Wireless metropolitan area networks (WMANs) enable users to establish wireless connections between multiple locations within a metropolitan area (for example, between multiple office buildings in a city or on a university campus), without the high cost of laying fiber or copper cabling and leasing lines. In addition, WMANs can serve as backups for wired networks, should the primary leased lines for wired networks become unavailable. WMANs use either radio waves or infrared light to transmit data. Broadband wireless access networks, which provide users with high-speed access to the Internet, are in increasing demand.
There are currently three different standards being researched and produced to support WMANs:
High Performance Radio Access (HIPERACCESS) is an interoperable standard tailored to give broadband access to both the home and small- and medium-sized enterprises, as well as to provide backhaul for mobile systems (e.g. W-CDMA, CDMA2000, GSM and GPRS). The ETSI Project Broadband Radio Access Networks (EP BRAN) working on the standard agreed the core technical specifications (i.e. the specifications for the Physical (PHY) Layer and for the Data Link Control (DLC) Layer) in early 2002, and is in the process of developing the convergence layer for support of different core networks, such as Internet Protocol (IP), Ethernet and Asynchronous Transfer Mode (ATM).
The HIPERACCESS standard was developed to provide a truly broadband system with bit rates of up to approximately 100 Mbit/s, although 25Mbit/sec is expected to be the most widely deployed rate. HIPERACCESS is targeted at high frequency bands, especially for the 40,5 - 43,5 GHz band. For these frequency bands TDMA will be used to provide multiple access.
High Performance Radio Metropolitan Area Network (HIPERMAN) is aimed at providing a broadband wireless solution for Metropolitan Area Networks. HIPERMAN will be an interoperable broadband fixed wireless access system operating at radio frequencies between 2 GHz and 11 GHz. The air interface will be optimized for Point-to-MultiPoint (PMP) configurations, but allows for flexible mesh network deployments as well. HIPERACCESS and HIPERMAN address the same markets but have been separated as the higher frequencies used in HIPERACCESS require different techniques to the lower frequencies used by HIPERMAN to deliver the required QoS and other system metrics.
The Institute of Electrical and Electronics Engineers Standards Association (IEEE-SA) sought to make Broadband Wireless Access (BWA) more widely available by developing IEEE Standard 802.16, which specifies the WirelessMAN Air Interface for wireless metropolitan area networks. The standard, which was published on 8 April 2002, was created in a two-year, open-consensus process by hundreds of engineers from the world's leading operators and vendors.
IEEE 802.16 addresses the "first-mile/last-mile" connection in wireless metropolitan area networks. It focuses on the efficient use of bandwidth between 10 and 66 GHz (the 2 to 11 GHz region with PMP and optional Mesh topologies by the end of 2002) and defines a medium access control (MAC) layer that supports multiple physical layer specifications customized for the frequency band of use.
The 10 to 66 GHz standard supports continuously varying traffic levels at many licensed frequencies (e.g., 10.5, 25, 26, 31, 38 and 39 GHz) for two-way communications. It enables interoperability among devices, so carriers can use products from multiple vendors and warrants the availability of lower cost equipment. The draft amendment for the 2 to 11 GHz region will support both unlicensed and licensed bands.
There are two basic types of WMANs: back haul and last mile.
Back haul is for enterprise networks, cellular-tower connection and Wi-Fi hotspots. It's an option for enterprises that can't afford to install or lease fiber to connect their facilities over a large campus or city. Back-haul WMANs also make sense when you can't justify a service provider's fiber 10-Mbps connection that requires six T1 leased lines at $50,000 a year. Fixed wireless is about half that price, without a monthly charge.
Although DSL or T1 work for back haul, a private broadband wireless system often provides 10 times faster transmissions. Capital and installation costs are about five times higher, but you get an ROI in just a few months. To interconnect a few sites, you can install one or more wireless PTP (point-to-point) links; for more sites, a private multipoint WMAN usually makes more sense.
Wireless back haul has the greatest short-term appeal, but last-mile solutions could establish wireless as an alternative to residential broadband DSL/cable modem. Some wireless ISPs, including TowerStream Corp., compete head-on with broadband, offering quick installation and lower cost, as well as wireless Internet service in areas without access. Last-mile WMANs are handy for temporary networks, too, such as large construction sites or areas where conventional network service is disrupted.
There are several models for metropolitan area networks. The simplest and most common (and not metro-wide at all) is the downtown hotzone. A hotzone is a contiguous cluster of Wi-Fi hotspots. Most cities set up downtown hotzones to promote themselves as business and high-tech centers. In some cities, public agencies, companies, hospitals, universities and community groups are knitting together hotspots into a network to provide broadband service to their members. The ambitions of these city projects are modest, but if they become popular, they encourage cities to expand the public access wireless network.
A few cities deploy a wireless network over a larger area, for example, a disadvantaged neighborhood. The purpose is to provide broadband service to a people whom the cable and DSL providers have abandoned. An example is Manchester 's EastServe which is deployed over a large neighborhood composed primarily of council houses and people on welfare. The ambitions of cities in building out these types of wireless broadband networks are modest and limited in scope. However, if they prove to be successful in revitalizing entire communities, they give cities another reason to invest in additional wireless broadband infrastructure.
The most ambitious type of wireless metropolitan area network is one which covers an entire city. There are already several successful city-wide networks operating in Finland , albeit in very small cities such as Vantaa and Porvoo. Truly large-scale wireless metropolitan area networks over mega-cities such as New York or Paris do not exist. There are many reasons for this. Cities do not see why they, instead of private parties, should build the network. Moreover, the costs are astronomical. Nevertheless, with the launch of several hardware products that make metro-wide wireless networks much cheaper and easier to deploy, some cities, such as New York, see the deployment of a wireless broadband network as a means for lowering the city government's massive telecommunications costs and fulfilling social/economic goals.
The advantages of using a WMAN are simple enough to distinguish. Intially, the cost of a WMAN is significantly less then fiber-based LANs for a number of reasons. WMANs extend, replaces or backs up existing fiber infrastructre within hours, saving time and money on personnel. WMANs also eliminates fiber trenching and leased line costs, a large portion of the cost in laying fiber.
Another significant advantage of implementing a WMAN is the fact that it bridges the “digital divide” by affordingly connecting communities that have not had the access to LANs and wireless internet connections.
Finally, the installation of a WMAN empowers companies, government agencies, etc. to rapidly expand their internet service into new markets and generate increased revenues.
One main disadvantage of a WMAN presents a very large area for a hacker to attempt a break in. Like any wireless access network, a wireless access point is a tempting target for someone to hack into a secure network. A WMAN is simply a larger WAN footprint, and thus presents a larger opportunity for a hacker.
Below are descriptions of the different types of wireless networks deployed in various cities.
Examples of downtown hotzones
- Hamburg : Germany 's biggest non-commercial WLAN. It is the centerpiece of the Hamburg -Always On program, which is run by Hamburg@work, Deutsche Telekom, Fujitsu Siemens Computers, Datenlotsen Information Systems and Siggelkow Computers. Hamburg@work is the city's initiative for new media, IT and telecommunications. According to the Hamburg@work, it is the most comprehensive free WLAN at the municipal level. There are about 41 hotspots with more planned for 2003 and 2004. Recently, Hotspot Hamburg added the luxurious Hotel Vier Jahreszeiten to its network. Guests and visitors enjoy free wireless access to the Internet in all of the hotel's rooms, in the lobby, convention areas, and the Indochine Bar. How does Hotspot Hamburg work? Locations such as restaurants, cafes, libraries and hotels receive the necessary hardware and software for free from the sponsors. The locations pay the ongoing volume-based charges for the T-DSL line which start at 50 Euros per month including 5 gigabytes of data volume. Each location has a special HOTSPOT HAMBURG logo indicating its participation in the network. The sponsors finance the hardware, installation, service and support for the individual WLANs and in return receive exclusive advertising space in the welcome screens, marketing materials and online sites. Travelers often look for Hotspot Hamburg locations signs first before going to locations that make them pay for access.
- Bochum : The Bochum downtown hotzone initiative is called "Kabel ab" (without cable). The network went live in May 2003 and boasts fifty hotspots in the Bermuda Dreieck (Bermuda Triangle) area which has a lot of cafés and beer gardens. Unlike Hamburg Hotspot, the network plans to charge for Wi-Fi access in the future, although for now, it is free. There are no connect time or data volume limits, but you do have to get a pre-paid scratch card (although this is still for free) with a personal code to use it. Bochum will add railway stations and the airport to the network soon. Kabel Ab is a joint venture among the City Council, TMR (local telco operator funded by local electricity companies and savings bank), Intel and the Bochum tourist information service (Bochum Marketing).
- Skellefteå ( Sweden ): Residents have access to wireless broadband connections at the city center, the campsite and sports complex. Next in line are the airport, hotels, golf course and other facilities. This is a project of Mobile City , conceived two years ago in Sweden , which is dedicated to research, testing and prototype development in wireless communications. The project has received financing from the EU structural funds, the County Council of Västerbotten and Skellefteå Municipality .
- Hasselt : city-wide public wireless access, according to Sinfilo, a Belgian wireless LAN operator. Sinfilo will be building out the network for the city and maintaining it as well. The first phase of the project consists of creating a wireless network in the city's main square, the Grote Markt. The later phases will expand wireless access throughout the city.
- Wellington (New Zealand): 100 hotspots and by November this year, the Wi-Fi service called CafeNet, will be available as well in Lambton Quay, the train station and other busy locations. CafeNet was set up by CityLink, a fibre optic network operator that was originally established by the Wellington City Council in 1995, but is today privately owned (although it has received recently $95,000 from the City Council to expand the CafeNet service). Like other municipalities setting up hotzones or building an entire wireless broadband infrastructure throughout the entire city, Wellington 's purpose in supporting CityLink is to promote economic development and make it more attractive for technology industries and workers.
- Adelaide ( Australia ): Australia 's largest public access wireless network is in its central business district and north Adelaide with 40 access points, each with a range of 200 meters line of sight. One of the reasons for setting up the network is to boost the state's IT reputation, and provide more opportunities for local startup companies. Many of these hotspots use city infrastructure such as traffic lights and lamp posts, identifiable by the citilan decal. They claim that anyone using a laptop or personal digital assistant (PDA) enabled with a wireless card within range of these emblems will be able to access citilan and roam across the city while still connected. The network is the result of a partnership among the Adelaide City Council, service providers Internode/Agile and AirNet, Cisco, the South Australian Government and mobile broadband consortium m.Net Corporation.
Other cities that launched hotzones (recently reported on Muniwireless.com) are: Bellevue ( Washington state), Milwaukee , Cleveland , St. Louis , Baton Rouge ( Louisiana ), Portland ( Oregon ), Baltimore and Pittsburgh .
The next step for the 802.16 working group is to add portability and mobility to the standard. In March 2002, the working group began the 802.16e Study Group on Mobile Broadband Wireless Access. This group will address many different mobility issues, including providing connectivity to moving vehicles within a base station's sector.
Additionally, a further improvement to the WMAN technology is the improvement to the range provided by the access points.
Wireless networking overview
HiperACCESS & HiperMAN
IEEE 802.16 Backgrounder (24 May 2002)
Metropolitan Area Networks: Challenges and Wireless Solutions
Compiled By: Andrew Draker
Posted in: May 2005