Interference Management Technology In Two-tier Macrocell-Femtocell Networks

Femtocell is a good solution to the shortcomings of the traditional Macrocell network indoor coverage,but with the widespread deployment of Femtocell,the cross-layer interference between the Macrocell network and the Femtocell network,and the interference in the same layer of Femtocell networks become increasingly apparent,which limits the upper limit of system performance in two-tier Macrocell-Femtocell network.Therefore,how to effectively suppress the interference in two-tier Macrocell-Femtocell network to improve the system performance is of great significance.Aiming at the interference problem,two improved algorithms are proposed in this thesis.To begin with,a joint algorithm associating the channel allocation method based on graph theory and the power controlling method based on path loss is proposed to solve the problem of cross-layer interference and common-layer interference in two-tier Macrocell-Femtocell networks.The algorithm is divided into three steps,Firstly,by using the knowledge of the graph theory,the interference map is constructed to carry out the channel allocation.And the orthogonal channel is adopted for interfering Femtocell to reduce the interference.Secondly,on the premise of guaranteeing the quality of the MUE and the HUE,the multiple SINR threshold and the Femtocell interference flags are set,and the corresponding interference level is set according to the channel quality.Thirdly,the corresponding power control is carred out according to the interference level,and reaching the ultimate goal of eliminating the cross-layer interference from the Femtocell to the macro user.The simulation results show that the proposed algorithm improves the signal-to-noise ratio as well as the throughput of the MUE and the HUE.Specifically,with ensuring the quality of service of the HUE and MUE,the HUE of the signal to noise ratio is well controlled between-6dB to 20 dB,which improves the overall system throughput.Besides,a two-tier of cooperative spectrum sensing algorithm based on optimal combining criterion is proposed to solve the cross-layer interference caused by spectrum sharing in the Macrocell-Femtocell network.The algorithm is divided into three steps,Firstly,by setting a double threshold,a specific implementation scheme of two layers spectrum sensing are given,and the detection probability and false alarm probability of two-tier are also deduced.Secondly,based on the difference of the reliability and the perceived results of cognitive Femtocell users,the weighted values of cognitive Femtocell users are deduced.Thirdly,the weighted results of all cognitive HUE are fused,and according to the judgment result,Femtocell selects the channel with less interference to reduce the interference.The simulation results show that the detection probability of each cognitive HUE of the proposed two-layer perceptual algorithm is higher than that of the traditional double threshold detection algorithm,and the optimal combination criterion can further improve the detection probability and anti-noise ability compared with the traditional fusion criterion in two-tier network.