Capacity enhancement by application of power control and multi-user receivers in a cellular radio system

Chapter 1 - Introduction Page 1 Chapter 1 INTRODUCTION In this Chapter a general overview of wireless networks and multi-user receivers is presented, focusing on some of the aspects of a wireless network, like frequency reuse and resource allocation that will be quoted and applied in the following chapters. 1.1 Wireless networks In many modern systems for wireless communication, the primary goal is to provide network access to a large number of mobile or stationary users. Such a communication system, where the users are dispersed over a geographical area but where their number and locations are not a priori known, is referred to as an area communication system or wireless network . The network consists of a fixed network part and a wireless part. The fixed one provides connections between base stations or Radio Access Ports (RAP) and PSTN (Public Switched Telephone Network), whereas the RAP provides the wireless connections to the mobiles. The area around a RAP where the transmission conditions are sufficient to maintain a connection of the required quality between a mobile and the RAP is denoted the coverage area. The transmission quality and thus the shape of these regions will, as we may expect, depend heavily on the propagation conditions and the current interference from other users in the system. Thus we will focus on an interference-limited system, where the number of simultaneous connections is larger than the number of radio-channels that the available bandwidth may produce. As we increase the number of terminals and RAPs that maintain connections, the interference will clearly rise, and this interference will be our main concern. If exactly the same channels are used in different parts of the service area at a large distance, the mutual interference may be quite low. In fact, at higher frequencies where the received signal level decays with the distance, we could reduce the interference power to any low level, by just increasing the distance between the receiver transmitted pairs. If RAPs and terminals are assigned channels with some care, we could even reuse the same channel several times within the coverage area with only moderate mutual interference. By reusing the channels, several connections can be established at the same time and more information can be transmitted. The capacity of the system is said to increase.