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5G air interfaces require channel measurements

11 Nov 2015  | Sheri DeTomasi

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5G wireless communications should bring enhanced network capacity, better peak data rates, and more reliable service in mobile communications systems. Many of the goals are 10x, 100x or 1000x today's performance but aren't achievable in the currently available spectrum below 6GHz. Therefore, new air interfaces are being investigated in Centimeter (cm) and Millimeter-wave (mmWave) frequencies up to 100GHz. Characterisation of the radio channel at mmWave frequencies presents many new challenges for engineers. Here are some of these challenges and some considerations.

To define new air interface standards, researchers will need to characterise the radio channel so they can understand how the signal will propagate. Researchers are using channel sounding techniques to collect the channel impulse response (CIR) data so they can extract channel parameters by using channel parameter estimation algorithms. The extracted data are then used for developing new channel models as shown in figure 1. Sounds straightforward and easy, right?

Well, not quite.

Figure 1: The model of a wireless transmission channel consists of channel sounding, estimating of channel parameters, and statistics.

Channel sounding measurement systems can range from simple to complex depending on parameters being estimated. When measuring time-varying channels with multi-path propagation, you need to understand the complex impulse response with time and phase information. In addition, one of the key challenges is being able to duplicate or validate the measurements with different measurement systems in similar conditions.

Key technical challenges include:

 • Signal generation and analysis at mmWave frequencies with greater than 500MHz bandwidth and with multi-channel support
 • Data capture and storage
 • Channel parameter estimations
 • Calibration and synchronisation
Now let's discuss considerations to help you address these challenges.

Signal generation and analysis
To meet the high demands for 5G, the air interface standards will likely include mmWave frequencies up to 100GHz, with 500MHz to 2GHz bandwidth, and with multi-channel support. That's a lot to consider. The requirements will place great demand on the channel sounding measurement system. The measurement system needs to support these core requirements and provide repeatable measurements. Key components for this measurement system will be a wideband DAC (Digital to Analog ('ue'?) Converter) in the form of a base band AWG (arbitrary waveform generator) and an ADC (analogue-to-digital converter) that will take the form of a wideband digitizer or oscilloscope to support the needed bandwidth and provide enough resolution to support the dynamic range needed to capture the signal. Also, because 5G is not yet defined, the test equipment should be flexible so that it can be configured and reconfigured as the test requirements and standards evolve.

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