When Do Non-Regenerative Two-Hop Relaying Networks Require a Global Phase Reference?


Stefan Berger and Armin Wittneben


IEEE Global Communications Conference (IEEE GLOBECOM 2009), Dec. 2009.

[BibTeX, LaTeX, and HTML Reference]


We consider a distributed wireless multiuser network with non-regenerative relays, where the gain factors are computed from channel estimates. They are to be chosen such that multiple signal paths add up coherently at the destinations ('distributed coherent beamforming'). In the presence of channel estimation errors, coherency is generally destroyed because the gain factors cannot be computed correctly. In this work, the channel estimates are assumed to be noiseless, but exhibit phase errors due to random and unknown local oscillator (LO) phases at the terminals. Without global phase reference at the nodes, the phase errors depend on the direction in which the individual point-to-point channels are measured. In some cases, coherency is completely destroyed while in others the system performance is not affected. We will still call the latter cases 'coherent', even if perfect channel state information (CSI) is not available. Based on this observation we derive a framework to determine which nodes in a two-hop network require a global phase reference in order to allow for coherent distributed beamforming. We consider four traffic patterns that differ in the utilization of the direct link and discuss all combinations of directions in which the single-hop channel matrices can be estimated.


Multiuser relaying, nonregenerative relays, coherent beamforming, cooperative relaying

Download this document:


Copyright Notice: © 2009 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.

This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.