Since the first short-range wireless networking technologies arrived in the
late 1990s, one standard has climbed to the top. Wi-Fi, also known by the IEEE
standard designation 802.11, maintains its domination over the world of computing
and electronics in general.
Yes, Bluetooth has it beat in terms of total deployment and chips sold, thanks
to its incorporation into a few jillion cell phones. But with over 120 million
chip sets shipped in 2005 and over 90% of all laptops enabled with the technology,
Wi-Fi has changed the way we network and use computers. Seemingly everyone's
laptop is wirelessly linked to company networks, home networks, and public access
points.
The cool thing about Wi-Fi is how it has developed over the years. Each new version of the standard boosts its operating range, data rate, reliability, and security. But that's not all. Wi-Fi continues to progress on numerous fronts, including work in some unexpected areas. In fact, there are five keys to its success.
1: CONTINUOUS STANDARD DEVELOPMENT
A quick history lesson of 802.11 reveals a progression of speed increases and
other improvements over the past 10 years (Table
1). Many older, original 802.11b products are still in play. However, most
wireless connectivity today is achieved through the latest standard, 802.11g,
which provides up to 54 Mbits/s in the 2.4-GHz band.
Maximum range is about 100 m, if the path is unobstructed. Most connectivity is in an obstructed multipath environment, though, so the rate backs off automatically to a much lower number (about 20 Mbits/s) with a range far less than 100 m.
The 802.11n standard promises data rates in excess of 100 Mbits/s using multiple-input/multiple-output
(MIMO) technology (see "How MIMO Works," ED Online 12998, at www.electronicdesign.com).
The standard remains in draft form, but IEEE Task Group n is getting close.
Companies already are selling "draft-n" chip sets and routers/gateways. These
products mostly comply with the standard, but they may not be fully compliant
in the end. Some companies say they can bring the product into full compliance
later with a software upgrade, yet that remains to be seen.
These "draft-n" offerings are the result of the pent-up frustration with the standardization process. It takes time to reach a consensus, and in some cases, it doesn't even result in a final standard. The recent Ultra-Wideband (UWB) standard process didn't yield a final design, so the IEEE task group was abandoned. Most designers hope that won't happen with 11n, but progress has been rocky.
Back in 2005, the two primary factions for the 11n technology essentially agreed to disagree, and work on 11n slowed. Some companies like Airgo Networks decided to go ahead with their own proprietary versions and started selling MIMO chips. Most of these products are quite successful, providing user speeds in excess of 100 Mbits/s over a greater range than traditional Wi-Fi.
More recently, a group of manufacturers came together to form the Enhanced Wireless Consortium (EWC) to create a compromise version of the standard. The EWC submitted its draft to the 11n Task Group, which accepted it with an 87% vote. That draft is now working its way through the standards process, with a target date of September 2007 for ratification. With both hope and an agenda, the 11n group is confident of reaching a final version.
Meanwhile, companies like Atheros, Broadcom, and Marvell are pushing their draft-n designs. Atheros and Broadcom also recently demonstrated the interoperability of their chips as a way to kickstart the market for this standard. Airgo offers its 802.11a/b/g-compatible chips with MIMO but doesn't characterize them as draft-n. Intel, Texas Instruments, and some of the other chip companies remain rather silent on the subject.
While non-standard products can be successful, the draftnproducts won't meet the desirable goal of full interoperability among similar products. That may be okay for home networking or small business products. But widespread use in enterprise local-area networks (LANs), public hot spots, and laptop computers requires fully interoperable products.
The testing and certification process provided by the Wi-Fi Alliance now ensures that interoperability. You can't put the Wi-Fi label on your product until you pass the test, and the test is based on the standard. As soon as the standard is final, the Wi-Fi Alliance will begin its 11n program. Caveat emptor (let the buyer beware) as far as draft-n products are concerned.
Big standards efforts like 11n aren't the only reasons why Wi-Fi stays strong.
Consider all of the smaller standards efforts that have been initiated to expand,
improve, and fine-tune 802.11 (Table 2). Security
is a good example of how the 802.11 standard continues to evolve. The earlier
security part of 802.11b known as Wired Equivalent Privacy (WEP) worked well,
but few users sought to activate it in their equipment. Also, WEP using the
RC4 encryption standard could be defeated, though it takes lots of effort.
This led to vendor-developed security measures such as the Temporal Key Integrity Protocol (TKIP). The Wi-Fi Alliance adopted TKIP as Wireless Protected Access (WPA), which uses RC4 but encrypts every packet with its own key. Now, WPA has evolved into WPA2. WPA2, using NIST's Advanced Encryption Standard (AES) with a 128-bit key, has become the 802.11i standard.
2: MESH NETWORKS
In mesh networks, any wireless node can talk to any other nearby adjacent node
to exchange information. This concept lets individual nodes extend their range
by sending data to a remote node through intermediate nodes that act as repeaters
or routers.
With such an arrangement, a few nodes can provide blanket coverage over a very wide area as signals hop from one node to another. The mesh scheme also makes the whole network more reliable by providing alternate paths from one node to another, even if one or more nodes are disabled.
The mesh scheme is inherent in short-range, low-power personal-area networks (PANs) such as ZigBee (IEEE 802.15.4). Proprietary mesh networks also can provide such coverage. This permits the implementation of wireless sensor networks and networks of wireless monitoring and control in large buildings and homes. Mesh networks are inherently self-forming and self-healing.
Wi-Fi mesh networking was first used in small community wireless networks in towns that lacked any kind of formal broadband service. Now, such mesh techniques have been adopted to implement municipal (muni) networks. Cities around the country are establishing these mesh networks for public safety (fire, police, EMS) as well as public works (street maintenance, water department) communications services. They also supply broadband access to local citizens. By using many access points (APs) with a mesh software overlay, any laptop, or other 802.11 transceiver, can communicate with the system over several square miles.
The main goal of most muni meshes is to improve city government services. They give city workers access to e-mail, the Internet, and any city databases or other resources from a laptop in a truck or from virtually any location. It saves time and, it's particularly helpful to police and fire services.
Another goal is to help cities bridge the "digital divide." Most large and midsize cities offer broadband services, but they're used primarily by their more affluent citizens. Whole areas of some cities are totally without broadband access, putting the citizens in these areas at a disadvantage. With a Wi-Fi mesh, any citizen can have access.
Finally, muni meshes are intended to boost the competitive nature of the local broadband markets. Cable TV and DSL companies initially fought the muni Wi-Fi movement. Now, some are joining in to get a piece of that action.
While muni mesh networks are a recent phenomenon, there's been considerable
activity around the country. Some smaller cities are already in operation, such
as Alexandria, Va., and Tempe, Ariz. Larger cities have systems under construction,
such as Philadelphia, San Francisco, and Phoenix. Pasadena and Ripon, Calif.,
Buffalo, Minn., and Oklahoma City have systems in operation or on the way. Even
a huge city like Houston, Texas, has a system in the request for proposal (RFP)
stage.
Wi-Fi was chosen simply because it's low in cost and easy to expand. It also works in portable (not mobile) situations. The availability of mesh systems from companies like Cisco, Motorola, and Tropos makes installation fast and easy, typically as easy as bolting the AP to a light pole.
More elaborate systems like Motorola's Motomesh combine the regular 2.4-GHz
unlicensed APs with special APs that operate in the relatively new 4.9-GHz public
safety band (see the figure). This band is
intended for use by police, fire, and other emergency services during disasters
and major security events.