Abstract:
The invention proposes a method of selecting an access base station in a user equipment of a wireless communication network, and the method generally includes the steps of: the user equipment selecting, among at least one base station, a small power base station preferably to perform an access, wherein a signal of each of the at least one base station covers the user equipment. Also the invention proposes a selecting access apparatus for selecting an access base station corresponding to the method. In an application scenario of the heterogeneous network including both small power base stations and macro base stations, the invention enables balanced usage of access resources in the heterogonous network while avoiding interference resulting from the preferable access to a macro base station with larger transmission power to thereby improve the overall performance of the heterogonous network and particularly a heterogonous network involving a hot zone.

Description:
FIELD OF THE INVENTION 
       [0001]    The present disclosure relates to a wireless communication network and particularly to a method and apparatus for selecting an access base station when a user equipment is powered on in the wireless communication network. 
       BACKGROUND OF THE INVENTION 
       [0002]    In a wireless communication network, the network constituted of a specific area covered by the network composed of a plurality of base stations (e.g., a macro base station and other small power base stations) is referred to a heterogeneous network. At present in a wireless communication network involving a heterogeneous network, a User Equipment (UE) selects a base station for an access and a cell corresponding thereto based upon the reference signal receiving strength principle when the user equipment is powered on such that the user equipment selects for an access only a base station corresponding to the receiving signal with the largest signal strength while disregarding other base stations/cells. Small power base stations (home eNBs/family eNBs) are generally introduced in the heterogeneous network, but few user equipments will select a small power base station for an access as a result of the foregoing principle of the user equipment selecting the cell/base station, thus resulting in the unbalanced accesses of the user equipments in the heterogeneous network and the consequential waste of wireless access resources. And also more user equipments select for an access a macro eNB with the largest transmission signal strength, which also results in more wireless interference with an adjacent cell, thus degrading the overall performance of the network. This will become particularly serious in the case of a hot-zone in the wireless communication network. 
       SUMMARY OF THE INVENTION 
       [0003]    The invention proposes a method and an apparatus for selecting an access base station/cell when a user equipment is powered on in order to solve the foregoing problems of increased wireless interference, wasted access resources of the small power base station and lowered network performance due to the access of the user equipment under the principle of the largest signal receiving strength. 
         [0004]    According to an embodiment of the invention, there is provided a method, in a user equipment of a wireless communication network, of selecting an access base station. The method comprises the step of: the user equipment selecting, among all base stations with signals covering the user equipment, a small power base station preferably to perform an access. 
         [0005]    According to another embodiment of the invention, there is provided a selecting access apparatus, in a user equipment of a wireless communication network, for selecting an access base station. The apparatus comprises: a base station selecting module for selecting a small power base station preferably among all base stations with signals covering the user equipment; and an access module for performing the access of the user equipment to the selected small power base station. According to another embodiment of the invention, if there is no small power base station among the all base stations with signals covering the user equipment, then selecting, among a plurality of macro base stations, a macro base station with largest signal strength of a corresponding receiving signal at the side of the user equipment to perform an access. 
         [0006]    With the method and apparatus of the invention, particularly in an application scenario of the heterogonous network, if both a small power base station and a macro base station are available to a user equipment to perform an access in the network, then the user equipment selects the small power base station preferably to perform the access instead of selecting only a signal source base station corresponding to a signal with the largest signal strength received by the user equipment to perform the access. This enables the balanced usage of access resources in the heterogonous network while avoiding interference resulting from the preferable access to a macro base station with larger transmission power to thereby improve the overall performance of the heterogonous network and particularly a heterogonous network involving a hot zone. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]    Other features, objects and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the drawings. 
           [0008]      FIG. 1  is a schematic diagram of a topology of a wireless network communication system according to an embodiment of the invention; 
           [0009]      FIG. 2  is a flow chart of a method, in a user equipment, of selecting an access base station according to an embodiment of the invention; 
           [0010]      FIG. 3  is a flow chart of a method for a user equipment to select a small power base station preferably to perform an access according to an embodiment of the invention; 
           [0011]      FIG. 4  is a structural block diagram of an selecting access apparatus for selecting an access base station in a user equipment of a wireless communication network according to an embodiment of the invention; and 
           [0012]      FIG. 5  is a structural diagram of a base station selecting module in the selecting access apparatus according to an embodiment of the invention. 
       
    
    
       [0013]    In the drawings, identical or similar reference numerals designate identical or similar step features or devices (modules). 
       DETAILED DESCRIPTION OF EMBODIMENTS 
       [0014]    Embodiments of the invention will be detailed illustratively below with reference to the drawings. 
         [0015]      FIG. 1  is a schematic diagram of a topology of a wireless network communication system according to an embodiment of the invention, where the wireless network communication system includes a user equipment  10 , a macro base station  13 , a small power base station  12  and a small power base station  11 . In addition, the wireless network communication system further comprises a macro base station MeNB 2 , a macro base station MeNB 1  and a small power base station HeNB 3  which are not illustrated. The three macro base stations and the three small power base stations constitute a heterogeneous communication network and cover in an overlapping manner an area where the user equipment  10  is located. Wherein connections between the macro base station  13 , the macro base station MeNB 2  and the macro base station MeNB 1  on one hand and the small power base station  12 , the small power base station  11  and the small power base station HeNB 3  on the other hand can be wired or wireless. 
         [0016]      FIG. 2  is a flow chart of a method, in the user equipment  10 , of selecting an access base station according to an embodiment of the invention. 
         [0017]    Firstly the user equipment  10  performs the step S 201  of scanning radio frequency channels to obtain a central carrier frequency when the user equipment is powered on. 
         [0018]    Next the user equipment performs the step S 202  of scanning a frequency band corresponding to the central carrier frequency obtained in the step S 201  to obtain receiving signals and signal strength information corresponding thereto. 
         [0019]    Then the user equipment performs the step S 203  of detecting cell identification information included in each of the receiving signals based upon contents of the receiving signals, wherein the detected cell identification information corresponds to the small power base stations and the macro base stations in the heterogeneous network of  FIG. 1 . 
         [0020]    Then the step S 204  is performed. The user equipment selects, among the base stations corresponding to the cell identification information obtained in the step S 203 , a small power base station preferably to perform an access. 
         [0021]      FIG. 3  illustrates a flow chart of a method for a user equipment to select a small power base station preferably to perform the access according to an embodiment of the invention. 
         [0022]    Firstly the step S 2041  is performed to determine whether small power base stations exist among the base stations corresponding to the cell identification information obtained in the step S 203 . 
         [0023]    If the result is “Yes”, then the step S 2042  is performed to select, among the existing small power base stations, a signal source base station corresponding to the receiving signal with the largest signal strength at the user equipment side to perform the access. 
         [0024]    If the result is “No”, then the step S 2043  is performed to select, among macro base stations, a signal source base station corresponding to the receiving signal with the largest signal strength at the user equipment side to perform the access. 
         [0025]    The method, in a user equipment, of selecting an access base station according to the invention will be further discussed in detail below with reference to  FIG. 1 ,  FIG. 2  and  FIG. 3 . 
         [0026]    According to an embodiment of the invention, the user equipment  10  in the wireless network communication system of  FIG. 1  is covered in an overlapping manner by the macro base station  13 , the small power base station  12  and the small power base station  11  as well as a macro base station MeNB 2 , a macro base station MeNB 1  and a small power base station HeNB 3 . When the user equipment  10  is powered on, the user equipment receives a signal S M3  at power of 41 dBm from the macro base station  13 ; receives a signal S H2  at power of 19 dBm from the small power base station  12  and a signal S H1  at power of 23 dBm from the small power base station  11  respectively; receives a signal S M2  at power of 7 dBm from the macro base station MeNB 2  and a signal S M1  at power of 11 dBm from the macro base station MeNB 1  respectively; and receives a signal S H3  at power of 9 dBm from the small power base station HeNB 3 . For the sake of simplicity, the signals received by the user equipment  10  from the respective base station have not been illustrated in  FIG. 1 . 
         [0027]    After the user equipment  10  is powered on, the user equipment firstly performs the step S 201  of  FIG. 2  to scan all radio frequency channels in an Evolved Universal Terrestrial Radio Access (E-UTRA) band to search for a central carrier frequency CCF (not illustrated). 
         [0028]    Next the user equipment  10  performs the step S 202  of further scanning a frequency band where the central carrier frequency CCF is located to obtain receiving signals in the frequency band: the signal S M1  (at the power of 11 dBm), the signal S M3  (at the power of 41 dBm), the signal S H2  (at the power of 19 dBm), the signal S H1  (at the power of 23 dBm), the signal S H3  (at the power of 9 dBm) and the signal S M2  (at the power of 7 dBm). 
         [0029]    Then the user equipment  10  performs the step S 203  of detecting cell identification information included in each of the receiving signals based upon contents of the receiving signals, wherein the detected cell identification information corresponds respectively to the small power base stations and the macro base stations in the heterogeneous network of  FIG. 1 , for example, the base station  10  detects, based upon pilot signals in the receiving signals, that the cell identification information in the signal S M1  is CII M1  and corresponds to the macro base station MeNB 1 , the cell identification information in the signal S M3  is CII M3  and corresponds to the macro base station  13 , the cell identification information in the signal S H2  is CII H2  and corresponds to the small power base station  12 , the cell identification information in the signal S H1  is CII H1  and corresponds to the small power base station  11 , the cell identification information in the signal S H3  is CII H3  and corresponds to the small power base station HeNB 3 , and the cell identification information in the signal S M2  is CII M2  and corresponds to the small power base station MeNB 2 . 
         [0030]    Alternatively the user equipment  10  can detect the cell identification information included in the receiving signals S M1  and like based upon synchronization signals or reference signals in the receiving signals, and a repeated description thereof will be omitted here. 
         [0031]    According to another embodiment of the invention, before the step S 203  or in the step S 202 , the user equipment  10  presets a signal strength threshold V threshold =19 dBm (not illustrated) and selects receiving signals with signal strength greater than or equal to the predetermined value. Base stations and receiving signal strength corresponding thereto at the user equipment  10  side configured in this embodiment are the signal S M3  at power of 41 dBm from the macro base station  13 ; the signal S H2  at power of 19 dBm from the small power base station  12  and the signal S H1  at power of 23 dBm from the small power base station  11  respectively; the signal S M2  at power of 7 dBm from the macro base station MeNB 2  and the signal S M1  at power of 11 dBm from the macro base station MeNB 1  respectively; and the signal S H3  at power of 9 dBm from the small power base station HeNB 3 . And based on the power values, the user equipment  10  can determine that among the signals from the base stations, the receiving signals with signal strength greater than or equal to the threshold V threshold  preset by the user equipment  10  are only the signal S H2 , the signal S H1  and the signal S M3 . Then in the step S 203 , only cell identification information included in the receiving signals S H2 , S H1  and S M3  with signal strength greater than the predetermined threshold is detected respectively as CII H2 , CII H1  and CII M3 , and thus sources thereof are determined respectively as the small power base station  12 , the small power base station  11  and the macro base station  13 . And in subsequent steps, the process is performed for the small power base station  12 , the small power base station  11  and the macro base station  13 . 
         [0032]    Then the user equipment  10  performs the step S 204  of selecting a small power base station, e.g., the small power base station  12 , the small power base station  11  or the small power base station HeNB 3 , preferably among the base stations corresponding to the cell identification information obtained in the step S 203  and performs the access according to the cell identification information included in the receiving signal corresponding thereto at the user equipment  10  side. According to another embodiment of the invention, all the signals from the base stations are filtered with the signal strength threshold V threshold  being a lower limit before the step S 203 , as described above, and only signals S H1  and S H2  among filtering results are signals from small power base stations, and the signal with stronger signal strength between S H1  and S H2  is the signal S H1 . The signal S H , includes the cell identification information CII H1  and corresponds to the small power base station  11 . Then the user equipment  10  selects the base station  11  to perform the access. 
         [0033]    According to an embodiment of the invention, the user equipment  10  firstly performs the step S 2041  illustrated in  FIG. 3  of determining whether there are small power base stations among the base stations corresponding to the cell identification information obtained in the step S 203 . Specifically the user equipment  10  determines that the base station  11 , the base station  12  and the base station HeNB 3  respectively corresponding to the signal S H1 , the signal S H2  and the signal S H3  are all small power base stations. 
         [0034]    According to the result of performing the step S 2041 , the user equipment  10  next performs the step S 2042  of selecting any one of the above three small power base stations to perform the access. Preferably the user equipment  10  selects, among the three small power base stations, a signal source base station corresponding to the receiving signal with the largest signal strength to perform the access. Specifically the user equipment  10  determines that, among the small power base stations, the receiving signal with the largest signal strength at the user equipment  10  side is the signal S H1  and the small power base station corresponding to the signal S H1  is the base station  11 , and then the user equipment  10  selects the base station  11  to perform the access. 
         [0035]    If the result of determination in the step S 2041  is “No”, for example, according to another embodiment of the invention, only three macro base stations, i.e., the macro base station MeNB 1 , the macro base station MeNB 2  and the macro base station  13 , are configured in the communication system, and correspondingly the power of the signal S M1  is 11 dBM, the power of the signal S M3  is 41 dBM, and the power of the signal S M2  is 7 dBM, then the user equipment  10  performs the step S 2043  of selecting the macro base station  13  corresponding to the signal S M3  with the largest signal strength among the above signals to perform the access. 
         [0036]    Furthermore those skilled in the art shall appreciate that the signal strength threshold V threshold  can further be introduced to further optimize the technical solution of selecting an access base station so that the cell identification information included in each of the receiving signals is detected respectively in the step S 203 , and in the step S 204 , the user equipment  10  determines that only signals S H2 , S H1  and S M3  among the signals have signal strengths above the threshold V threshold  and detects that the cell identification information included in the signals S H2 , S H1  and S M3  are CII H2 , CII H1  and CII M3  respectively. The base stations corresponding to the cell identification information CII M3 , CII H1  and CII H2  are the macro base station  13  and the small power base stations  11  and  12  respectively. Then the user equipment  10  selects, among the three base stations, one of the small power base stations  11  and  12  preferably to perform the access. Further preferably, the receiving signals corresponding to the small power base stations  11  and  12  are the signals S H2  and S H1  in which the signal S H1  is of the largest signal strength, and then the user equipment  10  selects the base station  11  corresponding to the signal S H1  to perform the access. Those skilled in the art shall appreciate that the procedure that all the receiving signals are filtered with the threshold V threshold  in the step S 203  as described above and the procedure that the base stations corresponding to the cell identification information are filtered directly with the signal strength threshold V threshold  in the step S 204  instead of filtering all the receiving signals in the step S 203  are substantially equivalent, which both come into the scope of the invention. 
         [0037]    According to another embodiment of the invention, if only the macro base station MeNB 2 , the macro base station MeNB 1  and the small power base station HeNB 3  are configured in the communication network and their corresponding receiving signals S M2 , S M1  and S H2  at the user equipment  10  side are at power of 7 dBm, 11 dBm and 9 dBm respectively, all of which are below the threshold V threshold =19 dBm preset in the user equipment  10 , then the user equipment  10  selects, among the signals S m2 , S M1  and S H2 , the signal S M1  with the largest signal strength. The user equipment  10  determines that the macro base station corresponding to the signal S M1  is the base station MeNB 1  and then selects the base station MeNB 1  to perform the access. It shall be noted that if the information of the signal S M1  has been filtered out because it is below the threshold V threshold =19 dBm in the step S 202 , then the step S 203  and the step S 204  will be performed again on the signal S M1 . 
         [0038]      FIG. 4  illustrates a structural block diagram of a selecting access apparatus  400  for selecting an access base station in the user equipment of a wireless communication network according to another embodiment of the invention. As illustrated in  FIG. 4 , the selecting access apparatus  400  includes a base station selecting module  401  for selecting a small power base station preferably among all base stations with signals covering the user equipment, and an access module  402  for performing the access of the user equipment  10  to the selected small power base station. The base station selecting module  401  is combined with the access module  402  to perform the selective access of the user equipment  10  to a base station with the signal covering the present use equipment. 
         [0039]    In another embodiment of the invention, the selecting access apparatus  400  further comprises a central carrier frequency obtaining module  403 , a signal receiving module  404  and a cell identification detecting module  405 . 
         [0040]    Firstly the central carrier frequency obtaining module  403  scans radio frequency channels to obtain a central carrier frequency CCF when the user equipment is powered on. 
         [0041]    The signal receiving module  404  scans a frequency hand corresponding to the central carrier frequency CCF to obtain receiving signals in the frequency band and also signal strength information of the receiving signals. 
         [0042]    The cell identification detecting module  405  detects cell identity information CII (not illustrated) included in each of the receiving signals obtained by the signal receiving module  404 . 
         [0043]      FIG. 5  illustrates a structural diagram of a base station selecting module in the selecting access apparatus according to an embodiment of the invention. The base station selecting module  401  includes a first selecting sub-module  4011 , a second selecting sub-module  4012  and a third selecting sub-module  4013 . 
         [0044]    The three sub-modules perform the corresponding selection scheme respectively according to the different input condition. If there are small power base stations among base stations of the wireless network where the user equipment  10  is located, then the first selecting sub-module  4011  selects one of the small power base stations to perform an access, wherein among all the small power base stations, the selected small power base station corresponds to a receiving signal with the largest signal strength at the user equipment  10  side. 
         [0045]    Alternatively if there are only macro base stations among base stations of the wireless network where the user equipment  10  is located, then the second selecting sub-module  4012  selects one of the macro base stations to perform an access, wherein, among all the macro base stations, the selected macro base station corresponds to a receiving signal with the largest signal strength at the user equipment  10  side. 
         [0046]    Alternatively if there are both small power base stations and macro base stations among base stations of the wireless network where the user equipment  10  is located, then, the third selecting sub-module  4013  selects one of the small power base stations to perform an access, wherein, among all the small power base stations, the selected small power base station corresponds to a receiving signal with the largest signal strength at the user equipment  10  side. 
         [0047]    The operation of the selecting access apparatus in the user equipment  10  for selecting an access base station will be further discussed in details below with reference to  FIG. 1 ,  FIG. 4  and  FIG. 5 . 
         [0048]    After the user equipment  10  is powered on, the central carrier frequency obtaining module  403  firstly scans radio all frequency channels in an Evolved Universal Terrestrial Radio Access (E-UTRA) band to search for a central carrier frequency CCF (not illustrated). 
         [0049]    Next the signal receiving module  404  further scans a frequency band where the central carrier frequency CCF is located to obtain receiving signals in the frequency band: the signal S M1  (at the power of 11 dBm), the signal S M3  (at the power of 41 dBm), the signal S H2  (at the power of 19 dBm), the signal S H1  (at the power of 23 dBm), the signal S H3  (at the power of 9 dBm) and the signal S M2  (at the power of 7 dBm). 
         [0050]    Then the cell identification detecting module  405  detects cell identification information included in each of the receiving signals based upon contents of the receiving signals, wherein the detected cell identification information corresponds respectively to the small power base stations and the macro base stations in the heterogeneous network in  FIG. 1 , and in this embodiment, for example, the cell identification detecting module  405  detects, based upon pilot signals in the receiving signals, that the cell identification information in the signal S M1  is CII M1  and corresponds to the macro base station MeNB 1 , the cell identification information in the signal S M3  is CII M3  and corresponds to the macro base station  13 , the cell identification information in the signal S H2  is CII H2  and corresponds to the small power base station  12 , the cell identification information in the signal S H1  is CII H1  and corresponds to the small power base station  11 , the cell identification information in the signal S H3  is CII H3  and corresponds to the small power base station HeNB 3 , and the cell identification information in the signal S M2  is CII M2  and corresponds to the small power base station MeNB 2 . 
         [0051]    Alternatively the cell identification detecting module  405  can detect the cell identification information included in the receiving signals S M1  and like based upon synchronization signals or reference signals in the receiving signals, and a repeated description thereof will be omitted here. 
         [0052]    According to another embodiment of the invention, the signal receiving module  404  further comprises a signal selecting module  4041  is with a preset strength threshold V threshold =19 dBm (not illustrated). Base stations and receiving signal strength corresponding thereto at the user equipment  10  side configured in this embodiment are the signal S M3  at power of 41 dBm from the macro base station  13 ; the signal S H2  at power of 19 dBm from the small power base station  12  and the signal S H1  at power of 23 dBm from the small power base station  11  respectively; the signal S M2  at power of 7 dBm from the macro base station MeNB 2  and the signal S M1 , at power of 11 dBm from the macro base station MeNB 1  respectively; and the signal S H3  at power of 9 dBm from the small power base station HeNB 3 . The receiving signals with signal strength greater than or equal to the predetermined signal strength threshold V threshold  are selected and further delivered to the cell identification detecting module  405  for processing. Specifically, based on the power values of signals from the respective base stations, the signal selecting module  4041  can determine that the receiving signals with signal strength greater than or equal to the preset threshold V threshold  are only the signal S H2 , the signal S H1  and the signal S M3 , which come respectively from the small power base station  12 , the small power base station  11  and the macro base station  13 . Then the signal selecting module  4041  only delivers the receiving signals S H2 , S H1  and S M3  to the cell identification detecting module  405  for detecting cell identification information CII H2 , CII H1  and CII M1  included in the respective signals. 
         [0053]    Then the base station selecting module  401  selects a small power base station, e.g., the small power base station  12 , the small power base station  11  or the small power base station HeNB 3 , preferably among the base stations corresponding to the cell identification information output from the cell identification detecting module  405  and performs the access according to the cell identification information included in the receiving signal corresponding thereto at the user equipment  10  side. Alternatively according to another embodiment of the invention, based upon the signal strength information of the signals S H2 , S H1  and S M3  obtained in the signal receiving module  404 , the base station selecting module  401  and the access module  402  selects preferably the cell identification information CII H1  included in the signal S H1  with the higher strength among the signals S H1  and S H2 , which have signal powers greater than or equal to the threshold V threshold , from the small power base stations and determines the small power base station corresponding to the cell identification information CII H1  as the base station  11  and then accesses the base station  11 . 
         [0054]    According to an embodiment of the invention, the base station selecting module  401  determines whether there are small power base stations among the base stations corresponding to the cell identification information output from the cell identification detecting module  405 . Specifically the base station selecting module  401  determines that the base station  11 , the base station  12  and the base station HeNB 3  corresponding to the signal S H1 , the signal S H2  and the signal S H3  are all small power base stations. 
         [0055]    Secondly the base station selecting module  401  selects any one of the above three small power base stations, i.e., the base station  11 , the base station  12  and the base station HeNB 3 , to perform the access according to the result of determination. Preferably the base station selecting module  401  selects, among the three small power base stations, a signal source base station corresponding to the signal with the largest signal strength received by the signal receiving module  404  to perform the access. Specifically, by comparing the signal strength information of the respective signals from the signal receiving module  404  (the signals from the signal receiving module  404  to the base station selecting module  401  are not illustrated), the base station selecting module  401  can determine that, among the small power base stations, i.e., the base station  11 , the base station  12  and the base station HeNB 3 , the receiving signal with the largest signal strength of the signal receiving module  404  is the signal S H3  and the small power base station corresponding to the signal S H3  is the base station  11 , and then the base station selecting module  401  instructs the access module  402  to access the base station  11 . 
         [0056]    According to another embodiment of the invention, only three macro base stations, i.e., the macro base station MeNB 1 , the macro MeNB 2  and the macro base station  13 , are configured in the communication system, and correspondingly the power of the signal S M1  is 11 dBM, the power of the signal S M3  is 41 dBM, and the power of the signal S M2  is 7 dBM, where the signal with the largest signal strength is the signal S M3 , and the base station corresponding to the signal S M3  is the macro base station  13 . Then the base station selecting module  401  selects the macro base station  13  and instructs the access module  402  to access the macro base station  13 . 
         [0057]    According to another embodiment of the invention, if the macro base station MeNB 2  and the macro base station MeNB 1  are configured and correspondingly their receiving signals at the user equipment  10  side are the signals S M2  and S M1  respectively at the power of 7 dBm and 11 dBm. And the small power base station HeNB 3  is configured and correspondingly the receiving signal at the user equipment  10  side is the signal S H3  at the power of 9 dBm. The powers of the above signals are all below a threshold Vthreshold=19 dBm configured in the signal selecting module  4041 . The base station selecting module  401  determines that the signal with the highest signal strength among the signals S M2 , S M1  and S H2  is the signal S M1  and the base station corresponding to the signal S M1  is the macro base station MeNB 1 , and then the base selecting module  401  instructs the access module  402  to access the macro base station MeNB 1 . 
         [0058]    It shall be noted that the foregoing embodiments are merely exemplary but are not intended to limit the invention. Any technical solutions without departing from the spirit of the invention shall fall into the scope of the invention, and different technical features appearing in different embodiments can be used in various combinations to attain advantageous effects. Furthermore any reference numerals in the claims shall not be construed as limiting the claims where they appear; the term “comprising” will not preclude a device(s) or step(s) which are not listed in other claims or the description; the term “a” or “an” preceding a device will not preclude presence of “a plural of” such devices; a function(s) of a plurality of devices included in an apparatus can be performed in the same hardware or software module; and the terms “first”, “second”, “third”, etc., are intended to mealy represent a name but not to suggest any specific order.