This paper focuses on the angle-of-arrival (AOA) target tracking problem using a mobile unmanned aerial vehicle (UAV) equipped with an angle-of-arrival (AOA) sensor to observe targets in an external-denied (no global positioning system, inertial navigation system aid) environment. The mathematical formulations are based on two known anchors. The extended Kalman filter (EKF) is modified to calculate the UAV’s and target’s absolute coordinates. To improve the tracking accuracy, a gradient-based UAV path optimization algorithm using simultaneous perturbation stochastic approximation (SPSA) is developed. The geometry of anchors and UAV impacts the estimation accuracy, especially when the selected anchors are close to the target. The simulations have demonstrated the effectiveness of the proposed scheme.

The true Crame/spl acute/r-Rao lower bound (CRLB) for the joint estimation of carrier phase and frequency is derived for transmission bursts with interleaved reference and phase-shift keying/quadrature amplitude modulated data symbols. Results are presented for the special cases of midamble, and preamble and postamble, pilot-symbol insertion. The derivation reveals that the CRLB is a function of the location of the reference symbols in the burst, the number of reference symbols, the number of data symbols, the signal-to-noise ratio and the data-modulation scheme. By distributing the reference symbols symmetrically about the center of the burst and analyzing relative to the middle of the signal vector, the joint frequency and phase estimation can be decoupled, and the optimal phase estimation is achieved. In the decoupled case, the phase CRLB is independent of the location of reference symbols in the burst. In a symmetrical burst, the use of a preamble and postamble is found to provide a lower frequency-estimation CRLB than that with a midamble. It appears that the frequency CRLB is reduced as the reference symbols are symmetrically distributed closer to the ends of the burst.

This paper derives the true Cramer-Rao lower bounds (CRLB) on the individual phase estimation and the coupled carrier phase and frequency estimation for transmission bursts with pilot-assisted PSK/QAM modulation. The reduction in frequency and phase CRLB due to introduction of embedded reference symbols increases as the modulation order increases. It is found that the better CRLB may be obtained if the reference symbols are distributed symmetrically in the burst, especially using a preamble and postamble. At low SNR, 5% pilot symbols in the burst reduces the bound on the phase standard deviation by a factor of 10 for QPSK or higher order modulated signals. The new CRLB for distributed pilot symbols are also presented. The comparison of the true CRLB and the CRLB of the pilot symbols has revealed that using only pilot symbols for estimation is an effective approach only if more than 5% of pilot symbols are in the burst and SNR /spl les/ 0 dB.

This paper presents the improvement of the spurious free dynamic range (SFDR) for digitisation using antenna arrays. Nonlinearities in the analogue-to-digital conversion degrade the overall SFDR of the digitisation process. We show that array processing, ie, the use of multiple sensors such as antennas or hydrophones with appropriate signal processing can improve the resulting SFDR at the beamform output. By taking advantage of spatial-temporal aliasing and the invisible regions, significant improvements can be obtained using linear, or more effectively, optimal beamforming.

The true Cramer-Rao lower bound (CRLB) is derived and evaluated for the estimation of carrier phase of Star 16-quadrature amplitude modulation (QAM) and can be simply applied to carrier frequency estimation. Different geometries are investigated by varying the ring ratio (RR). For signal-to-noise ratios (SNRs) between 6-15 dB, the CRLB with RR=3 is lower than that of Square 16-QAM. A modified phase estimator is presented, which closely follows the new CRLB. Investigation of symbol error performance in short packet length reveals Star 16-QAM to be superior to Square 16-QAM for SNR<13 dB, which is a reasonable operating range for a coded system. Although Square 16-QAM and Star RR=1.8 are optimum for a perfect receiver, when the effect of phase estimation is considered, we find Star RR=3 to be better for SNR below 10 dB.

In this paper, we present the true Cramer-Rao lower bounds (CRLBs) for the estimation of phase offset for common quadrature amplitude modulation (QAM), PSK, and PAM signals in AWGN channels. It is shown that the same analysis also applies to the QAM, FSK, and PAM CRLBs for frequency offset estimation. The ratio of the modulated to the unmodulated CRLBs is derived for all QAM, PSK, and PAM signals and calculated for specific cases of interest. This is useful to determine the limiting performance of synchronization circuits for coherent receivers without the need to simulate particular algorithms. The hounds are compared to the existing true CRLBs for an unmodulated carrier wave (CW), BPSK, and QPSK. We investigated new and existing QAM phase estimation algorithms in order to verify the new phase CRLB. This showed that new minimum distance estimator performs close to the QAM bound and provides a large improvement over the power law estimator at moderate to high signal-to-noise ratios.