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The rate-allocation problem, which has been aimed at minimizing the total transmit power in cooperative uplink systems, is investigated. Each user transmits over an orthogonal frequency band using cooperative broadcasting. The broadcasting nature of the wireless channel is exploited by allowing users to act as relays for one another. All users operate in the decode-and-forward mode. Depending on the number of relays that was selected by a user, we suggest two schemes: 1) the flow-optimized cooperative scheme (FCS) and 2) the single-relay cooperative scheme (SCS). We develop rate-allocation algorithms for them. In our simulation, we compare the outage performance of our schemes with two other schemes: 1) the orthogonal cooperative scheme and 2) direct transmission. Results indicate that our schemes achieve full diversity order and outperform other compared schemes. The algorithm for FCS achieves the optimality, whereas the algorithm for SCS is near optimal. In addition, our algorithms have fast convergence performance. SCS has a lower complexity than FCS, but it requires a higher total transmit power. However, the difference in total transmit power between FCS and SCS is not large under practical rate requirements. In addition to the total transmit power, we consider the improvement in the individual transmit powers of the users.
Date of Publication: Nov. 2009