UMTS / WCDMA tutorial [2] - system architecture

- the basic system architecture including the User Equipment - UE -, the Radio Network Subsystem, and the Core Network

This tutorial is in five pages dealing which address the different topics:
Introduction to UMTS / WCDMA [1]
The architecture of the UMTS / WCDMA elements [2]
The UMTS / WCDMA radio or air interface [3]
The UMTS / WCDMA channels [4]
The UMTS / WCDMA data coding and handover [5]

The network for UMTS can be split into three main constituents. These are the mobile station, called the User Equipment or UE, the base station subsystem known as the Radio Network Subsystem (RNS) and the core network.

User Equipment, UE

The UE for UMTS / WCDMA is equivalent to the mobile equipment used on GSM networks. Essentially it is the handset, although having access to much higher speed data communications, it can be much more versatile, containing many more applications. It consists of a variety of different elements including RF circuitry, processing, antenna, battery, etc.

For UMTS / WCDMA mobiles, as for any system, the circuitry used within the UE can be broadly split into the RF and base-band processing areas. The RF areas handle all elements of the signal, both for the receiver and for the transmitter. One of the major challenges for the RF power amplifier was to reduce the power consumption. The form of modulation used for W-CDMA requires the use of a linear amplifier. These inherently take more current than non linear amplifiers which can be used for the form of modulation used on GSM. Accordingly to maintain battery life, measures were introduced into many of the designs to ensure the optimum efficiency.

The base-band signal processing consists mainly of digital circuitry. This is considerably more complicated than that used in phones for previous generations. Again this has been optimised to reduce the current consumption as far as possible.

While current consumption has been minimised as far as possible within the circuitry of the phone, there has been an increase in current drain on the battery. With users expecting the same lifetime between charging batteries as experienced on the previous generation phones, this has necessitated the use of new and improved battery technology. Now Lithium Ion (Li-ion) batteries are used. These phones to remain small and relatively light while still retaining or even improving the overall life between charges.

The UE also contains a SIM card, although in the case of UMTS it is termed a USIM (Universal Subscriber Identity Module). This is a more advanced version of the SIM card used in GSM and other systems, but embodies the same types of information. It contains the International Mobile Subscriber Identity number (IMSI) as well as the Mobile Station International ISDN Number (MSISDN). Other information that the USIM holds includes the preferred language to enable the correct language information to be displayed, especially when roaming, and a list of preferred and prohibited Public Land Mobile Networks (PLMN).

The USIM also contains a short message storage area that allows messages to stay with the user even when the phone is changed. Similarly "phone book" numbers and call information of the numbers of incoming and outgoing calls are stored.

Radio Network Subsystem

This is the section of the UMTS / WCDMA network that interfaces to both the UE and the core network. It contains what are roughly equivalent to the Base Transceiver Station (BTS) and the Base Station Controller (BSC). Under UMTS terminology, the radio transceiver is known as the Node B. This communicates with the various UEs. It also communicates with the Radio Network Controller (RNC). This is undertaken over an interface known as the Iub. The overall radio access network is known as the UMTS Radio Access Network (UTRAN). The RNC component of the Radio Access Network (RAN) connects to the core network.

Core Network

The core network used for UMTS is based upon the combination of the circuit switched elements used for GSM plus the packet switched elements that are used for GPRS and EDGE. Thus for The Core The network is divided into circuit switched and packet switched domains. Some of the circuit switched elements are Mobile services Switching Centre (MSC), Visitor Location Register (VLR) and Gateway MSC. Packet switched elements are Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN). Some network elements, like EIR, HLR, VLR and AUC mentioned in Chapters 4 and 6 are shared by both domains and operate in the same manner that they did with GSM.

The Asynchronous Transfer Mode (ATM) is specified for UMTS core transmission. The architecture of the Core Network may change when new services and features are introduced. Number Portability DataBase (NPDB) will be used to enable the subscriber to change network provider while keeping their old phone number. Gateway Location Register (GLR) may be used to optimise the subscriber handling between network boundaries. MSC, VLR and SGSN can merge to become a UMTS MSC.

Further pages from this tutorial
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