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.</p

Design Considerations for Acquisition of BOC-modulated Galileo Signals

Abstract — In this paper we study the effect of the transition band in designing both FIR- and IIR-types of digital filters, as possible bandwidth-limiting receiver filters, during the CDMA code acquisition of a BOC-modulated and oversampled Galileo signal. It is shown that using an asymmetric transition band (i.e., the band between the passband and stopband frequencies) with respect to one fourth of the sampling rate, the performance, in terms of Root Mean Square Errors (RMSE), can be improved for both FIR and IIR filters compared to the situation with symmetric transition bands. As an optimum bound we have employed the ideal rectangular pulse (i.e. no bandwidth limitation). All investigated filtering methods still suffer from some performance degradation, compared to rectangular shaping. The analysis is done here for both static and fading multipath channels. I

Renfors,“Oversampling Limits for Binary Offset Carrier Modulation for the Acquisition of Galileo Signals

Code and frequency acquisition are important stages of today’s satellite systems, such as the European system Galileo. Newly proposed modulation types, such as Binary Offset Carrier (BOC) modulation, have triggered new challenges in the acquisition process. The features and properties of BOC-modulated code sequences are still not wellunderstood in the context of fast acquisition algorithms. Moreover, no research studies have been dedicated so far to the effects of oversampling in the presence of BOCmodulated pseudorandom signals. However, the oversampling factor is typically dictated by hardware limitations, and cannot be assumed to be always equal to unity. In this paper, we study the effects of oversampling on the BOCmodulated pseudorandom codes during the CDMA code acquisition process. We also focus on the design of the code-Doppler bin size and we give the conditions to be fulfilled in order to achieve good detection probabilities and low mean acquisition times. Simulation results are shown for realistic signals of the Galileo satellite system. I

Abstract SIDELOBES CANCELLATION METHOD FOR UNAMBIGUOUS TRACKING OF BINARY-OFFSET-CARRIER MODULATED SIGNALS ∗

The signals proposed for the future European Galileo system and the GPS M-code signals use split-spectrum-type modulations, such as Binary-Offset-Carrier (BOC) modulation. Sine and cosine BOC modulations multiply the spreading code with rectangular sub-carriers and create a split-spectrum signal with the main lobes shifted around the sub-carrier frequency. This type of modulation brings multiple peaks in the envelope of the correlation function, and thus, the acquisition and tracking become potentially ambiguous and therefore more challenging. In this paper we propose a new unambiguous tracking method, the Sidelobes Cancellation Method (SCM), which removes the threats brought by the side-peaks ambiguities, while keeping the same sharp correlation of the main peak and, thus, allowing for better tracking performance. In contrast to other methods already introduced in literature for the same purpose, the SCM has the advantage that it can be used with any sine and cosine BOC modulated signal. In order to cope with the side-peaks ambiguities, a separate correlation function is computed and stored in the receiver and the delay estimation is done according to this stored correlation function. The performance comparison is done in the presence of realistic multipath fading channels, with the main focus on short multipath delays scenarios.

PROCEEDINGS OF THE 3rd WORKSHOP ON POSITIONING, NAVIGATION AND COMMUNICATION (WPNC’06) Complexity Considerations for Unambiguous Acquisition of Galileo Signals

Abstract- In order to obtain a higher spectral separation from the BPSK-like signals, i.e. GPS C/A code, the signals proposed for future Galileo and GPS M-code signals are processed using split-spectrum type modulations, such as Binary Offset Carrier (BOC) modulation. These BOC modulations create deep fades (ambiguities) in the envelope of the Autocorrelation Function (ACF) of signal, and therefore the acquisition and tracking of these signals pose new challenges. To overcome these problems, two approaches have been recently proposed in literature, referred either as ”sideband techniques ” (Betz, Fishman &amp; al.) or ”BPSK-like ” techniques (Martin, Heiries &amp; al.). These methods allow the use of a higher search step in time domain, but employ an modified reference PRN code at receiver, which lead to an increase in implementation complexity. Moreover, the BPSK-like method does not work for odd BOC modulation orders. In this paper we present an extension of BPSK-like method, which provides a significantly lower complexity in the correlation part, and it works for both even and odd, sine and cosine BOC modulation orders. This technique is compared with the existing sideband methods in terms of performance and implementation complexity. As a benchmark, we also keep the ambiguous BOC processing. For a further decrease in implementation complexity, we investigate the effect of different IIR and FIR filtering structures used for the side-band selection in the receiver. We use here an interpolated FIR filter structure which provides a lower computational complexity than a direct form FIR filter and has similar performance with the others filters. The analysis is done in the presence of realistic multipath fading channels and the signals are modeled according to the current proposals for Galileo system Open Service (OS). 1 Background an

Acquisition Of Galileo Signals In Hybrid

Double-dwell acquisition structures have typically been proposed as better alternatives to single-dwell structures from the point of view of the Mean Acquisition Time (MAT). Traditional approaches divide the double-dwell structure into an acquisition stage with short integration time, followed by a verification stage with longer integration time, which should provide a smaller global false alarm probability than a single-dwell structure (i.e., only the acquisition stage)