| Summary: | UWB impulse radio (UWB-IR) has high potential in real time location systems, due to its fine temporal resolution and resilience to multipath fading in a hostile environment. However, existing systems faces challenges such as limited localization range, inefficient waveform generation, clock synchronization, sampling speed limitation, noise and interference, etc. In this thesis, several novel RF circuits are proposed, which intends to address these challenges at the circuits and system level.
An ultra wideband impulse radio (UWB-IR) transmitter which is implemented in monolithic microwave integrated circuit (MMIC) for precision real time location system is presented. The design completely eliminates most of the RF building blocks such as mixer, voltage controlled oscillator or power amplifier. It reads digital data and generates spectral emission mask compliant UWB pulses at the lower band. Fabricated on a commercial low cost 2 m GaAs HBT process, the transmitter MMIC peak power output is 20 dBm with power consumption of 0.8 mW at 1 MHz pulse repetitive rate.
An energy detection based UWB impulse radio receiver is designed and prototyped. It has a variable front-end conversion gain of up to 44 dB. The receiver MMIC is cascaded with a 500MHz baseband amplifier to achieve input tangential signal sensitivity (TSS) of -71 dBm. Equivalent time sampling using analogue to digital converters running at around a few MHz is utilized for precise time of arrival ranging with low cost components. Real time location system is constructed using the designed MMICs. Relatively long range (> 100 meters) is achieved by fully exploiting FCC’s peak power constraint efficiently and system level optimizations. Two dimensional wireless localization network utilizing time difference of arrival (TDOA) is constructed and test results covering an 80 90 m2 area. The measurement shows position error variance of less than 10 cm. Ranging at 200 m is demonstrated with range error variance smaller than 15 cm.
Finally, a comprehensive framework from synthesis to implementation of active matched filters for UWB Impulse Radio is presented. The method uses electrical delays and sums of UWB pulses coherently to strengthen the signal over white Gaussian noise. Theoretical analysis shows that the signal peak is maximized against noise, and an arbitrary transfer function could be realized by adjusting filter parameters. To verify the concept, a four-stage matched filter operating in 3-5 GHz with 360 degrees phase delay is demonstrated first. It is implemented in a commercial 2-μm GaAs HBT process and achieves a power gain of 13.8 dB with a 10 dB bandwidth of 1.3 GHz. Based on a similar architecture, another design is presented but with only half of the delay. It has a power gain of 15.9 dB at the centre frequency of 4 GHz and a 10 dB bandwidth of 2.3 GHz. An advantage of the proposed method is a precise control of the impulse response that can be matched to either symmetrical or asymmetrical UWB pulses by taking a time domain design approach.
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