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卷 59, 编号 12 (2016)
- 年: 2016
- 文章: 5
- URL: https://journals.rcsi.science/0735-2727/issue/view/10896
Article
Effect of aperture averaging and spatial diversity on capacity of optical wireless communication systems over lognormal channels
摘要
In this paper it is evaluated average channel capacity of an optical wireless communication system with aperture averaging and diversity reception over lognormal channels using a simple approximate closed form expression. The qualitative improvement in channel capacity is compared and investigated for various turbulence mitigation techniques: namely aperture averaging, diversity techniques such as maximal ratio combining and equal gain combining. Based on our study it is found that aperture averaging gives reasonably improved performance as compared to both types of diversity reception beyond certain turbulence strength. However, irrespective of turbulence strength, substantial improvement in capacity may be achieved with an array of direct detection receivers. Results obtained using the proposed expressions are in excellent agreement with those based on Monte Carlo simulations.
527-535
Heterogeneous performance evaluation of sophisticated versions of CFAR detection schemes
摘要
The detection of radar targets in a background, the statistical parameters of which are unknown and may not be stationary, can be effectively achieved through CFAR processors. The CA-CFAR scheme performs optimally for homogeneous and exponentially distributed clutter observations. However, it exhibits severe performance degradation in the presence of outlying target returns in the reference set or in regions of abrupt change in the background clutter power. The OS-CFAR processor has been proposed to solve both of these problems. Although this processor may treat target multiplicity quite well, it lacks effectiveness in preventing excessive false alarms during clutter power transitions. The TM-CFAR algorithm, which implements trimmed averaging after ordering, can be considered as a modified version of OS technique. By knowingly trimming the ordered samples, the TM detector may actually perform better than the OS processor. To simultaneously exploit the merits of CA, OS, and TM schemes, two combinations namely CAOS and CATM have been suggested. Each one of these versions optimizes good features of two CFAR detectors, depending on the characteristics of clutter and searched targets, with the goal of enhancing the detection performance under constant level of false alarm. It is realized by parallel operation of two standard types of CFARschemes. Our goal in this paper is to analyze these two developed versions in heterogeneous situations, to show to what extent they can improve the behavior of the conventional CFAR processors.
536-551
Estimation of duration of the rectangular optical pulse with unknown background intensity
摘要
The quasi-likelihood and asymptotically maximum likelihood algorithms of duration estimation have been synthesized and analyzed. The losses in estimation accuracy caused by a priori lack of knowledge of background intensity were also found.
552-561
Autonomous navigation of service spacecrafts on geostationary orbit using GNSS signals
摘要
In this paper we consider the possibilities of navigation of spacecrafts designed to service artificial Earth satellites on the geostationary orbit and of space debris removal in the near-Earth space using the signals of Global Navigation Satellite Systems. We have formulated the methodology for estimation of the signals availability of navigation satellites on the geostationary orbit through the utilization of almanac of GPS and GLONASS. It has been demonstrated that in the case of reception of navigation signals, which are radiated by the antenna system within the limits of main lobe of the radiation pattern (RP), the availability of satellite navigation signals on the geostationary orbit is very low even if we utilize GPS and GLONASS simultaneously. We present the simulation results of the received on the geostationary orbit navigation satellites using the signals radiated in the main lobes in the range from ±13.8 to ±23.5° for the L1 frequency, from ±13.8 to ±26° for the L2/L5 frequencies and in the side lobes in the range from ±30 to ±60° of RP of the satellite antennas. The simulation of the navigation satellites available on the geostationary orbit is given on the 24-hour time interval. Presented results are illustrated by the calculations of number of visible satellites and by the geometric factor.
562-566
Peculiarities of finding characteristic functions of the generating process in the model of stationary linear AR(2) process with negative binomial distribution
摘要
The linear random AR(2) autoregressive process having the negative binomial distribution has been considered. It has the form ξt + a1ξt-1 + a2ξt-2 = ςt, t ∈ Z, where {a1, a2 ≠ 0} are the autoregressive parameters; Z = {...,-1,0,1,...} is the sequence of integers; {ξt,t ∈ Z} is the random process with discrete time and independent values having the infinitely divisible distribution law that is called generating process. The method of finding the characteristic function of the generating process for linear autoregressive process having negative binomial distribution is presented. This inverse problem is solved by using properties of the characteristic function of stationary linear autoregressive process that can be presented in the Kolmogorov canonical form and as a linear stationary autoregressive process. An example of finding the Poisson spectrum of jumps and the characteristic function for the linear second order autoregressive process (AR(2)) with negative binomial distribution has been also presented.
567-573