Technologies of managing a transmission power of a base station in a wireless communication system are required for effective saving of energy in a communication system. Related to saving a transmission power, a technology of managing a transmission power of a base station (eNB: evolved Node B) by an EMS (Element Management System) is discussed in 3GPP TR 36.927.
1) No assistance: When increasing a user transmission power of a cell that is currently decreased because of an increase of a traffic load, it is not easy to know which cell transmission power should be increased. A method is discussed for increasing a transmission power by randomly selecting a specific cell from cells located adjacent to the cell whose traffic load is increased.
2) OAM (Operations, Administration and Maintenance) predefined “low-load periods” policies: When increasing a user transmission power of a cell that is currently decreased because of an increase of a traffic load, an EMS provides a “low-load period” counter value of cells whose transmission powers are decreased. A method is discussed for increasing a transmission power of the most appropriate cell with reference to “low-load period” counter values of each cell.
3) IoT (Internet of Things) measurements: When increasing a user transmission power of a cell that is currently decreased because of an increase of a traffic load, measurement of IoT is requested to adjacent cells. A method is discussed for increasing a transmission power of the most proper cell by using the measured IoT values of the adjacent cells.
4) UE (User Equipment) measurements: When increasing a user transmission power of a cell that is currently decreased because of an increase of a traffic load, transmission powers of adjacent cells are temporarily increased and transmission of a reference signal is requested. A method is discussed for increasing a transmission power of the most proper cell included in a measurement report if a terminal (UE) receives a reference signal and generates a measurement report.
5) Positioning information: When increasing a user transmission power of a cell that is currently decreased because of an increase of a traffic load, a method is discussed for increasing a transmission power of the most appropriate cell by combining a location of a terminal (UE), a location of a cell, and transmission power information of the cell.
However, the methods of managing a transmission power defined by 3GPP TR 36.927 has the following limitations. The no assistance method cannot give an optimal result because a cell is randomly selected to increase the transmission power. The OAM predefined “low-load periods” policies method cannot properly reflect the current radio wave situation because the EMS provides the “low-load period” counter provided by using a statistical value. Further, the IoT measurements method can select a cell that is not appropriate for an instantaneous value because the adjacent cells with a reduced transmission power measure and report the IoT only when requested. Further, the UE measurement method can generate an overhead because the measurement report is additionally set and received by a UE in a state of a cell having a high traffic load. Therefore, it is difficult to collect sufficient measurement reports for selecting an optimum cell. Further, the positioning information method can select an inappropriate cell because a big difference is generated between an actual radio wave environment and a radio wave environment modelled with transmission and reception locations of a radio wave.
Additionally, the method of identifying an increase or a decrease of a transmission power based on statistical data has the following problems. The statistical data must be newly collected because statistical characteristics change every time that a new cell is installed or an existing cell is uninstalled because of an increase/decrease of long-term user traffic. Therefore, the conventional method generates additional costs according to a change of the long-term user traffic because much time and high costs are required to collect reliable statistical data.
Further, additional costs are generated because new statistical data must be collected if a radio wave environment changes according to a change of a geographic feature due to construction of a new building or public works. If short-term user traffic increases greatly, the method based on statistical data cannot properly reflect the traffic change. If the transmission power is not increased promptly when the user traffic changes rapidly, the telecommunication quality experienced by a mobile communication user can deteriorate. Further, an optimum transmission power for the current situation cannot be provided because the statistical data is generated based on old information.
Related to prediction of a handover possibility, when a cell transmission power is decreased, a user receiving a service in a corresponding cell is handed over to an adjacent cell. However, if the adjacent cell cannot provide a radio wave intensity sufficient for enabling handover of the user, handover of the user may fail. With the technology currently defined by 3GPP TR 36.927, it is impossible to decrease the cell transmission power by predicting the success of handover.
Further, related to a throughput of a communication network, if a cell transmission power is increased, the transmission power of the corresponding cell may generate an interference to an adjacent cell. Accordingly, sometimes the total throughput of the communication network may not increase in accordance with the increase of cell transmission power. Therefore, with the technology currently defined by 3GPP TR 36.927, it is impossible to increase appropriately the cell transmission power by predicting a throughput improvement effect of a communication network.