Load Balancing And Resource Management For Small Cell Heterogeneous Networks

In recent years, rapid advance has taken place in internet, which greatly enriches our daily life. Meanwhile, this significant development in micro electronic technique, such as super-large-scale integration technology, makes our mobile devices more and more powerful. Now they are capable to offer all kinds of internet service to cater to our real-time service demands, including entertainment, work, communication etc. Therefore, mobile internet supported by mobile terminals is rising rapidly. As the traditional data service, consist of simple text and voice message, has transformed to comprehensive service, including text, voice, video etc, which have been a great challenge to the original cellular networks. To deal with the tremendous increase of data traffic, researches have paid great attention on how to take use of limit spectrum resource to realize high-quality data transmit. Small cell technology has been widely recognized as a potential solution to the problem above, and thus is treated as a key technique in future 5G communication system.It has been revealed in some researches that a large amount of network load arises from indoor environment. Therefore,3GPP deploys small base stations (SBSs) under the coverage of macro base stations (MBSs). On the one hand, SBSs shorten the transmit distances, and improve the quality of service (QoS). On the other hand, spectrum resource reuse in small cell networks is beneficial to improve the spectrum efficiency. Meanwhile, with wide development of SBSs, the coverage of the network can be greatly improved, as well as the QoS of the cell edge users. However, there are many new challenges left to be dealt with in small cell systems.In this paper, we first investigate the load balancing in backhaul constrained small cell net-works. Although SBSs can serve their nearby users, who originally connected to the MBSs, and offload for MBSs, the throughput of SBSs is constrained. On the development of each SBS, it will be allocated a dedicated backhaul link. Therefore, the capacity of the backhaul link limits the load of the SBS. In addition, consider the change of user distribution arising from user movement, it is important to design an adaptive load balancing mechanism. In this paper, we realize the load balancing by adaptively setting a bias value to the reference signal received power (RSRP) of each SBS. The utilization of the constrained backhaul link of SBSs is considered in case of resource waste or overload. Meanwhile, the call drop ratio of users also has influence on the bias value. By setting appropriate bias value for each SBS, our algorithm can efficiently make the SBSs offload for the MBS. In the meantime, a tradeoff can be achieved between the backhaul resource utilization and the call drop ratio of users.Secondly, we have studied the interference coordination in small cell networks. As the spec-trum resource is frequently reused among SBSs, complete interference exists among the network. In orthogonal frequency division multiplexing (OFDM) systems, the spectrum resource is divid-ed into many resource blocks from time and frequency dimensions. Then, these resource blocks are allocated to users. Therefore, by carefully optimizing the resource block allocation, we can decrease or avoid interference, and improve the transmit quality. In this paper, we are the first to propose a resource allocation mechanism, named 'allocate first, divide later', to realize interference coordination in small cell networks. In our method, the SBS will first allocate resource blocks ac-cording to SNR. Then, we take use of the Nash bargaining model to design a distributed algorithm to redivide those resource blocks with severe interference. Our method is the first one to let users make the decision to reallocate the resource blocks. According to the simulations, our method is proved to efficiently improve the QoS of users, as well as the spectrum efficiency.In the end, we investigate the resource allocation problem in LTE-U systems. Recently, LTE-U is widely recognized as a potential technique in future 5G communication systems, and has become a hotspot of the researches. In LTE-U systems, on the one hand, SBSs reuse the licensed bands to transmit signal, on the other hand, SBSs compete for the unlicensed bands of the WiFi system for their users to use. Therefore, it requires to jointly considering the licensed and unlicensed bands while optimizing resource allocation. On the licensed bands, as the spectrum resource is reused, a threshold is set to avoid severe interference. On the unlicensed bands, during channel competition, users in WiFi systems will experience more collision. Thus, the ratio that SBSs can occupy on the unlicensed bands is also limited in our method. In this paper, we design a joint licensed and unlicensed spectrum resource allocation by considering the interference on the licensed bands, as well as the channel compete collision on the unlicensed bands. We transform this problem into a convex optimization, and finally get the optimal policy.