Cell Reselection ----No dedicated physical channels

• Cell reselection is the process of selecting a new cell when the UE is not operating on a dedicated channel.

• UTRAN provides parameters to control reselection, but the UE changes cells autonomously.

Handover---Dedicated physical channels

• Handover is the process of adding or removing cells with which the UE is communicating on a dedicated channel.

• UE and UTRAN procedure that allows the UE to change from one cell to another, while the UE has dedicated radio resources allocated to it.

• UE provides measurements to UTRAN and UTRAN commands UE to perform a handover.

Types of cell reselection and Handover

Intra frequency• Within the same UMTS frequency: cell reselection or handover occurs

between cells on the same frequency.

Inter-frequency• Between different UMTS frequencies: cell reselection or handover occurs

between cells on different radio frequencies.

Inter-RAT• Between different radio access technologies (3G to 2G): cell reselection or

handover occurs between cells on different Radio Access Technologies.

Cell Reselection Criteria

Q measurement:

• Determines the quality of the cell• Used in S and R computations• For WCDMA cells: CPICH RSCP and CPICH Ec/No• For GSM cells: GSM Rx level

S criteria:

• Determines whether the cell is Suitable for camping.

R criteria:• Determines the Ranking of the cell relative to other neighbor cells and

serving cell.

During cell reselection, the UE takes measurements of neighbor cells provided in SIB 11 or 12, along with the serving cell. For each cell, the S and R criteria are computed. If the cell is suitable, as a function of the S criteria and the other characteristics of the cell, the cell is ranked against all other suitable cells.

If a cell other than the current serving cell is the highest ranked cell, then that cell is chosen for cell reselection.

The S criteria is used to determine whether the cell is suitable. For the serving cell and each neighbor cell, the UE is given the following parameters:

• qRxLevMin: Minimum CPICH RSCP for the cell to be suitable• qQualMin: Minimum CPICH Ec/No for the cell to be suitable

qRxLevMin: -115 to -25 dBm, -115 dBm

qQualMin: -24 to 0 dB, -16 dB

CPICH_Ec/No………measured by UE = Qqualmeas

CPICH_Ec/No > qQualMin

CPICH_Ec/No > -16 dB

CPICH_RSCP >qRxLevMin > -115 dBm

Definition of Ranking Criteria for serving cell:

Rs = Qmeas, s + Qhysts

Definition of Ranking criteria for neighbor cels:

Rn =Qmeas, n – Qoffsets, n

The R criteria is used to rank suitable neighbor cells and the serving cell to determine if there is a better cell than the serving cell. For the serving cell, the UE is given the following parameters:

• Qhyst1= Hysteresis applied to the serving cell on CPICH RSCP measurements.

• Qhyst2 = Hysteresis applied to the serving cell on CPICH Ec/No measurements.

For each neighbor cell, the UE is given the following parameters:

• Qoffset 1= offset applied to the neighbor cell on CPICH RSCP measurements.

• Qoffset 2 = offset appled to the neighbor cell on CPICH Ec/No measurements.

Cell Reselection- what to measure

We are using thresholds to control intra-frequency, inter-frequency and inter-RAT cell measurements, where the threshold for intra-frequency cell reselection is the highest and the threshold for inter-RAT is the lowest. The exact order of the search could be changed if the relative levels of the thresholds are chaned.

• Sintrasearch: specifies the threshold (in dB) for intra frequency measurements

• Sintersearch: specifies the threshold for inter frequency measurements

• Ssearch,RAT : specifies the threshold for inter-RAT measurements.

Squal is compared to different thresholds broadcast in the System Information to determine which kind of measurement (intra-frequency, inter-frequency and inter-RAT) the UE shall do.

Note: Squal is defined by Squal = Qqualmeas – qQualMin

Intra-frequency measurementsSqual is compared with the parameter sIntraSearch:• If Squal > sIntraSearch, the UE does not perform intra-frequency measurements.• If Squal ≤ sIntraSearch, the UE performs intra-frequency measurements.• If sIntraSearch is not sent for the serving cell, the UE performs intra-frequency measurements.

Inter-frequency measurementsSqual is compared with the parameter sInterSearch:• If Squal > sInterSearch, the UE does not perform inter-frequency measurements.• If Squal ≤ sInterSearch, the UE performs inter-frequency measurements.• If sInterSearch is not sent for the serving cell, the UE performs inter-frequency measurements.

Inter RAT measurements

Squal is compared with the parameter sSearchRatGsm:• If Squal > sSearchRatGsm, the UE does not perform measurements on GSM cells.• If Squal ≤ sSearchRatGsm, the UE performs measurements on GSM cells.• If sSearchRatGsm is not sent for the serving cell, the UE performs measurements on GSM cells.

3.6.1 First RankingAmong the GSM and FDD Cells verifying S criterion, UE shall perform ranking according to ranking R criterion, as specified above.

In a first step, the mobile shall always consider the CPICH RSCP / RxLev measurement and associated set of parameters (qHyst1, qOffset1sn):

UServing Cell: Rs = CPICH_RSCP + qHyst1

UEligible FDD Neighbour cellU: RnFDD = CPICH_RSCP – qOffset1sn

UEligible GSM Neighbour cellU: RnGSM = RxLev – qOffset1sn

3.6.2 Second RankingIn case an FDD cell is ranked as the best cell according to the first ranking, a second ranking of the FDD cells is applied at the CPICH EBCB/NBOB case with the associated set of parameters

(qHyst2, qOffset2sn):

UServing CellU: Rs = CPICH_Ec/No + qHyst2

UEligible FDD Neighbour cellU: RnFDD = CPICH_Ec/No – qOffset2sn

If is Squal< Sintrasearch………..no…… Do not need to measure any cells

Yes………..Measure Intra freq.cells

If is Squal < Sintersearch…….No….Measure intra freq. cells

Yes……measure intra and inter freq. cells

If Squal < Ssearch,RAT………….no measure intra and inter freq. cells.

Yes

Search intra-freq, inter-freq and inter RAT cells.

Categories of cells

1. Active set• Cells for which a radio link is established between UE and

UTRAN• UE is in soft or softer Handover with all cells in the active

set2. monitored set(neighbor)

• UTRAN provides the monitored set cells (also called neighbor list)• Most likely candidates for soft handover

3. detected set• All other cells which UE has detected and measured• Possible handover candidates

The UE keeps track of three sets of cells: A, M and D.

Active set: max: 3 (1 to 6)

Neighbor set: max 32

While measuring active and monitored set cells, the UE may find a cell that is in neither of those sets. This cell then becomes a member of the detected set. The UE may report one a detected set cell, causing UTRAN to adda that cell to either the monitored or active set.

Parameters for event triggered reporting:

Events as a function of the measurement type

• Intra- frequency: Events 1a to 1f

• Inter-frequency: events 2a to 2f

• Inter-RAT: events 3a to 3d

Time to Trigger: Interval between even detection and report sent.

Soft HO algorithm:Intra-Frequency Reporting events:

• Event 1a = add to active• Event 1b= drop from active• Event 1c = Swap ( only when active set is full)• Event 1d = Select only one 9stronger one)• Event 1e = Move to monitored set from detected set• Event 1f = Remove from monitored set

Inter-Frequency Reporting events:

• Event 2a = Select a best frequency• Event 2b= the estimated quality of the currently used frequency is

below a certain threshold and the estimated quality of a non used frequency is above a certain threshold

• Event 2c = the estimated quality of a non used frequency is above certain threshold

• Event 2d = the estimated quality of the currently used frequency is below a certain threshold

• Event 2e = the estimated quality of a non used frequency is below a certain threshold

• Event 2f = the estimated quality of the currently used frequency is above a certain threshold

Inter-RAT Reporting events:

• Event 3a = the estimated quality of the currently used UTRAN frequency is below a certain threshold and the estimated quality of the other system is above a certain threshold

• Event 3b= the estimated quality of the other system is below a certain threshold.

• Event 3c = the estimated quality of the other system is above a certain threshold

• Event 3d = Change of best cell in other system

SIB 1: Core network info. Timers and constants (UEs)

Example: T300, T307, N300

SIB 2: URA identities

SIB type 2 contains a list of up to 8 URA indenties that are valid in the current cell.

SIB 3 and SIB 4: Cell reselection parametersSIB3—used when the UE is in the idle modeSIB4—Connected mode

SIB 5 and SIB 6PCCPCH, SCCPCH, PRACH

SIB 5..idle modeSIB..connected mode

EX : Transport format set, transport channel combination setSF, Code number, timing offset, number of preamble cycles, paging indicator per frame

SIB7: fast changing parameters

UL interference

SIB11 and SIB12:

Intra frequency measurements Inter frequency measurementsInter RAT frequency measurementsTraffic volume measurements

SIB 11…. Idle mode

SIB 12…..Connected mode

SIB18 : PLMS info.

PLMN IDs of intra-freq neighborsPLMN IDs of inter-freq neighborsPLMN IDs of inter-RAT neighbors

PAGING MECHANISMS3.1 DRX CycleWhen camping normally on a cell, the UE keeps on monitoring the paging channel. In order to save some energy, a discontinuous reception mode (DRX) is used.The DRX cycle defined as the individual time interval between monitoring Paging Occasion for a specific UE. The UE needs only to monitor one Page Indicator (PI) in one Paging Occasion per DRX cycle.

The DRX cycle length is defined as MAX{2k, PBP}, where:• PBP is the Paging Block Periodicity and has the fixed value of 1 in UMTS-FDD.• k is an integer and can be specific by Core Network domain

MAX{2k, PBP},= MAX{26, 1},= 26 = 64 x 10ms = 640 ms= 0.64 sec

RACH PREAMBLES AND AICH TRANSMISSIONS4.1 Preambles Transmission by the UEWhen it accesses the network, the UE will send two kinds of signals over the air interface:• Preambles that are used to obtain the correct power to reach the network (Node B).

• After receiving an acknowledgement from the network through the AICH, the UE will send a RACH message so as to establish the RRC Connection.

Power Control on Common Channels (PRACH)The PRACH access protocol is composed of two different parts that the UE will send to the system: the preamble part and the message part.It is based on an access frame structure and on the regular radio frame structure. One access slot is twice a normal radio slot, i.e. 2 x 2560 chips, and one access frame is twice a radio frame long, i.e. 2 x 10ms.

The preamble part consists in the repetition of a preamble. The preamble is an identifier composed of a 16-chip signature repeated 256 times (4096 chips in total). Basically, the UE is assigned one of the 16 possible preamble signatures and transmits it at increasing power until it gets a response from the network. The parameter preambleSignature of the RACH objectdefines the set of allowed signatures of the PRACH preamble part.

Message Part:Once the UE has received an answer from the network (on the AICH), it will send the message part of the PRACH access. The message part is 10 or 20 ms long (split into 15 or 30 radio time slots) and is composed of a control part (layer 1 control information) and of a data part (service requirement itself, coming from the RACH transport channel).

The parameters related to the UE access on the PRACH can be separated in three categories:• Open loop power control• Power ramping for preamble retransmission• Preamble message part

UL Open Loop Power Control ParametersThe aim of the open loop power control is to determine the output power of the UE on its first transmission of the preamble part on the PRACH. This transmission power is based on the information received from the SIBs of the P-CCPCH and measurement of the CPICH_RSCP.

Pini(PRACH) = pcpichPower + UL_interference + constantValue - P-CPICH_RSCPWhere:• pcpichPower parameter defines the P-CPICH transmission power of the Node-B. It is broadcast in SIB 5.• UL_interference is a corrective term evaluating the average interference level on UL. It corresponds to the UL RTWP measured by the node B, it is broad cast in SIB 7. RTWP or RSSI.

RTWP is the Received Total Wideband Power, including noise generated in the receiver, within the bandwidth defined by the pulse-shaping filter.

In Alcatel-Lucent’s implementation, this is not a parameter; it corresponds to the UL RTWP measured by the Node-B. It is broadcast in SIB 7.• constantValue is a corrective term aiming to compensate RACH Processing Gain. It is broadcasted in SIB 5.

In the Pini equation stated above, we notice that the pcpichPower – CPICH_RSCP corresponds basically to the path loss between the Node-B and the mobile. The constantValue and UL_interference are there to fine-tune the mobile output power according to radio conditions.

Maximum power of UE

Since the UEs have their own maximum transmission power according to their power classes, the maximum effective UL transmission power used by the UE after a radio link setup is:

Maximum UL Tx Power = Min (maxAllowedUlTxPower; UE_Max_Tx_Power (UE Class))The maximum transmission power of the UE based on its power class is described below:Class 1……………. 33 dBmClass 2……………. 27 dBmClass 3……………. 24 dBmClass 4……………. 21 dBm

UE Class P_MAX1 +33 dBm2 +27 dBm3 +24 dBm4 +21 dBm

NOTE: The minimum output power of the UE is –50dBm for all classes

4.5.6.2.2 Type1 algorithm

type1 is the newly algorithm introduced in UA06.0 and is mainly based on:• neighbourCellPrio, between 0 and 62, defining for each FDD Cell a hierarchy within its neighbourhood (0 is the highest priority, 62 the lowest); note that two UMTSFddNeighbouringCell can NOT have the same neighbourCellPrio.• “sponsoring cells” which are the cells from the ASET• occurrence of each neighbouring cell within the sponsoring cells’ neighbourhood.