Human Resource

Chapter 1

INTRODUCTION TO WIRELESS

COMMUNICATIONS

1. INTRODUCTION

The birth of wireless communications dates from the late 1800s, when

M.G. Marconi did the pioneer work establishing the first successful radio

link between a land-based station and a tugboat. Since then, wireless

communication systems have been developing and evolving with a furious

pace. The number of mobile subscribers has been growing tremendously in

the past decades. The number of mobile subscribers throughout the world

increased from just a few thousand in the early 20th century to close to 1.5

billion in 2004.

The early wireless systems consisted of a base station with a high-power

transmitter and served a large geographic area. Each base station could serve

only a small number of users and was costly as well. The systems were

isolated from each other and only a few of them communicated with the

public switched telephone networks. Today, the cellular systems consist of a

cluster of base stations with low-power radio transmitters. Each base station

serves a small cell within a large geographic area. The total number of users

served is increased because of channel reuse and also larger frequency

bandwidth. The cellular systems connect with each other via mobile

switching and directly access the public switched telephone networks. The

most advertised advantage of wireless communication systems is that a

mobile user can make a phone call anywhere and anytime.

1.1 Technology Evolution

In the early stages, wireless communication systems were dominated by

military usage and supported according to military needs and requirements.

During the last half a century, with increasing civil applications of mobile

services, commercial wireless communication systems have been taking the

lead.

2 Introduction to Wireless Communications

1.1.1 Basic Principles

In a cellular network, an entire geographic area is divided into cells, with

each cell being served by a base station. Because of the low transmission

power at the base station, the same channels can be reused again in another

cell without causing too much interference. The configuration and planning

of the cell is chosen to minimize the interference from another cell and thus

maximum capacity can be achieved. The cell is usually depicted as a

hexagon, but in reality the actual shape varies according to the geographic

environment and radio propagation. Channel allocation is chosen based on

the density of the users. If a cell has many users to serve, usually more

channels are allocated. The channels are then reused in adjacent cells or

cluster of cells. The spatial separation of the cells with the same radio

channels, in conjunction with the low transmission power and antenna

orientation, keeps the co-channel interference at an acceptable level.

Mobility is one of the key features in wireless communication systems.

There is a need to track the users moving into different cells and changing

radio channels. A mobile switched to another channel in a different cell is

called handoff. A signaling and call processing procedure is needed to

support user mobility and handoff such that a mobile