N-GEN Communications Web-based Seminars ©NGCS

Seminar - An Overview of Communications Technologies

Module 9 - Wireless Systems and Technologies                                                                                   Slide 1 of 80                                                                                                    ________________

Objectives:

This module provides an introduction to wireless telecommunications, its underlying technological trends, and  associated standards. Wireless communications is envisioned to have a fabulous future enabling people to communicate, anywhere, anytime using any media. Does that mean we no longer worry about having to install expensive fiber optics and copper infrastructure? Most enterprises settled on landlines to support the long-term goal of integrating voice, data, image, and video to meet their needs. Over the last decade wireless technologies have evolved at a lightening pace and are now positioned to provide a cost-effective solution to enterprises for their multimedia applications. The wireless industry has made significant progress resolving some constraints, which have affected the widespread adoption of the technology. Some of the constraints are disparate standards, low bandwidth, and high infrastructure and service costs.

There are numerous applications for each of the different wireless technologies. The applications of wireless technologies can be divided into three categories: Voice and Messaging, Hand-held and other Internet-enabled devices, and Data Networking.

Voice and Messaging:
Cell phones, pagers, and commercial two-way business radios can provide voice and messaging services. These devices may be based on analog or digital standards that differ primarily in the way in which they process signals and encode information. The analog standard is Advanced Mobile Phone Service (AMPS). Digital standards are Global System for Mobile Communications (GSM), Time Division Multiple Access (TDMA), or Code Division Multiple Access (CDMA). Normally, devices operate within networks that provide metropolitan, statewide, or nationwide coverage. These large and costly networks are operated in the United States by carriers such as AT&T, Sprint, Verizon, local phone companies, etc. and operate in different frequency bands which are allocated by the FCC. In Canada the networks are operated by carriers such as Bell, Telus and Rogers and operate in different frequency bands, which are allocated by the Industry Canada. Throughput depends on the standard being used, but presently in the U.S. and Canada, these networks provide throughput rates up to 16 kilobits per second (Kbps).

There have been many advances in wireless systems notably in Paging, Two-way Mobile Data, Two-Way Dispatch and Two-Way Mobile Telephone. Two-way mobile telephony in the U.S. is offered by Cellular Systems operating in the 900 M HZ region of spectrum and by Personal Communications Services (PCS) Systems operating in the 1.9 G Hz region. New digital standards, also referred to as "Third-Generation Services" or 3G, are expected by 2004, and will provide 30 times faster transfer rates and enhanced capabilities. 

Because of the many standards, there are interoperability issues between networks, carriers, and devices. Generally, charges are based on per minute utilization or per number of messages. 

Hand-held and Internet-enabled devices:
Internet-enabled cell phones and Personal Digital Assistants (PDAs) have emerged as the newest products that can connect to the Internet across a digital wireless network. New protocols, such as Wireless Application Protocol (WAP), and new languages, such as WML (Wireless Markup Language) have been developed specifically for these devices to connect to the Internet. However, the majority of current Internet content is not optimized for these devices; presently, only email, stock quotes, news, messages, and simple transaction-oriented services are available. Other limitations include low bandwidth (less than 14 Kbps), low quality of service, high cost, the need for additional equipment, and high utilization of devices’ battery power. Nevertheless, this type of wireless technology is growing rapidly with better and more interoperable products.

Data Networking :
Wireless data networking falls in to three categories: Wireless Local Area Networks (WLANs), Broadband Wireless for multimedia applications (integrated data, voice, and video applications), and Bluetooth, an emerging wireless technology, for limited distances.

Wireless Local Area Networks:
Wireless Local Area Networks (WLAN) are implemented as an extension to wired LANs within a building and can provide the final few meters of connectivity between a wired network and the mobile user. WLANs are based on the IEEE 802.11 (a, b and g) standard. There are three physical layers for WLANs: two radio frequency specifications (RF - direct sequence and frequency hopping spread spectrum) and one infrared (IR). Most WLANs operate in the 2.4 GHz license-free frequency band and have throughput rates up to 2 Mbps. The new 802.11b standard is direct sequence only, and provides throughput rates up to 11 Mbps. Currently the predominant standard, it is widely supported by vendors such as Cisco, Lucent, Apple, etc. A new standard, 802.11a, operating in the 5 GHz license-free frequency band, provides throughput rates up to 54 Mbps. IEEE 802.11g is an enhancement of 802.11 b standard.

WLAN configurations vary from simple, independent, peer-to-peer connections between a set of PCs, to more complex, intra-building infrastructure networks. There are also point-to-point and point-to-multipoint wireless solutions. A point-to-point solution is used as a bridge between two local area networks, and to provide an alternative to cable between two geographically distant locations (up to 30 miles). Point-to-multi-point solutions connect several, separate locations to one single location or building. Both point-to-point and point-to-multipoint can be based on the 802.11b standard or on more costly infrared-based solutions that can provide throughput rates up to 622 Mbps (OC-12 speed).

In a typical WLAN infrastructure configuration, there are two basic components:

1.  Access Points — An access point/base station connects to a LAN by means of Ethernet cable. Usually installed in the ceiling, access points receive, buffer, and transmit data between the WLAN and the wired network infrastructure. A single access point supports an average twenty users and has a coverage varying from 20 meters in areas with obstacles (walls, stairways, elevators) and up to 100 meters in areas with a clear line of sight. A building may require several access points to provide complete coverage and allow users to roam seamlessly between access points.

2.  Wireless Client Adapter - A wireless adapter connects users via an access point to the rest of the LAN. A wireless adapter can be a PC card in a laptop, an ISA or PCI adapter in a desktop computer, or can be fully integrated within a handheld device.

Broadband Wireless
Broadband wireless technology allows simultaneous wireless delivery of voice, data, and video. It is considered a competing technology with Digital Subscriber Line (DSL) and Cable Modem. It is generally implemented in metropolitan areas and requires a clear line of sight between the transmitter and the receiving end. Broadband Wireless comes in two flavors: (1) Local multi-point distribution service (LMDS) and (2) Multi-channel multi-point distribution service (MMDS). Both operate in FCC and Industry Canada-licensed frequency bands.

1) LMDS is a high bandwidth wireless networking service in the 28-31 GHz range of the frequency spectrum and has sufficient bandwidth to broadcast all the channels of direct broadcast satellite TV, all of the local over-the-air channels, and high speed full duplex data service. The average distance between LMDS transmitters is approximately 1.5 kilometers (1 mile) apart.

2) MMDS operates at lower frequencies, in the 2 GHz licensed frequency bands. MMDS has wider coverage than LMDS, up to 35 miles, but has lower throughput rates. Companies such as Sprint and WorldCom own MMDS licenses in the majority of U.S. metropolitan areas.

Geosynchronous earth orbit (GEO) and low earth orbit (LEO) satellites represent another means for deploying wide-area broadband wireless solutions. Several issues exist here that are not present in other tower-based Broadband solutions:
        - The high cost of deploying the satellite infrastructure
         - Initial deployments represent proprietary technologies and any interoperability standards are three or
           more years away.
         - Fewer GEO satellites, because of their distance from earth, are needed to cover a given region and
           therefore are less costly to deploy. The greater distance, however, requires a miniature satellite dish
           (one meter) for adequate signal collection thus making their use in mobile wireless applications
           impractical.

LEO satellites, because of their lower earth orbit and stronger signal strength, are necessary for use in mobile applications where antenna size is a factor.

Whether it is tower-based or satellites, Broadband wireless still involves costly equipment and infrastructures. However, as it is more widely adopted, it is expected that the service cost will decrease and functionality will improve.

Bluetooth:
Bluetooth is a technical specification for low-cost, short-range wireless links between mobile PCs, mobile phones, and other portable handheld devices, and connectivity to the Internet. The Bluetooth Special Group is driving development of the technology and bringing it to the market. It includes promoter companies such as 3Com, Ericsson, IBM, Intel, Lucent, Motorola, Nokia, and over 1,800 Adopter/Associate member companies. Bluetooth covers a range of up to ten meters in the unlicensed 2.4GHz band. Because 802.11 WLANs also operate in the same band, there are interference issues to consider.

This module will cover:

1.0   Mobile systems concepts

2.0   Cellular systems concepts

3.0   Network Access methodologies: FDMA, TDMA, CDMA, CDPD, OFDM and DSSS

4.0   Modulation techniques: PSK and QAM

5.0   Mobile terrestrial wireless systems: 1G, 2G, 3g and 4G

6.0   Global System for Mobile (GSM)

7.0   Universal Mobile Telecommunications System (UMTS)

8.0   Fixed Terrestrial systems: LMDS, MMDS and WLL

9.0  LEO, MEO and GEO Satellites Broadband Technologies

10.0   Wireless Networking Standards (Home RF and Bluetooth) for the Broadband Internet home

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