This book is about the Universal Mobile Telecommunication System (UMTS). UMTS is the most important of the third generation (3G) mobile phone systems, which are gradually replacing the older second generation systems such as the Global System for Mobile Communications (GSM). 3G systems provide much faster communications than their predecessors, and this allows them to offer the user a wider range of services than before, such as high speed Internet access, video and interactive games.

My aim in this book has been to write a technical introduction to UMTS. As an important part of this, I have tried to give the reader a system level understanding of what all the different parts of UMTS are, and how they relate to each other. Such an understanding is hard to gain from the UMTS specifications or from the more specialised books on the subject, but is precisely what the newcomer to the system needs.

At the same time, I have kept the book short enough that it can be read cover to cover in a weekend. To do this, I have consciously left out many of the details that can be found in the specifications or in some of the other technical books on the subject. Accordingly, you won't find in this book an exhaustive description of issues such as the bit layouts in the physical channels, the contents of the system information blocks or the different types of measurement event.

In UMTS, the network elements communicate with each other by exchanging signalling messages, which are written using the signalling protocols that we introduced in Chapter 2. The signalling messages are organised into procedures, which define how the network elements interact with each other, and which ultimately control the operation of the system. These signalling procedures are the main theme of the next two chapters. In this chapter, we discuss the procedures which control the internal operation of the system, and which do not involve any communication with the outside world. In Chapter 5, we will discuss the procedures that are related to particular services, such as voice and GPRS.

Here, we start by reviewing the way in which the network manages its communications with the mobile, and the different internal states that a mobile can be in. We then describe the procedures that a mobile uses when it switches on, to discover the cells around it and establish communications with the network. This leads to a discussion of the techniques that are used to keep the system secure in the presence of intruders. The second half of the chapter describes the procedures that take place inside a mobile after it has switched on. These are covered in two sections, as the exact procedures depend on the internal state that the mobile is in. The chapter closes by describing how the mobile stops communicating with the network and switches off.

Mobile phones were first introduced in the early 1980s. In the succeeding years, the underlying technology has gone through three phases, known as generations. The first generation (1G) phones used analogue communication techniques: they were bulky and expensive, and were regarded as luxury items. Mobile phones only became widely used from the mid 1990s, with the introduction of second generation (2G) technologies such as the Global System for Mobile Communications (GSM). These use more powerful digital communication techniques, which have allowed their cost to plummet, and have also allowed them to provide a wider range of services than before. Examples include text messaging, email and basic access to the Internet.

Third generation (3G) phones still use digital communications, but they send and receive their signals in a very different way from their predecessors. This allows them to support much higher data rates than before, and hence to provide more demanding services such as video calls and high speed Internet access. This book is about the most popular third generation technology, the Universal Mobile Telecommunication System (UMTS).

The first chapter lays the foundations for the subjects covered later in the book. It begins by briefly describing the architecture of a mobile telecommunication system, and continues with a more detailed look at two important aspects of its operation: the communication protocols that manage the delivery of information to and from a mobile phone, and the special techniques that are used for radio transmission and reception.

This chapter describes the techniques that are used for radio transmission and reception between the mobile and the radio access network. The first section reviews the use of wideband code division multiple access for transmission and reception in release 99. It concentrates on the air interface's physical layer, which is where most of the important processes take place, but it also notes the procedures used in higher layers. We then describe a technique known as high speed packet access, which has been progressively introduced from release 5 with the aim of increasing the rate at which data can be transferred. Finally, we discuss the performance of UMTS, by noting the peak and average data rates that can be achieved, and the advantages and disadvantages that CDMA has compared with other multiple access techniques.

The material in this chapter is more technical than that in later chapters of the book. However, it is unnecessary to take it all in on a first reading, as most of the chapter is self-contained. Instead, a basic understanding of Section 3.1 will be enough for Chapters 4, 5 and 6.

Radio transmission and reception in release 99

In this first section, we will describe the techniques used for radio transmission and reception in release 99. This is probably the most important part of the system: it is crucial for the delivery of high data rates to the user, and it is the part that has changed the most since the days of GSM.

The action takes place in the air interface's transport protocols, which are illustrated in Figure 3.1.

This chapter serves as a system level introduction to UMTS. We begin by describing the 3rd Generation Partnership Project, which is the organisation that defines the architecture and operation of the system. We continue by examining the architecture of UMTS, the interfaces between the different hardware components, and the protocol stacks that they use. At the end of the chapter are two shorter sections that describe the data flows within the system and the allocation of frequency spectrum to third generation systems. By the end of this chapter, you should have an appreciation of how the system fits together, and be ready to take on the details that are covered later in the book.

The 3rd Generation Partnership Project

Most of the information in this book originates in the specifications that define the architecture and operation of UMTS. These specifications are written by an organisation called the 3rd Generation Partnership Project (3GPP). In this section, we will describe how 3GPP is organised, and go on to discuss the specifications themselves.

Organisation of 3GPP

The 3rd Generation Partnership Project was formed in December 1998, to produce the technical specifications for UMTS. The formation of 3GPP came during the International Telecommunication Union's selection process for 3G telecommunication systems, and the first set of specifications was used as the member organisations' submission to the ITU. More recently, 3GPP has developed the UMTS specifications further and has expanded its role to handle the specifications for GSM, which had previously been produced by the European Telecommunications Standards Institute (ETSI).

In the final chapter, we will look at some of the likely future developments of UMTS. We begin with the IP multimedia subsystem, which was introduced into the 3GPP specifications in release 5, and is intended for the delivery of real time, packet switched services to the user. We continue with a look at the long term evolution of UMTS, which is intended to be part of release 8, and will involve changes to the radio interface that will supply the user with much higher data rates than before. We conclude with an overview of the process for defining fourth generation systems, and a look at some of the likely candidates.

The IP multimedia subsystem

The IP multimedia subsystem (IMS) is an extra component of the fixed network. Its main objective is to deliver real time services such as voice and video over the core network's packet switched domain, which have not been supported by previous implementations of UMTS. This section describes the objectives and architecture of the IP multimedia subsystem. It then gives an overview of the protocols and operational procedures that it uses, and describes the services that have been defined for use on the IMS.

Objectives

The IMS is intended to bring three main benefits to network operators and to the user.

First, the IMS provides good end-to-end quality of service for packet switched data streams.

Having described the internal operation of UMTS in Chapter 4, we can go on to consider how the system provides services to the user. We begin by explaining how services are classified and how the network provides the user with the quality of service required. We then give a detailed description of the two most important services that UMTS provides: voice and the general packet radio service (GPRS). We focus on the signalling messages that set up, manage and tear down voice calls and data transfers, and also on the mechanisms that are used to transfer information between the mobile and the end device.

The second half of the chapter is a shorter account of the other services provided by UMTS. This account is in two parts. The first part covers the other services that are of interest to the user, such as the short message service (SMS) and the multimedia messaging service (MMS). The second part covers the toolkits that application developers can use to build up higher level services. The chapter closes with an overview of the procedures that are used for charging and billing.

Service classification

Ultimately, the purpose of UMTS is to provide services that the end user will pay for. The services defined by the 3GPP specifications fall into four categories.

User services define both the data transport mechanism and the application software, so they provide a complete end-to-end service for the user.

ARQ is a flexible and efficient technique for data transmissions. In hybrid ARQ, sub-packet schemes are more attractive for systems with burst errors than complete packet schemes. Although sub-packet schemes were proposed in ARQ systems, optimum sub-packet transmission is more effective to maximize throughput in a dynamic channel. Since convolutional codes are burst errors in decoding, the optimum sub-packet can be applied to convolutional codes. This chapter investigates the performance of sub-packet transmission for convolutionally coded systems. An efficient method is proposed to estimate the optimum number of sub-packets, and adaptive sub-packet schemes, i.e. schemes that enable a system to employ different optimum numbers of sub-packets under various conditions, are suggested to achieve maximum throughput in the system. Numerical and simulation results show that the adaptive sub-packet scheme is very effective for the convolutionally coded hybrid ARQ system, and it can provide higher throughput, smaller delay and lower dropping rate than complete packet schemes. Moreover, the adaptive sub-packet scheme can be flexibly used with packet combining techniques to further improve system throughput.

Introduction

In high-speed data communication systems, information sequences are transmitted usually in packets with fixed length. At a receiver, error correction and detection are carried out on the whole packet. If the packet is found in error, the receiver sends a request to the transmitter via a feedback channel, and then the whole packet is retransmitted. However, such a conventional complete-packet ARQ scheme is inefficient in the presence of burst errors.

In many of the systems and models in which stochastic resonance has been observed, the essential nonlinearity is effectively a single threshold. Usually SR occurs when an entirely subthreshold signal is subjected to additive noise, which allows threshold crossings to occur that otherwise would not have. In such systems, it is generally thought that when the input signal is suprathreshold, then the addition of noise will not have any beneficial effect on the system output.

However, the 1999 discovery of a novel form of SR in simple threshold-based systems showed that this is not the case. This phenomenon is known as suprathreshold stochastic resonance, and occurs in arrays of identical threshold devices subject to independent additive noise. In such arrays, SR can occur regardless of whether the signal is entirely subthreshold or not, hence the name suprathreshold SR. The SSR effect is quite general, and is not restricted to any particular type of signal or noise distribution.

This chapter reviews the early theoretical work on SSR. Recent theoretical extensions are also presented, as well as numerical analysis of previously unstudied input and noise signals, a new technique for calculating the mutual information by integration, and an investigation of a number of channel capacity questions for SSR. Finally, this chapter shows how SSR can be interpreted as a stochastic quantization scheme.

Introduction

Suprathreshold stochastic resonance (SSR) is a form of stochastic resonance (SR) that occurs in arrays of identical threshold devices. A schematic model of the system is shown in Fig. 4.1, and is described in detail in Section 4.3.

Ultra-wideband impulse radio is a promising radio technology for networks delivering extremely high data rates at short ranges. The use of extremely short duration pulses, however, makes the synchronization task more difficult. In this chapter a two-stage acquisition with serial search noncoherent correlator for time-hopping impulse radio is proposed. The proposed two-stage acquisition scheme gets chip timing synchronization, and aligns the phase of the local time-hopping code in two successive stages. With the aid of the flow-graph approach, analytical expressions are presented for the mean acquisition time and the probability of acquisition. Numerical results in a slow fading channel show that the proposed two-stage acquisition method can offer a much shorter mean acquisition time or much higher probability of acquisition than that delivered by conventional acquisition.

Introduction

As explained in Section 1.1, one of the design challenges provided by the wide bandwidth property of IR-UWB signals is timing acquisition, so a rapid acquisition algorithm is very important in IR-UWB communications. A few papers have focused on acquisition for TH IR-UWB signals. In [1] the authors analyze the acquisition performance of the IR-UWB signal. In [2] a generalized analysis of various serial search strategies is presented for reducing the mean acquisition time for IR-UWB signals in a dense multipath environment, and finally in [3] hybrid schemes for IR-UWB signal acquisition are proposed to trade off the speed of parallel schemes with the simplicity of serial search schemes.