Public Safety Spectrum Makes Mesh

By Eric Griffith

September 23, 2004

MeshNetworks has landed a license to make equipment utilizing the 4.9GHz radio band reserved for public safety use. Vendors of Wi-Fi-based mesh equipment probably won't follow this trend for a while, due to an FCC ruling.

MeshNetworks of Maitland, Fla., has made its name creating citywide networks that usually support first responder departments like police and fire. They do it with equipment that operates in various radio spectrums, including the 2.4GHz range used by 802.11b/g—though MeshNetworks doesn't use the 802.11/Wi-Fi standard (the company calls itself "radio-agnostic").

It's now adding another area of radio spectrum to its portfolio. MeshNetworks has been granted an "experimental license" from the Federal Communications Commission (FCC) to use the 4.9 GHz band. 50MHz of this spectrum (4940-4990 MHz) of radio was set aside by the FCC in early 2002 (in the wake of September 11) to be used exclusively by public safety departments.

"We put in an application, very straightforward, that from an engineering level had to be specific as to what we wanted to do," says Alf Young, technical marketing manager for MeshNetworks. "We're one of the first to be granted [rights to use 4.9GHz]."

Under the experimental license, MeshNetworks can test and deploy a total of 1000 nodes with 4.9GHz, with a maximum of 200 mesh nodes per demonstration network. The maximum Effective Radiated Power of each node will be 16 watts, an amount of power Young describes as "huge... that tells me the FCC is willing for experimental networks to be in places transmitting over several miles."

The company won't be doing away with its 2.4GHz or 5.8GHz lines of products. For one thing, MeshNetworks can't put new 4.9GHz equipment out to work with existing deployments. Young says the company would continue to support 2.4 anyway, because "there's going to be situations where [municipalities] can't get a license." It would be up to the venue to get the full license to actually deploy products with the 4.9GHz support.

MeshNetworks is certainly not alone in trying to make citywide wireless a reality, and is also not alone in seeing public safety as a primary market. The company's top competition is arguably Tropos Networks, which offers similar solutions, but uses Wi-Fi for the blackhaul and client connections.

Bert Williams, vice president of marketing at Tropos, says his company is interested in 4.9GHz spectrum for its products, but says there are technical issues it would face in trying to use it with Wi-Fi. "The FCC has defined the emissions mask, which restricts how much power can be transmitted at what frequencies in what channels, in a way that currently available 802.11a chipsets can't be downbanded to run at 4.9 without at least significant external circuitry, perhaps not at all," Williams says.

A white paper by Tropos says that 802.11 vendors using 4.9GHz would, under current rules, be allowed two non-overlapping 20MHz channels in that band, with a maximum total power output of 33 dBm (2W) per channel.

Williams cites Motorola as a company that used influence on this issue, which will exclude 802.11-based vendors from the market for 4.9GHz products.

"The 802.11 vendor community didn't catch on until it was too late," says Williams.

Motorola, it was announced last month, will be creating products based on the MeshNetworks Enabled Architecture (MEA).

The Tropos 4.9GHz white paper, issued in March 2004, says "In the future, Tropos Networks will extend its product line to incorporate 4.9 GHz in pure and hybrid 802.11/4.9 GHz systems," but it looks like that will will wait, as Tropos is working with other vendors, including Nortel, PacketHop, Bermai, and Cisco, to get the FCC to reconsider the emissions mask and allow experimental licenses above 20dBm.



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