Abstract:
Provided are a receiving device, a receiving method, and a computer program capable of more reliably ascertaining the number and power of transmitting antennas so as to more accurately find a base station. A first power of a first signal transmitted from a first transmitting antenna and a second power of a second signal transmitted from a second transmitting antenna are measured, and a determination is made as to whether the ratio of the first power and the second power is larger than a predetermined threshold value. When a determination is made that the ratio of the first power and the second power is larger than the threshold value, a presumption is made that the number of transmitting antennas is two.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a U.S. national stage of application No. PCT/JP2012/058427, filed on Mar. 29, 2012. Priority under 35 U.S.C.§ is claimed from Japanese Patent Applications No. 2011-074508 filed on Mar. 30, 2011, the disclosure of which is also incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a receiving device, a receiving method, and a computer program. 
       BACKGROUND ART 
       [0003]    In a wireless communication system such as Long Term Evolution (LTE), which is attracting attention as a next generation communication method, and being standardized by 3rd Generation Partnership Project (3GPP), it is determined on the basis of receiving quality information, such as Signal Received Power reported from a receiver, whether or not to perform a handover process between base stations. For that processing, in order to perform the handover process with an appropriate base station, it is needed to adequately estimate a signal received power. 
         [0004]    In a terminal device as a receiver, the power (RSRP) is estimated by using a reference signal sent from a base station. In such an operation, in the case where information data on the base station is not yet obtained, or in the case where the number of antennas is not yet informed from another base station, the number of antennas of the base station still remains unknown. 
         [0005]    In LTE; if the number of antennas of a base station is one, a reference signal of R 0  only is antenna-transmitted; and meanwhile, if the number of antennas of a base station is two, reference signals of R 0  and R 1  are antenna-transmitted; and then, if the number of antennas of a base station is four, reference signals of R 0 , R 1 , R 2 , and R 3  are individually antenna-transmitted. When the number of antennas is unknown, the power can be estimated at a terminal device by using the R 0 , which is transmitted in every case in common. 
         [0006]    As a conventional approach, there also exists a method of a wireless receiving device in a wireless communication system having a transmission diversity; in which a received information level of each characteristic symbol of each transmission antenna for transmission from a wireless transmission device is measured, the number of transmission antennas is estimated on the basis of the received information level, demodulation with respect to the estimated number of transmission antennas is preferentially carried out, and then a Cyclic Redundancy Check (CRC) is performed by using a CRC mask pattern in order to detect the number of transmission antennas (for example, refer to PTL 1). 
       CITATION LIST 
     Patent Literature 
       [0007]    {PTL 1} JP 2010-166348 A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0008]    Unfortunately, in such a method of estimating the power by using a reference signal R 0 , a base station cannot be found at a terminal device in the case where the reference signal R 0  is not transmitted at the base station having two or four transmission antennas because of a malfunction of an antenna, and the like. 
         [0009]    Thus, it is an objective of the present invention to provide a receiving device, a receiving method and a computer program that give a solution to the issue described above; and, in other words, which are able to notice the number of transmission antennas and the power more definitely, in order to find a base station more certainly. 
       Solution to Problem 
       [0010]    In order to give a solution to the issue described above; according to a first aspect of the present invention, provided is a receiving device including: a measuring means for measuring a first power of a first signal transmitted from a first transmission antenna, and a second power of a second signal transmitted from a second transmission antenna; a judgment means for judging whether or not a ratio between the first power and the second power is greater than a predetermined threshold value; and an estimation means for estimating that the number of transmission antennas is two, in the case where it is judged that the ratio between the first power and the second power is greater than the predetermined threshold value. 
         [0011]    According to a second aspect of the present invention, provided is a receiving method including: a measuring step for measuring a first power of a first signal transmitted from a first transmission antenna, and a second power of a second signal transmitted from a second transmission antenna; a judgment step for judging whether or not a ratio between the first power and the second power is greater than a predetermined threshold value; and an estimation step for estimating that the number of transmission antennas is two, in the case where it is judged that the ratio between the first power and the second power is greater than the predetermined threshold value. 
         [0012]    According to a third aspect of the present invention, provided is a computer program to operate a computer for an operation including: a measuring step for measuring a first power of a first signal transmitted from a first transmission antenna, and a second power of a second signal transmitted from a second transmission antenna; a judgment step for judging whether or not a ratio between the first power and the second power is greater than a predetermined threshold value; and an estimation step for estimating that the number of transmission antennas is two, in the case where it is judged that the ratio between the first power and the second power is greater than the predetermined threshold value. 
       Advantageous Effects of Invention 
       [0013]    According to the present invention, it becomes possible to provide a receiving device, a receiving method and a computer program that are able to notice the number of transmission antennas and the power more definitely, in order to find a base station more certainly. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  is a block diagram showing a configuration of a receiver according to LTE. 
           [0015]      FIG. 2  is a block diagram showing a configuration of a power measuring unit  14 . 
           [0016]      FIG. 3  is a flowchart for explaining a process of power measurement. 
           [0017]      FIG. 4  is a block diagram showing a configuration example of computer hardware. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0018]    A receiving device according to an embodiment of the present invention is explained below with reference to  FIG. 1  through  FIG. 4 . 
         [0019]      FIG. 1  is a block diagram showing a configuration of a receiver according to LTE. Being an example of a receiving device, a receiver  10  includes a Radio Frequency (RF) unit  11 , a Fast Fourier Transform (FFT) unit  12 , a channel estimation unit  13 , and a power measuring unit  14 . 
         [0020]    In the receiver  10 , the RF unit  11  A/D-converts (A/D stands for Analog/Digital) a signal received by a receiving antenna, which is not shown, from an analog signal to a digital signal. The FFT unit  12  transforms the digital signal into a datum of frequency components by way of a Fourier Transform. The channel estimation unit  13  estimates a channel estimation matrix that shows channel status, by using a known signal (Reference Signal) mapped beforehand in a frequency resource, out of the datum of frequency components. The power measuring unit  14  measures the power on the basis of the channel estimation matrix. 
         [0021]      FIG. 2  is a block diagram showing a configuration of the power measuring unit  14 . The power measuring unit  14  includes a judgment unit  31 , a measuring unit  32 , an antenna estimation unit  33 , and a power calculation unit  34 . 
         [0022]    The judgment unit  31  makes a judgment on whether or not a ratio between the power of a reference signal R 0  and the power of a signal R 1  is greater than a predetermined threshold value. The measuring unit  32  measures the power of the reference signal R 0  and the power of a reference signal R 1 . If it is judged that the ratio between the power of the reference signal R 0  and the power of the signal R 1  is greater than the threshold value, the antenna estimation unit  33  estimates that the number of transmission antennas is two. 
         [0023]    The power calculation unit  34  calculates a received power in such a way that; if it is estimated that the number of transmission antennas is two, an average of the power of the reference signal R 0  and the power of the signal R 1  gives a received power; and meanwhile if it is not estimated that the number of transmission antennas is two, the power of the reference signal R 0  becomes a received power. 
         [0024]      FIG. 3  is a flowchart for explaining a process of power measurement. 
         [0025]    At Step S 11 , the judgment unit  31  makes a judgment on whether the number of antennas at the base station is one or any other number, on the basis of the channel estimation matrix of the reference signal. If it is judged at Step S 11  that the number of antennas at the base station is any number other than one; namely, the number of antennas at the base station is two or four, or unidentified; operation progresses to Step S 12  so that the measuring unit  32  measures a power P0 of the reference signal R 0 , and a power P1 of the reference signal R 1 , on the basis of the channel estimation matrix of the reference signal R 0 , and the channel estimation matrix of the reference signal R 1 , respectively. 
         [0026]    At Step S 13 , the judgment unit  31  makes a judgment on whether or not the number of antennas at the base station is either number of two and four, on the basis of the channel estimation matrix of the reference signal. If it is judged at Step S 13  that the number of antennas at the base station is neither two nor four but the number of antennas at the base station is unidentified, operation progresses to Step S 14 . Then, at Step S 14 , the judgment unit  31  judges whether or not a quotient of ‘the power P1/the power P0’ is greater than a threshold value Tr, wherein the threshold value Tr is a predetermined threshold value. In other words, the judgment unit  31  judges whether a ratio between the power P1 and the power P0 is greater than the predetermined threshold value Tr. 
         [0027]    If it is judged at Step S 14  that the quotient of ‘the power P1/the power P0’ is greater than the threshold value Tr, the antenna estimation unit  33  judges that the number of antennas is two or more (i.e., the antenna estimation unit  33  estimates that the number of transmission antennas is two) so that operation progresses to Step S 15 . At Step S 15 , the power calculation unit  34  calculates a power P=(the power P0+the power P1)/2, and outputs the power P obtained as a result of the calculation as a received power, and then the operation of the power measurement finishes. 
         [0028]    In other words, the antenna estimation unit  33  estimates that the number of antennas is two, in the case where the ratio between the power P1 and the power P0 is judged to be greater than the predetermined threshold value Tr. 
         [0029]    If it is judged at Step S 13  that the number of antennas at the base station is either number of two and four, operation progresses to Step S 15  to calculate the power P=(the power P0+the power P1)/2, as described above, and outputs the power P obtained as a result of the calculation as a received power, and then the operation of the power measurement finishes. 
         [0030]    If it is judged at Step S 11  that the number of antennas at the base station is one, operation progresses to Step S 16 . Then, at Step S 16 , the measuring unit  32  measures a power P0 of the reference signal R 0 , on the basis of the channel estimation matrix of the reference signal R 0 , obtained by the channel estimation unit  13 . After Step S  16 , operation progresses to Step S 17  so that the power calculation unit  34  defines a power P with the power P0, and notifies of the power P obtained as a result of the calculation, as a received power (i.e., to output it as a received power), and then the operation of the power measurement finishes. 
         [0031]    If it is judged at Step S 14  that the quotient of ‘the power P1/the power P0’ is not greater than the threshold value Tr, operation progresses to Step S 17  to define a power P with the power P0, and notifies of the power P, as a received power, and then the operation of the power measurement finishes. 
         [0032]    In this way, even though there is no power in relation to a transmission antenna 0 of the base station (the reference signal R 0 ), an average power of the base station can appropriately be measured to find the base station, when the number of antennas at the base station is unknown for the receiver  10 . Moreover, receiving information data by using the measured result makes it possible to reduce the number of candidate data for demodulating &amp; decoding the information data so that the amount of processing operations and the power consumption can be reduced. 
         [0033]    As described above, in the case where the number of transmission antennas at the base station is unknown for the receiver  10 , each power of the reference signal R 0  and the reference signal R 1  is measured; and then if the power of the reference signal R 1  is sufficiently greater than the power of the reference signal R 0 , the number of antennas at the base station is judged (estimated) to be two or more; and in any other case, the number of antennas at the base station is judged (estimated) to be one. Thus, even when the power of the reference signal R 0  is small, the number of antennas at the base station is judged (estimated) to be two, if the power of the reference signal R 1  is great; so that the power can be estimated with an average of power data of the two antennas, and therefore the power of the base station having two transmission antennas can be estimated (calculated). 
         [0034]    The series of processes described above may be executed by means of hardware, and may also be executed by way of software. For executing the series of processes by way of software, a computer program constituting the software is installed into a computer, which is built in exclusive-use hardware, from a recording medium; or the software is installed from a recording medium, for example, into a general-purpose personal computer that can execute various functions with various computer programs being installed. 
         [0035]      FIG. 4  is a block diagram showing a configuration example of hardware of a computer that executes the series of processes described above by way of a computer program. 
         [0036]    In the computer; a central processing unit (CPU)  101 , a read only memory (ROM)  102 , and a random access memory (RAM)  103  are interconnected by using a bus  104 . 
         [0037]    Moreover, an I/O interface  105  is connected to the bus  104 . Connected to the I/O interface  105  are; an input unit  106  including a keyboard, a mouse, a microphone, and the like; an output unit  107  including a display, a speaker, and the like; a storage unit  108  including a hard disc, a non-volatile memory, and the like; a communication unit  109  including a network interface and the like; and a drive  110  for driving a removable medium  111  such as a magnetic disc, an optical disc, a magnetic optical disc, or a semiconductor memory. 
         [0038]    In the computer configured as described above, the CPU  101  loads a computer program, for example, stored in the storage unit  108 , to the RAM  103  by way of the I/O interface  105  and the bus  104 , and executes the program in order to carry out the series of processes described above. 
         [0039]    The computer program to be executed by the computer (the CPU  101 ) is recorded, for being provided, in the removable medium  111  as a package medium; such as, for example, a magnetic disc (including a flexible disc), an optical disc (Compact Disc-Read Only Memory (CD-ROM), Digital Versatile Disc (DVD), and the like), a magnetic optical disc, or a semiconductor memory; or the computer program is provided via a wired or wireless transmission medium such as a local area network, the Internet, or digital satellite broadcasting. 
         [0040]    Then, the computer program can be installed in the computer by way of being stored in the storage unit  108  through the I/O interface  105 , while the removable medium  111  being mounted on the drive  110 . Alternatively, the computer program can be installed in the computer by way of being stored in the storage unit  108 , while being received in the communication unit  109  by the intermediary of a wired or wireless transmission medium. In another way, the computer program can previously be installed in the computer by way of storing the program in advance in the ROM  102  or the storage unit  108 . 
         [0041]    Incidentally, the computer program to be executed by the computer may be a program with which processes are carried out in chronological order along the sequence explained in this specification document, or may be a program with which processes are carried out in parallel or at the time as required, such as, in response to a call. 
         [0042]    Furthermore, an embodiment of the present invention is not limited only to the embodiment described above, and various other variations may be made without departing from the concept of the present invention.