A Channel Sounder for Massive MIMO and mmWave Channels

Both massive multiple-input multiple-output
(MIMO) technology and use of frequencies in the range
24–100 GHz are considered essential for upcoming 5G systems.
Measurements of the new type of channels are needed, but this
is challenging due to the large number of channels in massive
MIMO and the short wavelength in the 24–100 GHz channels
(so-called mmWave channels). This article describes a sounder
system capable of measurements in both types of channels.
While the same sounding system supports simultaneous massive
MIMO and mmWave channels, the number of channels in each
band and in total is in practice limited. For massive MIMO in
the 300–6000 MHz band alone, arrays with up to 128 receiver
(Rx) elements are possible, receiving from 16 independent mobile
transmitter (Tx) antennas, where all channels are measured
within 1.3 ms and in a 200 MHz bandwidth. To the authors
knowledge, this is the first sounding system with this number
of channels and a speed necessary for measuring the dynamic
channels in typical application scenarios. For mmWave channels
the sounder operates in the range 18–40 GHz. For these bands
up to 2 Tx elements and 16 Rx elements can be measured. In
addition, the paper describes some measurements in both a
massive MIMO setup in an indoor sports arena and a mmWave
setup with a handheld device containing a 7-element array.