User/Node cooperation has recently been receiving much attention especially in wireless sensor networks. It is shown that spatial diversity can be achieved even in a single-antenna system by exploiting the underlying virtual antenna array structure of multiple users/nodes. So far, much work has been devoted to single-antenna networks with only the channel state information at the receivers (CSIR). Motivated by the increasing importance of Time Division Duplex (TDD) operation for future generation systems where channel state information is also available at the transmitter (CSIT), we consider CSIT-assisted user cooperation. Nevertheless, a constraint of limited capacity for control messages exchange among cooperating nodes is imposed, which is particularly true for a large cooperating group. In this paper, we further relax the constraint of a single antenna to an arbitrary number for all nodes. A simple and efficient cooperation protocol is proposed and analyzed for enhancing the transmission link quality.