Smart Antenna Chip Extends Wi-Fi Range, Speed, And Reliability

The key to microwave radio performance is a good antenna. While designers usually take the antenna for granted or see it as a necessary evil, it really is a major system component. Today, designers are paying more attention to what has often been an afterthought. Smart antennas, a new tool in their portfolio, adapt to existing conditions and optimize reception and transmission.

In that vein, the Javelin chip from fabless semiconductor company Motia implements smart antennas for Wi-Fi products. Combined with an array of four antennas, it can extend the range of any 802.11b/g transceiver by up to four times as well as enhance overall system performance and quality-of-service.

Wi-Fi products deliver coverage up to about 100 meters (over 300 feet) in general use. Yet obstacles like walls, floors, and ceilings shorten this range. So do reflections from multiple objects and other obstructions. Furthermore, while the range is limited, speed automatically drops as signal quality deteriorates. Reliability is the pits.

To solve this problem, the Javelin is inserted between the four-antenna array and the input to the Wi-Fi transceiver chip (see the figure). The chip, which works with any Wi-Fi transceiver chip set, uses an appliqu´ architecture that enables the technology to be used in any access point or client device.

The Javelin implements an adaptive array of four antennas similar to the two antenna diversity configurations now used on some access points. In the receive mode, the signals at each antenna are downconverted to a received-signal strength indicator (RSSI) value. The RSSI values are then weighed and combined to form the strongest possible output signal to the low-noise amplifier of the Wi-Fi chip set.

In the transmit mode, the signal from the transceiver is divided four ways. Each of those signals is shifted and amplified by the profile defined by the received signal before being combined and transmitted. The result is a 13-dB gain over a single antenna at one end of the transmission path. The overall gain rises to 18 dB if the Javelin is used at both ends of the system.

This fully analog device, dubbed the JAS100, is compatible with both 802.11 b and g systems. It's expected to be available by the end of the second quarter for less than $10, based on volume.