Research On Energy-efficient Strategy And System Performance Of Cooperative HARQ Mechanism In Distributed Wireless Networks

The rapid development of mobile communication technology promotes distributed wireless networks(DWNs),which do not rely too much on infrastructures through the use of mesh structures,have become one of the important network forms in the future mobile communication system.With the new green communication concept of energy conservation and environmental protection gradually enjoys popular support,it has become a research hotspot in the global communication field to satisfy the quality of service(QoS)of wireless users while pursuing a high-efficiency and low-energy communication environment.Cooperative hybrid automatic repeat request(HARQ)has been proved to be a promising error control technology for its outstanding ability in providing diversity gain and enhancing transmission reliability.Until now,there are still many challenges in the research and application of DWNs because of their complexity compared with traditional networks.Therefore,in the era of green communication,this dissertation,based on cooperative HARQ technology,studies,designs and improves the network strategies,which devote to save energy consumption and maintain other performance,of four popular DWNs: wireless sensor networks(WSNs),vehicular ad hoc networks(VANETs),flying ad hoc networks(FANETs)and IEEE 802.11 wireless local area networks(WLANs)with distributed coordination function(DCF),respectively.Moreover,the influence rule of various network parameters on system performance is analyzed and summarized in order to provide some theoretical references for the design and planning of the next generation mobile communication network.Specifically,the main contents of this dissertation are as follows:(1)Focusing on the poor anti-fading capability and energy constraint of WSNs,an improved energy-saving retransmission strategy is proposed based on a single-relay cooperative three-node system model.Six different HARQ protocols:(C-)HARQ-Type I,(C-)HARQ-CC and(C-)HARQ-IR are designed to investigate and compare the performance gain brought to the system by cooperative communication technology and different HARQ types.From the perspective of outage probability,the system throughput,energy efficiency and average transmission delay of the proposed retransmission strategy are quantitatively analyzed and their closed-form expressions under arbitrary maximum transmission number are derived based on Markovmathematical analysis method.The effectiveness of the proposed retransmission strategy in terms of energy conservation compared with other works and the pros and cons of the six HARQ protocols are verified and compared by numerical simulations.(2)Focusing on the node mobility and relay diversity in the VANETs based on hybrid vehicle communication(HVC)mode,four optimal relay selection schemes:Non-OR,SOR-AP,SOR-V and DOR-APV are proposed based on a more realistic dual-relay cooperative four-node system model,and the outage probability expressions of each communication link in the four schemes are calculated based on the HARQ-Type I.The closed-form expressions of system throughput and energy efficiency of the four schemes are derived by establishing a generalized two-dimensional discrete time Markov chain(DTMC)model and analyzing the one-step state transition probability and steady-state distribution of the four schemes,respectively.Finally,MATLAB numerical simulations compare and summarize the performance advantages and characteristics of the four optimal relay selection schemes,and provide some theoretical suggestions for the optimal relay selection of the future VANETs based on HVC mode.(3)Focusing on the high mobility and various positioning techniques of FANETs,an adaptive optimal relay number selection algorithm that can balance multiple system performance is designed based on a multi-relay cooperative(n+2)-node system model considering different distance information of relay nodes.After the outage probability expressions of all links in Nakagami-m fast fading channel are calculated by introducing the Meijer-G function,the binary functional expressions of system performance such as throughput,energy efficiency and the average transmission delay under arbitrary number of maximum transmission and cooperative relays are derived by establishing a three-dimensional DTMC model.Furthermore,a tradeoff factor called EDT is proposed to balance the three performance metrics and to determine the optimal number of relays.Finally,numerical experiments are conducted to prove the superiority of the proposed adaptive algorithm over its fixed relay number counterpart.(4)Focusing on the contention problem caused by multiple stations access channel in IEEE 802.11 WLANs under DCF,a cooperative media access control(C-MAC)protocol with soft combining HARQ,named as SPRCSMA(Super Persistent Carrier Sense Multiple Access)protocol,is proposed by modifying and improving the basic rules of traditional IEEE 802.11 MAC protocol.A two-dimensional DTMC model is established by introducing a special probabilityrepresenting the cooperation phase is completed “in advance”,and the closed-form expressions of system throughput,the average packet transmission delay and energy efficiency are obtained by solving the probability that a station transmits packet at any time slot.Six study cases are carried out to evaluate the impact of network parameters on system performance and to verify the performance advantage of SPRCSMA over other C-MAC protocols.