Abstract:
A base station which performs Multiple Input Multiple Output (MIMO) transmission. A processor configured to generate reference signals by spreading with four groups of orthogonal code sequences, each group of orthogonal code sequences including four orthogonal sequences, wherein the orthogonal code sequences correspond to transmission layers and each of the orthogonal code sequences has a length of four, and a transmit circuit configured to transmit the reference signals. The four groups include a first group where the orthogonal code sequences are Walsh code sequences, a second group where the orthogonal code sequences are represented by mirroring of the orthogonal code sequences in the first group, a third group where the orthogonal code sequences are represented by cyclic shifts of the orthogonal code sequences in the first group, a fourth group where the orthogonal code sequences are represented by mirroring of the orthogonal code sequences in the third group.

Description:
[0001]    The present application is a continuation application of U.S. patent application Ser. No. 14/995,771, filed Jan. 14, 2016, which is a continuation application of the U.S. patent application Ser. No. 14/636,533 filed Mar. 3, 2015, now U.S. Pat. No. 9,264,164, issued Feb. 16, 2016, which is a continuation U.S. patent application Ser. No. 13/618,302, filed Sep. 14, 2012, now U.S. Pat. No. 9,001,639, issued Apr. 7, 2015, which is a continuation of international patent application No. PCT/CN2010/071532, filed Apr. 2, 2010, the entire contents of each are wholly incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to transmission technology in the wireless communication system, and in particular to an orthogonal cover code generation apparatus and method and an orthogonal cover code mapping apparatus and method in a wireless communication system such as an LTE/LTE-A system. 
       BACKGROUND OF THE INVENTION 
       [0003]    The next-generation wireless communication system LTE-A (Long Term Evolution-Advanced) of 3 GPP requires providing a peak rate of 1 Gps and a peak spectrum efficiency of 30 bps/Hz in the downlink. This brings challenge to the transmission scheme in the physical layer of the system. A multi-antenna MIMO (Multiple Input Multiple Output) system is able to support parallel data flow sending thereby greatly increasing the system throughput. Typically, the independent forward error correction encoding is firstly performed on the parallel data flow in the multi-antenna transmission, and then the encoded code words are mapped into the corresponding data transmission layer. In one transmission, the number of all the layers supported by the system is also referred to as a Rank of this transmission. The process of transforming data in each layer into data on each physical antenna is referred to as a pre-encoding process for a signal. LTE-A Rel-10 supports a pre-encoding technology with maximum Rank of 8. 
         [0004]    The sending terminal should transmit pilot sequences used for channel estimation, namely demodulation reference signals (DMRSs), for the receiving terminal to perform MIMO decoding and related demodulation. The design of DMRSs should satisfy that DMRSs corresponding to each data transmission layer are mutually orthogonal, i.e. ensure that there is no interference between equivalent channels of pre-encoded channels of respective sending antennas. In a Rel-10 system, DMRSs corresponding to each data transmission layer are distinguished in the manner of frequency division multiplexing (FDM) and/or code division multiplexing (CDM). The code division multiplexing is implemented by spreading sequences whose correlation is ideal with orthogonal cover code sequences. The orthogonal cover code sequences usually employ Walsh Code sequences or Discrete Fourier Transform sequences. 
         [0005]    If the orthogonal cover code sequences are mapped in the time domain, i.e. spread in the time domain, it is usually assumed that the channels in the physical resources corresponding to the cover code sequences are identical. Assuming that a spreading factor of a spreading sequence is M, the channel response of the M OFDM symbols are considered to be identical. This assumption is true in the low speed environment. However, with the increasing moving speed of a mobile station, variations of the channel response of the M OFDM symbols increase and the orthogonality of the spreading codes are destroyed, leading to mutual interference between respective data transmission layers and thus reducing the accuracy of the channel estimation. 
         [0006]    Moreover, in the Rel-10 system, DMRSs are subjected to the same pre-encoding process as that for data and are mapped onto each sending antenna. The pre-encoding process performs linear superposition on the DMRSs corresponding to each of the code division multiplexed data transmission layers. If the DMRSs corresponding to the M data transmission layers are superposed in the same direction, a signal with amplitude of M is gotten; and if the DMRSs corresponding to the M data transmission layers are superposed in the opposite direction, they are mutually canceled out and a signal with amplitude of 0 is gotten. If such power imbalance of each of the sending antennas occurs in the entire frequency bandwidth, the efficiency of the transmission power may be reduced apparently. 
         [0007]    The reference documents of the present invention are listed in the following, which are incorporated herein by reference as if they are described in detail in the present description.
   1. [Patent Document 1]: Ishii Hiroyuki, Higuchi Kenichi, Base station apparatus, user apparatus and method used in mobile communication system (US 20100034077 A1);   2. [Patent Document 2]: Hooli Kari, Pajukoski Ka, et al., Method, apparatuses, system and related computer product for resource allocation (WO 2009056464 A1);   3. [Patent Document 3]: Kim Hak Seong, Yun Young Woo, et al., Method of transmitting scheduling reference signal (US 20100008333 A1);   4. [Patent Document 4]: Che Xiangguang, Guo Chunyan, et al., Variable transmission structure for reference signals in uplink messages (WO 2009022293 A2);   5. [Patent Document 5]: Cho Joon-young, Zhang Jianzhong, et al., Apparatus and method for allocating code resource to uplink ACK/NACK channels in a cellular wireless communication system (US 2009046646 A1);   6. [Patent Document 6]: Yang Yunsong, Kwon Younghoon, System and method for adaptively controlling feedback information (US 20090209264 A1); and   7. [Patent Document 7]: Pajukoski Kari P, Tiirola Esa, Providing improved scheduling request signaling with ACK/NACK or CQI (US 20090100917).   
 
       SUMMARY OF THE INVENTION 
       [0015]    Hereinafter, a brief summarization about the present invention is given, so as to provide basic understanding of some aspects of the present invention. However, it should be understood that this summarization is not an exhaustive summarization about the present invention. It does not intend to be used to either determine a key or important part of the present invention or define the scope of the present invention. Its object is only to give some concepts about the present invention in a simplified form and hereby acts as a preamble of more detailed descriptions which will be presented later. 
         [0016]    In view of the above mentioned situation in the prior art, the object of the present invention is to provide an orthogonal cover code generation apparatus and method and an orthogonal cover code mapping apparatus and method, which may solve one or more of the problems in the prior art. 
         [0017]    In order to achieve the above mentioned object, according to one aspect of the present invention, there is provided an orthogonal cover code generation apparatus, including: a first orthogonal cover code sequence group generation means for generating a first group of orthogonal cover code sequences C 1  represented by a matrix of [C n, 1 (1), C n, 1 (2), . . . C n, 1 (M)], which satisfy that any adjacent truncated sub cover code sequences [C 2j-1, 1 (2m−1), C 2j-1, 1 (2m)] and [C 2j, 1 (2m−1), C 2j, 1 (2m)] are also mutually orthogonal, wherein n is an index of N orthogonal cover code sequences included in the first group of orthogonal cover code sequences, M is a spreading factor of the orthogonal cover code sequence as a spreading sequence, N≦M, j is an integer satisfying 1≦j≦N/2, and m is an integer satisfying 1≦m≦M/2; a second orthogonal cover code sequence group generation means for performing column mirroring on the first group of orthogonal cover code sequences, so as to generate a second group of orthogonal cover code sequences C 2 ; a third orthogonal cover code sequence group generation means for performing cyclic shift processing of column vectors on the first group of orthogonal cover code sequences, so as to generate a third group of orthogonal cover code sequences C 3 ; and a fourth orthogonal cover code sequence group generation means for performing column mirroring on the third group of orthogonal cover code sequences, so as to generate a fourth group of orthogonal cover code sequences C 4 . 
         [0018]    According to another aspect of the present invention, there is further provided an orthogonal cover code mapping apparatus, including: the orthogonal cover code generation apparatus mentioned above for generating multiple groups of orthogonal cover code sequences, wherein the multiple groups of orthogonal cover code sequences comprise at least the first to fourth groups of orthogonal cover code sequences; and a spreading means for spreading pilot sequences with the multiple groups of orthogonal cover code sequences according to a predetermined mapping rule. 
         [0019]    According to another aspect of the present invention, there is further provided an orthogonal cover code generation method, including: a first orthogonal cover code sequence group generation step of generating a first group of orthogonal cover code sequences C 1  represented by a matrix of [C n, 1 (1), C n, 1 (2), . . . C n, 1 (M)], which satisfy that any adjacent truncated sub cover code sequences [C 2j-1, 1 (2m−1), C 2j-1, 1 (2m)] and [C 2j, 1 (2m−1), C 2j, 1 (2m)] are also mutually orthogonal, wherein n is an index of N orthogonal cover code sequences included in the first group of orthogonal cover code sequences, M is a spreading factor of the orthogonal cover code sequence as a spreading sequence, N≦M, j is an integer satisfying 1≦j≦N/2, and m is an integer satisfying 1≦m≦M/2; a second orthogonal cover code sequence group generation step of performing column mirroring on the first group of orthogonal cover code sequences, so as to generate a second group of orthogonal cover code sequences C 2 ; a third orthogonal cover code sequence group generation step of performing cyclic shift processing of column vectors on the first group of orthogonal cover code sequences, so as to generate a third group of orthogonal cover code sequences C 3 ; and a fourth orthogonal cover code sequence group generation step of performing column mirroring on the third group of orthogonal cover code sequences, so as to generate a fourth group of orthogonal cover code sequences C 4 . 
         [0020]    According to another aspect of the present invention, there is further provided an orthogonal cover code mapping method, including: an orthogonal cover code generation step of generating, according to the orthogonal cover code generation method mentioned above, multiple groups of orthogonal cover code sequences, wherein the multiple groups of orthogonal cover code sequences comprise at least the first to fourth groups of orthogonal cover code sequences; and a spreading step of spreading pilot sequences with the multiple groups of orthogonal cover code sequences according to a predetermined mapping rule. 
         [0021]    According to another aspect of the present invention, there is further provided a computer program product for realizing the orthogonal cover code generation method and/or the orthogonal cover code mapping method mentioned above. 
         [0022]    According to another aspect of the present invention, there is further provided a computer readable medium with the computer program codes for realizing the orthogonal cover code generation method and/or the orthogonal cover code mapping method mentioned above recorded thereon. 
         [0023]    According to another aspect of the present invention, there is further provided a wireless communication system including a transmission apparatus and a reception apparatus, wherein the transmission apparatus includes: a first orthogonal cover code sequence group generation means for generating a first group of orthogonal cover code sequences C 1  represented by a matrix of [C n, 1 (1), C n, 1 (2), . . . C n, 1 (M)], which satisfy that any adjacent truncated sub cover code sequences [C 2j-1, 1 (2m−1), C 2j-1, 1 (2m)] and [C 2j, 1 (2m−1), C 2j, 1 (2m)] are also mutually orthogonal, wherein n is an index of N orthogonal cover code sequences included in the first group of orthogonal cover code sequences, M is a spreading factor of the orthogonal cover code sequence as a spreading sequence, N≦M, j is an integer satisfying 1≦j≦N/2, and m is an integer satisfying 1≦m≦M/2; a second orthogonal cover code sequence group generation means for performing column mirroring on the first group of orthogonal cover code sequences, so as to generate a second group of orthogonal cover code sequences C 2 ; a third orthogonal cover code sequence group generation means for performing cyclic shift processing of column vectors on the first group of orthogonal cover code sequences, so as to generate a third group of orthogonal cover code sequences C 3 ; and a fourth orthogonal cover code sequence group generation means for performing column mirroring on the third group of orthogonal cover code sequences, so as to generate a fourth group of orthogonal cover code sequences C 4 , and wherein the reception apparatus includes a reception means for receiving the spread pilot sequences from the transmission apparatus. 
         [0024]    According to another aspect of the present invention, there is further provided a base station including the orthogonal cover code generation apparatus mentioned above. 
         [0025]    According to another aspect of the present invention, there is further provided a mobile station including the orthogonal cover code generation apparatus mentioned above. 
         [0026]    According to another aspect of the present invention, there is further provided a method in a wireless communication system including a transmission apparatus and a reception apparatus, the method comprising: at the transmitting apparatus, generating a first group of orthogonal cover code sequences C 1  represented by a matrix of [C n, 1 (1), C n, 1 (2), . . . C n, 1 (M)], which satisfy that any adjacent truncated sub cover code sequences [C 2j-1, 1 (2m−1), C 2j-1, 1 (2m)] and [C 2j, 1 (2m−1), C 2j, 1 (2m)] are also mutually orthogonal, wherein n is an index of N orthogonal cover code sequences included in the first group of orthogonal cover code sequences, M is a spreading factor of the orthogonal cover code sequence as a spreading sequence, N≦M, j is an integer satisfying 1≦j≦N/2, and m is an integer satisfying 1≦m≦N/2; performing column mirroring on the first group of orthogonal cover code sequences, so as to generate a second group of orthogonal cover code sequences C 2 ; performing cyclic shift processing of column vectors on the first group of orthogonal cover code sequences, so as to generate a third group of orthogonal cover code sequences C 3 ; and performing column mirroring on the third group of orthogonal cover code sequences, so as to generate a fourth group of orthogonal cover code sequences C 4 , and at the reception apparatus, receiving the spread pilot sequences from the transmission apparatus. 
         [0027]    According to the above mentioned technique scheme of the present invention, by performing column mirroring and cyclic shift processing of column vectors on a group of orthogonal cover code sequences, multiple groups of orthogonal cover code sequences are generated to randomize DMRS signals, so as to overcome the problems of imbalanced transmission power due to pre-encoding. Moreover, the orthogonal cover code sequences generated according to the present invention not only ensure orthogonality in one dimension, such as time domain spreading, but also provide orthogonality in time-frequency two-dimensions, thereby reducing the effect of the moving speed of a mobile station on the orthogonality of DMRSs of different data transmission layers and thus to improve the robustness of channel estimation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    The present invention may be better understood with reference to the detailed description given in conjunction with the accompany drawings as follows. Throughout all the accompany drawings, identical or similar reference numerals are used to represent identical or similar components. The accompany drawings together with the following detailed description are contained in the present specification and form part of the specification, for further illustrating the preferable embodiments of the present invention and explaining the principles and advantages of the present invention by way of example, in which: 
           [0029]      FIG. 1  shows a flow chart of an orthogonal cover code generation method according to an embodiment of the present invention; 
           [0030]      FIG. 2  shows an example diagram of four groups of orthogonal cover code sequences generated according to the present invention. 
           [0031]      FIG. 3  shows a flow chart of an orthogonal cover code mapping method according to an embodiment of the present invention; 
           [0032]      FIG. 4  shows a schematic view of downlink DMRSs in the Rel-10 system; 
           [0033]      FIG. 5  shows a schematic view of mapping the four groups of orthogonal cover code sequences generated according to the present invention into the downlink DMRS resources in the Rel-10 system; 
           [0034]      FIG. 6  shows a schematic view of power distribution of mapping the pre-encoded four groups of orthogonal cover code sequences generated according to the present invention onto a first sending antenna; 
           [0035]      FIG. 7  shows a schematic view of the orthogonality in time-frequency two-dimensions satisfied when the four groups of orthogonal cover code sequences generated according to the present invention are mapped into the downlink DMRSs in the Rel-10 system; 
           [0036]      FIG. 8  shows a structural block diagram of an orthogonal cover code generation apparatus according to an embodiment of the present invention; 
           [0037]      FIG. 9  shows a structural block diagram of an orthogonal cover code mapping apparatus according to an embodiment of the present invention; 
           [0038]      FIG. 10  shows a structural block diagram of a wireless communication system according to an embodiment of the present invention; 
           [0039]      FIG. 11  shows a structural block diagram of a base station according to an embodiment of the present invention; and 
           [0040]      FIG. 12  shows a structural block diagram of a mobile station according to an embodiment of the present invention. 
       
    
    
       [0041]    The skilled in the art should understand that, the elements in the accompany drawings are only shown for the sake of simplicity and clarity but not necessarily drawn to scale. For example, sizes of some elements in the accompany drawings may be enlarged relative to other elements so as to help to improve the understanding of the embodiments of present invention. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0042]    Exemplary embodiments of the present invention will be described below in conjunction with the accompanying drawings. For the sake of simplicity and clarity, not all of the features of practical implementations are described in the specification. However, it should be understood that during developing any of such practical implementations, many implementation-specific decisions should be made in order to achieve a specific object of a developer, for example to conform to the limitations relevant to a system or business, and those limitations may vary with different implementations. Moreover, it should also be understood that although the development work may be very complicated and time consuming but may simply be a routine task for those skilled in the art benefiting from this disclosure. 
         [0043]    It shall further be noted that only those device structures and/or process steps closely relevant to the solutions of the invention are illustrated in the drawings while other details less relevant to the invention are omitted so as not to obscure the invention due to those unnecessary details. 
         [0044]    Referring to the accompany drawings, the orthogonal cover code generation method and orthogonal cover code mapping method according to embodiments of the present invention are to be described in detail as follows. 
         [0045]      FIG. 1  shows a flow chart of an orthogonal cover code generation method according to an embodiment of the present invention. 
         [0046]    Firstly, in step S 110 , a first group of orthogonal cover code sequences C 1  is generated. The first group of orthogonal cover code sequences are represented by a matrix of [C n, 1 (1), C n, 1 (2), . . . C n, 1 (M)], which satisfy that any adjacent truncated sub cover code sequences [C 2j-1, 1 (2m−1), C 2j-1, 1 (2m)] and [C 2j, 1 (2m−1), C 2j, 1 (2m)] are also mutually orthogonal, where n is an index of N orthogonal cover code sequences included in the first group of orthogonal cover code sequences, M is a spreading factor of the orthogonal cover code sequence as a spreading sequence, N≦M, j is an integer satisfying 1≦j≦N/2, and m is an integer satisfying 1≦m≦M/2. Preferably, the first group of orthogonal cover code sequences C 1  may be Walsh Code sequences or Fourier Transform sequences. 
         [0047]    Next, in step S 120 , column mirroring is performed on the first group of orthogonal cover code sequences, so as to generate a second group of orthogonal cover code sequences C 2 . 
         [0048]    Next, in step S 130 , cyclic shift processing of column vectors is performed on the first group of orthogonal cover code sequences, so as to generate a third group of orthogonal cover code sequences C 3 . 
         [0049]    Finally, in step S 140 , column mirroring is performed on the third group of orthogonal cover code sequences, so as to generate a fourth group of orthogonal cover code sequences C 4 . 
         [0050]    Preferably, the first to fourth groups of orthogonal cover code sequences are respectively represented by a matrix C i =[C n,i (1), C n,i (2), . . . C n,i (M)], where i is an index of each group of orthogonal cover code sequences, the first to fourth groups of orthogonal cover code sequences satisfy that the column vectors of each group of orthogonal cover code sequences have different column numbers in a matrix of each group of orthogonal cover code sequences, and 
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         [0000]    composed of two adjacent groups of orthogonal cover code sequences C 2k-1  and C 2k  satisfy that 
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         [0000]    are mutually orthogonal, where k=1 or 2, 1 is an integer satisfying 1≦1≦M/2, n1 is an integer satisfying 1≦n1≦N, n2 is an integer satisfying 1≦n2≦N, and n1≠n2. 
         [0051]    Preferably, more groups of orthogonal cover code sequences may be generated according to processes similar to those in the steps S 130  and S 140  by changing the displacement of the cyclic shift of column vectors. 
         [0052]      FIG. 2  shows an example diagram of four groups of orthogonal cover code sequences C 1  to C 4  generated according to the present invention. In this example, there are totally generated four groups of orthogonal cover code sequences, with each group of orthogonal cover code sequences including four orthogonal sequences and the length of each orthogonal sequence being four. In this example, the generated orthogonal cover code sequences are Walsh sequences and the displacement of the cyclic shift processing of column vectors p=2. 
         [0053]      FIG. 3  shows a flow chart of an orthogonal cover code mapping method according to an embodiment of the present invention. 
         [0054]    Firstly, in step S 310 , multiple groups of orthogonal cover code sequences are generated according to the orthogonal cover code generation method shown in  FIG. 1 , where the multiple groups of orthogonal cover code sequences include at least the first to fourth groups of orthogonal cover code sequences. 
         [0055]    Finally, in step S 320 , pilot sequences are spread with the multiple groups of orthogonal cover code sequences according to a predetermined mapping rule. 
         [0056]    Preferably, in the spreading step, the orthogonal cover code sequences are subjected to mapping processing in one or both of time and frequency domains. 
         [0057]    Preferably, the mapping rule is intended to reduce a variation range of transmission power of the pilot sequences, or guarantee orthogonality of the pilot sequences in specific time-frequency two-dimensional resources. 
         [0058]    Preferably, in the spreading step, the multiple groups of orthogonal cover code sequences are made to be alternately present in the time-frequency resources corresponding to the pilot sequences of Frequency Division Multiplexing and/or Code Division Multiplexing in turn. 
         [0059]    Preferably, in the spreading step, the multiple groups of orthogonal cover code sequences are made to be alternately present in the time-frequency resources corresponding to the pilot sequences of Frequency Division Multiplexing and/or Code Division Multiplexing in turn in one of the following orders: (C 1 , C 2 , . . . , C K-1 , C K ), (C 2 , C 3 , . . . , C K , C 1 ), . . . (C K , C 1 , . . . , C K-2 , C K-1 ); (C K , C K-1 , . . . , C 2 , C 1 ), (C K-1 , C K-2 , . . . , C 1 , C K ), . . . , (C 1 , C K , . . . , C 3 , C 2 ), where K is the number of the multiple groups of orthogonal cover code sequences. 
         [0060]    Preferably, in the spreading step, a mapping order of the multiple groups of orthogonal cover code sequences in a first group of frequency domain resources of Code Division Multiplexing is made to be different from that in a second group of frequency domain resources of Code Division Multiplexing. 
         [0061]    Preferably, in the spreading step, the multiple groups of orthogonal cover code sequences are made to be alternately present in the adjacent first and second groups of frequency domain resources of Code Division Multiplexing in turn. 
         [0062]    Preferably, in the spreading step, Demodulation Reference Signals (DMRSs) of different data transmission layers of Code Division Multiplexing corresponding to two and four pilot symbols in the time domain are made to be mutually orthogonal, and the DMRSs of different data transmission layers of Code Division Multiplexing corresponding to four sub-carriers in the frequency domain are also made to be mutually orthogonal. Further preferably, in the spreading step, the DMRSs of different data transmission layers of Code Division Multiplexing corresponding to two adjacent pilot symbols in the time domain and two adjacent sub-carriers in the frequency domain are made to be mutually orthogonal. 
         [0063]    Preferably, in the spreading step, each physical resource block is made to contain at least the multiple groups of orthogonal cover code sequences. 
         [0064]    The orthogonal cover code mapping method according to the embodiment of the present invention is to be described in combination with the figures in detail as follows by taking an LTE-A Rel-10 system and 4 groups of orthogonal cover code sequences as an example. However, the skilled in the art should be clear that the present invention is not limited to the example described in the following. 
         [0065]      FIG. 4  shows a schematic view of downlink DMRSs in the Rel-10 system. If the data flow is 1 or 2, in each sub-frame of the LTE-A system, the pilot occupies 12 sub-carriers (Resource Element, RE) in the physical resource blocks (PRBs) of the sixth and seventh OFDM symbols and the thirteenth and fourteenth OFDM symbols. The pilots of the first layer and the second layer occupy the same PRB and they are distinguished by an orthogonal cover code of a length of 2. If the data flow is &gt;2, the DMRSs occupy extra 12 REs for transmitting the DMRSs of the third layer and the fourth layer. The pilots of the third layer and the fourth layer occupy the same PRB and they are distinguished by an orthogonal cover code of a length of 2. If the data flow is &gt;4, the number of the REs occupied by the DMRSs does not change and is still 24. Each data flow may be distinguished in the manner of the code division multiplexing (CDM) and/or the frequency division multiplexing (FDM). One of the feasible multiplexing manners is shown in  FIG. 4 . The first, second, fifth and seventh layers are multiplexed in the manner of CDM and are distinguished by an orthogonal cover code of a length of 4. The time-frequency resources occupied are represented by the dark grids in the figure, which are referred to as CDM group 1 for short. The third, fourth, sixth and eighth layers are multiplexed in the manner of CDM and are distinguished by an orthogonal cover code of a length of 4. The time-frequency resources occupied are represented by the grids with twills in the figure, which are referred to as CDM group 2 for short. Moreover, the first, second, fifth and seventh layers and the third, fourth, sixth and eighth layers are multiplexed in the manner of FDM. 
         [0066]      FIG. 5  shows a schematic view of mapping the four groups of orthogonal cover code sequences generated according to the present invention into the downlink DMRS resources in the Rel-10 system. It can be seen from the figure that the orthogonal cover code sequences are spread in the time domain. That is to say, the DMRSs corresponding to the same sub-carrier on the sixth, seventh, thirteenth and fourteenth OFDM symbols form a spreading code of a length of 4. For the time-frequency resource corresponding to CDM group 1, the generated four groups of orthogonal cover code sequences are mapped sequentially in turn in the order of C 1 , C 2 , C 3  and C 4 , so as to guarantee that all the orthogonal cover code sequences are included as much as possible in the entire frequency band corresponding to CDM group 1. For the time-frequency resource corresponding to CDM group 2, the generated four groups of orthogonal cover code sequences are mapped sequentially in turn in the order of C 4 , C 3 , C 2  and C 1 , so as to guarantee that all the orthogonal cover code sequences are included as much as possible in the entire frequency band corresponding to CDM group 2. The corresponding DMRS resources in each PRB, including CDM group 1 and CDM group 2, all in turn include all the four groups of orthogonal cover code sequences. For example, in the first PRB, all the four groups of orthogonal cover code sequences are included in the (k)th, (k+1)th, (k+5)th and (k+6)th sub-carriers. Therefore, the effect of randomizing pilot sequences is achieved and the peak power of the sending signal is effectively reduced. 
         [0067]      FIG. 6  shows a schematic view of power distribution of mapping the pre-encoded four groups of orthogonal cover code sequences generated according to the present invention onto a first sending antenna. It can be seen from the figure that if all the row vectors in the pre-encoding matrix are 1, after the column vectors matrixes of the 4 groups of orthogonal cover code sequences C 1 ˜C 4  are respectively multiplied by the row vectors of the pre-encoding matrix and the products are respectively added, on the (k)th sub-carrier, corresponding DMRSs of the first, second, eighth and ninth OFDM symbols are respectively 4, 0, 0 and 0; on the (k+1)th sub-carrier, corresponding DMRSs of the first, second, eighth and ninth OFDM symbols are respectively 0, 0, 4 and 0; on the (k+5)th sub-carrier, corresponding DMRSs of the first, second, eighth and ninth OFDM symbols are respectively 0, 0, 0 and 4; and on the (k+6)th sub-carrier, corresponding DMRSs of the first, second, eighth and ninth OFDM symbols are respectively 0, 4, 0 and 0. It is not difficult to see that the power of the DMRSs is uniformly distributed on the four OFDM symbols, so as to avoid the problem of imbalanced power. 
         [0068]      FIG. 7  shows a schematic view of the orthogonality in time-frequency two-dimensions according to the mapping method of the present invention. The orthogonal cover code sequences are spread in the time domain, and the four pilot symbols in each sub-frame respectively correspond to four column vectors of the generated orthogonal cover code sequences. If the length of spreading is 2, the orthogonal cover code sequences mapped in this way also guarantee that the sequences corresponding to two pilot symbols in each sub-frame are orthogonal. Moreover, the sequences corresponding to adjacent four sub-carriers in each pilot symbol also satisfy the orthogonality of a length of 4 in the frequency domain. Furthermore, on two adjacent sub-carriers within a same CDM group, the corresponding DMRSs of adjacent two OFDM symbols also form a spreading code of a length of 4, i.e. the orthogonality is provided in the time-frequency two dimensions. For example, for CDM group 1, on the (k+1)th and (k+6)th sub-carriers, corresponding DMRSs of the first and second OFDM symbols also form mutually orthogonal spreading codes of a length of 4. 
         [0069]    Although, in the above, the orthogonal cover code generation method and orthogonal cover code mapping method according to embodiments of the present invention are described in detail in conjunction with the accompanying drawings, the skilled in the art should understand that the flow charts shown in  FIGS. 1 and 3  are only exemplary, and the flow of the methods shown in  FIGS. 1 and 3  may be correspondingly modified according to practical applications and specific requirements. For example, the performing order of some steps in the methods shown in  FIGS. 1 and 3  may be adjusted or some processing steps may be omitted or added as required. 
         [0070]    The orthogonal cover code generation apparatus and orthogonal cover code mapping apparatus according to embodiments of the present invention are to be described in conjunction with the accompanying drawings as follows. 
         [0071]      FIG. 8  shows a structural block diagram of an orthogonal cover code generation apparatus  800  according to an embodiment of the present invention, where only the parts that are closely associated with the present invention are shown for the sake of simplicity and clarity. In the orthogonal cover code generation apparatus  800 , the orthogonal cover code generation method described above with reference to  FIG. 1  can be performed. 
         [0072]    As shown in  FIG. 8 , the orthogonal cover code generation apparatus  800  may include a first orthogonal cover code sequence group generation means  810 , a second orthogonal cover code sequence group generation means  820 , a third orthogonal cover code sequence group generation means  830  and a fourth orthogonal cover code sequence group generation means  840 . 
         [0073]    In the orthogonal cover code generation apparatus  800 , the first orthogonal cover code sequence group generation means  810  may be used for generating a first group of orthogonal cover code sequences C 1  represented by a matrix of [C n, 1 (1), C n, 1 (2), . . . C n, 1 (M)], which satisfy that any adjacent truncated sub cover code sequences [C 2j-1, 1 (2m−1), C 2j-1, 1 (2m)] and [C 2j, 1 (2m−1), C 2j, 1 (2m)] are also mutually orthogonal, where n is an index of N orthogonal cover code sequences included in the first group of orthogonal cover code sequences, M is a spreading factor of the orthogonal cover code sequence as a spreading sequence, N≦M, j is an integer satisfying 1≦j≦N/2, and m is an integer satisfying 1≦m≦M/2. 
         [0074]    The second orthogonal cover code sequence group generation means  820  may be used for performing column mirroring on the first group of orthogonal cover code sequences, so as to generate a second group of orthogonal cover code sequences C 2 . 
         [0075]    The third orthogonal cover code sequence group generation means  830  may be used for performing cyclic shift processing of column vectors on the first group of orthogonal cover code sequences, so as to generate a third group of orthogonal cover code sequences C 3 . 
         [0076]    The fourth orthogonal cover code sequence group generation means  840  may be used for performing column mirroring on the third group of orthogonal cover code sequences, so as to generate a fourth group of orthogonal cover code sequences C 4 . 
         [0077]    Since the specific and/or optional processing procedures of each component of the orthogonal cover code generation apparatus  800  are described in the above with reference to the flow chart of the method, the operation and the processing procedures of these components will not be described in detail any more to avoid repetition. 
         [0078]    It should be illustrated that the structure of the orthogonal cover code generation apparatus  800  shown in  FIG. 8  is only exemplary, and the skilled in the art may modify the structural block diagram shown in  FIG. 8  as required. 
         [0079]      FIG. 9  shows a structural block diagram of an orthogonal cover code mapping apparatus  900  according to an embodiment of the present invention, where only the parts that are closely associated with the present invention are shown for the sake of simplicity and clarity. In the orthogonal cover code mapping apparatus  900 , the orthogonal cover code mapping method described above with reference to  FIG. 3  can be performed. 
         [0080]    As shown in  FIG. 9 , the orthogonal cover code mapping apparatus  900  may include an orthogonal cover code generation apparatus  910  and a spreading apparatus  920 . 
         [0081]    In the orthogonal cover code mapping apparatus  900 , the orthogonal cover code generation apparatus  910  may be composed of an orthogonal cover code generation apparatus as shown in  FIG. 8  for generating multiple groups of orthogonal cover code sequences, where the multiple groups of orthogonal cover code sequences include at least the first to fourth groups of orthogonal cover code sequences. 
         [0082]    The spreading means  920  may be used for spreading pilot sequences with the multiple groups of orthogonal cover code sequences according to a predetermined mapping rule. 
         [0083]    Since the specific and/or optional processing procedures of each component of the orthogonal cover code mapping apparatus  900  are described in the above with reference to the flow chart of the method, the operation and the processing procedures of these components will not be described in detail any more to avoid repetition. 
         [0084]    It should be illustrated that the structure of the orthogonal cover code mapping apparatus  900  shown in  FIG. 9  is only exemplary, and the skilled in the art may modify the structural block diagram shown in  FIG. 9  as required. 
         [0085]      FIG. 10  shows a structural block diagram of a wireless communication system  1000  according to an embodiment of the present invention. As shown in  FIG. 10 , the wireless communication system  1000  may include a transmission apparatus  1010  and a reception apparatus  1020 , where the transmission apparatus  1010  may include the above mentioned orthogonal cover code mapping apparatus  900  and the reception apparatus  1020  may include a reception means  1030  for receiving the spread pilot sequences from the transmission apparatus  1010 . 
         [0086]      FIG. 11  shows a structural block diagram of a base station  1100  according to an embodiment of the present invention. As shown in  FIG. 11 , the base station  1100  may include the above mentioned orthogonal cover code generation apparatus  800 . 
         [0087]      FIG. 12  shows a structural block diagram of a mobile station  1200  according to an embodiment of the present invention. As shown in  FIG. 12 , the mobile station  1200  may include the above mentioned orthogonal cover code generation apparatus  800 . 
         [0088]    It is obvious that each operation procedure of the above mentioned methods according to the present invention may be performed in the manner of a computer executable program stored in a machine-readable storage medium. 
         [0089]    Moreover, the object of the present invention may also be achieved in the following manner, i.e. a storage medium which has the above mentioned executable program code stored therein is directly or indirectly provided to a system or device, and a computer or a central processing unit (CPU) in the system or device reads out and executes the above mentioned program code. In this case, the implementation of the present invention is not limited to a program and the program may be in any form such as an object program, a program executed by an interpreter or a script program provided to an operating system or the like, as long as the system or device has the function to execute the program. 
         [0090]    These machine-readable storage media mentioned above include but not limited to various memories and storage units, semiconductor devices, disk units such as optical disks, magnetic disks and magneto-optical disks, other media suitable to store information and so on. 
         [0091]    Moreover, the present invention may also be achieved in the following manner, i.e. a computer is connected to a corresponding website on the internet and computer program codes according to the present invention are downloaded and installed in the computer and are executed therein. 
         [0092]    It is obvious that each of the components or steps in the devices and methods of the present invention may be decomposed and/or may be recombined. These decompositions and/or re-combinations should be regarded as equivalent schemes of the present invention. Moreover, the steps carrying out the series of processes mentioned above may be naturally performed chronically in an order of description but not necessarily. Some of the steps may be carried out in parallel or independently from each other. 
         [0093]    Although the embodiments of the present invention are described in detail in conjunction with the accompanying drawings, it should be appreciated that the above mentioned embodiments are only for illustration of the present invention and do not limit the present invention. For the skilled in the art, various modifications and alternations may be made to the above mentioned implementations without departing the essential and scope of the present invention. Therefore, the scope of the present invention is only defined by the appended claims and their equivalent meanings. 
         [0094]    Although illustrative embodiments have been described herein, it should be understood that various other changes, replacements and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention. Furthermore, the terms “comprises,” “comprising,” or any other variation thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. 
         [0095]    According to various embodiments, the present disclosure provide the following solutions: