# A Hybrid Handover Scheme for Vehicular VLC/RF Communication Networks
###### Abstract  
Visible light communication (VLC) is a promising complementary technology to its radio frequency (RF) counterpart to satisfy the high quality-of-service (QoS) requirements of intelligent vehicular communications by reusing LED street lights. In this paper, a hybrid handover scheme for vehicular VLC/RF communication networks is proposed to balance QoS and handover costs by considering the vertical handover and horizontal handover together judging from the mobile state of the vehicle. A Markov decision process (MDP) is formulated to describe this hybrid handover problem, with a cost function balancing the handover consumption, delay, and reliability. A value iteration algorithm was applied to solve the optimal handover policy. The simulation results demonstrated the performance of the proposed hybrid handover scheme in comparison to other benchmark schemes. e 20242432 202424323 202424  
(RSSI) as a metric was evaluated in [4]. For properly supporting a high level of mobility, an HHO technique was studied based on the interference-to-noise ratio and interference-to-interference ratio in vehicular visible light networks [2]. A distance-based HHO procedure was proposed for a vehicle-to-infrastructure (V2I) VLC system, to maximize the signal quality subject to a predetermined missing handover rate constraint [5]. A novel architecture using a multipath-transmission control protocol was optimized to improve the handover performance in terms of network outage duration in vehicular VLC networks [6]. A dynamic soft handover algorithm based on coordinated multipoint (CoMP) transmission was investigated in [7; 8], which could maintain a stable signal quality regardless of vehicle velocity. A coordinated scheduling solution with a soft handover technique was offered to increase the achievable throughput and link reliability for VLC networks in [1]. Moreover, ref. [9] presented a two-tier LiFi network and analyzed the closed-form expressions of the received optical signal intensity, time-to-trigger, and user mobility for the cross-tier handover rate between primary and secondary cells. There have been several works investigating the VHO strategy for heterogeneous VLC/RF networks, because VHO is a process that can deal with the interruption of VLC links [10]. An MDP-based VHO scheme was investigated to balance the switching costs and the delay requirements of indoor VLC-RF systems in [11]. Considering load balancing, a two-way selection handover scheme was proposed to improve the overall system performance [12]. A fuzzy-logic (FL)-based decision-making VHO algorithm was proposed for radio frequency and optical wireless (RF/OW) systems, which was capable of providing better QoS to users in terms of packet transfer delay [3]. A load balancing scheme aiming at improving the user QoS was realized by soft handover in hybrid VLC/WiFi networks [13]. A flexible and holistic self-optimizing algorithm was proposed for highly mobile scenarios, which was able to control the handover parameters of all VLC APs under the coverage of the LTE eNodeB based on the Q-learning approach in [14]. The VHO threshold was derived based on an exact mathematical modeling of a vehicular VLC platoon in [15]. Among the above vertical handover solutions, the MDP-based method has been widely used in the handover strategies of heterogeneous networks [16; 17; 18; 19; 20]. A new efficient handover decision algorithm based on an MDP was proposed to optimize the overall service experience of users in millimeter wave heterogeneous networks in 5G cellular systems in [16]. Ref. [17] presented a novel energy-efficient and delay-aware handover decision policy based on an MDP for a macro-femo cell wireless network. For hybrid WiFi and infrared uplink transmission, a link switching scheme was presented based on an MDP, with the objective of minimizing the transfer delay of data [19].