Abstract:
Provided is a method of reducing power consumption of a base station. A method of operating a base station with low power consumption in a mobile communication system includes: reporting status information about a level of traffic being served by a base station in an active mode to an apparatus for managing power consumption of the base station; and switching from the active mode to an inactive mode in response to a mode change command from the apparatus.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2008-0128123, filed on Dec. 16, 2008, the disclosure of which is incorporated by reference in its entirety for all purposes. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The following description relates to a base station, and more particularly, to a technology for reducing power consumption of a base station. 
         [0004]    2. Description of the Related Art 
         [0005]    Generally, base stations consume power 24 hours a day, emitting heat and carbon dioxide. Therefore, high power consumption of base stations adversely affects the environment. 
       SUMMARY 
       [0006]    The following description relates to a method of reducing power consumption of a base station. 
         [0007]    According to an exemplary aspect, there is provided a method of operating a base station with low power consumption in a mobile communication system. The method includes: reporting status information about a level of traffic being served by a base station in an active mode to an apparatus for managing power consumption of the base station; and switching from the active mode to an inactive mode in response to a mode change command from the apparatus. 
         [0008]    The level of traffic is the number of call attempts made by user equipments (UEs) per unit time. 
         [0009]    The inactive mode is a discontinuous reception (DRX) mode. 
         [0010]    The base station is one of a home cell base station and a relay node. 
         [0011]    According to another exemplary aspect, there is provided a method of controlling power consumption of a base station using an external apparatus. The method includes: receiving information about a level of traffic being served by a base station; and controlling a power mode of the base station based on the received information. 
         [0012]    The controlling of the power mode includes: comparing the level of traffic with a predetermined threshold; and controlling the base station to operate in an active mode when the level of traffic is equal to or greater than the predetermined threshold and controlling the base station to operate in an inactive mode when the level of traffic is less than the predetermined threshold. 
         [0013]    The controlling of the power mode includes: comparing the level of traffic with first and second thresholds; and controlling the base station to operate in the active mode when the level of traffic is equal to or greater than the first threshold, controlling the base station to operate in the inactive mode when the level of traffic is less than the second threshold, and controlling the base station to hand a UE being served by the base station over to a nearby base station and then operate in the inactive mode when the level of traffic is equal to or greater than the second threshold and less than the first threshold. 
         [0014]    According to another exemplary aspect, there is provided a method of controlling power consumption of a base station using an external apparatus. The method includes: receiving information about a level of traffic being served by a base station from the base station in an active mode; comparing the level of traffic with a predetermined threshold; controlling the base station to operate in an inactive mode when the level of traffic is less than the predetermined threshold; monitoring the base station to detect call attempts to the base station in the inactive mode; and controlling the base station to operate in the active mode when the number of call attempts to the base station is equal to or greater than the predetermined threshold. 
         [0015]    According to another exemplary aspect, there is provided a method of controlling power consumption of a base station using an external apparatus. The method includes: receiving information about a level of traffic being served by a base station from the base station in an active mode; comparing the level of traffic with first and second thresholds; controlling the base station to operate in an inactive mode when the level of traffic is less than the second threshold and controlling the base station to hand a UE being served by the base station over to a nearby base station and then operate in the inactive mode when the level of traffic is equal to or greater than the second threshold and less than the first threshold; monitoring the base station to detect call attempts to the base station in the inactive mode; and controlling the base station to operate in the active mode when the number of call attempts to the base station is equal to or greater than the first threshold. 
         [0016]    Other objects, features and advantages will be apparent from the following description, the drawings, and the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention, and together with the description serve to explain aspects of the invention. 
           [0018]      FIG. 1  is a block diagram of a mobile communication access network; 
           [0019]      FIG. 2  illustrates a threshold of the number of call attempts made by user equipments (UEs) to a base station; 
           [0020]      FIG. 3  illustrates a discontinuous reception (DRX) cycle of a base station; 
           [0021]      FIG. 4  is a flowchart illustrating a process in which a network management server (NMS) determines the power mode of a base station; 
           [0022]      FIG. 5  is a flowchart illustrating a process in which a base station changes its power mode according to the measured level of traffic being served by the base station, under the control of an NMS; 
           [0023]      FIG. 6  illustrates a process in which a base station switches from a DRX mode to an active mode; and 
           [0024]      FIG. 7  is a flowchart illustrating a process in which a base station changes its power mode according to the measured level of traffic being served by the base station, under the control of an NMS. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    The above and other features and advantages of the present invention will become more apparent by describing exemplary embodiments thereof with reference to the attached drawings. Exemplary embodiments of the present invention will now be described in detail so that they can be readily understood and applied by those skilled in the art. 
         [0026]      FIG. 1  is a block diagram of a mobile communication access network. Referring to  FIG. 1 , the mobile communication access network consists of one or more home cell base stations (Home eNodeBs (HeNBs))  102 , a home gateway (HeNB GW)  103  which concentrates or distributes traffic of the HeNBs  102 , one or more multi-hop relay (MHR) nodes  104 , and one or more macro base stations (Macro eNodeBs (MeNBs))  105  which serve as mother stations of the MHR nodes  104 . 
         [0027]    A network management server (NMS)  107  controls and manages the operation of the mobile communication access network using a packet core network  106 . The NMS  107  operates and manages each of the HeNBs  102 , the HeNB GW  103 , the MHR nodes  104 , and the MeNBs  105 . In addition, the NMS  107  determines a power mode of a base station such as the HeNB  102  or the MHR node  104 . According to an embodiment, a base station has two power modes. One is an active mode, and the other is an inactive mode. In the active mode, the base station is powered on. In the inactive mode, the base station is in a sleeping state, that is, is powered off. According to an embodiment, the inactive mode may be a discontinuous reception (DRX) mode. 
         [0028]    A user equipment (UE)  101  can access the HeNBs  102 , the MHR nodes  104 , and the MeNBs  105  using a single model chip. When necessary, the UE  101  may include a modem chip needed to access a universal mobile telecommunication system (UMTS), a worldwide interoperability for microwave access (WiMAX), or the like. 
         [0029]      FIG. 2  illustrates a threshold of the number of call attempts made by UEs to a base station. 
         [0030]    Referring to  FIG. 2 , a base station compares a preset threshold with a measured level of traffic and determines its power mode. The threshold and the measured level may be defined as follows. 
         [0031]    {circle around (1)} A first threshold TH attempt (1) is an upper threshold of the number of call attempts made by UEs to a base station (MHR or HeNB) in a unit of time. 
         [0032]    {circle around (2)} A second threshold TH attempt (2) is a lower threshold of the number of call attempts made by UEs to a base station (MHR or HeNB) in a unit of time. 
         [0033]    {circle around (3)} A measured level N attempt  is the counted number of call attempts made by UEs to a base station (MHR or HeNB) in a unit of time. 
         [0034]    A base station operates in any one of the DRX mode and the active mode. When the following condition is satisfied, the base station operates in the DRX mode. 
         [0035]    Condition for DRX mode: N attempt &lt;TH attempt  (2). 
         [0036]      FIG. 3  illustrates a DRX cycle of a base station. Referring to  FIG. 3 , when the condition for the DRX mode is satisfied, a base station enters a DRX cycle. The DRX cycle is divided into an active period (On Duration) and a sleeping period (Opportunity for DRX) that are repeated. Specified signals are received or transmitted only in the active period. 
         [0037]    The base station monitors uplink signals in the active period to detect call attempts made by UEs to the base station. When detecting call attempts, the base station changes its power mode from the DRX mode to the active mode. 
         [0038]    Transmission timing information of an uplink signal is delivered to UEs using a system information block (SIB). The system information block (SIB) includes the cycle of a system to information block (a master information block (MIB), SIBx) transmitted from a small base station. The cycle of the SIB can be adjusted using the cycle of the system information block (MIB, SIBx) transmitted from the small base station. 
         [0039]    When an emergency call from a UE or a paging call of a network is detected, the base station quickly switches from the DRX mode to the active mode. To this end, the base station is continuously transmits a corresponding system information block (MIB, SIB 1 , SIB 2 , . . . , SIBn) and a reference signal to a UE. 
         [0040]      FIG. 4  is a flowchart illustrating a process in which the NMS  107  of  FIG. 1  determines the power mode of a base station. 
         [0041]    Referring to  FIG. 4 , the NMS  107  receives a status report from a base station (operation  401 ). The status report contains status information of traffic measured by the base station. The status information of traffic denotes information about a level of traffic served by the base station. The status information of traffic may be the measured level N attempt  mentioned earlier. The NMS  107  compares the measured level N attempt  with a threshold TH attempt  (operation  402 ). 
         [0042]    When the measured level N attempt  is equal to or less than the second threshold TH attempt  (2), the NMS  107  checks whether a power mode of the base station is in the active mode (operation  403 ). When the power mode of the base station is in the active mode, the NMS  107  commands the base station to switch from the active mode to the DRX mode (operation  406 ). 
         [0043]    When the measured level N attempt  is greater than the second threshold TH attempt  (2) and less than the first threshold TH attempt  (1), the NMS  107  checks whether there are any UEs communicating with the base station (operation  404 ). When a UE is found to be communicating with the base station, the NMS  107  commands the base station to forcibly hand the UE over to a nearby base station and then switch from the active mode to the DRX mode (operation  407 ). 
         [0044]    When the measured level N attempt  is equal to or greater than the first threshold TH attempt  (1), the NMS  107  checks whether the power mode of the base station is in the DRX mode (operation  405 ). When the power mode of the base station is in the DRX mode, the NMS  107  commands the base station to switch from the DRX mode to the active mode (operation  408 ). 
         [0045]    For convenience of implementation, the level of traffic served by a base station may be the number of outgoing calls or paging calls attempted by UEs. In addition, the second threshold TH attempt  (2), which is the number of call attempts per unit time, may be set to ‘zero.’ In addition, this may apply to a home cell base station (HeNB) which serves a small number of UEs. A communication system operator may select actual operating parameters for the threshold TH attempt  and the measured level N attempt  based on his or her system operation experience. When the first and second thresholds are set to the same value (the second threshold TH attempt  (2)=the first threshold TH attempt  (1)), operations  405  and  406  are omitted. 
         [0046]      FIG. 5  is a flowchart illustrating a process in which a base station changes its power mode according to the measured level of traffic being served by the base station, under the control of an NMS  504 . Referring to  FIG. 5 , an MHR node  501  is connected to the NMS  504  via a macro base station (MeNB)  502  and a packet core network (EPC)  503 . The MHR node  501  represents a small base station such as a home cell base station (HeNB). 
         [0047]    In the active mode, the MHR node  501  measures a level of traffic that it is serving and determines whether the measured level exceeds a predetermined threshold (operation  505 ). When the measured level exceeds the predetermined threshold, the MHR node  501  includes the measured level in a status report message and sends the status report message to the NMS  501  (operation  506 ). The NMS  504  receives the status report message from the MHR node  501  and compares the measured level with a predefined threshold to determine the power mode of the MHR node  501  (operation  507 ). The NMS  504  includes the determined power mode in a status command message and sends the status command message to the MHR node  501 . The MHR node  501  receives the status command message and switches from the active mode to the DRX mode (operation  508 ). 
         [0048]    The subsequent process is to reawaken the MHR node  501  in the DRX mode. There are two methods that can be used in this reawakening process. In a first method, the MeNB  502  measures the level of traffic of the MHR node  501  and sends the measured level to the NMS  504 . Then, the NMS  504  determines the power mode of the MHR node  501  and thus awakens the MHR node  501 . That is, the MeNB  502  monitors the status of the MHR node  501  under its jurisdiction and measures the level of newly generated traffic. When the measured level exceeds a predetermined threshold, the MeNB  502  sends a status report message containing the measured level to the NMS  504  (operations  509  and  510 ). Accordingly, the NMS  504  awakens the MHR node  501 , that is, commands the MHR node  501  to switch from the active mode to the DRX mode. 
         [0049]    In a second method, referring to  FIG. 6 , a MeNB  601  itself monitors uplink signals in a physical layer L1 and switches to the active mode when one or more call attempts by UEs is detected. The level of traffic is measured in a second layer (L2: media access control (MAC), radio link protocol (RLP), or packet data convergence protocol (PDCL)) of a base station, and a call attempt is detected in the physical layer L1. 
         [0050]    A communication service provider may select one of the above two methods in view of implementation complexity and system performance. In  FIG. 5 , if the base station is a home cell base station (HeNB) instead of the MHR node  501 , a home gateway (HeNB GW) plays the role of the MeNB  502 . 
         [0051]      FIG. 7  is a flowchart illustrating a process in which a base station changes its power mode under the control of an NMS  704  when the level of traffic being served by the base station is between the first threshold TH attempt (1) and the second threshold TH attempt (2). 
         [0052]    Referring to  FIG. 7 , the NMS  704  sends a status command message to an MHR node  701  to command the MHR node  701  to perform a handover operation and then switch to the DRX mode (operation  705 ). The status command message is delivered to the MHR node  701  via a packet core network (EPC)  703  and a macro base station (MeNB)  702  (operation  706 ). When receiving the status command message, the MHR node  701  identifies a UE that it is currently serving, hands the UE to a nearby base station, and then switches to the DRX mode (operation  707 ). The subsequent process is to reawaken the MHR node  701  in the DRX mode. This reawakening process is identical to that described above with reference to  FIG. 5 , and thus a detailed description thereof will be omitted. 
         [0053]    The process of  FIG. 7  is different from the process of  FIG. 5  in that the MHR node  701  hands a UE that it is serving over to a nearby base station. Here, the NMS  704  may select a target base station by comprehensively considering access network status parameters such as traffic load, billing level, interference level, and received signal level. In addition, the MHR node  701  may execute one of intra-radio access technology (RAT) handover (HO) and inter-RAT HO, according to radio environment and service characteristics. 
         [0054]    As apparent from the above description, a base station can operate in one of an active mode and a DRX mode according to the level of traffic that it is serving. Specifically, when no traffic is generated (e.g., at night), the base station changes its power mode from the active mode to the DRX mode. Thus, power consumption and carbon dioxide emission can be reduced, and interference between adjacent cells can be reduced. In particular, when the level of traffic being served by the base station is less than a predetermined level, the base station hands the traffic over to a nearby base station, thereby providing traffic concentration and improving efficiency of traffic operation. In addition, when no traffic is generated, the base station enters the DRX mode instead of being completely turned off. Thus, the base station can be normalized quickly (within about 100 ms), that is, can quickly change its power mode from the DRX mode to the active mode. The present invention is particularly effective when applied to a small base station such as a home cell base station (HeNB) or a relay node. 
         [0055]    While this invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The exemplary embodiments should be considered in a descriptive sense only and not for purposes of limitation. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention.