Performance Analysis For Wireless Opticalcommunications Systems Over M-Turbulence Channel

With the development of the communication technology, the demand for information exchanging, internet connecting, wireless communication and mobile communication is getting higher and higher. Optical wireless communication(OWC) has became a new economic and reasonable solution to broadband access in long term evolution(LTE) scheme for its several potential advantages, such as immunity to electromagnetic interference, high communication security, free license, easy to install and the huge capacity. This paper takes M-turbulence OWC as object, establishes a more practical channel model and further puts forward a scheme to improve its performance. The main contents can be summarized as follows:(1) After analyzing the characteristics of the atmospheric channel, a mathematical model of M-turbulence wireless optical communication system is put forward considering the effects of atmospheric attenuation, M-turbulence and non-zero pointing error. It is valid for every turbulence conditions. Finally, the probability density function of the M-turbulence channel fading is derived, which is more in line with the actual transmission scenario.(2) According to the probability density function of the M-turbulence channel fading and the research of the upper bound and lower bound of the instantaneous capacity, the ergodic capacity and the outage probability of the M-turbulence wireless optical communication system are analyzed. The research indicates that the transmission distance, optical signal to noise ratio(SNR) and the attenuation coefficient have a great influence on its performance. The gap between the lower and the upper bounds of the ergodic capacity is very small, and both of the bounds are much lower than that of the shannon bound, which is more consistent to the actual optical wireless transmission. Moreover, the outage probability reduces with the receiving radius of the receiver and the boresight error decreasing.(3) Taking advantage of high rate and the strong resistance to the high frequency selective fading of multicarrier modulation system, average bit error rate(BER) performance of an OWC system over M-turbulence channel employing direct current biased optical orthogonal frequency division multiplexing(DCO-OFDM) is analyzed. Considering that the signal of the OWC system restricted to be nonnegative, a direct current biased voltage is adding, and the nonlinear distortion of the direct current biased can be modeled as a fixed gain of the plus a random additive clipping noise. The results shows that the average BER is closely related to the average transmit power and the turbulence condition. Furthermore, the BER performance of the M-turbulence channel employing DCO-OFDM is improved by enhancing the direct current biased voltage to some extent.