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 sounder 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 article describes some measurements in both a massive MIMO setup in an indoor sports arena and an mmWave setup with a handheld device containing a 7-element array.