Abstract:
A radio communication apparatus performing time division duplex alternately switching a transmission period and a reception period by time dividing an identical frequency, includes the steps of: detecting a transmission signal to be transmitted to the antenna so as to perform radio transmission from an antenna commonly used for transmission and reception; and calculating a deviation time between the detection timing of the detected transmission signal and a preset reference timing, and for controlling switchover timing between the transmission period and the reception period based on the deviation time.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2008-119472, filed on May 1, 2008 the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The present invention relates to a radio communication apparatus performing time division duplex (TDD) in which transmission and reception are alternately switched by time dividing the same frequency, and more particularly a technique for preventing the inflow of a transmission signal into a circuit on the reception side. 
       BACKGROUND 
       [0003]    The time division duplex (TDD) in radio communication is a communication method applied to a communication standard such as WiMAX (Worldwide Interoperability for Microwave Access). By switching between transmission and reception time-by-time, full duplex communication is performed in the same frequency band, and thereby efficient use of frequency can be achieved. 
         [0004]      FIG. 1  is a diagram illustrating an exemplary configuration of a transmission/reception switch circuit in the TDD radio communication apparatus. An antenna  14  is commonly used for transmission and reception. A circulator  9  is provided for separating a transmission signal from a reception signal. By the above circulator  9 , the inflow of a signal from a transmitter unit  12  into a receiver unit  16  is prevented, and also the inflow of a reception signal from antenna  14  into transmitter unit  12  is prevented. By the function of circulator  9 , the transmission signal from transmitter unit  12  is transmitted from antenna  14 , and the reception signal received by antenna  14  is forwarded to receiver unit  16 . A capacitor  8  is a high frequency capacitor for cutting off a direct current component. Diode  6  is provided to prevent the inflow of the transmission signal leaked from circulator  9  into receiver unit  16 , and is controlled to turn on/off by means of a controller unit  20 . Controller unit  20  controls a switchover between the transmission period and the reception period. Based on preset and fixed switchover timing information, controller unit  20  controls to turn on/off the output of the control signal on the reception side. Namely, in the transmission period, controller unit  20  outputs a control signal on the reception side (supplies a specific voltage), so as to turn on diode  6 . As a result, the impedance of diode  6  is made to be substantially 0Ω, and thus, the inflow of the transmission signal leaked from circulator  10  into receiver unit  16  is prevented. On the other hand, in the reception period, by suspending the output of the control signal on the reception side (suspending the supply of the specific voltage), so as to turn off diode  6  and make the impedance of diode  6  infinite. Thus, the reception signal is not made to flow into diode  6 , and instead, made to flow into receiver unit  16 . 
         [0005]      FIG. 2  is a diagram illustrating a switchover state of transmission and reception in a normal case. In a normal state, transmitter unit  12  outputs the transmission signal during the transmission period, while receiver unit  16  receives the reception signal during the reception period. Also, in the transmission period, controller unit  20  outputs the control signal on the reception side. In contrast, in the reception period, controller unit  20  suspends outputting the control signal on the reception side. 
         [0006]    In Patent document 1, in case of communication between a single master station and a plurality of substations through the TDMA (Time Division Multiple Access) method, there is disclosed a configuration that each substation outputs the transmission signal during a transmission period successively assigned to each substation. Further, the configuration described below is disclosed: each substation outputs the transmission signal only when a transmission timing signal corresponding to the transmission period is input, and in contrast, when the transmission timing signal is not input, each substation suspends transmitting the transmission signal from a transmission radio section. 
         [0007]    [Patent document 1] the official gazette of the Japanese Unexamined Patent Publication No. Hei-8-186551. 
         [0008]    In the TDD radio communication apparatus, it is necessary to switch between transmission and reception at high speed. When the output timing of the transmission signal deviates due to an environmental temperature change, an apparatus failure, and the like, there is a risk of the occurrence of a large communication abnormality. More specifically, when the output timing of the transmission signal is delayed from normal output timing, causing the transmission signal output continued in the next reception period subsequent to the completion of the transmission period, the transmission signal flows into receiver unit  16 . 
         [0009]      FIG. 3  is a diagram illustrating a switchover state of the transmission and the reception in an abnormal case. In the figure, there is shown an abnormal state that the transmission signal is being output in the reception period. Before the completion of the transmission signal output, a shift to a reception period is made. As a result, a portion of the transmission signal flows into receiver unit  16 . Here, because the transmission signal power is extremely larger than the reception signal power, and receiver unit  16  is designed to receive a weak radio wave, there is a risk of causing damage or malfunction of circuit elements, such as am amplifier circuit (low noise amplifier, LNA), having a small tolerance of power. Further, because a portion of the transmission signal is not transmitted during the transmission period, the transmission signal power transmitted from the antenna is decreased. This disables transmission of data having integral quality to a radio space. 
       SUMMARY 
       [0010]    Accordingly, the objective of the present invention in regard to a radio communication apparatus and a method for controlling to switch between transmission and reception is to avoid the inflow of a transmission signal into a receiver unit caused by deviation between a transmission signal output timing and a transmission/reception switchover timing, and also to prevent quality deterioration of the transmission signal. 
         [0011]    A first structure of a radio communication apparatus according to the present invention, performing time division duplex alternately switching a transmission period and a reception period by time dividing an identical frequency, includes: an antenna commonly used for transmission and reception; a transmitter unit being electrically connected to the antenna and outputting a transmission signal; a receiver unit being electrically connected to the antenna and the transmitter unit, and processing a reception signal received by the antenna; a switch capable of switching between an operation for the transmission period to cut off inflow of the transmission signal to the receiver unit and an operation for the reception period to cut off inflow of the reception signal to the transmitter unit; a signal detector unit detecting the transmission signal; and a controller unit calculating a deviation time between detection timing of the transmission signal detected by the signal detector unit and a preset reference timing, and controlling switchover timing of the switch based on the deviation time. 
         [0012]    In a second structure of a radio communication apparatus according to the first structure, when the detection timing in a first transmission period is later than the reference timing, and the deviation time exceeds a predetermined time, the controller unit delays a switchover timing from a next reception period relative to the first transmission period to the next transmission period thereto by a predetermined adjustment time. 
         [0013]    In a third structure of a radio communication apparatus according to the second structure, the predetermined adjustment time is the deviation time or shorter. 
         [0014]    A switchover control method of transmission and reception in a radio communication apparatus according to the present invention, performing time division duplex alternately switching a transmission period and a reception period by time dividing an identical frequency, includes the steps of: a detection step for detecting a transmission signal to be transmitted to the antenna so as to perform radio transmission from an antenna commonly used for transmission and reception; and a control step for calculating a deviation time between the detection timing of the detected transmission signal and a preset reference timing, and for controlling switchover timing between the transmission period and the reception period based on the deviation time. 
         [0015]    It is preferable that, when the detection timing in a first transmission period comes later than the reference timing, and the deviation time exceeds a predetermined time, the control step delays a switchover timing from a next reception period relative to the first transmission period to a next transmission period thereto by a predetermined adjustment time. Additionally, it is preferable that, the predetermined adjustment time is the deviation time or shorter. 
         [0016]    According to the present invention, because the output period of the transmission signal interrupts the reception period in excess of the transmission period, it is possible to suppress the inflow of the transmission signal into the receiver unit to a minimum, and to prevent circuit breakage in the receiver unit. Also, it is possible to suppress the occurrence of a loss of transmission in which a portion of the transmission signal is not transmitted. 
         [0017]    Additional objects and advantages of the invention (embodiments) will be set forth in part in the description which follows, and in part will be obvious from the description, or maybe learned by practice of the invention. The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
         [0018]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0019]      FIG. 1  is a diagram illustrating an exemplary configuration of a transmission/reception switch circuit in the TDD radio communication apparatus, 
           [0020]      FIG. 2  is a diagram illustrating a switchover state of transmission and reception in a normal case, 
           [0021]      FIG. 3  is a diagram illustrating a switchover state of the transmission and the reception in an abnormal case, 
           [0022]      FIG. 4  is a diagram illustrating an exemplary configuration of a radio communication apparatus according to an embodiment of the present invention, 
           [0023]      FIG. 5  is a diagram illustrating an exemplary configuration of a transmission/reception switch circuit in the radio communication apparatus according to the present embodiment, 
           [0024]      FIG. 6  is a diagram illustrating a timing chart of the transmission/reception switchover control in the normal case according to the present embodiment, 
           [0025]      FIG. 7  is a flowchart of switchover control in controller unit  20 , according to the present embodiment, and 
           [0026]      FIG. 8  is a diagram illustrating a timing chart of transmission/reception switchover control in an abnormal case according to the present embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0027]    The preferred embodiment of the present invention is described hereinafter referring to the charts and drawings. However, the embodiment described below is not intended to limit the technical scope of the present invention. Like reference numerals refer to like configuration elements shown in  FIG. 1 . 
         [0028]      FIG. 4  is a diagram illustrating an exemplary configuration of a radio communication apparatus according to an embodiment of the present invention. A baseband unit  10  generates a transmission signal, so as to forward to a transmitter unit  12 . Transmitter unit  12  transmits the transmission signal from an antenna  14 . Also, a receiver unit  16  receives a reception signal from antenna  14 , so as to forward to baseband unit  10 . Baseband unit  10  performs demodulation processing of the reception signal. 
         [0029]    According to the present embodiment, a transmission signal detector unit  18  is provided on a path in the vicinity of antenna  14 , on which the transmission signal flows. Transmission signal detector unit  18  is configured of a detection circuit. When the transmission signal is output, transmission signal detector unit  18  outputs a detection signal which exceeds a predetermined threshold level. 
         [0030]    A controller unit  20  performs transmission/reception switchover control. Controller unit  20  outputs a control signal on the transmission side to a switch  22  on the transmission side, and also outputs a control signal on the reception side to a switch  24  on the reception side. By switching the output timing of the above control signals, controller unit  20  switches transmission and reception. 
         [0031]    Controller unit  20  according to the present embodiment acquires predetermined transmission/reception switchover timing information from baseband unit  10 , and also corrects transmission/reception switchover timing according to the detection signal from transmission signal detector unit  18 . According to the corrected transmission/reception switchover timing, controller unit  20  adjusts the output timing of both the control signal on the transmission side and the control signal on the reception side, and executes transmission/reception switchover control. More specifically, as described later, when the transmission signal is continued to output even after the completion of the transmission period (when the transmission signal output timing exceeds the transmission period), the transmission signal output is executed in the transmission period by making the next transmission period to be delayed for a specific time. 
         [0032]      FIG. 5  is a diagram illustrating an exemplary configuration of a transmission/reception switch circuit in the radio communication apparatus according to the present embodiment. Exemplary circuit configurations of switch  22  on the transmission side and switch  24  on the reception side are shown. Switch  22  on the transmission side and switch  24  on the reception side are formed of single-pole double-throw switches (SPDT switches), respectively configured of shunt-connected diodes. Switch  22  on the transmission side and switch  24  on the reception side are shunt connected at positions B and C, respectively, by a distance of ¼ wavelength from a branch point A, branching from antenna  14  commonly used for transmission and reception, to the transmitter unit  12  side and the receiver unit  16  side. Accordingly, the positions of the diode connections differ depending on the signal wavelength used. Although the two diodes are connected in parallel in the example of each switch  22 ,  24  shown in  FIG. 5 , each number of diodes is not limited to two, but a necessary number ( 1 ,  2 , . . . n) of diodes are used according to the necessity. Additionally, a capacitor  8  is a high frequency capacitor for cutting off a direct current component. 
         [0033]    In the transmission period, controller unit  20  outputs the control signal on the reception side, so as to turn on switch  24  on the reception side (to supply a specific voltage). Switch  22  on the transmission side is in an off state. At this time, the impedance of switch (diode)  24  on the reception side is decreased to 0Ω, and the connection point C becomes a short circuit point. Then, a point A deviating therefrom by a ¼ wavelength becomes an open circuit point (having infinite impedance). By this, there is formed a circuit in which the transmission side cannot identify the load on the reception side, and accordingly, the transmission signal flows from the branch point A to antenna  14  and, however, does not flow into the reception side. 
         [0034]    On the other hand, in the reception period, controller unit  20  outputs the control signal on the transmission side, so as to turn on switch  22  on the transmission side (to supply a specific voltage). Switch  24  on the reception side is in an off state. At this time, the impedance of switch (diode)  22  on the transmission side is decreased to 0Ω, and the connection point B becomes a short circuit point. Then, a point A deviating therefrom by a ¼ wavelength (λ) becomes an open circuit point (having infinite impedance). By this, there is formed a circuit in which antenna  14  cannot identify the transmission side, and accordingly, the reception signal flows from antenna  14  to the reception side via the branch point A and, however, does not flow into the transmission side. 
         [0035]    Additionally, the exemplary circuit shown in  FIG. 5  is an exemplary circuit in which a circulator is not used. However, in case of using the circulator, it may also be possible to apply the configuration shown in  FIG. 1 . 
         [0036]      FIG. 6  is a diagram illustrating a timing chart of the transmission/reception switchover control in the normal case according to the present embodiment. Based on the information of the initial value Mn (N=1, 2, 3, . . . ) in regard to switchover timing given in advance, controller unit  20  switches on and off the control signal on the transmission side and the control signal on the reception side, on the basis of each specific period. In  FIG. 6 , the transmission/reception switchover timing Mn as the initial value is set in controller unit  20 . Controller unit  20  first turns on the control signal on the reception side at timing M 1 . Then, one period thereafter, at timing M 2 , controller unit  20  turns off the control signal on the reception side, and at the same time, turns on the control signal on the transmission side. In other words, the duration from the timing M 1  to M 2  becomes a transmission period. Further, one period thereafter, at timing M 3 , controller unit  20  turns off the control signal on the transmission side, and at the same time, turns on the control signal on the reception side. In other words, the duration from the timing M 2  to M 3  becomes a reception period. The timing M 3  also becomes the start timing of the next transmission period. 
         [0037]    In the normal case, the transmission signal is output between a timing Ts and a timing Te, included in the transmission period (M 1  to M 2 ), and the reception signal is received between a timing Rs and a timing Re, included in the reception period (M 2  to M 3 ). The output start timing Ts of the transmission signal, the output end timing Te of the transmission signal, the reception start timing Rs of the reception signal, and the reception end timing Re of the reception signal are given in advance to controller unit  20 , as reference timings. The transmission period (M 1  to M 2 ) and the reception period (M 2  to M 3 ) are set longer than the transmission signal output period (Ts to Te) and the reception signal reception period (Rs to Re), respectively. The reason is that, even in case that the timings of the transmission signal output period (Ts to Te) and the reception signal reception period (Rs to Re) deviate to some extent, it is configured that the transmission signal output period and the reception signal reception period are fallen within the transmission period (M 1  to M 2 ) and the reception period (M 2  to M 3 ), respectively. 
         [0038]      FIG. 7  is a flowchart of switchover control in controller unit  20 , according to the present embodiment. Controller unit  20  switches on and off the control signal on the transmission side and the control signal on the reception side, based on the initial value Mn of the transmission/reception switchover timing which is given in advance. 
         [0039]    Controller unit  20  receives a detection signal from transmission signal detector unit  18 . When the level of the detection signal is a threshold level or greater, controller unit  20  decides that the transmission signal is being output, and retains the detection timing detecting that the signal level is the threshold level or greater (the transmission signal is transmitted) (S 102 ). 
         [0040]    Controller unit  20  calculates a deviation time Td (Ts′−Ts), which is a deviation time between the reference timing Ts of the transmission signal output start timing in the transmission period and a timing Ts′ (actual transmission signal output start timing) being retained in step S 102 , so as to decide whether the deviation time Td exceeds a predetermined time Ta (S 104 ). The deviation time Td is a delay time when the timing Ts′ has a delay relative to the reference timing Ts. 
         [0041]    The predetermined time Ta is set, for example, to be Ta=M 2 −Te, that is, a time from the transmission signal output end timing Te to the transmission period end timing M 2 . If the above deviation time Td exceeds the predetermined time Ta, the transmission signal output period exceeds the transmission period, and overflows to the reception period. As to the predetermined time Ta, it is not limited to the time (M 2 −Te). An appropriate time is settable by taking into consideration the rise times of the transmission period and the reception period, etc. 
         [0042]    When the deviation time Td is the predetermined time Ta or less, the on/off control of the control signal on the reception side and the control signal on the transmission side is performed, based on the transmission/reception switchover timing Mn being set as the initial value (S 106 ). The control to be performed when the deviation time Td is the predetermined time Ta or less is the same as the transmission/reception switchover control in a normal case shown in  FIG. 6 . 
         [0043]    On the other hand, when the deviation time Td exceeds the predetermined time Ta, controller unit  20  calculates an adjustment time Tc based on the deviation time Td (S 108 ), and corrects the switchover timing as the initial value to a switchover timing Mn′ based on the adjustment time Tc. Controller unit  20  then performs switchover control using the corrected switchover timing Mn′ as the start timing of the next transmission period (S 110 ). The adjustment time Tc is given by Tc=Td−Ta. More specifically, the start timing Mn′ of the next transmission period to the transmission period having detected the deviation time Td (namely, the end timing of the next reception period) is made to be Mn′=Mn+Tc. In other words, controller unit  20  delays the next transmission period start timing by the amount of the predetermined adjustment time (Td−Ta). Here, the adjustment time Tc is not limited to be (Td−Ta), but to be an appropriate time equal to the deviation time Td or smaller, taking the apparatus characteristic etc. into consideration. Additionally, the delayed switchover timing Mn′ has a limitation of not exceeding the reception start timing Rs of the reception signal. The reason is to prevent the overlap of signal transmission and reception. 
         [0044]      FIG. 8  is a diagram illustrating a timing chart of transmission/reception switchover control in an abnormal case (when the deviation time Td exceeds the predetermined time Ta), according to the present embodiment. In the transmission period (M 1  to M 2 ), it is detected that the deviation time Td between the actual transmission signal output start timing Ts′ and the reference timing Ts exceeds the predetermined time Ta. If the predetermined time Ta is set to be the time from the reference timing Te of the transmission signal output end timing to the initial value M 2  of the transmission period end timing, then, the transmission signal output is continued by a time (Td−Ta) exceeded from the transmission period end timing M 2 . Controller unit  20  sets the start timing M 3 ′ of the next transmission period to be [the initial value M 3 +the adjustment time (Td−Ta)]. By this, in case the transmission signal output timing is the same as immediately before, the next transmission signal output period falls within the transmission period, and does not overflow to the reception period. Because the transmission signal output timing does not greatly vary period-by-period, after the deviation is detected, the deviation can be absorbed by adjusting the next transmission period based on the deviation of the transmission signal output timing in the transmission period immediately before. Accordingly, it is possible to prevent the transmission signal from being output in an overflowed manner to the reception period. 
         [0045]    Thus, it is possible to suppress to the minimum the inflow of the transmission signal into the receiver unit caused by the transmission signal output in an overflowed manner to the reception period, and to prevent a circuit breakage of the receiver unit. Further, because the entire transmission signals are transmitted in the transmission period, it is possible to suppress the occurrence of a transmission loss caused by a failure in the transmission of a portion of the transmission signal. 
         [0046]    In the example described above, there has been shown an example that the output deviation time Td of the transmission signal is compared with the predetermined time Ta, and thereby the switchover timing is delayed by the amount of (Td−Ta). However, it is also possible to control to delay by the deviation time Td intact, as the adjustment time, when the deviation time Td is detected. By directly reflecting the deviation time Td to the correction of the switchover timing, it is possible to maintain the transmission signal output period in the transmission period to be constant, and more stable transmission can be secured. 
         [0047]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.