Enhancing WLANs through smart antennas

US-based Motia has developed a device that allows smart antennas to be incorporated into 802.11 systems without major modifications to existing products.

Instead of re-designing 802.11 chips to include the additional signal processing needed to implement a system using smart antennas, Stamford, CT-based Motia has developed Javelin – a standards-compliant device that allows smart antennas to be incorporated into 802.11 systems without major modifications to existing products.

The device itself can be used in an 802.11 system that incorporates an adaptive array. In such a system, a signal is received by several antenna elements, each with similar antenna patterns, and the received signals are then fed to the Javelin device which performs the necessary ‘weighting and combining’ of the signals before passing its RF output to a transceiver.

Because the output from the Javelin device had to be RF, Motia chose to process the signal in an analog fashion, rather than digitally. Although digital processing would have been easier to implement, this would have required baseband processing with 4 A/D’s and remodulation, which would have been a much costlier solution. In addition, digital processing introduces latency, which would have resulted in severe system problems.

To calculate the weights, the Javelin device uses a version of the MRC algorithm, which works for 802.11b, 802.11g, and 802.11a. To do so, the weights are calculated within 2 microseconds after the signal is received as this is the time allotted for the calculation in the 802.11a/g standard.

The Javelin device is fully standards compliant, and implementation at either the client or access point gives a performance improvement in any 802.11 system.

To demonstrate the effectiveness of the part, Motia has simulated the effectiveness of the device in an adaptive array using four antennas. In use, the Javelin ‘intelligently combines the signals received on the 4 antenna elements to significantly increase the signal to noise ratio’ of the system, according to Robert Warner, Motia’s Vice President of Marketing.

The SNR gain with the smart antenna, up to 18 dB when used at both client and access points, can be related to a range increase. Alternatively, the gain can also translate into a data rate increase in 802.11 systems since higher SNRs allow for higher data rates. One man who has tested the new concept is Bruce McNair, CTO of Novidesic Communications, and Distinguished Service Professor of Electrical and Computer Engineering at Stevens Institute of Technology.

‘Motia’s Javelin increases the performance of any Wi-Fi device, helping companies conquer one of the major roadblocks to success in this rapidly emerging market. My tests of Motia’s technology show a substantial improvement in range, throughput and uniformity of coverage, in side-by-side comparisons with standard 802.11 devices,’ he said. ‘In fact, I was able to achieve a range of 370 feet with just one milliwatt of transmit power; with Motia’s Javelin I got a solid connection, without it, there was no connection,’ he concluded.

On the web