Secrecy Rate of MISO Optical Wireless Scattering Communications

We consider the secrecy rate for the multiple-input single-output optical wireless scattering communication, where the detected signal can be characterized by discrete photoelectrons. Assuming a legitimate receiver and an eavesdropper, we propose two secure communication protocols, the non-jamming protocol, and the cooperative jamming protocol, where for the former the transmitter does not send jamming signals but for the latter the transmitter sends jamming signals. We formulate the corresponding power and duty cycle optimization problems for both protocols. We also analyze the properties on the optimal solution, and adopt the alternating optimization to obtain a tractable solution. Moreover, we analyze the condition on the positive secrecy rate for the case where all the sub-channels to the receiver are weaker than their counterparts to the eavesdropper, where the secrecy transmission cannot be realized via a non-jamming protocol. The performance of the proposed two protocols is evaluated by numerical results. It is seen that for the iterative optimization solution, two to three iterations suffice for the convergence of the secrecy rate.