Cooperative Diversity in Wireless Networks: Efficient Protocols and Outage Behavior

TLDR

The paper develops and analyzes low‑complexity cooperative diversity protocols to mitigate multipath fading in wireless networks. These protocols exploit space diversity through cooperating terminals that relay signals using amplify‑and‑forward, decode‑and‑forward, selection, and incremental relaying schemes, and their performance is characterized by outage probabilities in the high‑SNR regime. All protocols except fixed decode‑and‑forward achieve full diversity and are within 1.5 dB of optimum, offering distributed‑antenna space‑diversity benefits—though at the cost of spectral efficiency due to half‑duplex operation and possible extra hardware—while delivering significant power savings in any wireless setting lacking physical arrays.

Abstract

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-and-forward, 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-to-noise ratio (SNR) regime. Except for fixed decode-and-forward, all of our cooperative diversity protocols are efficient in the sense that they achieve full diversity (i.e., second-order diversity in the case of two terminals), and, moreover, are close to optimum (within 1.5 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 at the cost of 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.