Visible light communication (VLC) can provide an ultra-large bandwidth of 400 THz without spectrum authorization while offering high energy efficiency and green energy conservation, thereby making it an important candidate communication technology for sixth-generation mobile communication networks. D2D communication can directly establish a data transmission link between devices, and such links do not require passage through a base station. The VLC-D2D communication pattern can solve the communication connection problems of blind spot devices caused by VLCs line-of-sight link blockage and short communication distances.

A device-relay incentive mechanism using simultaneous lightweight information and power transfer (DRIM-SLP) was proposed for indoor visible light communication (VLC) to meet the communication requirements of large-scale device access and blind devices in the six-generation mobile communication networks. A network resource bidding allocation mechanism was introduced, and individual, reasonable, and incentive-compatible blind spot device payments were adopted. Then, VLC AP system revenue, payment rules for relay device incentives, utility functions of relay devices, VLC APs, VLC-D2D system utility functions, and social utility evaluation methods were designed to prevent malicious devices from disrupting the relay bidding. Then, the Lagrangian duality method was used to optimize the power allocation and bidding prices of the VLC APs and relay devices to improve the utility value of the relay devices and VLC APs as well as maintain a favorable environment for VLC-D2D resource bidding and auctions.

We use the Monte Carlo method to verify the performance of the proposed DRIM-SLP in an indoor environment of 10 m×10 m×3 m by comparing it with the random selection mechanism (RSM), HAMCG, SGMPT, and SGMPS (Table 1). Sixteen VLC APs are uniformly distributed on the indoor ceiling at a distance of 2.5 m apart. One RF AP is placed at the center of the ceiling, and |J|=3 DRs are randomly located in the area where the light is obstructed and cannot access the VLC network.

In response to the D2D communication demand for VLC communication coverage blind spots, by considering the selfish behavior of candidate VLC relay devices, owing to their own energy limitations or external benefits damage, a SLIPT-assisted indoor VLC-D2D relay utility incentive mechanism is proposed in this study. We design a utility function that can encourage devices to adopt reasonable bidding prices to create a favorable bidding resource environment and realize the maximum utility of the VLC AP while balancing the increase in relay equipment utility with the improvement in social utility. With the development of the six-generation mobile communication applications, by fully considering the interests of communication equipment and operators as well as incentivizing more terminal devices to share and unload VLC AP tasks, D2D can achieve a communication method with a larger communication range coverage, which is of great significance for improving indoor communication quality.

1) As the proportion of selfish devices in the system increases, the blind spot device access success ratios of DRIM-SLP, SGMPS, SGMPT, and HAMCG with incentive mechanisms begin to decrease, whereas the proposed DRIM-SLP decreases slowly and reached its highest value with a proportion of selfish devices (Fig. 2).

2) As the number of devices increases, both the normalized device utility and the VLC AP utility slowly increase. For a given number of devices, the proposed DRIM-SLP achieves the highest normalized utility value. When the number of devices is 24, the proposed DRIM-SLP mechanism can improve the normalized utility of the VLC AP and relay device by 22.87% and 1.2%, respectively (Fig. 3).

3) When the unit price of information transmission provided by blind-spot devices increases, both the mean social utility value and the mean utility value of DRIM-SLP increase (Fig. 4). When the preference coefficient for energy collection increases, the mean social utility value, VLC AP utility value, and relay device utility obtained by the DRIM-SLP increase simultaneously (Fig. 5).