First off, let’s get the definitions straight. WiMax, which stands for Worldwide Interoperability for Microwave Access, is a WAN technology that can beam broadband signals up to 50 kms from a mobile tower.
The 802.16 standard, which the WiMax Forum industry group is pushing, is designed to operate in unlicensed or licensed frequencies from 2GHz to 66GHz. It’s being touted initially as a last-mile alternative to DSL and cable modem. Ultimately, WiMax proponents see it as the basis for ubiquitous, continuous mobile wireless connectivity.
Picture mobile workers with dual WiMax/Wi-Fi cards on their laptops. They connect via WiMax while moving and switch to Wi-Fi at a hotspot or inside a Wi-Fi-enabled building. While WiMax is designed for long-range, high data-rate communications, ZigBee is at the other end of the scale, offering low data rates at short distances.
The ZigBee Alliance is the driving force behind the 802.15.4 technology, which operates in unlicensed spectrum, including the crowded 2.4GHz band. It can transfer a mere 250kbps of data within a range of 10m to 60m.
The big plus for ZigBee is that it requires minimal power, which means a ZigBee-based device could run for as long as five years on a single battery. The Alliance sees ZigBee playing a role in mesh wireless LANs, wireless desktop peripherals and industrial sensing devices that can be monitored wirelessly across a network.
The 802.16 standard aims to initially compete with DSL and cable modem services. It is expected to solve some problems that faced the multipoint multichannel distribution system (MMDS) license holders who tried to build a market in the mid-1990s, and current small operators using 802.11 to bridge the last mile.
From a single base station, an antenna can transmit as much as 75mbps of bandwidth for 3-5 kms. Throughput declines as the distance increases, but proponents say a WiMax signal can extend as far as 60km, depending on how wide a spectrum band is used.
“The demand for broadband is ever marching onward,” said Carlton O’Neal, vice-president of marketing for Alvarion, a developer of point-to-multipoint wireless systems.
“At the same time, the big carriers say they can do DSL and cable to X per cent of their users but they can’t do it to all,” he said.
With 802.16, those operators and others could use licensed or unlicensed bands to reach customers they can’t serve with the other technologies.
Industry observers have high hopes for 802.16. A recent study from ABI Research reports that broadband wireless equipment sales should surpass $US1.5 billion by 2008, mostly because of WiMax.
As with any attempt to create a standard, there are hurdles that need to be overcome.The 802.16 effort is a confusing alphabet soup, but proponents hope to converge various subsets under one all-encompassing WiMax label.
For example, 802.16a added the 2GHz to 11GHz bands to the original 802.16 proposal, which spanned frequencies from 10GHz to 66GHz. The 802.16a standard was ratified in January, but it doesn’t solve one of the main problems — expensive customer installation — that caused the MMDS market to fizzle in the mid-1990s.
MMDS operators spent as much as $US3000 per customer setting up external antennas on customer homes or offices, an analyst with The Yankee Group, Lindsay Schroth, said. “It was so difficult to get a return [on investment] so we saw them pull out of the market.”
The next version, 802.16d, eliminated the need for an outdoor antenna and would let vendors build PC cards to the standard so customers could access service anywhere there was coverage, vice-president of business development for Alvarion and a WiMax Forum board member, Mohammad Shakouri, said.
The WiMax Forum expected to start certifying 802.16d products in the second half of this year, and live networks might become available at the end of next year, Schroth said.
Not until 802.16e, however, will the standard support handoffs between base stations, making it truly mobile. While the WiMax Forum has more ambitious goals for the standard’s completion date, Schroth doesn’t expect certified products to hit the market until 2006 or 2007. Once the 802.16e standard was complete, the lettering system would disappear and all gear would be known just as 802.16, Shakouri said.
Intel said it hoped to see laptops with Wi-Fi and WiMax built in so mobile workers could use WiMax most of the time but switch to local-area Wi-Fi networks where available because they might offer higher capacity.
The 802.16 standard effort has significant momentum behind it, partly because of the WiMax Forum and Intel’s interest in the standard, but it still faces challenges. Even though AT&T and Covad Communications recently joined the WiMax Forum, no operator has officially signed up to build a network using the technology. In addition, a somewhat parallel effort is underway in the IEEE, the 802.20 standard, which is creating some confusion in the market. Mobile Broadband Wireless Access, or 802.20, is designed to provide broadband data in a mobile environment. The technology will operate in the under-3.5GHz spectrum bands and is supposed to deliver service at up to 256km per hour. It is possible to envision 802.20 being used to provide broadband access to mobile users in trains, for example. “(802.16)e and (802.)20 were born at sort of the same time in an acrimonious process,” said Marc Goldburg, CTO of ArrayComm, one of the founders of the 802.20 movement, along with Flarion and others.
From laptops to light bulbs
The 802.16 proponents point out how far ahead of the development curve they are than 802.20, which is far from being finalised as a standard.
The 802.16 developers might have a leg up in that they’ve already built the basis for 802.16e, but that can also be a hindrance.
There are a variety of possible uses for ZigBee technology. An 802.15.4 network can be arranged in a number of ways, but one option is a wireless mesh, with gateways scattered where necessary. “In mesh, control is de-centralised so there’s no single point that all information has to flow through,” CTO for Ember Corporation, Robert Poor, said. “Therefore, gateways can be plunked down anywhere opportunistically.”
One of the simplest applications that will employ 802.15.4 is lighting control. Instead of stringing wire behind walls to connect a switch to a light, an 802.15.4 radio in a battery-powered light switch could communicate with a radio on a light bulb in a fixture.
A division of Royal Philips Electronics NV is building 802.15.4 chips into certain types of lights.
The efficient power consumption of the technology means that switches, with their limited battery power, can sleep most of the time. They only turn on when switched, which wakes up the radio long enough for it to communicate with the nearest lamp. The lamp is plugged into a power source so the radio on the light bulb could be always on, listening for activity. If the closest lamp to detect communication from the switch isn’t the lamp the switch aims to turn on, it still works.
“That’s relayed through the network to the lamp that needs to go on,” Poor said.
Developers argue that building managers can use the technology to significantly cut down on energy costs. In an office, instead of hard-wiring one light switch to a dozen lights that might shine over a dozen cubicles, the lights over each cube could be wirelessly attached to a light switch that each worker can control in each cube.
Industrial businesses could use 802.15.4 to monitor all sorts of equipment, including meters.
Bluetooth couldn’t be used for these applications because it didn’t have efficient power consumption and each Bluetooth radio could talk to just seven other radios, Virk said.
But 802.15.4 might have its own set of political troubles slowing it down. Some of the architects of the standard created the ZigBee Alliance to narrow the specification so vendors could build interoperable products.
But makers of certain applications might prefer not to be interoperable with other products.
As a result, 802.15.4 is built so that data from a proprietary system can be passed along a standard ZigBee lighting system, for example, to build the most efficient network.
The ZigBee Alliance has set up a program to let independent manufacturers conduct a performance test.
“As a good citizen we’re working to grow this entire ecosystem the best we can, but frankly the jury is still out on which customers will insist on ZigBee and which may prefer maybe a lighter weight or more custom profile,” Poor said.