Research On Energy Harvesting And Edge Caching Based Transmission Technologies In Wireless Communication Networks

With the rapid development of emerging businesses and applications such as smart cities,augmented reality and so on,Internet of Things(IoT)and mobile Internet will become two main driving forces for the development of 5G.To address the energy shortage problem in IoT,wireless radio frequency(RF)energy transfer can power energy-constrained IoT nodes.Since wireless electromagnetic waves can simultaneously carry the electromagnetic energy and the information,the RF signal can further realize the simultaneous wireless information and power transfer(SWIPT).In SWIPT networks,how to design reasonable transmission strategy to achieve a trade-off between the rate and the energy is the key problem.Furthermore,in order to cope with the data traffic exploding problem in mobile Internet,the wireless edge caching technology can prestore hot contents in base stations(BSs)or user terminals.Then,during the service peak period,files requested by users can be directly served by neighboring users or BSs,which effectively alleviates the backhaul load,reduces the delay of the user acquiring the file and improves users' quality of experience(QoE).In wireless caching networks,how to design effective cache placement and transmission strategy is the key problem.Therefore,this thesis mainly investigates the transmission strategy design in SWIPT networks and the cache placement and transmission strategy in wireless edge caching networks.The main contents and contributions of this thesis are summarized as follows:1.Transceiver design in SWIPT networks with source-aided energy transferSince the wireless energy transfer results in the decrease of the wireless transmission rate,this thesis respectively studies the transmission strategy in full duplex(FD)and cooperative non-orthogonal multiple access(NOMA)based sender SWIPT networks,which can enhance the spectrum efficiency.Firstly,in the FD-SWIPT scenario,thanks to the FD technology,both the downlink and the uplink information secrecy can be guaranteed by the artificial noise(AN)sent by the FD-BS.The weighted sum of the uplink secrecy rate and the downlink secrecy rate is maximized by jointly designing the covariance matrices of transmit vector and AN vector,and the receiver vector of the FD-BS.Secondly,in the cooperative NOMA-SWIPT scenario,the wireless energy transfer can encourage the energy-limited strong user to relay the information of the weak user.Taking the minimum rate requirement of the weak user into account,the rate of the strong user is maximized by jointly optimizing the beamforming vector,the receiver vector and the power splitting factor.2.Transceiver design in SWIPT networks with destination-aided energy transferTo tackle the problem of insufficient energy supply for energy-limited relay nodes in cooperative networks,a destination-aided power transfer(DWPT)scheme is proposed and the corresponding transmission strategy is designed.Firstly,for a 3-node relay network,the destination node sends wireless energy to the relay node to enhance its energy collection.By optimizing the transmitter vector,the relay processing matrix and the receiver vector,the rate of the relay node is maximized while ensuring the minimum rate requirement of the source node.Secondly,in a 4-node cognitive cooperative network,the cognitive receiver and the primary receiver transfer the RF energy to the cognitive relay user.With the constraint of the minimum rate requirement of the primary user,the cognitive relay processing matrix,the cognitive beamforming vector and the power splitting factor are optimized to maximize the rate of the cognitive user.With the perfect channel state information(CSI),an optimal DWPT scheme and a low-complexity suboptimal DWPT scheme are designed.With the imperfect CSI,a robust beamforming design is given.3.QoE-driven cache placement and transmission strategy design in BS caching networksSince the quality of service(QoS)is used to evaluate the performance of video-dominant wireless caching networks and the updated frequency of the cache placement is much lower than that of the transmi ssion strategy,this thesis aims to maximize the weighted sum of user's QoE and formulates the joint optimization of cache placement and transmission strategy as a mixed-timescale problem.To solve this problem,the mixed-timescale problem is decoupled into two subproblems:the long-term cache placement problem and the short-term file transmission strategy problem.For the cache placement problem,based on the file popularity and the statistical channel information,both the centralized and distributed caching algorithms are proposed.For the file transmission strategy problem,with the given cache policy,the weighted sum of users' QoE is maximized by jointly optimizing the multicast precoding of multiple base stations.4.Mobility-aware cache placement design in D2D caching networksAs related researches neglect the large additional financial budget in D2D caching networks:the cache leasing cost of users,and the significant performance index:the file acquisition delay,this thesis designs the mobility-aware cache placement to minimize the transmission cost and the cache leasing cost,taking constraints of the file average delay and the user storage capacity into account.Firstly,based on the inter-contact user mobility model,the transmission cost,the cache leasing cost and the average delay of user obtaining requested files are derived.Then,the mobility-aware caching problem is formulated.To solve this problem,we investigate the special case where the file can be completely transmitted during one user contact,and the general case where the file needs to be transmitted via multiple user contacts.For the special case,a cache placement algorithm based on convex optimization theory is proposed.For the general case,a cache placement algorithm based on dynamic programming and a low-complexity cache placement policy based on the improved greedy algorithm are proposed.