Advanced broadband wireless access (BWA) systems such as mobile WiMax employ multiple-antenna technologies to enable high-capacity deployments that deliver advanced services to the end user. The business case for wireless networks based on these systems is strongly affected by the basestation architecture.
The basestation architecture determines two key parameters of the business model: the total infrastructure cost and the cost of deployment. The use of tower-top electronics in the basestation design reduces costs in both areas, particularly when multiple antenna technologies are used.
Multiple-antenna techniques include beam forming, interference cancellation, space/time coding and multiple-input, multiple-output (MIMO) coding. They are an integral part of all advanced broadband wireless air interfaces. These systems use arrays of antennas at the basestation to boost coverage and increase capacity and bandwidth efficiency to the levels required for true broadband services. Regardless of the specific technique, the performance gains from multiple-antenna processing increase with the number of antennas.
Current air interfaces are optimized for up to four basestation antennas, but supporting quad-element basestation arrays imposes challenges on the basestation architecture that directly affect the economics of the BWA business case.