Feixue Wang

Impact of reference element selection on performance of power inversion adaptive arrays

Antenna arrays with adaptive algorithms are widely used to provide anti-jamming abilities for Global Navigation Satellite System (GNSS) receivers, among which Power-Inversion (PI) algorithm is attractive for suppression of jammers before de-spreading of signals and simplicity for implementation. Most of previous works either selected the reference element arbitrarily or naturally selected the center element of the array geometry as reference. In this paper, we studied the effect of reference element selection on the performance of the adaptive array receivers. The results show that although the selection of reference element has negligible effects on interference cancellation, it does affect the array gain in the direction of desired signal as well as the array output signal-to-interference-plus-noise ratio (SINR). When the optimal reference element is selected, it will give more than 30% improvement in terms of available angular region under no SNR loss condition over arbitrary reference element selection.

Multitone-Based Non-linear Phase Variation Estimation for Analog Front-Ends in GNSS Receivers

For high precision GNSS applications, accurate online measurements and calibrations of non-linear phase variation of analog front-ends at receivers is indispensable. Previous approaches are designed for off-line measurements, which rely on expensive instruments such as vector network analyzer (VNA). Therefore, they cannot facilitate online measurements, where the frequency response of analog front-end varies over time. Against this background, a novel multitone-based estimation method is proposed. Specifically, a multitone signal is injected into the front-end, while maximum likelihood (ML) estimation and least square (LS) linear fitting are performed at the output signals in order to estimate the non-linear phase variation. The proposed method could be conveniently realized at the GNSS receivers for online measurements. The accuracy of the proposed method is validated through comparisons with a benchmark Agilent VNA.

Analysis for Cross Correlation in Multiplexing

Several multiplexing techniques may be used in next generation GNSS, including QPSK, Interplex, AltBOC, TD-AltBOC, Dual QPSK, POCET. Multiple signals on the same carrier could be multiplexed into a constant-envelope signal with these techniques. Increasing of signals would deteriorate the crossing correlation and its impact on receiving is analyzed. It is shown that cross correlation between signals in-phase has considerable influence; in contrast, the effect could be neglected to signals quadrature. Simulation and real data test is given in the end to support the conclusion, which could guide the selection of multiplex technique and spreading code of Compass.

Study on Channel Mismatch Estimation Method for GNSS Antenna Arrays

Channel mismatch may severely degrade the performance of GNSS antenna arrays, thus it must be calibrated in GNSS applications. Estimation of channel mismatch is the precondition and key of channel calibration. The estimation precision will influence the effect of calibration directly. However, few works on mismatch estimation could be found in previous literatures. In this paper, based on the modeling of the array channels, two kinds of method are proposed to estimate channel mismatch. Theoretical and simulative analysis show the feasibility and the good performance of the proposed methods which can make the estimation precision achieves the Cramer-Rao Bound (CRLB) asymptotically. Given input Signal-to-Noise ratio (SNR) equal to 20 dB and the data length of 1024, the variance of mismatch estimation can be reduced to the level of 10−4 according to numerical analysis and practical demonstration. The technique presented in this paper can be adopted to the calibration of antenna arrays.

Joint Implementation of Interference Suppression and Signal Acquisition for GNSS Antenna Array Receivers

It is well known that, signal acquisition has the lowest sensitivity of the whole GNSS (Global Navigation Satellite System) receiver operation. Signal acquisition could fail due to insufficiency of interference mitigation and signal attenuation during interference suppression and thus it has become the performance bottleneck in the presence of interference. When a GNSS receiver works at acquisition stage, for traditional array processing methods, it is difficult to enhance the satellite signal through array gain due to the lack of essential priori knowledge. In this paper, a novel anti-jamming algorithm is proposed. Compared with the traditional methods, which perform interference suppression and signal acquisition in sequence, the proposed method combines these two processes into a single algorithm. The main advantage is that, it is capable of providing array gain to enhance the desired signal at signal acquisition stage. Theoretical and experiment results show that, the proposed method could increase the signal-to-noise-ratio (SNR) N times at acquisition stage for a N elements antenna array, and thus improve the availability of the receivers significantly in harsh interference environment.

Analysis of The GEO multipath impact on Ionosphere-Free Combination Positioning in BDS system

The satellites constellation of BeiDou regional navigation satellite system (BDS) is different from GPS, which consists of Geostationary Orbit (GEO), Inclined Geosynchronous Orbit (IGSO) and Medium Earth Orbit (MEO). Due to the different constellation of navigation system, there should be some special characteristics of BDS to be analyzed thoroughly. For example, when used Ionosphere-Free Combination Positioning algorithm (IF) in BDS, the positioning accuracy performs worse than Single frequency positioning. This paper studies the genuine causes of this phenomenon initially. From the analysis, GEO multipath error should be the main reason which caused this phenomenon. GEO multipath error changes slowly, even calls “standing multipath error”. This paper analyzes this phenomenon and characteristics of GEO multipath error, then proposes an amended algorithm to estimate GEO multipath error. Finally used computed multipath error to correct Ionosphere-Free Combination Positioning. The simulation results show a significant promotion in positioning accuracy.

Multipath Effect on Phase Center Calibration of GNSS Antenna

Conventional phase center calibration is carried out in anechoic chamber, when in the outfield, the calibration values may be not useful because of the phase errors arose by multipath. In the paper, we present a model of antenna receiving signal; the model is improved by adding antenna model and the characterizations of right hand circular polarization and left hand circular polarization. Based on the model, we analysis the impact of up-to-down ratio on phase errors. As an example, we use a choke antenna to assess the performance of the simulation results. When the phase center variations tolerance is 2 mm, in order to mitigate the impact of phase center variations on high precision GNSS by using calibration values, the up-to-down ratios must be all higher than 15 dB.

Minimum Energy Block Technique Against Pulsed and Narrowband Mixed Interferers for Single Antenna GNSS Receivers

In this letter, we propose to mitigate the mixture of a pulsed interference and a narrowband interference (NBI). By exploiting the periodicity of pulsed interference, we proposed a minimum energy block technique to segment inputs into blocks and group consecutive blocks into batches. We choose these minimum energy blocks in all batches to estimate the power spectrum density (PSD) of NBI. The mixed interference can be suppressed by frequency-domain blanking (FDB) and time-domain blanking (TDB) techniques in serial. The proposed technique only requires prior knowledge of the period range of pulsed interference to control the block size and block number of each batch. The receiver operating characteristic (ROC) curves show that the proposed technique outperforms the conventional one and achieves a performance close to the ideal mitigation under harsh mixed interference scenarios.

Weak Signal Acquisition Performance for Different Pilot Channel Design Options

Pilot Channel without navigation message modulation is added in next generation GNSS for enhancing the acquisition performance in challenge environment. The pre-detection integration time of pilot channel is potential to exceed the bit width, so the receiver could obtain better acquisition sensibility. However, the benefit from pilot channel has not been thoroughly analyzed. The equivalent ideal detector factor is used to compare the performance of different power allocation options of data and pilot channel. The results show that when the data and pilot channel has the same power, the acquisition sensibility is not better than that of traditional signal in normal conditions. The conclusion has significance on the BDS modernized signal design.