New channel model for wireless communications
The FLOWS project was funded by the Fifth Framework Programme to realise a future for wireless communication systems where standards would converge to ensure reliable multimedia services of a higher performance. Multiple-Input multiple-output (MIMO) techniques were identified as a means of attaining the objectives set. Deploying multiple antennas at the transmitter and at the receiver, independent data streams can be transmitted simultaneous from all the antennas. Moreover, significant improvements in performance can be achieved by exploiting the diversity of transmission channels and effectively transmitting the signal over multiple fading channels. Nevertheless, to what extent MIMO techniques would be an efficient or even profitable alternative eludes researchers. A key for the development of spatial diversity and multiplexing techniques that could answer the demand for increased spectrum efficiency of wireless systems is the characterisation of the channel properties. A Wideband double directional propagation channel model (WDDCM) was, for this purpose, developed by project partners at the Instituto Superior Técnico in Portugal. Multipath propagation involves signals reaching the receiving antenna through two or more paths in a highly variable environment, and has as a consequence, the propagation channel to disperse. The channel response that ultimately affects the quality of services can, however, be estimated. Arrays of antennas at the base station and mobile terminal can be included in the WDDCM model to allow for the propagation channel's characterisation and the exploitation of multipath diversity. Though not originally designed for MIMO systems, it has been extended to provide a robust platform for the implementation and simulation of MIMO as well as adaptive antenna techniques. More specifically, to account for the antenna to antenna coupling, several modules have been added. The model was validated against measurements and already successfully applied for a prototype micro-strip patch antenna array, operating in the two frequency bands, UMTS and HiperLAN/2, covered by the FLOWS project.
