Inside the Keysight 5G channel sounding system
Frequent readers of the Test Cafe blog know that I’ve added a recent focus on 5G characterization and test systems. Why? It’s simple. Test Cafe discusses instrument architectures, particularly modular instrument architectures, and 5G presents a key opportunity for modular instrumentation.
5G (fifth generation) is the next generation of cellular communication standards. For more information about 5G, and why I believe 5G will be a boon for modular instruments, read my recent column, 5G to disrupt the test equipment market. Due to 5G’s greater bandwidth and massive number of channels, I made an unequivocal prediction for vendors: if you don’t have a modular solution, you won’t be playing a significant role in 5G. In a subsequent column I predicted that microwave would be coming to PXI, driven by many of the same dynamics.
Since that time, National Instruments and Keysight Technologies have introduced some exciting solutions in the 5G mmWave space, all based on modular instruments. Several weeks ago I described the internals of an NI system used by Nokia to create a 2x2 MIMO mmWave 5G prototype system, operating at 73 GHz. Now I’d like to take a look at the Keysight 5G channel sounding system.
Before I do, perhaps a little description of what channel sounding is all about. Channel sounding is a technique to measure and characterize the air interface of a RF communication network. That is, to characterize the mathematical transfer function from one or more transmit antennas to one or more receive antennas. 5G channel sounding is both mission critical and difficult. At mmWave frequencies the channel is not only complex (path reflections and attenuation), but dynamic as well. The channel characteristics change as any antenna moves or there is movement of a reflective surface.
The simplest model characterizes the channel between a single transmitter and single receiver:
But in the real world, the channel is dynamic, as exemplified by this image from Nokia Networks:
Here, users 1 and 2 may experience the same channel function due to their proximity, but their movement coupled with the movement of all the surfaces around them mean that the channel is constantly changing its characteristics. It is paramount that researchers characterize exactly what is to be expected in the spectrum of interest before deploying 5G devices (coupled with their complex beam forming algorithms).
So, what has Keysight done? Let's take a look.