Vendors advance WLAN mesh networks

CALABASAS, CALIF. - Strix Systems last week unveiled a redesigned outdoor wireless LAN mesh node, and a start-up named Cohda revealed plans to make such nodes more efficient in using radio spectrum.

The new Strix product packs more radios-as many as six in all - into a smaller package and doubles the number of users each radio can support. The result is that outdoor mesh networks can handle more users and traffic with fewer nodes.

The Strix Outdoor Wireless System (OWS) 2400-30 can support any combination of 802.11 radios for client access and backhaul in a 12-by-10-by-6-inch box, which is 30% smaller than the company's previous model. Typically, two radios are dedicated for the backhaul connections, one receiving and one transmitting. These links route client traffic over the mesh to nodes that have a wired connection to the Internet or a corporate network.

Users also could plug into these same slots radios that use the 4.9GHz bands, spectrum that is set aside for police, fire and emergency use. In early 2007, Strix plans to release 802.16 radios, which support fixed and mobile WiMAX connections. The OWS 2400-30 can hold any combination of these radios.

Version 3.0 of the Strix operating system doubles to 128 the number of users who can associate with each radio. Company executives say that each six-radio node has a maximum capacity of 100Mbps that can be shared among client and backhaul connections, or about three to six times the previous limit.

The software also incorporates a new code that lets each node make routing decisions, a technique that doesn't require an entire network to reconfigure around a failed link. That saves time, allows for building very large-scale networks and minimizes latency. Strix executives say internal tests show zero data loss and zero added latency over 10 hops through the mesh. The OWS 2400-30 is available, priced starting at $4,500.

Cohda has created technology to address a number of challenges facing mesh networks that result from the characteristics of the modulation technique used in 802.11g and 11a, and in WiMAX - orthogonal frequency division multiplexing. Reflected signals, called multipath, can create slight delays at a receiver. If this delay exceeds 40 microseconds, the receiver starts to drop packets, says Martin Suter, Cohda's CEO.

The solution typically has been to compensate for multipath interference and the drop in performance by adding more nodes - and therefore more cost and complexity, - to a mesh network.

Cohda has created digital signal-processing code, which it will license to OEMs such as Strix, that will let the radio receivers compensate for this delay spread. The code, Suter says, increases the sensitivity of receivers, helps to maintain non-line-of-sight radio links with mobile clients, increases the reliable transmission range by 75% and minimizes interference.

Suter declined to go into more detail, saying the product will be announced later in 2006. Cohda is in talks with several OEMs, he says, but he won't say which ones. The company raised $1.8 million in series A funding, after its founding in August 2005.n Total investment is about $5 million. Its American headquarters are in Orlando.