about 3G

1. UMTS FDD and TDD
FDD (Frequency Division Duplex)
Mobile Terminal Base station
TDD (Time Division Duplex)
TS TS
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Mobile Terminal Base station
TS: Time slot
12 Internal Use
FDD provides two distinct bands of frequencies for every user. The forward band provides traffic from
the bs to ms and reverse band provides traffic from the ms to bs
TDD uses time instead of frequency to provide both forward and reverse link. In TDD multiple user share
a single radio channel in time domain and individual users are allowed to access the channel in assigned
TS.

2. User Equipment UE
The UMTS UE is based on the same principles as the GSM MS—the separation
between mobile equipment (ME) and the UMTS subscriber identity module (SIM)
card (USIM).
UMTS can be divided into two essentially independent parts. The Core Network (CN) and the UMTS
Radio Access Network (UTRAN). The UTRAN is the “mobile” part, and the CN does all the underlying
work and passes information onto a PBN (e.g. BT, NTL etc). There are a number of interfaces between
these elements. The first principle interface is the Iu (also termed the reference point – since it is
between the CN and the UTRAN).
CN as used is almost the same as the standard GSM infrastructure, that is HLR, MSC/VLR, GMSC, SGSN,
GGSN, and so can be ignored for now. Clearly any CN technology could be applied, perhaps a mobile
network or a fixed network. The Iu interface between the RNC and the CN links the MSC and the SGSN
The UTRAN consists of one or more RNS (Radio Network Subsystems). An RNS is itself a sub-network
consisting of one RNC and at least one Node B (up to 80 Nodes B can be supported).
The RNC (Radio Network Controller) (RNC is the UMTS term for BSC) is responsible for control of
resources (and hence originates most of the RRC messages). If there is only one RNC assigned to a Node
B then the RNC is referred to as a Controlling RNC (CRNC). But if there are many RNCs associated with
Nodes B then there is a Serving RNC (SRNC) and Drift RNCs (DRNCs).
The SRNC for a UE is the RNC which terminates the Iu link to the CN and provides RANAP signalling. The
SRNC also performs all RRC signalling (L2 signalling such as handover and power control).
The DRNCs for a UE controls cells used by the UE, but no L2 messaging to the UE is originated here.

3. and the Node B in the UMTS term for BTS. The UTRAN contains a number of interfaces which are fully
open. This openness is designed to promote competition between manufacturers.
“Hard handover” would be the situation in which a mobile passed from the core of one cell, through the
handover region and into the core region of the neighbouring cell (the received power level of the
achieve a value which is above the given handover threshold, i.e. 4dB over the value of the handover
region of the original cell.
In 3G networks receiver diversity allows the UE to receive signals from more than one BS. The signals
are separated at the RAKE receiver and demodulated. These are then de-spread using the appropriate
code from each BS, but can then be added together to gain a coherent signal. This situation is called soft
handover, 2-way soft handover would be between two cells, 3-way soft handover would be between 3
cells.
Softer handover would occur when the UE passed between the coverage regions of sectors within the
same cell. In GSM this would be handled in exactly the same way as hard handover, 3G clearly uses an
approach which looks more like soft handover.