Wireless MANs

There's an increasing interest in the application of wireless technologies to MANs, particularly in line with wireless local loop deployments, delivery of Internet access and high-speed video transmissions, and the new role of wireless competitive local exchange carriers (CLECs).

The range of MANs is up to 30 miles (50 kilometers). The configuration can be point-to-point or multipoint. The data rates for MANs are low to medium; 9,600 bps up to 128Kbps is typical but in some arrangements, such as with the use of VSAT, up to 512Kbps may be feasible. Wireless LANs make use of both the licensed (800MHz to 935MHz range) and unlicensed (2.4GHz) bands. The technologies used to facilitate wireless MANs include microwave, infrared laser, and spread spectrum solutions.

Wireless Local Loop Applications

You can think of wireless local loop as an application. It doesn't speak to a particular technology. Various wireless alternatives can be deployed in order to activate the equivalent of the twisted-pair local-loop subscriber line. There are two major categories of wireless local loop:

Fixed wireless local loop Fixed wireless local loop involves a stationary installation. The main purpose is to dramatically reduce the cost of installing and maintaining the local loop plant, or subscriber lines. Distance in fixed wireless local loop is cost-insensitive, which is one of the advantages of this deployment. It is particularly used to provide the last mile/kilometer of connection, and the key advantage of the fixed-type category is that it uses a fixed antenna location, so it's relatively easy to use for traffic engineering, and it makes use of AC power.

Mobile wireless local loop Mobile wireless local loop involves the use of cellular telephone or cordless technology, along with satellites. This approach enables subscriber mobility, so you could use it as a replacement for a fixed line when you're in your home, but you could also move outside those boundaries and use it as a mobile line. The advantage is that you get greater roaming capability, but then you face a challenge in terms of traffic engineering, and the infrastructure design is more difficult than that of fixed wireless local loop.

Key applications for wireless local loop include addressing the needs of remote, rural, or isolated regions. It is also useful where rapid deployment is required. Wireline facilities require a minimum of 9 months for deployment, and many times it's 12 to 18 months, whereas with wireless techniques, deployment times are only 3 to 6 months. Another application for wireless local loop is for industrial or commercial sites, where there may be a need for temporary setups. Emergency and disaster relief are also greatly facilitated with wireless local loop systems for example, where there's been a hurricane, an earthquake, or another major disaster that disables the land-based facilities. Other potential applications include data collection and telemetry, surveillance, security, pay phones, and kiosks.

One thing to bear in mind is that as you go forward, whatever technology you consider should be looking forward to handling nonvoice traffic. As mentioned many times throughout this book, the major type of traffic growth is in the area of data, and increasingly it will also include more complex objects, such as images and full-motion video. So be sure to account for this data traffic as you're choosing a long-term solution.

Wireless Local Loop Options

Cellular, PCS, Local Multipoint Distribution Service (LMDS), Multichannel Multipoint Distribution Service (MMDS), and Direct Broadcast Satellite (DBS) are the main options in wireless local loop technologies:

Cellular Cellular is the best option in a rural area or an area that is not densely populated, where large distances separate subscribers. In this environment, you need the advantages of a large cell size and, hence, the cellular architecture serves well.

PCS PCS is best for metro areas that are densely populated because it works at a high frequency over a small coverage area, so the frequencies can be reused more frequently and can address growing metropolitan populations.

LMDS LMDS is not really intended to support mobile applications, but it is seen as being a good alternative for supporting very-high bandwidth, and it's aimed at both voice and high-speed data access. The key concern with LMDS is that it operates in a very high portion of the microwave frequency band, making it easily obstructed and suffers great distortions in the face of adverse environmental or weather conditions.

LMDS is terrestrial line-of-sight microwave, but it operates in the 10GHz to 45GHz range, depending on where in the world you are. A large frequency allocation of 1.3GHz operates in smaller microcells of 0.5 to 3 miles (1 to 5 kilometers), and within each system, it has the capability to serve 5,000 to 10,000 homes. Key applications of LMDS are wireless local loop, high-quality telephony, Internet access, two-way video, and security and energy management systems. LMDS promises downstream rates in the range of 51Mbps to 155Mbps and a return link of 1.5Mbps. But remember that the key issues here include frequency stability, interference from foliage, and rain fade. It appears that the first market for this service will be the business realm, rather than consumers.

MMDS MMDS involves terrestrial line-of-sight microwave. Because it is microwave, it does suffer from environmental interferences. But because it operates in the lower part of the frequency band, the 2GHz to 3GHz range, it is more tolerant of adverse conditions than its colleagues that operate at the higher bands (including LMDS). Again, operating at lower frequencies also means that it can have a larger range of coverage, and we're looking at a coverage cell of some 30 miles (50 kilometers).

MMDS can support up to 33 analog channels and more than 100 digital channels for purposes of digital TV. An MMDS set-top uses MPEG-2 for video compression decompression and MPEG-2 carries entertainment-quality video, at 6Mbps. MMDS is also referred to as wireless cable TV because it competes with cable television. It is one technique for providing fixed wireless access to the Internet, as well as two-way data services.

DBS DBS includes products such as Hughes DirectPC. This is not the same thing as Direct TV; DBS involves a different dish, a 21-inch dish. It provides for 400Kbps downstream from the Internet, and the reverse channel is the telephone subscriber line. DBS involves costs of around US$300 to US$500 for the equipment and a monthly charge of up to $40 per month. Hughes also recently announced DirectDSL, which offers ADSL downstream data rates. DBS can do well at delivering bulk volumes of data because of the high-speed downstream channel, and it should also eventually be capable of supporting multimedia. In the next year, new DBS systems will be making a significant difference. For example, AOL has a US $1.5 billion stake in Hughes Electronics (with two-way service planned for 2002), Wild Blue (formerly iSky; due to launch in 2002), Globalstart, and StarBand (a joint project of Gilat Satellite, Microsoft, Echostar and ING Furman Selz) are all moving in the DBS arena.

DirecTV Duo DirecTV Duo combines digital video programming and Internet access. In the next year or so we can expect to see several two-way interactive satellite systems being introduced that involve some very interesting partnerships.

Broadband capabilities at the local loop need to be supported by wireless alternatives, as well as by wireline. One option is to implement a point-to-multipoint topology that makes use of broadband technologies operating in the megabits per second range. Such a system would be capable of supporting Internet access as well as providing for VoIP. An advantage here is the greatly reduced cost for consumer traffic, and, ultimately, also for more interesting applications such as where voice becomes part of a greater set of applications that include data and multimedia.

Wireless CLECs play a big role in this arena, and the key issue is speed of deployment. Another important issue is the ability to deploy what are viewed as high-bandwidth data services for businesses on a reduced-cost basis. The wireless CLECs look to provide data rates of 56Kbps up to 45Mbps, which are normally associated with private-line alternatives. A popular band for this is 38GHz, but the actual spectrum allocation varies, depending on where you are in the world. Again, the wireless CLECs are business-oriented. They promise to lower the installation time and cost as compared to wire or fiber alternatives, and some of them will extend their offering to include wired facilities. But keep your eye on this space as there are continually new developments in broadband wireless, including the use of Free Space Optics, which is covered in Chapter 13, "Broadband Access Solutions."