Frequency segmented estimation in real-time active noise control
This thesis addresses three aspects of frequency estimation. First, the problem of accurately estimating frequencies in a multi-tonal signal is discussed with references to many techniques used today. Particularly, frequency estimation methods such as fast Fourier transform (FFT), Multiple Signal Classification (MUSIC), Quinn and Fernandes (Q&F) and a proposed frequency estimation approach called Optimal Frequency Estimation (OFE) are elaborated. This latter technique is proposed as a way to increase the estimation accuracy of tonal frequency components in a complex signal with limited data length. OFE is compared with FFT, MUSIC, a popular multi-tonal frequency estimation method, and the recent Q&F method. Signals with added Gaussian noise are used to investigate its estimation accuracy and variance empirically. The technique is shown to perform well on simulation data. Results demonstrate its superiority in estimating frequencies at signal to noise ratio from 24dB and above. Its computational effort in estimating frequencies is also shown to be efficient as OFE is based on gradient free convergence. Next, OFE is applied to a single input single output (SISO) control system developed recently to investigate its influence. The controller uses online plant estimation and it is extended to multiple input multiple output (MIMO) systems. The online plant estimation and control attenuates unknown disturbance tones through continuous tuning. A stability criterion is derived to demonstrate the need for accurate frequency estimation in the control scheme. The performance of the control algorithm OFE is investigated by computer simulation using an air duct system as an example. Results show that accurate frequency estimation is essential for a successful and stable attenuation. Finally, three hardware test rigs are designed to realize the above schemes for practical digital signal processing (DSP) laboratory experiments. Active sound control is studied on a microphone-speaker array for the SISO case. A novel satellite plate test rig is used to investigate micro-vibrations on board a spacecraft. An L-shaped enclosure modelled after a commercial compressor is constructed with shakers and accelerometers mounted for MIMO control. In conclusion, future work and implementation under more general cases are outlined.