Spreading Modulation Techniques in Satellite Navigation

Binary offset carrier (BOC) signal synchronization is based on the correlation between the received and locally generated BOC signals. Thus, the multiple side-peaks in BOC autocorrelation are one of the main error sources in synchronizing BOC signals. Recently, a new correlation function with no side-peaks was proposed for sine or cosine phased BOC signal synchronization by the authors [7]. In this paper, we propose a novel correlation function for composite binary offset carrier (CBOC) signals by using the similar method to that in [7], which has a better power ratio than the CBOC autocorrelation.

With the rapid development of Global Navigation Satellite Systems (GNSS). The binary offset carrier (BOC) signal was proposed to separate new navigation signal from traditional BPSK in frequency and it has better accuracy and anti-multipath performance compared with the BPSK of the same code rate. But the ambiguity caused by the multi-peaks of auto-correlation function makes traditional acquisition technique not applicable to BOC.A novel unambiguous acquisition algorithm for sine BOC signals is proposed in this paper. There are two types of local reference signals: the BOC signal and a designed binary auxiliary signal. They are both correlated with the received signals. Then, a correlation function unambiguous for acquisition of BOC signal is obtained by multiplying the two correlation results. In the acquisition stage of BOC(10,5), the detection probability of the proposed method is approximately 1.5 dB better than that of GRASS and 2 dB better than that of SPAR. For BOC(14,2), the detection probability advantages of the proposed method increase to 6 dB and 7.5 dB . In conclusion, the proposed method can eliminate ambiguity and has significant performance advantages compared with the above methods.

Binary Offset Carrier (BOC) modulation technology is gradually replacing the traditional BPSK modulation signal as the main modulation method of the new generation satellite navigation signal due to its superiority in multipath suppression performance and code tracking accuracy. However, the tracking and mis-locking problem of BOC signals has become a key point limiting the widespread application of BOC signals. In this paper, we use code reference waveform (CCRW) technology and optimized Bump-jump (BJ) algorithm to analyze the multipath performance of low-order BOC signals under five code reference waveforms. Aiming at the high peak BOC signal with many peaks and high peak-to-peak ratio, we propose a new code reference waveform ensures the high-order BOC signal has good anti-multipath performance and solves the problem of extremely easy mis-locking of its receiver.

The long PN code in a Binary Offset Carrier (BOC) modulated signal has a higher rate than the GPS C/A code, which makes the acquisition process in the new global navigation satellite system (GNSS) much more complex.To achieve a fast acquisition of the GNSS signal with a reduced number of correlators and low computational complexity, a two-stage deterministic compressed (DS) GNSS acquisition technique has been proposed.Nevertheless, the ambiguous threat of BOC signal isn't taken into account in the DS technique.To eliminate the ambiguity threat in the acquisition process of BOC (m, n) signal, an unambiguous deterministic compressed acquisition is proposed in this paper.The main idea of the proposed technique is to introduce a simplified GRASS algorithm in the second stage measurement.Theoretical analysis and simulation results show that, at the expense of some performance degradation the proposed technique can completely remove the undesired positive side peaks of BOC (m, n) signal, and reduce the chance of false peak acquisition compared with the DS technique.

Multipath is a dominant source of positioning errors in global navigation satellite system receivers. It is difficult to design multipath mitigation techniques for binary offset carrier (BOC) signals due to the complicated autocorrelation function of BOC signals and localized variations of multipath. In this paper, a dual high resolution correlators (DHRC) technique is proposed for BOC signals to mitigate code and subcarrier multipath errors, as well as the carrier multipath error that is neglected by common techniques. Based on the concept of dual binary phase-shift keying (BPSK) tracking, the BOC signal is decomposed into two BPSK signals located in the upper and lower sidebands, respectively, thereby transforming the multipath mitigation in the BOC signal into the multipath mitigation in the upper and lower sidebands. Two narrow correlation functions of the upper and lower sidebands are synthesized using multiple correlation values, so the multipath outside the main peak of the synthesized correlation function is eliminated. The peak value of the synthesized correlation function is reduced from the original ACF, resulting in a large noise error. Therefore, a complementary filter is designed to compensate the noise error. Theoretical analysis and simulation results demonstrate that the DHRC technique with complementary filters can significantly mitigate multipath errors for BOC signals with slight thermal noise performance loss.

The recent researches on the tracking of binary offset carrier (BOC) modulated signals have been studied focusing onresolving the ambiguity problem caused by the multiple side-peaks in BOC autocorrelation. In this paper, we proposea novel unambiguous BOC tracking scheme with an improved tracking performance by using partial-pulses of BOCsignals. Firstly, we observe that a sub-carrier consists of two partial rectangular pulses referred to as partial-pulses,and then, generate multiple partial-correlations composing the BOC autocorrelation. Finally, a correlation function withno side-peak is constructed by combining the partial-correlations, and then, a delay lock loop employing the proposedunambiguous correlation function adjusts the phase of the local BOC signals. From numerical results, it is confirmedthat the proposed scheme provides a better tracking performance than the conventional schemes in terms of thetracking error standard deviation.

The global navigation satellite system (GNSS) signal modulation type plays a crucial role in determining the performances of positioning, navigation and timing (PNT) services. Currently, the binary offset carrier (BOC) modulation signal and binary coded symbol (BCS) modulation signal are both bipolar signals, which greatly restrict the room of improving the GNSS signal performance. Therefore, multi-level coded symbol (MCS) modulation has received great attention in the field of GNSS signal design. The MCS modulation is the most extensive step-coded symbol modulation mode, where BOC modulation and BCS modulation are its special cases. Since the waveform symbol of the MCS modulation signal can be arbitrarily valued, the optimal GNSS signal can be designed. However, like the BOC modulation signal, the MCS modulation signal also has the problem of ambiguous tracking, and then results in a large pseudo range measurement error, which is unacceptable for the new generation GNSS with high accuracy. In recent years, the unambiguous tracking of GNSS signals has become a hot research subject in the navigation signal processing domain and many methods are presented, and those methods can be divided into three categories:BPSK-like method, bump jump (BJ) method, and side-peak cancellation (SC) method. However, these methods are designed for BOC signal, and they are not suitable for MCS signal. Therefore, in this paper we propose a general unambiguous tracking algorithm based on the pseudo correlation function (PCF), which is suitable for MCS modulated signals. Firstly, the unitary expression of MCS modulated signal based on waveform value vector is given, then the unitary formula of cross-correlation function for MCS signal is derived and the definition of PCF is given. Then the constraint condition which should be satisfied to realize unambiguous tracking is analyzed in depth, and the universal constructing method of two reference signals and the relationship between each other are derived according to this constraint condition, which brings great convenience for solving the specific MCS signal. The code tracking loop model of GNSS receiver based on the proposed method is illustrated. It is observed that the proposed method can receive different MCS signals under the same receiver loop framework, and can simplify the design of the receiver while eliminating the tracking ambiguous problem. Finally, as a special case of MCS signal, the applications of the proposed method in four kinds of BOC signals are discussed respectively, and then the waveform value vector of the reference signal and the unitary expression of code discriminator are derived. Simulation results show that the proposed method can effectively solve the ambiguous tracking problem of MCS signal, which has good performance and broad application prospect.

Binary offset carrier (BOC) modulation signals have been widely adopted in global navigation satellite systems (GNSSs) such as Galileo and modernized global positioning system [1] [2]. Although this kind of modulation offers excellent performances, a main drawback of BOC modulation is that ambiguous acquisition and biased tracking for its multi-peak autocorrelation function (ACF). This article presents herein a novel acquisition technique allows removal of side peaks thoroughly and acquire better acquisition performance. This scheme is applicable to BOC (n, n) modulation signals. Theoretical analysis and system simulation demonstrate the algorithm proposed has better performance in acquisition aspect compared with other typical algorithms under the influence of additive white Gaussian noise.

It is well known that code and carrier-phase multipath, which has been under study for over two decades, is the limiting error sources in high-precision differential GPS applications. In virtually every study, however, the effects of autocorrelation function are considered little. This article focuses on the bounds of code and carrier-phase multipath error in terms of GNSS (Global Navigation Satellite Systems) signals autocorrelation functions, which result from a fundamental theoretical description and mathematical modeling of GNSS receiver. Firstly, an overview of the characteristics of the BOC (Binary Offset Carrier) signal ACF (autocorrelation function) is given in the paper. The impact on the DLL (delay-lock loop) and PLL (phase lock loop) discriminator functions are derived in the followed section and consequently a general description of multipath errors are obtained for the BOC signals. This quantifies the influence of limited bandwidth on receiver tracking error due to multipath. Finally, the simulation results show a distinct change in the error envelope for BOC signals from which has been got using current GPS C/A code signal.

Navigation receivers of global positioning systems that are operated in complex electromagnetic environment must have an increased noise immunity characteristic. One way of such noise immunity rising is to use incoherent operating mode of navigation receiver. There are known processing algorithms for navigation signals with Binary Phase Shift Keying (BPSK) modulation. But in the near-term outlook Global Navigation Satellite Systems (GLONASS), Global Positioning Systems (GPS) and Galileo known navigation signals with Binary Offset Carrier (BOC) modulation will be radiated. Processing algorithms for such signals are not described in scientific literature. So it is interesting to work out processing algorithms for BOC modulated signals in incoherent operating mode of navigation receiver. The article is devoted to synthesis and analysis of incoherent subcarrier tracking system under receiving BOC (1,1) navigation signals. To synthesize an optimal tracking system, optimal estimation theory and dual estimation method are used that allow taking into account multi-peak a posteriori distribution of delay that caused by the periodic process (digital sinusoid) in the radio signal modulation function. When analyzing the synthesized estimation algorithm, the procedure for describing delay discriminators and dual variable discriminators were used in the form of a statistical equivalent, including discrimination and fluctuation characteristics. New equations have been obtained that describe optimal tracking system for incoherent mode of a navigation receiver. New expressions for delay and dual variable discriminators are derived. The article gives a scheme for these discriminators and formulas for their statistical characteristics. Simulated results are provided that illustrate accuracy characteristics enhancement. The obtained tracking algorithms may be used in the navigation consumer equipment of GLONASS, GPS, Galileo and other radio-navigation satellite systems operating with BOC(1.1) modulated signals.

Traditional group delay measurement methods include single carrier phase method and spectrum analysis method based on signal autocorrelation function, but these two methods have their own limitations in GNSS receiver group delay measurement. The single carrier phase method cannot measure the group delay of multi filters and downconverters stage connect channel directly, and the measurement accuracy of group delay of spectrum analysis method based on signal autocorrelation function will deteriorate greatly near the zero point of signal power spectrum. In order to solve the above problems, this paper proposes a BOC (bi-nary offset carrier) signal group delay measurement method, which can realize the simple and accurate measurement of GNSS receiver group delay. In this paper, a group delay measurement method is analyzed and simulated by software, and verifies the feasibility and accuracy of the method are verified by simulation.KeywordsBOC navigation signalGroup delayGNSS receiver

New three‐level binary offset carrier (BOC) subcarriers are constructed, based on which the non‐orthogonal alternative BOC (AltBOC) modulation and its unequal power generalised form are achieved. The new constant envelope modulations have achieved a lower hardware complexity, which provide a solution to dual‐frequency multiplexing problem confronted by BeiDou B2 frequency band.

It is well known that CDMA systems are capacity limited because of the code division multiple access noise. Most of the CDMA systems today use single modulation format such as non-return-to-zero with modulation schemes such as Gaussian minimum shift keying (GMSK) some form of quadrature phase shift keying (QPSK) or quadrature amplitude modulation (QAM). Because of the centered peak in the power spectral density (PSD) of these signals, the bandwidth is not efficiently utilized. There is another formatting scheme based on a generalization of Manchester coding which leads to signals with their PSD peak away from the center, and the PSD of these signals around the center is very small. These are generally known as split spectrum modulation signals, and the binary offset carrier (BOC) is one such example. Bandwidth efficiency can be improved by combining these two modulation formats beyond what is achievable using a single format. The capacity in this case is set by both the CDMA noise of each differently formatted signal and by the mutual interference between the NRZ and BOC signals. Mutual interference is reduced by the separation of the PSD peaks of the two formats there by resulting in the overall improved capacity. This concept of mixing the formats on the same link also will potentially provide the means to share the same frequency between two categories of users by assigning each group different formats possibly at different performance levels. In this paper a brief description of a scheme using this concept of mixing the modulation formats to achieve bandwidth efficiency is discussed. Simulation performed using SystemView/sup @/ software is described and the results obtained in support of the viability of this concept are also presented.

The binary offset carrier (BOC) modulation was initially developed for easy sharing of spectrum between GPS modernization signals and legacy binary phase shift keying (BPSK)-modulated signals in the same band. It is now adopted by all GNSS constellations as a BOC signal has a larger Gabor bandwidth, producing better ranging (accuracy and multipath) performance. However, general BOC signal acquisition and tracking encounters the problem of multiple peaks (less an issue for MBOC, though), and many methods have been proposed to address this issue. A simple method to avoid such an ambiguity is to extract the upper and lower sidebands of the split spectrum of a BOC signal, treat them separately as a BPSK signal each, and then combine the results so as to recover the reduced sideband signal strength. Coherent combining is more gainful than the noncoherent counterpart particularly when the incoming signal is weak and/or when a strong interference signal is present. In this paper, a long coherent combining and integration (LCCI) scheme is presented, which enables standalone acquisition of a BOC signal without external aiding from a network or an inertial navigation system (INS) under combined narrowband and matched spectral interference signals. The LCCI scheme burns through the strong interference via building up the desired signal while averaging out noise and interference. To build up the desired signal, it makes use of all information resources available (e.g., L1 and L2, upper and lower sidebands, odd and even chips, and/or I and Q components) and applies coherent combining and long coherent integration, followed by non-coherent accumulation if necessary. Issues and enabling techniques are presented in this paper. The LCCI scheme is implemented on a software defined receiver (SDR) platform consisting of FPGA and ARM. Results of real-time demo with input RF signals generated by a Spirent GPS Simulator are described in the paper.

With the development of satellite navigation technology, BOC (Binary Offset Carrier) signals are proposed and applied in navigation system. However, in the advantages of enhancing the utilized rating of the band resource, some new problems are also emerging in the acquisition processing. On the basis of analyzing the limitations of the existing methods in suppressing side peaks, a NCCFR (New Cross-Correlation Function Reconstruction) algorithm is proposed, in which different modulation coefficients are used to construct correlation function with a shifter phase. The simulation results show that the new algorithm can suppress first side peaks and restrain other side peaks.