Understanding LTE Downlink ACLR Measurements using 3041 and PXI Maestro

Transcription

1 Understanding LTE Downlink ACLR Measurements using 3041 and PXI Maestro Application Note The most important thing we build is trust Introduction Transmitter ACLR requirements defined in 3GPP section is the most commonly used unwanted emissions measurement methods performed on devices in manufacturing. This application note describes how to configure PXI Maestro for a variety of uses cases. The conformance requirement is the less stringent of two measurements which relate to either the absolute power dbm/mhz at the frequency offset or the dbc power at the frequency offset relative to the carrier power. For 3GPP V the relative limits are -44.2dBc and the absolute limits are:- Base station type Category A Wide Area Category B1 / B2 Wide Area Local Area BS Home BS Absolute Limit -13dBm/MHz -15dBm/MHz -32dBm/MHz -50dBm/MHz Example In the case of a Local Area BS where the device measured output power is +24 dbm for a 20MHz BW, then the absolute limit is -19dBm and the relative limit is -20.2dBm and hence the less stringent absolute limit applies. If the bandwidth is changed to 10MHz then the absolute limit is -22dBm, which more stringent than the relative limit of and hence the relative limit applies. The shaded areas in the table below show the less stringent requirement for each bandwidth and Local Area base station output power rating. Local Area BS ALCR Bandwidth Power 5MHz 10MHz 20MHz dbm Relative limit Absolute limit Relative limit Absolute limit Relative limit Absolute limit com/wireless

2 Configuring Maestro for DL ACLR measurements Maestro Analysis (spectrum) configuration settings enable the ACLR pass/fail result to be defined by the underlying analysis library and/or by the Maestro application. This provides a lot of flexibility but does require the user to fully understand how to configure. Two key configuration setting are the ACLR configuration mode and the ACLR Limit Mode. These determine how the outcome of the ACLR pass/fail measurement result is derived. The table below explains the outcome of these selections.

3 ACLR Configuration Mode Auto User Defined ACLR Limit Mode Category A Wide Area Category B1 Wide Area Category B2 Wide Area Local Home User Defined and filter settings are defined by 3GPP V Table (FDD) and Table (TDD). See appendix and filter settings are defined by the User defined ACLR Configuration setting. The Limit for each adjacent channel is the least stringent of -44.2dB or the absolute limits in the table below - as defined in 3GPP V Section and filter settings are defined by 3GPP V Table (FDD) and Table (TDD). See appendix and filter settings are defined by the User defined ACLR Configuration setting. The Limits are defined by the User Defined ACLR Limit setting, and must be specified as both a relative and absolute limit for each adjacent channel. The least stringent of these will be applied. Measurements The test group/point measurements that can be performed include. 1) ACLR absolute 2) ACLR applied limits 3) ACLR Pass/Fail (as determined by the settings in the above table) 4) ACLR Relative ACLR absolute results return an array of dbm values. A pass / fail verdict can be configured independent of any settings configured for the ACLR pass/fail measurement by applying limits to the absolute result in the normal Maestro manner. ACLR relative results return an array of dbc values. A pass / fail verdict can be configured independent of any settings configured for the ACLR pass/fail measurement by applying limits to the relative result in the normal Maestro manner. ACLR applied limits return the actual limits used to compute the ACLR Pass/Fail expressed in dbc. Where an absolute limit was chosen, it is expressed as a relative limit for this result. The limit value can be either a single value for all offsets or a different value for each offset. In the case where different values are used then the number of limit values must be equal to the number of frequency points in the ACLR limit settings (whether or not using user defined or Auto).

4 Use Case 1 Standard 3GPP ACLR Configuration & Limits The test plan calls for ACLR testing of a 20MHz BW Local Area BS using standard 3GPP ACLR offsets and limits. In this use case the test group/point settings should be configured as follows: ACLR Configuration Mode: Auto ACLR Limit Mode: Local Note when the ACLR Pass/Fail measurement is enabled, the limits used will the less stringent of the absolute or relative limits, irrespective of whether the ACLR Absolute or ACLR Relative results are enable or disabled. This is all that needs to be done for 3GPP ACLR testing. Use Case 2 User Defined Configuration & 3GPP Limits This use case is the same as Use Case 1 above except that a user defined configuration will be used for demonstration purposes. If non-standard offsets are required, the procedure is the same. In this use case the test group/point settings should be configured as follows: ACLR Configuration Mode: User Defined ACLR Limit Mode: Local User Defined ACLR Configuration: As per table below Index Alpha Bandwidth Frequency Offset MHz MHz MHz MHz MHz Note that the order of the offsets must be as shown in the table above. Use Case 3 Standard 3GPP Configuration & User Defined Limits This use case is the same as Use Case 1 above except user defined limits shall be used rather than the 3GPP ones. Note that the limits used in this example are the 3GPP ones, but the same principle can be used for non-standard limits. In this use case the test group/point settings should be configured as follows: ACLR Configuration Mode: Auto ACLR Limit Mode: User Defined User Defined ACLR Limit: As per table below Index Relative Limit (dbc) Absolute Limit Note that index 0 is the centre channel (reference) which does not contribute to the ACLR Pass/Fail result therefore the limits are unimportant.

5 Use Case 4 Customer wishes to ignore 3GPP ACLR conformance requirements for LTE TDD 20MHz but instead apply only a dbc relative limit to each of 4 offsets, -40, +40, -20, +20MHz. In this case the test group/point settings can be configured to either Auto or User Defined. Auto can be used because the offsets required correspond to the 3GPP offsets. The test group/point settings should be configured as follows: ACLR Configuration Mode: Auto ACLR Limit Mode: User Defined User Defined ACLR Limit: As per table below Index Relative Limit (dbc) Absolute Limit Note that index 0 is the centre channel (reference) which does not contribute to the ACLR Pass/Fail result therefore the limits are unimportant. Since the ACLR Pass/Fail measurement will always use the less stringent of the absolute or relative limits, the absolute limits must be chosen such that they are so stringent that the relative limits will always be chosen setting a very small number will accomplish this. This method of applying only a relative limit check will work just fine but is not recommended it is preferable (less confusing) to follow the method detailed in use case 5 instead. Use Case 5 This use case is the same as use case 4 the customer wishes to ignore 3GPP ACLR conformance requirements for LTE TDD 20MHz but instead apply only a dbc relative limit to each of 4 offsets, -40, +40, -20, +20MHz. In this case the test group/point settings can be configured to either Auto or User Defined. Auto can be used because the offsets required correspond to the 3GPP offsets. The test group/point settings should be configured as follows: ACLR Configuration Mode: User Defined ACLR Limit Mode: Doesn t matter User Defined ACLR Configuration: As per table below Index Alpha Bandwidth Frequency Offset MHz MHz MHz MHz MHz Note that the first offset (index 0) must be the carrier signal, the remaining offsets can be in any order provided that the same order is used for the result limits (see below). The ACLR relative measurement should be enabled and the ACLR Pass/Fail result disabled in the test group/point measurements. A limit is then applied by setting comparison type to compare with high limit. The Array limit type should be set to compare each element to a different value. Then the high limit values of dbc would be entered for the offsets starting with the reference value (which will be 0 and hence a limit value >0 is required) then followed by the remaining offsets in the same order as they were defined in the ACLR Configuration (table above).

6 This method of performing an ACLR measurement with only relative limits is arguably more intuitive that that shown in use case 4, so is recommended.

7 Appendix Channel bandwidth of E-UTRA lowest (highest) carrier transmitted BW Channel [MHz] Table : Base Station ACLR in paired spectrum BS adjacent channel centre frequency offset below the lowest or above the highest carrier centre frequency transmitted Assumed adjacent channel carrier (informative) Filter on the adjacent channel frequency and corresponding filter bandwidth ACLR limit 1.4, 3.0, 5, 10, 15, 20 BW Channel E-UTRA of same BW Square (BW Config ) 44.2 db 2 x BW Channel E-UTRA of same BW Square (BW Config ) 44.2 db BW Channel / MHz 3.84 Mcps UTRA RRC (3.84 Mcps) 44.2 db BW Channel / MHz 3.84 Mcps UTRA RRC (3.84 Mcps) 44.2 db NOTE 1: BW Channel and BW Config are the channel bandwidth and transmission bandwidth configuration of the E-UTRA lowest (highest) carrier transmitted on the assigned channel frequency. NOTE 2: The RRC filter shall be equivalent to the transmit pulse shape filter defined in [15], with a chip rate as defined in this table. For operation in unpaired spectrum, the ACLR shall be higher than the value specified in Table Channel bandwidth of E-UTRA lowest (highest) carrier transmitted BW Channel [MHz] Table : Base Station ACLR in unpaired spectrum with synchronized operation BS adjacent channel centre frequency offset below the lowest or above the highest carrier centre frequency transmitted Assumed adjacent channel carrier (informative) Filter on the adjacent channel frequency and corresponding filter bandwidth ACLR limit 1.4, 3.0 BW Channel E-UTRA of same BW Square (BW Config ) 44.2 db 2 x BW Channel E-UTRA of same BW Square (BW Config ) 44.2 db BW Channel / MHz 1.28 Mcps UTRA RRC (1.28 Mcps) 44.2 db BW Channel / MHz 1.28 Mcps UTRA RRC (1.28 Mcps) 44.2 db 5, 10, 15, 20 BW Channel E-UTRA of same BW Square (BW Config ) 44.2 db 2 x BW Channel E-UTRA of same BW Square (BW Config ) 44.2 db BW Channel / MHz 1.28 Mcps UTRA RRC (1.28 Mcps) 44.2 db BW Channel / MHz 1.28 Mcps UTRA RRC (1.28 Mcps) 44.2 db BW Channel / MHz 3.84 Mcps UTRA RRC (3.84 Mcps) 44.2 db BW Channel / MHz 3.84 Mcps UTRA RRC (3.84 Mcps) 44.2 db BW Channel /2 + 5 MHz 7.68 Mcps UTRA RRC (7.68 Mcps) 44.2 db BW Channel / MHz 7.68 Mcps UTRA RRC (7.68 Mcps) 44.2 db NOTE 1: BW Channel and BW Config are the channel bandwidth and transmission bandwidth configuration of the E-UTRA lowest (highest) carrier transmitted on the assigned channel frequency. NOTE 2: The RRC filter shall be equivalent to the transmit pulse shape filter defined in [15], with a chip rate as defined in this table. NOTE: If the above Test Requirements differ from the Minimum Requirement then the Test Tolerance applied for this test is non-zero. The Test Tolerance for this test and the explanation of how the Minimum Requirement has been relaxed by the Test Tolerance are given in Annex G.