A Cooperative Uplink Transmission Technique With Improved Diversity–Multiplexing Tradeoff

In this paper, a new decode-and-forward (DF) cooperative scheme is presented for half-duplex uplink transmission. The technique is based on a virtual multiple-input-multiple-output (MIMO) structure formed by the single-antenna source and relay nodes along with a multiantenna destination node. The new technique aims at providing increased diversity and multiplexing gains, contrary to existing approaches in which increased diversity gain is achieved at the cost of severe multiplexing gain loss. Furthermore, the proposed scheme is extended in a doubly opportunistic manner by incorporating both multiuser diversity and relay selection diversity. Novel criteria are suggested for selecting the best transmitting user and/or the best relays at each time slot. The theoretical outage probability and the corresponding diversity-multiplexing tradeoff curve of both the proposed technique and its opportunistic extension are derived. Indicative simulations verify the theoretical results and compare the performance of the proposed technique with the performance of existing cooperative schemes and of the noncooperative single-input-multiple-output (SIMO) system.