MIMO Transmission with Limited Feedback

During the past decade, multiple-antenna transmission (MIMO) systems have matured. However, when comparing their potential capacities with their achieved through-puts, we notice large gaps. The price for the MIMO advantages is increased cost for the transceiver hardware and antenna subsystems, combined with high algorithmic complexity in baseband processing and protocols. For instance, water filling and power loading do not seem feasible due to the large amount of required channel state information. State-of-the-art systems with MIMO enhancements like 3G cellular networks, WiMax, and WLAN support very limited feedback only. Nevertheless, adaptive modulation and coding (AMC) schemes, selective space-time coding, as well as antenna selection have shown that significant improvements are achievable even with very limited feedback. In this setting , MIMO-OFDM schemes are of central interest to industry and academia. For instance, an important challenge is to find an adequate representation of the MIMO channel's quality—independently of the system architecture and signal processing techniques currently available. A proper labeling or characterization of the MIMO channel quality regardless of the spatial processing to be used enables deciding on the reception or transmission strategy to use (e.g., with or without channel state information, to optimize diversity or rate, etc.) and, thus, on the amount of feedback that is required in transmission. MIMO transmission can be point-to-point or distributed; in fact, when looking not just into the physical layer, but also into the link layer, feedback load is especially critical in multiuser MIMO systems because of its much higher number of degrees of freedom. Opportunis-tic scheduling strategies have been developed, which (more or less heuristically) take into account the requirements on QoS. This special issue focuses on such transmission systems with limited feedback and provides an overview of the state of the art. We received 23 submissions, out of which we finally selected eleven for this special issue. The paper entitled " Antenna subset selection for cyclic prefix-assisted MIMO wireless communications over frequency selective channels " by A. Wilzeck and T. Kaiser is a tutorial paper on antenna selection techniques in broadband transmissions. In broadband MIMO systems aiming to provide high data rate links, the employed signal bandwidth is typically larger than the coherence bandwidth of the channel , so that the channel will be of frequency selective nature. While most contributions in literature consider only the frequency flat case, this paper shows how MIMO orthogonal frequency division multiplexing systems and MIMO single-carrier systems …