ENGN4536 Mobile Communications

Transcription

1 ENGN4536 Mobile Communications Dr Thushara Abhayapala Department of Engineering Faculty of Engineering & Information Technology Australian National University Semester 1, 2002 ENGN4536 Copyright 2002, Thushara D. Abhayapala 0

2 Wireless Communications System Definitions Base Station (BS): A fixed station usually located at the center of a coverage region and consist of transmitter and receiver antennas mounted on a tower Mobile Station (MS): e.g. Mobile phone hand set Control Channel: channel used for transmission of call setup, request, initiation or other control purposes Full Duplex: allows simultaneous two way communications- typically use two different channels Half Duplex: two way communication but one at a given time, uses one channel Hand off: Process of transferring a mobile station from one channel to another or one base station to another ENGN4536 Chapter 1 Introduction to Wireless Communication Systems 1

3 Mobile Switching Center (MSC): In a cellular system MSC connects base stations to PSTN Page: A brief message which is transmitted over entire service area Forward Channel: channel used to transmit from BS to MS Reverse Channel: channel used to transmit from MS to BS Transceiver: A device capable of simultaneously transmitting and receiving radio signals ENGN4536 Chapter 1 Introduction to Wireless Communication Systems 2

4 Paging Systems used to send brief messages to a subscriber could be a text or voice message see Fig 1.3 and read pages of the text book How does a paging system work? sender dial the paging system access number paging control system transmit the page through the service area using base stations which broadcast the page on a radio carrier (simulcast) and the intended handset receives the page. need reliable one way communication ( large transmit power and low data rates)/ ENGN4536 Chapter 1 Introduction to Wireless Communication Systems 3

5 Cordless Telephone Systems Full duplex systems radio connection between portable handset to a dedicated base station which is connected to PSTN operate only over few tens of meters primarily for in home use only ENGN4536 Chapter 1 Introduction to Wireless Communication Systems 4

6 Cellular Telephone Systems See Fig 1.5 of the textbook Provide wireless connection to PSTN Communication between BS and MS is defined by a standardcommon air interface (CAI) that defined four different channels. 1. Forward Voice Channel (FVC): BS MS 2. Reverse Voice Channel (RVC): MS BS 3. Forward Control Channel (FCC): BS MS 4. Reverse Control Channel (RCC): MS BS Control channels transmit and receive data messages that carry call initiation and service requests and are monitored by mobiles when they do not have a call in progress. ENGN4536 Chapter 1 Introduction to Wireless Communication Systems 5

7 FCC also continuously broadcast all of the traffic requests for all mobiles in the system. They are also used to perform automatic channel changes and hand offs. ENGN4536 Chapter 1 Introduction to Wireless Communication Systems 6

8 When a cellular phone is turned on... MS scans the group of FCC to determine the one with the strongest signal and then monitored that FCC If the FCC signal drops below a usable level, then MS scans the control channel in search of the strongest FCC signal. Normally, 5% of the available channel are control channels and the other 95% are voice channels. ENGN4536 Chapter 1 Introduction to Wireless Communication Systems 7

9 When a telephone call is placed to a mobile user MSC dispatches the request to all BS in the cellular system. 2. The mobile identification number (MIN), which is the subscriber s telephone number, is then broadcast as a paging message over all of the FCC throughout the cellular system. 3. MS receives the pager and responds by identifying itself over RCC. 4. BS relay the acknowledgement and inform the MSC of the handshake. 5. Then MSC instruct the BS to move the call to an unused voice channel within the cell. 6. BS signals to the MS (using FCC) to change frequencies to an unused FVC and RVC pair. 7. BS also transmit an alert over FCC to instruct the mobile to ring. ENGN4536 Chapter 1 Introduction to Wireless Communication Systems 8

10 8. see Fig 1.6 of the text book for the timing diagram. ENGN4536 Chapter 1 Introduction to Wireless Communication Systems 9

11 When a mobile originate a call... a call initiation request is sent on FCC (together with MIN, telephone number of the called party, maximum transmit power etc.) BS receivers this data and send it to MSC. MSC validates the request, make connection to the third party through PSTN. MSC instruct BS to instruct MS to move to an unused FVC/RVC pair. ENGN4536 Chapter 1 Introduction to Wireless Communication Systems 10

12 Roaming Roaming allows subscribers to operate in service areas other than the one from which service is subscribed. When a MS enters a city or another conuntry that is different from its home service area it is registered as a roamer in the new area. This process is accomplished over FCC (see chapter 10 for more detail) ENGN4536 Chapter 1 Introduction to Wireless Communication Systems 11

13 Discussion What are the challengers faced by cellular mobile communication systems? ENGN4536 Chapter 1 Introduction to Wireless Communication Systems 12

14 Why should you study this unit?... extract from the text book. The world is undergoing a major telecommunications revolution that will provide communication access to citizens, at any time any where there go. The wireless telecommunications industry requires engineers who can design, and understand the engineering trade-offs that must be made in any system. Such an understanding can only be achieved by mastering the fundamental technical concepts of wireless communications. These concepts are the subject of the remaining of this course. ENGN4536 Chapter 1 Introduction to Wireless Communication Systems 13

15 Read chapter 1 of Rappaport (NOW!) Homework Problems: 1.4(1.2),1.9(1.5), 1.13(1.8),1.15(1.10), 1.18(1.12) Please submit answers to problems in red during next Wednesday s lecture. Also read chapter 2 of the text book. It will help you to identify some of the emerging topics in this area. Also search the Web and to find out a topic for your projet. ENGN4536 Chapter 1 Introduction to Wireless Communication Systems 14