85 research outputs found
GNSS signal acquisition in the presence of sign transitions
The next generation of Global Navigation Satellite Systems (GNSS), such as Galileo [1] and GPS modernization [2], will use signals with equal code and bit periods, which will introduce a potential sign transition in each segment of the signal processed in the acquisition block. If FFT is used to perform the correlations a sign transition occurring within the integration time may cause a splitting of the main peak of the Cross Ambiguity Function (CAF) into two smaller lobes along the Doppler shift axis [3]. In this paper a method to overcome the possible impairments due to the lobe splitting is proposed and validated by simulatio
GNSS signal acquisition in the presence of sign transitions
The next generation of Global Navigation Satellite
Systems (GNSS), such as Galileo [1] and GPS
modernization [2], will use signals with equal code
and bit periods, which will introduce a potential
sign transition in each segment of the signal
processed in the acquisition block. If FFT is used to
perform the correlations a sign transition occurring
within the integration time may cause a splitting of
the main peak of the Cross Ambiguity Function
(CAF) into two smaller lobes along the Doppler
shift axis [3]. In this paper a method to overcome
the possible impairments due to the lobe splitting is
proposed and validated by simulation
HOW DOES AWARENESS OF TASK CONFLICT MOTIVATE WIKI-BASED COLLABORATIVE LEARNING? A DESIGN SCIENCE APPROACH
Lack of motivation is a serious problem in wiki-based collaboration process. The original wiki is designed to hide authorship information. Such design may hinder users from being aware of task conflict, resulting in undesired outcomes (e.g., lack of motivation, and suppressed knowledge exchange activities). This research-in-progress tries to motivate students to participate in wiki-based collaborative learning project by increasing awareness of task conflict. Two tools were proposed to solve problems caused by lack of task conflict clues, such as low level of motivation, content trust, knowledge exchange, and sense of audience. A field test was executed to evaluate new designs. We propose to invite active participants from the field test and use focus group interview to explain how awareness of task conflict motivates participation in collaborative learning. This research-inprogress has the potential to lead to various theoretical and practical implications. For example, the results will enhance the literature on task conflict and user motivation, help platforms design motivation mechanisms
Influence of active power output and control parameters of full-converter wind farms on sub-synchronous oscillation characteristics in weak grids
Active power outputs of a wind farm connected to a weak power grid greatly affect the stability of grid-connected voltage source converter (VSC) systems. This paper studies the impact of active power outputs and control parameters on the subsynchronous oscillation characteristics of full-converter wind farms connected weak power grids. Eigenvalue and participation factor analysis was performed to identify the dominant oscillation modes of the system under consideration. The impact of active power output and control parameters on the damping characteristics of subsynchronous oscillation is analysed with the eigenvalue method. The analysis shows that when the phase-locked loop (PLL) proportional gain is high, the subsynchronous oscillation damping characteristics are worsened as the active power output increases. On the contrary, when the PLL proportional gain is small, the subsynchronous oscillation damping characteristics are improved as the active power output increases. By adjusting the control parameters in the PLL and DC link voltage controllers, system stability can be improved. Time-domain results verify the analysis and the finding
Optimal Space-Depth Trade-Off of CNOT Circuits in Quantum Logic Synthesis
Due to the decoherence of the state-of-the-art physical implementations of
quantum computers, it is essential to parallelize the quantum circuits to
reduce their depth. Two decades ago, Moore et al. demonstrated that additional
qubits (or ancillae) could be used to design "shallow" parallel circuits for
quantum operators. They proved that any -qubit CNOT circuit could be
parallelized to depth, with ancillae. However, the
near-term quantum technologies can only support limited amount of qubits,
making space-depth trade-off a fundamental research subject for quantum-circuit
synthesis.
In this work, we establish an asymptotically optimal space-depth trade-off
for the design of CNOT circuits. We prove that for any , any -qubit
CNOT circuit can be parallelized to depth, with ancillae. We
show that this bound is tight by a counting argument, and further show that
even with arbitrary two-qubit quantum gates to approximate CNOT circuits, the
depth lower bound still meets our construction, illustrating the robustness of
our result. Our work improves upon two previous results, one by Moore et al.
for -depth quantum synthesis, and one by Patel et al. for :
for the former, we reduce the need of ancillae by a factor of by
showing that additional qubits suffice to build -depth, size --- which is asymptotically optimal --- CNOT
circuits; for the later, we reduce the depth by a factor of to the
asymptotically optimal bound . Our results can be directly
extended to stabilizer circuits using an earlier result by Aaronson et al. In
addition, we provide relevant hardness evidences for synthesis optimization of
CNOT circuits in term of both size and depth.Comment: 25 pages, 5 figures. Fixed several minor typos and a mistake about
CNOT+Rz circui
Reliability and economic evaluation of offshore wind power DC collection systems
One key directive to realize the global transition towards net-zero emission goals is to integrate more renewable energy resources into the generation mix. Due to higher and more consistent wind speeds, offshore wind farms (OWFs) have the potential to generate more energy at a steadier rate than their onshore counterpart. However, at the collection system level, all the OWFs use alternating current (AC) technology at present. Nonetheless, with an increasing capacity of the single wind turbine (WT) and larger distances to the shore, the use of direct current (DC) technology at the collection system level is beneficial. To select a suitable DC collection system topology, this paper proposes a comprehensive analytical reliability evaluation method, based on the Universal Generating Function technique, together with associated economic factors. Four candidates DC collection system options were evaluated with different WT capacities for a 400 MW OWF. The availability indices such as Generation Ratio Availability and Expected Energy Not Supplied were used to assess their reliability levels. The results show that the radial topology with a single platform DC/DC converter is more reliable and economical than the other candidate options
Resilient dynamic state estimation for multi-machine power system with partial missing measurements
Accurate tracking the dynamics of power system plays a significant role in its reliability, resilience and security. To achieve the reliable and precise estimation results, many advanced estimation methods have been developed. However, most of them are aiming at filtering the measurement noise, while the adverse affect of partial measurement missing is rarely taken into account. To deal with this issue, a discrete distribution in the interval [0,1] is introduced to depict mechanism of partial measurement data loss that caused by the sensor failure. Then, a resilient fault tolerant extended Kalman filter (FTEKF) is designed in the recursive filter framework. Eventually, extensive simulations are carried on the different scale test systems. Numerical experimental results illustrate that the resilience and robustness of the proposed fault tolerant EKF method against partial measurement data loss
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