3,596 research outputs found
SPS pilot signal design and power transponder analysis, volume 2, phase 3
The problem of pilot signal parameter optimization and the related problem of power transponder performance analysis for the Solar Power Satellite reference phase control system are addressed. Signal and interference models were established to enable specifications of the front end filters including both the notch filter and the antenna frequency response. A simulation program package was developed to be included in SOLARSIM to perform tradeoffs of system parameters based on minimizing the phase error for the pilot phase extraction. An analytical model that characterizes the overall power transponder operation was developed. From this model, the effects of different phase noise disturbance sources that contribute to phase variations at the output of the power transponders were studied and quantified. Results indicate that it is feasible to hold the antenna array phase error to less than one degree per power module for the type of disturbances modeled
A genetic algorithm for computing the k-error linear complexity of cryptographic sequences
Some cryptographical applications use pseudorandom
sequences and require that the sequences are secure in
the sense that they cannot be recovered by only knowing a
small amount of consecutive terms. Such sequences should
therefore have a large linear complexity and also a large k-error
linear complexity. Efficient algorithms for computing the kerror
linear complexity of a sequence over a finite field only exist
for sequences of period equal to a power of the characteristic
of the field. It is therefore useful to find a general and efficient
algorithm to compute a good approximation of the k-error
linear complexity. In this paper we investigate the design of a
genetic algorithm to approximate the k-error linear complexity
of a sequence. Our preliminary experiments show that the
genetic algorithm approach is suitable to the problem and that
a good scheme would use a medium sized population, an elitist
type of selection, a special design of the two point random
crossover and a standard random mutation. The algorithm
outputs an approximative value of the k-error linear complexity
which is on average only 19.5% higher than the exact value.
This paper intends to be a proof of concept that the genetic
algorithm technique is suitable for the problem in hand and
future research will further refine the choice of parameters
Time and Location Aware Mobile Data Pricing
Mobile users' correlated mobility and data consumption patterns often lead to
severe cellular network congestion in peak hours and hot spots. This paper
presents an optimal design of time and location aware mobile data pricing,
which incentivizes users to smooth traffic and reduce network congestion. We
derive the optimal pricing scheme through analyzing a two-stage decision
process, where the operator determines the time and location aware prices by
minimizing his total cost in Stage I, and each mobile user schedules his mobile
traffic by maximizing his payoff (i.e., utility minus payment) in Stage II. We
formulate the two-stage decision problem as a bilevel optimization problem, and
propose a derivative-free algorithm to solve the problem for any increasing
concave user utility functions. We further develop low complexity algorithms
for the commonly used logarithmic and linear utility functions. The optimal
pricing scheme ensures a win-win situation for the operator and users.
Simulations show that the operator can reduce the cost by up to 97.52% in the
logarithmic utility case and 98.70% in the linear utility case, and users can
increase their payoff by up to 79.69% and 106.10% for the two types of
utilities, respectively, comparing with a time and location independent pricing
benchmark. Our study suggests that the operator should provide price discounts
at less crowded time slots and locations, and the discounts need to be
significant when the operator's cost of provisioning excessive traffic is high
or users' willingness to delay traffic is low.Comment: This manuscript serves as the online technical report of the article
accepted by IEEE Transactions on Mobile Computin
Parallel generation of c[r]yptographically strong pseudo-random sequences
The operational disadvantages of perfectly secure cipher systems has led to the development of practically secure stream cipher systems. The security of such cipher systems depend on the strength of the keystream. In order to examine the strength of a sequence two different types of criteria are considered. Statistical tests, are designed to assess how a sequence with a particular property behaves randomly. Complexity measures, are applied to determine the complexity, or equivalently the unpredictability of a sequence. Sequences obtained by LFSR are considered as building blocks of pseudo-random (PR) sequence generators. Transformations on the decimal expansion of irrational numbers is an alternative method for generating PR sequences, which are studied and some encouraging results are reported
Orthogonal Pseudo-Random Sequence Enabled Cognitive and Emergency Communications
With the ever-increasing demands for the broadband mobile communications, it is becoming more and more difficult to accommodate all existing and emerging wireless services and applications due to the limited communication resources particularly radio spectrum. In addition, system parameters of wireless communications often need to be adapted due to the variation of channel characteristics and user demands. Cognitive communication is emerged as an effective technique, particularly to improve the utilization rate of limited communication resources adaptively according to the change in its operating conditions and requirements. To handle these challenges efficiently and reliably in cognitive radio scenario, cyclic prefix (CP) of the OFDM system is precoded in this thesis using pseudo-random sequence. This signaling link can effectively carry transmission parameters and system adaptation information. In first part of the thesis, mutual interference minimization and transmission power adaptation enabled by the additional signaling link are also investigated. In order to make use of this precoded cyclic prefix (PCP) signaling link, an efficient demodulation scheme is needed to reduce the implementation complexity. Therefore, a low complexity signaling demodulator along with a multipath combining technique to further improve the performance in real communication scenario like in multipath channel is proposed in the thesis. The final aspect of this thesis is the investigation of a robust communication system using digital television (DTV) transmitter identification watermark signal which is also a modulated pseudo-random sequence. The previous study on PCP signaling is thus extended to an emergency communication system using DTV watermark. It is found that watermark based communication system is more robust than the DTV broadcasting and can reach a much wider coverage with significantly increased network reliability, which is suitable for national emergency situations
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