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تعداد نتایج: 847114 فیلتر نتایج به سال:
The diversity order and coding gain are crucial for the performance of a multiple antenna communication system. It is known that Space-Time Trellis Codes (STTC) can be used to achieve the above objectives. In particular we can use STTCs to obtain large coding gains. Many attempts have been made to construct STTCs which achieve full-diversity and good coding gains, though a general method of con...
The recently developed theory of geometrically uniform trellis codes is applied to the case of multidimensional PSK constellations. The symmetry group of an L X MPSK constellation is completely characterized. Conditions for rotational invariance of geometrically uniform partitions of a signal constellation are given. Through suitable algorithms, geometrically uniform partitions of L X MPSK ( M ...
A maximum likelihood estimate for frequency carrier, phase leakage and amplitude of digital PSK modulated signals is presented. The three optimum parameters obtained are analyzed and compared with suboptimum realizations in the synchronization process. In order to achieve an efficient system a final structure is closed where each method is selected in order to get not only appropriated performa...
Some joint fingerprinting and decryption (JFD) schemes used for copyright protection were reported recently. However, most of them need to be investigated before practical applications. In this paper, the typical one proposed by Lemma et al. is investigated and evaluated. Since this scheme aims to distribute multimedia content by encryption and watermarking, some important performances determin...
This letter considers block-coded 8-phase-shiftkeying (PSK) modulations for the unequal error protection (UEP) of information transmitted over Rayleigh-fading channels. Both conventional linear block codes and linear UEP (LUEP) codes are combined with a naturally labeled 8-PSK signal set, using the multilevel construction of Imai and Hirakawa [1]. Computer simulation results are presented showi...
This contribution considers the Cramer-Rao bound (CRB) related to phase-independent carrier frequency estimation from a noisy PSK signal. Instead of estimating the frequency jointly with the carrier phase, we treat the phase as a nuisance parameter. Ideal symbol timing is assumed. Both cases of known data (training sequence) and random data are considered. We show that frequency estimation irre...
The laser line-width required in PSK homodyne communication systems with Dither phase-locked loop receivers are exactly evaluated. It is shown that second-order phase-locked loops require at least 0.2 pW of signal power per every Hz of laser line-width (this number refers to the system with the detector responsivity 0.94 A/W, damping ratio 0.707, and the phase error standard deviation 10°). Thi...
Over the years, Password-based Authentication (PA) techniques have been the widely used security mechanism that serves as a first level defence against unauthorised access. However, it is paramount that existing PA techniques should be improved upon in order to adequately protect computer systems and networks from password attacks. Thiswork presents aOne-TimeServerSpecific Password Authenticati...
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