Contents. UMTS Radio Access Network (UTRAN) UTRAN Architecture. Refresher: Some concepts. UTRAN Bearer Architecture.

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1 Contents UMTS Radio Access Network (UTRAN) T UMTS Networks Chapter 4 Päivi Savola UTRAN Architecture Base Station Radio Network Controller Radio Resource Management, QoS Control Functions Refresher: Some concepts UTRAN Architecture WCDMA users share a frequency band Identification with spreading codes Other signals as interference Concept of channels Logical Transport Logical Channels Physical Transport Channels Physical Ch. (User Equipment) (Base Station, Node B) (Radio Network Controller) UTRAN RNS CN RNS UTRAN Interfaces UTRAN Bearer Architecture Uu ( - ) Iub ( ) Iur ( ) Iu ( CN) Uu Iub Iur Iu CN UTRAN Uu Iub Iu CN End to End Service UMTS Bearer Service Radio Access Bearer Service Radio Bearer Service Iu Bearer Serv UTRA Service Physical Bearer Service 1

2 Bearer Architecture UTRAN creates and maintains communication between and CN Radio Access Bearer (RAB) is the illusion of a fixed communication path between and CN Iu Bearer Service Radio Bearer (RB) Base Station A base station covers one or more cells each cell has at least one TRX (Tranceiver) Iub Interface Common transport ports, Node B control port Dedicated communication contexts (traffic termination ports) Actual internal structure vendor dependent Base Station Responsibilities Implements the Uu radio interface Maintains WCDMA radio access physical channels Transfers information from transport channels to physical channels Uu: Modulation methods QPSK (Quadrature Phase Shift Keying) for downlink OQPSK (Offset Quadrature Phase Shift Keying) for uplink Modulation methods: QPSK Modulation methods: OQPSK Bits are expressed as different phase of the carrier 4 possible 2-bit combinations Data in I Branch Serial to parallel Oscillator 90 degree phase shift RF Out Combiner Bits and degrees: Similar to QPSK, but a 0,5 bit delay introduced to Q branch Smoother signal Data in I Branch Serial to parallel Oscillator 90 degree phase shift RF Out Combiner Bits and degrees: Q Branch Q Branch Delay 2

3 Uu: Multipath propagation Several multipath components are combined to achieve a better quality summed signal Helps to decrease the necessary signal power Less interference Prerequisite for soft handovers Microdiversity Combining multipath components inside one cell Receiver (RAKE) Macrodiversity Combining multipath components between cells In or D S Radio Network Controller Maintains interfaces Iub, Iur, Iu UTRAN Radio Resource Management (RRM) QoS and stability of the radio path Efficient management of the radio resources Protocol: RRC (Radio Resource Control) Control functions Supporting functions for RRM algorithms Setting up, maintaining and releasing RBs roles C (Controlling ) Controls the common transport and Node B communication contexts for the S (Serving ) holding the Iu bearer for the D (Drifting ) Communicates with the S thorough Iur Changing the S is called S relocation Handovers Reasons for handovers Signal quality Traffic balancing Handover initiation (MEHO, Mobile Evaluated Handover) S (NEHO, Network Evaluated Handover) 3

4 Handover types Hard handover Soft handover Active set: the set of cells uses Softer handover Power Control WCDMA capacity is interference dependent Power control is crucial from the system performance point of view Ideal: all signals of the same strength when they reach the Power Control: Mechanisms Open Loop Power Control (OLPC) Initial uplink from Closed Loop Power Control During an actual connection Inner Loop Power Control (-) Outer Loop Power Control () Power Control: Commands Transmission Power Commands (TPC) Sent by,, possibly Signal power can be requested to be increased or decreased by 1-3 db Larger steps possible in compressed mode (Slotted Mode) Admission Control In WCDMA the limiting factor is interference Admission Control means estimating wheter a new connection can be added Predicting load Compromising existing calls? Load management Real Time (RT) traffic Admission control RAB maintained in dedicated state Non-Real Time (NRT) traffic Packet scheduling Sophisticated traffic models needed for controlling resources effectively 4

5 Code management Scrambling and channelisation codes are maintained in the Scrambling code separates the cells Channelisation codes used to separate traffic when connection established Task Summary in UTRAN Power and handover control Power control, code generation Power, handover and admission control Packet scheduling, code management control functions System information broadcasting Transferring information between CN and Setting up signaling connections Managing RBs and RABs UTRAN mobility management System Information Broadcasting is responsible for UTRAN system information management Part of RRC Broadcast information organized in a structure Master Information Block (MIB) Scheduling Block (SB) System Information Block () System Information Structure SB SB MIB Signaling Connection Management S must establish a signaling connection between and CN Signaling Radio Bearer (SRB) RACH RRC: Connection Request Radio Link Setup RRC: Connection Request Setup FACH RRC: Connection Request Setup Complete DCCH 5

6 UTRAN Mobility Management Handovers Location updates sent by the Cell URA (UTRAN Registration Area) s allocate RNTI (Radio Network Temporary Identifier) to Used as identifiers withing UTRAN Maintaining Location Information connection status with UTRAN No connection to UTRAN Connection over common channels Connection over dedicated channels Connection almost idle or high mobility Mobility handling location is known by CN, if known at all location is known at cell level, cell update RRC operations performed location is known at cell level. With RT traffic handovers are performed, with NRT traffic cell update operations are performed location is known at URA level, URA update operations performed UTRAN Security Responsibilities with and Integrity checking Ciphering Additional tasks positioning Data maintenance and handling Cell information Summary maintains the Uu radio interface is responsible for managing the network RBs and RABs Control information 6