Patent Publication Number: US-6218986-B1

Title: Adaptive reception diversity method and adaptive transmission diversity method

Description:
This application is a division of U.S. patent application Ser. No. 09/053,063, filed Apr. 1, 1998, the contents of which are expressly incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an adaptive diversity apparatus for digital communication. 
     2. Description of the Related Art 
     A conventional adaptive diversity apparatus will be described with reference to FIG.  1  and FIG.  2 . FIG. 1 is a block diagram of the conventional adaptive diversity apparatus. FIG. 2 is a radiation pattern view of assistance in explaining reception (transmission) radiation pattern. In FIG. 1, complex signals which are received by reception antennas  1 ,  2 ,  3  and  4  at a time t, A/D converted and quasi-coherent detected complex signals are designated S 1 (t), S 2 (t), S 3 (t) and S 4 (t), respectively. 
     A reception radiation pattern controller  9  transmits complex weights W 1 (t), W 2 (t), W 3 (t) and W 4 (t) to multipliers  5 ,  6 ,  7  and  8 . The multipliers  5 ,  6 ,  7  and  8  multiply the abovementioned complex signals by the complex weights. The multiplied complex signals are added by an adder  12 . At this time, when the output of the reception radiation pattern controller  9  is S(t), the output S(t) can be expressed as the following formula (1): 
     
       
           S ( t )=Σ 1   4   W   i ( t ) S   i ( t )  (1) 
       
     
     By thus composing the reception signals from a plurality of antennas after multiplying them by appropriate complex numbers, it is possible to provide all the antennas with radiation pattern on a plane as shown in FIG.  2 . For example, in FIG. 2, when a desired signal is coming from the direction of the arrow  21  and an interference signal is coming from the direction of the arrow  22 , the reception radiation pattern controller  9  controls the radiation pattern as shown at the reference numeral  23  of FIG.  2 . That is, the controller  9  controls the radiation pattern so that the desired signal is received with high intensity and the interference signal is received with low intensity. Thereby, the reception performance can be improved. 
     A decider  11  outputs the result D(t) of hard decision of the composite signal S(t). An error detector  10  outputs the difference S(t)−D(t) between the composite signal S(t) and the detected result D(t). The reception radiation pattern controller  9  updates its output complex weights W 1 (t), W 2 (t), W 3 (t) and W 4 (t) based on the output of the error detector and S 1 (t), S 2 (t), S 3 (t) and S 4 (1). 
     For example, when the reception signal vector is expressed as Sig(t)=(S 1 (t), S 2 (t), S 3 (t), S 4 (t)) T  and the output of the reception radiation pattern controller, as W(t)=(W 1 (t), W 2 (t), W 3 (t), W 4 (t)) T , the updated complex weights can be expressed as the following formula (2): 
     
       
           W ( t+ 1)= W ( t )+μ( S ( t )− D ( t )) T   Sig ( t )  (2) 
       
     
     Here, μ is a step factor. 
     In the above-described conventional adaptive diversity apparatus, by successively updating the weights which are multiplied by the input signals from the antennas, even when the transmitting side moves, the radiation pattern can be formed in accordance with the movement. 
     In the conventional apparatus, when the movement speed of the transmitting side is low, the radiation pattern can be formed in accordance with the movement; however, when the movement speed of the transmitting side is high, since the complex weights do not converge, the processing by the reception radiation pattern controller cannot respond to the movement, so that a correct radiation pattern cannot be formed. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an adaptive diversity apparatus in which the transmission and reception performance is improved by causing a reception radiation pattern controller or a transmission radiation pattern controller to respond to the movement of a transmitting side or a receiving side to thereby form a correct radiation pattern even when the movement speed of the transmitting side or the receiving side is high. 
     To solve the abovementioned problem, according to the present invention, by estimating the movement direction of a communication partner, the radiation pattern is forcibly rotated to thereby form a correct radiation pattern. 
     Specifically, an adaptive diversity apparatus of the present invention comprises: reception radiation pattern control means for providing a reception signal from an antenna with a first reception radiation pattern by a first control signal; radiation pattern control means for providing the reception signal with a second reception radiation pattern by a second control signal based on an output of movement direction estimating means for estimating a movement direction of a transmitting side; and a reception signal processing system having multiplication means for multiplying the abovementioned reception signal by the abovementioned first control signal and the second control signal. 
     According to this feature, since the reception radiation pattern extracted and generated from the reception signal can be corrected at high speed in accordance with the movement of the transmitting side, the reception performance can be significantly improved. 
     Moreover, in the adaptive diversity apparatus of the present invention, the radiation pattern control means outputs the second control signal for controlling rotation of the first reception radiation pattern based on the output of the movement direction estimating means. According to this feature, by rotating the phase of the first reception radiation pattern, the reception radiation pattern can be surely and easily corrected. 
     Moreover, in the adaptive diversity apparatus of the present invention, the radiation pattern control means generates the second control signal so as to cancel a phase variation obtained by displacement of a direction of arrival. According to this feature, since a relative angle from a communication partner can be calculated by estimating from the reception signal the direction of arrival, radiation pattern control can be realized at a low cost. 
     Moreover, in the adaptive diversity apparatus of the present invention, the reception radiation pattern control means and the radiation pattern control means are provided independently of each other, and the reception signal, the first control signal and the second control signal are multiplied by single multiplication means. Thereby, the circuit is simplified, so that incorporation or mounting of the radiation pattern control means into an existing circuit is facilitated. 
     Moreover, in a case where the present invention is applied to an adaptive reception diversity apparatus, specifically, an arrangement is employed comprising: a plurality of antennas; movement direction estimating means for estimating a movement direction of a transmitting side; reception radiation pattern control means for providing reception signals from the antennas with reception radiation pattern; addition means for composing a plurality of inputs from the abovementioned antennas; radiation pattern control means for controlling rotation of the abovementioned reception radiation pattern based on an output of the abovementioned movement direction estimating means; decision means for performing hard decision of an output of the abovementioned addition means; and error detecting means for detecting an error between an output of the decision means and the output of the abovementioned addition means, to feed back the error to the abovementioned reception radiation pattern control means. 
     Moreover, in the adaptive diversity apparatus of the present invention, the radiation pattern correction control means obtains a relative phase variation due to a movement of the transmitting side at each of the plurality of disposed antennas based on the output of the movement direction estimating means, and generates the second control signal in accordance with each phase variation. Moreover, in the adaptive diversity apparatus of the present invention, the radiation pattern control means obtains a relative phase variation due to a movement of the receiving side at each of the plurality of disposed antennas based on the output of the movement direction estimating means, and generates the second control signal in accordance with each phase variation. According to these features, the conformity of the reception radiation pattern significantly improves, so that the overall reception accuracy of the apparatus improves. In view of improvement in accuracy, the provision of a greater number of antennas results in higher accuracy. 
     Moreover, in the adaptive diversity apparatus of the present invention, the following are provided: transmission radiation pattern control means for providing a transmission signal from an antenna with a first transmission radiation pattern by a first control signal; radiation pattern control means for providing the abovementioned transmission signal with a second transmission radiation pattern by a second control signal based on an output of movement direction estimating means for estimating a movement direction of a receiving side; and a transmission signal processing system having multiplication means for multiplying the abovementioned transmission signal by the first control signal and the second control signal. According to this feature, since the transmission radiation pattern composed into the transmission signal can be corrected at high speed in accordance with the movement of the receiving side, the transmission performance can be significantly improved. 
     Moreover, in the adaptive diversity apparatus of the present invention, the radiation pattern control means outputs the second control signal for controlling rotation of the first transmission radiation pattern based on the output of the movement direction estimating means. According to this feature, by rotating the phase of the first transmission radiation pattern, the transmission radiation pattern can be surely and easily corrected. 
     Moreover, in the adaptive diversity apparatus of the present invention, the radiation pattern control means generates the second control signal so as to cancel a phase variation obtained by displacement of a direction of arrival of a reception wave. According to this feature, since a relative angle from a communication partner can be calculated by estimating from the reception signal the direction of arrival of a reception wave, radiation pattern correction can be realized at a low cost. 
     Moreover, in the adaptive diversity apparatus of the present invention, the transmission radiation pattern control means and the radiation pattern control means are provided independently of each other, and the transmission signal, the first control signal and the second control signal are multiplied by single multiplication means. Thereby, the circuit is simplified, so that incorporation or mounting of the radiation pattern means into an existing circuit is facilitated. 
     Moreover, the adaptive diversity apparatus of the present invention can be applied to each of a reception portion and a transmission portion to form an adaptive diversity transmission and reception apparatus. Thereby, when a user uses, while moving, a portable radio communication apparatus time-divisional and alternately having a transmission slot and a reception slot, the transmission and reception accuracy improves. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a conventional transmission diversity apparatus; 
     FIG. 2 is a view of a reception (transmission) radiation pattern; 
     FIG. 3 is a block diagram of an adaptive reception diversity apparatus according to a first embodiment of the present invention; 
     FIG. 4 is a view of a reception (transmission) radiation pattern in the present invention; 
     FIG. 5 is an explanatory view of reception (transmission) phase rotation in the present invention; and 
     FIG. 6 is a block diagram of an adaptive transmission diversity apparatus according to a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be described with reference to FIG. 3 to FIG.  6 . 
     [First Embodiment] 
     FIG. 3 is a block diagram showing an adaptive reception diversity apparatus according to a first embodiment of the present invention. FIG. 4 is a view showing a reception (transmission) radiation pattern in the present invention. FIG. 5 is an explanatory view of reception (transmission) phase rotation in the present invention. 
     The adaptive reception diversity apparatus includes a plurality of antennas  101 ,  102 ,  103  and  104 ; a reception radiation pattern controller  109  for controlling inputs from the respective antennas so that they can be composed so as to have radiation pattern; multipliers  105 ,  106 ,  107  and  108  for multiplying the output from the reception radiation pattern controller and the inputs from the respective antennas; an adder  113  for composing the outputs of the multipliers; a decider  112  for performing hard decision of the output of the adder  113 ; an error detector  111  for detecting an error between the output of the adder  113  and the output of the decider  112 ; a movement direction estimator  110  for estimating the movement direction of the transmitting side; and a radiation pattern rotator  114  for rotating the radiation pattern based on the output of the movement direction estimator  110 . Operations of these elements will be described hereinafter. 
     The reception antennas  101 ,  102 ,  103  and  104  receive propagated radio waves. The number of antennas is not limited to four but may be a number other than four. The inputs from the respective antennas and the output (weight) of the reception radiation pattern controller  109  are multiplied by the adders  105 ,  106 ,  107  and  108  respectively, and are composed by the adder  113 . 
     Here, the input signals from the antennas at a time t are expressed in vector form as S(t)={S 1 (t), S 2 (t), S 3 (t), S 4 (t)} T  and the outputs (weights) of the reception radiation pattern controller which are to be multiplied by the signals from the respective antennas are W(t)={W 1 (t), W 2 (t), W 3 (t), W 4 (t)} T . Then, the output S(t) of the adder  113  can be expressed as the following formula (3): 
     
       
           S ( t )=Σ 1   4   W*i ( t ) T   S   i ( t )  (3) 
       
     
     The decider  112  performs hard decision of the output of the adder  113 . When the decision result is D(t), the error detector  111  outputs the difference between D(t) and S(t) and supplies the difference to the reception radiation pattern controller  109 . Based on the difference, the reception radiation pattern controller  109  updates the values of the weights to be multiplied by the input signals from the antennas. The reception radiation pattern in the first embodiment of the present invention is not finally decided by the updated algorithm. However, for example, the reception radiation pattern controller  109  updates the outputs according to the following formula (4): 
     
       
           W ( t+ 1)= W ( t )+μ( D ( t )− Sig ( t )) T   Sig ( t )  (4) 
       
     
     The movement direction estimator  110  estimates the movement direction of the transmitting side. The movement direction estimation may be performed by any method. Examples of the method include a method in which a GPS receiver is used on the transmitting side and position information is transmitted, a method in which a GPS is used on the receiving side and a relative movement direction is detected, and a method which uses reception radiation pattern generated from a reception wave as described later. 
     The radiation pattern rotator  114  rotates the reception radiation pattern in accordance with the estimated movement direction of the transmitting side. As shown in FIG. 5, when the direction of the transmitting side viewed from the receiving side is θ  301  and a position normalized by the wavelength is (x i , y i ) with respect to the reference point of each antenna element, the phase shift from a reference point  306  at an antenna position  305  situated at (x i , y i ) on an x-y plane can be expressed as the following formula (5): 
     
       
         {square root over ( x   i   2   +y   i   2 +L )} cos(φ+θ)  (5) 
       
     
     Here, φ is an angle  302  between the antenna position  305  and the reference point  306 . The angle  302  may be x i  cos θ−y i  sin θ. 
     Expressing in radians the phase shift expressed by the formula (5), 2π(x i  cos θ−y i  sin θ)  304 . This is the phase variation from the reference point  306  at the antenna position  305 . The incident angle θ may be obtained by any method. Examples of the method include a method in which the incident angle θ is obtained by using position information measured in a reception signal by use of a GPS receiver on the transmitting side, a method which uses a direction where the maximum gain of the radiation pattern formed by the reception radiation pattern controller is obtained, and a method which uses a direction where the desired signal power-to-interference signal power ratio is high irrespective of reception power. These methods are advantageous in cost reduction because a relative angle from a communication partner can be calculated by estimating from the reception signals the direction in which reception waves are transmitted. 
     When the transmitting side moves, by obtaining a distance change amount Δl i  between when the angle viewed from the receiver is θ+α and the angle viewed from the receiver is θ, and converting the distance variation into a value expressed in radians, a phase variation Δθ i  which affects the respective antennas can be obtained. By composing the inputs of the respective antennas after multiplying each of the inputs by a value which cancels the phase variation Δθ i , the direction of the radiation pattern of the antennas can be rotated. Specifically, since the distance difference from the reference point when the angle is θ+α can be expressed, for example, as the following formula (6), the distance variation Δl i  due to a movement of the transmitting side can be expressed as the following formula (7): 
     
       
         {square root over ( x   i   2   +y   i   2 +L )} cos(φ+θ+α)  (6) 
       
     
     
       
         {square root over ( x   i   2   +y   i   2 +L )} cos(φ+θ)−{square root over ( x   i   2   +y   i   2 +L )} cos(φ+θ+α)  (7) 
       
     
     Rewriting this formula, the following formula (8) is obtained: 
     
       
           Δl   i   =−2{square root over ( x   i   2   +y   i   2 +L )}{cos(φ−α/ 2)sin θ+sin(φ+α/2)cos θ}sin α/2  (8) 
       
     
     Obtaining the phase variation Δθ i  converting the distance variation into a value expressed in radians, the phase variation Δθ i  can be expressed as the following formula (9): 
     
       
         Δθ i   =−4π{square root over ( x   i   2   +y   i   2 +L )}{cos(φ−α/ 2)sin θ+sin(φ+α/2)cos θ}sin α/2  (9) 
       
     
     Thus, since the phases of the antennas are shifted by Δθ i  by a movement of a mobile station by an angle α, by multiplying the weight of each antenna by a conjugate complex number which cancels the variation, the signals from the respective antennas can be composed so that the phases of the signals coincide with one another at the reference point, that is, the radiation pattern is formed in the direction in which the mobile station moves by the angle α. As a result, the reception performance can be improved. The conjugate complex number to be multiplied is, for example, as shown in the following formula (10): 
     
       
         Δ W   i =cos(Δθ i )− j  sin(Δθ i )  (10) 
       
     
     The same results are obtained when a predetermined value is added to or multiplied by the distance variation Δl i , the phase variation Δθ i  and the conjugate complex number ΔW i  irrespective of i. 
     As described above, according to the first embodiment of the present invention, since the reception radiation pattern can be rotated in accordance with the movement of the transmitting side, even when the movement speed of the transmitting side or the receiving side is high, the reception radiation pattern controller or a transmission radiation pattern controller can conform to the movement. Consequently, a correct radiation pattern can be formed, so that the transmission and reception performance can be improved. 
     [Second Embodiment] 
     FIG. 6 is a block diagram of an adaptive transmission diversity apparatus according to a second embodiment in which the present invention is applied to a transmitter. 
     The second embodiment shown in FIG. 6 includes a transmission signal generator  401  for generating a transmission signal; a reception antenna  402 ; a movement direction estimator  403  for estimating a movement direction; a transmission radiation pattern controller  405  for forming a transmission radiation pattern; a radiation pattern rotator  404  for rotating the radiation pattern based on the output of the movement direction estimator; multipliers  406 ,  407 ,  408  and  409  for multiplying the output of the transmission radiation pattern controller and the transmission signal; and a plurality of transmission antennas  410 ,  411 ,  412  and  413 . A plurality of reception antennas may be provided. 
     The radiation pattern of the antennas is changed in the following manner: When the receiving side moves, by obtaining a distance variation Δl i  between when the angle viewed from the transmitter is θ+α and the angle viewed from the transmitter is θ, and converting the distance variation into a value expressed in radians, a phase variation Δθ i  which affects the respective antennas is obtained. By composing the inputs of the respective antennas after multiplying each of the inputs by a value which cancels the phase variation Δθ i , the direction of the radiation pattern of the antennas is rotated. 
     The transmission signal generated by the transmission signal generator  401  is multiplied by a transmission radiation pattern signal which is the output of the transmission radiation pattern controller  405 , and then, transmitted from the transmission antennas  410 ,  411 ,  412  and  413 . In that case, when the receiving side is moving, the radiation pattern rotator  404  rotates the radiation pattern in consideration of the movement direction of the receiving side which is estimated by the movement direction estimator  403 . Thereby, a sudden movement of the receiving side can be handled. 
     As is apparent from the description given above, according to the present invention, the radiation pattern at the time of reception can highly accurately conform to a movement of a transmitting side even when the movement speed is high. In addition, the radiation pattern at the time of transmission can respond to a movement of a receiving side even when the movement speed is high. 
     Further, by applying the present invention to each of a reception portion and a transmission portion, when a user uses, while moving, a portable communication apparatus time-divisional and alternately having a transmission slot and a reception slot, the transmission and reception accuracy improves.