The atmospheric two-dimensional optical code-division multiple-access (CDMA) systems using pulse-position
modulation (PPM) and Turbo-coded were presented. We analyzed the
bit-error rate (BER) of the proposed system using
pulse-position modulation (PPM) with considering the effects of the scintillation, avalanche photodiode noise, thermal
noise, and multi-user interference. We showed that the atmospheric two dimensional (2D) optical PPM CDMA systems
can realize high-speed communications when the logarithm variance of the scintillation is less than 0.1, and the
turbo-coded atmospheric optical CDMA system has better bit error rate(BER) performance than the atmospheric optical
PPM CDMA systems without turbo-coded. We also showed that the turbo-coded system has better performance than the
multi-user detection system.
KEYWORDS: Radon, Multimedia, Code division multiplexing, Telecommunications, Electronics, Communication engineering, Binary data, Matrices, Thermal effects, Signal to noise ratio
A new class of multilength, constant-weight two-dimensional multiwavelength optical orthogonal code (2D MWOOCs) with large capacity and good correlation properties is constructed based on multilength one-dimensional (1D) OOCs. The performance of these new MWOOCs in an optical code division multiple access (OCDMA) network with double-services is analyzed. The result shows that media with the shorter codewords performs much better than the media with longer codeword, and OCDMA system with these new multilength MWOOCs performs well. These features allow large capacity multimedia transmission in OCDMA system.
We propose a parallel interference cancellation technique for two-dimensional optical code division multiple access (OCDMA) system. In the proposed system, we estimate the multiple access interference (MAI) by group information codes. This new interference cancellation technique can be realized with simple structures. Performance analysis shows that it can improve the bit error rate (BER) performance, and increases the number of simultaneous users in the system.
A compact IR zoom telescope with diameter/length = 94/159 mm and magnification from 2 to 6 times at 8-12 microns is designed. Mechanically compensated zoom is adopted. Zooming lens and compensating lens groups possessing three roller followers for each are controlled by the stationary control cylinder on which there are three pairs of cam slots to which six followers are attached. When the outer cylinder having six linear slots is rotated, it will force the followers (i.e., the two lens mountings) to turn, resulting in smoothly turning and moving the two. The effect of air gap between the follower and the slot on backlash in the cam track is eliminated by special design of elastic construction of the roller follower. The image quality examed by MTF testing is satisfactory.
An infrared zoom telescope possessing the lenses made of germanium and working at -10 degree(s) to 40 degree(s)C and at 8 - 12 micrometers has been designed. The main problem to be solved is that the refraction index of Ge changes with the temperature, resulting in decollimation. For the purpose of lower production cost and reduced size and weight, a combination of mechanical passive athermalization by the collimating lens group with manual athermalization by the front lens which is chiefly utilized to focus the object is adopted. The lens mount is made of aluminum alloy. A pair of elements of mechanical passive athermalization, nylon/indium steel, is used to partially compensate the effect of variation of refraction index of Ge and expansion or contraction of aluminum alloy on the distance between the fixed and the collimating lens groups. The manually additional adjustment of the focusing lens, i.e., the front lens, is to partially compensate the distance between the front lens and the second lens group.
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