Study On Coordination Of Interlayer In Heterogeneous Hierarchical Wireless Networks

The current wireless network is facing huge challenges and deep changes:mobile traffic growing fast,data services getting diverse,wireless environment becoming complex.To meet the demand of the next-generation network,5th generation wireless systems(5G)develop more rigorous performance metrics for wireless networks.To deal with the requirements of 5G,heterogeneous networks(HetNets),which are integration of a variety of access technologies,become a vital research topic.Studies on HetNets rise to the occasion.HetNets have many advantages.For examples,they can densify the network to offer higher traffic density,or offer massive connection and diverse services by multiple radio access technologies.However,existing literatures on HetNets usually focused on cellular network and lacked study of the integration between cellular network and other radio access technologies.Alternatively,although they had considered the coexistence of multiple access technologies,they studied each access technology in isolation and lack consideration of interlayer coordination.This thesis focuses on the coordination of interlayer in hierarchical HetNets and studies theories,strategies and schemes of coordination to optimize the overall performance of the network.The thesis is organized as "theory-technology and scheme-network architecture".The innovation and contribution of the thesis are fourfold.1.The dense deployment theory of hierarchical HetNetsFocusing on the two-tier HetNets consisting of macro base stations and small base stations,the thesis studies the relation between the rate of network and the density of base stations.Utilizing Poisson point process,the thesis models the large-scale random network and derives the probability density function(PDF)of the distance from the user to its serving base station,the association probability of each tier network,and the PDF of the interference inside the network.The thesis has derived the network rate as a function of the base station density and found the optimal base station density that can maximize the network rate.The result reveals that the network rate is not a monotonic function of base station density.Therefore,excessive pursuit of densification is not correct.2.Load-aware offloading strategy in HetNetsFocusing on the coexistence of cellular network and the access technologies working at unlicensed band,the thesis studies the coordination strategies of interlayer for data offloading.Unlike the existing literatures that only focused on link rate,the thesis has considered the influence of MAC protocol on channel throughput.This is very important to unlicensed band networks that work at contention-based channels.Combining Poisson point process with the Markov chain,the thesis proposes a method to derive the throughput of the contention-based channel in irregular random networks,and obtains the close-form solution of channel throughput.The thesis also finds the relation among throughput,transmit power,and base station density.Based on these results,the thesis designs load-aware offloading strategies for different conditions from perspectives of power control and base station deployment.The simulation results show the scheme can obtain great network performance gain and save resources.3.Mobile nodes assisted offloading scheme in HetNetsFocusing on the hybrid network of cellular base stations and vehicles that are able to communicate on metropolitan streets,the thesis studies the scheme utilizing vehicles to offload data from cellular base stations.Via field measurement data,the thesis reveals the uneven distribution of data traffic density along the metropolitan streets.To deal with the overload of the intersection cell,the thesis proposes a vehicle-assisted offloading scheme.The thesis combines the traffic flow theory with communication models,derives the relation between the volume of offloading and the scheme settings,and models the traffic at intersection well at the same time.Based on these results,the thesis obtains the optimal scheme settings.Besides,the thesis has designed the architecture to enable the scheme.The simulation results show the scheme can obtain great performance gain.4.Network architecture design enabling interlayer coordination of HetNetsSince the current networks are closed among different networks and rigid in management,they canot support the interlayer coordination of HetNets.Introducing the concept of wireless network virtualization,the thesis has designed a new network architecture to realize the interlayer coordination in HetNets.The Thesis has pointed out the content and difficulties of wireless network virtualization,introduced the idea of architecture design and designed the logical architecture and function architecture of virtualized wireless network.The architecture can break the physical barrier between networks and realize the flexible network management.