Binary Offset Carrier Modulation Research Articles

The Effect of Cosine Phased BOC Modulation on the GNSS Receiver Search Process

The modernisation of GPS and the introduction of Galileo will introduce the use of Binary Offset Carrier (BOC) modulation. BOC will be implemented as either a sine or cosine sub-carrier modulation, which affects the spectral properties of the signal and the receiver search, acquisition and tracking processes. This paper addresses the effect of the various forms of BOC modulation on the receiver search process. Theory is developed to draw comparisons between search techniques and verified with computer simulation models.

Integrated NAV-COM Systems: Assisted Code Acquisition and Interference Mitigation

In this paper, the problem of code acquisition for global navigation satellite systems (GNSS) is investigated in the presence of interference. A low-complexity interference mitigation technique is proposed to combat the effect of interference, which offers the potential for improved performance especially when high power jammers affect the reception. For practical implementation, an integrated navigation-communication network architecture is proposed, composed by an assistance network to aid code synchronization and an interference management system, augmenting the GNSS local component to enhance the system quality of service. Accordingly, an overall assistance network is proposed to estimate the interference characteristics and broadcast them to conventional terminals along with a rough time and frequency reference to improve code acquisition performance. Analytical and simulated results are provided, in the presence of binary offset carrier (BOC) modulation, showing the clear potential of assistance GNSS to significantly improve performance and reduce terminal complexity at the same time.

Code Tracking Algorithms for Mitigating Multipath Effects in Fading Channels for Satellite-Based Positioning

The ever-increasing public interest in location and positioning services has originated a demand for higher performance global navigation satellite systems (GNSSs). In order to achieve this incremental performance, the estimation of line-of-sight (LOS) delay with high accuracy is a prerequisite for all GNSSs. The delay lock loops (DLLs) and their enhanced variants (i.e., feedback code tracking loops) are the structures of choice for the commercial GNSS receivers, but their performance in severe multipath scenarios is still rather limited. In addition, the new satellite positioning system proposals specify the use of a new modulation, the binary offset carrier (BOC) modulation, which triggers a new challenge in the code tracking stage. Therefore, in order to meet this emerging challenge and to improve the accuracy of the delay estimation in severe multipath scenarios, this paper analyzes feedback as well as feedforward code tracking algorithms and proposes the peak tracking (PT) methods, which are combinations of both feedback and feedforward structures and utilize the inherent advantages of both structures. We propose and analyze here two variants of PT algorithm: PT with second-order differentiation (Diff2), and PT with Teager Kaiser (TK) operator, which will be denoted herein as PT(Diff2) and PT(TK), respectively. In addition to the proposal of the PT methods, the authors propose also an improved early-late-slope (IELS) multipath elimination technique which is shown to provide very good mean-time-to-lose-lock (MTLL) performance. An implementation of a noncoherent multipath estimating delay locked loop (MEDLL) structure is also presented. We also incorporate here an extensive review of the existing feedback and feedforward delay estimation algorithms for direct sequence code division multiple access (DS-CDMA) signals in satellite fading channels, by taking into account the impact of binary phase shift keying (BPSK) as well as the newly proposed BOC modulation, more specifically, sine-BOC(1,1) (SinBOC(1,1)), selected for Galileo open service (OS) signal. The state-of-art algorithms are compared, via simulations, with the proposed algorithms. The main focus in the performance comparison of the algorithms is on the closely spaced multipath scenario, since this situation is the most challenging for estimating LOS component with high accuracy in positioning applications.

Performance of the Proposed Galileo CBOC Modulation in Heavy Multipath Environment

In the framework of the modernization plans of Global Navigation Satellite Systems (GNSS) a new Multiplexed Binary Offset Carrier (MBOC) modulation has been proposed as a possible Signal-In-Space (SIS) with improved performance with respect to the robustness against external sources of degradation. Discussion around such signal format are still on-going at the time of writing, anyway it is the most probable candidate signal that will be adopted by both GPS L1C and the Galileo E1 Open Service (OS) signals [( http://ec.europa.eu/dgs/energy_transport/galileo/documents/doc/2004_06_21_summit_2004_en.pdf , 2004)] as modernization of the present BOC(1,1). In the context of the integration between wireless communication and satellite navigation, one of the major problems is that usually the GNSS receiver has to work in a critical environment characterized by a heavy presence of multipath or interference sources. Some examples are urban canyons or light indoor spaces. These are also typical situations for the usage of personal communications systems. The new MBOC modulation have been studied with the specific goal to create a signal more robust with respect to multipath, bringing the high performance of Galileo in situations in which the present BOC(1,1) shows limitations. In this sense, future Location Based Services (LBS) provided on the basis of the GNSS OS will benefits from this intrinsic robustness of the signal. Throughout the paper a review of the MBOC structure will be presented, specifying that in the Galileo framework such a structure has been proposed in a version named Composite BOC (CBOC). In particular, the paper presents the simulation of the CBOC behavior in presence of multipath showing the extreme improvement with respect to other BOC solutions.

Analysis of Filter-Bank-Based Methods for Fast Serial Acquisition of BOC-Modulated Signals

Binary-offset-carrier (BOC) signals, selected for Galileo and modernized GPS systems, pose significant challenges for the code acquisition, due to the ambiguities (deep fades) which are present in the envelope of the correlation function (CF). This is different from the BPSK-modulated CDMA signals, where the main correlation lobe spans over 2-chip interval, without any ambiguities or deep fades. To deal with the ambiguities due to BOC modulation, one solution is to use lower steps of scanning the code phases (i.e., lower than the traditional step of 0.5 chips used for BPSK-modulated CDMA signals). Lowering the time-bin steps entails an increase in the number of timing hypotheses, and, thus, in the acquisition times. An alternative solution is to transform the ambiguous CF into an "unambiguous" CF, via adequate filtering of the signal. A generalized class of frequency-based unambiguous acquisition methods is proposed here, namely the filter-bank-based (FBB) approaches. The detailed theoretical analysis of FBB methods is given for serial-search single-dwell acquisition in single path static channels and a comparison is made with other ambiguous and unambiguous BOC acquisition methods existing in the literature.

Efficient Delay Tracking Methods with Sidelobes Cancellation for BOC-Modulated Signals

In positioning applications, where the line of sight (LOS) is needed with high accuracy, the accurate delay estimation is an important task. The new satellite-based positioning systems, such as Galileo and modernized GPS, will use a new modulation type, that is, the binary offset carrier (BOC) modulation. This type of modulation creates multiple peaks (ambiguities) in the envelope of the correlation function, and thus triggers new challenges in the delay-frequency acquisition and tracking stages. Moreover, the properties of BOC-modulated signals are yet not well studied in the context of fading multipath channels. In this paper, sidelobe cancellation techniques are applied with various tracking structures in order to remove or diminish the side peaks, while keeping a sharp and narrow main lobe, thus allowing a better tracking. Five sidelobe cancellation methods (SCM) are proposed and studied: SCM with interference cancellation (IC), SCM with narrow correlator, SCM with high-resolution correlator (HRC), SCM with differential correlation (DC), and SCM with threshold. Compared to other delay tracking methods, the proposed SCM approaches have the advantage that they can be applied to any sine or cosine BOC-modulated signal. We analyze the performances of various tracking techniques in the presence of fading multipath channels and we compare them with other methods existing in the literature. The SCM approaches bring improvement also in scenarios with closely-spaced paths, which are the most problematic from the accurate positioning point of view.

Symmetric Phase-Only Matched Filter (SPOMF) for Frequency-Domain Software GPS Receivers

The symmetric phase-only matched filter (SPOMF) is studied in this paper for processing GPS signals. The use of phase-only information is equivalent to equalizing the magnitude spectrum in contrast to the original spectrum that tapers off according to a sinc-function. This tends to accentuate the high frequency components corresponding to edges or transitions in the signals. As such, the SPOMF produces a much sharper peak (ideally a Dirac delta function) that is more accurate in timing and less sensitive to multipath. In addition, the same operation is applicable to both a binary phase shift keying (BPSK) modulated signal such as the GPS C/A-code and P(Y)-code and a binary offset carrier (BOC) modulation such as the GPS M-code and Galileo codes. More importantly, it only produces a single matching peak regardless of which modulation code is used.

Galileo civil signal modulations

Spectrum limitations for navigation systems require that the various navigation signals broadcast by the Galileo system must be combined and must utilize bandwidth-efficient modulations. At the L1 band, one of the most important questions is how to combine all the Open Service signals and the Public Regulated Service signal at the payload level, while maintaining good performance at reception. The Interplex modulation, a particular phase-shifted-keyed/phase modulation (PSK/PM), was chosen to transmit these signals because it is a constant-envelope modulation, thereby allowing the use of saturated power amplifiers with limited signal distortion. The Interplex modulation was also taken as baseline at the E6 band to transmit the three channels and the services associated on the same carrier frequency. At the E5 band, the modulation must combine two different services on a same constant envelope composite signal, while keeping the simplicity of a BOC implementation. The constant envelope Alternate Binary Offset Carrier (ALTBOC) modulation was chosen as the solution to transmit the Galileo E5 band signal. The main objective of this paper is to study these Galileo modulations. After the introduction, the E5 band signals are described, followed by the Alternate BOC modulation which has been chosen to transmit them. The second part describes the general formulation of the Interplex modulation and its key parameters for an optimal multiplexing of the Galileo L1 band signals. Since the Galileo Open Service signals at the L1 band are still not yet completely specified, different test cases are considered and their impact on the resulting choice for the Interplex modulation parameters is exposed.

Feedforward Delay Estimators in Adverse Multipath Propagation for Galileo and Modernized GPS Signals

The estimation with high accuracy of the line-of-sight delay is a prerequisite for all global navigation satellite systems. The delay locked loops and their enhanced variants are the structures of choice for the commercial GNSS receivers, but their performance in severe multipath scenarios is still rather limited. The new satellite positioning system proposals specify higher code-epoch lengths compared to the traditional GPS signal and the use of a new modulation, the binary offset carrier (BOC) modulation, which triggers new challenges in the delay tracking stage. We propose and analyze here the use of feedforward delay estimation techniques in order to improve the accuracy of the delay estimation in severe multipath scenarios. First, we give an extensive review of feedforward delay estimation techniques for CDMA signals in fading channels, by taking into account the impact of BOC modulation. Second, we extend the techniques previously proposed by the authors in the context of wideband CDMA delay estimation (e.g., Teager-Kaiser and the projection onto convex sets) to the BOC-modulated signals. These techniques are presented as possible alternatives to the feedback tracking loops. A particular attention is on the scenarios with closely spaced paths. We also discuss how these feedforward techniques can be implemented via DSPs.

Galileo Receiver Core Technologies

The modern satellite navigation system Galileo is developed by European Union. Galileo is a completely civil system that offers various levels of services especially for civil users including service with safety guarantee. Galileo system employs modern signal structure and modern BOC (Binary Offset Carrier) modulation. The Galileo Receiver is investigated in the frame of the GARDA project solved by consortium under leadership of Alenia Spacio - LABEN. The aim of Galileo Receiver Core Technologies subtask is to investigate the key problems of the Galileo receiver development. The Galileo code and carrier tracking subtask of the Galileo Receiver Core Technologies is carried out at the Czech Technical University. The problem was analysed and split to the particular tasks. The aim of this paper is focused on BOC correlator architecture. The correlation function of the BOC modulation is more complex with a plenty of correlation peaks. The delay discriminator characteristic of such signal has several stable nodes, which cause stability problem. The standard solutions of this problem like BOC non-coherent processing, very early - very late correlator and deconvolution correlator are analysed. The new correlator architecture for BOC modulation processing has been developed. The developed correlator has two outputs, one for fine tracking and the second one for correct node detection. The second output is based on comparison of the correlation function envelopes. The simplified method of correlation function envelope calculation is described in this paper. The correlator is planned to be tested in the GRANADA software simulator including a sophisticated method of correlator output combination.