Third Generation Mobile Networks (3G)
The challenge posed by the International Telecommunication Union (ITU) in the mid-1980s challenging the telecommunication industries to come out with a single system with a universal standard which is capable of providing better quality of service (QoS) and security as compared to 2G gave birth to the third generation (3G) mobile systems. The 3G system, unlike the 2G is all about digital voice and data and is intended to provide high-quality of voice, message, multimedia and web browsing (Tannenbaum and Wetherall, 2011).
Ten years after posing the challenge, ITU in 1997 offered a specification for the 3G called the IMT-2000. The IMT means International Mobile Communications and the 2000 stands for the year of launch, operation frequency and bandwidths. The specifications include high speed, wide range of services, mobility maintenance, security, roaming and mobile payments. Boudriga (2010:204) outlined the following security objectives of 3G: to accomplish the required mobile user authentication; to adopt the challenge and response authentication concept; to ensure message generated by user is adequately protected; to protect mobile users against misuse and theft of mobile systems; to ensure resources and services are protected; and to support emergency services.
There are many technologies that that proposed to the IMT-2000 specifications but only two became the most successful. These are: the WCMDA (Wideband Code Division Multiple Access) and UMTS (Universal Mobile Telecommunication Systems). But with the 3GPP (3G Partnership Project) agreements which consist of most important telecommunications industries and bodies proposed a standard specification for the 3G systems based on the GSM/GPRS extended network and the ETSI’s UTRA (Universal Terrestrial Radio Access) radio interface. The radio interface of the 3GPP is promoted by the 3GPP-2 by specifying an interface compatible with the IS-95 systems.
The 3G Network Architecture
The network architecture of 3G consists of three major parts: the user equipment (UE) or mobile station (MS); the radio access also called UMTS Terrestrial Radio Access Network (UTRAN); and the core network (CN).
The User Equipment or Mobile Station
This is the device which gives one access to use a mobile network service. It consists of a Universal Subscriber Identity Module (USIM) which allows the user to use a specific SIM card of his choice. The mobile device uses the UMTS techniques for its operation and operates in Circuit Switching (CS), Packet Switching, or both packet and circuit switching (PS/CS) mode.
The Radio Access Network (UTRAN)
The UTRAN which manages the radio access part of the network consist of the Node-B (Base Station) and the Radio Access Controller (RNC).
The Core Network
The core network consists of two domains, namely the Circuit-Switching (CS) and the Packet-Switching (PS) domain. The CS domain consists of the MSC, HLR, VLR, SCP and the AuC; while the PS domain consists of the SGSN and the GGSN. It main function is to provide a connection between the user and its destination on the internet and is also responsible for the storage and management of information. The third generation Universal Mobile Telecommunication System (UMTS) operates in two modes; TDD and FDD. In the FDD mode, it has a spectrum allocation of 1850 – 1910MHz for uplink and 2110 – 2170MHz for downlink and in the TDD mode, it has an allocation of 1900 – 1920MHz and 2010 – 2025MHz and each of these bands for the TDD mode is used for both uplink and downlink transmissions with a separation of134.8 – 245.2MHz (110MHz). The channel spacing is 5 in UMTS with a centre frequency of in the integral multiple of 200 KHz and chip rate of3.84Mc/s. the transmitter power output of the base station (UE) is21, 24,27, or 33dBm while receiver sensitivity of -121dBm for base station and -117dBm for UE at a bit rate of 10⁻ᵌ.the power control steps are 1,2, or 3dB for UE and 0.5 or 1dB for base station and the maximum possible change in the transmit power level on TPC commands are 26dB for UE and 12dB for base stations with a data rate of 144Kb/s in rural outdoor, 384Kb/s in urban/suburban outdoor; 2Mb/s in indoor or low-range outdoor.

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