Patent Publication Number: US-2010128620-A1

Title: Mobile communications system, base station apparatus, mobile station apparatus, and propagation state collecting method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to mobile communications systems, base station apparatuses, mobile station apparatuses, and propagation state collecting methods. 
     2. Description of the Related Art 
     In order to build and manage a communication area in a mobile communications system, it is necessary to grasp an incoming state (propagation state) of a radio wave (a wireless signal) from a surrounding base station at each location within the communications area and to set and change base station parameters based on the propagation state data collated with location information for a measurement location. The “propagation state” may include various states which may be measured at the mobile station side, including reception strength, frequency, polarization, and waveform, etc., of the radio wave from the surrounding base station as well as variations of the states over time. 
     Moreover, in order to respond to needs for conducting a smooth handover between the base stations, there is somewhat of an overlap between a surrounding portion of a communications area of a base station and a communications area of an adjacent base station. Thus, wireless signals come from the multiple base stations. Therefore, the surrounding base station at a measurement location includes not only a single base station at the center of a communications area that is selected as having the highest reception quality if a mobile station resides there, but also an adjacent single base station or adjacent multiple base stations. Moreover, depending on the environment, there may be a wireless signal incoming from a non-adjacent base station. 
     Conventionally, the base stations have been installed and managed by an operator at the communications provider side. The operator has conducted measurements at each location using a dedicated measurement device aboard a measurement vehicle, and set and changed the base station parameters based on the measurement results. 
     Non-Patent Document 1: 
     3GPP TSG RAN #35 RP-070209 Lemesos, Cyprus, 6-9 Mar. 2007 (http://www.3gpp.org/ftp/tsg_ran/TSG_RAN/TSGR — 35/D ocs/) 
     SUMMARY OF THE INVENTION 
     Problem(s) to be Solved by the Invention 
     As described above, the base stations have conventionally been installed and managed by the operator at the communications provider side. Thus, there are no particular problems when all the stations are managed by the communications provider. However, the situation has changed as a user-installed home base station (Home eNodeB: see Non-patent document 1) has emerged. The home base station may also be called “Home NodeB”, “Femto Cell”, or “Access Point”. 
     In other words, such a home base station is expected to be installed in the order of one set per household, for example. This means that the number of communications areas to be managed is going to be huge. Thus, it will be difficult for the operator at the communications provider side to make rounds to measure the propagation state as it has conventionally been done. 
     Moreover, the home base station is to be installed within the home, etc. Thus, it is difficult for the operator at the communications provider side to enter into the home, etc., to measure the propagation state. Therefore, it is not possible to measure an effect of a macro base station (a communications provider-installed relatively large-sized base station), which covers the communications area of the home base station on the home base station and on the mobile station within the communications area, which could cause a degradation, etc., of reception quality due to interference, etc. 
     The present invention is being proposed in light of the conventional problems as described above. The object of the present invention is to provide a mobile communications system, a base station apparatus, a mobile station apparatus, and a propagation state collecting method that make it possible for a mobile station which resides within an area covered by a base station (regardless of whether it is a macro base station or a home base station) to obtain the propagation state of a wireless signal from a surrounding base station (regardless of whether it is a macro base station or a home base station) as well as location information for a measurement location. 
     Means for Solving the Problem 
     In order to overcome the problem as described above, in an embodiment of the present invention, a mobile communications system is provided, including a unit which causes a mobile station apparatus residing within a communication area of an arbitrary base station apparatus to measure a propagation state of a wireless signal from a surrounding base station apparatus and which collects the measurement results; and a unit which obtains location information of the mobile station apparatus. 
     In an embodiment of the present invention, the mobile communications system may be provided, wherein the mobile station apparatus is caused to measure a location of the own apparatus, and the measured location is collected together with measurement results of the propagation state. 
     In an embodiment of the present invention, the mobile communications system may be provided, wherein the mobile station apparatus is caused to conduct a direct transmission in an uplink and a location of the mobile station apparatus is estimated in an adjacent base station apparatus with its wireless signal. 
     In an embodiment of the present invention, the mobile communications system may be provided, wherein a special signal for adjacent area measurement is transmitted from an adjacent base station apparatus, and the mobile station apparatus measures the propagation state based on the special signal. 
     In an embodiment of the present invention, the mobile communications system may be provided, including a unit which sends an instruction from a first base station apparatus which is one of adjacent base station apparatuses to a second base station apparatus which is the other of the adjacent base station apparatuses, the instruction being to cause a mobile station residing within a communications area of the second base station apparatus to measure a propagation state of a wireless signal from the first base station apparatus and report the measurement results to the first base station apparatus; and a unit which obtains, in the first base station apparatus, measurement results from the second base station apparatus. 
     In an embodiment of the present invention, the mobile communications system may be provided, wherein the first base station apparatus includes a unit which obtains the measurement results from the mobile station apparatus in a direct transmission in an uplink. 
     In an embodiment of the present invention, a base station apparatus is provided, including a unit which generates a broadcast signal instructing a mobile station apparatus residing in a communications area of the base station apparatus to measure a propagation state of a wireless signal from a surrounding base station apparatus; and a unit which receives measurement results of the propagation state from the mobile station apparatus. 
     In an embodiment of the present invention, a mobile station apparatus is provided, including a unit which receives, from a base station apparatus, a broadcast signal with instructions to measure a propagation state of a wireless signal from a surrounding base station apparatus; a unit which measures the propagation state of the wireless signal from the surrounding base station apparatus; and a unit which transmits, to the base station apparatus, the measurement results of the propagation state. 
     In an embodiment of the present invention, a method of collecting a propagation state is provided, including the steps of causing a mobile station apparatus residing within a communications area of an arbitrary base station apparatus to measure a propagation state of a wireless signal from a surrounding base station apparatus; and obtaining location information of the mobile station apparatus. 
     ADVANTAGE OF THE INVENTION 
     The mobile communications system, base station apparatus, mobile station apparatus, and propagation state collecting method according to the present invention make it possible for a mobile station which resides within an area covered by a base station to obtain a propagation state of a wireless signal from a surrounding base station as well as location information for a measurement location, thereby facilitating a remote measurement of the propagation state. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an exemplary configuration of a mobile communications system according to an embodiment of the present invention; 
         FIG. 2  is a diagram illustrating an exemplary configuration of base stations (macro base stations and a home base station); 
         FIG. 3  is a diagram illustrating an exemplary configuration of a mobile station; 
         FIG. 4  is a diagram illustrating a first exemplary process in an embodiment; 
         FIG. 5  is a diagram illustrating a second exemplary process in the embodiment; 
         FIG. 6  is a diagram illustrating a third exemplary process in the embodiment; and 
         FIG. 7  is a diagram illustrating a fourth exemplary process in the embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Description of Notations 
     
         
         
           
               1  Network 
               2 ,  2 # 1 ,  2 # 2  Macro base station 
               21  Network communication unit 
               22  Broadcast signal generator 
               23  Mobile station opposing communication unit 
               24  Antenna 
               25  Information memory 
               26  Location estimating unit 
               27  Measurement results transmitter 
               3  Home base station 
               4 # 1 ,  4 # 2  Macro cell 
               5  Home cell 
               6  Mobile station 
               61  Antenna 
               62  Base station opposing communication unit 
               63  Broadcast signal readout unit 
               64  Destination switching unit 
               65  Propagation state data measuring unit 
               66  Location data measuring unit 
               67  Information memory 
               68  Measurement results transmitter 
           
         
       
    
     BEST MODE OF CARRYING OUT THE INVENTION 
     Preferred embodiments of the present invention are described below. 
     System Configuration 
       FIG. 1  is a block diagram illustrating an exemplary configuration of a mobile communications system according to an embodiment of the present invention. 
     In  FIG. 1 , a network (NW)  1  includes a user control apparatus (S-GW: serving gateway or UPE: user plane entity), which controls user data; a base station control apparatus (MME: mobility management entity), which controls a base station; and a higher-level node. 
     To the network  1 , multiple macro base stations (Macro eNodeB)  2 # 1  and  2 # 2  are connected via a wired interface (S1 interface) and a home base station (Home eNodeB)  3  is connected via a wired circuit such as ADSL (asymmetric digital subscriber line), etc. Here, the macro base stations  2 # 1  and  2 # 2  are communications provider-installed relatively large-sized base stations, while a home base station  3  is a small-sized base station which is installed by an individual, etc. While it is possible, at the communications provider side, to grasp where the macro base stations  2 # 1  and  2 # 2  are installed, it is uncertain as to where the home base station is installed. 
     An area covered by a sector of the macro base station  2 # 1  is a macro cell  4 # 1 , while an area covered by a sector of the macro base station  2 # 2  is a macro cell  4 # 2 . Some overlapping portion is provided between the adjacent macro cells  4 # 1  and  4 # 2  to facilitate a smooth handover. An area covered by the home base station  3  is a home cell  5 . 
     A mobile station (UE: user equipment)  6  carried by a user resides in the home cell  5 . Here, the mobile station  6  is able to receive a wireless signal from the home base station  3  as well as a wireless signal from the macro base station  2 # 1 . 
       FIG. 2  is a diagram illustrating an exemplary configuration of macro base stations  2  ( 2 # 1  and  2 # 2 ) and the home base station  3 . 
     In  FIG. 2 , the macro base stations  2  and home base station  3  have a network communication unit  21 , which communicates via a network  1  with an adjacent base station (macro or home) or with a higher-level node; a broadcast signal generator  22 , which generates a broadcast signal for a mobile station  6  when a request for measuring the propagation state is received from a different base station or a higher-level node via the network communication unit  21 ; and a mobile station opposing communication unit  23 , which transmits the generated broadcast signal to the mobile station  6  via an antenna  24  and which receives, from the mobile station  6  via the antenna  24 , propagation state data (which accompanies location data if a location measurement function is available at the mobile station  6 ) as measurement results. 
     Here, the broadcast signal for the mobile station  6  includes the following: 
     (1) information indicating the base station (base station connected to or a different base station) for which the propagation state is measured (example: a cell ID for specifying a base station). It may be set to report for all cell information sets listed in a surrounding-cell list rather than to report for specified cell information sets (cell IDs, etc.); 
     (2) information indicating the base stations (a base station connected to, a different base station or multiple base stations) to which the measured propagation state data is to be reported (for example, cell IDs for specifying the base stations); 
     (3) whether it is possible to directly transmit, in uplink (UL) to an adjacent base station, the propagation state data (accompanied by location data if a location measurement function is available at the mobile station). The primary purpose of directly transmitting, in the uplink, the propagation state data is location estimation. Thus, a predetermined pattern of data may be used in lieu of the propagation state data; 
     (4) what triggers reporting of the propagation state data measured by the mobile station (instruction from a base station, time interval, reception level threshold value), which propagation state data are accompanied by location data if the location measurement function is available at the mobile station. Measurement and reporting timings may also be reported separately to distribute the load on the mobile station  6 ; and 
     (5) whether it is possible to conduct measurements using a special signal for adjacent-area measurement as well as information on necessary timings. 
     Moreover, in  FIG. 2 , the macro base stations  2  and home base station  3  include an information memory  25 , which carries propagation state data received at the mobile station opposing communication unit  23 , which data is accompanied by location data if the location measurement function is available at the mobile station  6 ; a location estimating unit  26 , which, in the absence of the location measurement function, conducts location estimation from an uplink transmit signal from the mobile station  6  and which stores the estimated location data in the information memory  25 ; and a measurement results transmitter  27 , which transmits, via the network communication unit  21  to the requestor, measurement results (the propagation state data and location data) stored in the information memory  21 . 
       FIG. 3  is a diagram illustrating an exemplary configuration of a mobile station  6 . 
     In  FIG. 3 , the mobile station  6  includes a base station opposing communication unit  62 , which communicates with a base station via an antenna  61 ; a broadcast signal readout unit  63 , which reads out a broadcast signal from a signal received at the base station opposing communication unit  62 ; and a destination switching unit  64 , which, in accordance with instructions in the broadcast signal, switches between base stations to which measurement results are reported. 
     Moreover, the mobile station  6  includes a propagation state data measuring unit  65 , which measures the propagation state of a predetermined base station in accordance with instructions in the broadcast signal; a location data measuring unit  66 , which measures the location of the own mobile station apparatus using GPS, etc.; an information memory  67 , which carries the measured propagation state and location data; and a measurement results transmitter  68 , which, when conditions for triggering in accordance with instructions in the broadcast signal, transmits, to a destination base station via the base station opposing communication unit  62 , measurement results (propagation state data, location data) stored in the information memory  67 . If what triggers the reporting is “instructions from the base station”, the measurement results transmitter  68  waits for instructions from a base station before transmitting the measurement results and transmits the measurement results upon receiving the instructions. Moreover, if what triggers the reporting is “time interval”, an event occurs internally at the specified time interval, and the measurement results are transmitted at the timing at which the event occurs. In this case, even when the event occurs, in a high load situation such as when communications are ongoing, the reporting timing may be staggered to achieve load distribution. Moreover, if what triggers the reporting is “reception level threshold value”, an event occurs internally when the reception level reaches the threshold value, and the measurement results are transmitted at the timing at which the event occurs. 
     PROCESS EXAMPLES 
     Process examples of the above embodiment are described below. While a case is exemplified of requesting measurement from the macro base station  2 # 1  to the home base station  3  and measuring, by the mobile station  6  which resides in an area covered by the home base station  3 , the propagation state from the macro base station  2 # 1 , the requestor base station and the requestee base station may be either of the macro base station type and the home base station type. Moreover, the propagation state of an arbitrary base station may be measured, by a mobile station which resides within an area covered by the own base station, either in accordance with a request from a higher-level node or voluntarily without going through a different base station. 
     First Exemplary Process 
       FIG. 4  is a diagram illustrating a first exemplary process in an embodiment. 
     In  FIG. 4 , the macro base station  2 # 1  makes a request, via a network  1 , for the propagation state of a wireless signal from the macro base station  2 # 1  within a communication area of a home base station  3  if there is a need to know, at the macro base station  2 # 1 , such propagation state (Steps S 101 , S 102 ). 
     In response, the home base station  3  makes a request, to the mobile station  6  which resides within the communications area of the own base station, for sending, to the home base station  3 , measurement data on the macro base station  2 # 1  (Step S 103 ). 
     The mobile station  6  obtains propagation state data such as a path loss of a pilot signal transmitted from the macro base station  2 # 1 , measures the location information of the own mobile station apparatus by means of GPS, etc., (Step S 104 ), and transmits the measurement results to the home base station  3  (Step S 105 ). 
     The home base station  3  transmits the received measurement results to the requestor macro base station  2 # 1  via the network  1  (Steps S 106 , S 107 ). If multiple mobile stations reside within the communications area of the home base station  3 , the home base station  3  may be arranged to be able to transmit the measurement results to the requestor macro base station  2 # 1  via the network when the measurement results are collected from all of the multiple mobile stations. 
     The process as described above makes it possible to grasp, to what extent, the radio waves from the macro base station  2 # 1  reach which locations within the communications area of the home base station  3 . 
     Second Process Example 
       FIG. 5  is a diagram illustrating a second process example of the embodiment, which process example represents a case such that a location measurement function is not available at the mobile station  6 . 
     In  FIG. 5 , the macro base station  2 # 1  makes a request, via the network  1 , for the propagation state of a wireless signal from the macro base station  2 # 1  within a communication area of the home base station  3  if there is a need to know, at the macro base station  2 # 1 , such propagation state (Steps S 111 , S 112 ). 
     In response, the home base station  3  returns an ACK (acknowledge) via the network  1  to the macro base station  2 # 1  (Step S 113 ). 
     Then, the home base station  3  makes a request to the mobile station  6  which resides within the communications area of the home base station  3 , for sending, to the home base station  3 , measurement data on the macro base station  2 # 1  (Step S 115 ). At this time, the home base station  3  also instructs the mobile station  6  to directly transmit, in an uplink to the adjacent macro base station  2 # 1 , propagation state data. 
     The mobile station  6  first obtains propagation state data such as the path loss of a pilot signal transmitted from the macro base station  2 # 1  (Step S 116 ). 
     Then, the measurement results data are directly transmitted in the uplink to the macro base station  2 # 1 , which is an adjacent base station (Step S 117 ). In the macro base station  2 # 1 , a location of the mobile station  6  is estimated from the arrival angle and the reception strength, etc., of a wireless signal transmitted directly from the mobile station  6 . If the direct transmission is normally received at the macro base station  2 # 1 , an ACK is returned from the macro base station  2 # 1  to the mobile station  6  (Step S 118 ). The mobile station  6  continues the process even if the ACK is not returned. 
     Then, the mobile station  6  transmits the measurement results to the home base station  3  (Step S 119 ), and the home base station  3  transmits the received measurement results via the network  1  to the requestor macro base station  2 # 1 . If multiple mobile stations reside within the communications area of the home base station  3 , the home base station  3  may be arranged to be able to transmit the measurement results to the requestor macro base station  2 # 1  via the network  1  when the measurement results are collected from all of the multiple mobile stations. 
     The measurement results are directly transmitted in the uplink from the mobile  6  to the macro base station  2 # 1  and also transmitted to the macro base station  2 # 1  via the home base station  3  and the network  1  to ensure that the measurement results are conveyed since the direct transmission in the uplink does not necessarily arrive normally. Moreover, the primary purpose of directly transmitting the propagation state data in the uplink is location estimation. Thus, a predetermined pattern of data may be used in lieu of the propagation state data, in which case it becomes mandatory for the measurement results to be transmitted to the macro base station  2 # 1  from the mobile station  6  via the home base station  3  and the network  1 . 
     The process as described above makes it possible to grasp at the macro base station  2 # 1  side, to what extent the radio waves from the macro base station  2 # 1  reach which locations within the communications area of the home base station  3 . 
     Third Process Example 
       FIG. 6  is a diagram illustrating a third process example of the embodiment, which process example uses a special signal for adjacent area measurement. In other words, a mobile station, which does not have measurement as its primary purpose, has a measurement accuracy of the propagation state data that is low relative to a dedicated measurement apparatus for use by an operator at the communications provider side, and thus may not be sufficient for use in managing the communications area. Then, the base stations to be measured cooperate and transmit a special signal for adjacent area measurement to increase the measurement accuracy. 
     In  FIG. 6 , the macro base station  2 # 1  makes a request, via the network  1 , for the propagation state of a wireless signal from the macro base station  2 # 1  within a communication area of the home base station  3  if there is a need to know, at the macro base station  2 # 1 , such propagation state (Steps S 131 , S 132 ). 
     In response, the home base station  3  reports measurement timing information via the network  1  to the macro base station  2 # 1  (Steps S 133 , S 134 ). 
     Then, the home base station  3  makes a request to the mobile station  6  which resides within the communications area of the own base station, for sending, to the home base station  3 , measurement data on the macro base station  2 # 1  (Step S 135 ). At this time, that the measurement be made using a special signal for adjacent area measurement is also provided together with the timing information. 
     The macro base station  2 # 1  transmits multiple times, in accordance with timing information reported from the home base station  3 , a special pilot signal for adjacent area measurement, which signal has increased transmit power (Step S 136 ). In alignment with timing information reported from the home base station  3 , the mobile station  6  receives the pilot signal transmitted from the macro base station  2 # 1  (Step S 137 ), and from statistical data such as the path loss at which time the pilot signal is transmitted, the propagation state data is obtained. A higher than usual transmit power as well as a possibility of measuring multiple times make it possible to increase the measurement accuracy and also make it possible to measure low-level base station information which cannot be measured normally. Moreover, the mobile station  6  conducts measurement with respect to location information of the own mobile station apparatus. Then, the measurement results are transmitted to the home base station  3  (Step S 138 ). 
     The home base station  3  transmits the received measurement results to the requestor macro base station  2 # 1  via the network  1  (Steps S 139 ,  140 ). If multiple mobile stations reside within the communications area of the home base station  3 , the home base station  3  may be arranged to be able to transmit the measurement results to the requestor macro base station  2 # 1  via the network  1  when the measurement results are collected from all of the multiple mobile stations. 
     The process as described above makes it possible to grasp at high accuracy at the macro base station  2 # 1  side to what extent, the radio waves from the macro base station  2 # 1  reach which locations within the communications area of the home base station  3 . 
     Fourth Process Example 
       FIG. 7  is a diagram illustrating a fourth process example of the embodiment, which process example, in a manner similar to the third process example, increases the accuracy of measuring the propagation state by using a special signal for adjacent area measurement. The fourth process example is arranged such that special codes are continuously transmitted in succession over a predetermined time period rather than transmitting multiple times the special pilot signal for the adjacent area measurement. 
     In  FIG. 7 , the macro base station  2 # 1  makes a request, via the network  1 , for the propagation state of a wireless signal from the macro base station  2 # 1  within a communication area of the home base station  3  if there is a need to know, at the macro base station  2 # 1 , such propagation state (Steps S 141 , S 142 ). 
     In response, the home base station  3  reports an ACK (acknowledge) via the network  1  to the macro base station  2 # 1  (Steps S 143 , S 144 ). 
     Then, the home base station  3  makes a request to the mobile station  6  which resides within the communications area of the own base station, for sending, to the home base station  3 , measurement data on the macro base station  2 # 1  (Step S 145 ). At this time, that the measurement is to use a special signal for adjacent area measurement is also instructed. 
     The macro base station  2 # 1  successively transmits a special code for adjacent area measurement that has an increased transmit power (Step S 146 ). The mobile station  6  receives multiple times a signal transmitted from the macro base station  2 # 1  (Step S 147 ), and from statistical data such as the path loss at which time the signal is transmitted, the propagation state data is obtained. A higher than usual transmit power as well as a possibility of measurements multiple times make it possible to increase the measurement accuracy and also make it possible to measure low-level base station information which cannot be measured normally. Moreover, as the signal from the macro base station  2 # 1  is successively transmitted, there is no need to align the timing, making it possible for the mobile station  6  side to receive at a free timing. Furthermore, the mobile station  6  conducts measurement with respect to location information of the own mobile station apparatus by means of GPS, etc. Then, the measurement results are transmitted to the home base station  3  (Step S 148 ). 
     The home base station  3  transmits the received measurement results to the requestor macro base station  2 # 1  via the network  1  (Steps S 149 , S 150 ). If multiple mobile stations reside within the communications area of the home base station  3 , the home base station  3  may be arranged to be able to transmit the measurement results to the requestor macro base station  2 # 1  via the network  1  when the measurement results are collected from all of the multiple mobile stations. 
     The process as described above makes it possible to grasp at high accuracy at the macro base station  2 # 1  side, to what extent the radio waves from the macro base station  2 # 1  reach which locations within the communications area of the home base station  3 . 
     CONCLUDING REMARKS 
     As described above, the embodiment of the present invention has the following advantages: 
     (1) The propagation state may be measured by a mobile station which resides within a communications area of each base station, making it possible to reduce the load at the communications provider side. 
     (2) Measuring the propagation state is made possible even within the communications area of the home base station installed within the household, etc. 
     (3) Base stations to be measured cooperate to make it possible to increase the accuracy of measurement. 
     (4) Overall, it is made possible to efficiently measure the propagation state to include surrounding cells as well as area overlap. 
     Preferred embodiments of the present invention have been described in the foregoing. The present invention has been described herein with reference to specific examples. However, it is clear that various modifications and changes may be applied thereto without departing from the broad spirit and scope of the claimed invention. In other words, the present invention should not be construed to be limited by the details of the specific examples and the attached drawings. 
     The present application claims priority based on Japanese Patent Application No. 2007-120264, filed on Apr. 27, 2007, the entire contents of which are hereby incorporated by reference.