Spectrum Sharing Schemes In Cognitive Wireless Networks

Wireless spectrum is an important type of fundamental and strategic resources for the development of information society.With the development of wireless services,we have witnessed an exponential growth in the demands for spectrum resoUrces,which makes the spectrum scarcity a serious problem.To address this challenge,we need to find ways to optimize spectrum allocation and improve spectrum utilization.Spectrum sharing,which allows multiple users to share the same spectrum resources,has been considered as one of the most promising approach to resolve the spectrum crisis.Currently,spectrum sharing can be achieved via either interweave sharing manner or underlay/overlay sharing manner.The interweave spectrum sharing allows unlicensed users to access idle spectrum resources,whereas,the underlay/overlay spectrum sharing allows unlicensed users to access spectrum resources being occupied by incumbent users as long as the communication performance achieved by incumbent users is not influenced.In this thesis,both sharing manners have been thoroughly investigated.The main contributions are summarized as follows.(1)When spectrum bands are significantly underutilized,the spectrum owner could lease them to secondary service providers(SSPs)for a medium/long period to gain profits,and the key problem is how SSPs utilize these idle spectrum resources to effectively provide services for its users.To solve this problem,based on a mesh cognitive radio network architecture,we propose a service auction based spectrum usage scheme,which includes a network scheduling based winner determination mechanism as well as a charging mechanism satisfying the auction truthfulness property.The proposed scheme can not only provide users with specialized services but also fully exploit the value of idle spectrum resources.When compared with existing schemes,the service-oriented auction scheme can relieve users from the spectrum auction processes,reduce the conflict among different users in the auction processes,and improve spectrum utilization.(2)When the availability of spectrum resources is dynamic,how to dynamically obtain the spectrum access right from the spectrum owner according to the users' service requests turns to be the key problem for SSPs.To solve this problem,we investigate the dynamic spectrum trading between spectrum owners and SSPs and propose a spectrum market framework with a specific design on market components,trading flows,and spectrum usage management.Based on this framework,we further design the optimal spectrum trading strategy for the SSP under a specific communication scenario,to satisfy users' service requests,and develop a truthful multi-round combinatorial auction scheme for the spectrum market.By using this scheme,SSPs can obtain the right to use idle spectrum resources and meet the service requests from users,and spectrum owners can obtain high monetary reimbursements.(3)For the small-scale underlay spectrum sharing,in order to manage the mutual interference among different users,we investigate,from the perspective on physical layer,how to use the interference alignment scheme to realize the underlay spectrum sharing,and propose an antenna-selection based interference alignment scheme.This scheme can guarantee the communication performance of incumbent users and completely eliminate the interference received at the secondary users.During the scheme development,we consider the impact of imperfect channel state information(CSI)and design a robust CSI filtering algorithm as well as a discrete stochastic optimization based antenna selection algorithm to eliminate the impact of CSI estimation error and achieve the optimal antenna combination with a low computational complexity.(4)For the underlay spectrum sharing,we further investigate how to use power control approach to suppress the interference to incumbent users and optimize the performance of secondary users when multi-hop transmissions are involved.Specifically,we develop an optimal multi-hop transmission scheme to achieve the optimal end-to-end transmission rate,which jointly considers the power control on each node,the spectrum allocation on each link,and the end-to-end flow routing.In this scheme,we particularly consider a situation where the positions of incumbent users cannot be known accurately,and formulate the schematic design as a stochastic optimization problem where the distance between the incumbent user and the secondary user is modeled as a random variable.Then,the underlay spectrum sharing can be achieved as long as the received interference at incumbent users is less than a threshold with certain confidence level.