3,219 research outputs found
GPS Carrier Tracking Loop Performance in the presence of Ionospheric Scintillations
The performance of several GPS carrier tracking loops
is evaluated using wideband GPS data recorded during
strong ionospheric scintillations. The aim of this study is
to determine the loop structures and parameters that enable
good phase tracking during the power fades and phase
dynamics induced by scintillations. Constant-bandwidth
and variable-bandwidth loops are studied using theoretical
models, simulation, and tests with actual GPS signals.
Constant-bandwidth loops with loop bandwidths near 15
Hz are shown to lose phase lock during scintillations. Use
of the decision-directed discriminator reduces the carrier
lock threshold by ∼1 dB relative to the arctangent and conventional Costas discriminators. A proposed variablebandwidth
loop based on a Kalman filter reduces the carrier
lock threshold by more than 7 dB compared to a 15-Hz
constant-bandwidth loop. The Kalman filter-based strategy
employs a soft-decision discriminator, explicitly models
the effects of receiver clock noise, and optimally adapts
the loop bandwidth to the carrier-to-noise ratio. In extensive
simulation and in tests using actual wideband GPS
data, the Kalman filter PLL demonstrates improved cycle
slip immunity relative to constant bandwidth PLLs.Aerospace Engineering and Engineering Mechanic
Application of multirate digital filter banks to wideband all-digital phase-locked loops design
A new class of architecture for all-digital phase-locked loops (DPLL's) is presented in this article. These architectures, referred to as parallel DPLL (PDPLL), employ multirate digital filter banks (DFB's) to track signals with a lower processing rate than the Nyquist rate, without reducing the input (Nyquist) bandwidth. The PDPLL basically trades complexity for hardware-processing speed by introducing parallel processing in the receiver. It is demonstrated here that the DPLL performance is identical to that of a PDPLL for both steady-state and transient behavior. A test signal with a time-varying Doppler characteristic is used to compare the performance of both the DPLL and the PDPLL
System architecture study of an orbital GPS user terminal
The generic RF and applications processing requirements for a GPS orbital navigator are considered. A line of demarcation between dedicated analog hardware, and software/processor implementation, maximizing the latter is discussed. A modular approach to R/PA design which permits several varieties of receiver to be constructed from basic components is described. It is a basic conclusion that software signal processing of the output of the baseband correlator is the best choice of transition from analog to digital signal processing. High performance sets requiring multiple channels are developed from a generic design by replicating the RF processing segment, and modifying the applications software to provide enhanced state propagation and estimation
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Analysis of Ionospheric Scintillations using Wideband GPS L1 C/A Signal Data
A non-real-time GPS receiver has been developed and
tested for use in scintillation analysis. The receiver consists
of a digital storage receiver and non-real-time software
acquisition and tracking algorithms. The goal of
this work is to shed light on the behavior of strongly
scintillating signals: signals which cause conventional
GPS receivers to lose carrier lock.
The receiver collects wideband GPS L1 digital data sampled at 5.7 MHz using an RF front-end and stores it
on disk for post-processing. It processes the data off-line
to determine carrier signal amplitude and phase variations
during scintillations. The main processing algorithms
are traditional code delay and carrier frequency
acquisition algorithms and special signal processing algorithms
that effectively function as a delay-locked loop
and phase-locked loop. The tracking algorithms use
non-causal smoothing techniques in order to optimally
reconstruct the phase and amplitude variations of a
scintillating signal. These techniques are robust against
the deep power fades and strong phase fluctuations
characteristic of scintillating signals.
To test the receiver, scintillation data were collected
in Cauchoeira Paulista, Brazil, from December 4 to 6,
2003. The data set spans several hours and includes
times when one or more satellite signals are scintillating.
The smoothing algorithm has been used to determine
the carrier amplitude and phase time histories
of the scintillating signals along with the distortion of
the pseudorandom noise (PRN) code’s autocorrelation
function. These quantities provide a characterization
of scintillation that can be used to study the physics of
scintillations or to provide off-line test cases to evaluate
a tracking algorithm’s ability to maintain signal lock
during scintillations.Aerospace Engineering and Engineering Mechanic
Telecommunications and data acquisition systems support for Voyager missions to Jupiter and Saturn, 1972-1981, prelaunch through Saturn encounter
The Deep Space Network has supported the Voyager Project for approximately nine years, during which time implementation, testing, and operational support was provided. Four years of this time involved testing prior to launch; the final five years included network operations support and additional network implementation. Intensive and critical support intervals included launch and four planetary encounters. The telecommunications and data acquisition support for the Voyager Missions to Jupiter and Saturn are summarized
Payload/orbiter signal-processing and data-handling system evaluation
Incompatibilities between orbiter subsystems and payload communication systems to assure that acceptable and to end system performamce will be achieved are identified. The potential incompatabilities are associated with either payloads in the cargo bay or detached payloads communicating with the orbiter via an RF link. The payload signal processing and data handling systems are assessed by investigating interface problems experienced between the inertial upper stage and the orbiter since similar problems are expected for other payloads
Tracking and data system support for the Viking 1975 mission to Mars. Volume 1: Prelaunch planning, implementation, and testing
The tracking and data acquisition support for the 1975 Viking Missions to Mars is described. The history of the effort from its inception in late 1968 through the launches of Vikings 1 and 2 from Cape Kennedy in August and September 1975 is given. The Viking mission requirements for tracking and data acquisition support in both the near earth and deep space phases involved multiple radar tracking and telemetry stations, and communications networks together with the global network of tracking stations, communications, and control center. The planning, implementation, testing and management of the program are presented
Ku-band system design study and TDRSS interface analysis
The capabilities of the Shuttle/TDRSS link simulation program (LinCsim) were expanded to account for radio frequency interference (RFI) effects on the Shuttle S-band links, the channel models were updated to reflect the RFI related hardware changes, the ESTL hardware modeling of the TDRS communication payload was reviewed and evaluated, in LinCsim the Shuttle/TDRSS signal acquisition was modeled, LinCsim was upgraded, and possible Shuttle on-orbit navigation techniques was evaluated
Engineering evaluations and studies. Volume 3: Exhibit C
High rate multiplexes asymmetry and jitter, data-dependent amplitude variations, and transition density are discussed
Theory of phaselock techniques as applied to aerospace transponders
Phaselock techniques as applied to aerospace transponder
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