Testing LTE Release 9 Features. Application Note. Products: R&S SMW200A R&S SMU200A R&S AMU200A R&S SMBV100A R&S CMW500 R&S TS8980

Transcription

1 Application Note Bernhard Schulz April MA210_1e Testing LTE Release 9 Features Application Note Products: R&S SMW200A R&S SMU200A R&S AMU200A R&S SMBV100A R&S CMW500 R&S TS8980 R&S FSW R&S FSQ R&S FSV R&S FSG LTE the fastest growing mobile radio standard had its beginnings in 3GPP Release 8. Initial improvements and new features were implemented in Release 9. This Application Note describes the T&M methods for LTE Release 9 features using Rohde & Schwarz instruments.

2 Table of Contents Table of Contents 1 Introduction LTE Rel. 9 signal generation Evolved MBMS (embms, MBSFN) Positioning methods Dual-layer beamforming (TM8) Multi-carrier and multi-rat base stations: Receiver Tests LTE Rel. 9 signal analysis Measurements with PRS Dual-layer beamforming measurements Multi-carrier and multi-rat base stations: Transmitter Tests LTE Rel. 9 with the CMW LTE in the CMW protocol tester LTE E2E throughput tests MLAPI + UL measurements parallel LTE in the CMW RF tester ( call box ) Data Application Unit (DAU) for CMW Channel simulation fading LTE Rel. 9 RF Conformance Test System TS Appendix Literature Additional Information Ordering Information...52 The following abbreviations are used in this application note for Rohde & Schwarz test equipment: The R&S SMW200A is referred to as the SMW. The R&S SMU200A is referred to as the SMU. The R&S AMU200A is referred to as the AMU. The R&S SMBV100A is referred to as the SMBV. The R&S FSQ is referred to as the FSQ. The R&S FSV is referred to as the FSV. The R&S FSW is referred to as the FSW. The R&S FSG is referred to as the FSG. The R&S CMW500 is referred to as CMW. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 2

3 Introduction Evolved MBMS (embms, MBSFN) 1 Introduction At the time that the first release of 3GPP Long Term Evolution (LTE Release 8) was adopted, several issues were not implemented. Moreover, there remained some room for small improvements and optimizations. All of these were brought together in Release 9, farther-reaching enhancements are specified in Release 10 (LTE Advanced). The following features were changed or added in Release 9: Multimedia broadcast multicast services (MBMS) for LTE (MBSFN) LTE MIMO: Dual-layer beamforming LTE positioning Public warning system (PWS) RF requirements for multi-carrier and multi-rat base stations Home enodeb specification (femtocell) Self-organizing networks (SON) A detailed description of the features is available in the White Paper: LTE Release 9 Technology Introduction [1]. This Application Note supplements the White Paper with a description of the T&M options available with the instruments offered by Rohde & Schwarz. Virtual antenna ports (AP) physical antennas The descriptions of the various features often refer to virtual antennas, called antenna ports. A set of antenna ports always uses a specific type of reference signals. The specification covers antenna ports based on the following cell configuration: Port 0 to 3: Cell-specific reference signals (CS-RS) Port 4: MBSFN-RS Port 5: UE-specific reference signals (DM-RS): Single-layer (TM 7) Port 6: Positioning reference signals (PRS) Port 7 and 8: UE-specific reference signals (DM-RS): Up to two layers (TM 8) The number of physical antennas in a base station is not defined. However, a minimum number can be specified. The number of physical antennas must match or exceed the number of layers to be transmitted. Therefore, a transmission with four layers needs at least four physical antennas. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 3

4 LTE Rel. 9 signal generation Evolved MBMS (embms, MBSFN) 2 LTE Rel. 9 signal generation For the SMx family of instruments, the new Release 9 features are combined into a separate option, LTE Release 9 + Enhanced Features (K84). This option is based on the Digital Standard EUTRA/LTE (K55) option. The description in this section assumes a basic understanding of how to handle LTE on the SMx. The following Rel.9 features are supported: Evolved MBMS (MBSFN) Positioning methods Dual-layer beamforming Multi-RAT The first three are LTE-specific accesses to the physical layer of the base station (enb) in the downlink, and therefore they are used to test the UE receiver. Multi-RAT refers to the multi-standard characteristics of the base station receiver in the uplink. Beyond the LTE-specific features, the SMU and the AMU both offer channel simulations with fading and AWGN. To work efficiently with the SMx, it is recommended that the various parameters be configured in the sequence shown in Fig. 1. Once the basic parameters (such as UL/DL and FDD/TDD) are defined, cell-specific parameters which are identical for all UEs and include bandwidth, MIMO mode and so on can be defined. Finally, UEspecific settings, including TX mode and UE category, as well as the subframe parameters are defined. This structure is referenced later in this document to indicate where the various features are configured (at the cell level or at the UE level). Fig. 1: Basic configuration steps for LTE in SMx. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 4

5 LTE Rel. 9 signal generation Evolved MBMS (embms, MBSFN) The term mapping describes how the virtual antenna ports are distributed amongst the physically present antennas. In the SMx through Release 9, up to four antennas can be simulated (four antennas require two SMUs). 2.1 Evolved MBMS (embms, MBSFN) The MBMS settings affect all UEs and are cell-specific, and therefore are configured under General DL Settings. Fig. 2: Where MBMS settings are made in the SMx. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 5

6 LTE Rel. 9 signal generation Evolved MBMS (embms, MBSFN) The first step is to select Mixed mode in the MBSFN Settings section. This means that both user data in the PDSCH and broadcast data in the MTCH will be transmitted in separate subframes. Fig. 3: Mixed mode in the MBSFN Settings section. Setting the frame/subframe structure for MBMS. In an LTE frame, which consists of ten subframes, a maximum of only six (FDD) or five (TDD) subframes can be reserved for MBMS. The remaining subframes are used for regular LTE operation, and the SYNC channels are not affected. Fig. 4: Configuring the subframes for MBMS (SIB type 2). 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 6

7 LTE Rel. 9 signal generation Evolved MBMS (embms, MBSFN) The Subframe Config (SIB Type 2) section, which in a real system contains information from the higher layers, defines how MBMS is applied in the frames and subframes. The Radio Frame Allocation Period and Radio Frame Allocation Offset fields define the interval at which frames with MBMS can occur. The Subframe Allocation Mode field defines whether MBMS is transmitted in one or four sequential frames. The distribution of MBMS into the individual subframes is coded in binary form using a bitmap. If the subframe allocation mode is set to one frame, then this bitmap is 6 bits in length (for the six free subframes available for MBMS). If the subframe allocation mode is set to four frames, then the length is 4 * 6 = 24 bit. The bitmap is entered into the SMx as a hexadecimal number in the Allocation Value field. In the example in Fig. 5, the allocation period is set to 8, the offset to 2 and the allocation mode is set to 4, the bitmap of 4 times resulting hexadecimal AAAAAA. Fig. 5: Example of an MBMS allocation compliant with 3GPP TS Fig. 6: SIB type 2 settings for the described example. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 7

8 LTE Rel. 9 signal generation Evolved MBMS (embms, MBSFN) Multiplexing MCCH and MTCH on PMCH In the example described above, the MCCH and MTCHs 0 to 2 are multiplexed on the PMCH. In the SMx, this is set in the PMCH Structure section. The example in Fig. 5 shows a common subframe allocation period of 64. The MCCH is always positioned in the first subframe, and the SMx automatically positions it correctly. This leaves three MTCHs, which are entered as three PMCHs. The modulation and coding scheme (MCS; a modulation of up to 64QAM is possible for MTCH) is also defined here. The position of the individual MTCHs is now defined using the start and end subframes. Only the assigned subframes, starting at zero, are included. In our example: MTCH (MCCH automatic) MTCH MTCH-2 from 8 on Fig. 7: PMCH structure. Further settings can be made in the Area Info (SIB Type 13) section (see Fig. 8). For example, if the Radio Frame Allocation Offset field from Fig. 6 was changed, the position of the MCCHs must be changed accordingly in the MCCH Offset field. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 8

9 LTE Rel. 9 signal generation Evolved MBMS (embms, MBSFN) Fig. 8: Settings for SIB type 13. The final step is to ensure that the SMU can generate the defined structure. This is done by changing the number of generated frames appropriately in the LTE main menu. In the example, the entire generated structure is 64 frames in length (the common subframe allocation period is 64 frames; see Fig. 5). Fig. 9: The number of generated frames must match the MBMS setup. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 9

10 LTE Rel. 9 signal generation Evolved MBMS (embms, MBSFN) Fig. 10 shows the timeplan for the downlink. As in the above example, three subframes per frame contain MBMS. As a result of the two-frame offset, the third frame is the first to contain MBMS (first subframe 20). In mixed mode operation, subframes that do not contain MBMS can be assigned regular PDSCH LTE data channels. The SMx sets the appropriate channels automatically. Therefore, no additional settings have to be made on the Frame Configuration screen (see Fig. 11). In this example, the third subframe of the third frame (subframe 23) contains a PMCH that is assigned MTCH content. Free segments can now be assigned PDSCH as usual. Fig. 10: OFDMA timeplan. Subframes with MBMS are green. This example shows frame 3, because the first two frames do not transmit MBMS (offset of two frames). Fig. 11: Frame Configuration screen. The third subframe of the third frame (i.e. subframe 23) contains a PMCH with MTCH content. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 10

11 LTE Rel. 9 signal generation Evolved MBMS (embms, MBSFN) TDD mode In principle, the same settings apply to TDD mode (TD-LTE). In this case, the subframes that can be allocated MBMS are dependent on the selected UL/DL configuration. Antenna port In LTE, MBMS is transmitted on antenna port 4. MIMO is not used. The SMx allows antenna port 4 to be mapped to various physical antennas in MBMS mode. These settings can be made in the MIMO section of the General DL Settings screen. MBSFN simulation In an MBSFN network, all base stations transmit the same signal at the same time. A UE receives the same signal from various base stations on different receive paths. The SMx can simulate an MBSFN network with three different receive paths. In the fading block, the signal generated in the baseband (as described above) is prepared for transmission on three different receive paths. The fading option provides the predefined profile LTE MBSFN 5 Hz. All settings are made automatically. Fig. 12: Simulation of three different receive paths in the fading block with predefined LTE MBSFN 5Hz profile. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 11

12 LTE Rel. 9 signal generation Positioning methods 2.2 Positioning methods A number of different scenarios can be generated for validating positioning methods: Generation of one LTE cell for verifying the various PRS configurations Multiple LTE cells in a single baseband (multi-carrier) with static channels and fixed delays for determining the delays for the individual LTE cells Multiple synchronized basebands, each with one LTE cell and fading, for determining delay differences in the faded channels In combination with GNSS signals For the first three scenarios, the SMx must generate LTE-specific methods for positioning, i.e. position reference symbols (PRS). PRS The PRS settings are cell-specific and therefore can be found under General DL Settings. Fig. 13: Where PRS settings are made in the SMx. The PRS settings are made under General Downlink Settings. On this screen, the segments with PRS can be set over time (subframes) and frequency (resource blocks, RB). Selecting the PRS State field enables the PRS segments. The PRS Configuration Index field defines the offset in the time axis (subframes) to the 0th subframe, taking the frame offset into consideration. The Number of PRS DL Subframes (N_PRS) field defines the number of sequential subframes that will contain PRS. This count includes any subframes that are available for PRS (no special subframes; only downlink subframes in TDD). The PRS Bandwidth field specifies which segment is used for PRS (how wide on the frequency axis). The PRS segment is always positioned at the center. Fig. 15 provides an example of the settings made in the OFDMA timeplan. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 12

13 LTE Rel. 9 signal generation Positioning methods Fig. 14: PRS settings in the SMx. Fig. 15: Visualization of the PRS settings in the timeplan. In this example, the PRS segment (blue crosshatching) is placed in two sequential subframes (N_PRS 2) in subframes 1 and 2 (Index1), with a width of 5 MHz (bandwidth). GNSS ((A) GPS, GPS P code, Galileo, GLONASS) To allow the receiver characteristics to be tested, it is possible to generate a GNSS signal in parallel to the LTE downlink signal. This can be done either in the second channel of an SMU (GPS, up to 4 satellites, option K44) or with an SMBV (up to 24 satellites). The SMBV supports the following GNSS standards: GPS, Option SMBV-K44 Assisted GPS, Option SMBV-K65 Galileo, Option SMBV-K66 GNSS Extension to 12 Satellites, Option SMBV-K91 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 13

14 LTE Rel. 9 signal generation Dual-layer beamforming (TM8) GNSS Enhanced (e.g. moving scenarios, multipath), Option SMBV-K92 GPS P code, Option SMBV-K93 GLONASS, Option SMBV-K94 GNSS Extension to 24 Satellites, Option SMBV-K96 Fig. 16: Example settings for simulating GPS satellites. 2.3 Dual-layer beamforming (TM8) Beamforming was first specified in LTE Release 8, and dual-layer beamforming was added in Release 9. For an in-depth discussion of beamforming, refer to the Rohde & Schwarz White Paper: Beamforming in LTE [2] as well as the Application Note: LTE Beamforming Measurements [3]. This application note limits itself to dual-layer beamforming (TM 8). The settings for (dual-layer) beamforming apply to the individual UEs, and therefore are made Frame Configuration -> Configure User (Fig. 17). 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 14

15 LTE Rel. 9 signal generation Dual-layer beamforming (TM8) Fig. 17: Where beamforming settings are made in the SMx. Although beamforming is a base station function, the UE receiver must also be able to understand a beamformed signal. The SMx provides predefined test signals that meet and exceed the tests defined in specification TS , Chapter 8.3 [6]. In addition to the required precoding, the SMU can also perform realtime fading (predefined profiles based on the specification), fading for MIMO setups (e.g. 2x2 and 4x2) and AWGN simulation. Beamforming mode TM 8 uses AP 7 and 8, which must be mapped to the physical RF ports on the SMU. One SMU can be used to simulate two antennas, and two interconnected SMUs can simulate up to four antennas. Fig. 18 shows the test setup with one SMU. Configurations with four TX antennas require two connected SMUs. Fig. 18: Block diagram for the UE receiver test; this example shows two antennas. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 15

16 LTE Rel. 9 signal generation Dual-layer beamforming (TM8) Phase-coherent generation The SMx signal generators use the SMx-B90 option to support phase-coherent generation of multiple signals. The signal paths within an instrument can be coupled, as can multiple instruments. Option SMx-B90 includes hardware that can be used to couple the local oscillators (LO). The LOs are coupled internally via a two-channel instrument (SMU, SMATE). Multiple instruments (SMU, SMATE, SMJ, SMBV) can be coupled via the appropriate LO IN/OUT jacks (located at the back of the instruments). Important note: In this case, phase coherence means that the phase difference between two signals is fixed, but not 0. This fixed, base phase difference (measurable using the FS-Z10 or ZVx, for example) has to be taken in account either when defining the settings on the generator or during the measurement itself. For more information on the SMx-B90 phase coherence option, refer to Phase Adjustment of Two MIMO Signal Sources with Option B90 [1]. Transmission Mode 8 Under General DL Settings, set the PDSCH Scheduling field to Auto/DCI (downlink control indicator). This allows the beamforming settings to be adjusted easily (in a more detailed screen), and the associated PDSCH settings are defined automatically. These settings are transmitted live in the PDCCH. You should also set the number of antennas to be simulated in the Global MIMO Configuration field. Up to four antennas are available. The individual basebands of the one or two SMUs then generate the signals for the individual antennas. Fig. 19: Number of antennas and assignment to the individual basebands in the SMU. In the Frame Configuration screen (Fig. 20), click Configure User. You can now make additional settings related to beamforming. Set the desired transmission mode (TM 8). 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 16

17 LTE Rel. 9 signal generation Dual-layer beamforming (TM8) Fig. 20: Frame Configuration screen in the SMU. Fig. 21: Set the transmission mode in the Configure User screen. TM 7 and TM 8 apply to beamforming. In TM 8, the SMU performs beamforming with the corresponding reference signals (DM-RS) by dividing two layers (codewords) over two or four antennas. The virtual antenna ports (AP) 7 and 8 are mapped to the physical antennas accordingly. The layers can be used for either one UE (single-layer MU beamforming) or two UEs (duallayer beamforming). To use Auto/DCI mode, additional settings must first be made in the PDCCH control channel. Click Configure PCFICH, PHICH, PDCCH to make these settings. The lower section of the screen lists the settings for the PDCCH (Fig. 23). TM 8 defines DCI formats 1A and 2B in accordance with [Table from 8]. APs 7 and 8 with DCI format 2B are used here for beamforming. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 17

18 LTE Rel. 9 signal generation Dual-layer beamforming (TM8) Dual-layer beamforming for single user In this situation, both layers are beamformed for a single UE (user). Fig. 22: Setting the user in dual-layer mode for one UE. Fig. 23: Setting the DCI format in the PDCCH for TM 8 with one UE: DCI format 2B. The data to be transmitted in the selected DCI format, and thus also the PDSCH settings, can be further configured by clicking Config Content. The transmitted bit pattern of the defined settings can be read in the bottom Data section (Fig. 24). The number and position of the resource blocks (RBs) can be set via Resource Block Assignment, while the modulation is set via Modulation and Coding Scheme [9].The two layers / codewords can be set differently (transport block 1 applies to layer 1 and transport block 2 applies to layer 2). 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 18

19 LTE Rel. 9 signal generation Dual-layer beamforming (TM8) Fig. 24: Example configuration of DCI format 2B for TM 8. In Auto/DCI mode, the PDSCH settings are prefilled automatically based on the parameters defined here (Fig. 25). The desired settings are also displayed in the timeplan. Two layers were allocated here (allocations 2.1 and 2.2 in Fig. 49) because dual-layer beamforming mode is set. Fig. 25: Example of an automatically defined PDSCH allocation in Auto/DCI mode (data source of the defined PDSCH allocation is set to User 1; in this example using Resource Block Assignment 1 and Modulation and Coding Scheme 0 (MCS 0), one RB is allocated with an offset of 37 RBs and QPSK modulation). Two layers/codewords are used automatically. The actual distribution (weighting) to the individual antennas is again carried out in the user settings under Antenna Mapping. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 19

20 LTE Rel. 9 signal generation Dual-layer beamforming (TM8) Click Config in the Antenna Mapping field for the individual user to select three different test modes. The available options in the Mapping Coordinates table vary depending on the number of antennas set under General DL Settings (see Fig. 19). Codebook: Fig. 26: Antenna mapping codebook. This is where the precoding weights are chosen based on the index that is selected from the tables in specification [8]. For TM 8, they are indices 0 to 2 for two antennas: Precoding weights for 2 antennas Codebook index j j Number of layers j j - Table 1: Allowed precoding weights for TM 8 (with two layers) for two antennas. Similarly, indices 0 to 15 are used for four antennas (table in [6]) Mapping Coordinates displays the defined weights, either in Cartesian or cylindrical coordinates. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 20

21 LTE Rel. 9 signal generation Dual-layer beamforming (TM8) Random codebook Fig. 27: Random codebooks for tests in accordance with TS36.521, section 8.3. In this case, the codebooks are randomly selected from the tables. This mode corresponds to test specification TS36.521, section 8.3. Because the weight settings change continually, Mapping Coordinates is not visible. Fixed weight Fig. 28: Fixed weight for TM 8 with two antennas. The weights can be set in Mapping Coordinates. They apply to all user allocations over the entire frame. Additionally the settings are displayed again in the Enhanced Settings for the allocation (Fig. 29). 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 21

22 LTE Rel. 9 signal generation Dual-layer beamforming (TM8) Fig. 29: Display of the beamforming settings in the allocation; this example shows TM 8 on APs 7/8 with codebook 0. Dual-layer beamforming for multiple users The individual layers are provided to various UEs (users) in the same way as in multiuser MIMO. To do this, two users are first created with different UE IDs in the Configure User screen. Fig. 30: Setting the users in dual-layer mode for two UEs. Note the different UE IDs. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 22

23 LTE Rel. 9 signal generation Dual-layer beamforming (TM8) Two users are also created in the PDCCH settings. Again, dual-layer mode with DCI format 2B is selected. Fig. 31: Setting the DCI format in the PDCCH for TM 8 with two UEs: DCI format 2B. The data to be transmitted in the selected DCI format, and thus also the PDSCH settings, can be further configured by clicking Config Content. The transmitted bit pattern of the defined settings can be read in the bottom Data section. The number and position of the resource blocks (RBs) can be set via Resource Block Assignment, while the modulation is set via Modulation and Coding Scheme [9]. Because multi-user mode is now used, the second codeword is disabled for both users by setting Redundancy Version to 1 and MCS to 0 (see Fig. 32) according to [6]. AP7 and AP8 are distinguished by the different setting of the New Data Indicator (see Fig. 33). 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 23

24 LTE Rel. 9 signal generation Dual-layer beamforming (TM8) Fig. 32: Example configuration of DCI format 2B for TM 8 in multi-user mode. The second codeword (CW) is disabled by setting Redundancy Version 1. Enabling the New Data Indicator in allocation 3 sets AP8. Fig. 33: Different antenna port (AP) settings in Dual-Layer Beamforming for multiple users. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 24

25 LTE Rel. 9 signal generation Multi-carrier and multi-rat base stations: Receiver Tests Fig. 34: Example of an automatically defined PDSCH allocation in Auto/DCI mode for MU beamforming (data source of the defined PDSCH allocation is set to User 1 and 2; in this example using Resource Block Assignment 1 and Modulation and Coding Scheme 0 (MCS 0), one RB is allocated with an offset of 37 RBs and QPSK modulation). Two independent layers, each with one codeword (CW), are automatically allocated for the various users. The settings for the weightings correspond to those described in single-user mode. 2.4 Multi-carrier and multi-rat base stations: Receiver Tests At a minimum, the MSR-BS must meet the receiver characteristics requirements from chapter 7 of TS Rohde & Schwarz signal generators, in particular the SMU and the SMBV, are available for receiver measurements on BS and MSR-BS. These instruments allow various test and reference signals to be generated for the required measurements. Software options allow generation of test signals for all of the standards required for the MSR-BS measurements, i.e. GSM/EDGE, WCDMA, TD-SCDMA and LTE FDD/TDD. Note, however, that channel coding for GSM is not supported by the GSM/EDGE option of the SMU or SMBV and needs to be done via a properly coded data list. An SMU with options for two RF paths and two basebands allows more complex test scenarios with only one instrument. This means, for example, that both interfering and useful signals can be generated on a single instrument. Other options also make it possible to add fading and noise to the signals. When using the internal baseband generator, the SMU can generate RF signals with a bandwidth of up to 80 MHz, the SMBV up to 120 MHz. A detailed description of the receiver test solutions of MSR-BS can be found in the Application Note: Measuring Multistandard Radio Base Stations according to TS [4]. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 25

26 LTE Rel. 9 signal analysis Measurements with PRS 3 LTE Rel. 9 signal analysis LTE analysis software provides users of the FSx family of instruments with an easy-tounderstand, user-friendly software application. The following options are integrated into the software: LTE FDD Downlink, Option K100 LTE FDD Uplink, Option K101 LTE Downlink MIMO, Option K102 LTE-A Uplink and MIMO, Option K103 LTE TDD Downlink, Option K104 LTE TDD Uplink, Option K105 Two versions of the software are available for the various analyzers: Users can choose the integrated version or the PC-based software program. The description in this section assumes a basic understanding of how to handle LTE on the FSx. The LTE Rel 9 changes in the physical layer affect the downlink. Measurements are therefore performed on the base station (BS) transmitters (enb). 3.1 Measurements with PRS Release 9 introduced new reference signals for PRS in the LTE downlink. These must be taken into consideration when performing transmitter measurements in an LTE BS. The PRS segments can be set in the Positioning Reference Signal section, which is found on the Downlink Advanced Signal Characteristics tab of the Demodulation Settings screen. Selecting the Present field indicates to the LTE analysis software that PRS should be enabled. The Configuration Index field defines the offset in the time axis (subframes) to the 0th subframe, taking the frame offset into consideration. The Num. Subframes (N_PRS) field defines the number of sequential subframes that will contain PRS. This count includes any subframes that are available for PRS (no special subframes; only downlink subframes in TDD). The Bandwidth field specifies which segment is used for PRS (how wide on the frequency axis). The PRS segment is always positioned at the center. Fig. 35: Setting the PRS segments in the LTE analysis software for the FSx. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 26

27 LTE Rel. 9 signal analysis Measurements with PRS Fig. 36 through Fig. 38 show various measurements. The dark blue crosshatching in Fig. 36 indicates the PRS segments. Fig. 37 lists all allocations that are found. The PRS is listed as Pos. RS, with modulation, power and EVM. Finally, Fig. 38 shows the constellation diagram for the PRS allocation. Fig. 36: Display of the allocation IDs in the LTE Analysis SW. The areas with blue crosshatching in the first and second subframe represent the PRS segments (outlined in red). 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 27

28 LTE Rel. 9 signal analysis Measurements with PRS Fig. 37: Display of the allocation summary in the LTE Analysis SW. Subframes 1 and 2 include the measured values for PRS (Pos. RS), along with other information. Fig. 38: A constellation diagram is also available for the positioning reference signals. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 28

29 LTE Rel. 9 signal analysis Dual-layer beamforming measurements 3.2 Dual-layer beamforming measurements Beamforming was first specified in LTE Release 8, and dual-layer beamforming was added in Release 9. For an in-depth discussion of beamforming, refer to the Rohde & Schwarz White Paper: Beamforming in LTE [2] as well as the Application Note: LTE Beamforming Measurements [3]. This application note limits itself to dual-layer beamforming (TM 8). The LTE analysis software for the FSx signal and spectrum analyzers can be used for the familiar LTE measurements, including power, EVM and spectrum, and also to verify that the beamforming transmission modes are implemented correctly. It displays up to four measurement screens in parallel. In beamforming mode TM 8, both the UE-specific reference signals and the data in the PDSCH are beamformed. All other channels remain unweighted, i.e. they are transmitted with no phase difference (0 ). This means that for the PDSCH and DM-RS, the constellations are rotated based on weighting. Testing single antennas in Transmission Mode 8 Fig. 39 shows the fundamental test setup. The antennas are switched one after the other to the input of an FSx. Fig. 39: Test setup for the base station transmitter test with LTE analysis software. In the LTE Analysis Software, open the Demodulation Settings dialog box and set the number of antennas (two in this example) in the MIMO Configuration section (Fig. 40), and set Antenna Selection to one single antenna mode (Antenna 1/2). TM8 uses two codewords on two layers. Set the Codeword-to-layer Mapping in the Enhanced Settings and then select Beamforming (UE-RS) as Precoding for an allocation (Fig. 41). The two code words are automatically prefilled in the Demodulation Settings (Fig. 40 and Fig. 41). It also allows multiple different beamformed allocations to be analyzed. All standard measurements can be performed. The setup with one analyzer allows all measurements on one single antenna and a demodulation of all channels except the UE-specific RS and PDSCHs. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 29

30 LTE Rel. 9 signal analysis Dual-layer beamforming measurements Fig. 40: Beamforming settings in the LTE analysis software for the FSx; TM 8 on one single antenna in this example. Fig. 41: Additional settings. The precoding is set to beamforming (UE-specific RS). In TM87, two codewords are mapped to two layers at antenna ports 7 and 8. Demodulation of beamformed channels in Transmission Mode 8 with two analyzers Using a setup with two analyzers (Fig. 42) and enabling the Compensate Crosstalk feature (Fig. 44) enables the LTE Analysis Software to demodulate PDSCH allocations with reference to DM-RS. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 30

31 LTE Rel. 9 signal analysis Dual-layer beamforming measurements Fig. 42: Test setup for the base station transmitter test with LTE analysis software. Fig. 43: Setup Demodulation settings with two analyzers: Set the Antenna Selection to All. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 31

32 LTE Rel. 9 signal analysis Dual-layer beamforming measurements Fig. 44: Enabling the Compensate Crosstalk to demodulate mixed weighted PDSCHs. Compensate Crosstalk allows compensation of layers with mixed weightings. As a result, EVM and constellation diagrams for the PDSCH can be evaluated. Fig. 45 shows an EVM measurement and a constellation diagram. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 32

33 LTE Rel. 9 signal analysis Dual-layer beamforming measurements Fig. 45: Summary EVM measurement on antenna 1 and constellation diagram of a beamformed QPSK-modulated data allocation (PDSCH) in TM 8. Fig. 46: PDSCH and UE-RS can be demodulated using the compensate crosstalk feature. This figure shows the listing in the allocation summary. Beamforming measurement The beamforming measurement determines the magnitude and phase of the UEspecific RS and displays them separately. For example, the phase differences for various antenna ports (AP) can be displayed. The measurement results can be selected for the individual antennas or antenna ports (in the Antenna Selection field under General Settings, and ports in the beamforming measurement under Beamforming Selection) (Fig. 47). You must also specify a subframe. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 33

34 LTE Rel. 9 signal analysis Dual-layer beamforming measurements Fig. 47: Selecting the antenna or antenna ports and the subframe for beamforming measurements. Fig. 48: Example beamforming measurements. The display includes both the amplitude and the phase response over frequency. Both screenshots are for antenna 2; AP7 is at the top and AP8 at the bottom. In this example, the phase difference is MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 34

35 LTE Rel. 9 signal analysis Multi-carrier and multi-rat base stations: Transmitter Tests 3.3 Multi-carrier and multi-rat base stations: Transmitter Tests At a minimum, the MSR-BS must meet the transmitter characteristics requirements from chapter 6 of TS The FSW, FSQ and FSV spectrum and signal analyzers can be used to perform TX tests on MSR-BS. The FSW, FSQ and FSV base units can be used for spectrum measurements as well as for measurements of spurious emissions, out-of-band emissions and adjacent channel leakage ratio. More extensive tests are possible with powerful options that are capable of analyzing and demodulating standard signals. Software options in the FSW, FSQ and FSV are available to support the standards GSM, WCDMA, LTE FDD/TDD and TD-SCDMA. In addition, a special Multi-Standard Radio Analyzer Mode (MSRA) to measure different standards in parallel is available for the FSW. In the MSRA operating mode, which is part of the basic software functions of the FSW analyzer, IQ-Data are captured over the full bandwidth (up to 160 MHz, depending on options) over a long period of time (up to 200 Msamples), and may be analyzed for various mobile radio standards. With this mode e.g. interactions between the different carriers can be found and the reasons for possible performance degradation can be traced. MSRA supports following mobile standards (depending on installed options): 3GPP FDD (W-CDMA) CDMA2000 1xEV-DO GSM LTE Fig. 49 shows the MSRA-View for an MSR signal example, which consists of a LTE and a W-CDMA carrier. The top shows the entire spectrum of the signal with the marked frequency ranges used by the applications. At the bottom, the results for the LTE part is shown on the left and the W-CDMA part on the right. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 35

36 LTE Rel. 9 signal analysis Multi-carrier and multi-rat base stations: Transmitter Tests Fig. 49: MSRA view with overview of the LTE and W-CDMA signal. A detailed description of the transmitter test solutions of MSR-BS can be found in the Application Note: Measuring Multistandard Radio Base Stations according to TS [4]. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 36

37 4 LTE Rel. 9 with the CMW500 LTE Rel. 9 with the CMW500 Multi-carrier and multi-rat base stations: Transmitter Tests The CMW can be used as a protocol tester (message analysis) as well as a radio communication tester (call box, RF test). In addition to LTE (FDD and TDD), the CMW offers other radiocommunication standards, including W-CDMA, GSM, CDMA2000, 1x-EV-DO. This makes it possible to test Inter-RAT scenarios, such as W-CDMA handover to GSM or LTE. Equipped with powerful hardware and various interfaces to wireless devices, the CMW can be used throughout all phases of LTE device development from the initial module test up to the integration of software and chipset, as well as for conformance and performance tests of the protocol stack of 3GPP standard-compliant wireless devices, see Fig. 50. Fig. 50 Consistent hardware and software concept for all device development phases. CMW500 LTE Release 9 LTE Features Positioning Reference Signal (PRS) Enhanced Cell ID (ecid) Dual Layer Beamforming (TM8) Public Warning System: Commercial Mobile Alert System (CMAS) Table 2: LTE Release 9 features in the CMW500 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 37

38 LTE Rel. 9 with the CMW500 LTE in the CMW protocol tester 4.1 LTE in the CMW protocol tester The CMW protocol tester provides developers of UE protocol stacks with a specification-conforming reference implementation of the air interface. The comprehensive functions of the programming interfaces and the highly detailed representation in the analysis tools can be used to quickly detect discrepancies in the DUT protocol stack. The widely used MLAPI interface provides the C++ programming interface to the protocol tester, allowing users to run predefined example or reference scenarios and also to develop and modify their own scenarios. The Message Composer allows users to compose send and receive constraints, whereas the Message Analyzer provides the means to analyze results and export constraints. The TestSuite Explorer defines configurations and manages suites, while the Project Explorer defines sequences and executes and manages the results. Finally, MS Visual Studio is available for developing and building test scenarios, while the Automation Manager provides full automation during the execution of all test cases and scenarios with minimal or no human interaction. The workflow is illustrated in Fig. 51. Fig. 51 Test case development workflow. The CMW protocol tester supports a very large number of test cases (TCs). Registered users can view a summary of the currently available TCs on the CMW Customer Web at 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 38

39 LTE Rel. 9 with the CMW500 LTE in the CMW protocol tester Fig. 52: Project Explorer with Release 9 test cases for LTE testing. Fig. 53: The Message Analyzer makes it easy and fast to analyze protocol logfiles. This example shows a logfile for a dual-layer beamforming scenario. The following options are available for testing Release 9 features: 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 39

40 LTE Rel. 9 with the CMW500 LTE in the CMW protocol tester CMW-KF500 LTE Example Scenarios Example scenarios for Release 9 Number Description Test ML_019 LPP capabilities ML_020 ML_021a ML_021b System information modification with CMAS Beamforming (Single Layer) Beamforming (Dual Layer) This scenario setups a Cell which is configured for Beamforming. Initial registration is performed without beamforming, then the transmission mode is changed to TM7 (for the single-layer case) or TM8 (for the dual-layer case). Directly after the TM change, the DCI format remains as 1A in the DL and is then changed to use single (DCI format 1) or dual layer (DCI format 2B) beamforming. There are two variants of this test for the single layer (ml_021a) and dual layer (ml_021b) cases. ML_024a ML_024b LPP: OTDOA Measurement LPP: E-CID Measurement The LTE Positioning Protocol using hyperbolic timedifference of arrival (TDOA) and enhanced cell ID (ecid) is for non-gnss devices, hybrid use and for GNSS-denied environments. MME issues the positioning request to E- SMLC which then commands UE and enb to perform positioning. The LTE Positioning Protocol (LPP) consists of three independent procedures: (i) capability exchange (LPP Request/Provide Capabilities)) (ii) assistance data exchange (LPP Request/Provide Assistance data, i.e. when the UE does not have the latest measurements)) (iii) location information exchange (LPP Request/Provide location information for AGNSS, OTDOA, ECID or location estimate) CMW-KF511 LTE MLAPI commercial mobile alert system (CMAS) This option contains 32 scenarios. See [7] for additional information. As an example for the process followed in CMAS, the LTE_CMAS_I00_01 procedure is listed here: BROADCAST CMAS MSG WITH SAME MESSAGE ID AND SAME SERIAL NUMBER IN CONNECTED MODE. In detail, the procedure is: 1. Keep sending a CMAS message with Message ID "A" and Serial Num "X" only. 2. Verify that UE displays the correct CMAS message on the UE screen. 3. Have user acknowledge the message. 4. Verify that the UE does NOT re-display the message after user's acknowledgment. 5. Now send a CMAS message with Message ID "A" and serial Num "X" but with an updated 4-bit Update Number and different message content. 6. Verify that UE displays the updated CMAS message on the UE screen. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 40

41 LTE Rel. 9 with the CMW500 LTE in the CMW protocol tester CMW-KF512 LTE LLAPI Rel-8/9 PHY scenarios At the moment this package contains different configurations according to Release 8 such as SPS and TTI bundling. The package will be extended with the Beamforming Transmission Modes TM7 and TM LTE E2E throughput tests In addition to message analysis, the main test requirement is to determine the throughput capabilities of the device under test (DUT), ideally allowing an E2E application to run a specific service of interest. The above illustrated tool chain and the LTE functionality offer an ideal environment to assess the DUT performance, including E2E testing. The Throughput Configuration Tools (TCT) for LTE allow users to configure a variety of throughput tests quickly and easily (Fig. 54). Fig. 54: Quick and convenient configuration of throughput tests with the TCT. This example shows the settings for dual-layer beamforming (TM8). The tests defined using the TCT are started as normal from the Project Explorer (Fig. 55). 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 41

42 LTE Rel. 9 with the CMW500 LTE in the CMW protocol tester Fig. 55: A TCT test in the Project Explorer. After the test case is started successfully, the throughput can be evaluated by starting the Protocol Testing Monitor (PTM), for example (see Fig. 56). The logging capabilities of the protocol tester and the message analyzer permit a detailed investigation of the message flow, making it easy to identify loss of performance due to incorrect behavior and/or protocol errors, for example. In addition to the throughput performance at RLC level, it is essential to identify the E2E capabilities of the device under test. This is necessary in order to understand the performance of a specific service at IP level. IP data has to be provided from a suitable application. The Data Application Unit (DAU, see 4.3) generates UPLANE traffic (IPERF, PING, FTP, HTTP, Video etc) as an internal solution. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 42

43 LTE Rel. 9 with the CMW500 LTE in the CMW RF tester ( call box ) Fig. 56: LTE throughput measurement with the protocol tester MLAPI + UL measurements parallel As mentioned above, the CMW can be used as both a protocol tester and an RF tester. It is even possible to install both protocol testing and RF testing software options, and consequently to run RF measurements in parallel to a MLAPI test scenario started in the protocol environment. The CMW radio communication tester offers a multievaluation mode for performing RF measurements as illustrated in Fig. 57 (see next section 4.2). It allows users to analyze the throughput and at the same time monitor whether basic Tx operation of the DUT is still running within 3GPP-specified limits. 4.2 LTE in the CMW RF tester ( call box ) When used as an RF tester, the CMW consists of a generator for the LTE downlink. It can play back ARB files generated using an external tool, such as WinIQSIM or MATLAB. An online generator is also available as an option. It permits rapid reconfiguration of the signal and dynamic elements, such as the transmit power control (TPC). 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 43

44 LTE Rel. 9 with the CMW500 LTE in the CMW RF tester ( call box ) Transmitter tests (TX) Measurements on the TX side of the DUT are made possible with the LTE Multi Evaluation option (see Fig. 57) for both FDD and TDD mode (options KM500 and KM550). The overview screen provides all measured results and scalar values for the essential measurements: UE power, error vector magnitude (EVM), RB allocation, frequency error, spectrum emission mask (OBW) and ACLR. Because measurements results are based on the same set of data, the individual results relate to each other, thus facilitating troubleshooting and debugging. Fig. 57: Multi-evaluation mode of LTE uplink measurement. The overview display in multi-evaluation mode can be adapted to the individual testing needs. For example, it may be necessary to closely monitor only two measurement results, or just one measurement result with a comparison of maximum and average values. The overview display can be configured to meet individual needs. Signaling and receiver tests (RX) The CMW also provides signaling. The "LTE signaling" firmware application (option KS5xx) allows users to emulate an E-UTRAN cell and to communicate with the UE under test. The UE can synchronize to the downlink signal and attach to the PS domain. A connection can be set up (3GPP-compliant RMC or user-defined channel). 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 44

45 LTE Rel. 9 with the CMW500 Data Application Unit (DAU) for CMW In addition to the signaling mode, a reduced signaling mode is supported. It allows users to set up a connection without any registration, attach and attach layer 3 signaling. As a result, modules supporting only layer 1 and 2 can be tested. This means that RX tests, such as BER or ACK/NACK measurements (BLER, throughput), can be performed in test mode on the DUT. Fig. 58: Extended BLER measurement overview. The CMW supports all RMC according to 3GPP TS [5] as predefined settings. The settings can also be configured individually by selecting "User Defined", or as fixed CQI channels (option KS510). End-to-end data tests can be performed using the DAU (see the next section). 4.3 Data Application Unit (DAU) for CMW The "Data Application Unit" (option B450A) makes it possible to test data transfer via TCP/IP or UDP/IP. It allows users to run Internet Protocol (IP) services on the CMW, such as file transfer and Web browsing. The DAU provides a common and consistent data testing solution on the CMW for all supported radio access technologies. The DAU is required when testing End-to-End (E2E) IP data transfer as well as when using the instrument for protocol testing (U-plane tests). Together with the DAU, IPbased measurement (option KM050) applications allow users to test and measure the properties of the IP connection, such as network latency or performance. The 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 45

46 LTE Rel. 9 with the CMW500 Channel simulation fading measurements support Internet protocols IPv4 (option KA100) and IPv6 (option KA150 on top of KA100). 4.4 Channel simulation fading In order to simulate the channel attributes for receiver tests, the CMW can be connected to the AMU via optional digital IQ interfaces. The baseband signals in the AMU are faded, and MIMO (e.g. 2x2) and AWGN are added. The two RF paths can be faded independently of one another. The AMU has predefined fading profiles for LTE in accordance with specification [5]. The fading parameters can also be changed separately. Fig. 59 Test setup for channel simulation with the CMW and AMU (two-channel with MIMO). 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 46

47 LTE Rel. 9 RF Conformance Test System TS8980 Channel simulation fading Fig. 60 Block diagram in AMU with 2x2 MIMO, fading and AWGN. 5 LTE Rel. 9 RF Conformance Test System TS8980 UEs have to pass various test phases during their development. In the early phase of R&D, the different components of the UE, such as baseband and RF part are tested independently from each other. During this time radiocommunication testers, signal generators (SG) and signal analyzers (SA) are typically used in non-signaling test environments in order to investigate RF receiver and transmitter characteristics of the UE. Pure baseband tests can be done by using simulation and verification via the IQ interface of the UE, which is connected to the IQ interface of channel emulators, SA and SG. As soon as a logical and physical call setup can be established, further tests on UE prototypes can be performed with the help of a signaling unit (SU) fitted to a radiocommunication tester such as CMW. Chipset and UE manufacturers will apply differing test specifications. There are internally defined specs, which are based on knowledge and prior experience. This is a main part of the test area. Other tests are derived from the 3GPP test specifications, for example [5]. As maturity of a UE design increases, more testing conditions are added. House test specifications [5] also contain LTE test scenarios with fading and interference conditions. Additionally, extreme test conditions with varying environmental factors, including supply voltage, humidity and temperature are defined for a UE. 1MA210_1e Rohde & Schwarz Testing LTE Rel. 9 Features 47