Abstract:
Systems, methods, and computer program products are provided for calculating an indicator of a quality of communication within a wireless communication access network and for estimating the available capacity of a base station within the wireless communication access network. In one exemplary embodiment, a method comprises receiving an indication, generated by a mobile terminal, of the quality of communication between the base station and the mobile terminal, and estimating the available capacity of the base station based on the received indication.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional application of, and claims the benefit of priority under 35 U.S.C. §120 from, U.S. application Ser. No. 14/450,340 filed Aug. 4, 2014, which is a continuation application of U.S. Pat. No. 8,798,620, issued Aug. 5, 2014, which claims the benefit of priority under 35 U.S.C. §119 from Japanese Patent Applications No. 2009-126951 filed May 26, 2009 and No. 2010-036147 filed Feb. 22, 2010. The entire contents of each of the above applications are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Technical Field 
         [0003]    The present invention relates to a method, a system, a mobile terminal and a computer program product. 
         [0004]    Description of the Related Art 
         [0005]    In Japan, a 3G mobile phone service called Third Generation was started in 2002. At first, exchange of small packets such as voice and mail was the main application. However, with the introduction of High Speed Downlink Packet Access (HSDPA) and the like, download of larger packets, such as download of a music file or watching of a shared video, has come to be performed. 
         [0006]    Furthermore, since a communication infrastructure can be structured cheaply and also since a user preference is shifting to packet transmission, shift to IP core network using IP Multimedia Subsystem (IMS) is taking place. 
         [0007]    However, although it is a well-known fact that a fixed network typified by the Internet has grown into a communication infrastructure indispensable to life, there are many issues relating to ensuring of security, stable Quality of Service (QoS), and the like. Thus, Next Generation Network (NGN) aims to ensure security and stable QoS by introducing IMS standardized by the Third Generation Partnership Project (3GPP). Furthermore, realization of Fixed Mobile Convergence (FMC) which uses the same IMS method and which enables to seamlessly use a mobile network and a fixed network is anticipated. 
         [0008]    Furthermore, in recent years, a mobile phone with Global Positioning System (GPS) has become widespread. Also, a mobile phone compliant with a plurality of wireless access methods and the introduction of a mechanism allowing a user to select a wireless access method in accordance with his/her preference are desired in the future. Additionally, JP-A-2008-298484 discloses a mobile terminal with GPS. 
         [0009]    A user preference includes preference relating to communication cost and preference relating to communication speed. For example, there may be a user who prefers high communication speed to low communication cost and a user who prefers low communication cost to high communication speed. The communication speed here is dependent on a wireless status (available wireless capacity) of a user. Accordingly, a technology of grasping the wireless status charming every moment becomes important. 
         [0000]    In light of the foregoing, it is desirable to provide a method, a system, a mobile terminal and a computer program product which are novel and improved, and which are for grasping the wireless status of the wireless communication device. 
       SUMMARY 
       [0010]    In one embodiment, a method is provided for estimating an available capacity of a base station within a wireless communication access network. The method comprises receiving an indication, generated by a mobile terminal, of the quality of communication between the base station and the mobile terminal, and estimating the available capacity of the base station based on the received indication. 
         [0011]    In another embodiment, a system is provided for estimating an available capacity of a base station within a wireless communication access network. The system comprises a communication unit for receiving an indication, generated by a mobile terminal, of the quality of communication between the base station and the mobile terminal, and a capacity estimation unit for estimating the available capacity of the base station based on the received indication. 
         [0012]    In another embodiment, a mobile terminal comprises a correlation detection unit for calculating a correlation output based on signals received by the mobile terminal, an indicator calculation unit for calculating, using the correlation output, an indication of the quality of communication between a base station and the mobile terminal, and a communication unit for transmitting, to the base station, the indication of the quality of communication is provided. 
         [0013]    In another embodiment, a method is provided for estimating an available capacity of a base station within a wireless communication access network. The method comprises receiving correlation outputs, generated by a mobile terminal, of a plurality of scrambling codes forming a specific scrambling code group, calculating, based on the received correlation outputs, an indication of the quality of communication between the base station and the mobile terminal, and estimating the available capacity of the base station based on the calculated indication of the quality of communication. 
         [0014]    In another embodiment, a tangible computer-readable medium is provided. The computer-readable medium includes program instructions for performing, when executed by a processor, a method comprising calculating a correlation output based on signals received by a mobile terminal, calculating, using the correlation output, an indication of the quality of communication between a base station and the mobile terminal, and transmitting, to the base station, the indication of the quality of communication. 
         [0015]    In another embodiment, a mobile terminal comprises a subcarrier rate detection unit for calculating an indication of the quality of communication between a base station and the mobile terminal using a detected ratio of a number of subcarriers not used as a communication resource among a total number of subcarriers available as a communication resource, and a communication unit for transmitting, to the base station, the indication of the quality of communication is provided. 
         [0016]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as described. Further features and/or variations may be provided in addition to those set forth herein. For example, the present invention may be directed to various combinations and subcombinations of several further features disclosed below in the detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is an explanatory diagram showing a first configuration example of a wireless communication system; 
           [0018]      FIG. 2  is an explanatory diagram showing a second configuration example of the wireless communication system; 
           [0019]      FIG. 3  is an explanatory diagram showing a third configuration example of the wireless communication system; 
           [0020]      FIG. 4  is a block diagram showing a hardware configuration of a mobile terminal; 
           [0021]      FIG. 5  is a functional block diagram showing a mobile terminal according to a first configuration example; 
           [0022]      FIG. 6  is a functional block diagram showing a mobile terminal according to a second configuration example; 
           [0023]      FIG. 7  is a functional block diagram showing a mobile terminal according to a third configuration example; 
           [0024]      FIG. 8  is a functional block diagram showing a mobile terminal according to a fourth configuration example; 
           [0025]      FIG. 9  is a functional block diagram showing a mobile terminal according to a fifth configuration example; 
           [0026]      FIG. 10  is a flow chart showing a flow of a wireless communication method performed by a mobile terminal; 
           [0027]      FIG. 11  is an explanatory diagram showing a configuration of an estimation server; 
           [0028]      FIG. 12  is a diagram for illustrating a method of identifying a current location based on a reception intensity from each of a plurality of base stations; 
           [0029]      FIG. 13  is a flow chart showing a first operation example of the estimation server, 
           [0030]      FIG. 14  is a flow chart showing a second operation example of the estimation server; 
           [0031]      FIG. 15  is a flow chart showing a third operation example of the estimation server; and 
           [0032]      FIG. 16  is a flow chart showing a fourth operation example of the estimation server. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0033]    Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the appended drawings. Note that, in this specification and the appended drawings, structural elements that have substantially the same function and structure are denoted with the same reference numerals, and repeated explanation of these structural elements is omitted. 
         [0034]    Additionally, in this specification and drawings, a plurality of structural elements having substantially the same functional configuration are sometimes distinguished from each other by a different alphabet letter added to a same numeral. For example, a plurality of structures having substantially the same functional configuration are distinguished from each other as necessary by being referred to as base stations  30 A,  30 B and  30 C. However, in case it is not necessary to distinguish between a plurality of structural elements having substantially the same functional configuration, only a same numeral is added thereto. For example, in case it is not particularly necessary to distinguish between the base stations  30 A,  30 B and  30 C, they will be collectively referred to as the base stations  30 . 
         [0035]    Furthermore, “DETAILED DESCRIPTION OF THE EMBODIMENTS” will be described in the order shown below. 
         [0036]    1. Configuration of Wireless Communication System
       1-1. First Configuration Example   1-2. Second Configuration Example   1-3. Third Configuration Example       
 
         [0040]    2. Hardware Configuration of Mobile Terminal 
         [0041]    3. Functional Configuration of Mobile Terminal
       3-1. First Configuration Example   3-2. Second Configuration Example   3-3. Third Configuration Example   3-4. Fourth Configuration Example   3-5. Fifth Configuration Example       
 
         [0047]    4. Operation of Mobile Terminal 
         [0048]    5. Configuration of Estimation Server 
         [0049]    6. Operation of Estimation Server
       6-1. First Operation Example   6-2. Second Operation Example   6-3. Third Operation Example   6-4. Fourth Operation Example       
 
         [0054]    7. Conclusion 
       1. Configuration of Wireless Communication System 
       [0055]    First, referring to  FIGS. 1 to 3 , first to third configuration examples of a wireless communication system, which is an embodiment of the present invention, will be described. 
       1-1. First Configuration Example 
       [0056]      FIG. 1  is an explanatory diagram showing a wireless communication system  1  of a first configuration example. As shown in  FIG. 1 , the wireless communication system  1  according to the first configuration example includes an estimation server  10 , a mobile terminal  20 , a plurality of base stations  30 A to  30 C, and an access network  40 . 
         [0057]    The access network  40  includes a core network of a telecommunications carrier, and a line connecting the core network and the base station  30 . The base station  30  can communicate with the estimation server  10  via a gateway  42  included in the access network  40 . 
         [0058]    The base station  30  controls the communication by the mobile terminal  20 . For example, the base station  30  relays data received from the mobile terminal  20  to an addressed destination, and when data addressed to the mobile terminal  20  is received, transmits the data to the mobile terminal  20 . Furthermore, the base station  30  can communicate with the mobile terminal  20  by using wireless multiple access such as frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). The code division multiple access will be briefly described in the following. 
         [0059]    According to the code division multiple access, 512 types of scrambling codes are defined, and any of the scrambling codes is assigned to each base station  30 . The base station  30  frequency-spreads a transmission signal by a spreading code (for example, a channelization code) in accordance with the type of the transmission signal or the mobile terminal  20 , and further frequency-spreads the transmission signal by using the assigned scrambling code and transmits the same. Additionally, the type of the transmission signal may be a common pilot channel (CPICH), a primary common control physical channel (P-CCPCH), a dedicated physical channel (DPCH), a synchronization channel (SCM), or the like. 
         [0060]    Furthermore, the SCM includes a primary SCM and a secondary SCM. The primary SCM and the secondary SCM are arranged at the beginning portion of each of 15 slots configuring one frame, and the primary SCH is spread by a C PSC  (Primary Synchronization Code) and the secondary SCH is spread by a C SSC  (Secondary Synchronization Code). 
         [0061]    There are 16 types of C SSC , and 64 combination patterns are prepared to be assigned to the 15 slots, each base station  30  is assigned with any of the 64 patterns, and the base station  30  frequency-spreads and transmits the secondary SCM in each slot according to the assigned pattern. Additionally, the 512 types of scrambling codes are divided into 64 groups, and each group is associated with any of the 64 C SSC  combination patterns. 
         [0062]    The mobile terminal  20  can communicate various data with other device via the base station  30 . The various data may be audio data such as music, a lecture, a radio program, or the like, image data such as a motion picture, a television program, a video program, a photograph, a document, a painting, a diagram, or the like, a game, software, or the like. 
         [0063]    Furthermore, in case of the mobile terminal  20  communicating with the base station  30 A as shown in  FIG. 1 , the mobile terminal  20  calculates an indicator of a quality of communication, the value of which can be used by the estimation server  10 , along with location identification information for identifying the current location of the mobile terminal  20 , to generate an estimate of available capacity of the base station  30 A. The detailed function of such mobile terminal  20  will be described in “3. Functional Configuration of Mobile Terminal.” 
         [0064]    Additionally; although the mobile terminal  20  is shown as an example of a wireless communication device in  FIG. 1 , the wireless communication device is not limited to such example. For example, the wireless communication device may be an information processing apparatus such is a personal computer (PC), a home video processing device (a DVD recorder, a video cassette recorder, or the like), a personal digital assistant (PDA), a home game machine, a home appliance, or the like. Also, the wireless communication device may be an information processing apparatus such as a mobile phone, a Personal Handyphone System (PHS), a portable audio playback device, a portable video processing device, a portable game machine, or the like. 
         [0065]    The estimation server  10  receives the indicator of the quality of communication and the location identification information from the mobile terminal  20  via the base station  30  and the gateway  42 . The estimation server  10  can estimate the available capacity of the base station  30  by using the indicator of the quality of communication and the location identification information that are received. The detailed configuration and operation of such estimation server  10  will be described later. 
       1-2. Second Configuration Example 
       [0066]      FIG. 2  is an explanatory diagram showing a wireless communication system  2  of a second configuration example. As shown in  FIG. 2 , the wireless communication system  2  according to the second configuration example includes the estimation server  10 , the mobile terminal  20 , a plurality of first base stations  30 A and  30 B, a first access network  40 , a plurality of second base stations  50 A and  50 B, and a second access network  60 . 
         [0067]    The first base station  30  is connected with the first access network  40 , and the second base station  50  is connected with the second access network  60 . Also, the estimation server  10  is connected with the first access network  40  via a gateway  42  arranged in a core network to which the first base station  30  belongs, and is connected with the second access network  60  via a gateway  62  arranged in a core network to which the second base station  50  belongs. 
         [0068]    This wireless communication system  2  according to the second configuration example allows the mobile terminal  20  to register location with the first base station  30 A and the second base station  50 A belonging to different core networks. Accordingly, the mobile terminal  20  can transmit the indicator of the quality of communication and the location identification information to the estimation server  10  via the gateway  42  or the gateway  62 . 
         [0069]    The estimation server  10  estimates the available capacity of the first base station  30 A and the available capacity of the second base station  50 A by using the indicator of the quality of communication and the location identification information that are received. Furthermore, as will be described in detail later, the estimation server  10  can select which of the first access network  40  and the second access network  60  is suitably used for the mobile terminal  20 . 
       1-3. Third Configuration Example 
       [0070]      FIG. 3  is an explanatory diagram showing a wireless communication system  3  of a third configuration example. As shown in  FIG. 3 , the wireless communication system  3  according to the third configuration example is configured based on the IMS. Specifically, the wireless communication system  3  according to the third configuration example includes the mobile terminal  20 , a plurality of base stations  30 A to  30 C, the access network  40 , a proxy-call session control function (P-CSCF)  72 , an interrogating-CSCF (I-CSCF)  74 , a serving-CSCF (S-CSCF)  75 , a home subscriber server (HSS)  76 , and an application server (AS)  78 . 
         [0071]    This wireless communication system  3  according to the third configuration example allows the mobile terminal  20  to perform communication via the base station  30  according to the IMS. Furthermore, according to the wireless communication system  3 , the S-CSCF  75 , the HSS  76  and the AS  78 , for example, function as the estimation server  10 . 
       2. Hardware Configuration of Mobile Terminal 
       [0072]    Next, a hardware configuration of the mobile terminal  20  will be described with reference to  FIG. 4 . 
         [0073]      FIG. 4  is a block diagram showing the hardware configuration of the mobile terminal  20 . The mobile terminal  20  includes a central processing unit (CPU)  201 , a read only memory (ROM)  202 , a random access memory (RAM)  203 , and a host bus  204 . Furthermore, the mobile terminal  20  includes a bridge  205 , an external bus  206 , an interface  207 , an input device  208 , an output device  210 , a storage device (HDD)  211 , a drive  212 , and a communication device  215 . 
         [0074]    The CPU  201  functions as an arithmetic processing device and a control device, and controls the entire operations of the mobile terminal  20  according to various programs. Furthermore, the CPU  201  may be a microprocessor. The ROM  202  stores programs, arithmetic parameters or the like to be used by the CPU  201 . The RAM  203  temporarily stores a program to be used by the CPU  201  in its execution, parameters that change appropriately in the execution, or the like. These are interconnected through the host bus  204  configured from a CPU bus or the like. 
         [0075]    The host bus  204  is connected to the external bus  206  such as a peripheral component interconnect/interface (PCI) bus through the bridge  205 . Moreover, the host bus  204 , the bridge  205  and the external bus  206  do not necessarily have to be configured separately, and the functions may be implemented in a single bus. 
         [0076]    The input device  208  is configured from input means to be used by a user to input information, such as a mouse, a keyboard, a touch panel, a button, a microphone, a switch or a lever, an input control circuit that generates an input signal based on the input by the user and outputs the input signal to the CPU  201 , and the like. The user of the mobile terminal  20  cart input various types of data to the mobile terminal  20  or issue an instruction for a processing operation by operating this input device  208 . 
         [0077]    The output device  210  includes, for example, a display device such as a liquid crystal display (LCD) device, an organic light emitting diode (OLED) device, or a lamp. Furthermore, the output device  210  includes an audio output device such as a speaker, a head phone, or the like. The output device  210  outputs reproduced content, for example. Specifically, the display device displays various types of information of reproduced image data or the like in the form of text or image. For its part, the audio output device converts reproduced audio data or the like to sound and outputs the sound. 
         [0078]    The storage device  211  is a data storage device configured as an example of a storage unit of the mobile terminal  20 . The storage device  211  may include a storage medium, a recording device for recording data on the storage medium, a read device for reading data out of the storage medium, a deletion device for deleting data recorded on the storage medium, or the like. The storage device  211  is configured from a hard disk drive (HDD), for example. The storage device  211  drives a hard disk, and stores programs to be executed by the CPU  201  and various types of data. 
         [0079]    The drive  212  is a reader/writer for the storage medium, and is built in or externally attached to the mobile terminal  20 . The drive  212  reads out information stored in an attached removable recording medium  24  such as a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory or the like, and outputs the information to the RAM  203 . 
         [0080]    The communication device  215  is an interface for communicating with the outside, for example. The communication device  215  may include a function of communicating with the base station  30  and a function of communicating with a GPS. 
       3. Functional Configuration of Mobile Terminal 
       [0081]    Next, a mobile terminal  20 - 1  according to a first configuration example will be described with reference to  FIG. 5 , a mobile terminal  20 - 2  according to a second configuration example will be described with reference to  FIG. 6 , a mobile terminal  20 - 3  according to a third configuration example will be described with reference to  FIG. 7 , a mobile terminal  20 - 4  according to a fourth configuration example will be described with reference to  FIG. 8 , and a mobile terminal  20 - 5  according to a fifth configuration example will be described with reference to  FIG. 9 . 
       3-1. First Configuration Example 
       [0082]      FIG. 5  is a functional block diagram showing the mobile terminal  20 - 1  according to the first configuration example. As shown in  FIG. 5 , the mobile terminal  20 - 1  according to the first configuration example includes a communication unit  220 , a correlation detection unit  230  for cell search, an indicator calculation unit  240 , a GPS receiving unit  250 , and a packet communication control unit  260 . The mobile terminal  20 - 1  according to the first configuration is applicable to the wireless communication system  1  according to the first configuration example, for example. The communication unit  220  is an interface to the base station  30 , and has a function of a receiving unit for receiving a wireless signal transmitted from the base station  30  and a function of a transmitting unit for transmitting a wireless signal to the base station  30 . Additionally, this configuration example assumes a case where the communication unit  220  receives, from the base station  30 , a wireless signal that is frequency-spread according to CDMA. Furthermore, wireless signals received by the communication unit  220  from k base stations  30  are expressed by the following formula 1, 
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             S k,0 , C k,0 , d k,0 : Transmission power of CPICH, spreading code waveform, data modulated signal waveform 
             S k,1 , c d,1 , d k,1 : Transmission power of Primary-CCPCH, spreading code waveform, data modulated signal waveform 
             S k,1 : Transmission power of DPCH spread by an i-th channelization code from k-th base station 
           
         
       
     
         [0086]    The first term of the right-hand side of formula 1 indicates the CPICHs from the k base stations  30 , the second term indicates the Primary-CCPCHs from the k base stations, the third trim indicates the DPCHs in C channels, the fourth term indicates the SCHs, and the fifth term indicates a background noise. Furthermore, C k,0  is a composite spreading code, and is spread by a scrambling code C sc,k  and a channelization code C ch,0 . 
         [0087]    The correlation detection unit  230  for cell search (correlation detection unit) can identify a scrambling code having the highest correlation output, i.e. the base station  30  with the smallest propagation loss, by performing a three-step cell search based on a wireless signal received by the communication unit  220 . In the following, the there-step cell search will be briefly described. 
         [0088]    First, the correlation detection unit  230  for cell search detects a correlation between a received signal and the C psc , and detects a timing of receiving a primary SCH (first step). Then the correlation detection unit  230  for cell search detects a pattern having the highest correlation with the received signal among the 64 C SSC  combination patterns by using the timing of receiving a primary SCH detected in the first step (second step). As a result, a scrambling code group is identified, and frame-based synchronization is secured. Then the correlation detection unit  230  for cell search detects the correlation between the received signal and each of 8 types of scrambling codes included in the identified scrambling code group, and identifies a scrambling code with the highest correlation output (third step). Additionally, the Primary-CCPCH and the DPCH are spread by a different channelization code, and thus they remain frequency-spread. 
         [0089]    The indicator calculation unit  240  (calculation unit) uses the correlation output obtained in the process of the cell search by the correlation detection unit  230  for cell search to calculate an indicator of the quality of communication for estimating the available capacity of the base station  30 . An example of calculation by the indicator calculation unit  240  will be described below. 
         [0090]    In the third step of the cell search, the CPICH, the Primary-CCPCH, and the DPCH are detected as signals that are multiplexed while still being spread, with regard to the correlation outputs for the other 7 types of scrambling codes. Here, taking the ratio of the chip rate of the spreading code to the symbol rate as a spreading factor (SF), an average value of 1/SF is detected as the correlation output due to the spreading. 
         [0091]    Here, when the number of DPCHs (i.e. the number of users of the base station  30 ) to be multiplexed grows, or when the number of HS-DSCHs (i.e. the number of high-speed downlink shared channels to be shared by a plurality of users in HSDPA) grows, the correlation output is greatly increased in spite of each DPCH or each HS-DSCH being spread, and thus, the correlation outputs for the other 7 types of scrambling codes are considered to become high. Similarly, when the interference from other cell grows, the interference wave from such other cell also increases the correlation output, and thus, the correlation outputs for the other 7 types of scrambling codes are also considered to become high. Accordingly, when the correlation output for the identified scrambling code is taken as a and the minimum value of the correlation outputs for the other 7 types of scrambling codes is taken as b, b/a is considered to become larger as the available capacity of the base station  30  decreases due to the increase in the number of users of the base station  30  or as the interference from other cell grows. 
         [0092]    Thus, the indicator calculation unit  240  calculates the above IA as the indicator of the quality of communication for estimating the available capacity. Additionally, an indicator is effective as the indicator of the quality of communication as long as it indicates the relationship between the highest correlation output and other correlation output, and thus the indicator of the quality of communication is not limited to the above b/a. For example, the indicator calculation unit  24  may calculate c/a as the indicator of the quality of communication, where c is an average value of the correlation outputs for the other 7 types of scrambling codes. 
         [0093]    The GPS receiving unit  250  functions as an acquisition unit for acquiring location information indicating the current location of the mobile terminal  20  by receiving and decoding a GPS signal transmitted from a satellite. Additionally, the location information obtained by the GPS receiving unit  250  corresponds to a subordinate concept of the location identification information enabling the identification of a location. 
         [0094]    The packet communication control unit  260  transmits the indicator of the quality of communication obtained by the indicator calculation unit  240  and the location identification information obtained by the GPS receiving unit  250  to the estimation server  10  outside the core network to which the base station  30  belongs via the gateway  42  of the core network. As a result, the estimation server  10  can estimate the available capacity of the base station  30 , for example, based on the indicator of the quality of communication and the location identification information. 
       3-2. Second Configuration Example 
       [0095]      FIG. 6  is a functional block diagram showing a mobile terminal  20 - 2  according to the second configuration example. As shown in  FIG. 6 , the mobile terminal  20 - 2  according to the second configuration example includes the communication unit  220 , the correlation detection unit.  230  for cell search, the indicator calculation unit  240 , and the packet communication control unit  260 . The mobile terminal  20 - 2  according to the second configuration is applicable the wireless communication system  1  according to the first configuration example, for example. 
         [0096]    The correlation detection unit  230  for cell search performs the three-step cell search as with the first configuration example, and the indicator calculation unit  240  calculates the indicator of the quality of communication based on the correlation output for each scrambling code obtained in the process of the three-step cell search. 
         [0097]    Furthermore, during the initial cell search and neighbouring cell search at the time of intermittent reception, the mobile terminal  20 - 2  is provided with scrambling codes of the neighbouring cells and the timing difference by a broadcast channel (BCH) or a paging channel (PCH). 
         [0098]    Thus, by performing correlation detection for each of scrambling codes assigned to the neighbouring cells, the correlation detection unit  230  for cell search can obtain a correlation output for each of the plurality of scrambling codes as a reception intensity from each of a plurality of base stations  30 . 
         [0099]    Here, the combination of the reception intensities from the plurality of base stations  30  is different depending on the location of the mobile terminal  20 - 2 . That is, since the location of the mobile terminal  20 - 2  can be identified based on the reception intensity from each of the plurality of base stations  30 , the reception intensity from each of the plurality of base stations  30  can be used as the location identification information. Additionally, a concrete method of location estimation based on the reception intensity from each of the plurality of base stations  30  will be described in “5. Configuration of Estimation Server.” 
         [0100]    The packet communication control unit  260  transmits the indicator of the quality of communication obtained by the indicator calculation unit  240  and the reception intensity from each of the plurality of base stations  30  obtained by the correlation detection unit  230  for cell search as the location identification information to the estimation server  10  outside the core network to which the base stations  30  belongs via the gateway  42  of the core network. As a result, the estimation server  10  can estimate the available capacity of the base stations  30 , for example, based on the indicator of the quality of communication and the location identification information. 
       3-3. Third Configuration Example 
       [0101]    Recently, Long Term Evolution (LTE) designed to increase the packet transmission/reception rate of a 3G mobile phone was developed, and the service is planned to start around 2010. LTE employs OFDM for downlink, SC(Single Carrier)-FDM for uplink, and further employs MIMO (Multiple Input Multiple Output), and thereby achieves a maximum 100 Mbps for downlink and maximum 50 Mbps for uplink. Accordingly, it is hoped for as a system that realizes a full-fledged high-speed wireless packet communication. 
         [0102]    A mobile terminal  20 - 3  according to a third configuration example described below is applicable the wireless communication system  1  according to the first configuration example which uses the LTE mentioned above, for example. 
         [0103]      FIG. 7  is a functional block diagram showing the mobile terminal  20 - 3  according to the third configuration example. As shown in  FIG. 7 , the mobile terminal  20 - 3  according to the third configuration example includes the communication unit  220 , the GPS receiving unit  250 , the packet communication control unit  260 , and an unused subcarrier rate detection unit  270 . 
         [0104]    The communication unit  220  is an interface to the base station  30 , and has a function of a receiving unit for receiving a wireless signal transmitted from the base station  30  and a function of a transmitting unit for transmitting a wireless signal to the base station  30 . Additionally, as described above, this configuration example assumes a case where the communication unit  220  receives an OFDMA signal from the base station  30 . 
         [0105]    As with the first configuration example, the OPS receiving unit  250  functions as an acquisition unit for acquiring location information indicating the current location of the mobile terminal  20 - 3  by receiving and decoding a GPS signal transmitted from a satellite. Additionally, the location information obtained by the GPS receiving unit  250  corresponds to a subordinate concept of the location identification information enabling the identification of a location. 
         [0106]    The unused subcarrier rate detection unit  270  detects the ratio of the number of subcarriers not used as a communication resource (unused subcarrier rate) among the total number of subcarriers in an OFDM symbol to which a physical downlink shared channel (PDSCH) is mapped. The frequency of detection of the unused subcarrier rate by the unused subcarrier rate detection unit  270  is determined by the tradeoff between power consumption and detection accuracy. 
         [0107]    Additionally, to alleviate the issue of interference, the base station  30  is assumed to make use of unused resources by nulling the subcarriers. Accordingly, the unused subcarrier rate detection unit  270  is assumed to be able to distinguish an unused resource by detecting power of each subcarrier. 
         [0108]    Here, the flow of basic operation by the mobile terminal  20 - 3  will be described. The mobile terminal  20 - 3  can identify a physical cell ID during the process of performing cell search for a base station  30  with the smallest propagation loss and acquiring synchronization between a primary synchronization signal (PSS) and a secondary synchronization signal (SSS). 
         [0109]    Furthermore, the mobile terminal  20 - 3  obtains information such as a system bandwidth notified by the base station  30  by decoding a physical broadcast channel (PBCH). Then, after performing location registration and the like to the base station  30 , the mobile terminal  20 - 3  starts communication by itself or goes into an idle state (RRC_IDLE state) until a paging is received. Additionally, when in the idle state, the mobile terminal  20 - 3  may, during the intermittent reception period, periodically search for a cell in a better condition or check whether there is a paging notified by a PDCCH. 
         [0110]    Furthermore, to reselect a cell, the mobile terminal  20 - 3  measures the reception quality of a serving cell (an already camped cell) and a neighbouring cell. Specifically, the mobile terminal  20 - 3  measures the reception quality by receiving a reference signal (RS) unique to a cell and obtaining the average reference signal received power. Furthermore, an indicator R-criterion is defined, and R-criteria R s  and R n  for the serving cell and the neighbouring cell are expressed by the following formulae 2 and 3. 
         [0000]      [Equation 2] 
         [0000]        R   s   =Q   means,s   +Q   hyst,s   (Formula 2)
 
         [0000]      [Equation 3] 
         [0000]        R   n   =Q   means,n   +Q   off   _   s,n   (Formula 3)
 
         [0111]    The Q hyst,s  is a parameter for controlling the degree of hysteresis to prioritize the R-criteria. The Q off   _   s,n  is an offset amount to be applied between the serving cell and the neighbouring cell. 
         [0112]    Next, the mobile terminal  20 - 3  decodes the PDCCH, which is a physical channel for transmitting control information, to check whether there is a paging. The PDCCH is assigned to 3 symbols at the beginning of each subframe configured by 14 symbols, and the mobile terminal  20 - 3  in the idle state can check whether there is a paging by decoding these 3 symbols in the intermittent period. 
         [0113]    To efficiently decode the PDCCH, a Common search space in which a PDCCH to be transmitted to all the mobile terminals is mapped and a UE-Specific search space in which a PDCCH to be transmitted to a specific mobile terminal is mapped are defined in the 3-symbol resource block. Paging information is transmitted being mapped to the Common search space, and thus it is considered sufficient that an idle mobile terminal  20 - 3  decodes at least the Common search space. 
         [0114]    Additionally, a cycle DRX of the intermittent reception is determined by the mobile terminal  20 - 3  by processing a paging parameter notified by the serving cell. The mobile terminal  20 - 3  can detect whether there is the above-described paging and also, can reselect a cell, according to the cycle DRX. For example, when the quality of the serving cell falls below a certain threshold value, the mobile terminal  20 - 3  performs measurement of the neighbouring cell more frequently than the cycle DRX, and reduces the risk of going out of service range. 
         [0115]    Furthermore, with regard to the measurement of the RSRP, the specification only defines the use of the RS unique to a cell, and how many RSs among RSs ea mapped in the frequency domain are to be used and how many RSs are among RSs mapped in the time domain are to be used depend on the application. 
         [0116]    Accordingly, the unused subcarrier rate detection unit  270  basically periodically detects the unused subcarrier rate separately from the measurement of the RSRP while taking power consumption into consideration. On the other hand, in case of measuring the RSRP in a region in which a PDSCH is mapped and by using all the RSs mapped in the frequency domain, the unused subcarrier rate detection unit  270  can also perform detection of the unused subcarrier rate together with the RSRP measurement. 
         [0117]    The packet communication control unit  260  transmits the location identification information obtained by the GPS receiving unit  250  and the unused subcarrier rate obtained by the unused subcarrier rate detection unit  270  as the indicator of the quality of communication to the estimation server  10  outside the core network to which the base station  30  belongs via the gateway  42  of the core network. As a result, the estimation server  10  can estimate the available capacity of the base station  30 , for example, based on the indicator of the quality of communication and the location identification information. 
         [0118]    Additionally, if the packet communication control unit  260  is replaced by an IMS-compliant unit that functions to comply with IMS, the mobile terminal  20 - 3  can be applied to the wireless communication system  3  according to the third configuration example shown in  FIG. 3 . 
       3-4. Fourth Configuration Example 
       [0119]      FIG. 8  is a functional block diagram showing a mobile terminal  204  according to a fourth configuration example. As shown in  FIG. 8 , the mobile terminal  204  according to the fourth configuration example includes the communication unit  220 , the correlation detection unit  230  for cell search, the indicator calculation unit  240 , the GPS receiving unit  250 , and the packet communication control unit  260 . The mobile terminal  20 - 4  according to the fourth configuration is applicable the wireless communication system  2  according to the second configuration example, for example. 
         [0120]    The mobile terminal  204  can register location with either of the first base station  30  and the second base station  50 . Accordingly, the correlation detection unit  230  for cell search and the indicator calculation unit  240  can acquire the indicator of the quality of communication for estimating the available capacity of the first base station  30  at the time of performing cell search for the first base station  30 , and can acquire the indicator of the quality of communication for estimating the available capacity of the second base station  50  at the time of performing cell search for the second base station  50 . 
         [0121]    As with the first configuration example, the GPS receiving unit  250  functions as an acquisition unit for acquiring location information (location identification information) indicating the current location of the mobile terminal  20 - 4  by receiving and decoding a GPS signal transmitted from a satellite. 
         [0122]    The packet communication control unit  260  transmits the location identification information obtained by the GPS receiving unit  250  and the indicator of the quality of communication for estimating the available capacity of the first base station  30  obtained by the indicator calculation unit  240  to the estimation server  10  via the gateway  42  of the core network to which the base station  30  belongs. Similarly, the packet communication control unit  260  transmits the location identification information obtained by the GPS receiving unit  250  and the indicator of the quality of communication for estimating the available capacity of the second base station  50  obtained by the indicator calculation unit  240  to the estimation server  10  via the gateway  62  of the core network to which the base station  50  belongs. As a result, the estimation server  10  can estimate the available capacity of both the base station  30  and the base station  50  based on the indicator of the quality of communication and the location identification information. 
       3-5. Fifth Configuration Example 
       [0123]      FIG. 9  is a functional block diagram showing a mobile terminal  20 - 5  according to a fifth configuration example. As shown in  FIG. 9 , the mobile terminal  20 - 5  according to the fifth configuration example includes the communication unit  220 , the correlation detection unit  230  for cell search, the indicator calculation unit  240 , the GPS receiving unit  250 , and an MS-compliant unit  280 . The mobile terminal  20 - 5  according to the fifth configuration is applicable the wireless communication system  3  according to the third configuration example, for example. 
         [0124]    The correlation detection unit  230  for cell search performs the three-step cell search as with the first configuration example, and the indicator calculation unit  240  calculates the indicator of the quality of communication based on the correlation output for each scrambling code obtained in the process of the three-step cell search. 
         [0125]    As with the first configuration example, the GPS receiving unit  250  functions as an acquisition unit for acquiring location information (location identification information) indicating the current location of the mobile terminal  20 - 5  by receiving and decoding a GPS signal transmitted from a satellite. 
         [0126]    The IMS-compliant unit  280  controls communication by SIP message, far example. According to the IMS, a control communication network and a media a communication network are completely separated, and, after IMS authentication, a radio resource is allocated at all times to the control communication network for exchanging SIP messages. That is, according to the IMS, a SIP message reaches the S-CSCF  75  from the mobile terminal  20 - 5  with high reliability. Also, a plurality of various types of message bodies, such as a message in a text format, can be included in the SIP message. 
         [0127]    Accordingly, the IMS-compliant unit  280  may add to the message body of the SIP message the location identification information obtained by the GPS receiving unit  250  and the indicator of the quality of communication obtained by the indicator calculation unit  240 . Then, the IMS-compliant unit  280  can transmit the SIP message to the S-CSCF  75 , the HSS  76  or the AS  78  on the home network side via the base station  30  and the P-CSCF  72 . Additionally, the IMS-compliant unit  280  may also encrypt the location identification information and the indicator of the quality of communication and add the same to the message body of the SIP message. 
       4. Operation of Mobile Terminal 
       [0128]    Heretofore, configuration examples of the mobile terminal  20  have been described with reference to  FIGS. 5 to 9 . Subsequently, the flow of a wireless communication method to be performed by the mobile terminal  20  will be described with reference to  FIG. 10 . 
         [0129]      FIG. 10  is a flow chart showing a flow of a wireless communication method performed by the mobile terminal  20 . As shown in  FIG. 10 , the communication unit  220  receives a wireless signal from the base station  30  (S 282 ), and the correlation detection unit  230  for cell search performs the three-step cell search based on the wireless signal received by the communication unit  220  (S 284 ). 
         [0130]    Then, the indicator calculation unit  240  calculates the indicator of the quality of communication for estimating the available capacity of the base station  30 , based on the size of the correlation outputs of a plurality of scrambling codes obtained in the process of the three-step cell search (S 286 ). For its part, the GPS receiving unit  250  acquires the location information (location identification information) indicating the current location of the mobile terminal  20  by receiving and decoding a GPS signal transmitted from a satellite (S 288 ). 
         [0131]    The packet communication control unit  280  transmits the indicator of the quality of communication obtained by the indicator calculation unit  240  and the location identification information obtained by the GPS receiving unit  250  in this manner to the estimation server  10  via the communication unit  220  (S 290 ). 
       5. Configuration of Estimation Server 
       [0132]    Next, the configuration of the estimation server  10  will be described with reference to  FIGS. 11 and 12 . 
         [0133]      FIG. 11  is an explanatory diagram showing the configuration of the estimation server  10 . As shown in  FIG. 11 , the estimation server  10  includes a communication unit  110 , a primary available capacity estimation unit  120 , a location identification unit  130 , an available capacity correction unit  140 , a storage unit  150 , and an access network selection unit  160 . This estimation server  10  is applicable the first to third configuration examples of the wireless communication system shown in  FIGS. 1 to 3 . 
         [0134]    The communication unit  110  is an interface to the mobile terminal  20 , and functions as a receiving unit for receiving the indicator of the quality of communication, the location identification information and the like transmitted from the mobile terminal  20 , for example, via the access network  40 . 
         [0135]    The primary available capacity estimation unit  120  (estimation unit) primarily estimates, from the indicator of the quality of communication received by the communication unit  110 , the available capacity of a cell (base station  30 ) with which the location of the mobile terminal  20  is registered. For example, when the indicator of the quality of communication is the b/a described above, the indicator of the quality of communication grows larger as the number of multiplexed DPCHs, which are channels allocated to other mobile, terminals, increases. Accordingly, the primary available capacity estimation unit  120  can primarily estimate the available capacity of the base station  30  based on the indicator of the quality of communication b/a. More specifically, the primary available capacity estimation unit  120  may estimate the available capacity of the base station  30  to be at a level that is higher as the indicator of the quality of communication b/a is smaller (the available capacity is higher), among a plurality of digital levels. 
         [0136]    Additionally, the indicator of the quality of communication IA is expected to be a constant value which is not dependent on the distance between the base station  30  and the mobile terminal  20 - 1 . For example, in case an AGC is not operating in a receiving circuit, each of the correlation outputs a and b will have a smaller value as the distance between the base station  30  and the mobile terminal  20 - 1  becomes greater. However, the values will become smaller at the same rate, and thus, the indicator of the quality of communication b/a is assumed to be constant, without being dependent on the distance between the base station  30  and the mobile terminal  201 . On the other hand, in case the AGC is operating in the receiving circuit, if the base station  30  is transmitting the same signal, the correlation outputs a and b ideally become constant, and thus, the indicator of the quality of communication b/a will also be a constant value. 
         [0137]    Furthermore, the influence of noise floor of the receiving circuit of the mobile terminal  20 - 1  on the available capacity of the base station  30  that is to be estimated based on the indicator of the quality of communication b/a is different depending on the distance between the mobile terminal  20 - 1  and the base station  30 . Specifically, as the mobile terminal  20 - 1  gets farther away from the base station  30 , the available capacity of the base station  30  will be estimated to be less than the actual available capacity due to the noise floor of the receiving circuit. This is because, since the noise floor of the receiving circuit is a random signal, the noise floor acts to increase the value of b as the mobile terminal  20 - 1  gets farther away from the base station  30 . However, the communication environment of the mobile terminal  20 - 1  existing at the cell edge far from the base station  30  is significantly poor, and thus, it is assumed that, even if the available capacity of the base station  30  is estimated to be less than the actual available capacity, the had influence is restrictive. 
         [0138]    The location identification unit  130  identifies the current location of the mobile terminal  20  based on the location identification information received by the communication unit  110 . For example, when the location identification information is the reception intensity from each of the plurality of base stations  30  described in “3-2. Second Configuration Example,” the location identification unit  130  identifies the current location of the mobile terminal  20  by the method described below. 
         [0139]      FIG. 12  is a diagram for illustrating the method of identifying the current location based on the reception intensity from each of the plurality of base stations  30 . Additionally, for the sake of explanation, the concept of a sector is not included. As shown in  FIG. 12 , the transmission power and the absolute gain of the transmission antenna of the base station  30 A are respectively referred to as W A  and G A , the transmission power and the absolute gain of the transmission antenna of the base station  30 B are respectively referred to as W B  and G B , and the transmission power and the absolute gain of the transmission antenna of the base station  30 C are respectively referred to as W C  and G C . 
         [0140]    Also, the coordinates of the base stations  30 A to  30 C are known, and the coordinate of the base station  30 A is A(0, 0), the coordinate of the base station  30 B is B(a, b), the coordinate of the base station  30 C is C(c, d), and the coordinate at Which the mobile terminal  20  is located is X(x, y). Also, it is assumed that the ratio of distances from point A, point and point C to point X is known. Furthermore, when taking the distance from point A to point X as variable z, the ratio of the square of the distance between point  13  and point X to z 2  as α, and the ratio of the square of the distance between point C and point X to z 2  as β, the following formulae 4 to 6 are obtained. 
         [0000]      [Equation 4] 
         [0000]        x   2   +y   2   =z   2   (Formula 4)
 
         [0000]      [Equation 5] 
         [0000]      ( x−a ) 2 +( y−b ) 2   =αz   2   (Formula 5)
 
         [0000]      [Equation 6] 
         [0000]      ( x−c ) 2 +( y−d ) 2   =βz   2   (Formula 6)
 
         [0000]    Here, a, b, c, d, a (&gt;1), and (&gt;1) are known values, and x, y, and z are variables. The following formula 7 is obtained from the formulae 4 and 5, and the following formula 8 is obtained from the formulae 5 and 60 
         [0000]    
       
         
           
             
               
                 
                   
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         [0141]    The formula 7 indicates the locus of a circle whose centre is (a/(1−α), b/(1−α)) and whose radius is a square root of the right-hand side. Similarly, the formula 8 indicates the locus of a circle whose centre is (c/(1−β), d(1−β)) and whose radius is a square root of the right-hand side. Accordingly, (x, y) satisfying the formulae 4 to 6 corresponds to the intersection of the loci of the two circles indicated by the formulae 7 and 8. 
         [0142]    On the other hand, received power densities P A , P B , and P C  from the base stations  30 A,  30 B and  30 C at X(x, y) are expressed by the following formulae 9 to 11. 
         [0000]    
       
         
           
             
               
                 
                   
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         [0143]    When W A =W B =W C  and G A =G B =G C , the following formulae 12 and 13 are obtained from the formulae 9 to 11. 
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                       12 
                     
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                       13 
                     
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         [0144]    The α and β will be known values by the above formulae 12 and 13. Additionally, even if the transmission outputs W A , W B  and W C  of the base stations  30 A to  30 C are different, the ratio of distances from respective base stations  30  to X(x, y) can be obtained, provided that information relating to the transmission outputs of the base stations  30 A to  30 C is notified by the BCH. The same can be said for a case where the transmission output of the CPICH is notified by the BCH. 
         [0145]    The location identification unit  130  can identify the current location of the mobile terminal  20  from the reception intensity, as the location identification information, from each of the plurality of base stations  30  by the above calculations. Additionally, when the location identification information is location information indicating latitude and longitude, the location identification unit  130  does not have to perform any special calculation. 
         [0146]    We will return to the description of the configuration of the estimation server  10  with reference to  FIG. 11 . As has been described, the primary available capacity estimation unit  120  estimates the available capacity of the base station  30  based on, for example, the indicator of the quality of communication b/a. However, as the mobile terminal  20  gets farther away from the base station  30 , the base station  30  will set, the amplitude of the DPCH allocated to the mobile terminal  20  to be larger, and thus the value of b will become larger. That is, the indicator of the quality of communication b/a will have a different meaning with regard to the available capacity of the base station  30  depending on the location of the mobile terminal  20 . 
         [0147]    In the following, the influence of the distance between the mobile terminal  20  and the base station  30  on the available capacity of the base station  30  that is estimated based on the indicator of the quality of communication b/a will be described in greater detail. Let us assume that the estimation server  10  has estimated the available capacity of the base station  30  based on an indicator of the quality of communication b 1 /a 1  received from the mobile terminal  20  that is attempting to start communication. Here, in case the mobile terminal  20  exists near the base station  30 , the base station  30  can multiple-transmit a DPCH for the mobile terminal  20  with low power. Accordingly, the influence on the available capacity (degree of congestion) of the base station  30  due to the start of signal transmission to this mobile terminal  20  existing near the base station  30  is small. That is, the amount of reduction in the available capacity of the base station  30  caused by the start of signal transmission to the mobile terminal  20  existing near the base station  30  is small. 
         [0148]    On the other hand, in case the mobile terminal  20  exists far from the base station  30 , the base station  30  will multiple-transmit a DPCH for this mobile terminal  20  with high power. Accordingly, the influence on the available capacity (degree of congestion) of the base station  30  due to the start of signal transmission to this mobile terminal  20  existing far from the base station  30  is large. That is, the amount of reduction in the available capacity of the base station  30  caused by the start of signal transmission to the mobile terminal  20  existing far from the base station  30  is large. 
         [0149]    Thus, the available capacity correction unit  140  (correction unit) corrects the available capacity of the base station  30  estimated by the primary available capacity estimation unit  120  by using the distance between the mobile terminal  20  and the base station  30 . Specifically, the available capacity correction unit  140  may correct the available capacity of the base station  30  estimated by the primary available capacity estimation unit  120  to a value smaller as the distance between the mobile terminal  20  and the base station  30  is increased. Additionally, the distance between the mobile terminal  20  and the base station  30  can be obtained from the difference between the location of the mobile terminal  20  identified by the location identification unit  130  and the known installation location of the base station  30 . 
         [0150]    The storage unit  150  is a storage medium storing user information, history information, communication cost information, available capacity information, and the like. Additionally, the storage unit  150  (user information storage unit, communication cost storage unit) may be a storage medium such as a non-volatile memory, a magnetic disk, an optical disk, a magneto optical (MO) disk, and the like. The non-volatile memory may be an electrically erasable programmable read-only memory (EEPROM), and an erasable programmable ROM (EPROM), for example. Also, the magnetic disk may be a hard disk, a discoid magnetic disk, and the like. Also, the optical disk may be a compact disc (CD), a digital versatile disc recordable (DVD-R), a Blu-ray disc (BD; registered trademark), and the like. 
         [0151]    When a plurality of access networks can be used by the mobile terminal  20  as shown in  FIG. 2 , the access network selection unit  160  (selection unit) selects an access network suitable for the mobile terminal  20  based on the available capacity corrected by the available capacity correction unit  140  and various types of information stored in the storage unit  150 . Concrete example of this selection will be described in “6-3. Third Operation Example” and “6-4. Fourth Operation Example.” 
       6. Operation of Estimation Server 
       [0152]    Heretofore, the configuration of the estimation server  10  has been described with reference to  FIGS. 11 and 12 . Subsequently, the first to fourth configuration examples of the estimation server  10  will be described with reference to  FIGS. 13 to 16 . 
       6-1. First Operation Example 
       [0153]      FIG. 13  is a flow chart showing the first operation example of the estimation server  10 . As shown in  FIG. 13 , first, when the communication unit  110  of the estimation server  10  receives the indicator of the quality of communication and the location identification information from the mobile terminal  20  (S 310 ), the primary available capacity estimation unit  120  primarily estimates the available capacity of the base station  30  based on the indicator of the quality of communication (S 320 ) Also, when the location identification information is not information directly indicating the latitude and longitude, the location identification unit  130  identifies the current location of the mobile terminal  20  based on the location identification information (S 330 ). Then, the available capacity correction unit  140  corrects the available capacity estimated by the primary available estimation unit  120  by using the distance between the mobile terminal  20  and the base station  30  (S 340 ). 
       6-2. Second Operation Example 
       [0154]      FIG. 14  is a flow chart showing the second operation example of the estimation server  10 . As shown in  FIG. 14 , the second operation example includes, after the processes of S 310  to S 340  shown in the first operation example, a process of further correcting the available capacity based on history information (S 350 ). The history information is stored in the storage unit  150 , and is information relating to the history of influences of the location information of many mobile terminals on the available capacity, information relating to the history of the QoSs that are actually obtained, and the like. The available capacity correction unit  140  further corrects, by using the history information, the available capacity that has been corrected in S 340  by using the location information. Let us assume, for example, that the history information includes the relationship between a previously estimated available capacity and the QoS, and that the QoS is less than the QoS expected from the estimated available capacity. In this case, the actual available capacity is considered to be less than the estimated available capacity, and thus, the available capacity correction unit  140  may correct the available capacity to be less. 
       6-3. Third Operation Example 
       [0155]      FIG. 15  is a flow chart showing the third operation example of the estimation server  10 . As shown in HG  15 , the third operation example includes, after the processes of S 310  to S 340  shown in the first operation example, storing of the available capacity (S 360 ) and selection of an access network (S 370 ). 
         [0156]    Specifically, the available capacity corrected by the available capacity correction unit  140  in S 340  is stored in the storage unit  150  (S 360 ). The storage unit  150  also stores user information indicating the preference of a user of the mobile terminal  20  on communication. Weighting on cost indicating that a user desires low cost, weighting on high communication speed indicating that a user desires high-speed communication, and the like, are set as the user information. This user information may be set based on a user operation on the mobile terminal  20 . Furthermore, the storage unit  150  stores communication cost information indicating the communication cost for each access network. For example, information indicating the communication cost per unit time, information indicating the communication cost per unit data amount, and the like, are assumed as the communication cost information, for example. 
         [0157]    Then, the access network selection unit  160  selects an access network suitable for the user of the mobile terminal  20  based on the available capacity stored in the storage unit  150 , the user information and the communication cost information (S 370 ). For example, when preference for cost is set in the user information of the mobile terminal  20 , the access network selection unit  160  refers to the communication cost information, selects an access network with the lowest communication cost, and notifies the mobile terminal  20 . On the other hand, when preference for high communication speed is set in the user information of the mobile terminal  20 , the access network selection unit  160  refers to the available capacity for each access network stored in the storage unit  150 , selects an access network with the highest available capacity, and notifies the mobile terminal  20 . Additionally, preference of a user may be set in the user information according to conditions. For example, preference for high communication speed is set in case of downloading a packet having a certain size or more, and preference for cost is set in other cases. 
       6-4. Fourth Operation Example 
       [0158]      FIG. 16  is a flow chart showing the fourth operation example of the estimation server  10 . As shown in  FIG. 16 , the fourth operation example includes, after the processes of S 310  to S 340  shown in the first operation example, storing of the available capacity (S 360 ) and selection of an access network (S 380 ). 
         [0159]    Specifically, the available capacity corrected by the available capacity correction unit  140  in S 340  is stored in the storage unit  150  (S 360 ). Furthermore, in this operation example, the communication cost is assumed to change depending on the available capacity, and the storage unit  150  stores variable cost information indicating the communication cost per available capacity. 
         [0160]    Then, the access network selection unit  160  selects an access network suitable for the user of the mobile terminal  20  based on the available capacity stored in the storage unit  150 , the user information and the variable cost information (S 380 ). Specifically, the access network selection unit  160  acquires communication costs in accordance with the available capacities of respective access networks, and in case preference for cost is set in the user information of the mobile terminal  20 , selects an access network with the lowest communication cost, and notifies the mobile terminal  20 . On the other hand, when preference for high communication speed is set in the user information of the mobile terminal  20 , the access network selection unit  160  refers to the available capacity of each access network stored in the storage unit  150 , selects an access network with the highest available capacity, and notifies the mobile terminal  20 . 
       7. Conclusion 
       [0161]    As has been explained, according to the embodiments of the present invention, the following effects can be obtained.
       The estimation server  10  can estimate the available capacity of the base station  30  with which the location of the mobile terminal  20  is registered based on an approximate value of an relative amplitude ratio (b/a) of DPCHs allocated to other mobile terminals.   Furthermore, the estimation server  10  notifies the mobile terminal  20  of the estimated available capacity of the base station  30 , thereby enabling the mobile terminal  20  to grasp the available capacity of the base station  30  with which the location of the mobile terminal  20  is registered.   Furthermore, the estimation server  10  can identify the location of the mobile terminal  20  even when a GPS function is not provided to the mobile terminal  20  as shown in the second configuration example or even when the mobile terminal  20  is at a location where it is hard to use the GPS function.   Furthermore, the estimation server  10  can select an access network best suited to a user at the time, according to the preference of the user of the mobile terminal  20 . Furthermore, even in a case of the communication cost changing depending on the relationship between supply and demand, the estimation server  10  can select an appropriate access network according to the changing communication cost.   Furthermore, by configuring the system according to IMS, as with the wireless communication system  3  according to the third configuration example, the mobile terminal  20  is enabled to communicate with the estimation server  10  (S-CSCF  75 , AS  78 , and the like) by using a SIP message.       
 
         [0167]    It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof. 
         [0168]    For example, an example has been described above where the mobile terminal  20  calculates the indicator of the quality of communication based on the correlation output of a scrambling code and notifies the estimation server  10  of this indicator of the quality of communication. However, the present invention is not limited to such an example. As a modified example, the mobile terminal  20  may notify the estimation server  10  of correlation outputs of a plurality of scrambling codes forming a specific scrambling code group, and the estimation server  10  may calculate the indicator of the quality of communication based on the notified correlation outputs and estimate the available capacity of the base station  30  from the indicator of the quality of communication. 
         [0169]    Furthermore, it is not necessary to perform each step in the processing of the estimation server  10  and the mobile terminal  20  in chronological order according to the sequence shown in the sequence chart or the flow chart. For example, each step in the processing of the estimation server  10  and the mobile terminal  20  may include the processing which is performed in parallel or individually (e.g. parallel processing or object processing). 
         [0170]    Furthermore, it is also possible to create a computer program for causing hardware such as the CPU  201 , the ROM  202 , and the RAM  203  that are built in the estimation server  10  and the mobile terminal  20  to perform functions that are the same as each structural element of the estimation server  10  and the mobile terminal  20  described above. A storage medium storing the computer program is also provided.