Demultiplexing spectrum-sharing field sources with distributed field probes

A complete characterization of multiple-device wireless interactions must include data relatable to the electromagnetic field radiated by each device under test (DUT). If these field sources are separable in time or frequency, they can be demultiplexed with a single probe antenna and time gating or bandpass filtering. Spectrum-sharing coexistence testing, however, may deal with simultaneous co-channel radiation. Communication channels may realize orthogonality in signal modulation or coding, for example, instead of time or frequency. These signals need an alternative to time or frequency as a basis to discriminate between signals in tests. We explore here distributed multi-probe detection as a means to address this problem. Simultaneous coherent detection of quadrature baseband at multiple probes provides degrees of freedom necessary to decompose modulated signals with different origins in space. The approximately deterministic simple propagation behavior in an anechoic chamber allows us to estimate channel delay, phase shift, and attenuation parameters between each combination of probes and DUTs. These parameters are sufficient to extrapolate a transfer matrix across frequency that we invert to compute a weighting matrix that deembeds the received superposition of DUT waveforms. We demonstrate experiments that demultiplex three DUTs: a 802.11n Wi-Fi link pair and a source of LTE traffic, all in overlapping channels near 2.4 GHz. The demultiplexed channels show clearly the channel occupancy of each DUT without time-gating or frequency filtering.