 Cellular and PCS
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Cellular System
Cellular systems rely on frequency re-use due to territory partitioning into "cells". Each cell has a different set of allocated frequency channels than any of its neighbors. Cells are placed/designed so that there are no gaps or overlaps. A simple model is to think of a grid of hexagons superimposed on the landscape (the shape of an actual coverage area is determined by geographical features and the placement of the base station).
Each cell is centered around a base station that handles communications with the mobile units in that cell via radio link, and also provides the connection to the system network either via radio or by wire. Cell size is determined by local traffic distribution and demand, with larger cells requiring higher power transmitters. System infrastructure handles such items as subscriber location and hand-off between cells for a roving mobile unit.
Because cellular systems are designed to handle communications with fast moving mobile units (i.e. cars), they typically use large cells (20 - 40 km radius), high powered base stations (50 to several hundred Watts output power), and moderate powered mobile units (1 to 5 Watts for hand-held, up to 20 Watts for car-mounted). Most systems operate in the 900 MHz frequency range.
Personal Communications System
Personal Communications Systems are radio telephone-based communications networks similar to cellular systems but designed for slower moving mobiles (e.g. a walking person vs. a car moving at highway speeds) and typically with campus or local coverage vs. global coverage. Like cellular systems, personal communications systems rely on frequency re-use from territory partitioning into cells, and have base stations in each cell that handle the communications between mobile units and the communications network. Since many PCS systems have limited geographical coverage, the network often has links to cellular services, other PCS networks, and conventional wired phones.
Cell size in a PCS network may be as small as 50 feet in radius. Most base stations are relatively low power (below 50 Watts); handsets typically emit less than 1 Watt. The relatively low output power of PCN systems coupled with the requirement for a highly portable handset has lead to a preference for 3 volt design in these systems. Frequency allocations are typically in the 1.8 to 2 GHz frequency range.
 Wireless Data
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Wireless Data
Wireless data applications focus on the exchange of data (as opposed to voice) over radio. In general these systems are characterized by a need for high data rates with very low bit error rates. Many proposed applications would make use of the same hardware and system infrastructure as installed or proposed cellular, personal communications, or cordless systems. Some systems, such as RAM, Ardis, and most VSAT networks, are uniquely conceived for data transfer. There are also proposals that would make use of the so-called "unlicensed" ISM bands.
The first systems on the market have predominantly used proprietary or closed standards. The resulting lack of inter operability between different manufacturer's equipment has limited the market growth of wireless data. Open standards such as IEEE 802.11 provide a possible answer to this situation.
 Wireless Local Loop
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Wireless Local Loop
Radio is becoming a popular alternative to copper wire as the connection media for plain old telephone service (POTS). This use of radio is sometimes called Fixed Wireless Access (FWA) or Fixed Radio Access (FRA), referring to the fact that the subscriber is not mobile. It is also known as Wireless Local Loop (WLL) or Radio in the Local Loop (RLL), referring to the telephone industry terminology for the interconnection between the subscriber and the telephone service.
System architecture uses a base station to relay telephone service to multiple subscribers, so WLL can be viewed as a point to multi-point radio system. A wide variety of both open and proprietary systems operating in many different frerquency bands have been proposed as WLL solutions.
 TV Distribution
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TV Distribution
- TV delivery applications encompass a multitude of services. These include:
- Entertainment
- Video Broadcasting of programming and videos, VOD/NVOD, Karaoke On Demand
- Information Services
- Data Broadcasting, Easy access to information reference sources
- Telecommuting
- Electrical Publishing / Distribution
- Personal Publishing, Personal Broadcasting, Software Distribution
- Electrical Personal Finance
- Electrical bank accounts, Home shopping
- Security and Community Socialization
- Personal Communications
- Video Telephony
- Wired, Wireless or Mobile Communications
A significant distribution method is direct broadcast via satellite. The radio portion of such a system consists of a receiving antenna (a passive component) and low noise block converter. The block converter translates the satellite signal from the frequency of transmission to an IF frequency that can be accepted by the set-top converter box. The most common bands for satellite TV reception are at 4 GHz (C band TVRO) and 12 GHz (Ku band DBS). Some transmission networks (such as MMDS) use terrestrial microwave relays rather than satellites.
The set-top converter, which takes a 900 MHz-1500 MHz IF and converts it for use on a single television channel, also has potential radio content. Interactive TV can use make use of radio signals for the "interaction", either from the TV to the network, or from the remote to the TV (though the latter is more likely to be an IR application). Cable networks increasingly have applications for radio style components, both in the form of line amplifiers and for new digitally modulated systems.
 Cordless Telephones
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Cordless Telephones
Cordless Telephone Systems use a radio link to "untether" a telephone handset, providing greater mobility and convenience. In the simplest systems, a conventional "wired in" handset is replaced by a base unit and a radio receiver. The base unit is wired into the telephone network, and provides a short distance radio link to it's paired handset. This eliminates the cord from the handset, allowing greater mobility when using the telephone.
Early implementations used a ratio of one base unit to one handset, transmitted unencrypted, analog modulated signals, and were connected to POTS (Plain Old Telephone Service). Later modifications include the use of digital modulation, encryption for security, ability to handle multiple handsets, and / or connection to specialized phone services.
Since cordless telephones are consumer products, price is a paramount consideration in the radio design, far outweighing performance or features. Many radio implementations to date have consisted of very simple circuitry using all discrete transistors to minimize cost. Broadcast power (and therefore unit range) are also limited to keep cost low.
Pagers
Pagers are small, extremely portable radio receivers that can convey brief messages to the user. The simplest pagers only indicate the presence of a message; more sophisticated models may actually receive a brief message for display. The most sophisticated pagers have an acknowledge-back feature allowing the user to send a response to the message.
The small size and portable nature of pagers has made low voltage / low current operation critical. Most pagers operate off of a single 1.5 V cell, and consume only milliamps of current when operating, and microamps when in idle. The consumer orientation of this application has also led to the selection of low cost, relatively unsophisticated radio techniques based largely on design with discrete transistors (similar to the practice in cordless telephones).
Pager networks make use of high-powered transmitters to send messages to the mobile receive unit. A high transmitted power reduces the sensitivity requirement on the receive unit. Networks are most commonly local (covering a single metropolitan area), with some wider regional and national or multi-national coverage networks now emerging.
 Additional Segments
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Index
