With the proliferation of IoT and smart cities, accurate position measurement indoors where GPS signals cannot reach has become a critical challenge. Since conventional RSSI triangulation methods suffer from reduced accuracy due to reflected wave interference, this study proposes a new indoor position estimation technique using Zigbee. Two methods are proposed. Proposed Method 1 uses the node with the highest RSSI value as the estimated position, while Proposed Method 2 adaptively switches between the conventional method and Proposed Method 1 based on signal quality. Experimental results show that in environments with large signal strength bias, Proposed Method 1 achieved 28% improvement in average error and 27% improvement in maximum error compared to the conventional method. In mobile environments, Proposed Method 2 achieved 28% improvement in average error and 36% improvement in maximum error, demonstrating the most balanced performance. These results demonstrate the feasibility of realizing a low-cost, real-time indoor position measurement system with environmental adaptability.
Digital frequency modulation using a direct digital frequency synthesizer (DDFS) and digital to radio frequency (RF) conversion using radio frequency digital to analog converter (RFDAC) enables accurate and identical ramp generation at RF frequencies. It eliminates the trade-off between modulation bandwidth and loop bandwidth of a PLL-based frequency modulation allowing high ramp slopes. Based on a developed DDFS & RFDAC, a C-Band radar is built. The system is supplied with a GPS locked reference clock to allow long term stability. A two hour measurement against an active radar reflector which provides sufficient signal-to-noise ratio (SNR) in 72m distance is conducted. PPM deviations in range due to atmospheric effects are observed due to the high stability of the system. The measurement shows a correlation with existing propagation models.
This paper presents a novel K-Band Quadrature Phase Shift Keying (QPSK) phase-modulated continuous-wave (PMCW) radar front end architecture with digital I/Q constellation phase compensation and I/Q channel imbalance correction. Although QPSK is a very common form of digital phase modulation, it is rarely reported for PMCW radar systems, especially those designed on printed circuit board (PCB) technology. A MATLAB simulation platform is also developed and presented to help verify the benefits of QPSK PMCW radar for range detection.
Frequency-modulated continuous wave (FMCW) is the dominant waveform scheme in modern automotive radar systems used in advanced driver assistance systems (ADASs). Nevertheless, the digital modulation scheme phase-modulated continuous wave (PMCW) has recently attracted considerable interest due to advantages such as high maximum unambiguous velocities. However, there remains a need for more thorough performance assessments comparing these waveforms in dynamic automotive scenarios. This work presents a flexible framework comprising a ray-tracing simulator and radar models for efficient automotive scenario generation and radar simulation. Using this framework, the performance of FMCW and PMCW radar systems is assessed in a typical automotive scenario. The evaluation demonstrates that the PMCW radar system exhibits superior performance in terms of target detectability in the given scenario.
This study examines the efficacy of digital self-interference cancellation for different modulation formats within the VHF band. A conventional least-squares polynomial approach is employed as the cancellation algorithm. The interference cancellation ratio of the analog modulation formats AM, FM, and PM is compared to that of OFDM in simulations and measurements. The simulations demonstrate superior cancellation of the self-interference signal of the analog modulation formats compared to OFDM. While the AM signal can be more effectively canceled only in a highly frequency-selective channel, the FM and PM signal can be canceled by 10 dB more in all simulated channels. In the measurements, the cancellation of the OFDM signal fails completely, while the analog signals are canceled to a similar degree as in the simulations. However, the cancellation of the AM is less effective. These results suggest that the digital self-interference cancellation is more effective for narrow-band signals.
