摘要 :
An error-correction scheme for an M-ary symmetric channel (MSC) characterized by a large error probability p/sub e/ is considered. The value of p/sub e/ can be near, but smaller than, 1-1/M, for which the channel capacity is zero,...
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An error-correction scheme for an M-ary symmetric channel (MSC) characterized by a large error probability p/sub e/ is considered. The value of p/sub e/ can be near, but smaller than, 1-1/M, for which the channel capacity is zero, such as may occur in a jamming environment. The coding scheme consists of an outer convolutional code and an inner repetition code of length m that is used for each convolutional code symbol. At the receiving end, the m inner code symbols are used to form a soft-decision metric, which is passed to a soft-decision decoder for the convolutional code. The effect of finite quantization and methods to generate binary metrics for M<2 are investigated. Monte Carlo simulation results are presented. For the binary symmetric channel (BSC), it is shown that the overall code rate is larger than 0.6R/sub 0/, where R/sub 0/ is the cutoff rate of the channel. New union bounds on the bit error probability for systems with a binary convolutional code on 4-ary and 8-ary orthogonal channels are presented. For a BSC and a large m, a method is presented for BER approximation based on the central limit theorem.
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摘要 :
The implementation issues of digital controllers with finite word length (FWL) considerations are addressed. Both the shift and delta operator parametrisations of a general controller structure are considered. A unified formulatio...
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The implementation issues of digital controllers with finite word length (FWL) considerations are addressed. Both the shift and delta operator parametrisations of a general controller structure are considered. A unified formulation is adopted to derive a computationally tractable stability related measure that describes FWL closed-loop stability characteristics of different controller realisations. Within a given operator parametrisation, the optimal FWL controller realisation, which maximises the proposed stability related measure, is the solution of a nonlinear optimisation problem. The relationship between the z-operator and /spl delta/-operator controller parametrisations is analysed, and it is shown that the /spl delta/ parametrisation has a better FWL closed-loop stability margin than the z-domain approach under a mild condition. A design example is included to verify the theoretical analysis and to illustrate the proposed optimisation procedure.
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Information extracted from multiple channels of the surface myoelectric signal (MES) recording sites can be used as inputs to control systems for powered upper limb prostheses. For small, closely spaced muscles, such as the muscl...
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Information extracted from multiple channels of the surface myoelectric signal (MES) recording sites can be used as inputs to control systems for powered upper limb prostheses. For small, closely spaced muscles, such as the muscles in the forearm, the detected MES often contains contributions from more than one muscle, the contribution from each specific muscle being modified by the dispersive propagation through the volume conductor between the muscle and the detection points. In this paper, the measured raw MES signals are rotated by class-specific principal component matrices to spatially decorrelate the measured data prior to feature extraction. This “tunes” the data to allow a pattern recognition classifier to better discriminate the test motions. This processing technique was used to significantly ($p; ≪;0.01$) reduce pattern recognition classification error for both intact limbed and transradial amputee subjects.
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An algorithm for synthesizing a better relational database scheme in elementary key normal form (EKNF) is developed. This algorithm eliminates not only extraneous attributes and other redundancies, but also superfluities from a gi...
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An algorithm for synthesizing a better relational database scheme in elementary key normal form (EKNF) is developed. This algorithm eliminates not only extraneous attributes and other redundancies, but also superfluities from a given set of functional dependences (FDs), based primarily on subset closures, Hamiltonian cycles of FDs, and equivalent subsets of attributes. Following this algorithm, a better LR-minimum FD covering is obtained. A more practical and efficient method for designing a relational database scheme in EKNF is then provided. The time complexity of the algorithm is polynomial.
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The problem of digital controller structures and the effect of finite-word-length (FWL) implementation on the closed-loop stability of digital feedback control systems is addressed. A framework is presented to derive two lower sta...
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The problem of digital controller structures and the effect of finite-word-length (FWL) implementation on the closed-loop stability of digital feedback control systems is addressed. A framework is presented to derive two lower stability bounds for a closed-loop system, which are controller structure dependent, and then to solve the optimal FWL controller structure problem by maximising one of these lower bounds. This yields an improved method to design optimal finite-precision controller structures with better numerical accuracy and closed-loop stability characteristics. Comparisons using numerical examples from two digital controller structures demonstrate that the procedure proposed for the more efficient measure yields an improved finite controller realisation with combined lower bits and higher lower stability bounds.
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A method of subcarrier lightwave modulation based on the self-sustained pulsation (SSP) of laser diodes is presented. The tunable microwave/millimeter-wave frequency subcarrier is generated by the laser diode itself under proper D...
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A method of subcarrier lightwave modulation based on the self-sustained pulsation (SSP) of laser diodes is presented. The tunable microwave/millimeter-wave frequency subcarrier is generated by the laser diode itself under proper DC biases. The subcarrier is frequency-modulated when the DC bias is superimposed with a small AC signal. No external modulation is needed. A theoretical analysis based on a double-section laser diode reveals that Hopf bifurcation is the origin of SSP. Theoretical calculations also show that the modulator has the potential of generating subcarriers up to 100 GHz by proper control of the device parameters V-channeled substrate inner-stripe (VSIS) GaAlAs laser diodes were used to generate 1-7-GHz SSP subcarriers. A preliminary subcarrier multiplexing (SCM) experiment demonstrated the transmission of 1-GHz modulation and video signals on a readily FM-modulated 6.3-GHz SSP subcarrier.
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Adjacent extra magnets can induce an additional impedance to an amorphous wire. We have studied the additional impedance passing through a magnetic ring and found that it is related to the electromagnetic characteristics, shapes,...
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Adjacent extra magnets can induce an additional impedance to an amorphous wire. We have studied the additional impedance passing through a magnetic ring and found that it is related to the electromagnetic characteristics, shapes, and locations of the extra magnet and the frequency of the ac excitation, regardless of the amorphous material properties and the extra magnetic field conditions. According to our theoretical analysis, the additional impedance severely reduces the magnetoimpedance change of the amorphous wire and destroys the giant magnetoimpedance characteristic. We therefore propose a return structure to diminish the additional impedance. Our experiments measured the impedances of an amorphous wire, a Cu wire, and the return structure with a variety of extra magnetic fields. The results confirmed the characteristics of the additional impedance and verified the effectiveness of the return structure.
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Large-scale applications of high-temperature superconductors require large critical current density J/sub c/. The limit of utilization is determined by the practical resistivity criterion and the current voltage characteristic of ...
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Large-scale applications of high-temperature superconductors require large critical current density J/sub c/. The limit of utilization is determined by the practical resistivity criterion and the current voltage characteristic of a superconductor which is highly nonlinear in these materials. Various models with different barrier-current dependencies U(J) have been developed to describe the flux motion in them but questions still remain. We show that these models may be unified to a general materials equation which gives a consistent description of different regimes of flux motion. We compare this equation with recent pertinent experiments and find fair agreements.
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A novel scheme using Brillouin optical time-domain reflectometry (BOTDR) and a fibre Bragg grating (FBG) sensor array simultaneously for long distance strain monitoring and accurate strain measurement of some key position is prese...
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A novel scheme using Brillouin optical time-domain reflectometry (BOTDR) and a fibre Bragg grating (FBG) sensor array simultaneously for long distance strain monitoring and accurate strain measurement of some key position is presented. BOTDR and FBG sensing parts are integrated into one system and a strain experiment is carried out. Experimental results show that the whole sensing system can work simultaneously without reference and achieve a strain distribution measurement as well as the point to point precise strain detection along a 20 km sensing fibre. The strain resolution of the system is 50 ;C;?5; for BOTDR and 1 ;C;?5; for FBG, respectively, along 20 km distance, while a spatial resolution of 2m can be achieved for the BOTDR part.
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Dropout is the term used to describe sporadic and long-duration signal loss in a tape recording system due to media defects or debris generated by the head-media interface. The main mechanism believed to cause dropouts is spacing ...
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Dropout is the term used to describe sporadic and long-duration signal loss in a tape recording system due to media defects or debris generated by the head-media interface. The main mechanism believed to cause dropouts is spacing loss during writing and/or reading. Dropouts are a major limiting factor in the performance of the magnetic tape channel, which makes understanding them a critical issue for future density improvements. In this paper, we analyze the peakshift behavior of signals during a dropout, which constitutes a significant but unexpected side effect. This peakshift was found to be caused during the recording process. Both experimental analysis and modeling have been used in this study.
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