Introduction to Wireless Telecommunications, Network Architecture, and Functions PART 1 Source: Wireless Mobile Networking with ANSI-41 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Introduction to Wireless Telecommunications, Network Architecture, and Functions Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Basics of Wireless Telecommunications CHAPTER 1 Source: Wireless Mobile Networking with ANSI-41 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. To begin to understand the ANSI-41 signaling protocol, it is necessary to understand some basics about wireless telecommunications. This chap- ter provides a general overview of the most important concepts in wire- less cellular telecommunications that apply to ANSI-41. For some read- ers, this will be a high-level review; for others, it may clarify some misconceptions and provide an overall understanding of cellular wire- less technology that will be useful in understanding ANSI-41. What Are Wireless Telecommunications? The concept of wireless telecommunications can be viewed from two per- spectives: the wireless subscriber’s and the wireless network’s. From the subscriber’s perspective, wireless telecommunications is a service that allows telephone calls to be made or received while the telephone equip- ment moved from place to place or while it is in motion. From this per- spective, the telephone handset (known as the mobile station) is wireless and affords the ability to be mobile. From the network’s perspective, wireless telecommunications is a service provided to end-users. Wireless telecommunications, within the context of ANSI-41, is a service based on a set of functions internal to the network known as mobility management. Mobility management functions enable the network to maintain location and subscriber status information so that end-users can make and receive calls while they move from place to place. Origin of Advanced Mobile Phone System Wireless telecommunications can be considered both a system and a service. The network equipment including antennas, radios, switches, databases, and all hardware and software within the network, repre- sents a wireless telecommunications system that provides wireless telecommunications service to subscribers. The first wireless telecommunications system based on cellular tech- nology was (and is) known as AMPS (Advanced Mobile Phone System), a Part 1: Introduction to Wireless Telecommunications 4 Basics of Wireless Telecommunications Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. technology developed by Bell Laboratories in 1947. The term cellular refers to a network of small cells or radio transceivers, each providing a limited range of radio coverage, which are linked by a computer-con- trolled switching system that manages subscriber mobility and interfaces to the fixed wire-line telephone network. The technology is based on cel- lular frequency reuse (described later), providing a high-capacity system and allowing network access using low-power mobile stations (typically less than 6 W). The radio transceiver modulation methods used are based on analog frequency modulation (FM) signals similar to those used for commercial radio, but at a higher frequency range and lower bandwidth. The first commercial cellular system in the United States became operational in Chicago in 1983. However, other countries around the world provided operational cellular systems several years earlier. Today, cellular systems based on AMPS technology are implemented in more than 100 countries. It is interesting to note, however, that there is no single worldwide standard for the implementation of these cellular systems. The different systems deployed generally represent differing radio technologies, each based on the concepts of AMPS. The networking technologies used to link the cells together are also quite different. These technologies are considered supplemental to the defining charac- teristics of AMPS (i.e., cells, frequency reuse, etc.). In fact, AMPS can operate within a variety of networking schemes. Some Basic Cellular Concepts Basic Radio Technology Cellular radio technology allows a subscriber to originate and receive telephone calls wherever compatible cellular radio coverage is provided. A cell is an individual radio coverage area controlled by a radio base sta- tion (BS) system. Individual calls within a single cell use different fre- quencies. These frequencies can be reused by other cells, provided that there is no interference with the other cells. The frequency reuse pat- tern of the cells is dependent on the distance between the cells and the radio transmission power. First-generation radio technologies (AMPS-based) use signals based on analog FM for speech transmission. Subsequent generations of radio technology for wireless systems include NAMPS (narrowband AMPS), which is also based on analog FM, and a variety of sophisticated digital Chapter 1: Basics of Wireless Telecommunications 5 Basics of Wireless Telecommunications Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. technologies based on TDMA (time division multiple access) and CDMA (code division multiple access). The cellular radio spectrum (range of allowable and available radio frequencies) used for these cellular system technologies is regulated by government agencies in different countries. In the United States, cellu- lar service providers are categorized by one of two sets of non-contiguous 25 MHz radio frequency bandwidths. PCS service providers are catego- rized by six sets of noncontiguous bandwidths: three sets of 30-MHz radio frequency bandwidths and three sets of 10-MHz radio frequency bandwidths. Cellular A-band and B-band Carriers The two sets of bandwidths licensed for cellular radio service are known as the A-band and the B-band. A-band carriers are cellular service providers originally termed the nonwire line licensees. These original licensees are companies that provide cellular service and are not associ- ated with any local wire line telephone company. B-band carriers are cellular service providers originally termed the wire line licensees. These licensees are companies that provide cellular service and are associated with the local wire line telephone company (i.e., the original Regional Bell Operating Company or RBOC) in the area where they provide cellular service. The concept of A-band and B-band carriers was devised as part of the Modification of Final Judgment (MFJ) consent decree in 1982 that broke up the AT&T/Bell system monopoly in 1984. The AMPS technology orig- inally developed by Bell Laboratories was given up to the seven RBOCs as part of the compromise to divest them from AT&T. The mandated provision to allow two cellular service provider licenses in a given geo- graphic area was designed to provide competition between an independ- ent cellular carrier and the cellular carrier owned by the local wire line carrier. Note that the cellular A- and B-band licenses are allowed to sup- port analog or digital radio technologies. Figure 1.1 depicts the cellular radio spectrum licenses in use today. Part 1: Introduction to Wireless Telecommunications 6 Basics of Wireless Telecommunications Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Figure 1.1 Cellular licensed frequencies that are in use today. The A’, B’, and A” bands were originally set aside for control functions, but can be used for normal traffic. PCS A–F-band Carriers In 1994, the U.S. government publicly auctioned six new sets of nation- wide wireless telecommunications licenses. These licenses had restric- tions on who could own them different from those of the original A and B-band licenses. They were no longer limited to what type of carrier could own them (i.e., local wire line or independent wireless); rather, restrictions were put on the total number and types of wireless licenses that a single carrier could own in a given market. In the U.S., PCS service providers are categorized by one of three sets of noncontiguous 30-MHz radio frequency bandwidths or one of three sets of noncontiguous 10 MHz radio frequency bandwidths. Note that the PCS A- through F-band licenses (see Figure 1.2) are allowed to sup- port only digital radio technologies, typically operating among cell sizes of much smaller radii than analogous cellular systems. Figure 1.2 depicts the PCS radio spectrum licenses in use today. Frequency Reuse Cellular frequency licenses provide for each mobile station to occupy 60 kHz of bandwidth (30 kHz for transmission and 30 kHz for reception) within an entire radio frequency (RF) allocation of 25 MHz for each of the two cellular carriers (A and B) in a given area (i.e., 12.5 MHz for transmit and 12.5 MHz for receive for each carrier). PCS frequency licenses provide for each mobile station to occupy 60 kHz of bandwidth Chapter 1: Basics of Wireless Telecommunications 7 Phone Transmit A' band B' band A'' band A band (10 MHz) 333 - 30 KHz channels B band (10 MHz) 333 - 30 KHz channels 824 825 835 845 846.5 849 (1 MHz) 33 - 30 KHz channels (1.5 MHz) 50 - 30 KHz channels (1.5 MHz) 83 - 30 KHz channels 20 MHz between transmit groups Base Station Transmit A' band B' band A'' band A band (10 MHz) 333 - 30 KHz channels B band (10 MHz) 333 - 30 KHz channels 869 870 880 890 891.5 894 (1 MHz) 33 - 30 KHz channels (1.5 MHz) 50 - 30 KHz channels (1.5 MHz) 83 - 30 KHz channels Basics of Wireless Telecommunications Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. (30 kHz for transmission and 30 kHz for reception) within an entire RF allocation of either 30 MHz (i.e., 15 MHz for transmit and 15 MHz for receive for each carrier) or 10 MHz (i.e., 5 MHz for transmit and 5 MHz for receive for each carrier). Note that although the terms cellular and PCS differentiate categories of frequency bandwidths, PCS systems employ the same basic technology of cellular systems. Cellular systems use a technique known as frequency reuse (see Fig- ure 1.3). A particular available channel frequency is transmitted from one base station at a power level that supports communications within a moderate cell radius around that base station (anywhere from a few hundred feet to about 50 miles!). Because this transmitted signal power is controlled to serve only a limited range, the same frequency can be transmitted simultaneously, or reused, by another base station, provid- ed there is no interference between it and any other base station using that same frequency. Figure 1.3 depicts a typical cellular frequency reuse model using a seven-cell pattern that provides uniform distances for channel reuse. In the model, each base station is considered to be located at the cen- ter of a hexagon, with the hexagons (or cells) labeled A through G repre- Part 1: Introduction to Wireless Telecommunications 8 20 MHz between transmit groups Phone Transmit A band (15 MHz) 449 - 30 KHz channels 1850 D band (5 MHz) 165 - 30 KHz channels B band (15 MHz) 448 - 30 KHz channels E band (5 MHz) 165 - 30 KHz channels F band (5 MHz) 165 - 30 KHz channels C band (15 MHz) 449 - 30 KHz channels 1865 1870 1885 1890 1895 1910 Base Station Transmit A band (15 MHz) 449 - 30 KHz channels 1930 D band (5 MHz) 165 - 30 KHz channels B band (15 MHz) 448 - 30 KHz channels E band (5 MHz) 165 - 30 KHz channels F band (5 MHz) 165 - 30 KHz channels C band (15 MHz) 449 - 30 KHz channels 1945 1950 1965 1970 1975 1990 Figure 1.2 PCS licensed frequencies in use today. Basics of Wireless Telecommunications Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. senting seven channel sets. The frequencies used for the channel sets in the A cells are the same, as are the frequencies in the B cells, C cells, etc. There are many possible frequency reuse patterns. Since the total number of channels for cellular and PCS is fixed, the selection of a reuse pattern and cell size determine how many subscribers can be supported in a given service area. Available capacity, however, is much greater than the actual number of channels accessible in a given cell. This is due to the nature of end-user calling behavior: not everyone wants to talk at the same time. A cell can typically serve 10 to 20 times more sub- scribers than the total number of channels supported. Digital Radio Digital radio technologies have been developed for use on the air (or radio) interface. These can dramatically increase the number of sub- scribers supported on the range of frequencies used for wireless telecom- munications systems (note that the analog NAMPS technology also pro- vides an increase in the number of subscribers supported). The two basic types of digital technology are time division multiple access (TDMA) and code division multiple access (CDMA). Many standards exist for the use of these basic technologies. TDMA is based on the use of time-interleav- ing of multiple signals to provide an apparently simultaneous transmis- Chapter 1: Basics of Wireless Telecommunications 9 radius r D C B G A F ED C B G A F E s e p a ra tio n d is ta n c e r Figure 1.3 Seven-cell frequency reuse pattern. Basics of Wireless Telecommunications Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. sion of those signals on a single radio frequency. CDMA is based on a technique known as direct sequence spread spectrum (DSSS) that digital- ly codes a base signal and employs different signal encoding patterns and frequency hopping to redistribute that base signal across a broad range of frequencies. Logical channels for each signal are created through the use of unique code sequences. TDMA and CDMA can provide many advantages over analog-based systems. Examples are better voice quality, increased capacity, less noise and interference, and the ability to provide digital services such as data and messaging. The ANSI-41 networking protocol is designed to support versions of these newer-generation digital technologies as well as the original analog systems. Handoff Handoff encompasses a set of functions, supported between a mobile station (MS) and the network, which allows the MS to move from one cell to another (or one radio channel to another, within, or between cells) while a call is in progress. The handoff function requires sophisticated coordination between the network and the MS to transfer the MS smoothly from one radio channel to another during a call. There are two types of handoff: intrasystem and intersystem. Intrasystem handoff (see Figure 1.4) is a handoff between two cells or radio channels that subtend the same mobile switching center (MSC). In this case, no coordination is required between MSCs to support the move- ment of an MS between cells. Intersystem handoff (see Figure 1.5) is a handoff between two cells subtending two different MSCs. This type of handoff requires specialized signaling between the two MSCs to coordinate the movement of the MS between the cells. Since the ANSI-41 protocol is concerned with intersystem operations, it provides the operations neces- sary to support intersystem handoff. Intrasystem handoff is not within the scope of ANSI-41 and is handled via proprietary methods at the MSC. There are three strategies for performing a handoff: MS controlled, network controlled, and MS assisted. These strategies differ mainly in which side of the radio interface determines when to hand off the MS to another channel. MS-controlled handoff is a technique where the MS itself continuously monitors the radio signal’s strength and quality. When predefined criteria are met, the MS checks the best candidate cell for an available traffic channel and requests that the handoff occur. Network-controlled handoff is a Part 1: Introduction to Wireless Telecommunications 10 Basics of Wireless Telecommunications Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. [...]... website Source: Wireless Mobile Networking with ANSI-41 CHAPTER 2 Wireless Telecommunications Standards Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Wireless Telecommunications Standards 16 Part 1: Introduction to Wireless Telecommunications... Source: Wireless Mobile Networking with ANSI-41 CHAPTER 3 Wireless Telecommunications Network Signaling Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Wireless Telecommunications Network Signaling 26 Part 1: Introduction to Wireless. .. signaling within and between wireless telecommunications networks Signaling is the primary mechanism used to transfer control information through the network This chapter provides an overview of wireless telecommunications networks and describes the different types of signaling used by the network to provide service to wireless subscribers What is a Wireless Telecommunications Network? The wireless. .. McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Wireless Telecommunications Network Signaling 28 Part 1: Introduction to Wireless Telecommunications known as intelligent networking Intelligent networking is a method for providing and interpreting information within a distributed network A distributed network is structured so that the network resources... using their mobile stations in a system other than the home system where the wireless subscription was established) 3 Subscribers can receive calls while roaming 4 Subscribers can activate and use supplementary call features while roaming (e.g., call forwarding) In the context of ANSI-41 intersystem operations, a wireless system is defined as a single mobile switching center (MSC) along with its associated... telecommunications network to disseminate and transport the call details that are used for billing and accounting purposes WG5 (wireless intelligent networking) is chartered to develop standards that define and support additions to the wireless network that use additional intelligent networking technologies These technologies include the standardization of call models and event triggers, which enable calls... (international applications) is charged with developing standards that define and support radio and networking applications outside North America WG7 (interfaces to other telecommunications networks) works on developing standards that define and describe the interfaces between the wireless telecommunications network and other types of networks For example, interfaces between the wireless telecommunications network... establishment of calls to and from the wireless subscriber These systems are directly responsible for managing transmission facilities, subscriber mobility, and call processing Data-based systems in the wireless telecommunications network are known as location registers Location registers provide a database (hence, the term data-based) along with service logic to actively control the wireless services provided... Wireless Telecommunications Chapter 1: 13 Basics of Wireless Telecommunications Basic Network System Architecture Wireless telecommunications networks are primarily comprised of the following four basic network elements (see Figure 1.6): ■ ■ ■ ■ Radio systems Switching systems Data-based systems (i.e., location registers) Operations, administration, and maintenance (OA&M) systems Figure 1.6 Basic wireless. .. information means Procedures—What to do with the information The protocol enables the effective use of the control information (i.e., signals) to provide meaningful communications within a network Signaling is the mechanism used to operate, control, and manage the wireless telecommunications network A good example of a signal is the common ringing alert signal we are all familiar with when someone is calling . Introduction to Wireless Telecommunications, Network Architecture, and Functions PART 1 Source: Wireless Mobile Networking with ANSI-41 Downloaded from Digital Engineering. subject to the Terms of Use as given at the website. Basics of Wireless Telecommunications CHAPTER 1 Source: Wireless Mobile Networking with ANSI-41 Downloaded from Digital Engineering Library @. (known as the mobile station) is wireless and affords the ability to be mobile. From the network’s perspective, wireless telecommunications is a service provided to end-users. Wireless telecommunications,