BER and outage probability of DPSK subcarrier intensity modulated free space optics in fully developed speckle.

In this paper a differential phase shift keying (DPSK) subcarrier intensity modulated (SIM) free space optical (FSO) link is considered in negative exponential atmospheric turbulence environment. To mitigate the scintillation effect, the selection combining spatial diversity scheme (SelC) is employed at the receiver. Bit error rate (BER) and outage probability (Pout) analysis are presented with and without the SelC spatial diversity. It is shown that at a BER of 10-6, a maximum diversity gain 25 dB is predicted. And about 60 dBm signal power is required to achieve an outage probability of 10-6, based on a threshold BER of 10-4

Coherent optical binary polarisation shift keying heterodyne system in the free-space optical turbulence channel

In this paper, analytical and simulation results for the bit error rate (BER) performance and fading penalty of a coherent optical binary polarization shift keying (2PolSK) heterodyne system adopted for a free space optical (FSO) communication link modeled as the log-normal and the negative exponential atmospheric turbulence channels are presented. The conditional and unconditional BER expressions are derived, demonstrating the comprehensive similarity between the 2PolSK and the binary frequency shift keying (2FSK) schemes with regards to the system sensitivity. The power penalty due to the non-ideal polarization beam splitter (PBS) is also analyzed. The receiver sensitivity employing 2PolSK is compared with other modulation schemes in the presence of turbulence and the phase noise. The results show that 2PolSK offers improved signal-to-noise ratio (SNR) performance compared to the binary amplitude shift keying (2ASK)

Performance Analysis of Different Modulation Techniques for Free-Space Optical Communication System

Free space optical system is a hot topic, which has gaining more and more attention. But,when the signal transmitted in the channel ,the performance could be severely degraded due to the atmosphere turbulent.The purpose of this paper is to find a most suitable modulation method for FSO system under FSO channel.The performance of power efficiencies,bandwidth efficiency,BER and SNR for the four modulation schemes have studied and compared in this paper include On-Off keying (OOK), Binary Phase Shift Keying(BPSK),Differential Phase Shift Keying(DPSK) and Quadrature Phase Shift Keying (QPSK) without atmospheric turbulence. Numerical   experiments show that BPSK and QPSK schemes are better compared to other schemes in BER performance and power requirements. When take intensity scintillation under Gamma-Gamma turbulence channel into consideration and the average BER is derived with Meijer-G function, BER performances of BPSK and QPSK scheme approximate the same .Compared with BPSK,BER performance for QPSK is 3dB lower .From the simulation results, modulation for BPSK is robust resist turbulence. As a result, BPSK scheme is suitable for free-space optical communication system