WCDMA Channels Channel Switch

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    WCDMA Channels &

    Channel switching

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    WCDMA Protocol stack OR WCDMA OSI model

    Physical channels

    (Code,frequency,etc)

    Logical channels

    (What is transmitted)

    Transport channels(How it is transmitted)

    Radio Resource Control (RRC)

    Physical Layer

    Medium Access Control (MAC)

    RLC RLC RLC

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    OSI reference model

    ProtocolProtocol Set of certain basic rulesSet of certain basic rules WCDMA protocol stack is based on OSI (open system interconnection)WCDMA protocol stack is based on OSI (open system interconnection)

    reference modelreference model

    OSI reference model ,developed by ISO, is a OSI reference model ,developed by ISO, is a set of seven layersset of seven layers..

    Each of this layer performs certain tasks on the data to make it travelEach of this layer performs certain tasks on the data to make it travel

    from one device to another over a network.

    These tasks at each layer,from one device to another over a network.

    These tasks at each layer,prepare it for the next layer.prepare it for the next layer.

    -- Layer 7: ApplicationLayer 7: Application -- This is the layer that actually interacts withThis is the layer that actually interacts with

    the user. For example if the user chooses to transfer files or readthe user. For example if the user chooses to transfer files or read

    messages , application layer interfaces with themessages , application layer interfaces with the operating systemoperating system..

    -- L

    ayer 6: PresentationL

    ayer 6: Presentation--

    Layer 6 takes the data provided by theLayer 6 takes the data provided by theApplication layer and converts it into a standard format that theApplication layer and converts it into a standard format that the

    other layers can understand.other layers can understand.

    -- Layer 5: SessionLayer 5: Session -- Layer 5 establishes, maintains and endsLayer 5 establishes, maintains and ends

    communication with the receiving device.communication with the receiving device.

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    Layer 4: Transport - This layer maintains flow control of data ,means that if data is coming from more than one application ,

    transport layer integrates it into a single stream for the physical

    network. It also provides error checking and recovery of data

    between the devices.

    Layer 3: Network This layer determines the way that the data willbe sent to the recipient. Logical protocols, routing and addressing are

    handled here.

    Layer 2: Data - This layer assigns the physical protocol to the data.

    Also, defines the type of network and the packet sequencing.

    Layer 1: Physical - This is the level of the actual hardware. It defines

    the physical characteristics such as connections, voltage levels andtiming.

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    For WCDMA the lower 3 layers are most important:For WCDMA the lower 3 layers are most important:

    Layer 1: Physical layerLayer 1: Physical layer-- This layer is responsible for transporting dataThis layer is responsible for transporting data

    across the available physical path (radio link). Main jobs of physical layeracross the available physical path (radio link). Main jobs of physical layer

    are :are :

    1. Forward error correction(FEC)1. Forward error correction(FEC)

    2. Interleaving2. Interleaving

    3. Transport channel multiplexing3. Transport channel multiplexing

    4. Channel quality measurements4. Channel quality measurements

    5. Synchronization5. Synchronization6. Spreading , scrambling, modulation6. Spreading , scrambling, modulation

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    According to the 3GPP WCDMA specs, the physical layer has 2 interfaces to

    the higher layers-

    1. To the data link layer (which is situated directly above the

    physical layer),with which data is exchanged in the form of transport

    blocks on transport channels. The transport blocks contain the user

    data and control data which are exchanged via the radio channel

    between the base station and UE.

    2. The physical layer also has a direct communications interface to

    the part of the layer which is responsible for managing the radio

    resources i.e. the RRC(Radio resource control).Using this interface ,

    the RRC directly controls the work of the physical layer. And vice

    versa, the physical layer directly transmits information about thecurrent channel quality to the RRC, based on which RRC undertake

    suitable measures in case the connection quality drops.

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    Some important measurements which physical layer must perform and report to

    RRC are :

    Measurement Explanation Mode Evaluation

    CPICH Ec/No Energy per chip/ RSSI Idle / Connected Periodic Or Upon Request

    CPICH RSCP Received Signal CodePower

    Idle / Connected Periodic Or Upon Request

    RSSI Received Signal StrengthIndicator

    Connected Periodic Or Upon Request

    TrCh BLER Estimate of BLER on RxTransport channel

    Connected Periodic Or Upon Request

    UE TX Pwr UE Transmit power Connected Periodic Or Upon Request

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    Layer 2 : Data link layerLayer 2 : Data link layer It is the upper neighbor of the physicalIt is the upper neighbor of the physicallayer.layer.3GPP3GPP divides it into the radio link control (RLC) and thedivides it into the radio link control (RLC) and the

    medium access control(MAC) layer. It delivers data block by block tomedium access control(MAC) layer. It delivers data block by block to

    layer 1 via transport channels (or fetches the data when receiving).layer 1 via transport channels (or fetches the data when receiving).

    In the other direction, layer 2 communicates with the adjoiningIn the other direction, layer 2 communicates with the adjoiningnetwork layer vianetwork layer via Logical channels.Logical channels.

    The RLC and MAC layers have the following essential functions:The RLC and MAC layers have the following essential functions:

    -- 1. Mapping of logical channels on transport channels1. Mapping of logical channels on transport channels

    -- 2. Selection of the transport format based on current needs2. Selection of the transport format based on current needs

    -- 3. Data encryption3. Data encryption

    -- 4. Error protection as a function of the desired QOS4. Error protection as a function of the desired QOS

    -- 5. Acknowledgement of data blocks and requests for retransmission in case of5. Acknowledgement of data blocks and requests for retransmission in case of

    errorserrors

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    Layer 3 : Network Layer(RRC Layer):Layer 3 : Network Layer(RRC Layer): RRC layer is directly above theRRC layer is directly above the

    layer 2 and is responsible for radio resource control. The main RRClayer 2 and is responsible for radio resource control. The main RRC

    tasks include :tasks include :

    1. Broadcasting of system information1. Broadcasting of system information

    2. Establishment and clear down a RRC connection2. Establishment and clear down a RRC connection

    3. Management of radio connections3. Management of radio connections

    4. Cell selection in IDLE mode4. Cell selection in IDLE mode

    5. Querying and evaluation of physical layer measurements5. Querying and evaluation of physical layer measurements

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    Channels are simply a tool for specifying and describing the variousChannels are simply a tool for specifying and describing the various

    communication and data related services. Various type of data iscommunication and data related services. Various type of data isexchanged between UE and base station over the radio channel. Toexchanged between UE and base station over the radio channel. To

    characterize this different type of data , we refer to different channels.characterize this different type of data , we refer to different channels.

    There are 3 different types of channels in WCDMAThere are 3 different types of channels in WCDMA

    1.1.Logical channels :Logical channels : Used for communication between Layer 3Used for communication between Layer 3

    (RRC) & Layer 2 (RLC/MAC). Depending on the information(RRC) & Layer 2 (RLC/MAC). Depending on the information

    content ,logical channels are characterized intocontent ,logical channels are characterized into traffic & Controltraffic & Control

    channels.channels.

    WCDMA CHANNELS :

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    Control Channel (Signaling)

    Broadcast Control Channel (BCCH)

    Paging Control Channel (PCCH)

    Dedicated Control Channel (DCCH)

    Common Control Channel (CCCH)

    Traffic Channel

    (User Data)

    Dedicated Traffic

    (DTCH)

    Common TrafficChannel (CTCH)

    LOGICAL CHANNELS

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    Broadcast control channel ( BCCH) : Point to multipoint ,DLBroadcast control channel ( BCCH) : Point to multipoint ,DL

    It is a broadcasting channel that supplies all the UEs with basic cellIt is a broadcasting channel that supplies all the UEs with basic cell

    and network parameters(eg. Frequency lists , code lists etc