الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Optical wireless communications (OWC) is becoming an attractive alternative medium to
optical fiber and radio frequency (RF) communications because OWC requires no
spectrum licensing and interference to and from other systems unlike radio and microwave
systems. In addition, the point-to-point laser signal is extremely difficult to intercept,
making it ideal for covey communications. Free space optical communications offer data
rates comparable to fiber optical communications at a fraction of the deployment cost
while extremely narrow laser beam widths provide no limit to the number of free space
optical links that may be installed in a given location. But, the performance of wireless
infrared transmission systems is severely impaired by noise and interference induced by
natural and artificial ambient light.
In order to combat the effects of ambient light on the system performance, both optical
filtering and electrical filtering are usually adopted. However, even when resorting to these
techniques, the optical power penalty imposed by the interference may be very large. In
particular, the interference produced by fluorescent lamps driven by electronic ballasts
imposes very large optical power penalties on systems operating at data rates up to a few
tens ofMbps.
In this thesis, many techniques are used to overcome the penalty induced by artificial light
interference and are analyzed. These techniques are used to reduce noise current or
removing it by using an electrical filter or a polarizer or both of them together. We are
going to display the effect of noise voltage, flicker voltage and signal to noise ratio of the
systems by changing each parameter to reach the best solution for reducing effect of noise
on OWe.
from this thesis, we can summarize the main results in the following points:
1. Using a single polarizer with a photodetector decreased noise and flicker
voltages by a factor equals to T” and improved SNR.
2. The differential method is better than using a single photodetector to reduce
the effect of ambient noise current.
3. The best SNR is obtained in the differential detector with two orthogonal
polarizers system and the worst one is in the system that uses a single
photodetector.
4. The best photodetector is that one that has tiny bandwidth, lowest excess
noise factor and, lowest current gain.
5. Using a polarizer with an electrical filter make improvement in SNR than
when using each of them individually.