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DISTRIBUTED WIRELESS COMMUNICATION SYSTEM full report

ABSTRACT

Wireless cellular communication systems have experienced a rapid growth during the last two decades. The first-generation (1G) systems were analog and provided wireless speech service. The major improvement in the transition to second-generation (2G) systems was the digital transmission technology, which enabled the use of error correction coding and increased service quality and capacity. The 2G systems have evolved further to provide also packet-switched data service in addition to the conventional circuit-switched services like the familiar speech service. Today, data rates of the order of hundreds or even thousands of kilobits per second are provided. Still, the 2G systems were designed mainly for wireless speech service.
As the markets have emerged for high-speed wireless multimedia, the old speech-optimized infrastructures are no longer enough. 2G systems, like the Global System for Mobile Communications (GSM), will continue to evolve to provide data services with data rates up to 384 kb/s. To go beyond this, new infrastructures that are suitable for the transmission of high-speed wireless data are being built all over the world. These infrastructures, called third-generation (3G) systems, are specified to provide data rates even greater than 2 Mb/s, which enables many new services, including streaming video, web browsing and file transfer. To be of interest to the customers, the new services should be cheap and of high quality. An important step for achieving these goals is the selection of the multiple access method. Wideband Code Division Multiple Access (Wideband CDMA or WCDMA) has been selected as the air interface for these networks.

The basic problems of wireless access are that the available spectrum is too limited and there is great attenuation of energy.These can be solved by frequency reuse and by reducing the maximum distance from the terminal to the nearest base station.
Distributed wireless communication system (DWCS) is a new architecture for a wireless access system with distributed antennas, distributed processors, and distributed controlling. The basic idea is to flatten the tree cellular structure. With distributed antennas, system capacity can be expanded through dense frequency reuse, and transmission power can be greatly decreased. With distributed processors controlling, the system works like a software or network radio, so different standards can coexist, and the system capacity can be increased by co-processing of signals to and from multiple antennas.
The beyond 3G ie. 4G mobile communications is aimed at much larger capacity and coverage requirements. DWCS is candidate architecture to fulfill these requirements.

INTRODUCTION

With the rapid progress in telecommunications, more and more services are provided on the basis of broadband communications, such as video services and high-speed Internet. With worldwide fundamental construction of a backbone network based on optical fiber providing almost unlimited communications capability, the limited throughput of the subscriber loop becomes one of the most stringent bottlenecks.Compared to the capacity of the backbone network, which is measured by tens of gigabits per second, the throughput of the subscriber loop is much lower, only up to hundreds of megabits
per second for wired systems (including fixed wireless access). However, for mobile access the throughput is even lower, and depends on the mobility of the terminal. For example, the peak data rate is only 2 Mb/s for 3G systems.
Since there will be more and more need for mobile services, the poor throughput of mobile access not only limits user applications based on interconnection, but also wastes the capability of the backbone network. This case is quite similar to the traffic conditions shown in Fig. a, which is an image of an ultra-wide expressway with a few narrow entrances.