UMTS FDD and TDD FDD (Frequency Division Duplex) Mobile Terminal Base station TDD (Time Division Duplex) TS TS Up Down Mobile Terminal Base station TS: Time slot 12 Internal UseFDD provides two distinct bands of frequencies for every user. The forward band provides traffic fromthe bs to ms and reverse band provides traffic from the ms to bsTDD uses time instead of frequency to provide both forward and reverse link. In TDD multiple user sharea single radio channel in time domain and individual users are allowed to access the channel in assignedTS.
User Equipment UEThe UMTS UE is based on the same principles as the GSM MS—the separationbetween 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 UMTSRadio Access Network (UTRAN). The UTRAN is the “mobile” part, and the CN does all the underlyingwork and passes information onto a PBN (e.g. BT, NTL etc). There are a number of interfaces betweenthese elements. The first principle interface is the Iu (also termed the reference point – since it isbetween 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 mobilenetwork or a fixed network. The Iu interface between the RNC and the CN links the MSC and the SGSNThe UTRAN consists of one or more RNS (Radio Network Subsystems). An RNS is itself a sub-networkconsisting 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 ofresources (and hence originates most of the RRC messages). If there is only one RNC assigned to a NodeB then the RNC is referred to as a Controlling RNC (CRNC). But if there are many RNCs associated withNodes 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. TheSRNC 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.
and the Node B in the UMTS term for BTS. The UTRAN contains a number of interfaces which are fullyopen. 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 thehandover region and into the core region of the neighbouring cell (the received power level of theachieve a value which is above the given handover threshold, i.e. 4dB over the value of the handoverregion of the original cell.In 3G networks receiver diversity allows the UE to receive signals from more than one BS. The signalsare separated at the RAKE receiver and demodulated. These are then de-spread using the appropriatecode from each BS, but can then be added together to gain a coherent signal. This situation is called softhandover, 2-way soft handover would be between two cells, 3-way soft handover would be between 3cells.Softer handover would occur when the UE passed between the coverage regions of sectors within thesame cell. In GSM this would be handled in exactly the same way as hard handover, 3G clearly uses anapproach which looks more like soft handover.