Research On Inter-Cell Interference Cancellation And Resource Allocation Algorithm In OFDMA System

Wireless communication systems are expected to support a wider range of communication services such as voice, video and multimedia services and so on. However, in wireless communication environment, the channel's time variability and the deficiency of wireless resources, such as bandwidth and power have challenged reliable communications. The key of solving wireless communication bottleneck problem is to enhance efficiency of wireless frequency resource, that is, on the premise of meeting quality of service, we will do our utmost to improve spectral efficiency and system capacity. With the development of broadband cellular systems, WiMAX (Worldwide interoperability for Microwave Access) and LTE (Long Term Evolution) of 3GPP (3rd Generation Partnership Project) all choose OFDMA (Orthogonal Frequency Division Multiple Access) as access technology to provide high spectral efficiency. However, the efficient allocation for limited wireless resource to meet demand of users'diverse service faces many technical challenges, resource allocation is a matter of prime importance. On the one hand, inter-cell interference (ICI) in multi-cell OFDMA system is more serious than CDMA (Code Division Multiple Access). On the other hand, resource allocation needs special consideration due to OFDMA system property itself. Therefore, study of ICI in OFDMA system and high efficiency resource allocation algorithm to improve system spectral efficiency is an important research topic.Currently, study of resource allocation in OFDMA system mainly focuses on single cell and downlink, however, resource allocation in single cell can't be simply expanded to multi-cell, meanwhile, various resource allocation algorithms leave a lot to be improved in users'fairness in single cell. Base on the analysis of literature in China and abroad, resource allocation algorithm in OFDMA system is studied in this paper. Start with subcarrier collision in multi-cell, the paper focuses on reducing ICI to improve spectral efficiency, while solving resource allocation in OFDMA system. These efforts improve the efficient use of resources in OFDMA system, which has positive significance and reference value for allocating resource, ensuring fairness among users and reducing the complexity. Focusing on resource allocation in multi-cell OFDMA system, the paper mainly studies the following questions:Firstly, ICI cancellation in OFDMA system is studied. Considering resource allocation focused on single cell, while multi-cell resource allocation less studed in recent years, according to the feature of multi-cell, the interference due to collision caused by subcarrier allocation is studied. Then, based on the analysis of interference collision probability of subcarriers in multi-cell, the ICI cancellation algorithm is studied and verified by simulation. In addition, the impact of soft frequency reuse (SFR) on eliminating ICI and power allocation for users capacity in cell edge and center are analyzed, which lay groundwork for the proposed improved algorithm in the following.Secondly, dynamic ICI cancellation algorithm is study. According to adverse effects of ICI for OFDMA system, and taking into account the deficiency of other ICI cancellation algorithms, the maximum ratio combining (MRC) ICI cancellation algorithm based on SFR is proposed. The building process of base station cooperation (BSC) is firstly presented, which provides the possibilities to MRC.Then the neighbor cell edge users use the same subcarrier. When the load in the cell is low, SFR is adopted to reduce ICI. The MRC is used to improve the performance of users in cell edge while the load is very high. The proposed algorithm not only has low complexity but also take the use of the ICI to increase overall system spectral efficiency by improving the performance of users in cell edge.Thirdly, the low complexity resource allocation algorithm in OFDMA system is investigated. In view of the high complexity of the existing subcarrier and power allocation algorithms, the low complexity resource allocation algorithm is proposed. Considering fairness mechanism in the subcarrier allocation, the user selects the subcarrier with the highest channel gain, and the next subcarrier is allocated until all the users are allocated a subcarrier. Based on the above subcarrier allocation, we propose a new kind of hybrid power distribution (HPD) algorithm which adopts waterfilling power distribution reducing iterative times due to decrease sorting for channel gain in the cell edge and equal power distributed scheme without iterative operation in the cell center. Compared with the waterfilling power distributed scheme in the whole cell, the results show that the system complexity decreases significantly, meanwhile, its capacity is higher than that of equal power, especially for users in cell edge.Fourthly, reducing uplink channel quality information (CQI) feedback algorithm is studied. According to the features that uplink CQI feedback are high and not fair enough due to subcarrier allocation, the reducing feedback resource allocation algorithm is proposed. Users in the cell center with higher SNR don't need feedback CQI, and users in the cell edge with lower SNR adopt 1 bit feedback when the load is low while the Best-M is adopted when the load is heavy. Meanwhile, according to the above Best-M project, the first user preference is proposed. On the premise of ensuring the necessary feedback information of resource allocation, the proposed algorithm trades off between complexity and performance, and meets the users'fairness.