Outage Constrained Transmit Approaches in Gaussian MIMO Relay Networks (OCTAGON)

点击翻译按钮获取中文摘要

Cooperative communications using multi-antenna relay nodes constitutes an important technology of future wireless networks to reliably convey information to a growing number of mobile users. In contrast to the well understood (multi-antenna) point-to-point channel, multiple-access channel, and broadcast channel, the field of cooperative communications where source(s) send messages to destination(s) with the help of assisting nodes (relays) still offers a rich set of challenges. Even if perfect CSI is assumed, the capacity of the simplest cooperative communication element, the three-node relay channel is still unknown. Therefore, the literature on relay channels is in general restricted to information-theoretic upper and lower capacity bounds. The even more complex assumption of fading channels further limits the state-of-the-art performance analysis to simplified scenarios and diversity-multiplexing tradeoff studies.In this research project, we intend to study (multi-antenna) Gaussian relay channels, assuming that only imperfect CSI is available at the transmitting nodes while the receiving nodes are aware of the channel states that are required for reliable decoding. After gaining knowledge for the basic three-node relay channel, we will investigate the multiple-access relay channel (MARC), where multiple sources convey information to one destination with the help of a single relay, the broadcast relay channel (BRC), where one source transmits information to multiple destinations with the help of a relay node, as well as networks where multiple relays support the communication from one source to one destination.Whereas the ergodic rate is the most important performance metric for fast fading channels, we focus on the case of slow fading, where the key event of interest is outage. In particular, we plan to study the maximization of the achievable rate(s) subject to a given upper bound on the outage probability in multi-antenna relay systems. Since the outage capacity (the maximum rate at a certain outage probability) is unknown, achievable lower bounds based on (partial) decode-and-forward (DF) schemes and an upper bound based on the cut-set-bound (CSB) will be investigated. The resulting chance constrained problem formulations are still difficult due to missing or too complex closed-form representations of the outage probabilities. Therefore, conservative and optimistic approximations of the probabilistic expressions have to be found in order to solve the optimizations with respect to the transmit covariance matrices and, therewith, bound the outage capacity of the three-node relay channel (with and without half-duplex constraints) and the multiple relay scenario. For the even more difficult multi-user scenarios, i.e., the MARC and the BC, the objective is to characterize the outage capacity region via inner bounds based on (partial) DF and an outer bound based on the CSB.