex Infrastructure Nodes: Achieving Long-Range with Half-Duplex Mobiles] (4MB PDF)

== Citation ==

{{{

@mastersthesis{Everett12Thesis,
  Author = {Evan Everett},
  School = {Rice University},
  Title = {Full-Duplex Infrastructure Nodes: Achieving Long-Range with Half-Duplex Mobiles},
  Url = {http://warp.rice.edu/trac/wiki/EverettMSThesis},
  Year = {2012}}
}}}