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A detailed look at the technologies and techniques needed to operate fixed broadband wireless access networks
In today s fast-paced corporate environment, it s more important than ever to be able to access data and communicate information from any location at any time. In turn, an increasing number of companies are taking advantage of fixed broadband wireless (FBW) solutions. With this comprehensive guide, you ll discover the technologies required for FBW and learn how to plan, deploy, and manage an access network. Based on his extensive experience in the field, Oliver Ibe begins by explaining the strengths and weaknesses of other leading technologies such as the cable network and DSL. He then explores all aspects of FBW, detailing everything from access and service provider networks and traffic models to quality of service, security issues, and emerging standards. He also uncovers the ATM-based and DOCSIS-based solutions as well as the time division duplex channel and the frequency division duplex channel access schemes. In addition, he provides a comprehensive look at the design solutions for delivering FBW services.
Throughout the book, Ibe presents both the theory and the practice of FBW access networks. Inside, you ll also find in-depth discussions on:
• Hamming, cyclic, BCH, Reed-Solomon, shortened cyclic, and turbo codes
• Issues in wireless MAC protocol design
• Duplexing techniques and frame formats
• Wireless ATM network architecture
• Wireless modem requirements
• Service provisioning in ATM-based networks
• Implementing VPNs and VLANs in FBW access networks
• Issues in FBW access network management
|Product dimensions:||7.52(w) x 9.20(h) x 0.66(d)|
About the Author
OLIVER C. IBE is the Chief Technology Officer of Sineria Networks, a wireless LAN solutions company. He previously worked for Digital Equipment Corporation and GTE Labs as a senior member of the technical staff; Cabletron Systems, Xyplex Networks, and NetSuite Development Corporation as senior network architect; and Adaptive Broadband Corporation and Spike Broadband Systems as the director of network architecture. He received his ScD degree in electrical engineering from the Massachusetts Institute of Technology.
Read an Excerpt
Fixed Broadband Wireless Access Networks and Services
By Oliver C. Ibe
John Wiley & SonsISBN: 0-471-23285-8
Chapter OneOverview of Fixed Broadband Wireless Access Networks
The explosive rate of growth of the Internet has led to a high demand for bandwidth. Prior to 1996, Internet access for residential users was almost exclusively made via the public switched telephone network (PSTN). Such access was made via modems running at 28.8 kbps or less over the twisted copper pair. Unfortunately, even today anyone connecting to the Internet via slower telephone modem connections will not fully utilize and enjoy what the Internet has to offer. In particular, such new applications as video conferencing, streaming video, and dynamic Web pages demand high-speed broadband access. Also, accessing the Internet via the PSTN stresses the network switches, which are optimized for short holding times for voice calls and not designed for the long holding times associated with Internet access.
The Telecommunications Act of 1996, which triggered deregulation of the telecommunications industry in the United States and many countries around the world, led to the development of several last-mile solutions to relieve the PSTN switches of the data traffic. These solutions include the digital subscriber line group of technologies that are generally referred to as xDSL, hybrid fiber coaxial (HFC) network, fiber-to-the-home (FTTH), and the fixed broadband wireless access network. These solutions haveone thing in common: They are broadband solutions, which means that they have the potential to provide data rates of at least 1 Mbps to the user. Also, they are always-on Internet access technologies. Thus, they have the potential to meet the growing demand for multimedia and voice applications.
Fixed broadband wireless access networks, which are sometimes referred to as wireless DSL, use high-frequency radio connections between two or more fixed sites to send and receive data, voice, and video traffic in a manner similar to wireline networks. These networks differ from mobile wireless by the fact that the endpoints in fixed wireless solutions are stationary and therefore less susceptible to the bandwidth and quality limitations associated with mobile wireless networks.
Benefits of Fixed Broadband Wireless Access Networks
As stated earlier, fixed wireless access networks represent one of many alternative last-mile solutions. Other solutions include xDSL, HFC, FTTH, and direct broadcast satellite. These solutions are illustrated in Figure 1.1.
The xDSL technologies are based on the twisted copper pair used to provide plain old telephone service. They can be provisioned for a distance of at most 18,000 feet (i.e., 3.4 miles) from the central office. However, this is not 3.4 miles as the crow flies, but 3.4 miles of cable run. Thus, a user may be within the 3.4 miles from the central office and still not be qualified to receive xDSL service. Also, the bandwidth available to each user of the service depends on how far the user is from the central office. In general, the farther a user is from the central office, the smaller the bandwidth available to that user. Furthermore, the service depends on the telephone infrastructure, which, in most cases, involves aging lines that need to be reconditioned. Thus, even though telephone service is ubiquitous in many countries, xDSL may not be available to all telephone subscribers due to poor telephone line conditions. Finally, deployment of xDSL is predicated on the availability of twisted pair cable from the user's home to the central office. Any user whose signal has to pass through optical fiber before reaching the central office does not qualify for the service. Incumbent local exchange carriers (ILECs) are more likely to offer xDSL services than any other service provider.
HFC is derived from the cable TV network and provides a two-way communication between the headend and the subscriber. It is a shared-medium technology that is primarily a residential access technology. Like a conventional local area network (LAN), the performance is a function of the number of active users. Also, it provides asymmetric service, with more traffic coming downstream from the headend to the users. HFC network services are exclusively provided by the cable network operators.
FTTH can provide up to OC-3 data rates to a user. However, fiber is expensive to install. Moreover, many communities have very stringent trenching laws that make it difficult to deploy FTTH in such communities. Thus, its availability is currently limited.
Broadcast satellite uses a low-orbit satellite to provide Internet access. It has the advantage of being available almost anywhere, which makes it a good candidate for point-to-multipoint applications. However, while the downstream path is a direct broadcast from the satellite, the upstream path from the user to the service provider uses a conventional phone line. Thus, it provides asymmetric service. Also, it does not provide a large bandwidth in comparison to other technologies.
Fixed broadband wireless access networks have several advantages over these alternative solutions. First, there are many places that do not have access to the last-mile access technologies discussed earlier. These include rural areas with low population density, remote geographical areas, and urban areas with aged communication infrastructure. Many Third World countries lack the basic telecommunications infrastructure required to support advanced communications systems. This lack of basic infrastructure, which is sometimes coupled with inhospitable terrain, makes conventional solutions prohibitively expensive and slow to deploy. Such places are good candidates for the fixed wireless broadband access solution, which can be deployed more rapidly than any of the other technologies. Even in those places where the other access technologies can be deployed, it is always easier to set up a fixed wireless access network than any other solution.
Also, fixed wireless access networks are more flexible than other technologies. Because today's Internet traffic seems to be asymmetrical, with more traffic coming downstream to the user than going upstream, most of the other solutions have been designed for today's applications; that is, to provide asymmetrical traffic. If the traffic pattern should change in the future to a method such as voice over IP (VoIP), which generates symmetrical traffic, these services will require a major overhaul of the system. With fixed wireless access networks, the use of such channel sharing schemes as time division duplex (TDD) makes it possible to quickly assign more channel capacity to the direction where it is needed most. (TDD is discussed in Chapter 6.)
A fixed broadband wireless access network does not require twisted pair conditioning, and the service provider does not have to worry about the 18,000-foot distance limitation, which are two problems associated with xDSL. Similarly, a fixed broadband wireless access network does not require costly filters needed to subdivide the cable, as in HFC. Because fixed wireless access networks are deployed in cellular configurations, all that is required is a transceiver arrangement at the customer's premises that is pointing toward a transceiver at the base station.
The fixed broadband wireless access network infrastructure can be deployed rapidly since it does not require running cables or wires to individual customers. Also, it does not require investment in labor-intensive tasks, such as digging trenches to bury cables. Once the base station is set up, the service provider can begin providing service to customers. This means that the service provider generates revenue quicker with fixed broadband wireless access networks than with any other competing last-mile access technology.
The fixed broadband wireless access network infrastructure is scalable, because the service provider does not need to overbuild the infrastructure to make it possible to connect every potential customer in an area prior to delivering service. The service provider can start with one segment of the coverage area, which is called a sector. Then as the need arises, new sectors can be added at the base station without impacting the existing customers.
The fixed broadband access network is simpler to maintain, and problems are more easily isolated and corrected than in other last-mile technologies. It is more reliable because there are no wires between the headend and the user that can be cut either accidentally or intentionally. This is particularly advantageous in hostile environments where an enemy can disrupt communication by downing telephone poles or cutting cables and wires. Thus, fixed broadband wireless access networks provide better customer service and lower maintenance costs.
The preceding facts account for the popularity of the fixed broadband wireless access network among the competitive local exchange carriers (CLECs) for both Internet and voice traffic services, as well as its increasing popularity in countries and areas that currently lack the basic telecommunication infrastructure. Table 1.1 summarizes the features of the various last-mile access technologies. In the table, SOHO stands for small office/home office.
Like high-speed cable and xDSL services, but unlike a dial-up modem service, the fixed broadband wireless access network provides an always-on Internet-access service. Typical applications are discussed next.
Multitenant Unit/Multidwelling Unit (MTU/MDU) Services
With single customer premises equipment (CPE) on a single building and existing coaxial cable or telephone lines, a service provider can provide broadband wireless access to the Internet for the tenants of the building. As will be discussed in Chapter 8, using the current twisted pair telephone lines the service provider can use a mini-DSL access multiplexer in the basement of the building to provide xDSL services that are not encumbered by the distance limitations.
Corporate Converged Networks
Fixed broadband wireless access networks enable service providers to build converged networks that permit voice, video, and data to be integrated onto one network. This makes possible such advanced applications as unified messaging, Web conferencing, and enhanced call-center systems.
Wireless Local Loop
In its original meaning, wireless local loop (WLL) refers to the solution that uses fixed wireless access networks to provision local-loop services (or connect the user to the PSTN). WLL is particularly attractive in the following scenarios:
* Places that require rapid telephone deployment but lack basic telephone infrastructure to the customer premises
* Places where the terrain is hostile or rocky for laying telephone cables
* Places where CLECs are compelled to deploy local-loop facilities to bypass the ILECs
The fact that the fixed broadband wireless access network is a packet-switched network enables the service provider to provision voice over IP (VoIP) service, which is currently less expensive than traditional circuit-switched telephone service. Along with VoIP, the service provider can bundle enhanced services that are not easily available in traditional circuit-switched telephone service.
Fixed wireless access networks can be used to provide wireless cable television service. One of the services defined for the multichannel multipoint distribution service (MMDS) is that of providing TV services in competition with the cable operators. MMDS is described later in this chapter.
A fixed broadband wireless access network is essentially a sectorized network that consists of two principal components: the customer premises equipment that enables a user in the customer's network to access wide area network (WAN)-based services, where the WAN is usually the Internet, and the base station that controls the CPEs within a coverage area. The base station consists of many access points or wireless hubs, each of which controls the CPEs in one sector. The access points are connected to a multiplexer, such as a switch, which aggregates the traffic from the different sectors and forwards it to a router that is connected to the service provider's backbone IP network.
The distance between the CPE and the base station depends on how the system is designed and the frequency band in which it operates. If it is designed as a line-of-sight (LOS) system, the distance is generally less than 5 miles. Typically systems that operate above the 20-GHz band are LOS systems. However, most of the early deployments of fixed broadband wireless access networks were based on LOS technologies because, even at the time of writing, non-line-of-sight (NLOS) systems were still very expensive to deploy. If the system is designed as an NLOS system, the distance between the CPEs and the base station can be up to 35 miles. NLOS systems use more advanced modulation schemes to overcome the transmission impairments that are discussed later in the book.
The air link capacity available to each sector depends on the modulation scheme used. As will be discussed later in the book, the most commonly used modulation schemes are the quaternary phase-shift keying (QPSK) and different variations of the quadrature amplitude modulation (QAM), the more commonly used being 16-QAM and 64-QAM. QPSK is mainly used in the upstream direction, which is the direction from the CPE to the base station, and 64-QAM is used in the downstream direction (or the direction from the base station to the CPEs). The 16-QAM can be used for either direction. In the QAM nomenclature, the numeral is called the modulation order; thus, the higher the modulation order used, the greater the data rate that the system can support. QPSK is functionally identical to 4-QAM, which means that it has a lower modulation order than 16-QAM.
Figure 1.2 shows the fixed broadband wireless access network architecture. It illustrates the components of a typical sector of the network. The wireless hub provides a wireless interface for receiving data from and transmitting data to the CPEs. The wireless hub is connected to the backhaul router via a switch. The switch can be an Ethernet switch or an asynchronous transfer mode (ATM) switch. The router is the default gateway to the Internet and to the service provider's IP backbone network. Note that there are three component parts of the CPE: the modem, the radio, and the antenna. The modem provides an interface between the customer's network and the fixed broadband wireless access network, while the radio provides an interface between the modem and the antenna. Some vendors integrate two or all of these components to form a compact CPE, while others have the three units as standalone systems.
Excerpted from Fixed Broadband Wireless Access Networks and Services by Oliver C. Ibe Excerpted by permission.
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Table of Contents
Overview of Fixed Broadband Wireless Networks.
Radio Communications Fundamentals.
Modulation Schemes for Wireless Networks.
Improving Wireless Channel Reliability.
Wireless Medium Access Control Protocols.
Radio Frequency Systems Engineering.
Fixed Broadband Wireless Access Network Services.
Fixed Broadband Wireless Access Network Planning.
Fixed Broadband Wireless Access Network Management.