Research On Networking And Resource Assignment Mechanism For Visible Light Communication

The development of high-speed broadband traffic and the explosive growth of data demand the high-speed and high-access wireless network.Moreover,the evolution of location based traffics makes the communication based on location information become important.Visible light communication(VLC)technology is considered as a promising candidate for indoor broadband communication due to the features of high capacity and integration capabilities for illumination and communication.However,the framework of indoor VLC networks that meet the needs of high capacity and the requirements of communication based on location information is a challenge.The dense cell VLC network can increase the network throughput,but the limited modulation bandwidth of on-the-shelf LED confines the capacity of VLC.The non-flat channel effect will degrade the quality of signals modulated on high frequency bands seriously,which limits the transmission rate and causes quality unfairness.Moreover,systematic communication scheme based on location information is still in its infancy.The accuracy of the location information will be degraded by the attenuation,which affects the processing procedure.In addition,inter-and intra-cell interferences in cellular networks decrease the quality of transmission and network throughput.The procedure of searching the optimized resources may lead to high complexity.To solve the issues above,this thesis discusses the dense cell network.The schemes in terms of multiple access and communication based on location information are designed.The resource assignment mechanism is also designed to improve the network throughput and decrease the complexity.The innovations are mainly:(1)Based on power-adaptive and multi-filter carrierless amplitude and phase modulation,a networking access scheme with fair quality and optimized capacity is proposed.In VLC networks,the limited modulation bandwidth of LED confines the amount of available resources,and the non-flat channel effect causes quality unfairness of signals modulated on different frequency bands.To improve the performance,the power adaptive and multi-filter carrierless amplitude and phase access(PA-MF-CAPA)scheme at MAC layer is designed.In PA-MF-CAPA,each filter resource in multi-dimensional CAP modulation is used by one user to access the network.Due to the overlapping spectrums of multiple filters,the network capacity is increased.To decrease the quality unfairness,a quadratic optimization model is designed to adapt the allocated power for signals modulated on different frequency bands.The experimental results show that the PA-MF-CAPA scheme increases the transmission rates compared to frequency division-based multi-band CAP access scheme,because the spectrums of multiple users using PA-MF-CAPA scheme is overlapping.The power adaptive procedure increases the transmitted power for users modulated on high frequency bands,which further improves the network throughput and also reduces the unfairness of quality.(2)A scheme to obtain accurate location information in location information-based communication network is proposed.To support the communication based on location information,this thesis designs the communication network based on location information.Moreover,to decrease the positioning error,the double-phased and correctional orthogonal frequency division multiplexing(OFDM)-based visible light positioning(DCO-VLP)scheme is proposed.In DCO-VLP,each OFDM subcarrier carries one positioning signal.The correctional method in DCO-VLP is conducted based on trilateration method.The mean square error of received signal strengths at the reference point and the actual received signal strengths is calculated.Thus,the impact of all received signals can be considered to improve the positioning accuracy.Under the condition of occlusion,the DCO-VLP scheme retransmits the positioning request to avoid the effect of the blocked LEDs.The simulation and experimental results show that the DCO-VLP scheme achieves better average positioning error than traditional trilateration method.When occlusion occurs,the DCO-VLP scheme avoids the effects of occlusion by sending requests again and thus decreases the average positioning error.(3)Based on decomposed layered graph and congestion game,a throughput optimized network resource assignment mechanism is proposed.In VLC network,the inter-cell interference degrades the network throughput,and the complexity for searching is high.Thus,this thesis designs the distributed congestion game and the layered graph decomposition-based best response dynamic(LGD-BRD)method.The utility function is set as the sum of signal to interference plus noise ratio of the current user and its potentially interferential users.The signal to interference plus noise ratio can be optimized by maximizing the utility function.In LGD-BRD method,the channel resources are classified by decomposing the layered graph,and users with their resources that will not cause inter-cell interference are partitioned into the same layer.At the same layer,all the users can be processed simultaneously.Thus,the number of combinations of resource assignment strategies is reduced,and the complexity is lowered.Based on the proposed congestion game,the simulation results show that the throughput of the LGD-BRD is lower than that of the BRD search method when the number of resource strategy increases.However,the search space by using the LGD-BRD method is reduced.Compared to the fractional frequency reuse method and nearest first method,the proposed resource allocation method improves the throughput.Thus,the proposed method can achieve balance between throughput and complexity.