A Virtual MIMO Framework for Transceiver Analysis and Design for Multipath Fading Channels

An understanding of the interaction between the channel and the signal space is key to reliable communication. Multipath fading channels exhibit inherent diversity that can be exploited via appropriate signaling and reception. In this paper, we develop a virtual MIMO framework for code division multiple access (CDMA) systems for maximally exploiting channel diversity at both the transmitter and receiver. At the heart of the framework are MIMO system representations with respect to appropriately chosen basis functions for the signal space. The framework unifies many existing systems and suggests new transceiver structures for bandwidth-efficient communication. For any transceiver structure, the framework clearly reveals the two key factors that affect system performance: the number of parallel channels created by the signaling scheme and the level of diversity associated with each parallel channel. The framework also makes it possible to derive closed-form expressions for ergodic and outage capacity for a variety of transceivers. We present a transceiver that has a simple capacity expression and whose outage capacity performance bounds that of the multipath channel. We also present a simple transceiver for transforming the temporal multipath channel into a virtual multiple antenna array system to which recently developed spacetime codes can be directly applied.