Multichannel SDR Platforms for Mobile PCL Applications Figure 14. Phase delays and time shifts after compensation. perfectly for the needs ofPCL applications in small moving platforms (e.g., drones). EXPERIMENTAL RESULTS FROM LIGHTWEIGHT SYSTEM SEA-BORNE PLATFORM The system installed on a navy ship has been equipped with pilot signal injection circuits (see Figures 8 and 9) and supported the method of full estimation ofphase shifts and time delays [20]. DAB broadcast transmitter (218.64 MHz) has been selected as the source of illumination and the sampling rate was set to 2 MHz. The receiving antennas installed on the ship for the purpose of PCL experiments are shown in Figure 12 (part of which has been used for the DAB signal acquisition described in this section). In Figure 13, we can see the plot of time delays and phase shifts estimated between the signals from different channels, and in Figure 14-the plot ofthe same parameters estimated again after compensation ofthe delays and shifts. 36 As we can see, the proposed method based on pilot signals allows us to reduce the phase shifts between the receiving channels down to 5 peak (ca. 2 rms value for x1[n], x2[n] pair) and to align the time shifts between the signals from different devices with one sample accuracy. There are still some glitches remaining in time shift and phase offset plots (Figure 14) at the moments of step changes in time delay due to discontinuity of the signals and relatively long period of pilot signals injection (5 s). Between these glitches, however, there are long intervals of clean signals (30.. .300 s) that allow performing PCL processing algorithm. The step changes in time shift and phase offset result from isochronous data transfer in USB link from SDR receivers and the host PC. In this mode, the host provides guaranteed bandwidth and bounded latency; data delivery takes priority over validity of data and no flow control or retries are allowed [6]. As a result, some packets of data can be lost if the sustained data throughput is too high for a given host performance. It must be noted that the quality of signal acquisition in the considered setup with two RSPduo devices depends significantly on the IEEE A&E SYSTEMS MAGAZINE APRIL 2022