CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application No. PCT/CN2012/082408, filed on Sep. 29, 2012, which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to the field of wireless communication technology, and more particularly to a method and an apparatus for sending and receiving a reference signal, and a terminal device. 
       BACKGROUND 
       [0003]    Reducing a reference signal of a communication system can reduce overhead of the communication system, so as to improve system capacity. Reducing overhead of the reference signal is an important means to reduce the overhead of the communication system. However, a terminal device needs to use the reference signal to complete timing and synchronous tracking, and performs demodulation and decoding operations only on this basis. While, a certain amount of reference signal symbols are necessary for a timing and synchronous tracking algorithm. If the number of the reference signal symbols is small, the terminal device cannot obtain good timing and synchronous tracking, and thus cannot guarantee good communication quality. Therefore, from the view of guaranteeing the communication quality, the terminal device should be provided with a certain amount of reference signals. 
         [0004]    There are various bandwidths in modern communication systems, for example, an LTE (long term evolution) communication system provides six types of bandwidths, i.e., 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz. When the overhead of the reference signal is reduced for such a system, the timing and synchronous tracking capacity of the terminal device needs to be considered, and a certain amount of reference signals need to be guaranteed. If the bandwidth is small, it is undesirable to reduce the overhead of the reference signal, or it is necessary to reduce the overhead of the reference signal as little as possible. 
         [0005]    Therefore, in view of processing capability of the terminal device and a guarantee of communication quality, it is necessary to select appropriate reference signal granularity according to the bandwidth when the overhead of the reference signal is reduced, rather than use the same method for reducing the overhead of the reference signal with respect to all the cases, such as different bandwidths. 
       SUMMARY 
       [0006]    This application provides a method and an apparatus for sending and receiving a reference signal, so as to solve the technical problem of large reference signal overhead. 
         [0007]    In one aspect, embodiments of the present invention provide a method for sending and receiving a reference signal on the premise of saving reference signal overhead, including: 
         [0008]    when a sending bandwidth and X satisfy a certain relationship, sending a reference signal symbol only once in every N subframes; and when the certain relationship is not satisfied, sending the reference signal on all the subframes or sending the reference signal on M subframes in every N subframes. Correspondingly, during reception of a terminal device, when a bandwidth and X satisfy a certain relationship, receiving a reference signal symbol only once in every N subframes; and when the certain relationship is not satisfied, receiving the reference signal on all the subframes or on M subframes in every N subframes. Here, one subframe has a duration of 1 ms, but does not exclude other values. 
         [0009]    In another aspect, embodiments of the present invention provide a method for adjusting a granularity of sending and receiving a reference signal, including: 
         [0010]    when the sending bandwidth changes, the granularity of sending the reference signal and the granularity of receiving the reference signal are also adjusted correspondingly. The adjustment method is given in the embodiments of the present invention. 
         [0011]    The sending device needs to indicate the terminal device whether the granularity of the reference signal changes with the granularity adjustment of reference signal; the terminal device needs to receive the signaling and may report to the sending device after the granularity change of the reference signal has been completed. The sending device considers that the granularity change of the reference signal has been completed after the reporting is received or the set timer times out, and enters a normal operation. A set of signaling and signaling procedures are given in the present invention. 
         [0012]    In still another aspect, embodiments of the present invention provide a sending apparatus for saving reference signal overhead, including: 
         [0013]    a first sending module, configured to send the reference signal according to the method for sending the reference signal and send the reference signal and other signals within the bandwidth; configured to adjust a granularity of sending the reference signal according to the change method of sending the reference signal, when the bandwidth changes; 
         [0014]    a second sending module, configured to send an indication signaling for indicating a terminal device a change in the granularity of the reference signal, when the bandwidth changes and the granularity of sending the reference signal also changes; 
         [0015]    a first processing module, configured to wait after the granularity of sending the reference signal changes, and perform subsequent processing when a certain time arrives; or 
         [0016]    configured to perform subsequent processing after a first acquiring module receives a feedback of an apparatus for receiving the reference signal. 
         [0017]    In still another aspect, embodiments of the present invention provide a terminal device, including: 
         [0018]    a first acquiring module, configured to receive the reference signal according to the method for receiving the reference signal; and configured to adjust a granularity of receiving the reference signal according to the method for adjusting the granularity of receiving the reference signal as described above, when the bandwidth changes; 
         [0019]    a second acquiring module, configured to receive a signaling for indicating a change in the granularity of the reference signal, or configured to receive a signaling for indicating a change in a bandwidth and the bandwidths before and after the change. 
         [0020]    a first sending module, configured to feed back an indication for indicating the terminal device has completed a granularity change of receiving the reference signal. 
         [0021]    Through the method of the embodiments of the present invention, when a bandwidth is greater than or equal to X, the system can effectively reduce the communication overhead by reducing the granularity of sending the reference signal. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0022]    In order to illustrate the technical solutions in embodiments of the present invention or the prior art more clearly, accompanying drawings needed in the embodiments or the prior art are illustrated briefly as follows. Apparently, the accompanying drawings are merely certain of embodiments of the invention, and persons skilled in the art can derive other drawings from them without creative efforts. 
           [0023]      FIG. 1  is a schematic diagram of a method for sending a reference signal by a sending apparatus on different bandwidths according to an embodiment of the present invention; 
           [0024]      FIG. 2  is a schematic diagram of a method for receiving a reference signal by a receiving apparatus on different bandwidths according to an embodiment of the present invention; 
           [0025]      FIG. 3  is a schematic flowchart of a corresponding granularity change of sending a reference signal when a bandwidth of a sending apparatus changes according to an embodiment of the present invention; 
           [0026]      FIG. 4  is another schematic flowchart of a corresponding granularity change of sending a reference signal when a bandwidth of a sending apparatus changes according to an embodiment of the present invention; 
           [0027]      FIG. 5  is a schematic flowchart of a granularity change of receiving a reference signal when a bandwidth of a terminal device changes according to an embodiment of the present invention; 
           [0028]      FIG. 6  is another schematic flowchart of a granularity change of receiving a reference signal when a bandwidth of a terminal device changes according to an embodiment of the present invention; 
           [0029]      FIG. 7  is a schematic structural diagram of an apparatus for sending a reference signal according to an embodiment of the present invention; and 
           [0030]      FIG. 8  is a schematic structural diagram of an apparatus for receiving a reference signal according to an embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0031]    The technical solutions in the embodiments of the present invention are hereinafter described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the embodiments described here are part of the embodiments of the invention and not all of the embodiments. All other embodiments, which can be derived by persons skilled in the art from the embodiments given herein without creative efforts, shall fall within the protection scope of the present invention. 
         [0032]    Reducing a reference signal of a communication system can reduce overhead of the communication system, so as to improve system capacity. Reducing overhead of the reference signal is an important means to reduce the overhead of the communication system. However, a terminal device needs to use the reference signal to complete timing and synchronous tracking, and performs demodulation and decoding operations only on this basis. While, a certain amount of reference signal symbols are necessary for a timing and synchronous tracking algorithm. If the number of the reference signal symbols is small, the terminal device cannot obtain good timing and synchronous tracking, and thus cannot guarantee good communication quality. Therefore, from the view of guaranteeing the communication quality, the terminal device should be provided with a certain amount of reference signals. 
         [0033]    There are various bandwidths in modern communication systems, for example, an LTE (long term evolution) communication system provides six types of bandwidths, i.e., 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz. When the overhead of the reference signal is reduced for such a system, the timing and synchronous tracking capacity of the terminal device needs to be considered, and a certain amount of reference signals need to be guaranteed. If the bandwidth is small, it is undesirable to reduce the overhead of the reference signal, or it is necessary to reduce the overhead of the reference signal as little as possible. 
         [0034]    Therefore, in view of processing capability of the terminal device and a guarantee of communication quality, it is necessary to select appropriate reference signal granularity according to the bandwidth when the overhead of the reference signal is reduced. 
         [0035]    As shown in  FIG. 1 , in S 101 , when a communication bandwidth is greater than or equal to X, a granularity of sending the reference signal is to send the reference signal once in every N subframes; however, when the bandwidth is less than X, the granularity of sending the reference signal is to send the reference signal on all the subframes or send the reference signal on M subframes in every N subframes. In S 102 , when the communication bandwidth is greater than X, the granularity of sending the reference signal is to send the reference signal once in every N subframes; however, when the bandwidth is less than or equal to X, the granularity of sending the reference signal is to send the reference signal on all the subframes or send the reference signal on M subframes in every N subframes. According to theoretical analysis and practice, a typical value of X is 5 MHz or 25 PRB, and 3 MHz or 15 PRB (corresponding to a bandwidth of LTE, the bandwidth of LTE includes 1.4 MHz (6 PRB), 3 MHz (15 PRB), 5 MHz (25 PRB), 10 MHz (50 PRB), 15 MHz (75 PRB) and 20 MHz (100 PRB), and a typical value of N is 5 subframes. In S 102 , when the communication bandwidth is less than X, the granularity of sending the reference signal cannot be reduced, that is, the reference signal is sent on all the subframes or in every N subframes, wherein the value of M makes its duration less than a period of N subframes. 
         [0036]    The advantageous effects of this sending method are that, when a bandwidth is greater than or equal to X, the system can effectively reduce the communication overhead by reducing the granularity of sending the reference signal, and meanwhile guarantee a certain amount of the reference signals and thus timing and synchronous tracking performances. When the bandwidth is less than X, in order to guarantee the timing and synchronous tracking performances, the sending device takes precedence to consider keeping a certain amount of the reference signals, and appropriately reduces the overhead of the reference signal while guaranteeing the performance. Such a sending method comes to a good compromise between communication quality and reducing overhead of the reference signal. 
         [0037]    Correspondingly, when a terminal device receives and uses the reference signal, a granularity of receiving the reference signal is adjusted correspondingly according to a change in the reference signal granularity at the sending end. 
         [0038]    As shown in  FIG. 2 , in S 201 , when a communication bandwidth is greater than or equal to X, a position of receiving the reference signal is to receive the reference signal once in every N subframes; when the communication bandwidth is less than X, the terminal device receives the reference signal on all the subframes for processing or there are M chances to receive the reference signal on M subframes in every N subframes. In S 202 , when the communication bandwidth is greater than X, the position of receiving the reference signal is to receive the reference signal once in every N subframes; when the communication bandwidth is less than or equal to X, the terminal device receives the reference signal on all the subframes for processing or there are M chances to receive the reference signal on M subframes in every N subframes. Correspondingly, the typical value of X is 5 MHz or 25 PRB, and 3 MHz or 15 PRB, and a typical value of N is 5 subframes. In S 202 , the values of N and M are the same with those as described in  FIG. 1 . 
         [0039]    The advantageous effects of this sending method are that, when a bandwidth is greater than or equal to X, the system can effectively reduce the communication overhead by reducing the granularity of sending the reference signal, and meanwhile guarantee a certain amount of the reference signals and thus timing and synchronous tracking performances. When the bandwidth is less than X, in order to guarantee the timing and synchronous tracking performances, the receiving device can acquire more reference signals for timing and synchronous tracking, so as to achieve robust performance. Such a receiving method can make use of the reference signal as much as possible to guarantee the timing and synchronous tracking performances and improve communication quality. 
         [0040]    During operation, the sending device may reduce the transmission bandwidth due to energy saving or other reasons, and further, the sending device also reduces the overhead of the reference signal, then the sending device also needs to adjust the granularity of sending the reference signal while adjusting the sending bandwidth. 
         [0041]    In  FIG. 3 , when a bandwidth of a sending device (a base station or a set of base stations) changes from being greater than or equal to X to being less than X, a granularity of sending a reference signal needs to be adjusted correspondingly, wherein sending the reference signal once in every N subframes (as shown in S 301 ) is changed into sending the reference signal on all the subframes or sending the reference signal on M subframes in every N subframes (as shown in S 304 ), where M is an integer greater than 1. While changing the bandwidth and changing the granularity of sending the reference signal, the sending device needs to send signaling for indicating a terminal device a change in the granularity of sending the reference signal, or indicating a terminal device a change in the system bandwidth and notifying the bandwidths before and after the change, or whether the bandwidth change exceeds a threshold corresponding to X, as shown in S 303 . The terminal device thus can know or infer that the granularity of sending the reference signal has changed, and thereby adjust the granularity of receiving the reference signal. The sending device needs to wait for a certain amount of time after adjusting the bandwidth and the granularity of sending the reference signal, because a certain amount of processing time is necessary for the terminal device to receive the signaling and adjust the granularity of receiving the reference signal. While waiting, the sending device can start its timer, if the timer starts from the change or sending a change instruction and ends at the L subframes, the sending device can consider that the terminal device has completed the granularity change of receiving the reference signal; or, while waiting, the sending device is waiting for feedbacks of the terminal device until all the feedbacks are received, and then the sending device starts to perform a normal operation on a new bandwidth, as shown in S 305 . 
         [0042]    In  FIG. 4 , when a bandwidth of a sending device (a base station or a set of base stations) changes from being less than X to being greater than or equal to X, the granularity of sending the reference signal needs to be adjusted correspondingly, wherein sending the reference signal on all the subframes or sending the reference signal in every N subframes (as shown in S 401 ) is changed into sending the reference signal once in every N subframes (as shown in S 404 ), where a time length corresponding to M is less than N subframes. While changing the bandwidth and changing the granularity of sending the reference signal, the sending device needs to send signaling for indicating a terminal device a change in the granularity of sending the reference signal, or indicating a terminal device a change in the system bandwidth and notifying the bandwidths before and after the change, or whether the bandwidth change exceeds a threshold corresponding to X, as shown in S 403 . The terminal device thus can know or infer that the granularity of sending the reference signal has changed, and thereby adjust the granularity of receiving the reference signal. The sending device needs to wait for a certain amount of time after adjusting the bandwidth and the granularity of sending the reference signal, because a certain amount of processing time is necessary for the terminal device to receive the signaling and adjust the granularity of receiving the reference signal. While waiting, the sending device can start its timer, if the timer starts from the change or sending a change instruction and ends at the L subframes, the sending device can consider that the terminal device has completed the granularity change of receiving the reference signal; or, while waiting, the sending device is waiting for feedbacks of the terminal device until all the feedbacks are received, and then the sending device starts to perform a normal operation on a new bandwidth, as shown in S 405 . 
         [0043]    Such a sending change procedure can achieve advantageous effects of the sending method shown in  FIG. 1 , besides, the granularity of sending the reference signal can be effectively adjusted when the sending device changes the bandwidths. Meanwhile, the signaling indication provided for the terminal device can effectively trigger the terminal device to timely adjust the granularity of receiving the reference signal, so that the sending device and the receiving device can be coordinated consistently, and communication effect can be improved. 
         [0044]    The terminal device needs to adjust the granularity of receiving the reference signal when receiving the reference signal, and may also need to notify the sending device that the granularity of receiving the reference signal has been adjusted completely. 
         [0045]    In  FIG. 5 , when a bandwidth of a terminal device changes from being greater than or equal to X to being less than X, a granularity of receiving a reference signal needs to be adjusted correspondingly, wherein receiving the reference signal once in every N subframes (as shown in S 501 ) is changed into receiving the reference signal on all the subframes or receiving the reference signal on M subframes in every N subframes (as shown in S 504 ), where a time length corresponding to M is less than N subframes. The terminal device firstly receives an signaling indication of the sending device, that is, indicating the terminal device a change in the granularity of sending the reference signal, or indicating the terminal device a change in the system bandwidth and notifying the bandwidths before and after the change, or whether the bandwidth change exceeds a threshold corresponding to X, as shown in S 503 . The terminal device thus can know or infer that the granularity of sending the reference signal has changed according to the signaling, and thereby adjust the granularity of receiving the reference signal. The terminal device may need to feed back to the sending device after the granularity adjustment of receiving the reference signal is completed, that is, notify the sending device that the granularity change of receiving the reference signal has been completed, as shown in S 505 . 
         [0046]    In  FIG. 6 , when a bandwidth of the terminal device changes from being less than X to being greater than or equal to X, a granularity of receiving a reference signal needs to be adjusted, wherein receiving the reference signal on all the subframes or receiving the reference signal on M subframes in every N subframes (as shown in S 601 ) is changed into receiving the reference signal once in every N subframes (as shown in S 604 ), where a time length corresponding to M is less than N subframes. The terminal device firstly receives an signaling indication of the sending device, that is, indicating the terminal device a change in the granularity of sending the reference signal, or indicating the terminal device a change in the system bandwidth and notifying the bandwidths before and after the change, or whether the bandwidth change exceeds a threshold corresponding to X, as shown in S 603 . The terminal device thus can know or infer that the granularity of sending the reference signal has changed according to the signaling, and thereby adjust the granularity of receiving the reference signal. The terminal device may need to feed back to the sending device after the granularity adjustment of receiving the reference signal is completed, that is, notify the sending device that the granularity change of receiving the reference signal has been completed, as shown in S 605 . 
         [0047]    Such a granularity change procedure of receiving the reference signal can achieve advantageous effects of the sending method shown in  FIG. 2 , besides, the signaling indication provided for the terminal device can effectively trigger the terminal device to timely adjust the granularity of receiving the reference signal, so that the sending device and the receiving device can be coordinated consistently, and communication effect can be improved. 
         [0048]      FIG. 7  shows a structural diagram of an apparatus for sending a reference signal, and the apparatus consists of a first sending module, a second sending module and a first processing module. 
         [0049]    The first sending module, as shown by  71 , is configured to send a reference signal according to the method for sending the reference signal as described above and send the reference signal and other signals within a bandwidth; and adjust a granularity of sending the reference signal according to the change method of sending the reference signal as described above, when the bandwidth changes; 
         [0050]    The second sending module is configured to send an indication signaling for indicating a terminal device a change in the granularity of the reference signal, when the bandwidth changes and the granularity of sending the reference signal also changes; 
         [0051]    The first processing module is configured to wait after the granularity of sending the reference signal changes, and perform subsequent processing when a certain time arrives; or 
         [0052]    configured to perform subsequent processing after a first acquiring module receives a feedback of an apparatus for receiving the reference signal. 
         [0053]    Such a sending device has advantageous effects that various modules support functions as described above, that is, sending the reference signal and a granularity change procedure of sending the reference signal. 
         [0054]      FIG. 8  shows a structural diagram of a terminal device, and the device consists of a first acquiring module, a second acquiring module and a first sending module. 
         [0055]    The first acquiring module is configured to receive a reference signal according to the method for receiving the reference signal as described above; and configured to adjust a granularity of receiving the reference signal according to the method for adjusting the granularity of receiving the reference signal as described above, when the bandwidth changes; 
         [0056]    The second acquiring module is configured to receive a signaling for indicating a change in the granularity of the reference signal, or configured to receive a signaling for indicating a change in a bandwidth and the bandwidths before and after the change. 
         [0057]    The first sending module is configured to feed back an indication for indicating the terminal device has completed a granularity change of receiving the reference signal. 
         [0058]    Such a receiving device has advantageous effects that various modules support functions as described above, that is, receiving the reference signal and a granularity change procedure of receiving the reference signal. 
         [0059]    The whole system consists of a sending device and a terminal device, when the system bandwidth changes, the sending device completes the granularity change of sending the reference signal according to the method for sending and changing the reference signal, as shown in  FIGS. 1 ,  3  and  4 , respectively, and sends a notification to the terminal device for indicating a change in the granularity of the reference signal. After receiving the notification of the granularity of sending the reference signal, the terminal device completes receiving of the reference signal and the granularity change of receiving the reference signal according to the method for receiving of the reference signal and the granularity change method of receiving the reference signal, or completes the granularity change of the reference signal and notifies to the sending device, as shown in  FIGS. 2 ,  5  and  6 , respectively. 
         [0060]    As a whole, the method for sending the reference signal, the change procedure of sending the reference signal, the sending device, the method for receiving the reference signal, the change procedure of receiving the reference signal and the terminal device, as described above, can effectively reduce the overhead of the reference signal and meanwhile guarantee the communication quality. The overhead of the reference signal cannot be reduced without limitation, but this reduction needs to consider performances, such as the timing and synchronous tracking, radio resource management (Radio Resource Management, RRM), demodulation and channel measurement feedback, and so on, and the timing and synchronous tracking needs a certain amount of reference signals. This raises a higher requirement on a system with a smaller bandwidth, that is, when the bandwidth is small, reference signals cannot be reduced greatly. The method for sending/receiving the reference signal, and the device for sending/receiving the reference signal as described above can effectively reduce the overhead of the reference signal when the bandwidth is large, and can appropriately reduce the overhead of the reference signal when the bandwidth is small, so as to guarantee the communication quality, when the bandwidth changes, the sending end and receiving end can consistently complete granularity change of the reference signal. 
         [0061]    It should be understood that, technical solutions of the present invention can be applicable to various communication systems, such as global system of mobile communication (Global System of Mobile communication, GSM), code division multiple access (Code Division Multiple Access, CDMA) system, wideband code division multiple access (Wideband Code Division Multiple Access, WCDMA) system, general packet radio service (General Packet Radio Service, GPRS), long term evolution (Long Term Evolution, LTE) system, LTE frequency division duplex (Frequency Division Duplex, FDD) system, LTE time division duplex (Time Division Duplex, TDD), universal mobile telecommunication system (Universal Mobile Telecommunication System, UMTS), worldwide interoperability for microwave access (Worldwide Interoperability for Microwave Access, WiMAX) communication system. 
         [0062]    It should also be understood that, in the embodiments of the present invention, a user equipment (User Equipment, UE) also can be called a terminal (Terminal), a mobile station (Mobile Station, MS), or a mobile terminal (Mobile Terminal) and so on, and the user equipment can communicate with one or more core networks via a radio access network (Radio Access Network, RAN), for example, the user equipment can be a mobile phone (or a “cellular” phone) and a computer with a mobile terminal, and thus can be, for example, portable, pocket, hand-held, computer-included, or vehicle-mounted mobile apparatuses which communicate voice and/or data with a radio access network. 
         [0063]    In the embodiments of the present invention, the base station can be a base station (Base Transceiver Station, BTS) in GSM or CDMA, or a base station (NodeB, NB) in WCDMA, or an evolved Node B (Evolutional Node B, ENB or e-NodeB) in LTE, and the present invention is not limited thereto. For ease of description only, the embodiments below will be described taking an eNB and a user equipment UE as examples. 
         [0064]    Understandably, in the embodiments described herein, the disclosed apparatus, method and system may be implemented in other modes. For example, the device embodiments above are illustrative in nature, and the units of the device are defined from the perspective of logical functions only and may be defined in a different method in practical application. For example, multiple units or modules may be combined or integrated into another system, or some features may be ignored or not executed. 
         [0065]    It should be appreciated by persons skilled in the art that, all or a part of the steps for implementing the method of the above embodiments may be completed by relevant hardware under the instruction of a program, and the program may be stored in a computer readable storage medium, when the program is executed, the steps in the method of the above embodiments are performed; the storage medium comprises various media capable of storing program codes, such as a ROM, a RAM, a floppy disk, or an optical disk and the like. 
         [0066]    The above descriptions are merely specific implementation methods of the present invention, but not intended to limit the protection scope of the present invention. Any modifications, variations or replacement that can be easily derived by persons skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope of the present invention. Therefore, the protection scope of the present invention is subject to the appended claims.
Embodiments of the present invention provide a method, an apparatus for sending and receiving a reference signal, and a terminal device. The method includes: when a bandwidth satisfies a given condition, sending or receiving a reference signal symbol only once in every N subframes; and when the given condition is not satisfied, increasing the sending or receiving of the reference signal. The method also includes adjusting a granularity of sending or receiving the reference signal with the change of the bandwidth, and the signaling and processes required during the adjustment process. By means of the method and apparatus, the reference signal overhead can be effectively reduced, while good communication quality is ensured, thereby achieving good compromise between communication effectiveness and reliability.