Research On Resource Optimization Technology In Cognitive Femtocell Network

With the rapid growth of indoor mobile data service.Femtocell technology arises at the historic moment to improve indoor user communication quality and increase indoor wireless signal coverage area.However,the emergence of Femtocell network will cause cross layer interference to the traditional Macrocell network.And as the number of Femtocell users continues to increase,co-tier interference of system is becoming more and more serious.The scarcity of spectrum resources makes it harder to deal with interference.Thus the reasonable spectrum management technology has become a hot spot in the research.Power is also an important factor affecting the system performance and interference.High transmit power can increase throughput but cause large interference,however,low transmit power can not achieve significant data transmission rate.Therefore the power management technology is also a means to improve the performance of the system and reduce the interference.In view of the above two-layer Femtocell and Macro-cell networks,this paper focuses on the resource optimization technology in Femtocell networks.The main work and innovation of this paper are summarized as follows:(1)Research on spectrum resource allocation scheme based on the guaranteed interference threshold.For Femtocell network downlink scenario,this paper proposes a spectrum allocation scheme based on classical graph coloring algorithm and guaranteed interference threshold,which avoids serious co-tier interference between users.The scheme uses the classical graph coloring algorithm to build an interference graph to avoid occupying the same sub-channels by adjacent users.In order to improve spectrum utilization and improve system performance,this paper proposes a spectrum redistribution scheme based on graph coloring.In the first step of the spectrum allocation,fewer sub-channels are allocated to more users,and the same sub-channels can not be occupied by adjacent users.In the second step spectrum allocation process,the channel is allocated to the users with smaller interference based on the interference threshold.And in order to improve the fairness of the system,the users in a certain range of interference are given priority to choose sub-channel.The simulation results verify the performance of the proposed scheme.The simulation results show that the proposed scheme can improve the network throughput.increase the spectrum utilization and ensure the fairness of the system.(2)Research on the cognitive spectrum and power allocation scheme of Femtocell network.For the uplink of the two-layer Macro-cell and Femtocell network,this paper presents a joint spectrum and power allocation scheme with spectrum cognitive ability.It can select reasonable sub-channels for Femtocell users to ensure normal macro-cell access,manage transmission power,and improve system performance.In the aspect of sub-channel selection,we incorporates the Femtocell network with cognitive radio technology to flexibly o'ccupy Macrocell network idle channels and channels with low cross-layer interference.In combination with the classical graph coloring principle,spectrum resources are allocated reasonably.In this paper,spectrum and power management are modeled as a form mechanism for coalition formation game.Users can independently leave the current alliance or join the new alliance,based on the principle of increasing the throughput of the system and ensuring that the individual users are not damaged.By recursively organizing the core of the alliance,the final game will converge to the recursion core.In order to ensure the normal communication of the Macrocell,Femtocell user terminal transmits a data stream using M/M/1 queue model to prevent data congestion and delay of communication.The simulation results have shown that the proposed spectrum and power allocation scheme can improve the network throughput.Compared with other scheme,this scheme can maintain good performance in a user intensive scenario.