Smart Antennas for Next Generation Wireless Systems

The adoption of multiple antenna techniques in future wireless systems is expected to have a significant impact on the efficient use of the spectrum, the minimisation of the cost of establishing new wireless networks, the enhancement of the quality of service, and the realisation of reconfig-urable, robust, and transparent operation across multitech-nology wireless networks. Although a considerable amount of research effort has been dedicated to the investigation of MIMO systems performance, results, conclusions, and ideas on the critical implementation aspects of smart antennas in future wireless systems remain fragmental. The objective of this special issue is to address these critical aspects and present the most recent developments in the areas of antenna array design, implementation, measurements , and MIMO channel modelling, robust signal processing for multiple antenna systems and interference-aware system level optimisation. In the area of antenna array design, the paper by T. Cooper et al. presents a tower-top smart antenna calibration scheme, designed for high-reliability tower-top operation and based upon an array of coupled reference elements which sense the array's output. The theoretical limits of the accuracy of this calibration approach are assessed and the expected performance is evaluated by means of initial proto-typing of a precision coupler circuit for a 2 × 2 array. The design of uniform rectangular arrays for MIMO communication systems with strong line-of-sight components is studied in the paper by F. Bøhagen et al., based on an orthogonality requirement inspired by the mutual information. Because the line-of-sight channel is more sensitive to antenna geometry and orientation, a new geometrical model is proposed in this paper that includes the transmit and receive orientation through a reference coordinate system , along with a spherical wave propagation model to provide more accurate propagation predictions for the line-of-sight channel. It is shown that the separation distance between antennas can be optimized in several cases and that these configurations are robust in Ricean channels with different K-factors. The paper by M. Mowlér et al. considers estimation of the mutual coupling matrix for an adaptive antenna array from calibration measurements. This paper explicitly incorporates the lack of information about the phase centre and the element factor of the array by including them in an iterative joint optimization. In particular, the element factor of the array is approximated through a basis expansion—the coefficients of the expansion are estimated by the algorithm. Analysis, simulations, and experimental results demonstrate the efficacy of …