WIRELESS NETWORKS


Network infrastructure provides essential voice and data communication capability for consumers and vendors in cyberspace . Evolving from electronic commerce (EC) to mobile commerce (MC), it is necessary for a wired network infrastructure, such as the Internet, to be augmented by wireless networks that support mobility for end users. Wireless networking technologies are advancing at a tremendous pace, and each represents a solution for a certain phase, such as 1G, 2G, and 3G, in a particular geographical area, such as the United States, Europe, or Japan. In this section, we will categorize them from the perspective of radio coverage: wireless local area networks, wireless metropolitan area networks, and wireless wide area networks.

Wireless Local Area Network

Devices used in wireless local area network (WLAN) technologies are lightweight (easy to carry) and flexible in network configuration. Therefore, WLANs are suitable for office networks, home networks, personal area networks (PANs), and ad hoc networks. In a one-hop WLAN environment, where an access point (AP) acting as a router or switch is a part of a wired network, mobile devices connect directly to the AP through radio channels. Data packets are relayed by the AP to the other end of a network connection. If no APs are available, mobile devices can form a wireless ad hoc network among themselves and exchange data packets or perform business transactions as necessary.

In Table 4, major WLAN technologies are compared in terms of maximum data transfer rate (channel bandwidth), typical transmission range, modulation techniques, and operational frequency bands. The various combinations of modulation schemes and frequency bands make up different standards, resulting in different throughputs and coverage ranges. A detailed coverage of modulation techniques is beyond the scope of this chapter, but interested readers can refer to Chapter 3 of a book by Pahlavan and Krishnamurthy (2002).

Table 4: Major WLAN standards

Standard

Maximum Data Rate

Typical Range (m)

Modulation

Frequency Band

Bluetooth

1 Mbps

5 ‚ 10

GFSK

2.4 GHz

802.11b (Wi-Fi)

11 Mbps

50 ‚ 100

HR-DSSS

2.4 GHz

802.11a

54 Mbps

50 ‚ 100

OFDM

5 GHz

HyperLAN2

54 Mbps

50 ‚ 300

OFDM

5 GHz

802.11g

54 Mbps

50 ‚ 150

OFDM

2.4 GHz

In general, Bluetooth technology supports very limited coverage range and throughput. Thus it is only suitable for applications in personal area networks. In many parts of the world, the IEEE 802.11b (Wi-Fi) system is now the most popular wireless network and is used in offices, homes , and public spaces such as airports, shopping malls, and restaurants . However, many experts predict that with much higher transmission speeds, 802.11a and 802.11g will replace 802.11b in the near future.

Wireless Metropolitan Area Network

The most important technology in this category is the cellular wireless network. Cellular system users can conduct mobile commerce operations through their cellular phones. Under this scenario, a cellular phone connects directly to the closest base station, where communication is relayed to the service site through a radio access network (RAN) and other fixed networks.

Originally designed for voice-only communication, cellular systems are evolving from analog to digital and from circuit-switched to packet-switched networks in order to accommodate mobile commerce (data) applications. Table 5 lists the classifications of standards in first generation (1G), second generation (2G, 2.5G), and third generation (3G) wireless cellular networks. 1G systems such as the advanced mobile phone system (AMPS) and total access control system (TACS) are becoming obsolete and thus will not play a significant role in mobile commerce systems. The global system for mobile communications (GSM) and its enhancement, general packet radio service (GPRS), have mainly been developed and deployed in Europe. GPRS can support data rates of only about 100 kbps, but its upgraded version enhanced data for global evolution (EDGE) is capable of supporting 384 kbps. In the United States, wireless operators use time division multiple access (TDMA) and code division multiple access (CDMA) technologies in their cellular networks.

Table 5: Major cellular wireless networks

Generation

Radio Channels

Switching Technique

Standards (Examples)

1G

Analog voice channels Digital control channels

Circuit-switched

AMPS
TACS

2G

Digital channels

Circuit-switched

GSM
TDMA

Packet-switched

CDMA

2.5G

Digital channels

Packet-switched

GPRS
EDGE

3G

Digital channels

Packet-switched

CDMA2000
WCDMA

Currently, most of the cellular wireless networks in the world follow 2G or 2.5G standards. However, there is no doubt that in the near future, 3G systems with quality-of-service (QoS) capability will dominate wireless cellular services. The two main standards for 3G are wideband CDMA (WCDMA), proposed by Ericsson, and CDMA2000, proposed by Qualcomm. Both use direct sequence spread spectrum (DSSS) in a 5 MHz bandwidth. Technical differences between them include a different chip rate, frame time, spectrum used, and time synchronization mechanism. The WCDMA system can inter-network with GSM networks and has been strongly supported by the European Union, which calls it the Universal Mobile Telecommunications System (UMTS). CDMA2000 is backward-compatible with IS-95, which is widely deployed in the United States.

In a wireless cellular system, a wired network called a radio access network (RAN) is employed to connect radio transceivers with core networks. Two examples of existing RAN architectures are UTRAN (UTRAN overall description, 1999) and IOS (MSC to BS interface inter-operability specification, 1999). Since UTRAN is the new radio access network designed especially for 3G UMTS (the Universal Mobile Telecommunications System), it deserves further description.

The architecture and components of UMTS and UMTS Terrestrial Radio Access Network (UTRAN) are shown in Figure 4 (Vriendt, Lain ƒ , Lerouge, & Xu, 2002). At the highest level, the UMTS network structure consists of the core network (CN) and UTRAN. The network subsystem (NSS) of GSM/GPRS is reused as much as possible in UMTS CN. Two service domains are supported in CN, circuit switching (CS) and packet switching (PS). By moving the NSS transcoder function from the base station subsystem to the core network, CS provides voice and circuit-switched data services. Evolving from GPRS, the packet-switched service provided by PS optimizes functional relationships between CN and UTRAN. UTRAN consists of radio network subsystems (RNS). Each RNS contains one radio network controller (RNC) and at least one Node B (base station). The RNC controls the logical resources for Node Bs in the UTRAN. Node B manages radio transmission and reception of one or more cells and provides logical resources to the RNC.


Figure 4: UMTS and UTRAN architecture (Vriendt et al., 2002)

Wireless Wide Area Network

In large geographic areas lacking the infrastructure of wireless cellular networks, satellite systems can be utilized to provide wireless communication services. Communication through satellites is very similar to the scenario in cellular systems, apart from the differences in transmission distance and coverage range. For example, a user in an airplane can use a satellite communication system to conduct mobile commerce transactions. The messages will first be sent to a base station and then forwarded to service provider sites. Satellite systems are generally categorized by the height of the orbit . Table 6 summaries their characteristics.

Table 6: Major satellite systems

Satellite System

Height of Orbit (km)

Coverage

Latency (ms)

Geosynchronous Earth Orbit (GEO)

35,863

1/3 of earth surface

270

Medium Earth Orbit (MEO)

5,000 ‚ 12,000

Several thousands miles

35 ‚ 85

Low Earth Orbit (LEO)

500 ‚ 1,500

One thousand miles

1 ‚ 7

In general, there are three communication configurations in satellite systems: point-to-point links, broadcast links, and VSAT. Point-to-point link configuration means two ground-based antennas establish a point-to-point link through a satellite. Broadcast links are configured so that one ground-based transmitter can establish a multicast channel with a number of ground-based receivers through a satellite. When subscriber stations are equipped with a low-cost very small aperture terminal (VSAT) system, they share satellite transmission capacity for transmission to a hub station, and the hub station can exchange and relay messages between subscribers. VSAT can thus provide two-way communication among subscribers.






Mobile Commerce Applications
Mobile Commerce Applications
ISBN: 159140293X
EAN: 2147483647
Year: 2004
Pages: 154
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