Experiments with a Low-Profile Beamforming MIMO System for WLAN Applications

MIMO technology has become one of the most promising techniques for enhancing the quality of services in many applications. For WLANs, the issue of MIMO technology has been officially addressed by the IEEE 802.11 n standard. In this standard, five MIMO operations - including spatial multiplexing, transmitting beamforming, space-time block coding, low-density parity-check encoding, and antenna selection - were described. Among these operations, the beamforming MIMO has the benefits of a low complexity with the highest improvement in signal-to-noise ratio. However, it is still requires high computational processing for estimating knowledge of the channel and for finding an appropriate steering vector. To reduce such computations, a selection of a fixed number of formed beams is proposed. In this paper, an experimental study of practically switched beamforming for WLAN applications is presented. Two types of antenna configurations, including 4×1 linear and 2×2 planar arrays, were considered. The results indicated the benefit of switched beamforming by improving average signal power strength by 10.25 dB. In addition, to reduce the burden of estimating the channel, the concept of selecting the best steering vector from the received signal strength instead of the channel information is proposed for low-profile beamforming MIMO systems. The prototype was completely constructed and practically tested. The results confirmed the successful improvement of the proposed prototype over using an omnidirectional antenna for WLAN applications.