Hardware Implementation of Signal Processing in Smart Antenna Systems for High Speed Wireless Communication

Smart antennas basically attempt to enhance the desired signal power and suppress the interferers by beamforming toward the DOA (direction-of-arrival) of the desired signal and nullsteering in the case of the interferences’ DOAs in line-of-sight (LOS) situation. This paper considers a smart antenna system for cellular base station application. The signals at the base station are received through the scattering process from the local scatterers around the mobile station because the antenna is usually deployed higher than surrounding scatterers. In this case, although the fading across the antenna elements spaced by λ/2 is highly correlated, the AS is typically only a few degrees. Hence, the angle domain approach exploiting the DOA information can be useful. Moreover, only the DOAs are commonly useful channel information in both uplink and downlink channels of Frequency Division Duplex (FDD) systems where each link uses different frequency. This is because the average angular power spectrums in both links are almost identical. Thus, in an uplink, we can estimate the channel parameters with the received data that have passed the channel and apply the estimated DOA information to downlink beamforming. In a downlink channel, smart antenna transmitters can focus the energy to the desired user using the DOA information, and thus reduce the interference for other users. This is the most significant feature of the angle domain approach with DOA estimation. This paper mainly aims at the practical and general applications of signal processing implementation of a smart antenna system for wireless cellular basestation systems. While theoretical studies are useful for analyses and simulation purposes, their implementation in real hardware and their validation with actual measurement data will be a meaningful challenge. This paper studies general signal processing independent of specific communication systems and hardware platforms. This paper proposes the smart antenna system based on the DOA estimation of incident signals, which includes fast DOA estimation and beamforming processors. The prototype system integrating signal processors on field programmable gate arrays (FPGAs) was manufactured and the evaluation testbed was configured. The prototype system employs an 8-element antenna array for 5 GHz band and an RF transceiver for each branch. The functionality of the baseband smart antenna processor was verified through hardware simulations and laboratory experiments. The entire hardware system, including RF, antenna arrays, and air interface, at both the transmitter and receiver configurations were also tested in a radio anechoic chamber. Smart antenna systems, especially those based on DOA estimations, usually require high computational performance for array signal processing. Apart from the hardware complexity