WiMAX Makes a Mesh

Mesh networks traditionally have been fairly isolated with low enough overall usage that portions of the mesh could be used to provide backhaul for other parts of the mesh network. However, as mesh networks become more common and more frequently trafficked, operators of these networks will be looking for better backhaul options, as well as a long-haul mechanism capable of linking islands of mesh networks together.

Bruce Gustafson, vice president of marketing for WiMAX and mesh at Nortel Networks, said that 3G networks have provided an example in which the amount of backhaul bandwidth many operators need to support 3G traffic is much more than what they expected.

“In a mesh, if you're using a portion of the mesh for backhaul and there gets to be enough traffic, you could conceivably get to the point where the mesh gets overloaded,” Gustafson said. “You want to have a lot of drains out of the mesh.”

Nortel is in the process of taking its mesh network algorithms and incorporating them into its WiMAX technology.

Thus far, two smaller vendors, SkyPilot Networks and Strix Systems, also have announced plans to incorporate WiMAX technology into their mesh architectures.

SkyPilot Networks, a broadband wireless equipment vendor that traditionally has been a supplier of point-to-multipoint fixed wireless gear, recently launched its first product effort in the burgeoning market for municipal wireless mesh networking. That platform, the SkyExtender DualBand, is a dual-band radio mesh architecture based on a marriage of the company's synchronous mesh protocol and advanced antenna array technology. Such dual-band solutions hint at how WiMAX and traditional mesh technology will be integrated. The SkyExtender DualBand currently employs Wi-Fi backhaul in the unlicensed 5.8 GHz band and the 4.9 GHz band for public-safety communications, with dedicated access via 2.4 GHz Wi-Fi, to avoid interference with the backhaul portion of the network, said Brian Jenkins, vice president of product management for SkyPilot Networks.

Most first-generation mesh architectures aimed at municipal applications have been single-band solutions, in which backhaul and access use the same 2.4 GHz frequency. Now, after a couple of years during which mesh networking has begun to gain traction and during which the list of major municipalities pursuing wireless networks has grown rapidly, dual-band solutions like those from Strix Systems and now SkyPilot represent a second-generation approach to mesh networking.

SkyPilot's dual-band radio approach may fit the description of a second-generation municipal mesh networking architecture, but the company has already set its sights on the third-generation move to incorporate WiMAX.

In September, the company announced that it had chosen Fujitsu Microelectronics America's WiMAX system-on-a-chip to power a WiMAX mesh solution SkyPilot has under development for a planned launch next year. SkyPilot's current plan is to create an architecture employing the capabilities of the 802.16d-2004 standard and having the platform ready to submit for WiMAX Forum certification in April 2006. The company has long been a member of the WiMAX Forum.

SkyPilot's Jenkins added, “What we're doing now is a Wi-Fi metro mesh architecture that will evolve to WiMAX. WiMAX will become the mesh backhaul, and Wi-Fi will provide the access to clients.”

Strix, which currently offers a dual-band radio mesh, announced in early October it will also use WiMAX in its dual-radio approach (As with SkyPilot's system, 2.4 GHz is used for access while 5.8 GHz is used for backhaul). Furthermore Strix uses a frequency division duplexing scheme for mesh, with dedicated radios for transmitting and receiving. This helps keep latency to minimal levels and allows it to minimize network points of presence (to the transport network) down to one for every 60 Wi-Fi nodes, according to Cyrus Irani, vice president of advanced development and strategy.

Irani said that Strix doesn't consider WiMAX a superior technology to Wi-Fi when used in a mesh network, and Strix is capable of getting WiMAX-like performance using optimized 802.11g technology. But there are benefits to WiMAX in that it can be deployed over licensed spectrum, which will be in far greater demand when wireless local area network and metropolitan area network unlicensed frequencies start getting very crowded, Irani said.

The unlicensed 5.8 GHz and licensed 3.5 GHz bands are the first ones being targeted by the WiMAX Forum in its ongoing product certification process.

Regardless, the use of multiple bands in a single WiMAX/Wi-Fi mesh environment will provide important service benefits for service providers.

“You really can't use one radio for access and for backhaul as well; you need a second radio,” said MetroFi's Haas.

MetroFi is currently using SkyPilot's new SkyExtender DualBand system in deployments in Santa Clara and Cupertino in California, and Haas said he eventually wants to evolve the company's backhaul method to WiMAX.

A WiMAX backhaul solution also would have an economic edge to which all municipalities and their network builders can relate. Wireless backhaul overall is usually much less expensive than using a T-1 or fiber link for backhaul, and it gives service providers an operational cost savings that ultimately translates to lower-cost service.

“We have to sell broadband for $20, and that's the reality of the situation,” Haas said. “If you've got radios that provide 400 square feet to 600 square feet of coverage, you'll need 20 to 30 radios per square mile, and then you've got backhaul.”