2.1.1.1 Second Generation (2G)
The first generation (1G) telephone technologies were designed for analogue voice delivery until they were replaced by the second generation (2G) technologies. There were a number of standards designed across the world independently for 1G which means the equipments were not supported across boundaries of countries or regions. For example, Nordic Mobile Telephony (NMT) is the first fully automatic cellular 1G phone system, and it was deployed in eastern Europe, Russia etc, while Advanced Mobile Phone System (AMPS) developed by Bell Labs was widely used in the North America and Australia. Replacing 1G, the second generation wireless telephone technologies move from analogue to digital signals and were mainly designed for voice services and slow data transmissions. Global System for Mobile Communications (GSM) [21] developed by the European Telecommunications Standards Institute (ETSI) is the dominant standard among 2G tech- nologies. It was designed as a replacement for first generation cellular networks and is a standard still in use. Compared with 1G, it provides better call quality and a low cost call alternative, simple messaging service. Moreover it is widely supported, enabling roaming and solving the boundary problem occurred in 1G. However, the maximum cell site range
of GSM is only 120 km, although it is expanded from the old limit of 35 km1.
A typical GSM system consists of three parts: base station subsystem, switching sys- tem and operation and maintenance centre. The Base Station Subsystem (BSS) consists of multiple Base Transceiver Stations (BTS) and a Base Station Controller (BSC) which provides all control functions and physical link between Mobile Service Switching Centre (MSC) and BTS. BTS provides the radio interface with mobile subscribers which are nor- mally mobile devices registered with a Subscriber Identity Module (SIM). The Network Switching Subsystem (NSS) is responsible for connecting calls between a GSM user and another party such as another GSM user. As the core element of the switching subsystem,
Figure 2.2 GSM architecture
MSC is responsible for call setup and maintenance, resource management, call handover and data encryption. Call processing and subscriber information is contained in several databases that are used by the MSC. The databases are divided into Home Location Regis- ter (HLR) which stores permanent data about subscribers, Visitor Location Register (VLR) which stores temporary information about subscribers, Authentication Centre (AUC) used for user identification and Equipment Identification Register (EIR) which stores data about equipment identity. The Operation Maintenance Centre (OMC) supervises the operation of switching system blocks connected to it. It basically monitors and reports traffic, tak- ing care of call failures. The implementation of OMC is called the Operation and Support System (OSS) connected to all equipment in the switching system and to the BSC. An illustration of the components in a GSM network is shown in Figure. 2.2.
2.1.1.2 Two Point Five Generation (2.5G)
The two point five generation (2.5G) is an extension of the 2G services. The main novelty is the introduction of packet-switched networks into the circuit-switched domain, used in traditional 2G networks. The two widely supported technologies General Packet Radio Service (GPRS) [22] and Enhanced Data rates for Global Evolution (EDGE) [23] are standards evolved from 2G providing Internet services to existing 2G networks.
GPRS is a technology for GSM networks, which adds packet switching protocols. It was first standardized by the European Telecommunications Standards Institute (ETSI) and
is now maintained by the 3rd Generation Partnership Project (3GPP)2. The standard im-
proves the efficiency of network resources as information is broken up into packets and re- sources are allocated during the handling of individual packets only. The packet switching feature implies that GPRS provides best effort service instead of the guarantee of quality of service (QoS), provided by circuit switched networks.
3GPP EDGE is sometimes considered as a third generation standard but it is generally deployed on existing 2G networks. It is a technology designed for mobile phones to im- prove data transmission rates. EDGE is compatible with existing GSM networks and offers a maximum speed of 384 kbps to IP-based networks.
2.1.1.3 Third Generation (3G)
The third generation mobile telecommunications (3G) standardized by the International Mobile Telecommunications-2000 (IMT-2000) is a generation of standards designed for wireless communications. It is required that 3G provides a data rate of at least 200 kbps while most 3G services offer higher speed than the requirements.
Universal Mobile Telecommunications System (UMTS) [24], also known as WCDMA (Wideband Code Division Multiple Access) developed by the 3GPP is a widely deployed 3G technology based on GSM networks. It has both circuit switched and packet switched
elements. UMTS achieves higher spectral and bandwidth efficiency through utilization of wide-band code division multiple access. The data transfer rate has been increased to 45 Mbps which is a significant improvement. UMTS specifications deal with three main components of the network: Core Network (CN), The UMTS Radio Access Net- work (UTRAN) and User Equipment (UE). The core network uses the same core network standard as GSM/EDGE. Although the same structure is supported which indicates easy migration for existing GSM operators, the cost of purchasing spectrum licenses and over- laying UMTS is high. UTRAN consists of one or multiple base stations which directly provide connection to mobile equipments.
CMDA2000 as a family of 3G standards uses Code Division Multiple Access (CDMA)
as the multiplexing technique to provide broadband data rate up to 14.7 Mbps3. CDMA2000
transmits on one or several pairs of 1.25 MHz radio channels, while UMTS transmits on a pair of 5 MHz-wide radio channels. Unlike UMTS, CDMA2000 is backward compatible with its former generation known as cdmaOne, which was first standardized in 1993.
2.1.1.4 Fourth Generation (4G)
As a successor of 2G and 3G technologies, 4G is the fourth generation of wireless com- munication standards, the requirements of which have been specified by the International
Telecommunications Union (ITU)4. 4G technologies are required to support peak bitrate of
100Mbps for high mobility communications and 1Gbps for low mobility communications. 4G provides a flexible channel bandwidth between 5 and 20 MHz. Another requirement of 4G standards is smooth handover within various types of networks and dynamical resource allocation to improve efficiency and user experience.
3GPP Long Term Evolution [25], normally referred as LTE was developed by the 3GPP to provide higher speed and network capacity. LTE Advanced [26] is the current 3GPP proposal for 4G standards and is an enhancement of the LTE standard. It introduces
3http://www.qualcomm.com/media/documents/wireless-networks-rev-b-enhanced-mobile-broadband-
all,2010.
multicarrier which enables the use of wide bandwidth for high speed data transmissions. Another significant contribution of LTE Advanced is the wise use of advanced topology networks with deployment of low power nodes.