## 1 Introduction
The serial multi-hop relay is a multi-hop relay transmission mode, which includes amplify-and-forward (AF) transmission and decode-and-forward (DF) transmission [25; 26; 27; 28]. [PERSON] et al. [26] analyzed the performance of the multi-hop FSO communication system with AF relay and CSI assistance, and derived mathematical expressions of the end-to-end communication performance of the system under the Gamma-Gamma turbulence with pointing errors, such as the ABER and ergodic channel capacity. [PERSON] et al. [28] proposed and analyzed two novel serial multi-hop relay-assisted hybrid FSO/RF communication systems. The multi-hop parallel relay is a multi-hop cooperative diversity transmission mode [29; 30]. [PERSON] et al. [31] proposed a parallel multi-hop FSO communication system and derived the outage probability expression of the system under the Log-Normal turbulence environment. The simulation results show that the parallel multi-hop FSO communication system can significantly improve the communication performance compared with the serial or parallel relay scheme. [PERSON] et al. [32] deduced the mathematical expressions of the ABER and outage probability of the parallel multi-hop FSO communication system with the DF protocol and the Exponentiated Weibull (EW) turbulence. Furthermore, the effects of different turbulence intensity, receiver aperture size and different hops on the ABER performance of the system were further analyzed. Thus, motivated by the above mentioned facts and considering its military and disaster recovery applications, in this paper, we propose a new multi-hop parallel hybrid communication scheme combining the hybrid FSO/RF parallel transmission mode and the multi-hop parallel relay-aided communication mode--that is, the multi-hop parallel hybrid FSO/RF system. The hybrid FSO/RF parallel transmission mode has the advantages of both the large capacity of the FSO sub-link and the reliability of the RF sub-link. And the multi-hop parallel relay-aided communication mode has the advantages of wide coverage, long transmission distance and strong disaster recovery capability. Therefore, the multi-hop parallel hybrid FSO/RF communication system has better communication performance, higher reliability, wider coverage, longer transmission distance and stronger recovery capability. Then, the performance of the multi-hop parallel hybrid system is analyzed. The major contributions of our work are as follows:  
* We first propose a multi-hop parallel hybrid FSO/RF communication system. The communication system with this structure has not been reported in the existing literature. * The PDF and CDF of the output SNR of the parallel multi-hop hybrid system are derived with the DF protocol considered. The FSO sub-link experiences the Gamma-Gamma turbulence with pointing errors, and the RF sub-link suffers Nakagami-\(m\) fading channel. * Through the analysis of communication performance, the new expressions of the end-to-end ABER and outage performance of the multi-hop parallel hybrid FSO/RF system, the hybrid FSO/RF direct link and the FSO-only direct link are derived. * The effects of different modulation modes, different turbulence intensities, different pointing errors, different RF fading channels and different relay-aided structures on the performance of the multi-hop parallel hybrid system, the hybrid FSO/RF direct link and the FSO-only direct link are compared and analyzed. The remainder of the paper is structured as follows. In Section 2, the multi-hop parallel hybrid FSO/RF link system model is presented, and the statistical characteristics of the FSO sub-link, the RF sub-link, and the hybrid FSO/RF one-hop link are described. The end-to-end performance expressions of the multi-hop parallel hybrid system are derived in Section 3. Numerical results and discussions are provided in Section 4, and finally, our concluding remarks are summarized in Section 5.