Patent Publication Number: US-2011069660-A1

Title: Femtocell and resource allocation method thereof

Description:
PRIORITY 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/243,551 filed on Sep. 18, 2009, which is hereby incorporated by reference herein. 
    
    
     FIELD 
     The present invention relates to a femtocell and a resource allocation method thereof; more particularly, the present invention relates to a femtocell and a resource allocation method thereof that can solve the problems of dead zones. 
     BACKGROUND 
     A femtocell is a cellular access point that can be deployed in a network system to extend coverage (especially indoor coverage) of a mobile operator and reduce the cost of deploying a macrocell. A femtocell is sometimes referred to as a home base station, a small cellular base station, or a Home (e)NodeB in the 3 rd  Generation Partnership Project (3GPP). 
       FIG. 1A  depicts a conventional network system  1  that adopts a femtocell  11 . At the back end, the femtocell  11  is connected to the network (including a gateway  15  and a core network  13 ) of the mobile operator by an existing wired network technology (e.g., through a Digital Subscriber Line (DSL) modem or through a cable modem). At the front end, the femtocell uses a licensed wireless frequency band, so no change need to be made on user equipments  12 ,  14 ,  16  subscribing the network. The user equipments  12 ,  14 ,  16  use the best link quality with their neighboring femtocell, such as the femtocell  11 . 
     From the viewpoint of femtocells, there are two kinds of members (i.e. user equipments that subscribe the network): Closed Subscriber Group (CSG) member and non-CSG member. A CSG member is granted to access the femtocell, while a non-CSG member is treated as a foreigner and may not access the femtocell. Access modes provided by femtocells can be categorized into three types: closed access mode, open access mode, and hybrid access mode. A femtocell that is in a closed access mode means that only a CSG member can access the femtocell. A femtocell that is in an open access mode means that both a CSG member and a non-CSG member can access the femtocell, and they are treated equally. Finally, a femtocell that is in a hybrid access mode means that a CSG member has a higher priority than a non-CSG does. 
     For a femtocell that is in a hybrid access mode, both uplink and downlink transmissions introduce dead zones.  FIG. 1B  illustrates an uplink transmission scenario that causes a dead zone  102  to CSG members, such as the user equipment  14 . In  FIG. 1B , the femtocell  11  is in a hybrid access mode, the user equipment  14  is a CSG member, and the user equipment  12  is a non-CSG member. When the femtocell  11  runs out of service, it blocks the non-CSG members, such as the user equipment  12 . The user equipment  12  then establishes a link with the macrocell  17 . The user equipment  12  has to boost its power to increase the probability of successful uplink transmission with the macrocell  17 . Nevertheless, the transmissions between the user equipment  14  and the femtocell  11  will be interfered by the user equipment  12  and have poor qualities. The area that is interfered by the user equipment  12  and has poor transmission quality is called a dead zone  102 . 
       FIG. 1C  illustrates a downlink transmission scenario that causes a dead zone  104  to non-CSG members, such as the user equipment  12 . Likewise, the femtocell  11  is in a hybrid access mode, the user equipment  14  is a CSG member, and the user equipment  12  is a non-CSG member. The user equipment  12  is blocked by the femtocell  11  and then connected to the macrocell  17 . Since the user equipment  12  is closer to the femtocell  11  than to the macrocell  17 , the downlink transmissions between the user equipment  12  and the macrocell  17  are interfered by the femtocell  11  and have poor qualities. The area that is interfered by the femtocell  11  and has poor transmission quality is called a dead zone  104 . 
     According to the above descriptions, there is a need to solve the problems of dead zones of the current femtocells. 
     SUMMARY 
     An objective of certain embodiments of the present invention is to provide a resource allocation method for use in a femtocell. The resource allocation method comprises the steps of: (a) enabling the femtocell to assign a first region of a frame as a Closed Subscriber Group (CSG) region according to a priority region threshold, and (b) enabling the femtocell to assign a second region of the frame as a non-CSG region according to the priority region threshold. It is noted that the CSG region and the non-CSG region are exclusive. 
     Another objective of certain embodiments of the present invention is to provide a femtocell. The femtocell comprises a storage unit and a processing unit. The storage unit is configured to store a priority region threshold. The processing unit is configured to assign a first region of a frame as a CSG region according to a priority region threshold and assign a second region of the frame as a non-CSG region according to the priority region threshold. It is noted that the CSG region and the non-CSG region are exclusive. 
     The femtocell and the resource allocation method thereof of certain embodiments of the present invention utilize a priority region threshold to divide a frame into a CSG region and a non-CSG region. Regarding the non-CSG region, a user equipment that is a non-CSG member to the femtocell has a higher priority to use resources within the non-CSG region than a user equipment that is a CSG member does. If there is an available resource in the non-CSG region, a user equipment that is a CSG member is able to use it. Regarding the CSG region, a user equipment that is a CSG member to the femtocell has a higher priority to use resources within the CSG region than a user equipment that is a non-CSG member does. By doing so, the problems of dead zones can be eased. 
     The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention. It is understood that the features mentioned hereinbefore and those to be commented on hereinafter may be used not only in the specified combinations, but also in other combinations or in isolation, without departing from the scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates a conventional network system that adopts a femtocell; 
         FIG. 1B  illustrates an uplink transmission scenario that causes a dead zone to CSG members; 
         FIG. 1C  illustrates a downlink transmission scenario that causes a dead zone to non-CSG members; 
         FIGS. 2A ,  2 B, and  2 C illustrate a first embodiment of the present invention; 
         FIGS. 2D ,  2 E,  2 F,  2 G,  2 H, and  2 I individually illustrate a frame being assigned a CSG-region and a non-CSG region; 
         FIG. 2J  illustrates a frame conforming to the Long Term Evolution (LTE) standard; and 
         FIG. 3  illustrates a flowchart of a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following descriptions, the present invention will be explained with reference to various example embodiments; nevertheless, these embodiments are not intended to limit the present invention to any specific example, environment, embodiment, applications, or particular implementations described in these example embodiments. Therefore, descriptions of these example embodiments are only provided for purpose of illustration but not to limit the present invention. It should be appreciated that elements unrelated directly to the present invention are omitted from the embodiments and the attached drawings. 
       FIGS. 2A and 2B  illustrate a first example embodiment of the present invention. A femtocell  21  is connected to a core network  25  through a gateway  23  using wired network technology. Two user equipments  27 ,  29  are wirelessly connected to the femtocell  21 . The user equipment  27  is a CSG member to the femtocell  21 , while the user equipment  29  is a non-CSG member to the femtocell  21 . The femtocell  21  comprises a storage unit  211 , a processing unit  213 , a transceiver  215 , and a network interface  217 . The femtocell  21  is connected to the gateway  23  via its network interface  217 . The user equipments  27 ,  29  are individually connected to the transceiver  215  of the femtocell  21 . 
     The storage unit  211  is configured to store a priority region threshold. When the processing unit  213  has to process a frame  20 , the processing unit  211  assigns a first region of a frame as a CSG region  201  according to the priority region threshold and assigns a second region of the frame as a non-CSG region  202  according to the priority region threshold. It is noted that the CSG region  201  and the non-CSG region  202  are exclusive. Regarding the CSG region  201 , CSG members have higher priority to use resources in this region than non-CSG members do. When there are an available resource in the CSG region  201 , non-CSG members can use them. Regarding the non-CSG region  202 , non-CSG members have higher priority to use resources in this region than the CSG members do. When there is an available resource in the non-CSG region  202 , CSG members could use them. 
     The processing unit  213  may assign the CSG-region and the non-CSG region of a frame according to the priority region threshold through various ways as shown in  FIGS. 2D ,  2 E,  2 F,  2 G,  2 H, and  2 I.  FIGS. 2D ,  2 E,  2 F,  2 G,  2 H, and  2 I individually illustrate a frame, wherein the horizontal axes represent frequency, the vertical axes represent time, and each small rectangle represents a scheduling unit. Specifically, each of the scheduling units represents a smallest unit of the resources that can be assigned to a user equipment. In  FIGS. 2D ,  2 E,  2 F,  2 G,  2 H, and  2 I, scheduling units in grey color belong to non-CSG region, scheduling units in white color belong to CSG region, and the priority region threshold is set in a way that 40% of the scheduling units of a frame belong to the non-CSG region and 60% of the scheduling units of a frame belong to the CSG region. In  FIGS. 2D and 2E , the CSG-region and the non-CSG region are assigned on a frequency division basis. In  FIGS. 2F and 2G , the CSG-region and the non-CSG region are assigned on a time division basis. In  FIG. 2H , the CSG-region and the non-CSG region are assigned according to a pattern. In  FIG. 2I , the CSG-region and the non-CSG region are assigned randomly. 
     To elaborate the idea of a scheduling unit, an example of a frame  22  conforming to the Long Term Evolution (LTE) standard is given in  FIG. 2J . The frame  22  comprises ten subframes  220 . Each of the subframes  220  is divided into two slots in the horizontal axis and is divided into a plurality of resource blocks in the vertical axis. A duration of a slot is 0.5 ms. After the division, each of the subframes  220  comprises a plurality of physical resource blocks  220   a . In the LTE standard, a physical resource block  220   a  comprises six or seven Orthogonal Frequency-Division Multiplexing (OFDM) symbols in the horizontal axis and twelve subcarriers in the vertical axis. Given the above LTE frame  22 , a scheduling unit may comprises only one single physical resource block, two consecutive physical resource blocks in the horizontal direction, etc. It is noted that the present invention does not limit the number of physical resource blocks comprised in a scheduling unit. In addition, the present invention is not limited to the LTE standard. 
     To achieve better performance, the priority region threshold may be decided according to the location of the femtocell  21  and/or the density of user equipments in the coverage of the femtocell  21 . For example, two parameters may be used to evaluate the goodness of the priority region threshold: the effective data rate when using only one or more macrocells (denoted as Eff_data_rate macro     —     only ) and the effective data rate when adopting the femtocell  21  (denoted as Eff_data_rate with     —     femtocell ). If the priority region threshold can make Eff_data_rate with     —     femtocell  being greater than Eff_data_rate macro     —     only , the priority region threshold is a good one. Therefore, one may use the following equation to derive the priority region threshold: 
       Eff_data_rate macro     —     only &lt;Eff_data_rate with     —     femtocell   (1)
 
     The equation (1) is equivalent to the following equation: 
     
       
         
           
             
               
                 
                   
                     
                       
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     wherein the parameter M 0  represents the macrocell, the parameter x represents the user equipment (e.g. the user equipments  27 ,  29 ), and the parameter k denotes the femtocell (e.g. the femtocell  21 ). The parameter r represents the system capacity. The parameter γ is calculated by the reference signal received power (RSRP) function, which is familiar to people skilled in the art. In addition, the parameter μ represents the average number of the user equipments, the parameter α k,x  represents the resource amount that the user equipment required from the femtocell, and the parameter α k  represents the priority region threshold. For better performance, 
     
       
         
           
             
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     The following descriptions will focus on the usages of the CSG region  201  and the non-CSG region  202 . It is assumed that the user equipment  27  just handovers to the femtocell  21 . The processing unit  213  acquires a user type of the user equipment  27 . The processing unit  213  determines that the user type of the user equipment  27  is CSG. Afterwards, the processing unit  213  allocates at least one scheduling unit in the CSG region  201  of the frame  20  to the user equipment  27 . It is noted that the number of scheduling units in the CSG region  201  assigned to the user equipment  27  is adjustable and is not used to limit the scope of the present invention. In this embodiment, the processing unit  213  may further determines that if at least one scheduling unit is available in the non-CSG region  202 . If there is at least one available scheduling unit in the non-CSG region  202 , the processing unit  213  will allocates at least one available scheduling unit in the non-CSG region  202  to the user equipment  27 . Similarly, the number of scheduling units in the non-CSG region  202  assigned to the user equipment  27  is adjustable and is not used to limit the scope of the present invention. 
     It is assumed that the user equipment  29  just handovers to the femtocell  21 . The processing unit  213  acquires a user type of the user equipment  29 . The processing unit  213  determines that the user type of the user equipment  29  is non-CSG. Afterwards, the processing unit  213  allocates at least one scheduling unit in the non-CSG region  202  of the frame  20  to the user equipment  29 . It is noted that the number of scheduling units in the non-CSG region  202  assigned to the user equipment  29  is adjustable and is not used to limit the scope of the present invention. In this embodiment, the processing unit  213  may further determines that if at least one scheduling unit is available in the CSG region  201 . If there is at least one available scheduling unit in the CSG region  201 , the processing unit  213  will allocates at least one available scheduling unit in the CSG region  201  to the user equipment  29 . Similarly, the number of scheduling units in the CSG region  201  assigned to the user equipment  29  is adjustable and is not used to limit the scope of the present invention. 
     According to the above descriptions, it is learned that the femtocell  21  assigns a CSG region and a non-CSG region in a frame according to a priority region threshold. Thereafter, CSG members (e.g. the user equipment  27 ) have higher priorities to use the CSG region  201  and non-CSG members (e.g. the user equipment  29 ) have higher priorities to use the non-CSG region  202 . It is noted that when frames are classified into uplink frames and downlink frames, two priority region thresholds can be used, wherein one priority region threshold is for uplink frames and the other priority region threshold is for downlink frames. 
     A second embodiment of the present invention is a resource allocation method, whose flowchart is drawn in  FIG. 3 . The resource allocation method can be used in a femtocell, such as the femtocell  21  in the first embodiment. 
     First, the resource allocation method executes step S 301  to enable the femtocell to assign a first region of a frame as a CSG region according to a priority region threshold. Then, step S 303  is executed to enable the femtocell to assign a second region of the frame as a non-CSG region according to the priority region threshold. It is noted that the step S 303  may be executed before the step S 301 . The resource allocation method then executes step S 305  to enable the femtocell to acquire a user type of a user equipment. In step S 307 , the resource allocation method enables the femtocell to determine whether the user type is CSG. If the user type is CSG, then steps S 309  to S 315  are executed. If the user type is not CSG, it means that the user type is non-CSG and then steps  317  to  321  are executed. 
     When the user type is CSG, step S 309  is executed to enable the femtocell to allocate at least one scheduling unit in the CSG region to the user equipment. Afterwards, step  311  is executed to enable the femtocell to determine whether at least one scheduling unit is available in the non-CSG region. If it is yes in step S 311 , then the step S 313  is executed to enable the femtocell to allocate at least one scheduling unit of the non-CSG region to the user equipment. Next, step S 315  is executed to finish the resource allocation method. If it is no in step S 311 , the resource allocation method proceeds to the step S 315  directly. 
     When the user type is non-CSG, step S 317  is executed to enable the femtocell to allocate at least one scheduling unit in the non-CSG region to the user equipment. Afterwards, step  319  is executed to enable the femtocell to determine whether at least one scheduling unit is available in the CSG region. If it is yes in step S 319 , then the step S 321  is executed to enable the femtocell to allocate the scheduling unit of the CSG region to the user equipment. Next, step S 323  is executed to finish the resource allocation method. If it is no in step S 319 , the resource allocation method proceeds to the step S 323  directly. 
     In addition to the aforesaid steps, the second embodiment can also execute all the operations set forth in the first embodiment. How the second embodiment executes these operations will be readily appreciated by those of ordinary skill in the art based on the explanation of the first embodiment, and thus will not be further described herein. 
     The femtocell and the resource allocation method thereof of the present invention utilize a priority region threshold to divide a frame into a CSG region and a non-CSG region. Regarding the non-CSG region, a user equipment that is a non-CSG member to the femtocell has a higher priority to use the resource within the non-CSG region than a user equipment that is a CSG member does. If there is available resource in the non-CSG region, a user equipment that is a CSG member is able to use it. Regarding the CSG region, a user equipment that is a CSG member to the femtocell has a higher priority to use the resource within the CSG region than a user equipment that is a non-CSG member does. By doing so, the problems of dead zones can be eased. 
     Since a frame comprises both a CSG region and a non-CSG region, both CSG members and non-CSG members can be served by the femtocell. The problems of dead zones caused by macrocells can be avoided. In addition, in the condition that all the CSG members have been served and the CSG region still has available scheduling units (i.e. resources), non-CSG member can use them. Likewise, in the condition that all the non-CSG members have been served and the non-CSG region still has available scheduling units (i.e. resources), CSG member can use them. Therefore, the data rate of the user equipments served by the femtocell can be increased as well. 
     The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.