The spectral characteristics of navigation alternative binary offset carrier modulated signals (AltBOC signals)

Analytical expressions are obtained for spectral densities and energy spectra of single elements and single periods of modulating functions of alternative binary offset carrier modulated signals (AltBOC signals) for new-generation satellite radio navigation systems (SRNSs) (in particular, the Galileo system). The spectral characteristics are presented and analyzed for an elementary (two-component) AltBOC signal, a complete AltBOC with a time-variable envelope (a four-component complete AltBOC signal), and a complete AltBOC with a constant envelope (an eight-component complete AltBOC signal) in the case when the multiplicity coefficient of meander pulses has an arbitrary value. Plots are depicted, and the properties of energy spectra of single elements of modulating functions of all groups of AltBOC signals are discussed in the cases of the following modulation types: AltBOC(10, 10), AltBOC(15, 10), AltBOC(20, 10), and AltBOC(25, 10).     

Correlation functions of complete AltBOC signals with a constant envelope

The structure of the modulating function (MF) of a complete alternative binary offset carrier modulated signal (AltBOC signal) with a constant envelope (eight-component complete AltBOC signal) is considered. Analytical expressions for the correlation functions (CFs) of single elements of the MFs of complete AltBOC signals with a constant envelope are derived at typical values of multiplicity coefficient N _m of meander pulses (N _m = 2 and 3). Plots of the CFs of single elements of the MFs of complete AltBOC signals with a constant envelope are obtained for N _m = 2 and 3. The properties of these CFs are discussed. With the help of the Fourier transform applied to the CFs, the energy spectra (spectral power densities) of single elements of the MFs of complete AltBOC signals with a constant envelope are calculated at N _m = 2 and 3. In illustrating examples, most attention is focused on complete AltBOC signals with a constant envelope at the carrier frequency f _car = 1191.795 MHz for the AltBOC (15, 10) modulation and the repetition rate of the elements of ranging-code pseudorandom sequences f _s = 10f _ref = 10.23 MHz, where the reference (base) frequency is f _ref = 1.023 MHz. These signals are applied in the Galileo European satellite radio navigation system (SRNS) and, as is supposed, in the Chinese BeiDou-2/Compass SRNS.     

Correlation functions of BOC and AltBOC signals as the inverse Fourier transforms of energy spectra

The navigation signals with sine binary offset carrier (sinBOC), cosine BOC (cosBOC), and alternative BOC (AltBOC) modulations are discussed. A technique for calculating the correlation functions (CFs) of the single components of modulating functions (MFs) inherent to the given signals, which is based on the inverse Fourier transform (IFT) of energy spectra, is proposed. This technique makes it possible to derive analytical expressions for the CFs characterizing the single components of the MFs of sinBOC and cosBOC signals and complete AltBOC waveforms with a constant envelope at the multiplicity coefficients N_m = 2?4. The graphs of CFs are constructed. Several illustrating examples, in which most attention is paid to sinBOC, cosBOC, and AltBOC signals employed in the Galileo satellite radio-navigation system and the global positioning system, are presented.     

The correlation functions of single elements of the modulating functions of double complex meander noise-like navigation signals (alternative binary offset carrier modulated signals)

The correlation characteristics of elements of complex meander pseudo-random sequences (PRSs) are analyzed. These sequences are the basis for forming double complex meander (DCM) noise-like signals (alternative binary offset carrier modulated signals—AltBOC signals) applied in new-generation satellite radio navigation systems (in particular, the European Galileo and Chinese Bei-Dou/Compass systems). Analytical expressions are obtained for the correlation functions (CFs) of single complex meander symbols (MSs) and for the cross CFs (CCFs) of the sine and cosine components of complex MSs. Formulas for the CFs of single elements of the modulating functions (MFs) of an elementary (two-component) AltBOC signal and a four-component AltBOC signal are derived for typical values of multiplicity coefficient N _m (N _m = 2 and 3). Plots of CFs and CCFs are depicted, and the properties of these functions are discussed. The Fourier transform is applied to obtain the energy spectra of single MSs of an elementary AltBOC signal and a complete four-component AltBOC signal. In the examples, the attention is focused on AltBOC signals with the AltBOC (15, 10) modulation and the repetition rate of PRS elements f _s = 10 f _ref = 10.23 MHz, where the reference frequency is f _ref = 1.023 MHz.     

Correlation functions of single symbols of meander signals in new-generation satellite radio navigation systems

Mathematical models of meander noise-like signals (binary offset carrier modulated signals (BOC signals)) of new-generation satellite radio navigation systems (SRNSs), in particular, the modernized GPS, the Galileo system, and the QZSS are presented. An analytic expression for the correlation function (CF) of single symbols of meander pulses is obtained for the arbitrary value of the multiplicity coefficient. The properties of CFs of various meander symbols are analyzed. The features of CFs are revealed for the even and odd values of the multiplicity coefficient. Examples of CFs are considered, and CFs of single symbols of BOC signals applied in new-generation SRNSs are plotted.     

Complex meander pseudorandom code sequences and alternative binary offset carrier modulation (AltBOC modulation) in new-generation satellite navigation systems

Complex meander pseudorandom sequences (MPRSs) that are the basis for formation of alternative binary offset carrier modulated signals (AltBOC signals) for new-generation satellite radio navigation systems (in particular, the Galileo and Compass systems) are considered. The properties and characteristics of MPRSs are analyzed. Analytical expressions for the spectral densities and power spectrum densities of complex and complex conjugate meander symbols (MSs) of the MPRS of a ranging code are found for various values of the multiplicity coefficient of meander pulses. The modulating function of an elementary AltBOC signal is considered. The power spectrum densities of complex and complex conjugate MSs are plotted and analyzed for typical values of the multiplicity coefficient.     

Correlation functions of complete CBOC signals derived as the inverse Fourier transform of energy spectra

For the complete composite binary offset carrier (CBOC) signals of new-generation global satellite radio-navigation satellite systems (SRNSs), analytical expressions for correlating functions (CFs) characterizing the single components of the modulating function are derived in terms of the inverse Fourier transform (IFT) of energy spectra at different fractional coefficients. The CF calculation technique is based on the energy spectra of complete CBOC signals represented as a partial sum of the series of cosines of the angles that are multiples of the angle γ_CBOC = ωτ_M2, where τ_M2 is the meander-pulse duration of the subcarrier oscillation of binary offset carrier (BOC) signals with BOC(6,1) modulation. In a number of cases, the IFT of energy spectra applied to calculating the CFs of complete CBOC signals is preferable (in particular, from the viewpoint of labor intensiveness) to the procedures by which CFs are obtained using the general definition. The CFs graphs constructed with the help of complete CBOC signals employed in the E1 band of the Galileo SRNS are presented.     

An Unambiguous Tracking Method Based on Pseudo Correlation Function for AltBOC(15,10) Signal

The Galileo E5 or COMPASS B2 signal is the most precision civil and most challenging navigation signal which will be available in the near future for regular navigation. The excellent performance of this signal was reached by Alternative Binary Offset Carrier (AltBOC) modulation, which is specially designed for high precision range measurement and which is featured by extremely wide bandwidth. However, this modulation presents some drawbacks. The most severe one is the ambiguity problem in AltBOC signal acquisition and tracking, which introduces a large bias in the pseudo-range measurement. In order to solve this problem, an unambiguous tracking method based on a pseudo correlation function for AltBOC(15,10) modulation signal is proposed in this paper. It employs two local signals and a novel combination function, which completely removes side peaks from the correlation function while keeping the sharp main peak. Impacts of multipath on the proposed method are also investigated. Simulation results demonstrate that the proposed method is totally unambiguous while exhibiting an average multipath performance with respect to the existing unambiguous tracking methods.     

Unambiguous S‐curve shaping technique for multipath mitigation in Global Navigation Satellite Systems alternative binary offset carrier signals

Global Navigation Satellite Systems positioning accuracy indoor and urban canyons environments are greatly affected by multipath because of distortions in its autocorrelation function. In this paper, we propose a new multipath mitigation technique based on the concept of S‐curve shaping for the new alternative binary offset carrier (AltBOC)‐modulated signals, which will most likely be used in both European Galileo system and Chinese Compass system. The definition of an optimum S‐curve is employed to reduce the false lock points and to improve the multipath mitigation capability via determining the shape of the local code tracking reference function. The structure of the proposed code tracking loop for AltBOC signals is quite simple and only requires one complex correlator. Results demonstrate that the proposed technique provides superior multipath mitigation performance compared with the conventional receiver correlation techniques and removes the ambiguity completely. Copyright © 2012 John Wiley & Sons, Ltd.     

AltBOC信号捕获技术研究

交替二进制偏移载波（AltBOC）信号是应用于Galileo导航系统E5频段的新型导航信号,该信号包含E5a和E5b两个边带,调制四路独立的导航信号。传统的捕获技术是对其中的一路信号进行捕获,仅能利用25%的信号功率,影响了捕获性能。因此在单边带捕获的基础上,采用双边带非相干联合和相干联合捕获两种方法,并进行了理论分析。最后仿真验证了理论分析的正确性。     

BOC调制信号频谱特性及仿真分析

BOC调制技术是一种广泛应用于GPS的现代化以及伽利略系统中新型信号调制技术。为研究其频谱特性,分析了BOC调制技术的基本原理及信号的产生过程,应用Matlab软件对其频谱特性进行了仿真,阐述了这种信号调制方式的优点;此外对其扩展技术MBOC,CBOC,TMBOC以及AltBOC做了简要介绍,对进一步研究导航信号现代化具有一定意义。     

导航发射信道对双频复用信号质量的影响

在新一代全球导航卫星系统建设中,双频联合恒包络复用技术得到了广泛的应用。由于信号在星上传输过程中会产生失真,所以需要分析不同双频复用信号通过发射信道后的信号质量。首先建立了一个基于实际发射信道的模型,然后主要分析了AltBOC(Alternate Binary Offset Carrier)、TD-AltBOC(Time Division Alternate Binary Offset Carrier)、ACE-BOC(Asymmetric Constant Envelope Binary Offset Carrier)等不同双频复用方案通过发射信道后的功率谱、星座图、鉴相曲线过零点偏差、相关损失。对三种调制方式进行对比,结果表明在考虑捕获灵敏度的情况下,应优先考虑ACE-BOC调制方式。     

改进K-means算法对AltBOC信号组合码序列的盲估计

针对恒包络交替二进制偏移载波(Alternate Binary Offset Carrier, AltBOC)调制信号组合码序列难以估计的问题，提出了利用改进K-means算法进行信号组合码盲估计方法。该方法首先通过引入互调分量以及重建副载波的方式构建AltBOC信号模型，然后在接收端将AltBOC信号分段成单倍组合码周期窗长的不重叠观测数据矩阵，并利用相似性原理从观测数据中选择最优的样本作为K-means聚类中的初始均值向量，最后通过K-means算法迭代优化数据样本与其聚类均值向量的平方误差，完成对AltBOC信号组合码序列的盲估计。计算机仿真结果表明，利用该算法在信噪比-15dB下能够较为精确地估计AltBOC信号组合码序列。      

Composite spread spectrum signals with uniform amplitude envelope for satellite radio-navigation systems

A method for generating the composite spread spectrum signals of satellite radio-navigation system based on linear equilibrium and nonequilibrium multiplexing of components is proposed to ensure the uniform amplitude envelope of a resultant signals. This makes it possible to solve the main problem of the given systems related to the low energy efficiency of signal amplification in the satellite radio receiver due to the substantial peak factor of an emitted signal.     

Navigational GBOC signals and their energy spectra

The modulation functions (MFs) of generalized binary offset carrier (GBOC) signals of promising satellite radio-navigation systems, such as Galileo (European Union), global positioning system (GPS) (USA), and BeiDou/Compass (China), is estimated. Analytical expressions for the spectral density and energy spectrum of the single component of the GBOC-signal MF are obtained at different pulse multiplicity coefficients N _RSO of rectangular subcarrier oscillations and different duty cycles ρ. The spectra characterizing the important particular cases, namely, binary offset carrier and binary phase-shift keying signals are analyzed by means of the derived general formulas for GBOC signals. The Mathcad software package is used to construct graphs and discuss the properties of the energy spectra of single components entering into the GBOC-signal MF for the following types of modulation: GBOC(1, 1, ρ), GBOC(2, 2, ρ), and GBOC(10, 5, ρ).     

On the representation of CPM signals by linear superposition ofimpulses in the bandpass domain

A novel signal generation concept for continuous phase modulations (CPMs) with modulation index 1/2 based on real impulses is presented. With this concept, bandpass CPM signals can be generated directly in one step instead of the two consecutive steps, namely, the generation of the complex envelope and the modulation of the carrier by the complex envelope, which are necessary in conventional signal generators. Mathematical expressions for both the real impulses and the bandpass CPM signals are derived and a simple modulator structure is discussed. Examples for the real impulses are given. Among these are the well-known CPM schemes of minimum shift keying (MSK), sinusoidal frequency shift keying (SFSK), and Gaussian minimum shift keying (GMSK). As an example, the validity of the novel signal generation concept is shown for the latter CPM scheme     

Detection of symbol rate of unknown digital communication signals

A new detection method for the symbol rate of unknown PSK (phase shift keying) and QAM (quadrature amplitude modulation) passband input signals is presented. In the detector, the input signal envelope obtained from the analytic signal is used to extract a line spectrum corresponding to the symbol rate. Simulation results show that the detector using absolute-valued signal envelope can detect the symbol rate accurately even for the input signal having small excess bandwidth.<>     

Method for superimposing data on amplitude-modulated signals

The principles of a new modulation scheme are described which permit an additional data channel to be superimposed on conventional DSBAM signals without increasing band-width or envelope distortion. This scheme, named zero synchronous frequency modulation (ZSFM), requires additional signal processing and provision for combined AM/FM at the transmitter. At the receiver, the data signal is detected by a simple frequency demodulator, while envelope detection of the AM signal is performed in the usual way.     

Linear Amplification with Nonlinear Components

A technique for producing bandpass linear amplification with nonlinear components (LINC) is described. The bandpass signal first is separated into two constant envelope component signals. All of the amplitude and phase information of the original bandpass signal is contained in phase modulation on the component signals. These constant envelope signals can be amplified or translated in frequency by amplifiers or mixers which have nonlinear input-output amplitude transfer characteristics. Passive linear combining of the amplified and/or translated component signals produces an amplified and/or translated replica of the original signal.     

The design of FM pulse compression signals

This paper gives a procedure for designing an FM signal of arbitrary envelope shape so that it will have a specified spectral modulus and hence, a specified autocorrelation function. The design procedure, which is based upon an approximate analysis, gives best results when the duration-bandwidth product of the signal is large, and it is therefore useful in the design of pulse compression signals. Examples are given to illustrate the design procedure and to show in a general way how the quality of the approximate solution depends upon the duration-bandwidth product of the signal and upon the shape of the signal envelope and the modulus of the signal spectrum.