Abstract: Accurate delay tracking in multipath environments is one of the prerequisites of modern GNSS receivers. Several solutions have been proposed in the literature, both feedback and feedforward. However, this topic is still under active research focus, especially for mass-market receivers, where selection of lowcomplexity, nonpatented methods is preferred. Among the most encountered delay tracking structures implemented in today's receivers, we have the narrow correlator and the double-delta correlators. Both are heavily covered by various patents. The purpose of this paper is to introduce a new, generic structure, called multiple gate delay (MGD) structure, which covers also the patented correlators but offers much more flexibility in the design process. We show how the design parameters of such a structure can be optimized, we argue the performance of this structure via detailed simulation results based on various simulators, such as Matlab/Simulink-based tool, GRANADA, and we test the implementation feasibility of MGD structures on actual devices, via SystemC and FPGA prototyping. One of the main advantages of the proposed structure is its high degree of flexibility, which allows the designer to choose among, to the authors' knowledge, nonpatented solutions with delay tracking accuracy comparable with that of the current state-of-art trackers.
Abstract: 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.
Abstract: 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.
Abstract: The goal of this paper is to report the results of a comprehensive statistical analysis of
the urban wireless channels, based on WCDMA eld-measurements data. The applications
of our study are in the area of WCDMA-based mobile phone positioning. The
target here is the analysis of the Line-of-Sight (LOS) and Non Line-of-Sight (NLOS)
situations and of the statistical distributions of their parameters, such as the delays
and amplitudes. The distribution of the rst arriving path is tested against several theoretical
distributions, such as Rayleigh, Rician, and Nakagami-m distributions. The
estimated delay of the rst arriving path is compared to the LOS delay estimated via
GPS, in order to detect NLOS situations. The estimation of the mobile speed, based on
eld-measurements data is also carried out and compared to the speed estimation based
on the GPS link. The measurements were conducted in urban environment, downtown
Helsinki.
Abstract: Estimation of the Carrier to Noise Ratio (CNR) is
one of the most important functionalities of the GPS/Galileo
receivers. However, the conventional GPS receivers are not able
to satisfy the CNR estimation requirements for the location based
services, E-911, and moderate indoor reception. In this paper we
derive a total of seven moment based CNR estimators and present
the results for the simulation based BOC (Binary Offset carrier)
modulated signal and the measurement based BPSK (Binary
Phase Shift Keying) modulated signal. We compare the results
of the different estimators and find the most robust estimator.
Abstract: The Binary Offset Carrier (BOC) modulation, proposed
for future Galileo and GPS M-code signals, provides a
high spectral separation from BPSK-modulated signals,
such as GPS C/A code. This modulation type introduces
new challenges in the delay-frequency acquisition and
tracking processes, because it creates multiple peaks in
the envelope of the autocorrelation function (ACF).
In this paper, we analyze the performance of the Sidelobe
Cancellation Method (SCM) which is used to
suppress or diminish the contribution of sidelobes, when
acquiring the BOC modulated signals. In order to provide
a further decrease in sidelobes amplitudes and thus to
enhance the performance, we use the SCM approach in
conjunction with two differential correlation methods,
where correlation is performed using consecutive outputs
of coherent integration. The proposed methods are
analyzed in the presence of multipath fading channels,
considering parameters specified in the proposals for
Galileo system.
Abstract: Recently, aMultiplexed Binary Offset Carrier (MBOC) modulation
has been recommended by the GPS-Galileo Working
Group on Interoperability and Compatibility in order to increase
the tracking abilities of Galileo Open Service signals and of
GPS L1 civil signal. MBOC modulation also ensures a better
spectral separation with C/A codes. The purpose of this paper
is to analyze the MBOC properties in time and frequency
domain and to present a unitary theoretical model of MBOC
waveforms. First, several spectral properties of MBOC signals
are presented, namely: spectral separation coefficients with
GPS signals, root-mean-square bandwidth and maximum value
of the spectrum. Second, two implementations of MBOC signals
are discussed and a generic baseband model for them is
introduced. Third, a unified theoretical formula for the autocorrelation
function of MBOC-modulated pseudorandom codes
is derived. Finally, the advantage of a theoretical framework for
the MBOC correlation properties is emphasized via an example
of tracking multipath performance in multipath channels. The
theoretical findings are also validated via simulations.
Abstract: The ever-increasing public interest on 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.
Abstract: The Binary Offset Carrier (BOC) modulation which
has been proposed for future Galileo and GPS M-code signals,
provides a higher spectral separation from BPSK-modulated
signals, such as GPS C/A code. The absolute value of the autocorrelation
function of a BOC signal has a narrower main lobe,
which may increase the resolution of delay estimates, but also
presents deep fades, which may lead to a higher number of timing
hypotheses to acquire the signal. In order to get rid of these
ambiguities, several approaches have been proposed in literature,
which provide an unambiguous BPSK-like shape of correlation
function. In this paper we analyze, compare and develop further
two BPSK-like methods which allow to acquire a BOC-signal
unambiguously. The focus is on hybrid search, where several
time-frequency bins are searched in parallel.
We introduce here a modified version of a BPSK-like method
which decreases the receiver complexity and is valid for both
odd and even BOC orders. We analyze both single-side band
(SSB) processing (i.e., only one band is used) and dual-side band
(DSB) processing (i.e., upper and lower bands are combined
non-coherently). While eliminating the ambiguities in autocorrelation
function, both SSB and DSB processing present some
performance degradation, induced by the band selection and
non-coherent processing. The analysis is done in the presence
of multipath fading channels. As a benchmark, we keep also the
ambiguous BOC processing. We consider parameters specified in
the proposals for Galileo system Open Service (OS), respectively
Publicly Regulated Service (PRS).
I. INTRODUCTION
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 &
al.) or ”BPSK-like” techniques (Martin, Heiries & 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).
Abstract: The Global Navigation Satellite system
(GNSS) is experiencing an exponential growth of the
consumer segment demand. Many applications emerged
after the E-911/E-112 regulations. Positioning needs to be
carried out in all the environments covered by the wireless
communication services, including the most constraining
areas such as obstructed indoor environments. Different
techniques have emerged already in the market claiming
some navigation capabilities indoors. However, they usually
have an accuracy of some tens of meters, at best. In some
cases, with the deployment of pseudolites, indoor navigation
shows decent performance, but there is still a question
of whether GPS has a ”good enough” signal structure
for such applications in the first place. In this paper,
measurement-based modeling results with the purpose of
giving further insight on the real satellite-to-indoor channel
characteristics are described.
Abstract: The acquisition of CDMA signals in adverse
mobile communication channels has been studied for more
than five decades. However, the introduction of new standard
proposals for the future European satellite system (i.e.,
Galileo) and for the modernized GPS has triggered new interest
in fast and reliable acquisition strategies for CDMA systems
with very high spreading factors (e.g., length of 10230
chips or higher). Typically, the double-dwell serial search
strategies have been preferred for CDMA signal acquisition.
Few papers have addressed also the problem of hybrid and
parallel search strategies, but typically, the choice of the best
number of dwells has not been discussed. The goal of this
paper is to introduce a generic method for the computation of
the Mean Acquisition Time (MAT) for multiple-dwell hybridsearch
acquisition blocks and to compare the performance
of several multiple-dwell structures for CDMA systems with
high spreading factors. It will be shown here that increasing
the number of dwells does not always increase the performance
from the point of view of the MAT. We also discuss
the influence of various parameters on the selection of
the multiple-dwell strategy and we present simulation results
for a realistic Galileo signal.
Abstract: CDMA is the multiple access technique selected for the 3G mobile communications systems and it has a significant role in the research beyond 3G systems. CDMA systems over wireless channels have to cope with fading multipath propagation, which makes the channel estimation an important issue in CDMA receivers. Despite a significant amount of scientific literature on CDMA receivers, there are still open problems regarding the multipath delay and coefficient estimation in hostile environments and the design of low-complexity DSP-based channel estimators for CDMA applications. Good multipath delay estimation techniques can also find their applicability in mobile phone positioning, which is an area with many challenging questions. Additionally, theoretical measures of performance in CDMA detection in the presence of fading multipath channels have mainly been derived for ideal channel estimators. However, developing such analytical models in the presence of channel estimation errors can decrease significantly the computational time when analyzing the performance of different algorithms.
The research results presented in this thesis are focused on three main axes: channel estimation algorithms for low-complexity Rake receivers (with the main focus on the delay estimation part), code synchronization schemes for closely spaced multipath scenarios (including the applications in WCDMA positioning), and analytical studies of the performance of Rake receivers in the presence of multipath fading channels and delay estimation errors. First, the algorithms for the estimation of the main parameters of a fading channel are described, focusing on the channel complex coefficients and the multipath delays. The estimation of some other channel parameters (e.g., Doppler spread, noise variance) is briefly overviewed and a new channel estimation filter with adaptive filter length and fixed coefficients is derived. The problematics of closely spaced paths are emphasized and several solutions are proposed to deal with this situation. Second, two practical applications of the aforementioned channel estimation techniques are shown. The first one is a low-complexity Rake receiver based on interpolation, with incorporated channel estimation block. The second application is the mobile positioning, for which purpose several link-level solutions for the estimation of the delay of the first arriving path are presented. Third, we discuss the main techniques for the theoretical computation of the bit error probability (BEP) of a Rake receiver in the presence of multipath fading channels. The effects of the channel estimation errors on BEP analysis are also discussed. The last part of this thesis is a collection of nine publications that contain the main results of the author's research work. New algorithms and architectures for the multipath delay estimation in fading channels are introduced and their performance is studied under various CDMA scenarios. A semi-analytical method for computing BEP of a Rake receiver in the presence of code synchronization errors is also presented.
