5G air interfaces need channel measurements: Page 3 of 3

November 02, 2015 //By Sheri DeTomasi
5G air interfaces need channel measurements
Sheri DeTomasi lloks at why 5G air interfaces will need channel measurements to meet the upcoming technical challenges.
Calibration and synchronization

Calibration and synchronization are paramount to getting accurate, repeatable results. Synchronization of the transmitter and receiver subsystems can be achieved using two Rubidium clocks to provide a stable, high precision synchronized 10MHz reference clock to the transmitter and receiver as shown in Figure 2. In addition, triggering must be used to synchronize the sounding stimulus signal generation and acquisition. With-in a mmWave measurement system shown in Fig. 2, the following calibrations need to be considered:
  • System calibration, also called "back-to-back" calibration, involves physically connecting the transmitter to the receiver to align the frequency reference and system clocks. This can then be used to get accurate amplitude, phase and time of arrival estimates.
  • The differential IQ outputs of a baseband AWG can have timing, gain and quadrature errors, which can impact signal quality. An IQ mismatch calibration is used to address any imbalance of the in-phase and quadrature-phase signal that is output from the AWG.
  • The multichannel, wideband digitizer or oscilloscope can have inter-channel time and phase variants that will impact the measurement results. Various methods can be used to measure the cross-channel skew. One method is to measure the magnitude and phase differences across a large frequency range for each channel and apply a wideband correction filter.
  • Antenna and power calibration also need to be considered. Check with the antenna manufacturer for calibration data. If not provided, antenna array phase pattern measurement could be performed in a microwave chamber and compared with the theoretical performance of the antenna array.


Figure 2. Measurement System includes Rubidium clocks for precise Tx and Rx synchronization and acquisition trigger to align signal generation and data capture.


Conclusion

There are many challenges in the characterization of new 5G mmWave air interfaces. When considering time-varying channels with multipath propagation, the measurement systems can be complex. The measurement system should support mmWave, wideband signals and multiple channels, calibration, and synchronization. Such support can produce accurate and repeatable measurements with good channel parameter estimation algorithms for the characterization and development of realistic and accurate channel models.

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