The high-level architecture for a typical wireless base station incorporating smart antenna technology is illustrated in Figure 1[4]. This architecture consists of an array of M transmit antennas and N receive antennas, each with an associated RF/IF processing chain. The smart antenna processing generally takes place in the baseband signal processing subsystem, consisting of one or more channel cards implemented using programmable technologies that include application-specific standard processors (ASSPs), field-programmable gate arrays (FPGAs), digital signal processors (DSPs) and general-purpose processors (GPPs), The interfaces between the various hardware components and subsystems are facilitated through APIs that access device drivers specific to the hardware.

The advantages inherent in smart antenna technologies are compelling more and more communications systems engineers to incorporate these technologies into their advanced wireless systems. These systems are also increasingly using software-defined radio (SDR) technologies to reduce operations and maintenance costs (OPEX), speed time to market, improve network interoperability, and allow new features and capabilities to be added to the radio system while in service and without the need for a hardware upgrade.

Members of the SDR Forum foresaw these trends and in 2004 formed the smart antenna working group (SAWG) under the forum's technical committee. The charter of this working group is to specify a standardized API for smart antenna systems operating in an SDR network, providing interoper-ability and compatibility among systems produced by different vendors with different functions. The working group specifically focused on allowing various kinds of beamforming systems, diversity systems and MIMO systems to all be managed together in an open architecture SDR network.

In order for the SDR system to exploit the merits of a smart antenna, the SAWG determined that it was necessary to define an open-architecture that allowed all of the different kinds of smart antenna technologies to be properly reconfigured by software download. The basic principle of the open-architecture smart antenna system suggested by SAWG is to partition the entire smart antenna system according to function, with each partition referred to as a “component.” After partitioning the system into components, the SAWG then defined a separate API for controlling each component, which as a whole defines the “SA API specification.”

It was important that the SA API be approached in such a way that any non-smart antenna system can easily be converted to an SA architecture. More specifically, the SAWG defined a requirement on the SA API that it should be possible to convert any communication system into a smart antenna system by simply plugging in the smart antenna software modules implemented in accordance with the SA API. In other words, the SA API defines the components and API's needed for non-smart antenna systems to be extended with smart antenna technology. Consequently, the SA API should facilitate a new commercial-off-the-shelf (COTS) market for smart antenna modules by driving economies of scale in manufacturing and thus significantly reducing the investment cost for smart antenna systems. In addition, service providers should be able to upgrade their non-smart antenna system to include smart antenna technology by integrating the smart antenna module into their network.

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