Jiaolong Wei

Analysis of Combined Effects of Multipath and CW Interference on Coherent Delay Lock Loop

Multipath and continuous wave (CW) interference can cause severe performance degradation of global navigation satellite system receivers. Therefore, effects of multipath or CW interference have been analyzed separately in many papers. However, when multipath and interference exist at the same time, it hasn’t been discussed whether their effects on code tracking performance are independent, and the combined effects of multipath and CW interference haven’t been analyzed. This paper analyzes the combined effects of multipath and CW interference on the code tracking performance of coherent delay lock loop (DLL). An analytical expression of code tracking error envelope is suggested for coherent DLL and can be used to assess combined effects of multipath and CW interference. This analytical expression shows that multipath may change the slope of discrimination function, which causes the problem that effects of multipath and CW interference aren’t independent. Therefore, multipath effects on the slope of discrimination function are discussed in this paper. It is shown that smaller correlator spacing can decrease the multipath effect on the slope of discrimination function. However, when the finite bandwidth is taken into account, the smaller correlator spacing can’t suppress the multipath effect on the slope of discrimination function effectively. The combined effects of multipath and CW interference depend on many factors. The GPS C/A signal is taken as an example of the application of the derived expression to discuss how these factors affect the code tracking performance, and simulation validation shows the availability of theoretical results.

Unambiguous combined correlation functions for sine-BOC signal tracking

Binary offset carrier (BOC) modulated signal has been widely employed in modern global navigation satellite system (GNSS). However, the multiple peaks auto-correlation function of BOC signal leads to tracking ambiguity problem. For high-order BOC signal, the above problem becomes more severe. We propose an unambiguous tracking method based on combined correlation functions for sine-BOC signal. The main feature of this technique is that two new local reference waveforms are used. Based on the cross-correlation functions between the BOC signal and these two local reference waveforms, unambiguous combined correlation functions without any main positive side-peaks are generated. To achieve unambiguous tracking for sine-BOC signal, we present two non-coherent discriminator functions, denoted as V1 and V2. The theoretical expressions of code tracking error in thermal noise are derived. Then, the impact of thermal noise and multipath is analyzed with the help of numerical simulations. Results show that V1 is easier to implement and has relatively better multipath mitigation performance at the expense of some performance degradation in code tracking error. V2 has better code tracking accuracy and provides the most robust code tracking process for high-order sine-BOC signal, but two additional complex correlators are required.

General AltBOC Modulation with Adjustable Power Allocation Ratio for GNSS

Alternative Binary Offset Carrier (AltBOC) modulation signal has the constraint of an equal power allocation scheme. Thus, it is not flexible enough to meet different requirements. To solve this problem, we propose a General AltBOC (GAltBOC) modulation. The proposed technique can achieve the same function as AltBOC. Meanwhile, its power allocation ratio can be adjusted when required. The detailed derivation of the GAltBOC modulation is presented, and three representative cases as well as the signal properties are discussed. To further improve the combination efficiency, we develop the Interlacing GAltBOC (IGAltBOC) modulation based on the GAltBOC modulation. The Power Spectrum Density (PSD) and correlation functions of the proposed signals are verified by simulation. The code tracking error and implementation complexities are analysed and compared with existing methods. Results show the proposed signals indeed enhance the flexibility of power allocation ratio with the same level code tracking accuracy. Compared with AltBOC modulation, the proposed signal can reach a higher combination efficiency at the expense of relatively higher implementation complexity. Compared with Asymmetric Constant Envelope Double-sideband (ACED) modulation, the proposed signals have significantly lower complexity of signal generation, which is helpful in simplifying the signal generation in the payload transmitter.

Unambiguous Acquisition/Tracking Technique for High-Order Sine-Phased Binary Offset Carrier Modulated Signal

The binary offset carrier (BOC) modulated signals have been widely employed in global navigation satellite systems due to its outstanding performance. The BOC signal can share frequency spectrum with traditional BPSK signal, meanwhile provide better code tracking accuracy. However, the multiple peaks auto-correlation function of BOC signal results in the acquisition and tracking ambiguity problem. Several methods have been proposed to remove the ambiguity, but they mainly focus on the low modulation order BOC signal, and not efficient enough for high-order BOC signal. In this paper, we propose an unambiguous acquisition/tracking technique for high-order sine-phased BOC signal. The key of this technique is to design a new local auxiliary signal. With the help of the cross-correlation function between the BOC signal and the local auxiliary signal, we obtain a combined correlation function without major positive side peaks. The proposed acquisition and tracking schemes are presented. The theoretical false alarm and detection performance are given, and the theoretical code tracking error in thermal noise is derived. The performance of the proposed method is analyzed by theory and simulation. Results show that for high-order sine-BOC signal, the proposed technique can remove the ambiguity threat. Compared with the existing methods, our method has a significant improvement in terms of acquisition sensitivity and code tracking performance.

A Quasi-constant Envelope Multiplexing Technique for GNSS Signals

A significant feature of the modernised Global Navigation Satellite System (GNSS) signals is that there are multiple signal components needing to be transmitted on a carrier frequency. How to combine these signal components into a constant envelope composite signal is a challenge. Existing constant envelope modulation techniques have some limitations, and are not effective enough. To solve this problem, we propose a quasi-constant-envelope multiplexing technique in this paper. The proposed method is based on numerical optimisation, and can work in two ways. The corresponding objective functions are provided. To verify the performance of the proposed method, we present three application examples. Results show that the first variation of our method can reach the same combining performance as Phase-Optimised Constant-Envelope Transmission (POCET). In the second variation, the combining efficiency can be pre-set. We can reach higher combining efficiency than POCET, and the envelope of the composite signal becomes quasi-constant. Furthermore, the inter-modulation signals in the final composite signal are adjustable. With the help of the proposed method, we can learn more details of the combining scheme than with POCET.

Performance Analysis on Single Sideband of TD-AltBOC Modulation Signal

TD-AltBOC modulation signal is a new signal. Similar to AltBOC(15,10) signal, TD-AltBOC signal contains lower and upper sideband signals. From the view of the selection of PN codes for lower and upper sideband signals’ pilot components, there are two schemes to achieve TD-AltBOC, namely to choose different PN codes or the same PN code. For considering the cost and complexity of receivers, only the lower sideband signal may be received for mass market receivers. When the receiver is only tracking lower sideband signal’s pilot component, due to the non-ideal PN codes and the effect of upper sideband signals, a asymmetrical correlation function may be obtained, which causes the cross zero point of discriminator curve to move, so code tracking bias error is introduced. In this paper, we analyze the reason and condition why correlation function is asymmetry, and make performance analysis on single sideband of TD-AltBOC modulation Signal. Simulation results show that the selection of PN codes for data component may cause correlation function asymmetry. In order to reduce the effect on single sideband reception and reach the same performance with AltBOC(15,10), the selection of PN codes has to meet requirement of this paper.

A Research of Code Tracking Loop for Navigation Signal Based on DS/FH Modulation

Facing the increasingly complex electromagnetic environment, it is an attempt to introduce DS/FH hybrid spread spectrum technology to the field of TT&C. For DS/FH receiver, despreading and dehopping proceed respectively. However if DS/FH navigation signal is dealt with in the same way, there is no difference between DS/FH navigation signal and the existing DS signal. The code tracking algorithm proposed in this paper makes full use of frequency hopping information so that the correlation peak becomes very sharp. Computer simulation shows that the code tracking accuracy of DS/FH navigation signal reaches at 0.0028 m (CNR = 40 dB Hz) and the maximum of the multipath error envelope is 0.062 m (MDR = −10 dB), far better than the performance of existing navigation signals.

Correlation Side-Peaks Cancellation Technique for Sine-BOC Signal Tracking

With the development of GNSS systems, BOC modulation signal has been widely used in the modernized GPS, Galileo, and Beidou. BOC signal has the split power spectrum density (PSD), which has better compatibility with GPS C/A signal. Furthermore, the PSD of BOC signal has more high frequency components, which results in better code tracking performance and multipath mitigation performance than BPSK signal. Because of the sub-carriers, the autocorrelation function (ACF) of BOC modulation signal has a main peak and some side peaks. The traditional delay locked loop (DLL) may be locked on the side peaks of ACF, which causes the extra tracking error. In this paper, an unambiguous tracking method is proposed for BOC modulation signal. The received BOC signal is correlated with two different local reference signals with the tailored waveform to obtain correlation outputs. Then the correlation outputs are combined to eliminate side peaks and obtain the combined correlation with one peak. The early minus late power (EMLP) discriminator can be used to lock on the sole peak of the combined correlation function. This unambiguous tracking techniques has been analyzed for BOC (1, 1) signal in the simulation. The simulation results show that this technique can achieve the unambiguous tracking for BOC signal and maintain the same level of the tracking performance as the traditional tracking loop.

PRIS: A Novel Complex Sequence Construction Method

Unexceptionally, modern global Navigation Satellite System (GNSS) adopt Direct Sequence Spread Spectrum (DSSS) signal structure, in which, correlation property of Pseudo Random Noise (PRN) code play an important role of affecting its rejection performance to Narrow Band Interference (NBI) and Multiple Address Interference (MAI). In order to mitigate the cross-correlation performance degradation due to tiered code construction, this paper proposes a new method for constructing complex sequence of GNSS civil signal. Based on any primary sequence of length L, Pseudo Random Initiate State (PRIS) transformation is used to construct a complex sequence of length NL, and a feasible generator scheme is presented. Simulation and analysis results shows, the acquisition complexity of PRIS sequence is similar to tiered code, and the correlation property of PRIS sequence is 4–5 dB better than tiered code, which approaches the performance of random sequence of length NL. The proposed method is applicable to civil GNSS signal designing, and is helpful to improve the receiving performance in challenge environment without distinct additional complexity, which will be attractive to GNSS users around the world.

Interlacing Dual-Sideband Enhanced Alternative BOC (IDEAl-BOC) Modulation and Its Application for GNSS

Alternative binary offset carrier (AltBOC) modulated signal can combine two QPSK signals located at two close frequency bands into a constant envelope signal. It can achieve better code tracking accuracy and anti-multipath performance, thus Galileo E5 signal uses AltBOC (15, 10) modulation. However, the four signal components of AltBOC modulation have to be allocated the same power. To solve this problem, we propose a constant envelope dual-sideband enhanced alternative BOC (DEAl-BOC) modulation technique. In the case of not increasing signal generation complexity, DEAl-BOC technique can adjust the power ratio of four signal component according to different requirements, and only the phase look-up table needs to be updated. When the combined efficiency is decreased slightly, the signal generation complexity can be reduced by half. Based on DEAl-BOC, we present the interlacing dual-sideband enhanced alternative BOC (IDEAl-BOC) modulation. The main advantage is that IDEAl-BOC can improve further the combined efficiency while keeping power ratio constant, this means IDEAl-BOC can reach higher combined efficiency than AltBOC for the case of equal power ratio.