Zhang Naitong

A novel fractional wavelet transform and its applications

The wavelet transform (WT) and the fractional Fourier transform (FRFT) are powerful tools for many applications in the field of signal processing. However, the signal analysis capability of the former is limited in the time-frequency plane. Although the latter has overcome such limitation and can provide signal representations in the fractional domain, it fails in obtaining local structures of the signal. In this paper, a novel fractional wavelet transform (FRWT) is proposed in order to rectify the limitations of the WT and the FRFT. The proposed transform not only inherits the advantages of multiresolution analysis of the WT, but also has the capability of signal representations in the fractional domain which is similar to the FRFT. Compared with the existing FRWT, the novel FRWT can offer signal representations in the time-fractional-frequency plane. Besides, it has explicit physical interpretation, low computational complexity and usefulness for practical applications. The validity of the theoretical derivations is demonstrated via simulations.

Investigating path loss characteristics of UWB signals in vacancy indoor environment based on time-domain technique

Abstract The path loss analysis model based on 5 rays in vacancy indoor environment is proposed. The relationship between multipath overlapping and the path loss is analyzed mathematically. Time-domain technique is introduced to compute reflection coefficient in a very short time interval. A 5 rays path loss calculation method, which is satisfactory accurate, is developed. 5 typical environments are involved to analyze and generalize the common path loss characteristics in vacancy indoor environment. The simulation result shows that the path loss can be characterized as 3 zones with different path loss exponent as distance between transmitter and receiver increasing.

Pulse shaping method to compensate for antenna distortion in ultra-wideband communications

In the ultra-wideband (UWB) communication systems, a critical spectral mask is released to restrict the allowable interference to other wireless devices by the Federal Communications Commission (FCC), and then some pulse shaping methods have been presented to fulfil the mask. However, most pulse shaping methods do not consider the antenna distortion which cannot be neglected in the UWB communication systems compared with the conventional systems. To this end, an orthogonal wavelet based pulse shaping method is proposed in this paper to integrate compensation of antenna distortion into pulse shaping. Simulation results show that the novel pulse shaping method can be used to achieve compensation for antenna distortion, optimization of transmission power spectrum, and simplification of the algorithm, as well as simple implementation of the pulse generator.

Simplified calculation of UWB signal transmitting through a finitely conducting slab

Abstract A simplified closed-form analytic solution for UWB impulse signal transmitting through a finitely conducting slab is proposed. The approach first requires evaluating the impulse response of the slab and then convolving it with the specified incident field waveform. To obtain the impulsive transmitting field, either for vertical or horizontal polarization, approximations to the refraction coefficients and propagation loss are made, which can be proved to be accurate enough, comparing with their frequency domain solutions. Thereby, it permits simplified closed-form expressions in the time domain for both terms. The resulting transient response for the transmitting impulse field is then given by convolution of the time domain refraction coefficients and time domain propagation loss. A numerical example of an incident monocycle transmitting through a slab using this technique, is presented, to illustrate the effective use of the method.

Transmission Characteristics of Ultra-Wide Band Impulse Signals

A simplified analytic solution for UWB impulse signal transmitting through a finitely conducting slab is proposed in this paper. To obtain the impulsive transmitting field, either for vertical or horizontal polarization, approximations to the refraction coefficients and propagation loss are made. Thereby, it permits simplified closed-form expressions in the time domain for both terms. The resulting transient response for the transmitting impulse field is then given by convolution of the time domain refraction coefficients and time domain propagation loss. The simulations of incident monocycle transmitting through slabs of different materials and thickness are presented by applying the simplified time domain analytic solution to illustrate the characteristics of transmission and give some results in simplification of transmission field analysis in indoor channel modeling.

Research on handover algorithm to reduce the blocking probability in LEO satellite network

Abstract Based on the characteristics of guaranteed handover (GH) algorithm, the finite capacity in one system makes the blocking probability (PB) of GH algorithm increase rapidly in the case of high traffic load. So, when large amounts of multimedia services are transmitted via a single low earth orbit (LEO) satellite system, the PB of it is much higher. In order to solve the problem, a novel handover scheme defined by multi-tier optimal layer selection is proposed. The scheme sufficiently takes into account the characteristics of double-tier satellite network, which is constituted by LEO satellites combined with medium earth orbit (MEO) satellites, and the multimedia transmitted by such network, so it can augment this systematic capacity and effectively reduces the traffic load in the LEO which performs GH algorithm. The detailed processes are also presented. The simulation and numerical results show that the approach integrated with GH algorithm achieves a significant improvement in the PB and practicability, as compared to the single LEO layer network.

Anti-Spoofing Extended Kalman Filter for Satellite Navigation Receiver

There is a threat to the satellite navigation receiver from satellite signal spoofing because traditional algorithms for navigation solution may not fulfill the accuracy requirements of continuous navigation with spoofing signals. Therefore, an anti- spoofing filter has been proposed for accurate navigation with the spoofing signals. In this approach, the conventional extended Kalman filter is modified using the weight matrix of robust M- estimator, which is improved to decrease the computational complexity with enough navigation accuracy. Simulation of traditional extended Kalman filter, snapshot least squares estimation and the proposed anti-spoofing M-estimator based extended Kalman filter suggests that the proposed M-estimator based extended Kalman filter could effectively eliminate the influence of spoofing signal to the navigation solution accuracy with low complexity to realize.

Performance Evaluation of UWB System in the Presence of Timing Jitter Based on Novel Modified Hermite Functions

A class of novel pulses based on modified Hermite functions (NMHPs) for UWB communications is presented according to spectral emission constraints of Federal Communications Commission (FCC) mask and the requirement of short pulse for multiple access. The proposed pulses constitute orthogonal sets and have a constant pulse width regardless of the order, moreover, have no DC component and have an adjustable central frequency, which are important properties in the UWB pulse shaping technologies. Theoretical analyses and simulation results show that the higher order of the proposed pulse has a better anti-jitter performance in both single-link and the multi-access UWB systems than that of the other lower orders and Scholtzs pulse when jitter is not very severe. It provides a flexible and systematic method for designing UWB pulses that both conform to FCC mask and offer good anti-jitter performance.

Analysis of UWB Pulsed Field Diffracted by a Perfectly Conducting Wedge

UWB pulse diffracted by a perfectly conducting wedge in both frequency domain and time domain is proposed in this paper. By introducing a numerical solution for the transition function, the diffraction coefficient is investigated by using UTD in the frequency band between 0 to 20 GHz. A directly time domain analysis is also carried out by using TD-UTD. The frequency dependence of the diffraction coefficients for both vertical and horizontal polarization is linked with pulse distortion, which gives a perspective view of diffraction process for UWB pulse propagation within the indoor environment.

Pulse Shaping for UWB Communications in Dense Multipath

For high-speed UWB systems working in dense multipath environments, Inter Pulse Interference (IPI) is a primary obstacle to achieving good performance. The impact of the pulse waveform on the IPI is analysed. The analysis in this paper shows that the IPI becomes the lowest when the spectrum of the waveform is rectangular in pass band. For practical considerations, the spectrum of the waveform is restricted by the spectral mask and the distribution of energy of pulse should be concentrated in a time slot, so a compromise should be made between these issues in waveform design. The optimal pulse waveform restraining the IPI, which is meanwhile compliant with the FCC spectral mask, is designed as an example.For high-speed UWB systems working in dense multipath environments, inter pulse interference (IPI) is a primary obstacle to achieving good performance. The impact of the pulse waveform on the IPI is analysed. The analysis in this paper shows that the IPI becomes the lowest when the spectrum of the waveform is rectangular in pass band. For practical considerations, the spectrum of the waveform is restricted by the spectral mask and the distribution of energy of pulse should be concentrated in a time slot, so a compromise should be made between these issues in waveform design. The optimal pulse waveform restraining the IPI, which is meanwhile compliant with the FCC spectral mask, is designed as an example