Research On Interference Coordination Technology Based On Decision Theory In OFDMA System

In the multi-cell OFDMA system, inter-cell interference (ICI) is the main factor to limit the system performance. Because inter-cell interference coordination (ICIC) technique is easy to implement and has good ICI avoidance performance, ICIC becomes highly popular. This thesis studies ICIC technique based on Partially Observable Markov Decision Process (POMDP) theory, ICI is viewed as a collision between channels which are allocated to cell-edge users of neighbor cells, the overall system performance is determined by the collision probabilities and the impact of a given collision on the signal-to-interference-and-noise ratio (SINR) associated with the colliding channels, collision probabilities are reduced by making optimal POMDP decision. For different scenarios, this thesis proposes three kinds of ICIC models, which are the general POMDP model, the POMDP model under interval feedback and the Cen-POMDP model of multi-user. The solutions of these three models are also discussed in this thesis.First part is the general POMDP model, based on the statistic information of ICI from neighbor cell and the channel quality information feedback by cell-edge user, ICIC process is modeled as a POMDP problem, channels that can avoid ICI from neighbor cell are allocated to cell-edge users through make optimal decision in POMDP. A simple algorithm of POMDP model is suggested, and this part proposes a Monte Carlo sampling method to calculate the likelihood relation of SINR and ICI approximately.The second part discussed the model of POMDP-based ICIC under the condition that cell-edge users feedback channel quality information to base station periodically. For the case of with observation and without observation, we define the updated process of belief vector and the rule of making optimal decision in the model.The third part is the Centralized Partially Observable Markov Decision Process (Cen-POMDP) model of ICIC, which is designed for the case that there are many cell-edge users in one cell. Every cell-edge user submits the same POMDP model of ICIC, base station needs to develop a joint optimal strategy for all users in the cell based on every cell-edge user’s ICIC demand and features of the respective POMDP model, the channels allocated to every cell-edge user must be different. Finally, the solution of Cen-POMDP model is transformed into a integer programming problem with constraints. the POMDP model of ICIC makes use of statistic information of ICI from neighbor cell, so there is no need for base stations to cooperation, which saves the system overhead of inter-cell communication; in addition, every base station calculates the ICIC strategy distributed, which insures that the system structure is flat and simple. Simulation result indicates that the ICIC technique based on POMDP can reduce the collision probability of channels effectively, mitigate the SINR degradation that such collisions may cause, and improve the performance of cell-edge users.