Title: Test Tolerance analysis for TS 34.122 Test case 8.2.2.6.2

Source: CATT

1 Introduction

The test case in section 8.2.2.6.2 of 34.122, UTRA to E-UTRA TDD cell reselection: E-UTRA is of lower priority, has not been completed. The measurement uncertainty and test tolerance is missed. This document describes the process to derive the Test Tolerances. The calculations are provided in the accompanying spreadsheet.

2 Test case in TS 34.122

The test conditions are defined in the following extract from TS34.122 v9.6.0.

In the current test case, the S_{prioritysearch1} is missed, it should be added as maximum value, 62dB i.e. -41dBm/1.28MHz to let UE search and measure any priority inter-RAT cell. Additionally, the S_{prioritysearch2} = 0dB and Ssearch _E-UTRA is added also, but they are not verdict in the test case.

8.2.2.6.2 UTRA to E-UTRA TDD cell reselection: E-UTRA is of lower priority

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<<Some clauses skipped>>

8.2.2.6.2.4.2.1 Initial conditions

This test scenario comprised of 1UTRA TDD serving cell ,and 1E-UTRA TDD cell to be re-selected.Test parameters are given in table 8.2.2.6.2.4.2.1-1, 8.2.2.6.2.4.2.1-2 and 8.2.2.6.2.4.2.1-3.The test consisits of two successive time periods,with time duration of T1 and T2 respectively. At T1 the UE is camped on to cell1. Cell2 is of lower priority than cell1.

<<Table 8.2.2.6.2.4.2.1-1 skipped>>

Table 8.2.2.6.2.4.2.1-2: Cell specific test parameters for cell re-selection UTRA TDD to E-UTRA TDD test case (cell 1)

Parameter	Unit	Cell 1 (UTRA)
Timeslot Number		0			DwPTS
		T1		T2	T1	T2
UTRA RF Channel Number (Note1)		Channel 1
PCCPCH_Ec/Ior	dB	-3		-3
DwPCH_Ec/Ior	dB				0	0
OCNS_Ec/Ior	dB	-3		-3
	dB	11		-3	11	-3
	dBm/1.28 MHz	-80
PCCPCH RSCP	dBm	-72	-86		n.a.	n.a.
Propagation Condition		AWGN
Qrxlevmin	dBm	-103
Qoffset1s,n	dB	C1, C2: 0
Qhyst1s	dB	0
Snonintrasearch	dB	Not sent
Threshserving, low	dB	24 (-79dBm)
Threshx, low  (Note2)	dB	46 (-94dBm)
Sprioritysearch1	dB	62
Sprioritysearch2	dB	0
SsearchE-UTRA	dB	Not send
Note1: In the case of multi-frequency cell, the UTRA RF Channel Number is the primary frequency’s channel number. Note2: This refers to the value of Threshx, low which is included in UTRA system information, and is a threshold for the E-UTRA target cell

Table 8.2.2.6.2.4.2.1-3: Cell specific test parameters for cell re-selection UTRA TDD to E-UTRA TDD test case (cell 2)

Parameter	Unit	Cell 2
		T1	T2
E-UTRA RF Channel Number		2
BWchannel	MHz	10
PBCH_RA	dB	0	0
PBCH_RB	dB
PSS_RB	dB
SSS_RB	dB
PCFICH_PA	dB
PHICH_PA	dB
PHICH_PB	dB
PDCCH_PA	dB
PDCCH_PB	dB
PDSCH_PA	dB
PDSCH_PB	dB
OCNG_RANote1	dB
OCNG_RBNote1	dB
Qrxlevmin	dBm/15kHz	-140	-140
	dBm/15kHz	-98
RSRP	dBm/15kHz	-87	-87
	dB	11	11
Threshx, high (Note2)	dB	24(-79dBm)
Propagation Condition		AWGN
Note1:  OCNG shall be used such that cell is fully allocated and a constant total transmitted power spectral density is achieved for all OFDM symbols. Note2: This refers to the value of Threshx, high which is included in E-UTRA system information, and is a threshold for the UTRA target cell

……

3 Discussion

In the test case, there are two cells, cell 1 (UTRA cell) and cell 2 (E-UTRA cell) with lower priority. The test case consists of two successive time periods, T1 and T2. During T1, UE selects cell 1 due to its signal is stronger than threshold and is of higher priority. During T2, UE is expected to reselect to cell 2 due to cell 1 signal becomes lower than threshold. The values of Srxlev for each cell versus time, together with the thresholds are shown in figure 1.

Figure 1 Srxlev in cell reselection process

3.1 Selection criterion for UTRA

The selection criterion is satisfied according to the equation from TS 25.304 v9.6.0 clause 5.2.3.1.2:

Srxlev = Q_rxlevmeas – (Q_rxlevmin + Q_{rxlevminoffset}) – Pcompensation

The values in this equation are derived as follows:

• Srxlev is evaluated for each cell at T1 and T2.

• Q_rxlevmeas is the measured cell Rx level value (P-CCPCH RSCP) as given in table 8.2.2.6.2.4.2.1-2.

• Q_rxlevmin for the UTRA cell is -103dBm/1.28MHz as given in table 8.2.2.6.2.4.2.1-2.

• Q_{rxlevminoffset} is only taken into account as a result of a periodic search for a higher priority PLMN while camped normally in a VPLMN, and is therefore not applicable here.

• Pcompensation = 0 according to the table in TS 25.304 v9.6.0 clause 5.2.3.1.2, provided (UE_TXPWR_MAX_RACH – P_MAX) is negative. UE_TXPWR_MAX_RACH must therefore be lower than P_MAX.

The equation therefore reduces to:

Srxlev = Q_rxlevmeas – Q_rxlevmin

which is drawn for each cell at T1 and T2 in the diagram above.

Cell 1 (UTRA) at T1 has P-CCPCH RSCP -72dBm so Srxlev = -72 – (-103) = 31.

Cell 1 (UTRA) at T2 has P-CCPCH RSCP -86dBm so Srxlev = -86 – (-103) = 17.

3.2 Selection criterion for E-UTRA

For Cell 2 (E-UTRA) the selection criterion is satisfied according to the equation from TS 36.304 v8.9.0 clause 5.2.3.2:

The values in the equation for Cell 2 E-UTRA Srxlev are derived as follows:

• Srxlev is evaluated at T1 and T2

• Qrxlevmeas is the Measured cell RX level value (RSRP) as given in table 8.2.2.6.2.4.2.1-3

• Qrxlevmin for the E-UTRA cell is -140dBm as given in table 8.2.2.6.2.4.2.1-3

• Qrxlevminoffset is only taken into account as a result of a periodic search for a higher priority PLMN while camped normally in a VPLMN, and is therefore not applicable here.

• Pcompensation =0 according to the table in TS 36.304 v8.7.0 clause 5.2.3.2, provided (P_EMAX – P_PowerClass) is negative. P_EMAX must therefore be lower than P_PowerClass.

The equation therefore reduces to:

Srxlev = Qrxlevmeas – (Qrxlevmin) which is drawn for each cell at T1 and T2 in the diagram above.

Cell 2 (E-UTRA) at T1 has RSRP -87dBm so Srxlev = -87 – (-140) = 53.

Cell 2 (E-UTRA) at T2 has RSRP -87dBm so Srxlev = -87 – (-140) = 53.

3.3 Thresholds

The thresholds for UTRA are defined in TS 25.304 v9.6.0 clause 5.2.6.1.5:

Thresh_{x, low}

A Srxlev based threshold used by the UE for cell reselection towards an equal or lower absolute priority layer when absolute priorities are applied. A threshold is defined for each absolute priority layer.

Thresh_{serving, low}

This threshold is used in the rules for cell reselection when absolute priorities are used. It specifies the limit for Srxlev in the serving cell below which the UE may perform cell reselection to a cell on a lower absolute priority layer.

S_{prioritysearch1}

This threshold is used in the measurement rules for cell re-selection when absolute priorities are used. It specifies the value of Srxlev in the serving cell controlling the rate of inter-frequency and inter-RAT measurements.

S_{prioritysearch2}

This threshold is used in the measurement rules for cell re-selection when absolute priorities are used. It specifies the value of Squal in the serving cell controlling the rate of inter-frequency and inter-RAT measurements.

The thresholds for E-UTRA are defined in TS 36.304 v8.9.0 clause 5.2.4.7:

Thresh_{x, high}

This specifies the threshold used by the UE when reselecting towards the higher priority frequency X than current serving frequency. Each frequency of E-UTRAN and UTRAN, each group of GERAN frequencies, each band class of CDMA2000 HRPD and CDMA2000 1xRTT might have a specific threshold.

S_{nonintrasearch}

This specifies the threshold (in dB) for E-UTRAN inter-frequency and inter-RAT measurements.

3.4 Test case verdict

The design of the test case relies on the UE being able to measure RSRP and P-CCPCH RSCP during T1 and T2, and correctly compare it to the signal thresholds. In this test case, only signal level threshold is used.

A detailed analysis of the test case is given in section 5 of this document.

4 Choice and values of uncertainties to be specified

The SS provides two cells on different frequencies with AWGN. We propose to control the following parameters:

• AWGN absolute power on cell 1 frequency, I_oc ± 0.7dB

• AWGN absolute power on cell 2 frequency, N_oc ± 0.7dB

• Ratio of cell 1 signal / AWGN, Î_or / I_oc ± 0.3dB

• Ratio of cell 1 code level / I_or , Ec / I_or ± 0.1dB

• Ratio of cell 2 signal / AWGN, Ê_s / N_oc ± 0.3dB

This choice forms a minimum set, so the superposition principle can be applied if necessary. For these test cases, the signals are not faded, and the values for Ê_s / N_oc and Î_or / I_oc are chosen to be similar to equivalent parameters in LTE and W-CDMA. The absolute levels of N_oc and I_oc are specified as ±0.7dB, similar to the uncertainty for other absolute power values such as RefSens. The Ec / I_or is specified as ± 0.1dB in TS34.122.

5 Calculation of Test Tolerances

General approach

The general approach is given in the steps below:

1. Copy the originally specified key parameters from the core requirements

2. Where relevant, calculate derived parameters from the core requirements

3. Define uncertainties for a minimum set of parameters

4. Define controlled parameters (critical to the test verdict), calculate sensitivity factors and uncertainty

5. Determine which original or derived parameters to offset (apply Test Tolerances to) and by how much

6. Recalculate original or derived parameters including Test Tolerances

7. Check that the controlled parameters meet requirements to get the correct test verdict

Each step is explained below, and the calculations are given in the accompanying spreadsheet.

a) Original specified key parameters

The key parameters are copied from Table 8.2.2.6.2.4.2.1-2 and Table 8.2.2.6.2.4.2.1-3 in TS 34.122. The key parameters are selected as the minimum set to define the cell power levels, and which are subject to a test system uncertainty which may affect the verdict of the test. Some signalled parameters Q_rxlevmin, Thresh_{x, high}, Thresh_{serving, low}, and Thresh_{x, low} are also copied, although these are not subject to uncertainty.

The key parameters appear in section a) of the accompanying spreadsheet. The layout for Cell 1 and Cell 2 are similar to Table 8.2.2.6.2.4.2.1-2 and Table 8.2.2.6.2.4.2.1-3 in TS 34.122, but the AWGN is given a separate set of columns for each frequency. This allows the spreadsheet calculations to be done in a consistent way.

b) Derived parameters

A number of derived parameters are calculated, using the base information in a). The reason for deriving each additional parameter is given in the “Comment” column of section b) in the accompanying spreadsheet. The UE compares Srxlev values to thresholds, so the RSRP and RSCP values need to be converted to Srxlev.

In this test case, the UE compares Srxlev values to thresholds, so a further step is done to calculate the difference between Srxlev and the thresholds:

• (Cell 1 Srxlev –Thresh_serving_low)

• (Cell 1 Srxlev –Thresh_x_high)

• (Cell 1 Srxlev - Sprioritysearch1)

• (Cell 2 Srxlev – Thresh_x_low)

• (Cell 2 Srxlev - Snonintrasearch)

c) Uncertainties

The choice of uncertainties is covered in section 4 of this document. They appear in section c) of the accompanying spreadsheet.

d) Controlled parameters critical to verdict

A diagram giving the Cell 1 and Cell 2 Srxlev values during T1 and T2 is provided in section 3 of this document. It also includes the relevant thresholds. This is the most appropriate view to analyse the critical parameters for this test.

From 34.122 clause 8.2.2.6.2, Cell 2 is of lower priority than Cell 1.

1. Before the start of T1 in the first iteration of the test, the UE has selected Cell 1 (high priority).

2. During T1, the UE is required to reselect to Cell 1 (higher priority). The conditions for the reselection towards higher priority are:

• The higher priority Cell 1 must be good enough, expressed as Srxlev ≥ Thresh_{x, high} with a margin of at least 6dB (from TS 36.133 clause 4.2.2.5.2)

• Thresh_{x, low} is not applicable during T1 (only applies when reselecting towards lower priority Cell 2)

• Thresh_{serving, low} is not applicable during T1 (only applies when reselecting towards lower priority Cell 2)

• S_{nonintrasearch} is specified for Cell 2, which is the serving cell at the start of T1 (for iterations of the test after the first). The UE will search for inter-RAT layers of higher priority, according to TS 36.133 clause 4.2.2.5, provided Cell 1 exceeds the S_{nonintrasearch} threshold. This is required to ensure the UE searches every T_{higher_priority_search} = (60 * N_layers) seconds as specified in TS 36.133 clause 4.2.2. Although TS 36.133 clauses 4.2.2 and 4.2.2.5 do not give any dB figures relating to S_{nonintrasearch}, other clauses such as 4.2.2.5.1 specify a margin of at least 6dB so this seems a reasonable working assumption.

• S_{prioritysearch1} is specified for Cell 1 as maximum value, 62dB. The UE will search and measure all inter-frequency and inter-RAT layers with any priority according to TS 25.123 clause 4.2.2.5a.

• Cell 1 must meet the P-CCPCH RSCP and DwPCH side conditions (level, Ec/Io) in TS25.123 clause 9.1.1.1.1.2. Although it does not seem clear that these values are applicable for the UE during reselection (see applicability statement at start of clause 9.1), it seems reasonable to adopt the side conditions for the UTRA cell. The side condition for Io has not been taken into account as the required margin for reselection is specified without any condition on Io.

• Cell 2 must meet the RSRP and SCH side conditions (level, Es/Iot) in TS 25.123 clause 4.2.2.5a.

3. During T2, the UE is required to reselect to Cell 2 (lower priority). The conditions for the reselection towards lower priority are:

• Thresh_{x, high} is not applicable during T2 (only applies when reselecting towards higher priority Cell 1)

• The higher priority Cell 1 must be bad enough, expressed as Srxlev ≤ Thresh_{serving, low} interpreting TS 25.123 clause 4.2.2.5a, absolute priorities scenario, to require a margin of at least 6dB.

• The lower priority Cell 2 must be good enough, expressed as Srxlev ≥ Thresh_{x, low} with a margin of at least 6dB (from TS 25.123 clause 4.2.2.5a)

• Cell 1 must meet the P-CCPCH RSCP and DwPCH side conditions (level, Ec/Io) for a detectable cell.

• Cell 2 must meet the RSRP and SCH side conditions (level, Es/Iot) in TS 25.123 clause 4.2.2.5a.

The critical conditions are related to the 9 controlled parameters listed in section d) of the accompanying spreadsheet. They have been derived by study of the test case diagram and by careful reading of the relevant clauses in TS 25.123 and TS 36.133. The reason for each parameter being critical to the test verdict is given briefly in the “Comment” column of section d) in the accompanying spreadsheet. Information about the value to be achieved is given later in the “Comment” column of section g) in the spreadsheet.

Having identified the parameters critical to the test verdict which need to be controlled, we now need to consider how they are affected by the parameters which can be set by the test equipment. The sensitivity factors are the ratio (effect on a critical parameter y / a test equipment uncertainty x), and are usually in dB/dB. In this RRM test case for most parameters there is a simple one-to-one relationship between the parameters that can be set by the test equipment, and their effect on parameters determining the test verdict. The sensitivity factors are therefore derived by inspection as one or zero.

For example, an error of 1dB in the absolute AWGN level Ioc would cause 1dB error in the Cell 1 RSCP, so the sensitivity factor is 1.000 during T1 and T2. It would also cause 1dB error in the derived parameter (Cell 1 Srxlev - Thresh_x_high), so the sensitivity factor is also 1.000 during T1 and T2. However the same error of 1dB in the absolute AWGN level Ioc would cause no change to Cell 1 Ior/Ioc, because all other powers are specified relative to Ioc, so the sensitivity factor is zero.

In some cases, the sensitivity factor is an intermediate value. For example, the Cell 1 Ior/Ioc has an effect on P-CCPCH_Ec/Io which depends on ratios of the powers making up the total. In such cases a sensitivity factor value between 0 and 1 results. It is important to calculate these correctly to obtain the overall uncertainty.

For example,

• During T1, The effect of Cell 1 Ior/Ioc uncertainty on Cell 1 P-CCPCH_Ec/Io is x 0.074.

These factors can also be derived intuitively, by considering the relative powers in step b). For example, Ioc forms 7.4% / (7.4%+92.6%) of the total power Io, which is 0.074. A change in the Cell 1 Ior/Ioc has very little effect on the ratio of P-CCPCH power to overall power, because the Ior makes up most of the overall power.

Having filled in the matrix of sensitivity factors, the accompanying spreadsheet calculates the overall uncertainty for each controlled parameter, taking into account the uncertainties and sensitivity factors for each parameter that can be set by the test equipment. This process follows the superposition principle. More details and explanation can be found in section 4 of TS 36.903. Uncertainties are calculated separately for T1 and T2.

The normal procedure of combining uncorrelated uncertainties root-sum-square is followed.

e) Determine parameters to offset

• During T1 and T2, the uncertainties do not take Cell 1 P-CCPCH Ec/Io, DwPCH Ec/Io or P-CCPCH RSCP power outside the allowed range, therefore no offsets are required.

• During T1 and T2, the side condition in TS 25.123 clause 4.2.2.5a is easily met by Cell 2 due to Es/Iot equal to 11dB, and the RSRP power is easily met, therefore no offsets are required.

• During T1 the UE is required to reselect to UTRA Cell 1 (high priority). The Srxlev of high priority Cell 1 is set to be above Thresh_{x, high} with a margin of 7dB, and the uncertainties do not reduce the margin to less than the core requirement of ³ 6 dB in TS 36.133, therefore no offsets are required.

• During T2 the UE is required to reselect to E-UTRA Cell 2 (low priority). The Srxlev of high priority Cell 1 is set to be below Thresh_{serving, low} with a margin of 7dB, and the uncertainties do not reduce the margin to less than the assumed requirement of ≤ -6 dB interpreting TS 25.123, therefore no offsets are required.

• During T2 the UE is required to reselect to E-UTRA Cell 2 (low priority). The Srxlev of low priority Cell 2 is set to be above Thresh_{x, low} with a margin of 7dB, and the uncertainties do not reduce the margin to less than the core requirement of ³ 6 dB in TS 25.123 clause 4.2.2.5a, therefore no offsets are required.

• The UE will search for inter-RAT layers of higher priority, according to TS 36.133 clause 4.2.2.5, provided Cell 2 Srxlev exceeds the S_{nonintrasearch} threshold by a margin of at least 6dB. This margin is numerically the same as that for (Cell 2 Srxlev – Thresh_x_low), so is already met

The check that all other controlled parameters meet their required range is done in step g). In theory it is possible for steps e) to g) to be iterative, or possibly even steps c) to g) to be iterative, but this test case can be done without such iteration.

f) Parameters modified by Test Tolerances

Based on the decision in e), the set of parameters in a) and b) is reproduced in section f) of the accompanying spreadsheet, but this time modified by the Test Tolerances (applied offsets). In this case the offsets are all zero.

Re-derived parameters are calculated using the same methods as were used in step b).

g) Check controlled parameters Min/Max

Using a format similar to that in step d), the nominal value of each controlled parameter is recalculated.

The minimum and maximum values, due to variability from uncertainties, of controlled parameters is then calculated and compared against the requirements (Required margin relative to threshold, Es/Iot range, RSRP level..). It is not necessary to calculate all parameters during each time interval T1 and T2, so a selection is made of those critical to the test verdict. The critical requirement for each parameter is given briefly in the “Comment” column of section g) in the accompanying spreadsheet. The cases closest to limit (in these test cases, all limits are one-sided) are identified by turquoise cells in the spreadsheet. If all requirements are met, then the exercise is complete.

It can be seen that with the uncertainty values and Test Tolerances proposed, all the requirements are met.