Research On Radio Resource Management In Heterogeneous Networks Based On LTE/LTE-Advanced

Nowadays, the various kinds of traffic demands in cellular networks are growing at an exponential rate. Therefore, some physical layer technologies including orthogonal frequency division multiplexing (OFDM) and multiple-input multiple-output have been introduced to satisfy these demands in Long Term Evolution (LTE) system and Long Term Evolution-Advanced (LTE-A) system. With deep research of the technologies, the spectral efficiency of a point-to-point link is approaching its fundamental limits, and the further improvement of cell gains is not easy to achieve. With the consideration of network layer, more macrocells can be deployed to attempt to achieve cell splitting gains, but the soulation may cause high inter-cell interference. Consequently, the3rd Generation Partnership Project proposed the heterogeneous networks (HetNets) based on LTE system and introduced three low-power base stations:Relay, Femto and Pico. In LTE cellular networks, macro station is used to provide basic coverage, and the small stations are used to enhance deep coverage of some particular scenarios, increase the system capacity and raise the user experience. Up to now,3GPP has done a great deal of work on small stations standardization.Moreover, it is particularly important to research radio resource management (RRM) of heterogeneous networks based on low-power base station deployment in order to get a substantial increase in the spectral efficiency per unit cell. For example, the selection of low-power node, subcarrier assignment, power allocation, inter-cell interference analysis and coordination should be considered in the heterogeneous networks. Obviously, resource allocation, interference analysis and management will be the two important parts of RRM, and algorithms of RRM need to constantly update the upgrade in order to adapt to new deployment scenarios and network architecture. The paper firstly introduces basic theory, key technologies and network architecture of LTE/LTE-A system. Further, the paper depicts some elementary knowledge of heterogeneous networks including network model and network technologies. At last, the radio resource management, including resource allocation and interference management, is studied and investigated in heterogeneous networks with Relay, Femto and Pico nodes. Some hot issues are well solved in this paper, such as, resource allocation of two-hop Relay system、cross-slot interference analysis of Time Division Duplexing (TDD) system、inter-cell interference coordination of Pico system.Our research points of the paper can be composed of following parts:Firstly, the paper studies the resource allocation problem in two-hop cooperative relaying cellular systems. Most existing works on resource allocation only considered some parts of all influential factors. Under power constraints and users’quality of serves (QoS) requirements, an optimization problem, including relay selection, power allocation, and subcarrier assignment, is formulated in the paper. In order to obtain the optimal solution of the problem, we utilize the mathematical tools to analyze the problem. Due to convex optimization features of the resource allocation problem, the optimal solution can be acquired only by adopting the exhausted search algorithm. In the paper, a suboptimal solution with sub-gradient method according to the Lagrangian formulation and dual problem is proposed. Simulation results prove that the new algorithm can achieve low outage probability and superior capacity performance with acceptable complexity. The method has very obvious practical significance.Secondly, the paper proposes a resource allocation scheme in a two-hop relay system. The scheme can provide more degrees of freedom due to dynamic frequency reuse. The resource allocation problem is divided into two sub-problems, and two corresponding sub-algorithms are proposed. The first sub-problem partitions all frequency blocks into two virtual groups which are called super group and regular group, respectively. The two groups without rigid boundaries are frequency resource sets which are allocated macrocell and relay cell. The second sub-algorithm focuses on the problem how to select relay node for every UE with suitable power and subcarrier. Numerical results show that our proposed scheme can achieve superior SINR performance and higher throughput.Thirdly, LTE TDD system allows for asymmetric uplink/dowlink (UL/DL) configuration and satisfies different UL/DL traffic demands by seven different semi-statically configured UL/DL configurations. Howerer, the interferences between UL and DL including base station-to-base station, UE-to-UE, and base station-to-UE interference need to be considered, when different cells configure different frame types. Particularly, the interference scenarios are more complex in heterogeneous networks based on Femto deployment. Therefor, the paper analyzes and evaluates cross-slot interference. Meanwhile, we give the advice about system coexistence in various deployment scenarios and frame configurations.Fourth, the cross-slot interference also should be analyzed and evaluated in heterogeneous networks based on Pico deployment. Especially, more complicated and serious interference occours due to the introduction of cell range extension (CRE) technology in Pico cell. Also, we give the advice about system coexistence in various deployment scenarios and frame configurations.Finally, the paper proposes an efficient inter-cell interference coordination scheme in co-channel scenario based on the above analysis of heterogeneous network. The basic idea is that only primary interfering sources of each scenario avoiding using the same resource used by interfered victim, and other interfering sources can reuse frequency resource. The proposed algorithm considers the primary interference factors relative to system performence. Therefor, the proposed ICIC scheme can achieve superior throughput performance, especially for cell edge user.