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Transcript of UTRAN Radio Resource Management - Startseite TU Radio Resource Management uIntroduction ... (Ed.),...

  • UTRAN Radio Resource Management

    u Introductionu Handover Control

    u Soft/Softer Handoveru Inter Frequency Handover

    u Power Controlu Closed Loop Power Controlu Open Loop Power Control

    u Interference Management

    u Load Control

    u Call Admission Controlu Congestion Control

    u Packet Data Transmission

    u Packet Data Controlu Dynamic Scheduling

    BTS 1

    BTS 3

    BTS 2UE

  • UMTS Networks 2Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

    References

    H. Holma, A. Toskala (Ed.), WCDMA for UMTS, Wiley, 5th edition, Wiley, 2010H. Kaaranen, et.al., UMTS Networks: Architecture, Mobility and Services,

    Wiley, 2001. (see chapter 4)

    A. Viterbi: CDMA: Principles of Spread Spectrum Communications, AddisonWesley, 1995.

    J. Laiho, A. Wacker, T. Novosad (ed.): Radio Network Planning andOptimisation for UMTS, Wiley, 2001

    T. Ojanper, R. Prasad, Wideband CDMA for Third Generation MobileCommunication, Artech House, 1998.

    R. Prasad, W. Mohr, W. Konhuser, Third Generation Mobile CommunicationsSystems, Artech House, March 2000.

    3GPP standards:

    u TS 25.214: Physical Layer Procedures (esp. power control)u TR 25.922: Radio Resource Management Strategiesu TR 25.942: RF System Scenarios

  • UMTS Networks 3Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

    u Efficient use of limited radio resources (spectrum, power, code space)u Minimizing interferenceu Flexibility regarding services (Quality of Service, user behaviour)u Simple algorithms requiring small signalling overhead onlyu Stability and overload protectionu Self adaptive in varying environmentsu Allow interoperability in multi-vendor environments

    Radio Resource Managementalgorithms control theefficient use of resourceswith respect tointerdependent objectives: cell coverage cell capacity quality of service

    RRM High-Level Requirements

  • UMTS Networks 4Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

    RRM Components

    Radio Resource Management

    MediumAccessControl

    Packet DataControl

    LoadControl

    HandoverControl

    PowerControl

    Core Network/ other RNCs

    Physical layer

    typically inRNC

    typically inNodeB

  • UMTS Networks 5Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

    Handover Control: Basics

    General: mechanism of changing a cell or base station during a call or session

    Handover in UMTS:u UE may have active radio links to more than one Node Bu Mobile-assisted & network-based handover in UMTS:

    u UE reports measurements to UTRAN if reporting criteria (which are set bythe UTRAN) are met

    u UTRAN then decides to dynamically add or delete radio links dependingon the measurement results

    Types of Handover:u Soft/Softer Handover (dedicated channels)u Hard Handover (shared channels)u Inter Frequency (Hard) Handoveru Inter System Handover (e.g. UMTS-GSM)u Cell selection/re-selection (inactive or idle)

    All handover types require heavy support from the UMTS network infrastructure!

  • UMTS Networks 6Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

    Macro Diversity & Soft Handover (Wrap-Up)

    Downlink: combining in the mobile stationUplink: combining in the base station and/or radio network controller

    NodeB 1NodeB 2

    UE

  • UMTS Networks 7Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

    Soft/ Softer Handover

    u In soft/softer handover the UE maintains active radio links to more than oneNode B

    u Combination of the signals from multiple active radio links is necessary

    Soft Handoveru The mobile is connected to (at least) two cells belonging to different NodeBsu In uplink, the signals are combined in the RNC,

    e.g. by means of selection combining using CRCSofter Handover

    u The mobile is connected to two sectors within one NodeBu More efficient combining in the uplink is possible like

    maximum ratio combining (MRC) in the NodeB instead of RNC

    Note:u In uplink no additional signal is transmitted, while in downlink each new link

    causes interference to other users, therefore:u Uplink: HO general increase performanceu Downlink: Trade-off

  • UMTS Networks 8Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

    Soft and Softer Handover in Practice

  • UMTS Networks 9Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

    Soft Handover Control

    Measurement quantity, e.g.EC/I0 on CPICH

    Relative thresholds dadd &ddrop for adding & dropping

    Preservation time Tlink toavoid ping-pong effects

    Event triggered measurementreporting to decreasesignalling load

    MeasurementQuantity

    Link to 1 Link to 1 & 2 Link to 2 time

    CPICH 1

    CPICH 2

    ddrop

    NodeB 1 NodeB 2

    dadd Tlink

    UE

    soft handoverarea

  • UMTS Networks 10Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

    Soft Handover Simulation Results

    Soft handover significantly improves the performance, but

    0%

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    5 15 25 35 45 55

    Offered Traffic [Erlang per site]

    Out

    age

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    babi

    lity

    (Blo

    ckin

    gan

    dD

    ropp

    ing)

    1 linkmax 2 SHO linksmax 4 SHO linksmax 6 SHO links

  • UMTS Networks 11Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

    Soft Handover Simulation Results II

    the overhead due to simultaneous connections becomes higher!

    0

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    Max. Active Set Size

    Mea

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    umbe

    rofA

    ctiv

    eLi

    nks

  • UMTS Networks 12Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

    Handover f1 f2 always neededbetween layers

    Hierarchical cell structure (HCS)

    Macro Micro Macro

    f1f2

    f1

    Handover f1 f2 neededsometimes at hot spot

    Hot-spot

    f1

    f2f1 f1

    Hot spot

    Inter-Frequency Handover

    u Hard handoveru Inter-frequency measurements of target cell needed in both scenariosu Mobile-assisted handover (MAHO)

    u slotted (compressed) mode for inter-frequency measurements to find suitabletarget cell

    u also supports GSM system measurementsu Database assisted handover (DAHO)

    u no measurements performed on other frequencies or systemsu use cell mapping information stored in data base to identify the target cell

  • UMTS Networks 13Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

    Cell Selection/Re-selection

    u Handover when UE is idle or there is noactive connection between UE andUTRAN

    u Goal: find a suitable cell to camp on

    u The cell to camp on is chosen by the UEon measured link quality Q, e.g. EC/I0 onCPICH (after cell-search)

    u Cell re-selection with hysteresis H toavoid ping-pong effects

    u Additional offsets for Q on differentfrequencies, e.g. to support hierarchicalcells

    u Mapping functions for Q between UMTSand GSM to support priorities

    u Cell selection and re-selection mainlyperformed internally in UE, but controlledby UTRAN with broadcast of neighbourcell frequencies and control parameters(hysteresis, mapping, etc.)

    NodeB 1NodeB 2

    UE

    Q1 > QminQ1 > Q2

    Cell selection border

    Q1 Q2

  • UMTS Networks 14Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

    Power Control: Basics

    Controls the setting of the transmit power in order to:u Keep the QoS within the required limits, e.g. data rate, delay and BERu Minimise interference, i.e. the overall power consumption

    Power control handles:u Path Loss (Near-Far-Problem), Shadowing (Log-Normal-Fading) and

    Fast Fading (Rayleigh-, Ricean-Fading)u Environment (delay spread, UE speed, ) which implies different

    performance of the de-interleaver and decoder

    Uplink: per mobileDownlink: per physical channel

    Three types of power control:u Inner loop power controlu Outer loop power control (SIR-target adjustment)u Open loop power control (power allocation)

    Downlink power overload control to protect amplifieru Gain Clipping (GC)u Aggregated Overload Control (AOC)

  • UMTS Networks 15Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

    Near-Far Problem: Spreading sequences are not orthogonal

    (multi-user interference) Near mobile dominate Signal to interference ratio is lower for far

    mobiles and performance degrades

    The problem can be resolved throughdynamic power control to equalize allreceived power levels

    AND/OR

    By means of joint multi-user detection

    Near-Far Problem Power Control (Wrap-Up)

    NodeB

    UE 1

    UE 2

  • UMTS Networks 16Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

    Closed Loop Power Control

    u Closed loop power control is used on channels, which are established in bothdirections, such as DCH

    u There are two partsu Inner Loop Power Control (ILPC): receiver generates up/ down

    commands to incrementally adjust the senders transmit poweru Outer Loop Power Control (OLPC): readjusts the target settings of the

    ILPC to cope with different fading performance

    NodeB

    UE

    control command: Up/DownExample: Uplink Closed Loop Power Control

    Inner Loop(1500 Hz)

    SIR > SIRtarget ?

    Outer Loop( 100Hz)

    target adjustmentBLERtarget

    RNC

  • UMTS Networks 17Andreas Mitschele-Thiel, Jens Mueckenheim Oct. 2012

    Impact of Power Control

    -8

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    pow

    er/

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