摘要 :
This paper presents an iterative channel tracking and symbol decoding for combined bit-interleaved coded modulation (BICM) and orthogonal frequency-division multiplexing (OFDM) systems over time-varying channels. The proposed sch...
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This paper presents an iterative channel tracking and symbol decoding for combined bit-interleaved coded modulation (BICM) and orthogonal frequency-division multiplexing (OFDM) systems over time-varying channels. The proposed scheme alternates between a maximum a posteriori (MAP) decoder and a Kalman filter (KF) to track the channel taps. A key assumption in formulating the model is that the state-space model is perfectly specified. However, decision-directed detection methods make use of the decoded symbols to form the state-space model and may be inaccurate due to misdecoded symbols. The KF lacks robustness to outliers, and therefore, filter divergence may occur and give rise to error propagation, bringing about the well-known “error floor” phenomenon. A novel approach to minimize the state-space mismatch is presented in this paper. In particular, we introduce a new component in the iterative receiver, which evaluates the filter''s performance. By performing a statistical comparison of the innovation process against the theoretical predicted values, the new component adapts the number of decoded symbols used for channel tracking according to their reliability, thus reducing the mismodeling effect. We give an analysis of the effect of misdecoded symbols on the KF and how misdecoded symbols affect the channel frequency response estimation error. It is shown that this method can significantly reduce the error propagation effect, leading to a reduced bit error rate (BER).
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The newly constructed Qinghai-Tibet Railway connecting Golumd and Lhasa is the highest railway in the world, which is located on the hinterland of Qinghai- Tibet Plateau with the average altitude of above 4000 m. Therefore, the ex...
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The newly constructed Qinghai-Tibet Railway connecting Golumd and Lhasa is the highest railway in the world, which is located on the hinterland of Qinghai- Tibet Plateau with the average altitude of above 4000 m. Therefore, the external insulation of electric equipments will be affected by the atmospheric conditions in the high altitude regions. In contrast to many test investigations in the artificial climate chamber, there are few ones at the high altitude sites of 3000 m and above. In the paper, the ac artificial pollution tests of four types of composite insulators are carried out at three high altitude sites of 2820 m, 3575 m and 4484 m along the Qinghai-Tibet Railway. The test results show that the ac pollution flashover voltages in high altitude regions are affected not only by the pollution grades but also by the atmospheric parameters. The pollution flashover voltages will decrease with the increase of air pressure but increase with the decreases of ambient temperature. The exponent characterizing the influence of equivalent salt deposit density is 0.26 to 0.32 and the exponent characterizing the influence of non-soluble deposit density is 0.12 to 0.16, the influence of non-soluble deposit density cannot be neglected. The exponent characterizing the influence of air pressure is 0.507 to 0.587. The exponent characterizing the influence of ambient temperature is about 0.20. Considering the combined influence of the air pressure and ambient temperature, the ac flashover voltage of the polluted composite insulators will decrease by 4.0% to 6.4% for the altitude increased per 1000 m.
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A few new results are presented relating to model reference control (MRC) and model reference adaptive control (MRAC) for nonlinear uncertain plants of a very general nature. No a priori knowledge about the structure of uncertaint...
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A few new results are presented relating to model reference control (MRC) and model reference adaptive control (MRAC) for nonlinear uncertain plants of a very general nature. No a priori knowledge about the structure of uncertainties (plant terms and coefficients) is assumed, nor is any constant bound on their values. Such plant models result from many applications. In particular, if uncertainties represent some unmodelled dynamic effects, they will depend on the system states and so be unbounded. The Lyapunov type of stability is considered. A new MRAC law has been developed, which provides stable tracking to within a certain computable tolerance. The paper includes a few examples of the application of the developed adaptive controller to nonlinear plants with potentially unbounded terms. The tracking control of robotic manipulators has been especially elaborated.
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The existence of the five-fold twinned structures was observed in 3.4 nm FePt nanoparticles, and other n-fold structures were also been found in magnetic nano-grains in recording media. An analytical model, following the spirit o...
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The existence of the five-fold twinned structures was observed in 3.4 nm FePt nanoparticles, and other n-fold structures were also been found in magnetic nano-grains in recording media. An analytical model, following the spirit of the Stoner–Wohlfarth model, is brought up to study the anisotropy field distribution of FePt or other magnetic nanoparticles with twinned or n-fold structures, based on simple statistical calculations of twin regions' volumes. It is found that the nanoparticle has an effective uniaxial anisotropy, and the average anisotropy field is substantially reduced compared to that of the single crystal. The calculated anisotropy distributions are also compared with the empirical distribution functions used in micromagnetic simulations.
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Two circuits are proposed for double edge-triggered D flip-flops (DETDFFs). A DETDFF responds to both edges of the clock pulse. As compared with positive or negative edge-triggered flip-flops, a DETDFF has advantages in terms of p...
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Two circuits are proposed for double edge-triggered D flip-flops (DETDFFs). A DETDFF responds to both edges of the clock pulse. As compared with positive or negative edge-triggered flip-flops, a DETDFF has advantages in terms of power dissipation and speed. Delay figures for these circuits are measured by simulation. It is shown that these circuits are faster and have lower transistor counts than previously reported circuits. It is shown that these flip-flops can be used at 320-400-MHz clock frequency in a 2- mu m technology.
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A high-speed binary counter and a divider using a new carry propagation scheme is presented. The critical logic depth is one and the maximum fan-in of gates can be reduced to two, independent of the number of bits in both the coun...
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A high-speed binary counter and a divider using a new carry propagation scheme is presented. The critical logic depth is one and the maximum fan-in of gates can be reduced to two, independent of the number of bits in both the counter and the divider. The hardware grows linearly with the number of bits, making them well suited for a wide range of applications.
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