Analysis of coherent-OFDM modulation for FSO communication over distribution with pointing errors

In this paper, we have analyzed a proposed coherent-orthogonal frequency division multiplexing (Co-OFDM) free space optical (FSO) communication system under  distribution channel model. The proposed Co-OFDM FSO system contains a heterodyne mixer at the receiver section, which is used to convert the optical frequency to radio frequency (RF). After that, a carrier recovery circuit is used and then a synchronization circuit is used to correct the timing and phase of the received signal. Here, we derived an ABER expression and outage probability expression for the Co-OFDM FSO communication system under  distribution channel model. We analyzed the results for different atmospheric turbulence (AT) conditions, pointing errors and the number of subcarriers. We have analyzed the system outage probability with varying received optical power and pointing error for different SNR thresholds and also analyzed for different AT conditions. In the results, we observed that the ABER performance improves as AT conditions improve, as the number of subcarriers decreases and as the pointing error decreases. Also, we observed that when AT conditions get worse, then to get same outage probability, we have to increase the SNR threshold. We have compared the Co-OFDM FSO system with popular modulation techniques PAM and PPM under  distribution channel model.

Automated summary

In this paper, a Coherent-Orthogonal Frequency Division Multiplexing (Co-OFDM) free space optical (FSO) communication system under  distribution channel model is analyzed. The system includes a heterodyne mixer to convert optical frequency to radio frequency at the receiver section. A carrier recovery circuit and a synchronization circuit are used to correct the timing and phase of the received signal. ABER expression and outage probability expression for the Co-OFDM FSO communication system are derived. The system performance is analyzed under different atmospheric turbulence (AT) conditions, pointing errors, and the number of subcarriers. It is observed that the ABER performance improves with better AT conditions, fewer subcarriers, and reduced pointing error. When AT conditions worsen, the SNR threshold needs to be increased to maintain the same outage probability. The Co-OFDM FSO system is compared with PAM and PPM modulation techniques under  distribution channel model.