Research On Enhanced Interference Coordination Techniques In Hetnet Of LTE-Advanced

Wireless data traffic has been vastly growing in recent years. Since the traditional cellular network can not meet this growing need, LTE-A heterogeneous networks(HetNets) have been proposed to increase the radio spectrum efficiency. In a HetNet architecture, in addition to macro cells, low power node (LPN) stations can also be deployed in network, and they typically share the same frequency band as the macro cells. The performance of LPN can be severely affected by the high power macro cell. In order to solve the cross-tier interference problem, LTE standards support a time domain pattern for muting transmissions of macro, which is also called enhanced Intercell Interference Coordination (elCIC). In eICIC, the interference caused by a macro cell to LPN can be mitigated by having the macro cell reduce the transmission power of its subframes. These are known as Zero Power Almost Blank Subframes (ZP-ABS) during which there is no data transmission or Low Power Almost Blank Subframes (LP-ABS) during which the transmission power of the macro cells.Firstly, we consider a non-uniform 2-tier HetNets composed of pico cells and macro cells, where the number of pico cells under each macro cell is different. We coordinated use of ZP-ABS and LP-ABS, and allow different transmission powers for the macro cells on ABS. We formulate an optimization problem which aims to maximize the proportional fairness utility of the system. To maximize the proportional fairness utility of the system, in addition to finding the suitable transmission powers of each macro cell on LP-ABS, we also need to jointly consider the user association problem, i.e., which users should connect to the pico cells, resource allocation problem, i.e., how much resource should be assigned to each user associated with the cell, the ABS proportion, i.e., what percentage of subframes should be set to LP-ABS. We decouple the joint problem into four subproblems and iteratively solve each of them in an alternating manner. Simulation results show that for the non-uniform topology, our proposed algorithm improves the system throughput compared to both ZP-ABS and same transmission power of macro cells in LP-ABS. In addition, the algorithm guarantees user fairness and converges quickly.Next, we consider a new non-uniform HetNets where pico cells are located close to the center of the macro cells and the number of user equipment (UE) in each pico cell are different When the pico cell are located close to the center of the macro cells, the pico cell users are more susceptible to the interference from the macro cell, therefore the use of LP-ABS would be similar to ZP-ABS, since even a low strictly positive power during the LP-ABS would cause too much interference to the pico UEs. In order to solve the new problem, the resource blocks (RBs) during an ABS as those reserved for macro cell use exclusively and those reserved for pico cell use exclusively [1]. The percentage of RBs assigned to the pico cells is called the frequency band partition (FBP) parameter. In addition, we allow each macro cell to use different FBP parameters, as well as different powers during the LP-ABS. We formulate an optimization problem which aims to maximize the proportional fairness utility of the system, and jointly consider the user association problem, the resource allocation, the ABS proportion, the FBP parameter, and the transmission power of the macro cells on LP-ABS. We decouple the joint problem into five subproblems and iteratively solve each of them in an alternating manner. Simulation results show that for the non-uniform topology which pico cells located close to the center of the macro cells, and each pico has a different number of users, our proposed algorithm improves the system throughput compared to both ZP-ABS and LP-ABS. In addition, the algorithm guarantees user fairness and converges quickly.