Abstract:
A wireless transmitting apparatus according to the present invention, comprising: N (N is two or more integer) pieces of antennas capable of transmitting a wireless signal; and a selector which selects L (L is one or more integer, and L≦N) pieces of antennas from said N pieces of antennas and selects the types of signals to be transmitted from the selected L pieces of antennas.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims benefit of priority under 35USC§119 to Japanese Patent Application No. 2002-143560, filed on May 17, 2002, the entire contents of which are incorporated by reference herein. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a wireless transmitting apparatus, a wireless communication system and a method of wireless transmission which communicates a wireless signal by using a plurality of antennas.  
           [0004]    2. Related Art  
           [0005]    [0005]FIG. 6 is a block diagram showing schematic configuration of a conventional wireless communication system. The wireless communication system of FIG. 6 has a transmitting apparatus  30  having a plurality of transmission antennas  1   a - 1   d,  and a receiving apparatus  40  having a plurality of reception antennas  4   a - 4   d.  The transmitting apparatus  30  transmits different transmission symbols on the same resource (for example, the same time or the same frequency) from a plurality of transmission antennas  1   a - 1   d.  The receiving apparatus  40  receives the transmission symbols transmitted from the transmitting apparatus  30  by using the reception antennas  4   a - 4   d.    
           [0006]    The wireless communication system of FIG. 6 improves communication quality per one user by using the transmission symbols with redundancy to each other by the transmission antennas  1   a - 1   d,  as compared with a wireless communication system using a single antenna. The technique increasing transmission capacity by cooperation of a plurality of transmission antennas  1   a - 1   d  is called as transmission diversity.  
           [0007]    In order to improve communication quality, coding is performed at a transmission side, and a plurality of transmission antennas transmit different transmission symbols on the same resource, such as a space-time coding and a space-time block coding.  
           [0008]    According to these methods, although it is possible to improve communication quality, the following drawbacks occur.  
           [0009]    1. Power consumption increases.  
           [0010]    2. When there is a correlation in propagation path status between a transmitter and a receiver, communication capacity lowers, that is, a diversity gain is not obtained. Therefore, an advantage by using a plurality of antennas is lost.  
           [0011]    The technique called as a MIMO (Multiple Input Multiple Output), which increases communication capacity by providing a plurality of antennas at transmitted side and received side, is proposed.  
           [0012]    In the MIMO, although it is possible to increase communication capacity, the following drawbacks occur.  
           [0013]    3. Decryption processing at received side becomes heavy.  
           [0014]    4. Power consumption increases.  
           [0015]    There is a problem in which power consumption is spent in vain and useless signal processings are performed, when the propagation path status is terrible.  
           [0016]    As these countermeasures, D. A. Gore et al. of Stanford University publishes at an International convention a research for expressing in matrixes the propagation path status between the transmitter and the receiver, and selecting the number of transmission antennas in accordance with ranks of matrixes (“Selecting an optimal set of transmit antennas for a low rank matrix channel”, Gore, D. A.; Nabar, R. U.; Paulraj, A. Acoustics, Speech, and Signal Processing, 2000. ICASSP &#39;00. Proceedings. IEEE International Conference on , Volume: 5 2000, PP.2785-2788 vol.5).  
           [0017]    It is assumed that various information in which the amount of information and property of information are completely different is transferred, and each user transmits different information such as priority. In this case, in current transmission diversity, there is a problem in which a control in accordance with the required quality is impossible.  
         SUMMARY OF THE INVENTION  
         [0018]    An object of the present invention is to provide a wireless transmitting apparatus, a wireless communication system and a method of wireless transmission capable of reducing power consumption, improving communication quality, and performing control in accordance with request quality.  
           [0019]    According to the present invention, a wireless transmitting apparatus, comprising:  
           [0020]    N (N is two or more integer) pieces of antennas capable of transmitting a wireless signal; and  
           [0021]    a selector which selects L (L is one or more integer, and L≦N) pieces of antennas from said N pieces of antennas and selects the types of signals to be transmitted from the selected L pieces of antennas. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 is a diagram showing a schematic configuration of a first embodiment of a wireless communication system according to the present invention.  
         [0023]    [0023]FIG. 2 is a block diagram showing one example of internal configuration of a baseband signal processor.  
         [0024]    [0024]FIG. 3 is a flowchart showing processing procedure of a selector of the first embodiment.  
         [0025]    [0025]FIG. 4 is a flowchart showing processing procedure of a selector of the second embodiment.  
         [0026]    [0026]FIG. 5 is a block diagram showing schematic configuration of a fourth embodiment of a wireless communication system according to the present invention.  
         [0027]    [0027]FIG. 6 is a block diagram showing schematic configuration of the conventional wireless communication system.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    Hereinafter, a wireless transmitting apparatus, a wireless communication system, and a method of wireless transmission according to the present invention will be more specifically described with reference to drawings. The present invention has a feature in which the number of antennas and a method of transmitted and received diversity by a plurality of antennas are selected based on propagation path status and transmission information.  
         [0029]    As the properties of information, it is assumed that various information such as binary data, image (moving image), sound and streaming data for distributing information to a lot of people, and information adding priorities which relate to transmission order for each user and is set for each user may be included in the information.  
         [0030]    As a method for selecting the number of antennas used for transmission and reception and the information transmitted and received by a plurality of antennas, the following two methods are mainly supposed. One method is to select the information transmitted and received by a plurality of antennas based on the propagation path status, and to select the number of the antennas based on the properties of the information. Another method is to select the number of the antennas based on the propagation path status, and to select the information transmitted and received by a plurality of antennas based on the transmission information.  
         [0031]    (First Embodiment)  
         [0032]    In the first embodiment, information transmitted and received by a plurality of antennas is selected based on the propagation path status, and the number of the antennas is selected based on the properties of the transmission information.  
         [0033]    [0033]FIG. 1 is a block diagram showing schematic configuration of a first embodiment of a wireless communication system according to the present invention. The wireless communication system of FIG. 1 has a transmitting apparatus  10  having a plurality of transmission antennas  11   a - 11   d,  and a receiving apparatus  20  having a plurality of reception antennas  21   a - 21   d.    
         [0034]    The transmitting apparatus  10  has a plurality of transmitters provided for the transmission antennas  11   a - 11   d,  respectively, a baseband signal processor  13  and a selector  14 . The receiving apparatus  20  has a plurality of receivers  22   a - 22   d  provided for the reception antennas  21   a - 21   d,  respectively and a baseband signal processor  23 .  
         [0035]    Transmission data  101  inputted to the transmitting apparatus  10  is provided to the baseband signal processor  13  and the selector  14 . The selector  14  selects the number of the antennas and the information transmitted and received by a plurality of antennas.  
         [0036]    The selection result of the selector  14  is transmitted to the baseband signal processor  13 . The baseband signal processor  13  performs a prescribed signal processing based on the selection result of the number of the antennas and the selection result of the information transmitted and received by a plurality of antennas transmitted from the selector  14 .  
         [0037]    The signal after the signal processing is transmitted from one of the transmission antennas  11   a - 11   d  via at least one of four transmission parts  12   a - 12   d.    
         [0038]    [0038]FIG. 2 is a block diagram showing one example of internal configuration of the baseband signal processor  13 . Because of simplification of drawing, FIG. 2 shows block configurations in the case of having two transmission antennas.  
         [0039]    As shown in FIG. 2, the baseband signal processor  13  has a plurality of encoders for encoding the transmission data, a switch  32  for selecting a plurality of encoders, and a plurality of switches  33   a  and  33   b  for selecting and outputting the transmission symbols encoded by a plurality of encoders  31   a - 31   c.    
         [0040]    A plurality of switches  33   a  and  33   b  are connected to the transmitters different from each other. The switch  32  performs the selection operation based on the signal from the selector  14 .  
         [0041]    The encoder  31   a  outputs the encoding data so that the same transmission symbol S 1  is outputted from two transmission antennas. The encoder  31   b  outputs the encoding data at time 2t (even turns) so that the transmission symbol S 0  is outputted from one transmission antenna, and the transmission symbol S 1  is outputted from another transmission antenna. The encoder  31   b  outputs the encoding data at odd turns so that the transmission symbol −S 1 * is outputted from one transmission antenna, and the transmission symbol S 1  is outputted from another transmission antenna. The “*” means a complex conjugate.  
         [0042]    The receiving apparatus  20  receives the transmission signal from the transmitter  10  in at least one of the reception antennas  21   a - 21   d,  and then transmits the received signal to the baseband signal processor  23  via the corresponding receivers. The baseband signal processor  23  performs a prescribed signal processing and then outputs the received signal. The baseband signal processor  23  transmits a feedback signal  201  indicating the propagation path status and properties of transmission information to the transmitting apparatus  10 .  
         [0043]    When the transmission symbols encoded by the encoder  31   b  is received, the receiving apparatus  20  decodes the transmission symbols by using a method disclosed in U.S. Pat. No. 6,185,258, thereby improving transmission quality. When the transmission symbols encoded by the encoder  31   c  is received, the receiving apparatus  20  separates the transmission symbols by using the method disclosed in U.S. Pat. No. 6,097,771, thereby improving transmission efficiency.  
         [0044]    The selector  14  of the present embodiment selects the number of antennas and the information transmitted and received by a plurality of antennas, based on the propagation path status and the properties of the transmission information. More specifically, the selector  14  selects the information transmitted and received by a plurality of antennas based on the propagation path status and selects the number of antennas based on the properties of the transmission information.  
         [0045]    [0045]FIG. 3 is a flowchart showing processing procedures of the selector  14  in the first embodiment. In FIG. 3, a method of transmitted and received diversity is selected based on the propagation path status, and the number of antennas is selected based on the properties of the transmission information.  
         [0046]    First of all, a signal i indicating the properties of the transmission information and a signal h indicating the propagation path status are acquired (step S 1 ).  
         [0047]    Threshold values I2, I3 and I4 (I2&lt;I3&lt;I4) for variably changing the number of the antennas, and a threshold value H for variably changing the method of the transmitted and received diversity are set (step S 2 ). The threshold values I2, I3 and I4 are determined based on the types of the transmission signals such as voice, data and streaming data. The threshold value H is determined by using a ratio of signal power to noise power, a ratio of signal power to interference power, or a correlation value of the propagation path status.  
         [0048]    It is determined whether or not the signal i indicating the properties of the transmission information is no less than the threshold value I2 (step S 3 ). If not i≧I2, instead of the transmitted and received diversity using a plurality of transmission antennas  11   a - 11   d,  the wireless communication using only one transmission antenna is performed (step S 4 ).  
         [0049]    If determined to be “yes” in step S 2 , it is determined to be i≧I3 (step S 5 ). If determined to be “no”, two transmission antennas are used, and it is determined that the signal h indicating the propagation path status is less than a threshold value H (step S 6 ).  
         [0050]    If no less than the threshold value H, it is determined that the propagation path status is good, and the signals different from each other are transmitted from two transmission antennas, for example, alike the space-time coding (STC) (step S 7 ). If less than the threshold value H, it is determined that the propagation path status is bad, and the same signal is transmitted from two transmission antennas (step S 8 ). The processings of steps S 7  and S 8  are performed by switching signals by the switch  32  of the baseband signal processor  13  of FIG. 2 based on the signal from the selector  14 .  
         [0051]    On the other hand, if determined to be “yes” in step S 5 , it is determined whether or not to be i≧I4 (step S 9 ). If determined to be “no”, it is determined to use three transmission antennas. Next, it is determined whether or not the signal h indicating the propagation path status is less than a threshold value H (step S 10 ). If no less than the threshold value H, three transmission antennas transmit the signals different from each other (step S 11 ). If less than the threshold value H, three transmission antennas transmit the common signal from three transmission antennas, respectively (step S 12 ).  
         [0052]    If determined to be “yes” in step S 9 , four transmission antennas  11   a - 11   d  are used. It is determined whether or not the signal h indicating the propagation path status is less than the threshold value H (step S 13 ). If no less than the threshold value H, four transmission antennas  11   a - 11   d  transmit from the transmission antennas  11   a - 11   d  the signals different from each other, respectively (step S 14 ). If less than the threshold value H, four transmission antennas  11   a - 11   d  transmit the same signal, respectively (step S 15 ).  
         [0053]    The above-mentioned processings of steps S 7 , S 11  and S 14  of FIG. 3 may be performed by the encoders  31   b  and  31   c  of FIG. 2.  
         [0054]    In the flowchart of FIG. 3, the number of the used transmission antennas  11   a - 11   d  is gradually increased based on the signal i indicating the properties of the information. However, the number of the used transmission antennas  11   a - 11   d  may be gradually decreased.  
         [0055]    According to the first embodiment, the information transmitted and received by a plurality of antennas is selected based on the propagation path status, and the number of the antennas is selected based on the properties of the transmission information. Because of this, it is possible to change the number of the used antennas based on the properties of the information, thereby performing the wireless communication suitable for required quality.  
         [0056]    (Second Embodiment)  
         [0057]    In a second embodiment, the number of antennas is selected based on the propagation path status, and information transmitted and received by a plurality of antennas is selected based on properties of transmission information. Since the second embodiment has the same block configurations as those of first embodiment, description of the block configurations will be omitted.  
         [0058]    [0058]FIG. 4 is a flowchart showing processing procedure of the selection part  14  in the second embodiment. FIG. 4 shows a processing procedure in which the number of the antennas is selected based on the propagation path status, and the information transmitted and received by a plurality of antennas is selected.  
         [0059]    First of all, the signal i indicating the properties of the transmission information and the signals h 1 -h 4  indicating the propagation path status are acquired based on a feedback signal  201  from the receiving apparatus  20  (step S 21 ). The threshold value H for variably changing the number of the antennas and a threshold value I for variably changing the transmitted and received diversity system are set (step S 22 ). The threshold value H is set based on the ratio of signal power to noise power, the ratio of signal power to interference power, or a correlation value of the propagation path status. The threshold value I is set based on properties of transmission information such as voice, data and streaming data.  
         [0060]    It is determined whether or not the correlation value of the signals h 1 -h 4  indicating the propagation path status is no more than the threshold value H (step S 23 ). If the correlation value is no more than the threshold value H, transmission from either one of the transmission antennas is inhibited (step S 24 ). For example, the correlation value between the signals h 2  and h 3  indicating the propagation path status is no more than the threshold value, either one of the transmission antenna corresponding to the signal h 2  or the transmission antenna corresponding to the signal h 3  is not used.  
         [0061]    It is determined that the signal i indicating the properties of the information is less than the threshold value I (step S 25 ). If less than the threshold value, the same signal is transmitted by a plurality of transmission antennas  11   a - 11   d  (step S 26 ). If no less than the threshold value, the signals different from each other are transmitted from a plurality of transmission antennas  11   a - 11   d  (step S 27 ).  
         [0062]    According to the second embodiment, the number of antennas is selected based on the propagation path status, and the information transmitted and received by a plurality of antennas is selected based on the properties of the transmission information. Because of this, with regard to information in which the amount of information such as voice is small, but instantaneity is required, a plurality of transmission antennas  11   a - 11   d  are used for transmitting the same information. With regard to information in which the amount of information such as data and moving image is large, but instantaneity is not so much required, a plurality of transmission antennas  11   a - 11   d  transmit the information different from each other.  
         [0063]    In the second embodiment, it is possible to arbitrarily change methods of transmitting and receiving the wireless signal.  
         [0064]    (Third Embodiment)  
         [0065]    In a third embodiment, a threshold inherent in each user is set.  
         [0066]    For example, in the second embodiment, when a user A performs communication of high priority and communication having a large amount of information such as moving image, the threshold values I2, I3 and I4 in steps S 3 , S 5  and S 9  are set lower.  
         [0067]    On the other hand, when a user B performs communication of low priority, and communication of the same information as that of user A, the threshold values I2, I3 and I4 in steps S 3 , S 5  and S 9  of FIG. 3 are set large. Therefore, user A can accept more allocation of the transmission antennas  11   a - 11   d  than user B, thereby performing communication by priority.  
         [0068]    According to the third embodiment, since the threshold value is individually set for each user, it is possible to perform wireless communication in order of priority for each user. It is possible to perform wireless communication in accordance with availability of users.  
         [0069]    (Fourth Embodiment)  
         [0070]    In a fourth embodiment, history information of the threshold value is stored, and the threshold value is set with reference to previous threshold value.  
         [0071]    [0071]FIG. 5 is a block diagram showing schematic configuration of a fourth embodiment of a wireless communication system according to the present invention. In FIG. 5, the same reference numbers are attached to the common constituents as those of FIG. 1. Hereinafter, different points will be mainly described.  
         [0072]    The transmitting apparatus  10  of FIG. 5 has a storage  15 , in addition to configurations of FIG. 1. The storage  15  stores previous changing history information of the threshold value for variably changing the number of antennas and the threshold value for variable changing the transmitted and received information.  
         [0073]    The selector  14  sets the above-mentioned threshold value based on the changing history information of the threshold value stored in the storage  15 .  
         [0074]    According the fourth embodiment, new threshold value is set based on the previous changing history information of the threshold value. Because of this, there is no likelihood to mistake the setting of the threshold value, thereby easily and quickly setting an optimum threshold value.  
         [0075]    In the above-mentioned embodiment, the example in which the maximum number of antennas is four, the threshold values for selecting the antennas is provided three, the number of selecting the information transmitted and received by a plurality of antennas is two, and the number of selecting the threshold value in the case is one has been described. However, these numbers are not limited to the above-mentioned embodiment. For example, the maximum number of antennas is N, the number of selecting the information transmitted and received by a plurality of antennas is L, the number of selecting the threshold values for changing the number of antennas is (N−1), and the number of selecting the threshold value to change the selection of the information transmitted and received by a plurality of antennas may be provided (L−1). The threshold values may be changed for every one constant time period, or for each time when the information is transmitted. Or the threshold values may be changed by random.