02 RA41562EN02GLA0 LTE Radio Interface Protocols and Procedures Ppt

8/20/2019 02 RA41562EN02GLA0 LTE Radio Interface Protocols and Procedures Ppt

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LTE Radio Interface Protocols and Procedures

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As in UMTS, the radio interface consists of three horizontal layers;

• Layer 1: Physical Layer • Layer 2: Medium Access Control (MAC), Radio Link Control (RLC) and Packet Data

Convergence Protocol (PDCP).

• Layer 3: Radio Resource Control (RRC). It exists only at control plane side.

All radio interface protocols are implemented in the user equipment and eNB, as result ofsimplified radio network architecture in E-UTRAN. However, the concept of PhysicalChannels, Transport Channels and Logical Channels are maintained from UTRAN.


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In downlink piggybacking of NAS messages is used only for one dependant (i.e. with jointsuccess/ failure) procedure: bearer establishment/ modification/ release. In uplink NASmessage piggybacking is used only for transferring the initial NAS message duringconnection setup.

Once security is activated, all RRC messages on SRB1 and SRB2, including thosecontaining NAS or non-3GPP messages, are integrity protected and ciphered by PDCP.NAS independently applies integrity protection and ciphering to the NAS messages.


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The transport channels defined in the downlink are:

•Broadcast Channel (BCH),•Paging Chanel (PCH) and

•Downlink Shared Channel (DL-SCH).

The physical channels defined in the downlink are:

•Physical Downlink Shared Channel (PDSCH),

•Physical Downlink Control Channel (PDCCH),

•Physical Broadcast Channel (PBCH),

•Physical Control Format Indicator Channel (PCFICH)

•Physical Hybrid ARQ Indicator Channel (PHICH)

•In addition, there are Reference Signal (RS), Primary Synchronisation Signal (PSS)and Secondary Synchronisation Signal (SSS) in the downlink.

The transport channels defined in the uplink are:

•Random Access Channel (RACH) and

•Uplink Shared Channel (UL-SCH).

The physical channels defined in the uplink are:

•Physical Random Access Channel (PRACH),

•Physical Uplink Shared Channel (PUSCH),

•Physical Uplink Control Channel (PUCCH).

•In addition, there are Demodulation Reference Signal (DMRS) and SoundingReference Signal (SRS) in the uplink.


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• Broadcast of system information.− Including NAS common information.

− Information applicable for UEs in RRC_IDLE, e.g. cell (re-)selection parameters,

neighbouring cell information and information (also) applicable for UEs in

RRC_CONNECTED, e.g. common channel configuration information.

• RRC connection control.− Paging.

− Establishment/ modification/ release of RRC connection, including e.g. assignment/

modification of UE identity (C-RNTI), establishment/ modification/ release of SRB1 and

SRB2, access class barring.

− Initial security activation, i.e. initial configuration of AS integrity protection (SRBs) and AS

ciphering (SRBs, DRBs).

− RRC connection mobility including e.g. intra-frequency and inter-frequency handover,

associated security handling, i.e. key/ algorithm change, specification of RRC context

information transferred between network nodes.

− Establishment/ modification/ release of RBs carrying user data (DRBs).

− Radio configuration control including e.g. assignment/ modification of ARQ configuration,

HARQ configuration, DRX configuration.

− QoS control including assignment/ modification of semi-persistent scheduling (SPS)

configuration information for DL and UL, assignment/ modification of parameters for UL rate

control in the UE, i.e. allocation of a priority and a prioritised bit rate (PBR) for each RB.

− Recovery from radio link failure.

• Inter-RAT mobility including e.g. security activation, transfer of RRC context information.

• Measurement configuration and reporting.− Establishment/ modification/ release of measurements (e.g. intra-frequency, inter-frequency

and inter- RAT measurements).

− Setup and release of measurement gaps.

− Measurement reporting.

• Other functions including e.g. transfer of dedicated NAS information.

• Generic protocol error handling.

• Support of self-configuration and self-optimisation.


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• Header compression and decompression of IP data flows using the ROHC protocol.

• Transfer of data on user plane or control plane.• Maintenance of PDCP sequence numbers.

• in-sequence delivery of upper layer PDUs at re-establishment of lower layers.

• Duplicate elimination of lower layer SDUs at re-establishment of lower layers for radiobearers mapped on RLC AM.

• Ciphering and deciphering of user plane data and control plane data.

• Integrity protection and integrity verification of control plane data.

• Timer based discard.

• Duplicate discarding.


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RLC functions according to transfer mode.

• Transfer of upper layer PDUs.• Error correction through ARQ (only for AM data transfer).

• Concatenation, segmentation and reassembly of RLC SDUs (only for UM and AM datatransfer).

• Re-segmentation of RLC data PDUs (only for AM data transfer).

• Reordering of RLC data PDUs (only for UM and AM data transfer).

• Duplicate detection (only for UM and AM data transfer).

• RLC SDU discard (only for UM and AM data transfer).

• RLC re-establishment.

• Protocol error detection (only for AM data transfer)


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• Mapping between logical channels and transport channels.

• Multiplexing of MAC SDUs from one or different logical channels onto transport blocks(TB) to be delivered to the physical layer on transport channels.

• Demultiplexing of MAC SDUs from one or different logical channels from transportblocks (TB) delivered from the physical layer on transport channels.

• Scheduling information reporting.

• Error correction through HARQ.

• Priority handling between UEs by means of dynamic scheduling.

• Priority handling between logical channels of one UE.

• Logical Channel prioritisation.

• Transport format selection.


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• Error detection on the transport channel and indication to higher layers.

• FEC encoding/decoding of the transport channel.• Hybrid ARQ soft-combining.

• Rate matching of the coded transport channel to physical channels.

• Mapping of the coded transport channel onto physical channels.

• Power weighting of physical channels.

• Modulation and demodulation of physical channels.

• Frequency and time synchronisation.

• Radio characteristics measurements and indication to higher layers.

• Multiple Input Multiple Output (MIMO) antenna processing.

• Transmit Diversity (TX diversity).

• Beamforming.

• RF processing.


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In general, RRC signalling covers the following procedures

System informationIncludes broadcasting of system information (scheduling and notification of changes),system information acquisition and acquisition of SI messages.

Connection control

Includes paging, RRC connection establishment, initial security activation RRC connectionreconfiguration, counter check, RRC connection re-establishment, RRC connectionrelease, radio resource configuration and radio link failure actions.

Measurement

Includes measurement configuration, Layer 3 filtering and measurement reporting.

Inter-RAT mobility

Includes handover to E-UTRA, mobility from E-UTRA and inter-RAT cell change.

Other

Includes DL/UL information transfer and UE capability transfer.


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RRC connection establishment involves the establishment of SRB1. E-UTRAN completesRRC connection establishment prior to completing the establishment of the S1 connection,i.e. prior to receiving the UE context information from the EPC. Consequently, AS securityis not activated during the initial phase of the RRC connection. During this initial phase ofthe RRC connection, the E-UTRAN may configure the UE to perform measurementreporting. However, the UE only accepts a handover message when security has beenactivated.

Upon receiving the UE context from the EPC, E-UTRAN activates security (both cipheringand integrity protection) using the initial security activation procedure. The RRC messagesto activate security (command and successful response) are integrity protected, whileciphering is started only after completion of the procedure. That is, the response to themessage used to activate security is not ciphered, while the subsequent messages (e.g.used to establish SRB2 and DRBs) are both integrity protected and ciphered.

After having initiated the initial security activation procedure, E-UTRAN initiates theestablishment of SRB2 and DRBs, i.e. E-UTRAN may do this prior to receiving theconfirmation of the initial security activation from the UE. In any case, E-UTRAN will applyboth ciphering and integrity protection for the RRC connection reconfiguration messagesused to establish SRB2 and DRBs. E-UTRAN should release the RRC connection if theinitial security activation and/ or the radio bearer establishment fails (i.e. security activationand DRB establishment are triggered by a joint S1-procedure, which does not supportpartial success).

For SRB2 and DRBs, security is always activated from the start, i.e. the E-UTRAN doesnot establish these bearers prior to activating security.


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Access Stratum (AS) security comprises of the integrity protection of RRC signalling(SRBs) as well as the ciphering of RRC signalling (SRBs) and user data (DRBs).

The integrity protection algorithm is common for signalling radio bearers SRB1 and SRB2.The ciphering algorithm is common for all radio bearers (i.e. SRB1, SRB2 and DRBs).Neither integrity protection nor ciphering applies for SRB0.

RRC integrity and ciphering are always activated together, i.e. in one message/ procedure.RRC integrity and ciphering are never de-activated. However, it is possible to switch to a'NULL' ciphering algorithm (eea0).


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With this procedure, the UE is requested to check if, for each DRB, the most significantbits of the COUNT match with the values indicated by E-UTRAN


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The purpose of this procedure is to re-establish the RRC connection, which involves theresumption of SRB1 operation and the re-activation of security.

A UE in RRC_CONNECTED, for which security has been activated, may initiate theprocedure in order to continue the RRC connection. The connection re-establishmentsucceeds only if the concerned cell is prepared i.e. has a valid UE context. In case E-UTRAN accepts the re-establishment, SRB1 operation resumes while the operation ofother radio bearers remains suspended. If AS security has not been activated, the UEdoes not initiate the procedure but instead moves to RRC_IDLE directly


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The RRC protocol is responsible for the basic configuration of the radio protocol stack. Butnote that some radio management functions (scheduling, physical resource assignment forphysical channels) are handled by layer 1 and layer 2 autonomously.

MAC and layer 1 signalling has usually delays that are within 10 ms, whereas RRCsignalling usually takes something around 100 ms and more to complete an operation.


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Inter-3GPP RAT mobility is achieved either:

•Inter-RAT handover •Cell reselection

•Cell change order (CCO) with Network Assisted Cell Change (NACC)


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PDCP is used for SRBs and DRBs mapped on DCCH and DTCH type of logical channels.PDCP is not used for any other type of logical channels

In general, PDCP covers the following procedures:

Data Transfer Procedures

Procedures for SRB and DRBs mapped to either RLC UM or RLC AM.

Re-establishment Procedures

Re-establishment procedure for SRB and DRBs mapped to either RLC UM or RLC AM.

PDCP Status Report

Procedure to report missing PDUs and/or failed decompressed PDU

PDCP Discard

Header Compression and Decompression

The procedure covers the selection of supported protocols and profiles, configuring theheader compression (including parameters), header compression and decompression.

Ciphering and Deciphering

The ciphering algorithm and key to be used by the PDCP entity are configured by upperlayers.

Integrity Protection and Verification

The integrity protection algorithm and key to be used by the PDCP entity are configured byupper layers.


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Services provided to upper layers

• Transfer of user plane data.• Transfer of control plane data.

• Header compression.

• Ciphering.

• integrity protection.

Services expected from lower layers

• Acknowledged data transfer service, including indication of successful delivery of PDCPPDUs.

• Unacknowledged data transfer service.

• In-sequence delivery, except at re-establishment of lower layers.

• Duplicate discarding, except at re-establishment of lower layers.


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In general, RLC protocol covers the following procedures:

Data Transfer ProceduresRLC provides 3 data transfer modes to the upper layer, i.e. Transparent Mode (TM),Unacknowledged Mode (UM) and Acknowledged Mode (AM).

ARQ Procedures

Includes retransmission, polling and status reporting processes.

SDU Discard Procedure

Re-establishment Procedure


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In general, MAC protocol covers the following procedures:

Random Access ProcedureIn MAC, the Random Access procedure comprises the resource selection, preambletransmission, contention resolution and completion processes.

Maintenance of Uplink Time Alignment

This procedure is related to Timing Advance adjustment for uplink transmission.

DL-SCH Data Transfer

Two most important processes in this procedure are DL assignment and Downlink HARQ.

UL-SCH Data Transfer

This procedure covers UL grant, Uplink HARQ, Scheduling Request (SR), Buffer Status

Reporting (BSR) and Power Headroom Reporting.PCH Reception

BCH Reception

Discontinuous Reception (DRX)

The UE may be configured by RRC with a DRX functionality, either in RRC_IDLE orRRC_CONNECTED state.

MAC Reconfiguration

MAC Reset

Semi-persistent Scheduling


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• A MAC PDU consists of:

• A MAC header • Zero or more MAC SDU

• Zero or more MAC control elements, and

• optionally padding

• Both the MAC header and the MAC SDUs are of variable sizes.

• A MAC PDU header consists of one or more MAC PDU subheaders:

• Each subheader corresponds to either a MAC SDU, a MAC control element orpadding.


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• A MAC PDU consists of a MAC header and zero or more MAC Random AccessResponses (MAC RAR) and optionally padding.

•The MAC header is of variable size.

• A MAC PDU header consists of one or more MAC PDU subheaders

•each subheader corresponding to a MAC RAR except for the Backoff Indicatorsubheader.

•Padding may occur after the last MAC RAR. Presence and length of padding is implicitbased on TB size, size of MAC header and number of RARs.


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The first steps after switching on the mobile are the following:

1. Primary Synchronization Signal PSS – from which the mobile can acquire frequencyand slot synchronization. Once the UE successfully detects the sequence used in PSS,it easily determines physical-layer identity – which could have values 0,1 or 2 – basedon the root sequence.

2. Secondary Synchronizations Signal SSS – from which the mobile can learn what is theframe structure (10 ms in LTE). Once the UE successfully detects the sequence usedin SSS, it may calculate the physical-layer cell id group – with values range from 0 to167.

From step 1 and 2, the UE now is having reference of Physical-layer Cell Identity of thecurrent cell.

3. The Physical-layer Cell Identity is used to determine the sequence that is used as

Reference Signals RS. RS is placed evenly and transmitted with defined power,therefore it can be used in channel estimation and subject to measurement.

4. The Physical-layer Cell Identity is also used to derive scrambling sequence of PBCH.By using this sequence and channel estimation result, UE is now able to decodePBCH. PBCH gives the UE the system information contained in MIB, i.e. DL bandwidth,PHICH configuration and System Frame Number SFN.


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Because the SIBs are placed on the PDSCH then the mobile should now read the PDSCH.The steps are the following:

5. PCFICH (Physical Control Format Indicator Channel) indicates how many symbols inthe beggining of each subframe (1 subframe is having 1 ms in LTE) are allocated forthe PDCCH. This is beacuse the size of the PDCCH may be changed based on severalvariables like cell bandwith, cell load ...

6. PDCCH (Physical Downlink Control Channel) – from this channel the mobile can learn:what are the physical resources allocated for the mobile and where are they placed inthe time and frequency

7. Finally the UE may read the PDSCH to read the broadcasted system information.

After the mobile is reading the system information from the PDSCH the next step is the socalled cell selection and reselection. The basic ideea is that the UE is measuring

several cells and is selecting the best one with the help of the thresholds from thesystem information


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For the initial random access the steps are the following

8A – the mobile is selecting randomly one preamble. There are in total 64 preamblesavailable preambles in one cell. In this case with A it is intended to note the first randompreamble

8C – If no answer is received from the Node-b then the mobile is repeating the preamble.In this example with C is noted the 3rd preamble. That means that the assumption is thatafter three preambles the UE is receiving an answer from the Node-B


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In the next step the mobile should receive the answer to the preamble. However, theanswer is sent on the PDSCH. Therefore the steps are as follows:

9. PCFICH (Physical Control Format Indicator Channel) indicates how many symbols inthe beggining of each subframe (1 subframe is having 1 ms in LTE) are allocated for thePDCCH. This is beacuse the size of the PDCCH may be changed based on severalvariables like cell bandwith, cell load ...

10. PDCCH (Physical Downlink Control Channel) – from this channel the mobile can learn:what are the physical resources allocated for the mobile and where are they placed in thetime and frequency

11. PDSCH – containing the random access response. In this message the id of thetransmitted preamble should be included. Also the Node-B allocates to the mobile the C-RNTI = Cell Radio Network temporary Identity. C-RNTI is allocated by the eNB serving aUE when it is in active mode (RRC_CONNECTED). This is a temporary identity for theuser only valid within the serving cell of the UE. It is exclusively used for radiomanagement procedures.

12. PUSCH Physical UL Shared Channel. The mobile is sending the actual higher layermessage – RRC Connection Request. The message should include the C-RNTI allocatedin 11 and also TMSI = Temporary Mobile Subscriber Identity (or a random number if TMSInot available). This is because IMSI should be never sent on the air interface.

13. PDSCH – contention resolution message. As explained this message is only sent if theNode-B could decode the message number 12 from the mobile. The message shouldcontain the C-RNTI allocated in 11 and also TMSI or a the same random number sent bythe mobile.


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The message flow for the DL transmission is as following (please note that for simplicitythe notation of the messages counter is restarted from 1).

1. DL reference Signals - Used for channel estimation and measurements

2. PUCCH – used in this in scenario to indicate the CQI based on the measurementsperformed in the previous step. Please note that PUCCH or PUSCH could be useddepending on whether the mobile is having some UL data transmission or not. Fordetails please refer to the section “UL Transmission”

3. PCFICH indicates how many symbols in the beggining of each subframe (1 subframeis having 1 ms in LTE) are allocated for the PDCCH. This is beacuse the size of thePDCCH may be changed based on several variables like cell bandwith, cell load ...

4. PDCCH (Physical Downlink Control Channel) – from this channel the mobile can learn:what are the physical resources allocated for the mobile and where are they placed in

the time and frequency. Also the modulation and coding scheme should be indicated5. PDSCH – data transmission (this is the web page from the Internet)

6. ACK or NACK for the user data on 5. This is for HARQ retransmission

7. In Case of NACK then the user data sent 5 has to be retransmitted.


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The message flow for the UL transmission is as follows:

1. PUCCH – the mobile is requesting the Node-B to schedule some physical resourcesfor the UL transmission. Please note that the Node-B is in charge of the UL schedulingalso. Also note that the scheduling request is only needed for applications with QoS likebest effort. For application with higher QoS like VoIP there is no need for thescheduling request since the resources have to be granted

2. UL sounding reference signal – used for the channel dependent scheduling. For detailsplease refer to the section “UL Transmission”

3. UL Demodulation Signal. Used for channel estimation reasons. For details please referto the section “UL Transmission”

4. PDCCH – used in this scenario to indicate the UL grant, that is, what are the physicalresources which could be used by the mobile for the UL transmission

5. PUSCH – this is the actual user data transmission (the user is sending the requestwww.nsn.com)

6. PHICH – this is actually on DL channel on which the ACK or NACK for the HARQ aretransmitted

7. PUSCH – retransmission of user data if 6 is indicating NACK.


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CCE: Control Channel Element

REG: Resource Element GroupRE: Resource Element


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MIB: Master Information Block

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02 RA41562EN02GLA0 LTE Radio Interface Protocols and Procedures Ppt