Abstract
The coherent receiving method can improve the sensitivity of an optical signal receiver for free space optical communication system effectively. To implement coherent receiving, the phase offset between the local laser in the receiver and the received optical signal through the atmosphere needs to be measured and estimated. The commonly used algorithm is the Viterbi-Viterbi phase offset estimation method (VVPE) and this method always produces great errors especially with low SNR (signal to noise ratio). To improve the estimation performance, we present a new method combing the VVPE with the Kalman filter (VVPE-KF) to estimate the phase offset. This method can lower the estimation error by no less than 60%, when the SNR is low. To verify the performance of this new method, the constant parameter channel and atmosphere turbulence channel are employed to evaluate the algorithm. The impact of the atmosphere turbulence intensity on the tracking error is discussed.
Highlights
In an optical wireless communication system, the received optical signal is always weak as a result of the geometric loss, atmospheric absorption, and misalignment loss
Modulation information, information, and θθk isisthe phase offset between thethe space optical signal and and the local laser modulation the phase offset between space optical signal the local needing to be estimated
We present the simulation experience results of the Viterbi-Viterbi phase offset estimation method (VVPE)-KF and the VVPE-MF. In this we present the simulation experience results of the VVPE with the Kalman filter (VVPE-KF)
Summary
In an optical wireless communication system, the received optical signal is always weak as a result of the geometric loss, atmospheric absorption, and misalignment loss. In order to implement the coherent receiving, the phase offset and the frequency between the signal and the local laser need to be measured and estimated. The Viterbi-Viterbi phase estimation (VVPE) algorithm is the most commonly used method to measure the phase offset, and it has been demonstrated to be effective for coherent receiver within a certain range of SNR [16,17]. A new algorithm combining VVPE with the Kalman filter is presented for satellite-to-ground downlink. With both constant parameter channel and atmosphere turbulence channel, this new method can reduce phase offset estimation error greatly with low SNR. The performance of this new algorithm is less affected by the atmosphere turbulence than the traditional algorithm
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