Coordinated and distributed MIMO [Guest Editorial]

The impetus for this feature topic was spurred by the technical trend in wireless communications: the need for high bit rates (~1 Gb/s) in future wireless systems. However, due to the limited transmit power, the transmission distance cannot be long if the desired transmission rate is very high. In order to have a reasonable coverage area in each cell, antennas centrally attached to the base station in conventional mobile systems should be distributed through the entire cell via wires (or fibers) so that the wireless transmission distance between mobile units and base stations can be shortened. Moreover, reception of one signal at different locations provides spatial diversity against fading. Such network architecture is called a distributed antenna system (DAS). In order to reduce the transmission distance and provide diversity gain, the distributed multiple-input multiple-output (MIMO) concept is introduced to achieve broadband wireless transmission. In addition, coordination from multiple adjacent cells is needed to efficiently use the distributed MIMO. Therefore, coordinated and distributed MIMO becomes crucial. The key to implement coordinated and distributed MIMO is to have the mobiles communicate simultaneously with several remote antennas with perfect coordination between these antennas.