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Wireless Mobile Communications

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There are a variety of wireless communication systems for transmitting voice, video, and data in local or wide areas. There are point-to-point wireless bridges, wireless local area networks, multidirectional wireless cellular systems, and satellite communication systems.

This topic discusses "mobile" wireless technologies that provide voice and data communication services to mobile users who use cell phones, PDAs, Internet terminals, and related computing devices. Refer to "Wireless Communications" for a list of related wireless topics.

The number of wireless mobile devices is increasing globally. Users equipped with portable computers, PDAs (personal digital assistants), and a variety of small wireless communication devices increasingly need to connect to corporate networks, perform database queries, exchange messages, transfer files, and even participate in collaborative computing. At the same time, wireless systems are achieving higher data rates to support Internet and other data-related applications. The newest mobile communication systems are targeting data rates as high as 2 Mbits/sec.

Cellular Systems and Topology

A cell in a cellular system is a roughly circular area with a central transmitter/receiver base station as shown in Figure W-6 (although the base station may be located off-center to conform to local topology). The station is raised up on a tower or placed on top of a building. Some are located on church steeples. The station has a 360-degree omnidirectional antenna (except when directional transmissions are required) that is tuned to create a cellular area of a specific size. Cells are usually pictured as hexagonal in shape and arranged in a honeycomb pattern. Cell size varies depending on the area. In a city, there are many small cells, while rural area may have very large cells.

Cellular topology provides a way to maintain an adequate number of call channels even though the actual number of channels available to the entire service area is small. This is possible through frequency reuse. Each cell is assigned a set of channel frequencies, and no adjoining cells may use those frequencies. However, cells further away may use those frequencies because the distance between cells provides a buffer zone that prevents frequency interference.

The system is scalable, even though it has a finite number of channels. If channel demand increases in a specific area (such as a metro area), the service provider can divide cells into a number of smaller cells. Transmitter power is turned down to fit the new smaller cell size and channel frequencies are allocated so that no adjoining cells use the same channels. However, channel reuse is possible in cells that are at least one cell apart. Thus, frequency reuse and smaller cell size allow the system to scale. Metro areas may have many small cells while rural area may have large cells. The cell size is designed to accommodate the number of people in the area.

When a user turns a phone on, its phone number and serial number are broadcast within the local cell. The base station picks up these signals and informs the switching office that the particular device is located within its area. This information is recorded by the switching office for future reference. An actual call takes place when the user enters a phone number and hits the Send button. The cellular system selects a channel for the user to use during the duration of the call.

As users travel, they may move from one cell to another, necessitating a handoff and the selection of a new channel. While in the vicinity of a cell, mobile phone users are under the control of the transmitter/receiver in that cell. A handoff takes place when the base station in one cell transfers control for a user's call to a base station in another cell. When a base station begins to lose a user's signal, it notifies base stations in all the surrounding cells that the user may be moving into their cells. As the user moves into a new cell, the base station in that cell takes over the call. The frequency of the call is changed to a frequency used in the new cell during the transition. This is because adjoining cells cannot use the same frequencies.

From Analog to Digital Systems

Mobile wireless analog communication systems have been around since the 1950s. The early systems were single channel "over-and-out" systems. Instead of a cellular configuration, a single radio tower serviced a metropolitan area, which severely limited the scalability of the systems. Service quality varied depending on the location of the caller. Later systems added multiple two-way channels but still had limited capacity.

Analog cellular services were introduced by AT&T in the 1970s and became widespread in the 1980s. The primary analog service in the United States is called AMPS (Advanced Mobile Phone Service). There are similar systems around the world that go by different names. The equivalent system in England is called TACS (Total Access Communications System).

The AMPS system is a circuit-oriented communication system that operates in the 824-MHz to 894-MHz frequency range. This range is divided into a pool of 832 full-duplex channel pairs (1 send, 1 receive). Any one of these channels may be assigned to a user. A channel is like physical circuit, except that it occupies a specific radiofrequency range and has a bandwidth of 30 kHz. The circuit remains dedicated to a subscriber call until it is disconnected, even if voice or data is not being transmitted.

Cellular systems are described in multiple generations, with third- and fourth-generation (3G and 4G) systems just emerging:

  • 1G systems    These are the analog systems such as AMPS that grew rapidly in the 1980s and are still available today. Many metropolitan areas have a mix of 1G and 2G systems, as well as emerging 3G systems. The systems use frequency division multiplexing to divide the bandwidth into specific frequencies that are assigned to individual calls.

  • 2G systems    These second-generation systems are digital, and use either TDMA (Time Division Multiple Access) or CDMA (Code Division Multiple Access) access methods. The European GSM (Global System for Mobile communications) is a 2G digital system with its own TDMA access methods. The 2G digital services began appearing in the late 1980s, providing expanded capacity and unique services such as caller ID, call forwarding, and short messaging. A critical feature was seamless roaming, which lets subscribers move across provider boundaries.

  • 3G systems    3G has become an umbrella term to describe cellular data communications with a target data rate of 2 Mbits/sec. The ITU originally attempted to define 3G in its IMT-2000 (International Mobile Communications-2000) specification, which specified global wireless frequency ranges, data rates, and availability dates. However, a global standard was difficult to implement due to different frequency allocations around the world and conflicting input. So, three operating modes were specified. According to Nokia, a 3G device will be a personal, mobile, multimedia communications device that supports speech, color pictures, and video, and various kinds of information content. Nokia's Web site ( provides interesting information about 3G systems. There is some doubt that 3G systems will ever be able to deliver the bandwidth to support these features because bandwidth is shared. However, 3G systems will certainly support more phone calls per cell.

  • 4G Systems    On the horizon are 4G systems that may become available even before 3G matures (3G is a confusing mix of standards). While 3G is important in boosting the number of wireless calls, 4G will offer true high-speed data services. 4G data rates will be in the 2-Mbit/sec to 156-Mbit/sec range, and possibly higher. 4G will also fully support IP. High data rates are due to advances in signal processors, new modulation techniques, and smart antennas that can focus signals directly at users. OFDM (orthogonal frequency division multiplexing) is one scheme that can provide very high wireless data rates. OFDM is described under its own heading.

The move to digital technologies opened up the wireless world. It improved capacity, reduced equipment costs, and allowed for the addition of new features. Reduced handset costs meant more people were vying for services and taxing systems. 3G systems add more capacity. In addition, packet technologies were developed that use bandwidth more efficiently. The primary 1G and 2G digital systems are listed here.

  • Analog cellular    These are the traditional analog systems such as AMPS and TACS that use frequency division multiplexing. AMPS operates in the 800-MHz range, while TACS operates in the 900-MHz frequency range.

  • Hybrid analog/digital cellular  (usually called digital cellular)     These systems are analog AMPS systems in which digitized voice and digital data is modulated onto the analog sine wave of the channel being used. They operate in the same 800-MHz range as analog AMPS and even use the same topology and equipment configuration (cells, towers, etc.). The access method may be either TDMA or CDMA, as discussed in the next section.

  • GSM (Global System for Mobile Communications)    This is a second-generation mobile system designed from the ground up without trying to be backward compatible with older analog systems. GSM is popular in Europe and Asia, where it provides superior roaming ability among countries. It uses TDMA, but Europe is moving from this system into 3G systems based on a wideband form of CDMA.

When digital cellular services were being designed in the early 1980s, the choice was to design a system that was backward compatible with existing analog systems (and used the same frequency allocation) or to design a whole new system. The European community had about seven incompatible analog services, so it created the GSM system from scratch to operate in the 900-MHz range (and later in the 1,800-MHz range).

In the U.S., the digital cellular systems were developed using the AMPS frequency allocation and the TDMA and CDMA access methods. See "CDMA (Code Division Multiple Access)" and "TDMA (Time Division Multiple Access)." In addition, the FCC allocated new bandwidth in the 1,900-MHz frequency range to accommodate what was called PCS (Personal Communication Services). PCS refers to the 1,900-MHz frequency allocation and to mobile systems that provide services beyond voice (such as digital services that support caller ID, messaging, and other features).

Cellular Standards

Keeping track of the analog and digital cellular standards can be difficult. Table W-2 lists the most common standards.

Reference Name



Frequency Band(s)


Analog cellular


FDMA analog cellular

800 MHz

The AMPS standard. Does not support N-AMPS.

Analog cellular (enhanced)


FDMA analog cellular

800 MHz

Same as above, but also includes N-AMPS and authentication support.

Narrowband-AMPS (N-AMPS)


FDMA analog cellular

800 MHz

Divides one FDMA channel into three smaller channels. Meant for PDA and messaging.

Local AMPS


FDMA analog cellular

800 MHz

A low-power cellular system designed for local (in-building) use.

TDMA digital cellular, also
called D-AMPS (digital-AMPS)


TDMA digital cellular

800 MHz

Same as AMPS, except uses digital TDMA to divide each channel into three time-slotted channels. Does not directly support data.

TDMA digital cellular (enhanced)


TDMA digital cellular

800 MHz

An enhancement to above (TIA/EIA/IS-54) that supports circuit- switched data at 9,600 bits/sec.

CDMA digital cellular


CDMA digital cellular

800 MHz
1,900 MHz

Uses spread spectrum radio and code division multiplexing to put up to
20 conversations on a single band. Data rate is 16 Kbits/sec.

CDMA digital cellular (revision b)


CDMA digital cellular

800 MHz
1,900 MHz

A software upgrade to IS-95a that can allocate up to four 16-Kbit/sec channels to a user, allowing up to
64 Kbits/sec for data.

HDR (high
data rate)

IS-95c compatible



A Qualcomm proprietary IP-based wireless data service.




900 MHz

GSM was designed by the European community as a digital system to replace analog system.




1,800 MHz

This is GSM expanded to the
1,800 MHz range.

Table W-2: Wireless mobile standards

Wireless Data Networking

While early cellular systems were focused on voice, there is now a lot of interest in supporting data transmissions. The older analog and analog/digital hybrid networks were limited in their data rates, but new standards are emerging with a focus on high data rates.

In a circuit-switched wireless network, a dedicated radio channel is allocated to a single transmission. As long as data transmissions are long and continuous (file transfers), a circuit is used efficiently. However, most data transmissions are bursty, and dedicating an entire circuit to them is usually a waste of valuable wireless bandwidth. During idle periods when no data is being sent, bandwidth is still dedicated to the user and not available for others to use.

Packet-switching schemes are best for bursty data traffic. Several packet-switching schemes may be used. In one technique, packets from many users are multiplexed over a single channel. In another technique, packets are inserted into the idle space on any available channel. The busier the network, the less bandwidth that will be available for data. An entire network may be designed just for packet data. Most wireless data systems offer minimal data rates, usually in the 10-Kbit/sec range. That's really only useful for short messaging and occasional Web page lookups. However, new wireless protocols bond multiple channels to increase data rates.

The billing methods help differentiate circuit versus packet switching methods. When you connect over a circuit-switched line, the phone company bills you for the entire duration of the call. With packet-switching systems, you are typically billed by the packet.

Several packet data schemes are outlined here:

  • CDPD (Cellular Digital Packet Data)    CDPD provides packet switching on AMPS systems. Data packets are sent when there is idle time on a channel. The system has a limited data rate, usually about 9,600 bits/sec. The CDPD Forum has more information at

  • Data over GSM networks    A channel bonding technique called HSCSD (high speed circuit switched data) extends GSM channel capacity to 14.4 Kbits/sec and allows up to four channels to be combined to provide up to 57.6 Kbits/sec throughput.

  • GPRS (General Packet Radio Service)    Provides packet switching for TDMA circuit-switched networks and data rates of 115 Kbits/sec or higher. GPRS is a tunneling protocol that delivers IP packets across the mobile network to a router that puts them on the Internet.

  • EDGE (Enhanced Data Rates for Global Evolution)    Improves GSM system data rates with the modified 8PSK (phase shift keying) modulation technique. The combination of GPRS and EDGE boosts the data rate of GSM to 384 Kbits/sec.

Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.
All rights reserved under Pan American and International copyright conventions.