Wu Siliang

A Novel Adaptive Digital Predistortion for RF Power Amplifier Linearization Based on Simplified Volterra Series

Adaptive digital predistortion (ADPD) is an effective approach to compensate for nonlinear distortion introduced by RF power amplifiers (PAs). Volterra series is applicable for predistorter design to linearize memory PAs; however, the number of its kernels to be identified increases greatly with its degree and memory length. In this paper, a simplified Volterra series (SVS) predistorter model is proposed. By only preserving partial Volterra kernels in the region near the main diagonal, the structure is simplified and computational complexity is reduced dramatically. Through MATLAB simulations using a Wiener-Hammerstein PA model and a two-carrier WCDMA wideband signal, linearization performances of SVS-based predistorters are demonstrated in terms of suppressing spectral regrowth.

High sensitivity acquisition algorithm for DSSS signal with data modulation

In direct sequence spread spectrum communication both for satellite-to- ground and inter-satellite links, the system constrains due to radio frequency spectral occupation, channel data throughput and link performances in terms of data channel coding which might result in a signal structure where the symbol duration is shorter than the pseudo code period. This can generate some difficulties in the DSSS signal acquisition due to the polarity inversion caused by the data modulation. To eliminate the influence due to polarity inversion, this paper proposes a novel acquisition algorithm based on the simultaneous search of the code phase, data phase and Doppler frequency. In the proposed algorithm the data phase is predicted and the correlation period for the coherent integration can be set equal to the symbol duration. Then non-coherent accumulation over different symbol is implemented in order to enhance the acquisition algorithm sensitivity; the interval of non-coherent accumulation is the least common multiple between the symbol duration and the pseudo code period. The algorithm proposed can largely minimize the SNR loss caused by data polarity inversion and enhance acquisition performance without a noticeable increase in hardware complexity. Theoretical analysis, simulation and measured results verify the validity of the algorithm.

A fast integrity algorithm for the ultra-tight coupled GPS/INS system

This paper discusses current integrity algorithms to deal with ultra-tight coupled GPS/INS system failures. Using the simulated output of the aircraft based INS and GPS receiver, current integrity algorithms are evaluated. A new algorithm based on detection of the growth rate of a typical test statistic is presented. Results show that the new algorithm detects slowly growing ramp-type failures faster than the current methods. This will enable early detection of such errors for enhanced integrity performance.

An FFT-based acquisition algorithm for spread-spectrum signal in high dynamic

In this paper, acquisition methods for spread-spectrum signal used in a radar system are researched. The analysis shows that a serial search method cannot meet time requests, and FFT-based algorithm which consume much less time can meet the acquisition requirement. Resampling and methods such as zero-padding, linear-interpolation and sinc-interpolation involved are analyzed. Simulation and experiment results indicate that the FFT-based acquisition algorithm can meet radar design requirement, and Blackman-windowed sinc-interpolation prior to FFT can reach the best correlation performance.

A new method of the detection of weak signal based on randomized Hough transform

A new method for the detection of polynomial phase signal is developed. The Doppler echo signal is first processed by time-frequency analysis and then the polynomial curves in the time-frequency presentation is detected by randomized Hough transform (RHT). This work extends RHT into the signal detection and overcomes the shortcoming of Hough transform. The key factors of performance of this algorithm are studied and simulations are carried out for validation.

Anti-SEU design of signal processor of space-borne spread spectrum transponder

To solve the problem of function failure of space-borne spread spectrum transponder caused by single event upsets(SEUs), the anti-SEU design of signal processing machine of space-borne spread spectrum transponder is studied in this paper. The design adopts SRAM-based FPGAs, DSP and anti-fuse FPGA to achieve SEU hardening signal processing machine. The transponder using the method can avoid failure caused by SEUs.

Design and implementation of noise simulation circuit for a noncoherent spread-spectrum system IF signal simulator

The noise simulation circuit of noncoherent spread-spectrum system intermediate frequency (IF) signal simulator is designed based on FPGA and DSP. This circuit generates white Gaussian noise (WGN), calculates coefficients of signal-to-noise ratio (SNR) refer to the specified SNR of each channel and according to these coefficients to generate spread-spectrum IF signal for transmitting to simulate the actual receive signal of responder beacon (RSP). It has been verified that the result of test meets the requests of system.

Coherent detection and ambiguity resolution for Frequency Diversity Separated Subarray Radar

Radar system using separated subarrays can improve both angular accuracy and resolution at a reduced cost as well as easier transportation. However, the inherent ambiguities due to the existence of grating lobes deteriorate the performance greatly. Frequency diversity technique can be adopted to reduce the ambiguities. In this paper we have investigated the coherent detection and ambiguity resolution performance of the Frequency Diversity Separated Subarray Radar (FDSSR). We have introduced a structure that is suitable for spacial and temporal coherent processing. Based on this structure, one detector is developed for detection of target with unknown amplitude embedded in Additive White Gaussian Noise (AWGN) with known power using the generalized likelihood ratio test (GLRT). Performance of this detector has been evaluated analytically. The results show that the FDSSR with coherent processing obtains better performance compared with its counterpart using single frequency.

Application of Kalman filter in Three Beidou Geostationary Satellites passive dynamic positioning

Aimed at the movement model of Three Beidou Geostationary Satellites passive dynamic positioning receiver and the noise characteristics of the receiving signal, the turn model is applied to represent exactly the movement pattern of the receiver, and a Kalman filter algorithm based on turn model is presented in this paper. By filtering the Three Beidou Geostationary Satellites passive dynamic positioning results, the emulation experiment shows that the algorithm can eliminate most random errors in the dynamic positioning. Compared with the traditional Kalman filter algorithms, the algorithm presented in this paper is charactered with easy realization, well application and high positioning precision, and a good result is obtained in the practical application.

Detection and estimation of Doppler signal using HHT marginal spectrum

A new method based on Hilbert-Huang transform (HHT) marginal spectrum is proposed to detect the Doppler signal and estimate the Doppler shift in this paper. This method first iteratively decompose the Doppler signal into a number of intrinsic mode functions (IMFs) Which are monocomponent. Then Hilbert transform is applied to each IMF to calculate Hilbert spectrum, and HHT marginal spectrum is obtained by integrating Hilbert spectrum with respect to time. The emergence of the Doppler signal can be detected in terms of the maximum amplitude of HHT marginal spectrum larger than the preset threshold. The amount of Doppler shift is estimated as the difference between the radar center frequency and the frequency, at which the band pass spectrum of the received signal is centered. Simulation experiments show that HHT marginal spectrum is a promising approach for the detection and estimation of Doppler signal.