Patent Publication Number: US-2012039238-A1

Title: Method for saving power of wireless communication system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/303,728, filed on Feb. 12, 2010 and entitled “Methods and Apparatuses for Network Energy Saving in Wireless Communication Systems”, the contents of which are incorporated herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to wireless communication systems, and more particularly, to network energy saving for wireless communication systems. 
     2. Description of the Prior Art 
     Conventional wireless communication systems, such as the global system for mobile communications (GSM), third generation partnership project (3GPP) universal mobile telecommunications system (UMTS)/high speed packet access (HSPA) system, 3GPP long term evolution (LTE)/LTE-Advanced system, and worldwide interoperability for microwave access (WiMAX) system, are deployed with a set of base stations in serving areas. These base stations radiate system signals to cover serving areas and usually provide service continuity with mobility throughout their serving areas. In order to provide these services, base stations consume large power to radiate system signals within nominal coverage areas all the time. However, users do not always access wireless systems for 24 hours a day. Part of power radiation from base stations is obviously wasted while only few or even no user is accessing systems. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method for saving power of a wireless communication system. The method comprises turning off a first frequency bandwidth unit of a first frequency band of the wireless communication system according to a predetermined condition, comprising turning off the first frequency bandwidth unit within a serving area according to the predetermined condition; wherein the serving area is covered by at least one cell, and a base station is located in the cell; wherein the predetermined condition is that amount of mobile stations within the serving area is lower than a predetermined number; wherein the first frequency band comprises a plurality of frequency bandwidth units including the first frequency bandwidth unit. 
     The present invention further provides a method for saving power of a wireless communication system. The method comprises turning off a first radio covered space unit of the wireless communication system according to a predetermined condition; wherein a base station is located at the first radio covered space unit; wherein the predetermined condition is that no mobile station is present in the first radio covered space unit. 
     The present invention further provides a device for saving power of a wireless communication system. The device comprises means for turning off a first frequency bandwidth unit of a first frequency band of the wireless communication system according to a predetermined condition; wherein the first frequency band comprises a plurality of frequency bandwidth units including the first frequency bandwidth unit. 
     The present invention further provides a device for saving power of a wireless communication system. The device comprises means for adjusting radiation power of a base station of the wireless communication system according to a predetermined condition; wherein the predetermined condition is locations of mobile stations. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flowchart illustrating a power-saving process for a wireless communication system on frequency domain of the present invention. 
         FIG. 2  is a diagram illustrating a first embodiment of the present invention. 
         FIG. 3  is a diagram illustrating a second embodiment of the present invention. 
         FIG. 4  is a diagram illustrating a third embodiment of the present invention. 
         FIG. 5  is a flowchart illustrating a power-saving process for a wireless communication system on space domain of the present invention. 
         FIG. 6  is a diagram illustrating a fourth embodiment of the present invention. 
         FIG. 7  is a diagram illustrating a fifth embodiment of the present invention. 
         FIG. 8  is a flowchart illustrating a power-saving process for a wireless communication system on space domain of the present invention. 
         FIG. 9  is a diagram illustrating a sixth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides methods for saving network energy by turning off some cells/carriers of the wireless communication system according to various criteria. Furthermore, the present invention also provides methods for handling handovers for the wireless communication systems adopting the power-saving schemes of the present invention. 
     In the following description, the term “mobile station” (MS) and “base station” (BS) can be interpreted differently depending on the wireless communication system applied. For example, in LTE system, the mobile station means the user equipment and the base station means the evolved node B (eNB); in WiMAX system, the mobile station means the user computer and the base station means the access point (AP). Additionally, the term “serving area” can be interpreted as the area one BS serves, or an area that is overlapped by several cells, or, as a whole, the wireless communication system serves. 
     Please refer to  FIG. 1 .  FIG. 1  is a flowchart illustrating a power-saving process  1000  for a wireless communication system on frequency domain of the present invention. The process  1000  comprises the following steps: 
     Step  1010 : Start; 
     Step  1020 : Turn off at least one frequency bandwidth unit of a wireless communication system according to a predetermined condition for a serving area; 
     Step  1030 : End. 
     In step  1020 , one frequency bandwidth unit can be interpreted as a carrier of one frequency band. For example, the frequency band is at 900 MHz, and the frequency bandwidth unit is set to be 20 MHz, so that in the frequency band of 900 MHz, a carrier can be 900 MHz and another carrier can be 920 MHz. The predetermined condition can be: within the serving area of a wireless communication system/BS(s), the amount of active MS is less than a predetermined number. For example, the predetermined number is 5, and if within the serving area, the amount of the MS is 10, any of carriers of the wireless communication system is not turned off; if within the serving area, the amount of the MSs is 4, at least one of the carriers of the wireless communication system can be turned off. 
     Please refer to  FIG. 2 .  FIG. 2  is a diagram illustrating a first embodiment according to the power-saving process  1000  on frequency domain of the present invention. As shown in  FIG. 2 , a wireless communication system  1  deploys multiple carriers  12 ,  14 ,  102 ,  104 , and  106  on frequency bands  10 , and  100 . In the frequency band  10 , there are two carriers  12  and  14  used to offer system services over the serving area  11 . In the frequency band  100 , there are three carriers  102 ,  104 , and  106  used to offer system services over the serving area  11 . The system coverage of the carrier  12  consists of multiple cells and each cell is similar to the cell  18 . It is assumed that a BS is located within a cell and the BS radiates system signals with suitable power to provide coverage of the cell, which may be the serving area  11 . Coverage areas of other carriers  14 ,  102 ,  104 , and  106  are also formed in similar way. 
     When system load of the wireless communication system  1 /the BS(s) is normal or high, e.g. the amount of MSs (within the serving area  11 ) is higher than a predetermined number, the carriers  12 ,  14 ,  102 ,  104 , and  106  are supposed to be turned on and provide services to MSs. When system load of the wireless communication system  1 /the BS(s) is not high or whenever it is possible to handle user services by less carriers, e.g. the amount of MSs (within the serving area  11 ) is lower than the predetermined number, the wireless communication system  1 /the BS(s) can initiate a power-saving process such as the power-saving process  1000 , and turns off at least one of the carriers. Consequently, for active and camped MSs, they can be handed over or cell re-selected on to other carriers which are kept on transmitting system signals. In other words, if an active MS is camped on a carrier and the carrier is about to be turned off by the wireless communication system  1 /the BS(s), then the active MS can camp on to another carrier which will not be turned off by wireless communication system  1 /the BS(s). In this way, after some carriers are empty of MSs (no MS present), transmission of system signals on these carriers can be turned off and power consumption (of the wireless communication system  1 /the BS(s)) will be saved accordingly. 
     An extension from the first embodiment of the present invention in  FIG. 2  is to keep at least one carrier turning on in each frequency band, e.g. frequency band  10  or  100 , since there might be a new MS powered on and will scan on one of frequency bands  10  and  100 . Keeping at least one carrier turning on in each frequency band can provide few impact to MS camp-on performance. In  FIG. 2 , within frequency band  10 , the carrier  12  is decided to be always turned on, and thus the carrier  14  can be decided to be selectively turned off to save power according to the predetermined condition. Within frequency band  100 , the carrier  102  is decided to be always turned on, and thus the carriers  104  and  106  can be decided to be selectively turned off to save power according to the predetermined condition. In both frequency bands  10  and  100 , there are still at least carriers  12  and  102  respectively always kept on to serve active/idle MS and/or new camp-on MS. 
     Additionally, still referring to  FIG. 2 , the frequency bands  10  and  100  can be, for example, 450 MHz, 700 MHz, 900 MHz, 1800 MHz, or 2.0 GHz, etc. The carriers  12  and  14  are carriers at around the range of the frequency band. For example in case the frequency band  10  is at 900 MHz, the carrier  12  can be 900 MHz and the carrier  14  can be 920 MHz. The bandwidth of both carriers can be 20 MHz, or 10 MHz, etc. There is no restriction to their bandwidth sizes. In  FIG. 2 , the number of frequency bands can be from one to any number larger than one. There can be one or multiple carries deployed in frequency bands independently. The selected carrier(s)  12  can be one or even more than one. For example, if there is a need, the carriers  102  and  104  can be further decided to be always turned on for providing services or enhancing transmission quality, and the carrier  106  can be decided to be selectively turned off for saving power according to the predetermined condition. 
     Please refer to  FIG. 3 .  FIG. 3  is a diagram illustrating a second embodiment according to the power-saving process  1000  on frequency domain of the present invention. As shown in  FIG. 3 , a wireless communication system  2  deploys carriers  22 ,  202 ,  204 , and  222  on frequency bands  20 ,  200 , and  220 , and there are MSs  242 ,  244 , and  246  present in the serving area  21 . In the frequency band  20 , there is one carrier  22  used to offer system services over a serving area  21 . In the frequency band  200 , there are two carriers  202  and  204  used to offer system services over the serving area  21 . In the frequency band  220 , there is one carrier  222  used to offer system services over the serving area  21 . The system coverage of the carrier  22  consists of multiple cells and each cell is similar to the cell  28 . There is assumed a BS located within a cell and the BS radiates system signals with suitable power to provide coverage of the cell. Coverage areas of other carriers  202 ,  204  and  222  are also formed in a similar way. 
     When system load of the wireless communication system  2 /the BS(s) is normal or high, e.g. the amount of MSs (within the serving area  21 ) is higher than a predetermined number, the carriers  22 ,  202 ,  204 , and  222  are supposed to be turned on and provide services to the MSs. When system load of the wireless communication system  2 /the BS(s) is not high or whenever it is possible to handle user services by less carriers, e.g. the amount of MS (within the serving area  21 ) is lower than the predetermined number, the wireless communication system  2 /the BS(s) can initiate a power-saving process such as the power-saving process  1000  to turn off several carriers. For active and camped MSs, they can be handed over or cell re-selected on to other carriers which are kept on transmitting system signals. In other words, if an active MS is camped on a carrier and the carrier is about to be turned off by the wireless communication system  2 /the BS(s), then the active MS can camp on to another carrier which will not be turned off by wireless communication system  2 /the BS(s). In this way, after some carriers are empty of MSs (no MS present), transmission of system signals on these carriers can be turned off and power consumption (of the wireless communication system  2 /the BS(s)) will be saved accordingly. 
     In the second embodiment of  FIG. 3 , the wireless communication system  2 /the BS(s) can consider accessibilities of frequency bands of three MSs  242 ,  244 , and  246 . For example, assuming the MS  242  is capable of accessing the two frequency bands  20  and  200 , the MS  244  is capable of accessing the two frequency bands  20  and  220 , and the MS  246  is only capable of accessing the frequency band  220 . The frequency bands  20  and  220  can be decided to be always turned on and the frequency band  200  can be decided to be turned off for power-saving, i.e. the carriers  202  and  204  will be turned off under some condition for power-saving. The MS  242  can be scheduled to camp on the frequency band  20 , i.e. camping on the carrier  22 . The MS  244  can be scheduled to camp on either the frequency band  20  (i.e. camping on the carrier  22 ) or the frequency band  220  (i.e. camping on the carrier  222 ). The MS  246  can be scheduled to camp on the frequency band  220 , i.e. camping on the carrier  222 . 
     An extension from the second embodiment of  FIG. 3  is that if there is more than one carrier on the selected frequency bands, those carriers can be down selected again to keep only one or few carriers to provide services and turn off the others to save power. 
     Another set of extensions from the second embodiment of  FIG. 3  is that the MSs to be considered can be extended as considering one of (1) all MSs on market; (2) all MSs registered in the wireless communication system  2 ; (3) only MSs are in active state with on-going communication. 
     Additionally, still referring to  FIG. 3 , the frequency bands  20 ,  200 , and  220  can be, for example, 450 MHz, 700 MHz, 900 MHz, 1800 MHz, or 2.0 GHz, etc. The carriers  22 ,  202 ,  204 , and  222  are carriers at around the range of the frequency bands. For example in case the frequency band  200  is at 900 MHz, the carrier  202  can be 900 MHz and the carrier  204  can be 920 MHz. Bandwidths of both carriers can be 20 MHz, or 10 MHz, etc. There is no restriction to their bandwidth sizes. In  FIG. 3 , the number of frequency bands can be from one to any number larger than one. There can be one or multiple carries deployed in frequency bands independently. The selected carrier(s)  22  can be the only one or even have more than one carrier in the selected frequency band  20 . Similarly, the selected carrier(s)  222  can be one or even more than one in the selected frequency band  220 . 
     Please refer to  FIG. 4 .  FIG. 4  is a diagram illustrating a third embodiment according to the power-saving method  1000  on frequency domain of the present invention. As shown in  FIG. 4 , a wireless communication system  3  deploys multiple carriers  32 ,  302 ,  304 , and  332  on frequency bands  30 ,  300 , and  330 , and there are three MSs  342 ,  344 , and  346  present in the serving area  31 . In the frequency band  30 , there is one carrier  32  used to offer system services over the serving area  31 . In the frequency band  300 , there are two carriers  302  and  304  used to offer system services over the serving area  31 . In the frequency band  330 , there is one carrier  332  used to offer system services over the serving area  31 . The system coverage of the carrier  32  consists of multiple cells and each cell is similar to the cell  38 . It is assumed that a BS is located within a cell and the BS radiates system signals with suitable power to provide coverage of the cell. Coverage areas of other carriers  302 ,  304 , and  332  are also formed in a similar way. 
     When system load of the wireless communication system  3 /the BS(s) is normal or high, e.g. the amount of MSs (within the serving area  31 ) is higher than a predetermined number, these carriers  32 ,  302 ,  304 , and  332  are supposed to be turned on and provide services to the MSs. When system load of the wireless communication system  3 /the BS(s) is not high or whenever it is possible to handle user services by less carriers, e.g. the amount of MSs (within the serving area  31 ) is lower than the predetermined number, the wireless communication system  3 /the BS(s) can initiate a power-saving process such as the power-saving process  1000  to turn off several carriers. For active and camped MSs, they can be handed over cell re-selected on to other carriers which are kept on transmitting system signals. In other words, if an active MS is camped on a carrier and the carrier is about to be turned off by the wireless communication system  3 /the BS(s), then the active MS can camp on to another carrier which will not be turned off by the wireless communication system  3 /the BS(s). In this way, after some carriers are empty of MSs (no MS present), transmission of system signals on these carriers can be turned off and power consumption (of the wireless communication system  3 /the BS(s)) will be saved accordingly. 
     In the third embodiment of  FIG. 4 , the wireless communication system  3 /the BS(s) can consider accessibilities of frequency bands of three MSs  342 ,  344 , and  346 . For explanation of the third embodiment of  FIG. 4 , it is assumed that the MS  342  is capable of accessing the three frequency bands  30 ,  300 , and  330 , the MS  344  is capable of accessing the three frequency bands  30 ,  300 , and  330 , and the MS  346  is capable of accessing the two frequency bands  30  and  330 . The frequency bands  30  and  330  are both capable of supporting the MSs  342 ,  344 , and  346 . In the third embodiment of  FIG. 4 , a lower frequency band is decided to be always turned on, i.e. the frequency band  30 , since carriers of a lower frequency band can provide larger coverage and consume less power. The frequency band  30  is then chosen to be kept on and the frequency bands  300  and  330  are turned off, i.e. carriers  302 ,  304 , and  332  are turned off for power-saving. 
     An extension from the third embodiment in  FIG. 4  is that if there is more than one carrier on the selected frequency bands, those carriers can be down selected again to keep only one or few carriers to provide services and turn off the others to save power. 
     Another set of extensions from the third embodiment in  FIG. 4  is that the MSs to be considered can be extended as considering one of (1) all MSs on market; (2) all MSs registered in the wireless communication system  3 ; (3) only MSs are in active state with on-going communication. 
     Additionally, still referring to  FIG. 4 , the frequency bands  30 ,  300 , and  330  can be, for example, 450 MHz, 700 MHz, 900 MHz, 1800 MHz, or 2.0 GHz, etc. The carriers  32 ,  302 ,  304 , and  332  are carriers at around the range of the frequency bands. For example in case the frequency band  300  is at 900 MHz, the carrier  302  can be 900 MHz, and the carrier  304  can be 920 MHz. Bandwidth of both carriers can be 20 MHz, or 10 MHz, etc. There is no restriction to their bandwidth sizes. In  FIG. 4 , the number of frequency bands can be from one to any number larger than one. There can be one or multiple carries deployed in frequency bands independently. The selected carrier(s)  32  can be the only one or even have more than one carriers in the selected frequency band  30 . 
     Please refer to  FIG. 5 .  FIG. 5  is a flowchart illustrating a power-saving process  5000  for a wireless communication system on space domain of the present invention. The process  5000  comprises the following steps: 
     Step  5010 : Start; 
     Step  5020 : Turn off at least one radio covered space unit of a wireless communication system according to a predetermined condition; 
     Step  5030 : End. 
     In step  5020 , one radio covered space unit can be interpreted as a cell or a sector, depending on the wireless communication system, and the predetermined criterion can be: there is no MS present. For example, if within a cell, there is no MS present, then the cell can be turned off; on the other hand, if an MS is present in a cell, then the cell is turned back on. 
     Please refer to  FIG. 6 .  FIG. 6  is a diagram illustrating a fourth embodiment according to the power-saving process  5000  on space domain of the present invention. As shown in  FIG. 6 , a wireless communication system  4  deploys a carrier  400  and there are a set of cells  402 ,  404 ,  406 , and  408  and lots of cells similar to the cell  408 . There is one MS  422  present in the cell  402 , two MSs  442  and  444  are present in the cell  404 , and three MSs  462 ,  464 , and  466  are present in the cell  406 . No MS is present in the cell  408  and its similar cells. 
     In more detail, the fourth embodiment of  FIG. 6  is to turn off power of those unused cells, e.g. the cell  408  and its similar ones, where no MS is present. For the used cells, e.g. cells  402 ,  404 , and  406  where MSs are present, their system signals are remained transmitted for services. 
     An extension from the fourth embodiment of  FIG. 6  is to keep on the transmission of system signals for the cells having MSs present and their neighboring cells. If an MS is present in a cell A, then the six cells surrounding the cell A will be kept turning on. This extension might provide better service continuity for the MSs, but with lower power-saving performance. 
     In further detail, still referring to the fourth embodiment in  FIG. 6 , a cell having MSs present might be clustered like three cells  402 ,  404 , and  406  shown in  FIG. 6  or randomly appear within the coverage of the wireless communication system  4 . For those cells without MS present, their transmission of system signals can be turned off to save power, especially during some special period, like deep night. 
     Additionally, in  FIG. 6 , the carrier  400  can be one or more than one carrier covering the same serving area. The fourth embodiment in  FIG. 6  can also be used simultaneously with previous described embodiments. 
     Please refer to  FIG. 7 .  FIG. 7  is a diagram illustrating a fifth embodiment according to the power-saving process  5000  on space domain of the present invention. As shown in  FIG. 7 , a handover handling mechanism is introduced into the power-saving scheme of the present invention. In  FIG. 7 , there is shown the same system scenario as shown in  FIG. 6  additionally with two cells  432  and  434  turning on. It is assumed that wireless communication system  5  adopts power-saving scheme as shown in  FIG. 6 , and the MS  462  is active and transmitting voice/data and is close to the boundary of the cell  406 . Under such condition, in order to handle the mobility and providing seamless service continuity for the MS  462 , the cells in the vicinity of the MS  462  will be turned on. For example, the cells  432  and  434  are turned on since they are candidate cells for the MS  462  to handover to. In other words, if a turned-off cell becomes a handover candidate for a served MS, the cell will be turned on accordingly. 
     Please refer to  FIG. 8 .  FIG. 8  is a flowchart illustrating a power-saving process  8000  for a wireless communication system on space domain of the present invention. The process  8000  comprises the following steps: 
     Step  8010 : Start; 
     Step  8020 : Adjust radiation power of a base station according to a predetermined condition; 
     Step  8030 : End. 
     In step  8020 , the radiation power of a BS is for transmitting signals to the MSs served by the BS, and the predetermined condition can be some parameters indicating information of the served MS such as locations of the served MSs or received signal strength. For example, if the MSs served by the BS are all close to the BS, then the radiation power of the BS can be reduced; if some MSs served by the BS are far from the BS, then for providing services to those MSs, the radiation power of the BS can be increased. Simply speaking, the spirit of the process  8000  is to reduce the radiation power of the BS down to a certain level that still allows the mobile stations to be able to maintain required services. 
     Please refer to  FIG. 9 .  FIG. 9  is a diagram illustrating a sixth embodiment according to the power-saving process  8000  on space domain of the present invention. As shown in  FIG. 9 , a wireless communication system  6  deploys a carrier  60 . There are supposed be lots of cells, but for simplicity only one cell  600  is drawn for explanation of the present invention. Within the cell  600 , there are two MSs  602  and  604  present for the wireless communication system  6 . 
     The sixth embodiment of  FIG. 9  is to refer to the pathloss parameters and/or location based information and try to adjust the radiation power of the BS. In other words, the predetermined condition of  FIG. 9  can be received signal strength or locations of mobile stations. If the pathloss and/or location parameters shows that both MSs  602  and  604  are near the BS or have chance to reduce downlink power without affecting or only minor affecting the service quality, the radiation power of the BS can be reduced to provide coverage as shown the cell  660 . That is, before the radiation power of the BS is adjusted, the cell of the BS is to be the cell  600 ; after the radiation power of the BS is reduced, the cell  600  is shrunk and becomes the cell  660 . However, since MSs  602  and  604  are still in the coverage of the cell  660 , the reduction on the radiation power of the BS will not affect any transmission performance between the MSs  602  and  604  and the BS. Meanwhile, the radiation power of the BS can be saved. 
     In further detail, still referring to the sixth embodiment of  FIG. 9 , the reduced radiation power of the BS can be have multiple levels according to measurement results. Due to mobility of MSs  602  and  604 , the adjustment of BS transmission power can be adjusted to insure providing good enough downlink quality for MSs  602  and  604 . For example, when a MS  602  is moving toward the edge of cell  660 , the BS should increase (tune back) its radiation power to increase coverage, which means the cell  660  is enlarged to be the cell  600 . In this way, the service quality and continuity of the BS to the MS  602  is maintained. 
     Furthermore, the cell  600  can adjust its own power according to the situation inside the cell itself. Each cell in the system carrier  60  can perform similar power adjustment for power saving. While there is handover opportunity to other cells or incoming the cell, the power level of the cell can be then tuned back to its original cell planned level to provide seamless handover procedure. 
     To sum up, the present invention provides power-saving process for the wireless communication system, especially for the BS(s), which consumes the most power of the entire wireless communication system. By turning off some unused carriers, cells, or reducing the radiation power of the BS(s), the power consumption of the entire wireless communication system can be greatly reduced while the service quality remains the same, providing great convenience for users. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.