Research On MAC Protocol Based On Indoor Visible Light Communication

Nowadays,with the rapid development of wireless communication technology,visible light communication(VLC)based on light-emitting-diode(LED)has attracted significant interests from both the industry and academia.Compared to the ever-popular radio-based wireless communication,VLC presents an alternate with potential for high bandwidth and data rates,high transmit power,high security,harmlessness to human body and minimal electromagnetic interference with RF systems.As the sub-layer of data link layer,the VLC system performance is largely affected by the MAC.Indeed,the MAC protocol defined in IEEE standard 802.15.7and various other MAC protocols only work in half-duplex and single-node mode,which has many restricts on the transmission efficiency and up-downlink rates.So it is an urgent problem needed to be solved to achieve the up-downlink and multiple nodes simultaneous transmission.In this thesis,we focus on the research of the above problems based on the characteristics of IEEE standard of the MAC protocol,the main work is as follows:In this paper,a novel full-duplex MAC protocol for VLC networks is proposed.Different from half-duplex operation,full-duplex operation allows concurrent sending and receiving of data frames between uplink and downlink.It can effectively mitigate the hidden terminal problem and improve fairness among all nodes.To increase the probability of full-duplex transmission,then further propose a self-adaptive minimum contention window(SACW)full-duplex MAC protocol that can significantly increase the probability of duplex operation.The key idea here is to allow the central node to monitor the data traffic in real-time,and control the channel access probability by changing the contention window adaptively.This way,the probability of a successful full-duplex transmission can be controlled and the downlink can achieve higher throughput if needed.The experimental study shows that the proposed MAC protocol can effectively mitigate channel collisions and achieves significantly higher system throughput.a spread-spectrum MAC protocol based on code division multiple access(CDMA)is proposed.Assign a unique code for each node by the CDMA technology,then each node encoded the data which they send by their unique code,this method enabling simultaneous transmission of the node and avoiding transmission interferencebetween nodes by transmit data to the correct receiver.Then with the spread-spectrum technology,extend the narrow-band data which is transmitted by the transmitter of the VLC system,and send it out after modulation.When the wide-band signal received by the receiver,we de-spread this signal to original narrow-band data by the same signal processing method,so as to realize visible light communication.Experimental study shows that this proposed MAC protocol can greatly improves bandwidth utilization,as well as the transmission efficiency and accuracy.