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