Antenna Systems & Technology - Fall 2011 - (Page 9)

FEATURE ARTICLE Selectable Multi-Beam Smart Antennas By David Hayes and Ian Russell • Plasma Antennas Limited Within wireless communications systems, smart antennas offer improved quality of service (QoS), across a range of user densities, from tightly packed city centers to sparsely populated rural areas. MIMO systems use a combination of multiple antennas and multiple signal paths to provide diversity gain and significantly higher data rates than traditional SISO channels. Beamforming systems, by contrast, exploit coherency to increase the power transmitted in the direction the signal is to be sent and, as an added benefit, also minimize interference elsewhere. On receive, they enhance the receiver sensitivity in the direction of the wanted signals and can decrease the sensitivity in the direction of interference and noise. In the licensed bands, beamforming antennas can reduce RF power requirements, limit co-network interference and enhance frequency re-use. Within the unlicensed bands, which are often congested and limited by interference, they facilitate interference cancellation and dynamic re-routing of traffic. More generally, beamforming antennas enable cost-effective deployments due to their higher gain and extended coverage when compared to more conventional omni and tri-sector antenna deployments. Figure 1. Planar and Cylindrical Smart Antennas Selectable multi-beam (SMB) antennas represent an interesting class of smart antennas that can provide both beamforming and MIMO gain. As shown in Figure 1, SMB antennas provide beamforming and electronic beamsteering capabilities, from a single compact aperture, by allowing a beam position to be selected from a set of beam patterns. Beamforming gain is utilized by selecting the optimal beam position based on signal strength indicators and interference ratios (e.g. RSSI, CNIR). Typically, a node equipped with an SMB antenna maintains a routing look-up table used to associate beam positions with a set of target network nodes. For example, in a basic application scenario, a nomadic vehicular subscriber station would scan through beam positions in order to select the optimal beam for connection to the desired relay point or base station. Similarly, a fully-wireless pico base station deployed on street furniture would select the beam position that provides the best connection into a wireless backhaul network. In advanced applications, high-speed beam selection supports Spatial TDMA, with the active beam being multiplexed between target network nodes in real-time on a sub-frame basis. Selectable Multi-Beam Antennas SMB Antenna Fundamentals SMB antennas are primarily characterized in terms of their form factor, gain, frequency coverage, polarization, instantaneous bandwidth, number of beams and angular coverage. Plasma Antennas has researched and developed both planar and cylindrical SMB antennas providing beam selection over sectoral and 360° fields of view respectively. WWW.ANTENNASONLINE.COM FALL 2011 ANTENNA SYSTEMS & TECHNOLOGY 9 http://www.antennafactor.com http://WWW.ANTENNASONLINE.COM

Table of Contents for the Digital Edition of Antenna Systems & Technology - Fall 2011

Planning of Advanced Wireless Systems
Selectable Multi-Beam Smart Antennas
AISG OOK Modem Implementations
Antenna Systems 2011: Conference Preview
Editor’s Choice
Antennas
Components
Test & Measurement
Manufacturing/Design
Base Stations
Marketplace, Advertising Index & Calendar of Events
Industry News

Antenna Systems & Technology - Fall 2011