Radio interface procedures

3,974 views

Published on

Published in: Technology, Business
2 Comments
0 Likes
Statistics
Notes
  • Be the first to like this

No Downloads
Views
Total views
3,974
On SlideShare
0
From Embeds
0
Number of Embeds
13
Actions
Shares
0
Downloads
200
Comments
2
Likes
0
Embeds 0
No embeds

No notes for slide
  • Within UTRAN system information is broadcasted with the help of the RRC messages
    System Information,
    Paging Type I, and
    System Information Change Indication.
    Most system information parameters are determined by the RNC. The Node B is informed about the parameters via the NBAP message BCCH Information. Some system parameters can be made available by the Node B, such as interference values, which change fast. Given the system information, the UE is capable to decide, whether or how to access the PLMN via the existing cell.
    System information is organised in System Information Blocks (SIBs). System information is grouped into SIB 1 to SIB 18. Each SIB is responsible to carry a specific content. For instance, SIB 12 holds measurement control information and parameters. Depending on the UE‘s RRC state, is reads specific SIBs, and uses the transmitted parameters.
    There is a huge amount of SIBs, which have to be read by the UE. This requires a lot of battery power. Therefore, a Master Information Block (MIB) was introduced, which gives references and scheduling information about the SIBs. The MIB is transmitted in every 8th radio frame on the P-CCPCH (on position SFN mod 8 = 0, and with a TTI of 20 ms). For most of the SIBs used within the system, the MIB may carry a value tag. The only exceptions are SIB 15.2, SIB 15.3 and SIB 16. If a value tag is unchanged, the corresponding system information has not been modified. Thus, there is no need for the UE to read the SIB. SIB 7 has no value tag. It changes with each occurrence. Scheduling information is used to inform the UE, where and when a specific system information is transmitted.
  • In this course module, we focus our interest on the RRC Connection Establishment procedure, which is part of the RRC Connection Management procedures.
    The purpose of the RRC Connection Establishment procedure is to create a RRC connection between the UE and UTRAN. To do so, the UE sends the RRC Connection Request message to the RNC. The UE was in the RRC idle mode, and higher layer protocols in the UE request a signalling connection to UTRAN.Please note, that an RRC connection establishment is always initiated by the UE. It is transmitted via the logical channel CCCH.
    UTRAN returns a response. If UTRAN accepts the UE‘s RRC Connection Request, it returns the message RRC Connection Setup message. The UE gets all relevant parameters regarding the signalling bearers, transport channels, and physical channels. From the RNC point of view, it is not just sufficient to inform the UE about the signalling resources. The Node B must also get all relevant parameters to serve the UE on the radio interface adequately, and to relay data between the Iub-interface and Uu-interface. Before the RNC returns the RRC Connection Setup message to the UE, it uses the UTRAN specific signalling protocol NBAP to send these parameters to the Node B. If UTRAN denies access to the UE, it returns the message RRC Connection Reject. Both messages are returned to the UE via a FACH.
    If the UE has received the message RRC Connection Setup, it returns the RRC Connection Setup Complete message to the RNC, using the transport channel DCH.
  • When a UE is switched on, it enters the RRC idle mode. In the RRC idle mode, there is no connection on the access stratum level between the UE and UTRAN. UTRAN has no information about UEs in the RRC idle mode. If UTRAN wants to address the UE, it must use non-access stratum identifiers, such as IMSI or TMSI and LAI. In the RRC idle mode, the UE monitors the BCCH, and when it is registered to the CN, it also listens to paging occasions on its PICH.
    The UE is in the RRC idle mode, when it is powered on. Is it possible, that in this state, the UE has an active connection? The answer is yes – after a PDP context activation, the UE has an active connection an SGSN. There are to packet switched mobility management states: ps idle and ps dedicated state. In the ps idle state, there are no transmission resources allocated to the active PDP context between the UE and the SGSN. A higher layer connection exists, but UTRAN has no information about the UE‘s location. The UE is in the RRC idle mode.
    The transition from the RRC idle mode to the RRC connected mode can only be initiated by the UE by sending the RRC Connection Request message to UTRAN. If common transport channels used to exchange messages and data between the UE and UTRAN, the UE is identified by a Radio Network Temporary Identity (RNTI). As can be seen in the figure on the right hand side, the UE can be in one of four sub-states, when it is in the RRC connected mode. The sub-states depend on the connectivity level between the UE and UTRAN. The set of usable transport channels depend also on the sub-states. For instance, the DCHs are not available in the sub-states CELL_PCH and CELL_URA. The UE leaves the RRC idle mode when sending the RRC Connection Request message to UTRAN. When UTRAN accepts the UE‘s request, the UE enters either the sub-state CELL_DCH or CELL_FACH.
  • What are the characteristics of the individual sub-states, when the UE is in the RRC connected mode?
    CELL_DCHIn this sub-state, dedicated physical channels are allocated to the UE. DCCH and – if configured – DTCH information can be transmitted. There no need to identify the UE on a dedicated channel, because the physical channels are exclusively allocated to this UE. UTRAN knows the active set cells for the radio links and thus the location of the the UE. Also downlink shared channels can be allocated to the UE. In this state, the UE is capable to receive RRC messages on the DCCH (and BCCH, if it owns specific capabilities). The cell system information is broadcasted on the FACH. The UE reads the cell system information and acts accordingly. For instance, it determines the measurement quality and the reporting events from the cell system information.
  • CELL_FACHThis state was introduced for traffic situations, where only small amounts of data have to be transmitted. This is the case when only higher layer signalling information (NAS signalling) or small amount of user data (e.g. SMS messages) have to be transmitted. In this case, an exclusive allocation of one physical channel to the UE would result in a waste of resources. The UE is capable to receive and transmit DCCH and – if configured – DTCH information. Only common transport channel FACH can be used by the UE to transmit higher layer data, which it has to share with other UEs. It has to monitor the FACH permanently in the downlink, not to miss user data for it. The UE‘s FACH is mapped on one S-CCPCH. In the uplink, it uses the shared transport channels for user data transfer, such as the RACH. The UE is only connected to one cell, and this is the location information, known within UTRAN. No soft handover takes place in this sub-state. The UE is responsible for cell re-selection. By listening to the cell system information from the BCCH, it gains all relevant measurement qualities, threshold values, neighbourhood lists to perform the cell re-selection process. Other relevant information is also learned from the BCCH. The UE receives RRC messages on the BCCH, CCCH and DCCH channels. Due to the discontinuous type of traffic, UTRAN can command the UE to perform periodic cell updates.
  • The remaining two sub-states – CELL_PCH and URA_PCH – were introduced to cope with inactive data users. Just think about users, who surf in the Internet. After downloading some files, they work with the data, and for a longer time, no transmission takes place. If this is the case, access stratum resources can be released when moving in one of the two states.
    In both states, no DCCH nor DTCH is allocated to the UE. No exchange of data is possible between the UE and UTRAN. If the UE wants to transmit something, it must move first internally to the sub-state CELL_FACH. The UE listens to the cell system information, broadcasted on the BCCH. It performs measurements accordingly, and is responsible for cell-reselection. In addition to that, it periodically looks for a PLMN with a higher priority. When UTRAN wants to transmit data to the UE, it must be paged first. Therefore, the UE has to monitor paging occasions on its PICH, i.e. it receives RRC messages both on the BCCH and the PCCH.
    CELL_PCHIn this sub-state, the UE‘s current cell is known to the RNC. If the RNC wants to exchange data with the UE, it only needs to page the UE there. If the UE changes the cell, it must perform a cell update. Also periodical cell updates can be requested by UTRAN. To perform updates, the UE must change to the CELL_FACH sub-state. (Please note, that no uplink transmission is allowed in CELL_PCH/URA_PCH.)
    URA_PCHURA stands for UTRAN Registration Area. If the UE is in the CELL_PCH and moving fast, a lot of cell updates have to be performed. URAs are a combination of one or several cells under one C-RNC. URAs may overlap, i.e. a cell may belong to several URAs. If UTRAN wants to transmit something to the UE, it must page the UE within the URA. The UE is responsible for URA updates – when it changes the URA – and periodic URA updates – when required by UTRAN.
  • In this course module, we focus our interest on the RRC Connection Establishment procedure, which is part of the RRC Connection Management procedures.
    The purpose of the RRC Connection Establishment procedure is to create a RRC connection between the UE and UTRAN. To do so, the UE sends the RRC Connection Request message to the RNC. The UE was in the RRC idle mode, and higher layer protocols in the UE request a signalling connection to UTRAN.Please note, that an RRC connection establishment is always initiated by the UE. It is transmitted via the logical channel CCCH.
    UTRAN returns a response. If UTRAN accepts the UE‘s RRC Connection Request, it returns the message RRC Connection Setup message. The UE gets all relevant parameters regarding the signalling bearers, transport channels, and physical channels. From the RNC point of view, it is not just sufficient to inform the UE about the signalling resources. The Node B must also get all relevant parameters to serve the UE on the radio interface adequately, and to relay data between the Iub-interface and Uu-interface. Before the RNC returns the RRC Connection Setup message to the UE, it uses the UTRAN specific signalling protocol NBAP to send these parameters to the Node B. If UTRAN denies access to the UE, it returns the message RRC Connection Reject. Both messages are returned to the UE via a FACH.
    If the UE has received the message RRC Connection Setup, it returns the RRC Connection Setup Complete message to the RNC, using the transport channel DCH.
  • The RRC Connection Setup message is used to specify the (signalling) radio bearer, the transport channel and the physical channel characteristics both in the UL and downlink directions. The RRC Connection Setup message is sent from the RRC layer in the RNC to the RRC layer in the UE. The UE‘s RRC uses management interfaces to the configure the „lower“ layers accordingly.
    If only the physical layer characteristics are modified, then the RRC layer only has to interact with the PHY layer. A modification may affect scrambling and modulation. A new channelisation code may be deployed for the connection, which has no impact to the higher layers. The PHY layer is for instance responsible for radio measurements, and the RNC can change measurement quantities or threshold values. Again, this has no impact on the higher layers.
    If the transport channels are modified, then this has an effect both on the MAC (Medium Access Control) layer and the PHY layer. The MAC layer is responsible for Transport Format selection, identification of UEs on the common and shared resources, ciphering and de-ciphering, random access control, etc.
  • The RRC Connection Setup message is used to specify the (signalling) radio bearer, the transport channel and the physical channel characteristics both in the UL and downlink directions. The RRC Connection Setup message is sent from the RRC layer in the RNC to the RRC layer in the UE. The UE‘s RRC uses management interfaces to the configure the „lower“ layers accordingly.
    If only the physical layer characteristics are modified, then the RRC layer only has to interact with the PHY layer. A modification may affect scrambling and modulation. A new channelisation code may be deployed for the connection, which has no impact to the higher layers. The PHY layer is for instance responsible for radio measurements, and the RNC can change measurement quantities or threshold values. Again, this has no impact on the higher layers.
    If the transport channels are modified, then this has an effect both on the MAC (Medium Access Control) layer and the PHY layer. The MAC layer is responsible for Transport Format selection, identification of UEs on the common and shared resources, ciphering and de-ciphering, random access control, etc.
  • In case of a mobile terminated call (MTC), the process starts with paging. Paging
    is the procedure by which a mobile network attempts to locate the UE within its
    location area before any other network-initiated procedure can take place.
    If the UE originates the call, paging is not needed and the UE directly requests
    RRC connection setup.
    After having established an RRC connection, the UE starts setting up a signalling
    connection to the CN. For that, a new radio link is needed.
    Finally, the radio access bearer setup procedure builds a radio access bearer
    service between the UE and the core network (CN), and the call is established.
  • Radio interface procedures

    1. 1. Agenda • Radio Interface Overview • Cell Synchronisation • Idle Mode Procedures ▪ Broadcast of system Information ▪ PLMN selection ▪ Cell Selection and Reselection • RRC Connection Setup Procedure • CS AMR Call Establishment • PS Call Establishment • Handover Procedures : Softer, Soft, Inter-RAT
    2. 2. Introduction UE is powered up Cell search Radio frame synchronisation UE is powered up Cell search Radio frame synchronisation Read BCCH Read BCCH Cell selection Register with core network Originating AMR speech call Handovers Release of AMR speech call AMR Speech call Cell selection Register with core network Originating PS Call Cell State Transitions PS Data call
    3. 3. Radio Interface Overview
    4. 4. UTRAN UTRAN UE Uu CN Radio Network Subsystem ( RNS ) circuit MSC / VLRswitched ( cs ) domain Iu-CS Iub RNC Uu Iur UE Iub RNC Iu-PS Radio Network Subsystem ( RNS ) SGSN packet switched ( ps ) domain
    5. 5. Protocol Stacks • Communication between the UE, RNC and circuit switched core makes use of • Uu interface protocol stack • Iub interface protocol stack • Iu,cs interface protocol stack • A interface protocol stack Multimedia Gateway RNC Node B 3G MSC Uu Iub • Protocol stacks include both user and control planes Iu,cs A
    6. 6. CS Radio Interface Protocol (RIP) Control Plane • The radio interface protocol control plane allows RRC signalling between the RNC and UE • RRC signalling is communicated across the Iub using the Iub user plane protocol stack i.e. using Frame protocol and AAL2 based ATM • Acknowledged or unackowledged mode RLC is used between the UE and RNC UE RNC RRC RRC RLC-C RLC-C No de B MAC MAC FP AAL2 WCDMA L1 WCDMA L1 Uu FP AAL2 ATM ATM Phy Phy I ub
    7. 7. CS Radio Interface Protocol (RIP) User Plane • The 3G MSC provides connectivity to the circuit switched core and PSTN • Transparent mode RLC is used between the UE and RNC • AAL2 based ATM is used to transfer user plane data across the Iub and Iu,cs interfaces UE M ultim e dia G W e.g. vocoder e.g. vocoder RNC RLC-U RLC-U No d e B MAC MAC Iu,cs UP Iu,cs UP Uu A Law PCM, etc FP AAL2 WCDMA L1 A Law PCM, etc PSTN FP WCDMA L1 3G M SC AAL2 AAL2 AAL2 ATM ATM ATM Phy Phy Phy I ub ATM Link Layer Phy I cs u, Link Layer Phy Phy A Phy
    8. 8. AS and NAS Signalling CN Iu edge node UE NAS signalling and User data i.e. MM, PMM & CC, SS, SMS, SM UTRAN RNC Access Stratum Signalling (Uu Stratum) RRC Access Stratum Signalling (Iu Stratum) RANAP
    9. 9. UMTS QoS Architecture TE MT CN Iu edge node UTRAN CN Gateway TE End-to-End Service TE/MT Local Bearer Service UMTS Bearer Service = UMTS QoS Radio Access Bearer Service Radio Bearer Service Iu Bearer Service UTRA FDD/TDD Service Physical Bearer Service CN Bearer Service Backbone Bearer Service External Bearer Service
    10. 10. Radio Interface Protocol Architecture Control Plane Signalling control control control User Plane RRC Layer control RBs PDCPPDCP PDCP control RLC Layer RLC RLC RLC BMC RLC RLC RLC RLC RLC LogCHs MAC Layer TrCHs PHY Layer PhyCHs
    11. 11. WCDMA Frame • Radio frame: A radio frame is a processing duration which consists of 15 slots. The length of a radio frame corresponds to 38400 chips. • Slot: A slot is a duration which consists of fields containing bits. The length of a slot corresponds to 2560 chips 0 1 2 3 4 5 6 7 10ms 8 9 10 11 12 13 14
    12. 12. Cell Search Procedure Radio Interface Synchronisation
    13. 13. Cell Synchronisation Phase 1 – P-SCH Detect cells Acquire slot synchronisation Phase 2 – S-SCH Acquire frame synchronisation Identify the code group of the cell found in the first step Phase 3 – P-CPICH ► Determine the exact primary scrambling code used by the found cell Measure level & quality of the found cell
    14. 14. Step 1- Slot synchronization ◄ ►
    15. 15. Slot Synchronization PSC : Primary synchronization code – – – – PSCH 256 chip sequence transmitted in each slot interval Same for all cells and slot intervals Mobile Station uses the PSC to acquire slot synchronization The sot timing of the cell can be obtained by detecting peak values in the matched filter TS Boundary Matched filter Stored PSCH 2560 chips
    16. 16. Step 2 - Frame Synchronization SSC: Secondary synchronization code – 256 chip sequence transmitted in parallel with PSC. – In general different for different cells and slot intervals – 16 different ‘256 chip’ sequence ( 16 secondary synch code) – Code word of 15 consecutive SSC indicates ‘cell scrambling code group’ – There are 64 such code groups – UE checks in each slot 16 possible SSC sequences and select which gives the highest correlation value => 15 codes are selected – The cyclic shift is unique and gives the frame synchronization and the scrambling code group Slot No. 0 1 2 14 Group1 Group2 Group3 SSC1 SSC1 SSC2 ….. SSC16 SSC1 SSC1 SSC5 ….. SSC10 SSC1 SSC2 SSC1 …… SSC12 SSC9 SSC12 SSC10 ….. ….. Group64 …… SSC10 ◄
    17. 17. SSC Allocation for S-SCH scrambling code group slot number 0 1 2 3 4 5 6 7 8 9 10 11 12 13 1 4 group 00 1 1 2 8 9 10 15 8 10 16 2 7 15 7 16 group 01 1 1 5 16 7 3 14 16 3 10 5 12 14 12 10 group 02 1 2 1 15 5 5 12 16 6 11 2 16 11 15 12 group 03 1 2 3 1 8 6 5 2 5 8 4 4 6 3 7 group 04 1 2 16 6 6 11 15 5 12 1 15 12 16 11 2 group 05 1 3 4 7 4 1 5 5 3 6 2 8 7 6 8 group 62 9 11 12 15 12 9 13 13 11 14 10 16 15 14 16 group 63 9 12 10 15 13 14 9 14 15 11 11 13 12 16 10 11 15 5 I monitor the SSCH
    18. 18. Step 3 - Scrambling Code Identification • With the help of the SCH, the UE was capable to perform chip, TS, and frame synchronisation. Even the cell‘s scrambling code group is known to the UE. • But in the initial cell selection process, it does not yet know the cell‘s primary scrambling code. • There is one primary scrambling code in use over the entire cell, and in neighbouring cells, different scrambling codes are in use. There exists a total of 512 primary scrambling codes. How does UE identify Cell’s primary scrambling code ( 1 out of 512 codes)
    19. 19. Step 3 - Scr ambling code Identification 1) Long Scrambling code :262143 Codes 2) To speed up the cell search => only 8192 codes 3) 8192 code grouping: 512 groups of 16 codes each (512*16 = 8192) 4) 16 codes in each group => first code is Primary scrambling code and 15 codes are Secondary scrambling codes 5) Again 512 codes are further divided into 64 groups of 8 codes 6) These 64 groups map to the 64 scrambling code group used at stage 2 during frame synchronization • That way UE limits its Primary Scrambling code search to just 8 codes • At this stage max 8 attempts to find out the Primary Scrambling code of the cell 7) Each cell is allocated one Primary scrambling code ( Carrying P-CPICH, PCCPCH, PICH, AICH and S-CCPCH) 8) Other channels can use Primary scrambling code or secondary scrambling codes from the same group
    20. 20. Primary Common Pilot Channel (P-CPICH) 10 ms Frame Synchronisation Channel ( SCH ) 2560 Chips256 Chips CP P-CPICH applied speading code = cell‘s primary scrambling code ⊗ C ch,256,0 • Phase reference • Measurement reference Cell scrambling code? I get it with trial & error! P-CPICH
    21. 21. Timing Relationship Slot 1 Slot 2 Slot 15 Slot 1 Cp Primary SCH Cp Cp Cs1 Secondary SCH Cs2 Cs1 Primary CCPCH 256 chips 2560 - 256 chips Primary CPICH
    22. 22. Cell Synchronisation Procedure: Summary When a UE is switched on, it starts to monitor the radio interface to find a suitable cell to camp on but it has to determine, whether there is a WCDMA cell nearby. If a WCDMA cell is available, the UE has to be synchronised to the downlink transmission of the system information – transmitted on the physical channel P-CCPCH – before it can make a decision, in how far the available cell is suitable to camp on. Initial cell selection is not the only reason, why a UE wants to perform cell synchronisation. This process is also required for cell re-selection and the handover procedure. Cell synchronisation is achieved I three phases • Step 1: Slot synchronisation – During the first step of the cell search procedure the UE uses the SCH"s primary synchronisation code to acquire slot synchronisation to a cell. This is typically done with a single matched filter (or any similar device) matched to the primary synchronisation code which is common to all cells. The slot timing of the cell can be obtained by detecting peaks in the matched filter output. • Step 2: Frame synchronisation and code-group identification – During the second step of the cell search procedure, the UE uses the SCH"s secondary synchronisation code to find frame synchronisation and identify the code group of the cell found in the first step. This is done by correlating the received signal with all possible secondary synchronisation code sequences, and identifying the maximum correlation value. Since the cyclic shifts of the sequences are unique the code group as well as the frame synchronisation is determined. • Step 3: Scrambling-code identification – During the third and last step of the cell search procedure, the UE determines the exact primary scrambling code used by the found cell. The primary scrambling code is typically identified through symbol-by-symbol correlation over the CPICH with all codes within the code group identified in the second step. After the primary scrambling code has been identified, the Primary CCPCH can be detected. And the system- and cell specific BCH information can be read. If the UE has received information about which scrambling codes to search for, steps 2 and 3 above can be simplified.
    23. 23. Broadcast of System Information Cell search Radio frame synchronisation Read BCCH
    24. 24. Channels carrying System Information Logical Channels Transport Channels Physical Channels P-SCH S-SCH CPICH BCCH BCH P-CCPCH PCCH PCH S-CCPCH PICH CCCH DCCH DTCH FACH HSDSCH DCH AICH HS-PDSCH HS-SCCH DPDCH DPCCH
    25. 25. System Information UTRAN System Information ( ) NBAP: BCCH Information RNC UE Node B •Master Infor mation Block (MIB) -- Refer ence to other system Infor mation blocks and scheduling blocks •Scheduling Blocks (SB1/SB2) MIB -- Refer ences to other system Infor mation blocks •(SIB1-SIB18) -- Contains the actual system Infor mation SB1 SIB 1 SIB 2 SIB 11
    26. 26. Contents of SIB Type SIB Type1: 1. CN Common GSM-MAP NAS system information LAC CS Domain Specific info ( T3212 Timer value, ATT) PS Domain specific info ( RAC, NMO) 2. UE Information UE Timers and constants in IDLE mode UE Timers and constants in connected mode SIB Type 2: UTRAN mobility information elements URA identity (1..maxURA)
    27. 27. SIB 3 SIB Type 3 Parameters for cell selection and reselection 1. Cell Identity 2. Cell selection and reselection info 3. Cell access Restriction
    28. 28. SIB Type5 Contains parameters for the configuration of common and Physical channels 1. SIB6 indicator 2. PhyCH information elements PICH power offset AICH power offset PCCPCH info PRACH sys info list SCCPCH system information CBS DRX Level 1 information
    29. 29. SIB Type 7 Contains the fast changing parameters 1) UL interference ( -110 to -70 dBm)
    30. 30. SIB Type 11 Contains measurement control information to be used in the cell 1. FACH measurement occasion info FACH Measurement occasion cycle length coefficient inter frequency FDD measurement indicator inter-RAT measurement indicators 2. Measurement control Sys info Use of HCS (Enumerated(not used, used)) Cell selection and Reselection quality measure inter-freq meas sys info intra-freq meas sys info inter-RAT meas sys info Traffic volume meas sys info UE internal meas sys info
    31. 31. SIB Type 13,14 and 15 SIB Type 13: Contains ANSI-41 information SIB Type 14: Contains UL Outer Loop Power parameters Meant only for TDD SIB Type 15: Contains information pertaining to UE based positioning methods
    32. 32. SIB Type 16 Contains radio bearer, transport channel and physical channel parameters to be stored by UE in idle and connected mode. The info is used during handover to UTRAN 1. RB Information elements 2. TrCH Information Elements 3. PhyCH Information Elements
    33. 33. SIB Type 17 and SIB Type 18 SIB Type 17 Only for TDD SIB Type 18 PLMN identities for neighbouring cells
    34. 34. Cell Selection UE is powered up Cell search Radio frame synchronisation Read BCCH Cell selection
    35. 35. Cell Selection Criterion S • Which cells are suitable for (initial) cell selection and reselection, so that the UE can camp on them? • This is determined by the UE based on the cell selection criterion S. •It is fulfilled, when •Srxlev > 0 AND Squal > 0 in the FDD mode, and •Srxlev > 0 in the TDD mode. • Squal delivers the cell Selection quality value (dB). •The UE determines it according to this formulary: Squal = Q qualmeas – Qqualmin •The UE measures the received signal quality Qqualmeas of the cell. It is based on CPICH Ec/N0 (dB) for FDD cells. (CPICH Ec/N0 is averaged.) •The operator determines for each cell the minimum required received level Qqualmin (dB) at the UE. This value is the broadcasted. Its integer value can range between –24 and 0 dB. •A cell is not suitable for cell selection and re-selection, if the measured received signal quality level is below Qqualmin. • Srxlev stands for the cell selection receive level value (dB). •The UE determines it this way: Srxlev = Q rxlevmeas - Qrxlevmin – Pcompensation •Q rxlevmeas is the cell RX level measured by the UE, based on the CPICH RSCP for FDD cells (dBm), and the averaged received signal level for
    36. 36. Cell Selection Criterion S (in the FDD mode) Q qualmeas (dB) (CPICH Ec/N0) S-Criterion fulfilled Squal > 0 Squal > 0 AND Srxlev > 0 Qqualmin (–24...0) Qrxlevmin (–115...–25) Q rxlevmeas (dBm) CPICH RSCP Pcompensation suita ble cell? Srxlev > 0
    37. 37. Cell Selection Criterion S • If the UE determines the cell‘s RX level value Q rxlevmeas and Qrxlevmin calculated the Srxlev accordingly, it may have good RX level which means, that a good DL connection can be established. • But the UE‘s own output power capability has to be taken under consideration. This is done with •Pcompensation = max ( UE _ TXPWR _ MAX _ RACH – P _ MAX, 0 ) ( dB ) • In order to access a cell, the UE has to use the common channel PRACH. • The operator determines the maximum cell radius by limiting the maximum TX power level, a UE can use on the PRACH. This is the UE_TXPWR_MAX_RACH (dBm). • UE_TXPWR_MAX_RACH can range – according to the specifications between –50 dBm and 33 dBm. On the other hand, there is the UE‘s maximum RF output power, given by P_MAX (dBm).
    38. 38. Cell Selection Criterion S ell size defining parameters: Qrxlevmin Qqualmin I am outsi de   I am inside, but have not enough -50 .. 33 power dBm sation E _ TXPWR _ MAX _ RACH – P _ MAX, 0 )
    39. 39. (Initial) Cell Selection Process • There exist two cell selection procedures: • Initial Cell Selection •The UE has to find a suitable cell of the PLMN, which was selected by the NAS. •To do so, the mobile phone scans all radio frequency carriers of UTRA. Hereby, the UE focuses its cell search to the suitable cell on each carriers. •As soon as the mobile phone has found a suitable cell, it selects it. • Stored Information Cell Selection •To speed up the cell selection process – for instance, when the UE is switched on again – information about UTRA carriers, even cell parameters such as cell scrambling codes can be stored in the UE. •The UE uses this information to find a suitable cell of the PLMN, which was selected by the NAS. •If the cell selection based on stored information in the UE fails – e.g. the selected PLMN cannot be found – the UE continues the cell selection process based on the Initial Cell Selection procedure. • Both for Initial Cell Selection and Stored Information Cell Selection, a cell is only suitable for the UE to camp on, if it fulfils the cell selection criterion S: •Srxlev > 0 AND Squal > 0 in the FDD mode, and •Srxlev > 0 in the TDD mode.
    40. 40. (Initial) Cell Selection Process Once a suitable cell is found this cell is selected Squal = Q qualmeas – Qqualmin > 0 Srxlev = Q rxlevmeas – Qrxlevmin Initial Cell Selection ( scan RF channel ) or – Pcompensation > 0 Stored Information Cell Selection  I have to find a suitable cell
    41. 41. Cell Selection When Leaving the RRC Connected Mode • Active Set cells as candidates for cell selections; if not suitable, then • Stored information cell selection Squal > 0 Srxlev > 0
    42. 42. Nokia Parameters for Cell Selection • WCEL: QrxlevMin •The minimum required RX level in the cell. •This parameter is part of SIB 3. •[-115 ... –25] dBm, step 2 dBm; default: -115 dBm. • WCEL: QqualMin •The minimum required quality level in the cell (Ec/No). •This parameter is part of SIB 3. •[-24 ... 0] dB, step 1 dB, default: -18 dB. • WCEL: UEtxPowerMaxPRACH •This parameter defines the maximum transmission power level a UE can use on PRACH. •The value of the parameter also effects the cell selection and reselection procedures. •The value of the parameter is sent to UE in the Cell selection and re-selection of SIB 3 and 4 of the serving cell. [..]
    43. 43. Cell Reselection
    44. 44. Cell reselection Neighbour list from BCCH Measurement criteria Measured neighbours S – criteria Suitable neighbours R – criteria Best ranked cell Re-selection if not serving cell
    45. 45. Cell Reselection: Measurement Rules • As part of the network planning process, the operator has to determine the threshold values, which trigger the cell re-selection process by the UE. • The operator has also to decide, whether to use the HCS. The BCCH is used to inform the UE about the use of HCS. • Intra-Frequency measurement threshold S intrasearch •If this parameter is not sent in the serving cell, the UE must always perform intra-frequency measurements. If it is transmitted and Sx > S intrasearch , the UE does not perform intrafrequency measurements. If Sx <= S intrasearch , it performs intrafrequency measurements. • Inter-Frequency measurement threshold S intersearch •If this parameter is not sent in the serving cell, the UE must always perform inter-frequency measurements. If it is transmitted and Sx <= S intersearch , it must perform inter-frequency measurements, but if Sx > S intersearch , there is no need to perform this type of measurement. • Inter-RAT measurement threshold S searchRAT m •If this parameter is not sent in the serving cell, the UE must always perform inter-system measurements. If it is transmitted and Sx > S searchRAT m , it won‘t conduct measurements on cells of
    46. 46. Cell Reselection: Measurement Rules Ssearch RAT Intrafrequency Interfreqency InterRAT EC/N0 = -14 dB Example: Nokia Qqualmin = -18 dB, Sintrasearch = 10dB, m S intersearch S intrasearch Intra-frequency IntraInter-frequency frequency -10 dB Sx = Squal ( in FDD mode) No need to measure neighbour cells -8 dB When to perform measurements serving cell
    47. 47. Cell Reselection: R-Criterion • After checking the measurement thresholds, the UE has detected suitable cells to camp on. • But which of the remaining candidate cells is the best one for cell reselection? • For that, a cell-ranking criterion R was specified: •R s = Q meas,s + Qhyst s (for the serving cell) •R n = Q meas,n - Qoffset s,n (for candidate neighbouring cells for cell reselection) • The serving cell and the remaining candidate cells are ranked according to criterion R. • The cell ranked with the highest value R is the best cell for the UE to camp on. • Qhyst s gives a hysteresis value to make the serving cell more attractive and thus delay the cell re-selection. It exists in two versions: •It ranges between 0 and 40 (step size 2). • The value Qoffset is an offset given for each individual neighbouring cell, which ranges between –50 and 50 dB, with default set to 0.
    48. 48. Cell Reselection: R-Criterion • Is the cell re-selection initiated immediately after the UE ranks a neighbouring cell to be the best? •If so, we could face a ping-pong effect – a UE often performing cell reselection between two neighbouring cells. •To avoid this, the operator uses the time interval value Treselection, whose value ranges between 0 and 31 seconds. •Only when a cell was ranked Treselection seconds better then the serving cell, a cell reselection to this cell takes place. •In addition to this, a UE must camp at least 1 second on a serving cell, before the next cell re-selection may take place. • How often are the cell re-selection criteria evaluated? •This is done at least once every DRX cycle for cells, for which new measurement results are available.
    49. 49. Cell Reselection: R-Criterion R n > R s => “cell reselectio Q meas R s = Q meas,s + Qhyst s R n = Q meas,n - Qoffset s,n Q meas,n Rn Q meas,s Qhyst s Rs Qoffset s,n Treselection
    50. 50. Nokia Parameters for Cell Reselection • WCEL: UseOfHCS •This parameter indicates whether the serving cell belongs to a Hierarchical Cell Structure (HCS). •This parameter is part of SIB 11/12. •0 (HCS not used), 1 (HCS in use); default: 0. • WCEL: Sintrasearch •The threshold for intra-frequency measurements, and for the HCS measurement rules. •This parameter is part of SIB 3. •[0 ... 20] dB, step 2 dB, default: 10 dB. • WCEL: Sintersearch •The threshold for inter-frequency measurements, and for the HCS measurement rules. •This parameter is part of SIB 3. •[0 ... 20] dB, step 2 dB, default: 8 dB. • WCEL: Ssearch _ RAT •The RAT-specific threshold for inter-RAT measurement rules. •This parameter is part of SIB 3. •[0 ... 20] dB, step 2 dB, default: 4 dB.
    51. 51. UE is powered up Register with Core Network Cell search Radio frame synchronisation Read BCCH Cell selection Register with core network Originating AMR speech call Handovers Release of AMR speech call
    52. 52. Register with the Core Network • The UE registers with the CS core domain • CS domain registering is an IMSI attach • Registering is achieved by establishing an RRC connection and sending UE is powered up Cell search Radio frame synchronisation NAS messages to the CS core Read BCCH • RRC CONNECTION ESTABLISHMENT • LOCATION UPDATING PROCEDURE Cell selection Register with core network Originating AMR speech call Handovers ► Release of AMR speech call
    53. 53. UTRAN Specific Signalling Protocols RNS Node B UE I ub :N B RNC AP A RA N -CS: Iu P 3G-MSC/VLR RRC I uPS :R AN AP 3G-SGSN Iur: RNSA P RNC RNS
    54. 54. RRC Connection Establishment
    55. 55. RRC Connection Establishment UE Node B [RACH] RRC Connection Request RNC accept ed [FACH] RRC Connection Setup [DCH] RRC Connection Setup Complete RNC UE [RACH] RRC Connection Request [FACH] RRC Connection Reject rejecte d
    56. 56. RRC Modes UTRA RRC Connected Mode GSM-UMTS Handover URA_PCH CELL_PCH GSM Connected Mode UTRA: Inter-RAT Handover Release RR Connection CELL_DCH Release RRC Connection CELL_FACH Release RRC Connection Establish RRC Connection GPRS Packet Transfer Mode Cell Reselection Release of a TBF Establish RRC Connection (UE camps on UTRAN cell) Idle Mode Initiation of a TBF Establish RR Connection (MS in GPRS Packet Idle Mode) (MS camps on a GERAN cell) (adopted from TS 25.331 V3.12.0)
    57. 57. CELL_DCH State • DCCH and – if configured – DTCH • Dedicate physical channel in use • UE location known on active set cell level • UE responsible for measurement reporting • RRC messages on DCCH active set cell active set cell
    58. 58. CELL_FACH State • DCCH and – if configured – DTCH • FACH used for higher layer data transfer, • UE monitors FACH permanently • Uplink transmission on RACH • UE location known on serving cell level • UE performs cell re-selection • UE responsible for measurement reporting • Cell system information on BCCH • RRC messages on BCCH, CCCH and DCCH serving cell
    59. 59. CELL_PCH and URA_PCH State • • • • • no DCCH and DTCH Before uplink transmission ⇒ UE moves to CELL_FACH UE must be paged RRC messages on BCCH and PCCH In CELL_PCH - UE location known on cell level - UE performs cell re-selection and cell updates • In URA_PCH - UE location known on URA level - UE performs cell re-selection and URA updates URA – UTRAN Registration Area
    60. 60. RRC Connection Establishment UE Node B [RACH] RRC Connection Request RNC accept ed [FACH] RRC Connection Setup [DCH] RRC Connection Setup Complete RNC UE [RACH] RRC Connection Request [FACH] RRC Connection Reject rejecte d
    61. 61. Signalling Radio Bearers RRC Connection Setup ( ) UE RRC Signalling NAS Signalling RNC op t io na l RRC layer RB0 RB1 RB2 RB3 RB4 RLC UL: TrM DL: UM RLC UL & DL: UM RLC UL & DL AM RLC UL & DL AM RLC UL & DL AM CCCH DCCH DCCH DCCH DCCH MAC Radio Bearer LogCH
    62. 62. RRC Connection Setup message RRC Connection Setup ( ) UE NAS Signalling RNC user plane RRC layer RB configuratio n Radio Bearer PDCP BMC RLC LogCH TrCH configuratio n PhyCh configuratio n MAC TrCH PHY PhyCH
    63. 63. Signalling Channel configuration Data RRC signalling Logical Channels DCCH 1-4 Transport Channels Physical Channels DCH 1 DPCH
    64. 64. RRC Connection Setup message RRC Connection Setup ( ) UE NAS Signalling RNC user plane RRC layer RB configuratio n Radio Bearer PDCP BMC RLC LogCH TrCH configuratio n PhyCh configuratio n MAC TrCH PHY PhyCH
    65. 65. RRC Connection Setup Node-B UE RRC RNC RRC Connection Setup Request ( CCCH on RACH) NBAP Signalling Bearer NBAP Radio Link Setup Request Radio Link Setup Response RRC NBAP NBAP establishment ALCAP ALCAP RRC RRC Establish Request Establish Response RRC Connection Setup (CCCH on FACH) RRC Connection Setup Complete (DCCH on DCH) ALCAP ALCAP RRC RRC CN
    66. 66. AMR Speech Call UE is powered up Cell search • The AMR speech call can be either mobile originated or mobile terminated • The following slides present a mobile originated call Radio frame synchronisation • The first step is to establish an RRC connection. This is done in the same way as for the IMSI attach procedure • The only difference is that the establishment cause specified in the RRC Read BCCH Connection Request message is specfied as originatingConversationalCall Cell selection Register with core network Mobile Terminated Call (MTC) Cell re-selections Mobile Originated Call Paging RRC Connectio n Iu-CS Connection Radio Access Bearer AMR speech call Handovers Release of AMR speech call
    67. 67. Iu-CS Call Setup For internal use 76 © Nokia Siemens Networks Presentation / Author / Date
    68. 68. Overview of Setting Up Call Mobile Terminated Call (MTC) Mobile Originated Call Paging RRC Connection Service Request Radio Access Bearer
    69. 69. Iu-CS Call Setup (CM Service Request) UE Node-B MSC RNC RRC Connection Setup RRC Initial Direct Transfer CM Service Request RRC RANAP RANAP RRC Initial Direct Transfer CM Service Accept RRC Initial UE Message CM Service Request Initial UE Message CM Service Accept RANAP RANAP
    70. 70. Iu-CS Call Setup (CM Service Request) UE Node-B MSC RNC RRC Connection Setup RRC Initial Direct Transfer CM Service Request RRC Initial UE Message RANAP CM Service Request RANAP Security Mode Command RRC Uplink Direct Transfer (Set up) RRC RANAP RANAP RRC Downlink Direct Transfer (Call Proceeding) RRC Direct Transfer (Setup) Direct Transfer ( Call Proceeding) RANAP RANAP
    71. 71. Overview of Setting up an AMR call Mobile Terminated Call (MTC) Mobile Originated Call Paging RRC Connection Iu_CS connection Radio Access Bearer
    72. 72. Iu-CS Call Setup (RAB Setup) UE Node-B MSC RNC RRC Connection Setup & CM Service Request & Call Setup RANAP NBAP ALCAP NBAP Procedures ALCAP Procedures RAB Assignment Request RANAP NBAP ALCAP Establish Request/Confirm ALCAP ALCAP RRC RRC Radio Bearer Setup Radio Bearer Setup complete RRC RRC RANAP RANAP RAB Assignment Response
    73. 73. Call Setup UE Node-B RNC MSC RRC Connection Setup, Iu CS Call Setup, Radio Bearer Setup Alerting Connect Connect Acknowledge Call Established
    74. 74. Release of AMR Speech Call • The call is released in a controlled manner when either the originating or terminating terminal hangs-up UE is powered up Cell search Radio frame synchronisation • The RRC connection is released and the UE returns to RRC Idle mode Read BCCH Cell selection Register with core network AMR speech call Release of AMR speech call
    75. 75. Release of AMR Speech Call UE Node B MSC RNC Call Established Direct Transfer (Disconnect) Direct Transfer (Release) Direct Transfer (Release Complete) Iu Release Command Iu Release Complete RRC Connection Release RRC Connection Release Complete RRC Connection Release Complete RRC Connection Release Complete Radio Link Deletion Request Radio Link Deletion Response ALCAP: Release Request ALCAP: Release Response ALCAP: Release Request ALCAP: Release Response Call Released •UE r etur ns to Idle Mode

    ×