Introduction to Mobile Radio Communications

Evolution of Mobile Radio Communications

•The first wirelinetelephone system was introduced in the year 1877. Mobile communication systems as early as 1934 were based on Amplitude Modulation (AM)

•During the World War II and the development of Frequency Modulation (FM) technique by Edwin Armstrong, the mobile radio communication systems began to witness many new changes.

•Mobile telephone was introduced in the year 1946.

•The development of the cellular concept in the 1960s at the Bell Laboratories.

•Initially, mobile communication was restricted to certain official users.

•Advanced Mobile Phone System (AMPS) was the first U.S. cellular telephone system and it was deployed in 1983.

The Worldwide Mobile Subscriber Chart

Brief Evolution of Mobile Radio Communications

•Major Mobile Radio Systems

–1934 -Police Radio uses conventional AM mobile communication system.

–1935 -Edwin Armstrong demonstrate FM

–1946 -First public mobile telephone service -push-to-talk

–1960 -Improved Mobile Telephone Service, IMTS -full duplex

–1960 -Bell Lab introduce the concept of Cellular mobile system

–1968 -AT&T propose the concept of Cellular mobile system to FCC.

–1976 -Bell Mobile Phone service, poor service due to call blocking

–1983 -Advanced Mobile Phone System (AMPS), FDMA, FM

–1991 -Global System for Mobile (GSM), TDMA, GMSK

–1991 -U.S. Digital Cellular (USDC) IS-54, TDMA, DQPSK

–1993 -IS-95, CDMA, QPSK, BPSK.

•The number of cellular telephone users grew from 25000 in 1984 to around 3 billion in the year 2007 and the demand rate is increasing day by day.

Present Day Mobile Communication

•Since the time of wireless telegraphy, radio communication has been used extensively.

•The range of mobility was defined by the transmitter power, type of antenna used and the frequency of operation.

•With the increase in the number of users, accommodating them within the limited available frequency spectrum became a major problem.

•To resolve this problem, the concept of cellular communication was evolved.

•The present day cellular communication uses a basic unit called cell.

•Each cell consists of small hexagonal area with a base station located at the  center of the cell which communicates with the user.

•To accommodate multiple users Time Division multiple Access (TDMA), Code  Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA)  and their hybrids are used.

Radio Transmission Techniques

•Simplex System: Simplex systems utilize simplex channels i.e., the communication is unidirectional. The first user can communicate with the second user. However, the second user cannot communicate with the first user. One example of such a system is a pager.

•Half Duplex System: Half duplex radio systems that use half duplex radio channels allow for non-simultaneous bidirectional communication. The first user can communicate with the second user but the second user can communicate to the first user only after the first user has finished his conversation.

•Full Duplex System: Full duplex systems allow two way simultaneous communications. Both the users can communicate to each other simultaneously. This can be done by providing two simultaneous but separate channels to both the users.

Multiple Accessing Techniques

Basic Cellular System

Operational Channels

Examples of Mobile Radio Systems

•Examples

–Cordless phone

–Remote controller

–Hand-held walkie-talkies

–Pagers

–Cellular telephone

–Wireless LAN

•Mobile -any radio terminal that could be moves during operation

•Portable -hand-held and used at walking speed

•Subscriber -mobile or portable user.

•Classification of mobile radio transmission system

–Simplex: communication in only one direction

–Half-duplex: same radio channel for both transmission and reception (push-to-talk)

–Full-duplex: simultaneous radio transmission and reception (FDD, TDD)

•Frequency division duplexing uses two radio channel

–Forward channel: base station to mobile user

–Reverse channel: mobile user to base station

•Time division duplexing shares a single radio channel in time.

Paging Systems

•Conventional paging system send brief messages to a subscriber

•Modern paging system: news headline, stock quotations, faxes, etc.

•Simultaneously broadcast paging message from each base station (simulcasting)

•Large transmission power to cover wide area.

Cordless Telephone System

•Cordless telephone systems are full duplex communication systems.

•First generation cordless phone

–in-home use

–communication to dedicated base unit

–few tens of meters

•Second generation cordless phone

–outdoor

–combine with paging system

–few hundred meters per station

Cellular Telephone Systems

•Provide connection to the PSTN for any user location within the radio range of the system.

•Characteristic

–Large number of users

–Large Geographic area

–Limited frequency spectrum

–Reuse of the radio frequency by the concept of “cell’’.

•Basic cellular system: mobile stations, base stations, and mobile switching center.

•Communication between the base station and mobiles is defined by the standard common air interface (CAI)

–forward voice channel (FVC): voice transmission from base station to mobile

–reverse voice channel (RVC): voice transmission from mobile to base station

–forward control channels (FCC): initiating mobile call from base station to mobile

–reverse control channel (RCC): initiating mobile call from mobile to base station.