Patent Publication Number: US-10313895-B2

Title: Wireless communications method and system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Application is a continuation of International Application No. PCT/CN2014/088819, filed on Oct. 17, 2014, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to the wireless communications field, and in particular, to a wireless communications method and system. 
     BACKGROUND 
     An existing base station (BS) communicates with user equipment (UE) in a broadcasting manner in which a beam is extremely wide, coverage is wide, user equipment in a same sector of beams can be distinguished only by frequencies, each user equipment occupies small bandwidth in a given frequency bandwidth, and a system capacity is small because time-division multiplexing is used. By contrast, a millimeter wave has a higher frequency band and a narrower beam. A high-gain directional narrow beam may be implemented by using a beamforming technology, so that each user equipment can perform space division multiplexing/frequency division multiplexing by using multiple narrow beams to obtain a multiplexing gain and improve a communication capacity. 
     In beamforming technology, an antenna distance needs to be not greater than ½ of a wavelength. However, in a line of sight (LOS) situation, non-correlation of multiple-input multiple-output (MIMO) channels requires an antenna distance to be greater than a specific value, and a greater antenna distance indicates a lower antenna correlation. Therefore, for a large-scale array antenna system with a high frequency band, because an antenna diameter is limited and an antenna distance is relatively small, it is difficult to meet a Rayleigh length of LOS-MIMO so as to ensure non-correlation between MIMO channels. In a conventional technology, communication quality of a MIMO communications system is relatively poor. 
     SUMMARY 
     In view of this, the present invention provides a wireless communications method and system. Transmit/receive antennas are separated to respectively split transmit/receive antenna units into M/N subarrays and form M/N beams with low correlation that are separate in space. Therefore, a transmission-dimensional structure similar to MIMO is formed, transmit modes of the transmit/receive antennas are obtained by means of searching, and relatively high communication quality is ensured. 
     According to a first aspect, a wireless communications system is provided, including a transmit end, where the transmit end includes a transmit module having at least two antenna units, the transmit module transmits M narrow beams with different spatial directions according to a quality of service (QoS) requirement, and switches a transmit mode according to a preset switching rule, and a set of the spatial directions of the M narrow beams forms a transmit mode and a receive end, where the receive end includes a receive module having at least two antenna units, the receive module receives N beams according to the QoS, and a transmission channel is formed between the transmit end of the M narrow beams and the receive end of the N beams; the receive end calculates transmission channel quality in different transmit modes, searches for a transmit mode that meets the QoS requirement, and feeds back the transmit mode to the transmit end, or feeds back a transmit mode with optimal channel quality to the transmit end if transmission channel quality corresponding to all transmit modes is traversed but no transmit mode that meets the QoS requirement is found; and both M and N are integers greater than or equal to 1. 
     According to a second aspect, a wireless communications method is provided, including enabling, according to a quality of service requirement, a transmit module of a transmit end to transmit M narrow beams with different spatial directions and a receive module of a receive end to receive N beams, so as to form a transmission channel, where both M and N are integers greater than or equal to 1, switching a transmit mode according to a preset switching rule, where a set of the spatial directions of the M narrow beams forms a transmit mode, obtaining channel quality in a current transmit mode according to signals received by the N beams of the receive end and searching for a transmit mode that meets the QoS requirement and feeding back the transmit mode to the transmit end, or feeding back a transmit mode with optimal channel quality to the transmit end when transmission channel quality corresponding to all transmit modes is traversed but no transmit mode that meets the QoS requirement is found. 
     In the wireless communications method and system provided in the embodiments of the present invention, a transmit module transmits M narrow beams according to a QoS requirement, and a receive end receives N beams according to the QoS requirement, so as to form an N×M transmission channel. Transmission channel quality in different transmit modes is calculated to learn a transmit mode that meets the QoS requirement. If no transmit mode that meets the QoS requirement is found, a transmit mode with optimal channel quality is fed back to a transmit end. Therefore, communication quality can be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To describe the technical solutions in the present invention more clearly, the following briefly describes the accompanying drawings required for describing the implementation manners. Apparently, the accompanying drawings in the following description show merely some implementation manners of the present invention, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts. 
         FIG. 1  is a schematic structural diagram of a wireless communications system according to an embodiment of the present invention; 
         FIG. 2  is a schematic module diagram of a wireless communications system according to a first embodiment of the present invention; 
         FIG. 3  is a schematic diagram of transmitting a narrow beam by a transmit module; 
         FIG. 4  is a schematic diagram of a module of a processing unit shown in  FIG. 2 ; 
         FIG. 5  is a schematic module diagram of a feedback unit shown in  FIG. 2 ; 
         FIG. 6  is a schematic module diagram of a configuration unit shown in  FIG. 2 ; 
         FIG. 7( a )  to  FIG. 7( c )  are schematic diagrams of transmission modes and resource allocation that are in different QoS; 
         FIG. 8  is a schematic module diagram of a wireless communications system according to a second embodiment of the present invention; 
         FIG. 9  is a flowchart of a wireless communications method according to a first embodiment of the present invention; and 
         FIG. 10  is a flowchart of a wireless communications method according to a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The following clearly describes the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are merely some but not all of the embodiments of the present invention. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. 
     Referring to  FIG. 1  and  FIG. 2 , a first embodiment of the present invention provides a wireless communications system. The wireless communications system includes a transmit end  100  and a receive end  200 . Data may be transmitted between the transmit end  100  and the receive end  200  by using a wireless communications method. The transmit end  100  includes a transmit module  120  having at least two antenna units. The transmit module  120  transmits M narrow beams with different spatial directions (beams with relatively narrow coverage) according to a quality of service (QoS) requirement, and switches a transmit mode according to a preset switching rule. A set of the spatial directions of the M narrow beams forms a transmit mode. 
     Referring to  FIG. 1  to  FIG. 3 , in this embodiment of the present invention, the transmit end  100  may be a base station (BS) or user equipment (UE), and has a transmit module  120 , and the transmit module  120  includes at least two antenna units. The transmit end  100  includes a transmit control unit  110 , and the transmit control unit  110  controls, according to a QoS requirement in a system, the transmit module  120  to transmit M narrow beams with different spatial directions. A set of the spatial directions of the M narrow beams forms a transmit mode. If a spatial direction of a first narrow beam is α 1 , a spatial direction of a second narrow beam is α 2 , . . . , and a spatial direction of an M th  narrow beam is α M , a current transmit mode is denoted as {α 1 , α 2 , . . . , α M }. 
     In this embodiment of the present invention, the transmit end  100  further includes a first switching rule preset unit  130 , and the first switching rule preset unit  130  presets a switching rule of a transmit mode of the transmit end  100 , so that the transmit control unit  110  switches the transmit mode of the transmit end  100  according to the switching rule that is set by the first switching rule preset unit  130 . Specifically, after obtaining the switching rule provided by the first switching rule preset unit  130 , the transmit control unit  110  sets, according to a transmit mode defined by the switching rule, the spatial directions of the M narrow beams transmitted by the transmit end  100 . For example, for a possible switching rule, definitions may be as follows: Entire space is divided into M areas, and the spatial direction of the narrow beam is determined by two parameters: θ and φ, where θ is a horizontal angle of the narrow beam, and φ is a pitch angle of the narrow beam. A space area allocated to a first narrow beam is [θ 1min , θ 1max ] and [φ 1min , φ 1max ], that is, the first narrow beam, that is, a beam 1 scans the space area [θ 1min , θ 1max ] and [φ 1min , φ 1max ]. Similarly, a space area allocated to a k th  narrow beam, that is, a beam k (2≤k≤M) is [θ kmin , θ kmax ] and [φ kmin , φ kmax ], and the beam k scans the space area [θ kmin , θ kmax ] and [φ kmin , φ kmax ], so that the spatial direction of the narrow beam varies in these space areas. 
     It should be noted that, in another embodiment of the present invention, space may be set to partitions in another manner. For example, three-dimensional rectangular coordinates or another representation method may be used to represent a definition of the spatial direction, or partitioning does not need to be performed. In addition, the switching rule defined by the first switching rule preset unit  130  may have another definition. For example, a transmit mode may be switched according to a preset codebook order. For a mode switched according to a preset codebook order, space may be divided, and beams are switched according to respective codebooks; or space does not need to be divided, and M narrow beams are entirely switched according to a specific rule. Space division and beam switching are simultaneously performed, and the space division is not limited herein. Generally, the first switching rule preset unit  130  switches a switching rule each time a preset period T1 expires, that is, the transmit end  100  switches a transmit mode each time the period T1 expires. For example, an original transmit mode is a first transmit mode, the transmit mode is switched to a second transmit mode after one period T1 and is switched to a third transmit mode after two periods T1, and by analogy, the transmit mode is switched to a t th  transmit mode after t−1 periods T1. 
     In this embodiment of the present invention, the receive end  200  may be a BS or a UE, the receive end  200  has a receive module  220 , and the receive module  220  includes at least two antenna units. The receive end  200  includes a receive control unit  210 , and the receive control unit  210  instructs, according to the QoS, the receive module  220  to receive N beams, so that a transmission channel is formed between the transmit end  100  and the receive end  200 . A known sequence is a sequence that includes information known to both the transmit end  100  and the receive end  200 , and different narrow beams load mutually different known sequences. Preferably, the known sequences loaded by different narrow beams are orthogonal to each other, so that the known sequences can be distinguished by using the N beams of the receive end  200 . 
     Referring to  FIG. 2  to  FIG. 4 , in this embodiment of the present invention, the receive end  200  further includes a processing unit  230  that is configured to process signals received by the N wide beams from the transmit end  100 . Specifically, the processing unit  230  includes a first calculation unit  231  and a second calculation unit  232 . A channel matrix H may be used to represent the transmission channel. The channel matrix H is an N×M matrix. A matrix element H nm  (i≤n≤N, i≤m≤M) indicates a channel fading coefficient between an n th  wide beam and an m th  narrow beam, and the channel fading coefficient may be estimated according to an existing channel estimation algorithm, so that the first calculation unit  231  obtains the channel matrix H through calculation. The second calculation unit  232  calculates a channel capacity of the transmission channel according to the channel matrix H. For example, in a possible implementation manner, the second calculation unit  232  may perform SVD decomposition on the channel matrix H to obtain a channel singular value of the channel matrix H, and the SVD decomposition performed on the channel matrix H is: 
     
       
         
           
             
               
                 
                   
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     Q is a smaller value in M and N, and the channel singular value meets a relationship λ 1 ≥λ 2 ≥ . . . ≥λ Q ≥0; it is assumed that there are r channel singular values greater than 0 in λ i  (1≤i≤Q), that is, a rank of the channel matrix H is r; after the foregoing SVD decomposition, the transmission channel may be regarded as a composition of r independent parallel subchannels, each subchannel is corresponding to one channel singular value λ i  (1≤i≤r) of the channel matrix H, and the channel singular value λ i  (1≤i≤r) is used to represent an amplitude gain of a corresponding subchannel, for example, λ 1  represents an amplitude gain of a first subchannel, and λ 2  represents an amplitude gain of a second subchannel; and a greater amplitude gain indicates that the subchannel is more suitable for data transmission. The second calculation unit  232  further calculates the channel capacity of the transmission channel according to the channel singular value by using a Shannon&#39;s equation, and a calculation formula is: 
                     I   =       ∑     i   =   1     r     ⁢       log   2     ⁡     (     1   +     S   ⁢           ⁢   N   ⁢           ⁢     R   ·     λ   i   2           )           ,           (   2   )               
where
 
     I is the channel capacity of the transmission channel, and SNR is a signal-to-noise ratio that is generated in a signal amplification process of the receive end  200 . 
     It should be noted that, in another embodiment of the present invention, the second calculation unit  232  may calculate the channel capacity by using another algorithm, and a method for calculating the channel capacity is not specifically limited in the present invention. 
     Referring to  FIG. 2  to  FIG. 5 , in this embodiment of the present invention, the receive end  200  further includes a feedback unit  240 . The feedback unit  240  includes a determining unit  241 , a sorting unit  242 , and a notification unit  243 . The determining unit  241  determines whether the channel quality obtained by the second calculation unit  232  through calculation meets the QoS. If a current transmit mode of the transmit end  100  is a t th  transmit mode, the receive end  200  obtains t th  channel quality through calculation, and compares the t th  channel quality with the QoS to determine whether the t th  channel quality meets the QoS. When the determining unit  241  determines that the t th  channel quality meets the QoS, the notification unit  243  feeds back, to the transmit end  100 , feedback information such as the t th  transmit mode, information about the t th  channel quality, and a corresponding precoding matrix. The precoding matrix may be a codebook sequence number selected from a codebook set according to the channel quality, or may be a matrix that includes first K columns of a V matrix obtained by means of the SVD decomposition and that is used as a precoding matrix of the transmit end, where K is a maximum transmission data stream quantity of the transmission channel. When the determining unit  241  determines that the channel quality of the t th  transmit mode does not meet the QoS, the sorting unit  242  sorts the t th  transmit mode and previous t−1 transmit modes according to the channel quality. For example, the transmit modes may be sorted in ascending/descending order according to magnitude of the channel quality. Then, if after the transmit end  100  traverses all transmit modes in the first switching rule preset unit  130 , the determining unit  241  still finds no transmit mode that meets the QoS, the notification unit  243  sends, to the transmit end  100  according to a sorting result of the sorting unit  242 , feedback information such as a transmit mode with optimal channel quality, the corresponding channel quality, and a precoding matrix. Specifically, the notification unit  243  sends the feedback information to the receive control unit  210 . The receive control unit  210  forms a wide beam by using a predefined beamforming algorithm, loads the feedback information to the wide beam, and then controls the receive module  220  to transmit the wide beam. 
     It should be noted that, in another embodiment of the present invention, the feedback information transmitted by the receive end  200  may not include the precoding matrix, and the transmit end  100  may automatically obtain information about the precoding matrix according to the channel quality fed back by the receive end  200 . For example, multiple groups of precoding matrices are defined in the Long Term Evolution (Long Term Evolution, LTE) protocol, and the transmit end  100  may select a required precoding matrix from the LTE protocol according to the channel quality. 
     Referring to  FIG. 6  and  FIG. 7 , in this embodiment of the present invention, the transmit end  100  further includes a configuration unit  140 . After the feedback information sent by the receive end  200  by using the wide beam is received by using the M narrow beams of the transmit end  100 , the transmit control unit  110  sets the transmit mode of the transmit end  100  to the transmit mode fed back by the receive end  200 . The configuration unit  140  selects a transmission mode for and allocates a resource to the transmit module  120 . Specifically, the configuration unit  140  includes a decision unit  141  and a transmit configuration unit  142 . The decision unit  141  sets a decision threshold λ o . When the channel singular value λ i  (1≤i≤r) is greater than or equal to the decision threshold λ o , it indicates that a subchannel corresponding to the singular value is suitable for data transmission. On the contrary, it indicates that the subchannel corresponding to the singular value is not suitable for data transmission. The decision unit  141  collects statistics about a quantity of channel singular values greater than or equal to the decision threshold λ o  in the channel singular value λ i  (1≤i≤r). For example, when there are K channel singular values greater than λ o  in λ i  (1≤i≤r), it indicates that the maximum transmission data stream quantity of the transmission channel is K. It may be understood that, in another embodiment of the present invention, when the second calculation unit  232  calculates the channel capacity by using another algorithm, the decision unit  141  performs determining in a manner corresponding to the algorithm, to obtain a quantity of streams suitable for data transmission, and this is not specifically limited in the present invention. 
     In this embodiment of the present invention, the transmit configuration unit  142  selects a transmission mode and a resource allocation scheme according to the maximum transmission data stream quantity and the QoS. For example, when K=1, that is, only one data stream can be transmitted on the transmission channel, the transmit end  100  may generate one wide beam by using all antenna units to perform communication (in this case, only one narrow beam is output, that is, a single output case), that is, a beamforming working mode shown in  FIG. 7( a ) . When K&gt;1, for a QoS requirement that has a relatively high requirement for communication quality, as shown in  FIG. 7( b ) , K data streams may be used to simultaneously transmit same data, that is, a beam 1, a beam 2, and a beam 3 (a case in which K=3, or K may be another value) transmit same data, and then transmit power is allocated to the beam 1, the beam 2, and the beam 3 by using the precoding matrix, that is, a transmission diversity gain is achieved by using multiple narrow beams. When K&gt;1, for a QoS requirement that has a relatively large requirement for a rate, as shown in  FIG. 7( c ) , when communication quality is ensured, data streams may be used to transmit different data, that is, a beam 1, a beam 2, and a beam 3 transmit different data. Transmit power is allocated to the beam 1, the beam 2, and the beam 3 by using the precoding matrix, that is, a multiplexing gain is achieved by using multiple narrow beams. The transmit configuration unit  142  sends the transmission mode and the resource allocation scheme to the transmit control unit  110 . The transmit control unit  110  controls, according to the transmission mode and the resource allocation scheme, the transmit module  120  to send a corresponding narrow beam and allocate power to each narrow beam, so as to perform data transmission with the receive end  200  in the transmission mode by using the resource allocation scheme. 
     It should be noted that, it may be learned from the foregoing description that the transmission channel used for transmitting the M narrow beams of the transmit end  100  and the N beams of the receive end  200  may be a single-input single-output (M=N=1) case, a multiple-output signal-input (M&gt;1, N=1) case, a single-output multiple-input (M=1, N&gt;1) case, a multiple-input multiple-output (M&gt;1, N&gt;1) case, or the like. A specific channel mode is determined by factors such as the QoS requirement and channel quality actually obtained through calculation. This is not specifically limited in the present invention. 
     In this embodiment of the present invention, a transmit end  100  transmits M narrow beams according to a QoS requirement, and a receive end  200  receives N wide beams according to the QoS requirement, so as to form a transmission channel. A transmit mode of the transmit end  100  is switched according to a switching rule that is preset by a first switching rule preset unit  130 , and a processing unit  230  obtains channel quality of the transmit channel in different transmit modes through calculation, so as to search for a transmit mode that meets the QoS or a transmit mode that has optimal channel quality. A configuration unit  140  chooses, according to feedback information of the receive end  200  and according to an actual need, to perform beamforming, transmission diversity, or transmission multiplexing. In the present invention, a structure similar to a transmission channel is construed, and a group of transmission channels with good channel quality are obtained by means of searching. In comparison with a conventional beamforming system, a diversity gain or a multiplexing gain can further be obtained. 
     Referring to  FIG. 8 ,  FIG. 8  is a module diagram of a wireless communications system according to a second embodiment of the present invention. In this embodiment of the present invention, the wireless communications system includes units and modules in the foregoing first embodiment. A difference is that the receive end  200  receives and detects M narrow beams of the transmit end  100  by using N narrow beams. In this case, a channel gain of the transmission channel is determined by both a transmit mode of the transmit end  100  and a receive mode of the receive end  200 , and a set of spatial directions of the N narrow beams of the receive end  200  forms a receive mode. 
     In this embodiment of the present invention, the receive end  200  further includes a second switching rule preset unit  250 , and the second switching rule preset unit  250  sets a switching rule of the receive mode of the receive end  200 , to switch the receive mode of the receive end  200 . A switching period of the second switching rule preset unit  250  is T2, T2 is a predetermined multiple of T1, and the predetermined multiple is a quantity of transmit modes included in the first switching rule preset unit  130 . For example, it is assumed that the switching period of the first switching rule preset unit  130  of the transmit end  100  is T1 and the first switching rule preset unit  130  includes M 1  switching rules (that is, M 1  transmit modes). In this case, the period T2 of the second switching rule preset unit  250  is T1×M 1 . That is, after the transmit end  100  traverses all transmit modes in the first switching rule preset unit  130  once, the second switching rule preset unit  250  of the receive end  200  switches the receive mode once. It is assumed that the second switching rule preset unit  250  of the receive end  200  includes N 1  switching rules (that is, N 1  transmit modes). After the receive end  200  traverses all receive modes, M 1 ×N 1  transmission channels are generated in total, and correspondingly, there are M 1 ×N 1  channel matrices. In this embodiment of the present invention, H11 may be used to represent a channel matrix formed by using a first transmit mode and a first receive mode, and Hij (1≤i≤M 1 , 1≤j≤N 1 ) represents a channel matrix formed by using an i th  transmit mode and a j th  receive mode. 
     In this embodiment of the present invention, a first calculation unit  231  of the processing unit  230  calculates each channel matrix Hij, a second calculation unit  232  obtains, through calculation, a channel singular value of each channel matrix Hij according to the channel matrix Hij that is obtained by the first calculation unit  231  through calculation, and then, calculates a channel capacity of each channel matrix Hij. The determining unit  241  of the feedback unit  240  determines whether channel quality of the channel matrix Hij meets the QoS, and if the channel quality of the channel matrix Hij meets the QoS, the notification unit sends, to the receive control unit  210 , information such as the channel quality, a transmit mode, and a receive mode that are of the channel matrix meeting the QoS. The receive control unit  210  sets the receive mode of the receive end  200  to the receive mode (that is, a receive mode that meets the QoS) sent by the notification unit  241 , and feeds back, in this receive mode, the transmit mode that meets the QoS and channel quality information to the transmit end  100 . If the determining unit  241  determines that the channel matrix does not meet the QoS, the sorting unit  242  sorts the channel matrices according to channel capacities of the channel matrices. When the receive end  200  finds, after traversing all receive modes in the second switching rule preset unit  250 , no channel matrix that meets the QoS, the notification unit  243  transmits, to the receive control unit  210 , feedback information such as a channel matrix with an optimal channel capacity, a corresponding transmit mode, a corresponding receive mode, and corresponding channel quality. The receive control module  210  sets, according to the information of the notification unit  243 , the receive mode of the receive end  200  to the receive mode fed back by the notification unit  243 , and feeds back, to the transmit end  100  in this receive mode, a transmit mode and channel quality that are of a transmission channel with a maximum channel capacity. After the transmit end  100  receives and jointly detects, by using the M narrow beams, the feedback information transmitted by the receive end  100 , the transmit mode of the transmit end  200  is set to the transmit mode fed back by the receive end  200 . 
     In this embodiment of the present invention, data is transmitted between the transmit end  100  and the receive end  200  in a transmit mode and a receive mode that meet the QoS or have a maximum channel capacity. If a channel matrix that is obtained by the sorting unit  242  by means of sorting and that meets the QoS or has the maximum channel capacity is H45, that is, when the transmit mode of the transmit end  100  is a fourth transmit mode and the receive mode of the receive end  200  is a fifth receive mode, the transmission channel has the maximum channel capacity, the transmit mode of the transmit end  100  is set to the fourth transmit mode, the receive mode of the receive end  200  is set to the fifth receive mode, and data is transmitted in this transmit mode and this receive mode, so that the transmission channel can obtain a gain as large as possible, to meet the QoS requirement. 
     In this embodiment of the present invention, the transmit mode of the transmit end  100  and the receive mode of the receive end  200  are simultaneously switched, so that a transmission channel with a relatively large gain can be obtained, to meet a high QoS requirement in a system. 
     Referring to  FIG. 9 ,  FIG. 9  shows a wireless communications method according to a first embodiment of the present invention, and the method includes at least the following steps. 
       101 . Enable, according to a quality of service requirement, a transmit module of a transmit end to transmit M narrow beams with different spatial directions and a receive module of a receive end to receive N beams, so as to form a transmission channel, where both M and N are integers greater than or equal to 1. 
     In this embodiment of the present invention, a wireless communications system includes a transmit end  100  and a receive end  200 . The transmit end  100  may be a base station (BS) or user equipment (UE), and the receive end  200  may also be a BS or UE. The transmit end  100  includes a transmit module, the receive end  200  includes a receive module, the transmit module and the receive module each include at least two antenna units, and the antenna units may be configured to transmit or receive a wide beam or a narrow beam. The transmit module and the receive module may be phased array antennas, the phased array antenna includes a phase shifter, the phase shifter may control a spatial direction of a narrow beam transmitted by the antenna unit and control, by setting a phase-shift value of the phase shifter, the transmit end to transmit narrow beams with different spatial directions. 
     In this embodiment of the present invention, when the wireless communications system receives the QoS requirement, the transmit module of the transmit end  100  transmits M narrow beams with different spatial directions according to the QoS requirement, and the receive end  200  receives N beams according to the QoS requirement. The transmit module and the receive module each include at least two antenna units, and both M and N are integers greater than 1 or equal to 1. 
       102 . Switch a transmit mode according to a preset switching rule, where a set of the spatial directions of the M narrow beams forms a transmit mode. 
     In this embodiment of the present invention, the M narrow beams each load a known sequence, and the known sequence is a sequence that includes information known to both the transmit end  100  and the receive end  200 . The M narrow beams each load the known sequence, and known sequences loaded by different narrow beams are different from each other. Preferably, the known sequences loaded by different narrow beams are orthogonal to each other, so that the receive end  100  can distinguish the M narrow beams. 
     In this embodiment of the present invention, the transmit end  100  transmits the M narrow beams (a beam 1 to a beam 4 shown in  FIG. 3 ) with different spatial directions, and spatial directions of different narrow beams are different. A set of the spatial directions of the M narrow beams forms a transmit mode. If a spatial direction of a first narrow beam is α 1 , a spatial direction of a second narrow beam is α 2 , . . . , and a spatial direction of an M th  narrow beam is α M , a current transmit mode is denoted as {α 1 , α 2 , . . . , α M }. 
     In this embodiment of the present invention, switching the transmit mode is changing a spatial direction of the narrow beam, and at least one narrow beam has different spatial directions in any two different transmit modes. A changing rule of the spatial direction of the narrow beam may be provided in the switching rule. For example, for a possible switching rule, definitions may be as follows: Entire space is divided into M areas, and the spatial direction of the narrow beam is determined by two parameters: θ and φ, where θ is a horizontal angle of the narrow beam, and φ is a pitch angle of the narrow beam. A space area allocated to a first narrow beam is [θ 1min , θ 1max ] and [φ 1min , φ 1max ], that is, the first narrow beam, that is, a beam 1 scans the space area [θ 1min , θ 1max ] and [φ 1min , φ 1max ]. Similarly, a space area allocated to a k th  narrow beam, that is, a beam k (2≤k≤M) is [θ kmin , θ kmax ] and [φ kmin , φ kmax ], and the beam k scans the space area [θ kmin , θ kmax ] and [φ kmin , φ kmax ], so that the spatial direction of the narrow beam varies in these space areas. 
     It should be noted that, in another embodiment of the present invention, space may be set to partitions in another manner. For example, three-dimensional rectangular coordinates or another representation method may be used to represent a definition of the spatial direction, or partitioning does not need to be performed. In addition, the switching rule may have another definition. For example, a transmit mode may be switched according to a preset codebook order. For a mode switched according to a preset codebook, space may be divided, and beams are switched according to respective codebooks; or space does not need to be divided, and M narrow beams are entirely switched according to a specific rule. Space division and beam switching are simultaneously performed. The space division is not limited herein. Generally, the transmit end  100  switches a transmit mode each time a preset period T1 expires, and the transmit mode may be marked. For example, an original transmit mode is a first transmit mode, the transmit mode is switched to a second transmit mode after one period T1 and is switched to a third transmit mode after two periods T1, and by analogy, the transmit mode is switched to a t th  transmit mode after t−1 periods T1. 
       103 . Obtain channel quality in a current transmit mode according to signals received by the N wide beams of the receive end. 
     Specifically, the following steps may be included. 
     First, a channel matrix H in the current transmit mode is calculated according to the signals received by the receive end and the known sequences. 
     In this embodiment of the present invention, the M narrow beams transmitted by the transmit end  100  are propagated according to spatial directions specified in space, and the receive end  200  receives and jointly detects signals of the M narrow beams by using the N wide beams, so as to form an N×M transmission channel. A channel gain of the transmission channel is determined by both the transmit end  100  and the receive end  200 , a gain of the receive end  200  is a fixed gain, and transmission channels with different gains may be obtained by searching for a transmit mode of the transmit end  100 . 
     In this embodiment of the present invention, a channel matrix H may be used to represent the transmission channel, the channel matrix H is an N×M matrix, a matrix element H nm  (i≤n≤N, i≤m≤M) in the channel matrix indicates a channel fading coefficient between an n th  wide beam and an m th  narrow beam, and the channel fading coefficient may be provided according to an existing channel estimation algorithm, so as to obtain the channel matrix H. 
     Then, SVD decomposition is performed on the channel matrix H to obtain a channel singular value of the channel matrix H, and a channel capacity of the transmission channel is calculated according to the channel singular value. 
     In this embodiment of the present invention, after generating the channel matrix H, the receive end  200  may calculate channel quality of the transmission channel. The channel quality is evaluated mainly by the channel singular value and the channel capacity. In a possible implementation manner, the channel singular value may be obtained by performing the SVD decomposition on the channel matrix H, and the SVD decomposition performed on the channel matrix H is: 
                     H   =       U   ⁡     [           λ   1                                                               λ   2                                                             ⋱                                                             λ   Q           ]       ⁢     V   H         ,           (   1   )               
where
 
     Q is a smaller value in M and N, and the channel singular value λ 1 ≥λ 2 ≥ . . . ≥λ Q ≥0; it is assumed that there are r channel singular values greater than 0 in λ i  (1≤i≤Q), that is, a rank of the channel matrix H is r; after the foregoing SVD decomposition, the transmission channel may be regarded as a composition of r independent parallel subchannels, each subchannel is corresponding to one channel singular value λ i  (1≤i≤r) of the channel matrix H, and the channel singular value λ i  (1≤i≤r) is used to represent an amplitude gain of a corresponding subchannel, for example, λ 1  represents an amplitude gain of a first subchannel, and λ 2  represents an amplitude gain of a second subchannel; and a greater amplitude gain indicates that the subchannel is more suitable for data transmission. The channel capacity of the transmission channel may be given by using a Shannon&#39;s equation: 
                     I   =       ∑     i   =   1     r     ⁢       log   2     ⁡     (     1   +     S   ⁢           ⁢   N   ⁢           ⁢     R   ·     λ   i   2           )           ,           (   2   )               
where
 
     SNR is a signal-to-noise ratio that is generated in a signal amplification process of the receive end  200 . 
     It should be noted that, in another embodiment of the present invention, the channel capacity may be calculated by using another algorithm, and this is not specifically limited in the present invention. 
       104 . Search for a transmit mode that meets the QoS requirement and feedback the transmit mode to the transmit end, or feedback a transmit mode with optimal channel quality to the transmit end when transmission channel quality corresponding to all transmit modes is traversed but no transmit mode that meets the QoS requirement is found. 
     Specifically, the following steps may be included. 
     First, when channel quality of the transmit mode meets the QoS, the transmit mode that meets the QoS and channel quality information corresponding to the transmit mode are fed back to the transmit end, or otherwise, the transmit modes are sorted according to the channel quality, and searching is performed in a next transmit mode. 
     In this embodiment of the present invention, the transmit end  100  switches the transmit mode according to a period T1, and similarly, the receive end  200  calculates the channel quality corresponding to the transmit mode according to the period T1. If a current transmit mode of the transmit end  100  is a t th  transmit mode, the receive end  200  obtains t th  channel quality through calculation. The receive end  200  compares the QoS with the t th  channel quality that is generated through calculation and that is corresponding to the t th  transmit mode, to determine whether the t th  channel quality meets the QoS. The QoS mainly includes a transmission rate requirement and an error rate requirement. When the t th  channel quality obtained by the receive end  200  through calculation meets the QoS, the receive end  200  sends, to the transmit end  100  by using a wide beam, feedback information such as the t th  transmit mode, information about the t th  channel quality, and a corresponding precoding matrix. The precoding matrix information may be a codebook sequence number selected from a codebook set according to the channel quality, or may be a matrix that includes first K columns of a V matrix obtained by means of the SVD decomposition and that is used as a precoding matrix of the transmit end, where K is a maximum transmission data stream quantity of the transmission channel. When the receive end  200  determines that the channel quality of the current transmit mode does not meet the QoS, the receive end  200  sorts the t th  transmit mode and previous t−1 transmit modes according to the channel quality. For example, the transmit modes may be sorted in ascending/descending order according to magnitude of the channel capacity. 
     Then, when no transmit mode that meets the QoS is found after all transmit modes in the switching rule are traversed, a transmit mode with an optimal channel capacity and corresponding channel quality are fed back to the transmit end by using a wide beam. 
     In this embodiment of the present invention, when the transmit end  100  finds, after traversing all transmit modes in the switching rule, no transmit mode that meets the QoS, the receive end  200  sends, to the transmit end  100  according to a sorting result by using a wide beam, feedback information such as a transmit mode with a maximum channel capacity, channel quality, and a precoding matrix. 
     It should be noted that, in another embodiment of the present invention, the feedback information may not include the precoding matrix, and the transmit end  100  may automatically select information about the precoding matrix according to the channel quality fed back by the receive end. For example, multiple groups of precoding matrices are defined in the Long Term Evolution (LTE) protocol, and the transmit end  100  may select a required precoding matrix from the LTE protocol according to the channel quality. 
       105 . Set a transmit mode of the transmit end to the transmit mode fed back by the receive end. 
     In this embodiment of the present invention, the receive end  200  generates a wide beam, and loads the feedback information on the wide beam. The feedback information transmitted by the receive end  200  is received and jointed detected by using the M narrow beams of the transmit end, a modulation and coding scheme (MCS) is selected according to the feedback information to complete a precoding operation, and the transmit mode of the transmit end  100  is set to the transmit mode fed back by the receive end  200 . The transmit mode fed back by the receive end  200  may be a transmit mode that meets the QoS, or may be a transmit mode that does not meet the QoS requirement, but this transmit mode is a transmit mode with an optimal channel capacity in all transmit modes. 
       106 . Select a transmission mode for and allocate a resource to the transmit module of the transmit end according to the QoS requirement, and the channel quality and the transmit mode that are fed back by the receive end. 
     In this embodiment of the present invention, the transmit end  100  may select the transmission mode and allocate the resource according to the QoS requirement of a system and the feedback information of the receive end  200  by using the following steps. 
     First, a maximum transmission data stream quantity that can be supported by the transmission channel is obtained. 
     Specifically, in this embodiment of the present invention, after the SVD decomposition is performed on the channel matrix H, r non-zero singular values λ i  (1≤i≤r) are obtained, and if a value of λ i  is relatively small, it indicates that a subchannel corresponding to the singular value λ i  has a relatively small amplitude gain, and data may be submerged by noises when the subchannel is used to transmit the data. The transmit end  100  sets a decision threshold λ o , and when the channel singular value λ i  (1≤i≤r) is greater than or equal to the decision threshold λ o , it indicates that a subchannel corresponding to the singular value is suitable for data transmission, or on the contrary, the subchannel is not suitable for data transmission. If there are K channel singular values greater than λ o  in λ i  (1≤i≤r), it indicates that the transmission channel can simultaneously transmit a maximum of K data streams. 
     Then, a transmission mode and a resource allocation scheme are selected according to the maximum transmission data stream quantity and the QoS requirement. 
     Specifically, in this embodiment of the present invention, the QoS requirement mainly includes a rate requirement and an error rate requirement. When K=1, that is, only one data stream can be transmitted on the transmission channel, the transmit end  100  may generate one narrow beam by using all antenna units to perform communication, that is, a beamforming working mode. As shown in  FIG. 7( a ) , a spatial direction of the narrow beam is a spatial direction of the first narrow beam in the transmit mode that is fed back. When K&gt;1, for a QoS requirement that has a relatively high requirement for communication quality, as shown in  FIG. 7( b ) , data streams may be used to transmit same data, that is, a beam 1, a beam 2, and a beam 3 transmit same data, and then transmit power is allocated to the beam 1, the beam 2, and the beam 3 by using the precoding matrix, that is, a diversity gain is achieved by using multiple narrow beams. When K&gt;1, for a QoS requirement that has a relatively large requirement for a rate, as shown in  FIG. 7( c ) , when communication quality is ensured, data streams may be used to transmit different data, that is, a beam 1, a beam 2, and a beam 3 transmit different data. Transmit power is allocated to the beam 1, the beam 2, and the beam 3 by using the precoding matrix, that is, a multiplexing gain is achieved by using multiple narrow beams. 
     It should be noted that, it may be learned from the foregoing description that the transmission channel in this embodiment of the present invention may be a single-input single-output (M=N=1) case, a multiple-output signal-input (M&gt;1, N=1) case, a single-output multiple-input (M=1, N&gt;1) case, an MIMO (M&gt;1, N&gt;1) case, or the like. A specific channel mode is determined by factors such as the QoS requirement and channel quality actually obtained through calculation. This is not specifically limited in the present invention. 
     It may be understood that, in another embodiment of the present invention, when the channel capacity is calculated by using another algorithm, a manner corresponding to the algorithm is used in the present invention to perform determining, to obtain a stream quantity that is suitable for data transmission, and this is not limited in the present invention. 
     In this embodiment of the present invention, a transmit end  100  transmits M narrow beams according to a QoS requirement, and a receive end  200  receives the M narrow beams according to the QoS requirement by generating N wide beams, so as to form a transmission channel. A transmit mode of the transmit end  100  is switched according to a preset switching rule. The receive end  200  processes the M narrow beams transmitted by the transmit end  100 , to obtain channel quality information corresponding to the transmit mode. A transmit mode that meets the QoS is obtained by means of searching and is fed back to the transmit end  100 , so that the transmit end  100  sets the transmit mode of the transmit end  100  to the transmit mode fed back by the receive end  200 , to choose, according to an actual need, to perform beam forming, transmission diversity, or transmission multiplexing. In the present invention, a structure similar to a transmission channel is construed, and a group of transmission channels with good channel quality are obtained by means of searching. In comparison with a conventional beamforming system, a diversity gain or a multiplexing gain can be obtained. 
     Referring to  FIG. 10 ,  FIG. 10  is a wireless communications method according to a second embodiment of the present invention, and the method includes at least the following steps. 
       201 . Enable, according to a quality of service requirement, a transmit module of a transmit end to transmit M narrow beams with different spatial directions and a receive module of a receive end to receive N beams, so as to form a transmission channel, where both M and N are integers greater than or equal to 1. 
     In this embodiment of the present invention, a transmit end  100  and a receive end  200  each are a BS and may transmit or receive a narrow beam. 
       202 . Switch a transmit mode according to a preset switching rule, where a set of the spatial directions of the M narrow beams forms a transmit mode. 
       203 . Obtain channel quality in a current transmit mode according to signals received by the N narrow beams of the receive end. 
     In this embodiment of the present invention, the receive end receives the M narrow beams of the transmit end by using the N narrow beams, to form a transmission channel. A channel gain of the transmission channel is determined by both a transmit mode of the transmit end  100  and a receive mode of the receive end  200 , and different transmit modes and different receive modes form transmission channels with mutually different channel gains. A set of spatial directions of the N narrow beams form a receive mode. 
       204 . Switch a receive mode of the receive end according to a preset switching rule, and calculate channel quality of channel matrices formed by using different transmit modes and different receive modes, where a set of spatial directions of the N narrow beams forms a receive mode. 
     In this embodiment of the present invention, because the channel gain of the transmission channel is determined by both the transmit mode of the transmit end and the receive mode of the receive end, the transmit mode of the transmit end and the receive mode of the receive end need to be simultaneously switched, so as to search for a transmission channel that meets a QoS or that has relatively high channel quality. Specifically, the receive end  200  presets a switching rule, and switches the receive mode of the receive end  200  according to the switching rule. A switching period of the receive mode of the receive end  200  is T2, and T2 is a preset multiple of a period T1. The preset multiple is a quantity of switching rules. If the transmit end  100  has M 1  switching rules (each rule is corresponding to one transmit mode), T2=T1×M 1 , the transmit mode of the transmit end  100  and the receive mode of the receive end  200  are simultaneously switched, and the receive end  200  switches the receive mode once after the transmit end  100  traverses transmit modes once. It is assumed that the receive end  200  has N 1  switching rules (that is, N 1  transmit modes). After the receive end  200  traverses all receive modes, M 1 ×N 1  transmission channels are generated in total, and correspondingly, there are M 1 ×N 1  channel matrices. In this embodiment of the present invention, H11 may be used to represent a channel matrix formed by using a first transmit mode and a first receive mode, and Hij (≤i≤M 1 , 1≤j≤N 1 ) represents a channel matrix formed by using an i th  transmit mode and a j th  receive mode. 
       205 . When channel quality obtained by the receive end through calculation meets the QoS, feedback a transmit mode that meets the QoS and channel quality information corresponding to the transmit mode to the transmit end. 
     First, when the channel quality of the channel matrix meets the QoS, a receive mode that meets the QoS is set to the receive mode of the receive end, and the transmit mode that meets the QoS and the channel quality are fed back to the transmit end in this receive mode, or otherwise, the channel matrices are sorted according to the channel quality. 
     In this embodiment of the present invention, the receive end  200  calculates channel quality of each channel matrix Hij, compares the channel quality with the QoS to determine whether the channel quality meets the QoS, and if the channel quality meets the QoS, generates the channel quality that meets the QoS, corresponding transmit mode information, and corresponding receive mode information. After the receive mode of the receive end  200  is set to the receive mode that meets the QoS, the channel quality that meets the QoS and the corresponding transmit mode are fed back to the transmit end  100  in this receive mode. If the channel quality does not meet the QoS, the channel matrix and a previously obtained channel matrix are sorted. For example, sorting is performed according to a channel capacity. 
     Then, when no channel matrix that meets the QoS is found after all receive modes in the switching rule are traversed, the receive mode of the receive end is set, according to a sorting result, to a receive mode with a maximum channel capacity, and a transmit mode with a maximum channel capacity and channel quality are fed back to the transmit end in this receive mode. 
     In this embodiment of the present invention, when the receive end  200  finds, after traversing all switching rules, that is, after traversing all receive modes, no channel matrix that meets the QoS, the receive end  200  obtains, according to a sorting result, a receive mode and a transmit mode that are corresponding to the channel matrix with highest channel quality, and after the receive mode of the receive end  200  is set to the receive mode of the channel matrix with the highest channel quality, the channel quality of the channel matrix with the highest channel quality and a corresponding transmit mode are fed back to the transmit end  100  in the receive mode. 
     It should be noted that, in this embodiment of the present invention, the switching rule of the transmit mode of the receive end  200  may be the same as or different from the switching rule of the transmit mode of the transmit end  100 . This is not limited in the present invention. 
       206 . Set a transmit mode of the transmit end to the transmit mode fed back by the receive end. 
     In this embodiment of the present invention, feedback information (spatial directions of the N narrow beams are defined by the receive mode that is obtained in step  205  and that meets the QoS or a receive mode with a maximum channel capacity) on the N narrow beams of the receive end  200  is received and jointly detected by using the M narrow beams of the transmit end  100 , a modulation and coding scheme (MCS) is selected according to the feedback information to complete a precoding operation, and the transmit mode of the transmit end  100  is set to the transmit mode fed back by the receive end  200 . 
       207 . Select a transmission mode for and allocate a resource to the transmit module of the transmit end according to the quality of service requirement, and the channel quality and the transmit mode that are fed back by the receive end. 
     In this embodiment of the present invention, the transmit mode of the transmit end  100  and the receive mode of the receive end  200  are simultaneously switched, so that a transmission channel with a relatively large gain can be obtained, to meet a high QoS requirement in a system. 
     The foregoing descriptions are examples of implementation manners of the present invention. It should be noted that a person of ordinary skill in the art may make certain improvements and polishing without departing from the principle of the present invention and the improvements and polishing shall fall within the protection scope of the present invention.