Cooperative Diversity in Wireless Networks: Low-Complexity Protocols and Outage Behavior

We develop and analyze low-complexity cooperative diversity protocols that combat fading induced by multipath propagation in wireless networks. The underlying techniques exploit space diversity available through cooperating terminals’ relaying signals for one another. We outline several strategies employed by the cooperating radios, including fixed relaying schemes such as amplify-and-forward and decode-andforward, selection relaying schemes that adapt based upon channel measurements between the cooperating terminals, and incremental relaying schemes that adapt based upon limited feedback from the destination terminal. We develop performance characterizations in terms of outage events and associated outage probabilities, which measure robustness of the transmissions to fading, focusing on the high signal-tonoise (SNR) ratio regime. Except for fixed decode-and-forward, all of our cooperative diversity protocols achieve full diversity (i.e., second-order diversity in the case of two terminals), and are close to optimum Manuscript submitted January 22, 2002; revised Mar. 30, 2004. The material in this paper was presented in part at the Allerton Conference on Control, Communications, and Signal Processing, Urbana, IL, October 2000, and the International Symposium on Information Theory, Washington, DC, June 2001. The work of J. N. Laneman and G. W. Wornell has been supported in part by ARL Federated Labs under Cooperative Agreement No. DAAD19-01-2-0011, and by NSF under Grant No. CCR-9979363. J. N. Laneman was with the Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology (MIT) and is now with the Department of Electrical Engineering, University of Notre Dame, Notre Dame, IN 46556 USA (email: [email protected]). G. .W. Wornell is with the Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139 USA (email: [email protected]). The work of David N. C. Tse has been supported in part by NSF under grant No. ANI-9872764. He is with the Department of Electrical Engineering and Computer Science, University of California, Berkeley, CA 94720 USA (email: [email protected]). March 30, 2004 DRAFT IEEE TRANS. INFORM. THEORY (UNDER REVIEW) 2 (within 1.5 decibels (dB)) in certain regimes. Thus, using distributed antennas, we can provide the powerful benefits of space diversity without need for physical arrays, though at a loss of spectral efficiency due to half-duplex operation and possibly additional receive hardware. Applicable to any wireless setting, including cellular or ad-hoc networks—wherever space constraints preclude the use of physical arrays— the performance characterizations reveal that large power or energy savings result from the use of these protocols.