Emulating Realistic Bidirectional Spatial Channels for MIMO OTA Testing

Figure 11

An illustration of the measurement system. Blue indicates the downlink and red denotes the uplink. Note that low noise amplifiers (LNAs) were used in the uplink, because the signals received by probes may have low signal to noise ratio (SNR). In the downlink, the amplification is typically done for signals with good SNRs. Different local oscillators are used in the RF channels serving uplink and downlink, especially in FDD case. All local oscillators in a fading emulator (or a set of fading emulators) typically share a common reference clock to guarantee stable synchronization. The reference clock can be taken, for example, from a satellite clock signal and distributed to different units.