Array signal processing or array processing has diverse applications including radar and sonar systems. An array of multiple sensors can provide spatial selectivity in receiving signals. In general, the more sensors, the better spatial selectivity can be achieved. Exploiting this spatial selectivity, we can have a clearer signal or less performance degradation due to interfering signals. An important application of array processing in cellular communication systems is smart antennas. The base stations equipped with antenna arrays for spatial selectivity can be considered as smart antenna systems. In cellular systems, since the performance is degraded by the inter-cell interference (which is the signal transmitted from adjacent cells where the same frequency band is used for communications), it is important to mitigate inter-cell interference. Smart antennas can mitigate inter-cell interference using the spatial selectivity and improve the performance of cellular systems.

In this chapter, we focus on signal combining and related techniques for array processing and discuss how array processing can be applied to smart antenna systems.

Antenna arrays

An antenna array is an array of antenna elements that allows spatial processing, which is also called array processing. For array processing, we need to take into account array configuration and spatial characteristics of signals. Array processing can be extended in both space and time domains. In this case, spatial and temporal processing is to be jointly performed. Array processing can be considered for both signal reception and transmission.