Study On Link Quality Improvement Techniques Based On Cooperative Communication In Heterogeneous Networks

Recently,due to the continuous development and progress of wireless communication technology,mobile data services become more and more popular.The data show that more than 60% of voice services and 80% of the data traffic services have occurred in the indoor areas,while the traditional Macrocell network has a comparative advantage in terms of coverage,but there are obvious deficiencies in hot zone coverage such as indoor areas.Heterogeneous network is the solution to the above problems from the network architecture aspects,through the introduction of Femtocell to improve the quality of service and spectrum resource utilization of indoor users,but also,there are many problems such as cross-tier interference and frequent handover.Their existence will lead to excessive system drop rate,affecting the normal communication of Macrocell users adversely.Therefore,this paper uses cooperative communication technology to solve the above problems,and enhance the uplink and downlink communication quality of Macrocell users.The main research contents are as follows:Firstly,the reasons for the introduction and the development process of Femtocell are briefly described,and analyzing three access modes which user access to Femtocell access point and the importance of deploying Femtocell emphatically.Analyzing and comparing Amplify and Forward protocol and Decode and Forward protocol in detail,and the outage probability performance of Decode and Forward protocol is better than Amplify and Forward protocol from the simulation results.Meanwhile,the uplink and downlink system models of Femtocell/Macrocell heterogeneous network is constructed,and the link quality of Macrocell users is analyzed on the basis of system model.Then,the downlink of Macrocell user in heterogeneous network is studied.Downlink collaboration usually uses inter-base station collaboration which requiring a lot of shared informationin.In order to avoid this problem,the Femtocell user acts as the relay node and the cooperative communication between the macrocell base station and the Femtocell user is proposed in this paper.Simultaneously,in order to select a suitable relay node,a cooperative Femtocell user selection algorithm is proposed.The algorithm learns from the idea of soft handover,by introducing the duration and set the signal-to-noise threshold to select the appropriate relay nodes and build two relay sets: the relay candidate set and the relay selection set,and obtains a relay set which is stable performance and beneficial to the Macrocell user.The theoretical analysis and simulation results show that the cooperative scheme based on Femtocell user does improve the downlink bit error rate and throughput performance of the Macrocell user.Finally,the uplink of Macrocell user in heterogeneous network is studied.Due to the path loss between the Macrocell user in edge areas and the Macrocell base station is serious,resulting in the communication link between the Macrocell user in edge areas and the Macrocell base station is often interrupted.In order to solve this problem,the Femtocell access point acts as the relay node and the cooperative communication between the Femtocell access point and the Macrocell user is proposed in this paper,and the performance of Macrocell user was analyzed in two forwarding modes,which was Amplify and Forward and Decode and Forward.Moreover,in the manner of Decode and Forward is also analyzed two cases: one is to consider the Femtocell user is idle;the other is to consider Femtocell user is in communication.Then,the uplink performance of Macrocell user is simulated,and the results show that the cooperative scheme based on Femtocell access point is significantly superior to the direct transmission in terms of the uplink outage probability and bit error rate performance of Macrocell users.