In wireless communication systems, a signal propagates through a wireless environment, and in a case of a number of access points are deployed (e.g., base stations in a cellular network, Access Points (APs) in a Wireless Local Area Network (WLAN) system, etc.), then if the adjacent access points operate at the same frequency, then interference between adjacent cells will occur in the majority of the systems (e.g., an Orthogonal Frequency Division Multiplexing (OFDM) system, a Code Division Multiple Access (CDMA) system, etc.), so that spectrum resources may be underutilized, thus reducing transmission performance of the wireless systems.
Taking the OFDM system as an example, a Long Term Evolution (LTE) system is a 4th-Generation (4G) wireless communication system based upon the OFDM technology in which a base station allocates time-frequency resources over different sub-carriers for terminals to transmit service data signals without any interference between subscribers in a cell, but if different cells operate over the same frequency resource, then inter-cell interference will occur. Taking a Time Division-Long Term Evolution (TD-LTE) system as an example, uplink and downlink transmission in a cell in the TD-LTE system operates at the same frequency, thus making the problem of interference more pronounced.
There may be two categories of inter-cell interference (four types of inter-cell interference in total) in a multi-cell Time Division Duplex (TDD) network. The first category of inter-cell interference occurs in sub-frames with the same transmission direction in adjacent cells as illustrated in FIG. 1a and FIG. 1b, where interference to downlink reception at a User Equipment (UE) in the present cell due to downlink transmission from a base station in an adjacent cell is referred to type-1 interference; and interference to uplink reception at a base station in the present cell due to uplink transmission from a UE in the adjacent cell is referred to as type-2 interface. The first category of inter-cell interference occurs in both of the TDD and FDD systems, and is general adjacent-cell interference.
The second category of inter-cell interference occurs in sub-frames with different transmission directions in adjacent cells. As illustrated in FIG. 2, when there is concurrent transmission in a different direction in the adjacent cell, uplink reception at the base station in the current cell may be subject to interference from a downlink transmission signal of the base station in the adjacent cell, which is referred to as type-3 interference; and also downlink reception at the UE in the adjacent cell may be subject to interference from an uplink transmission signal of the UE in the present cell, which is referred to as type-4 interference. The second category of inter-cell interference may only occur in the TDD system, and particularly if uplink and downlink resources are configured flexibly for the adjacent TDD cell, then the second category of inter-cell interference will also be referred to as cross-timeslot interference in the TDD system.
In the technology of Inter-Cell interference Coordination (ICIC) in the existing LTE system, the base station and an adjacent base station exchange load indication and high-interference indication information of the adjacent base stations with each other, and interference is coordinated between the cells served by the base stations in a distributed coordination mode in such a way that if there is a high load and serious interference in the cell1, then center subscribers in the adjacent cell2 will access all the frequency resources in the cell, and less resources will be allocated for edge subscribers, or the edge subscribers will access a part of the resources, so that signals of the subscribers in the cell1 can be transmitted. However information in the ICIC technology in the LIE system is exchanged roughly, and the resources are not coordinated between the base stations in a real-time manner; and both existing simulations and applications have demonstrated that the effect of the ICIC technology may not be satisfactory for interference coordination between the cells to improve the capacity of the system.
At present, mobile communication become increasingly popular so that there are a dramatically increasing number of mobile subscribers, and an explosively growing demand for traffic of mobile services. In view of the development trend at present, traffic will be increased by a factor of 1000, the number of connected devices will be increased by 100, and there will be a peak rate of 10 Gbps, all of which are capacity demands as proposed for the 5G mobile communication system being studied. In order to satisfy these demands, inter-cell interference shall be minimized while the cells are deployed densely in the wireless communication systems to thereby guarantee the performance of the system.
If cells are deployed densely, then this scenario will be characterized in that there is a small radius of the cells, center subscribers may not be distinguished obviously from edge subscribers, and all the subscribers may suffer from inter-cell interference; the cells are deployed so densely that there is no a direct interface for all cells for signaling transmission and the cells are deployed so densely that there are a large number of cells involved in inter-cell interference coordination. The problem of inter-cell interference in the scenario where the cells are deployed densely may become more pronounced and serious than that in the macro network deployment scenario, and if signaling is exchanged in a distributed mode, then a large amount of signaling will be transmitted, thus overloading the inter-cell interfaces; and such a large number of nodes are involved that the effect of the distributed interference coordination algorithm may not be satisfactory.