Setting up an LTE Measurement

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

Connect your signal to the VSA
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
Configure the LTE demodulator
1. Select the LTE demodulator
2. Set Duplex Mode
3. Set Direction
4. Preset to Standard for a selected bandwidth
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
Run the measurement

LTE Measurement Setup Procedure

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.
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 ADC Analog-to-Digital Converter. Input ranges that are too high increase noise, which increases errors reported in error summary data, such as EVM Error 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.
Configure the LTE demodulator

To configure the demodulator to use a E-UTRA Evolved 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 FDD Frequency Division Duplex: A duplex scheme in which uplink and downlink transmissions use different frequencies but are typically simultaneous. or TDD Time 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.
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-RS Cell-specific RS, P-SS Primary Synchronization Signal, S-SS Secondary Synchronization Signal, PCFICH Physical Control Format Indicator Channel, PBCH Physical Broadcast Channel, PDCCH Physical Downlink Control Channel, PHICH Physical Hybrid ARQ Indicator Channel, P-RS Positioning Reference Signal, MBSFN-RS Multicast-Broadcast Single Frequency Network Reference Signal, PMCH Physical Multicast Channel).
  - See the Downlink user allocations topic for instructions on configuring user allocations (PDSCH Physical Downlink Shared Channel, UE-RS UE-specific Reference Signal).
2. Uplink
  - See the Uplink user allocations topic for instructions on configuring user allocations (PUSCH Physical Uplink Shared Channel, PUCCH Physical Uplink Control Channel, PRACH Physical 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.
Run the Measurement

Press the Restart () button to restart the measurement.

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