Cognitive Cooperation for the Downlink of Frequency Reuse Small Cells
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Research Article Cognitive Cooperation for the Downlink of Frequency Reuse Small Cells Salam Akoum,1 Marie Zwingelstein-Colin,2 Robert W. Heath Jr.,1 and Merouane Debbah3 1
Wireless Networking and Communications Group, Department of Electrical and Computer Engineering, The University of Texas at Austin, 1 University Station C0803, Austin, TX 78712-0240, USA 2 IEMN/DOAE, UMR 8520, University Lille Nord de France, 59000 Lille, France 3 Ecole Superieure d’Electrecite (SUPELEC), Alcatel-Lucent Chair on Flexible Radios, 3 rue Joliot-Curie, 91192 Gif sur Yvette Cedex, France Correspondence should be addressed to Marie Zwingelstein-Colin, [email protected] Received 1 June 2010; Revised 28 September 2010; Accepted 16 November 2010 Academic Editor: Robert Schober Copyright © 2011 Salam Akoum et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. We develop a cooperative diversity protocol coded over space, time, and frequency to achieve improved quality of service for mobile users in the downlink of small-cell frequency reuse networks. The proposed protocol, called cooperative frequency reuse (CFR), leverages the cellular frequency reuse concept to create space and frequency diversity among pairs of adjacent base stations. The CFR protocol is compatible with the half-duplex mode and is distributed in the sense that each base station acts in autonomy, without the need of a centralized entity. It is implemented in two phases. During the first phase, each base station independently serves its own users on its dedicated frequency band. It simultaneously listens to the symbols transmitted by neighboring base stations. Cognitive cooperation is introduced in the second phase, where each base station transmits on two frequency bands to the scheduled users in both base stations, by means of an appropriately chosen distributed space time code based on the Golden code. We analyze and discuss the performance of the proposed protocol in terms of bit error rate, probability of outage, and ergodic sum rate under different scenarios. Simulation results show that the proposed protocol yields considerable improvement over direct transmission frequency reuse strategies.
1. Introduction Small-cell wireless networks provide increased capacity and higher area spectral efficiency [1–3]. The benefits reaped from these networks come, however, at the expense of increased cochannel interference, especially at the cell edge. Conventional cellular networks manage the interference problem by requiring adjacent base stations (BSs) to transmit on different frequency bands. This mechanism is called frequency reuse (FR). It increases the reliability of the cellular networks while at the same time incurring a poor spatial reuse of the expensive frequency spectrum [1]. Fractional frequency reuse (FFR) achieves a higher spatial reuse of the spectrum and is suggested for
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