Setting up an LTE Measurement

This topic provides information on connecting and successfully demodulating a signal using the LTELong Term Evolution demodulator. A typical measurement includes the following measurement setup process (each step is discussed in the following text).

1. Connect your signal to the VSA
2. Configure measurement setup and input parameters
   1. Set the Center Frequency
   2. Set the Frequency Span
   3. Configure the Input Range
   4. Configure Triggering (when required)
   5. Verify input signal and initial parameter settings
3. Configure the LTE demodulator
   1. Select the LTE demodulator
   2. Set Duplex Mode
   3. Set Direction
   4. Preset to Standard for a selected bandwidth
4. Setup LTE signal parameters

   1. Downlink parameters

   2. Uplink parameters

   3. Set the Result Length, Measurement Interval, and Measurement Offset

   4. Set Mirrored Spectrum when necessary

5. Run the measurement

LTE Measurement Setup Procedure

1. Connect your Signal to the VSA

   • Single or multiple channel connection
     

     Connect the antenna signals to the hardware input channels.

     Click Input > Channels and select the number of channels.

   • I+jQ connections

     Connect the I and Q signals to the measurement hardware. To configure the VSA, choose one of the I+jQ selections: Input > Channels > I + jQ.

     Notes for I+jQ input:

     • Selecting an I+jQ configuration enables DC coupling.
     • Use User Correction to correct for any offset or gain imbalance between the I and Q signals.
     • Range is set independently for the I and Q inputs, but can be coupled by selecting the Couple Paired Channels parameter.

   • Recorded signal

     Recall the recorded signal by selecting File > Recall > Recall Recording

     The center frequency and input range will be set by the recording.

     Information about sample LTE signals included with the 89600 VSA software can be found in the Demo and Recorded Signals topic.

   For more information about your specific measurement hardware, see the Measurement Hardware book.

2. Configure Measurement Setup and Input Parameters

   1. Set the Center Frequency

      By default, the center frequency of each measurement channel must be set to within approximately ±0.5x subcarrier spacing (7.5 KHz at the default subcarrier spacing) of the carrier frequency of the LTE signal connected to that channel, otherwise the demodulator may not be able to lock onto your signal.

      Frequency lock range can be extended to 2.5x subcarrier spacing by selecting Extended Freq Lock.

   2. Set the Frequency Span (optional)

      At this point, you can set the frequency span for the signal. The span should be larger than the bandwidth of the LTE signal, and, for best results, set the span according to the LTE standard.

      This step is optional because clicking Preset to Standard (this is part of Step 3 below) will set the span according to the LTE standard for the selected bandwidth.

   3. Configure the Input Range

      The input range must be set correctly to obtain accurate measurements. Input ranges that are too low overload the measurement hardware's ADCAnalog-to-Digital Converter. Input ranges that are too high increase noise, which increases errors reported in error summary data, such as EVMError vector magnitude (EVM): A quality metric in digital communication systems. See the EVM metric in the Error Summary Table topic in each demodulator for more information on how EVM is calculated for that modulation format..

   4. Set up triggering (optional) 

      The default triggering mode is set to "FreeRun." However, you can configure a different type of configuring if you wish (such as an external frame trigger).

   5. Verify the input signal and initial parameter settings 

      View your signal in the frequency domain (Spectrum trace) to verify the parameters you set.

3. Configure the LTE demodulator

   To configure the demodulator to use a E-UTRAEvolved Universal Terrestrial Radio Access Test Model, see Selecting LTE Test Models.

   1. Click MeasSetup > Demodulator > 3G/4G Cellular > LTE to enable the LTE demodulator properties and measurement parameters.

   2. Set Duplex Mode to FDDFrequency Division Duplex: A duplex scheme in which uplink and downlink transmissions use different frequencies but are typically simultaneous. or TDDTime Division Duplex: A duplexing technique dividing a radio channel in time to allow downlink operation during part of the frame period and uplink operation in the remainder of the frame period.

      For TDD:

      1. Set uplink-downlink configuration (UL/DL Config)

      2. Set special subframe configuration (Dw/GP/Up Len)

   3. Set Direction to uplink or downlink

   4. Preset to Standard: choose bandwidth

      Demodulator measurement parameters will be set to typical values (see Using a Standard Setup topic) when Preset to Standard is used to select an LTE bandwidth.  In addition to setting the demodulator parameters, the sample rate (and measurement span) will be set according to the standard for the chosen bandwidth.

4. Setup LTE signal parameters

   These parameters are not autodetected and will need to be set when the default values are not correct for your signal.

   1. Downlink

      • See the Downlink Control Channel Properties topic for information about control/broadcast channel settings (C-RSCell-specific RS, P-SSPrimary Synchronization Signal, S-SSSecondary Synchronization Signal, PCFICHPhysical Control Format Indicator Channel, PBCHPhysical Broadcast Channel, PDCCHPhysical Downlink Control Channel, PHICHPhysical Hybrid ARQAutomatic Repeat Request 1) A distinct unit of data that is carried on an ARQ-enabled connection. Such a unit is assigned a sequence number, and is managed as a distinct entity by the ARQ state machines. Block size is a parameter negotiated during connection establishment. 2) automatic retransmission request - A signal used in digital communications systems used to signal the transmitting device to retransmit a block of data. Indicator Channel, P-RSPositioning Reference Signal, MBSFN-RSMulticast-Broadcast Single Frequency Network Reference Signal, PMCHPhysical Multicast Channel).
      • See the Downlink user allocations topic for instructions on configuring user allocations (PDSCHPhysical Downlink Shared Channel, UE-RSUEUser Equipment (e.g. cell phone)-specific Reference Signal).

   2. Uplink

      • See the Uplink user allocations topic for instructions on configuring user allocations (PUSCHPhysical Uplink Shared Channel, PUCCHPhysical Uplink Control Channel, PRACHPhysical Random Access Channel).

   3. Set the Result Length, Measurement Interval, and Measurement Offset

      Result Length determines the available analysis data in terms of the number of slots + symbols. Set Result Length to capture the desired data. 

      Measurement Interval specifies the data that will be demodulated, and Measurement Offset specifies an offset from the beginning of the Analysis Start Boundary to the Measurement Interval.

   4. Set Mirrored Spectrum when necessary

      LTE demodulation provides a feature that lets you configure the demodulator to conjugate the complex time-domain waveform. This has the effect of flipping the spectrum around the VSA's center frequency.

5. Run the Measurement

   Press the Restart () button to restart the measurement.

   For help when your signal is not demodulating correctly, see the Troubleshooting topic.

See Also

Measurement Speed Considerations

Troubleshooting

Using a Standard Setup

About Opts BHD and BHE: LTE Modulation Analysis