Research Of Cooperative Transmission Methods For Multi-Source Single-Destination Networks With Energy Harvesting

The rapid development of wireless communication technology places higher demands on battery lifetime and transmission reliability for wireless devices.On the one hand,radio frequency energy harvesting technology,an emerging energy harvesting strategy,can solve the problem of difficult energy supply and prolong the battery lifetime of wireless devices prominently in low-power communication systems.On the other hand,Cooperative communication is an effective method to combat signal fading and improve transmission reliability in wireless communication process by forming a virtual MIMO system among users.Cooperative transmission technology based on radio frequency energy harvesting inherits the advantages of the above two methods,which has recently received widely attention by researchers.Multi-source single-destination networks are the typical application scenarios for this technology.For example,several sensor nodes cooperatively send collected data to the sink node by wireless transmission technology is common in the energy constrained wireless sensor networks.Although some preliminary researches on this technology have been conducted in multi-source single-destination networks,the existing relay selection methods have a common problem of narrow selection range,and no work in the open literature has considered the jointly optimization with other low-overhead mechanisms,such as packet aggregation technology.This thesis focuses on the investigation of cooperative transmission methods in multi-relay scenarios for energy constrained multi-source single-destination networks.The main works are as follows:1.For the multi-source single-destination networks with radio frequency energy harvesting,considering the destination node transmit information and energy simultaneously in the downlink,a source-based selection cooperation method in the uplink is proposed.This method can overcome the limitation that only one best relay available in conventional cooperation strategies by combining selection cooperation scheme and feedback mechanism reasonably.Instead of choosing the relay node with the maximum relay-destination channel as the unique best relay,any relay node is capable to be the best relay if it has enough energy and correctly decodes the information from the source node and the feedback frames from the destination node.Besides,we optimize the energy usage modes at relay nodes by limiting them forward source message at the lowest power required for reliable cooperation,rather than at full power.As a result,the proposed method expands the range of relay selection and improves node utilization rate.Furthermore,based on the proposed method,this thesis also develops best relay selection algorithms for both centralized and distributed scenarios,which improve the transmission performance.2.For the multi-source single-destination networks which support aggregation and de-aggregation,a source-based aggregation cooperative transmission approach is investigated.By using packet aggregation technology,the approach does not require dedicated cooperative transmission slots for retransmissions,each source node cooperatively forwards packets overheard from other nodes in the form of aggregation at its assigned time slot.So it is significantly efficient in achieving gains in both spectral efficiency and energy efficiency.Besides,this thesis also proposes packet selection algorithms,which improve transmission reliability.3.The proposed cooperative transmission methods for multi-source single-destination networks with radio frequency energy harvesting are simulated.Also,this thesis analyzes the performance of proposed relay selection strategies.The simulation results show that the proposed cooperative transmission approaches improve transmission reliability obviously,and performance gain in spectral efficiency can be further achieved when jointly optimization with packet aggregation mechanism.The work in this thesis has reference value for applying cooperative transmission technology based on radio frequency energy harvesting in wireless networks.