Figure 29. Measured constellation diagrams for different modulations (FSK/GMSK/QPSK/π/4-DQPSK) and data rates [139] © 2013 IEEE. (AoA) under line-of-sight operation. However, in typical warehouse management scenarios, the line-of-sight between the reader and tag is likely to be blocked by objects or personnel. UWB radars are promising to ensure robust localization under different scenarios as UWB signals can penetrate through obstacles and superior ranging accuracy can be enabled through signal time-of-arrival (TOA) measurements. Multipath can be resolved, and interferences are suppressed by the TOA estimator [113]. A UWB pulsed radar SoC has been presented in [32], where the on-chip pulse generator is used to transmit the pulses, and the received signal is processed with coherent mixing and integration by the RX AFE. Ranging and respiration monitoring of the human subject can be achieved based on the UWB radar SoC. The die photograph of the chip is shown in Fig. 18(f). The schematic of the 4-channel sampling CMOS impulse-radio (IR) UWB transceiver for radar sensing is illustrated in Fig. 30, where the transmitter, the 4-channel receiver, and the embedded FIRST QUARTER 2022 digital control module are integrated on a single chip [32]. The indoor and outdoor human walking traces measured by the radar are shown in Figs. 31 (a) and (b). Tx Ant Spectrum Control TX Clock 3 Embeded Controller Triple-DLL 4 RX Clocks Rx Ant 4-ch ADC LNA Integrator THS This Work Off-Chip LNA Figure 30. Schematic of an IR radar sensor for vital sign monitoring [32] © 2014 IEEE. IEEE CIRCUITS AND SYSTEMS MAGAZINE 61 Control and Signal Processing Command X-Tal Reference