Performance Analysis And Application Of Cognitive Stop-and-Wait HARQ Driven By The User's Behavior

With the large-scale deployment and widespread application of 5G mobile systems,the demand for spectrum resources in mobile systems will increase significantly in the future,and the limited nature of spectrum resources will make the contradiction between supply and demand increasingly prominent.Adopting more advanced spectrum resource management methods is an important means to improve spectrum efficiency and relieve supply-demand conflicts in 5G mobile communication systems.Research shows that cognitive radio technology is one of the most promising technologies to solve such problems.The basic idea of this technology is to adjust adaptively communication parameters by learning the communication environment without interfering with the normal operation of the authorization system,so as to achieve highly reliable and low-latency communication.Therefore,it is necessary to design efficient and reliable data link layer protocol.In this paper,the performance of the cognitive stop-and-wait HARQ protocol is analyzed theoretically,and a cooperative transmission strategy is also designed based on this protocol.Firstly,the behavior of cognitive users occupying the licensed spectrum is modeled and analyzed,and corresponding mathematical models are established from the perspective of signal detection and data packet arrival rules of authorized users,respectively.For the former,the probability of cognitive users occupying the licensed spectrum when imperfect sensing is given by establishing a 4-state discrete Markov model.For the latter,an equivalent M/M/1/N queuing model is established to characterize the behavior of cognitive users occupying the licensed spectrum,and the probability of occupying licensed spectrum when imperfect sensing is also given.Secondly,an 8-state discrete Markov model,which comprehensively considers the actual state of the licensed spectrum,the cognitive user's sensing result,and the state of the cognitive data packet,is established to describe the state of the cognitive stop-and-wait HARQ in the single-pair cognitive user scenario.By solving the steady-state distribution of this model,the throughput and average packet delay expressions of the cognitive stop-and-wait HARQ protocol are given.At the same time,the upper bound of cognitive stop-and-wait HARQ protocol throughput is?1-p_e??(1-p_on)²by analyzing the components of the steady-state vector,where _ep is the average error probability and p_on is the steady-state probability that the authorized spectrum is in the"busy"state.By numerical simulation,the analysis found that the factors affecting the performance of the cognitive stop-and-wait HARQ protocol are the quality of the wireless channel,the sensing ability of the cognitive user,and the behavior of the authorized user.It is suggested to improve the throughput of the cognitive stop equation HARQ by improving the cognitive user sensing ability.Then,based on the equivalent M/M/1/N queuing model,combined with dual-threshold energy-sensing technology,the throughput,average packet delay,and average sensing delay of the cognitive stop-and-wait HARQ protocol are given under in a single-cluster cognitive scenario.In particular,the outage probability is used to approximate the average packet error probability,in order to analyze the influence of the communication distance between the cluster head and the cognitive users in the cluster on the performance of the protocol.Numerical simulation results show that the throughput decreases with increasing communication distance.It is suggested that the cognitive system can terminate data transmission when the communication distance is large.Finally,a collaborative strategy,which uses the behavior of authorized users as a trigger condition and two full-duplex cognitive base stations assist the authorized system to retransmit failed data packets,is proposed.This strategy perfectly integrates in-band full-duplex technology with cognitive radio technology.Compared with the traditional half-duplex relay mode,it can achieve the purpose of simultaneously improving the throughput of the cognitive system and the authorization system.At the same time,on the premise that independent non-homogeneous Nakagami-m fading channels are selected,closed expressions for the outages probability and throughput of the authorization system and the cognitive system are given,respectively.Through simulation verification,the factors affecting the performance of the strategy include self-interference suppression capability of full-duplex base stations and the behavior of authorized users and the number of full-duplex cognitive base stations.