Abstract:
A time division duplexing (TDD) transmission/reception apparatus and method are provided. The TDD transmission/reception apparatus includes: a transmitter which generates a transmitted signal; an antenna which transmits the transmitted signal to an external device and receives a received signal from an external device; a receiver which restores source data by demodulating the received signal; and a polarized duplexer which has a first end connected to the transmitter and the receiver and a second end connected to the antenna and comprises an inclined surface, the inclined surface polarizing the transmitted signal and the received signal such that the directivity of the transmitted signal and the directivity of the received signal are perpendicular to each other.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION  
       [0001]     This application claims the benefit of Korean Patent Application No. 10-2005-0013895, filed on Feb. 19, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a time division duplexing (TDD) transmission/reception apparatus and method, and more particularly, to a TDD transmission/reception apparatus and method which can enhance the efficiency of transmission/signal reception path isolation by polarizing transmitted signals and received signals with the aid of a polarized duplexer having an inclined surface such that the directivity of the transmitted signals is perpendicular to the directivity of the received signals.  
         [0004]     2. Description of the Related Art  
         [0005]     Time division duplexing (TDD) transmission/reception apparatuses use the same frequency band to transmit and receive signals. TDD transmission/reception apparatuses time-divide the transmission/reception of signals and downlink signals to an access point (i.e., a TDD base station) for a predetermined time period and then uplink signals from the access point for another predetermined time period.  
         [0006]     In the case of using the same frequency band to transmit and receive signals as mentioned above, part of transmission power may be reflected by an antenna port and thus be infiltrated into a signal reception path of a reception system regardless of how perfectly the impedance of an antenna matches the impedance of a transmission/reception apparatus, thus resulting in a high signal reception path gain. A high signal reception path gain may considerably damage the reception system and adversely affect the reception sensitivity of the reception system, thereby lowering the reception capabilities of the transmission/reception apparatus. In addition, noise signals generated by a transmitter during the reception of received signals may interfere with the received signals, thereby lowering the reception capabilities of the transmission/reception apparatus.  
         [0007]     Therefore, TDD transmission/reception apparatuses need an apparatus and method for minimizing the possibility of transmitted signals interfering with received signals by isolating a signal reception path from a signal transmission path.  
         [0008]      FIG. 1  is a block diagram of a conventional TDD transmission/reception apparatus having radio frequency (RF) switches  150  and  155  for isolating a signal transmission path from a signal reception path. Referring to  FIG. 1 , the TDD transmission/reception apparatus includes a transmitter  100 , a receiver  105 , a high power amplifier (HPA)  110 , a circulator  115 , a band pass filter (BPF)  120 , an antenna  125 , and a synchronization signal generator  185 . The transmitter  100  includes a modulator  130 , an up converter  135 , an RF amplifier  140 , a step attenuator  145 , and the RF switch  150 . The receiver  105  includes a demodulator  180 , a down converter  170 , a step attenuator  165 , a low noise amplifier  160 , and the RF switch  155 .  
         [0009]      FIGS. 2A and 2B  illustrate examples of the format of a frame of the conventional TDD transmission/reception apparatus illustrated in  FIG. 1 . Referring to  FIGS. 2A and 2B , an uplink and a downlink are conducted at different times. In detail, referring to  FIG. 2A , an uplink and a downlink are conducted with an uplink-downlink ratio of 16:6. Referring to  FIG. 2B , an uplink and a downlink are conducted with an uplink-downlink ratio of 13:9. The synchronization signal generator  185  generates synchronization signals which turn on or off the RF switches  150  and  155  in response to the synchronization with an uplink with a downlink at a uniform interval TTG. The RF switch  150  in the transmitter  100  is turned on in response to a synchronization signal generated by the synchronization signal generator  185  and is turned off during a downlink period. On the other hand, the RF switch  155  in the receiver  105  is turned off during an uplink period and is turned on during the downlink period. A signal transmission path and a signal reception path can be isolated from each other by controlling the turning on or off of the RF switches  150  and  155 .  
         [0010]     The operation of the conventional TDD transmission/reception apparatus using the RF switches  150  and  155  will now be described in detail. The modulator  130  generates a transmitted signal to be transmitted, and the up converter  135  up-converts the frequency of the transmitted signal such that the transmitted signal can be readily transmitted. The RF amplifier  140  amplifies the transmitted signal, and the step attenuator  145  attenuates the power of the transmitted signal in steps. Thereafter, the transmitted signal is input to the HPA  110  only for an uplink period, and the HPA  110  amplifies the transmitted signal so that the transmitted signal has a very high power, and outputs the amplified result.  
         [0011]     The RF switch  155  in the receiver  105  receives a received signal received via the antenna  125  from the circulator  115  only for a downlink period, and outputs the received signal to the LNA  160 . The LNA  160  amplifies the received signal while minimizing noise. The step attenuator  165  attenuates the power of the received signal in steps, and the down converter  170  down-converts the frequency of the received signal. The demodulator  180  demodulates the received signal output by the down converter  170 , thereby restoring desired source data.  
         [0012]     The antenna  120  amplifies a transmitted signal. Then, the antenna  120  emits the amplified result to the air and receives a received signal from the air. The BFP  120  filters a transmitted signal and a received signal to a frequency band used by the conventional TDD transmission/reception apparatus, and the circulator  115  transmits a transmitted signal output by the HPA  110  to the BPF  120  and transmits a received signal received via the antenna  120  to the receiver  105 .  
         [0013]     As described above, in a case where a conventional TDD transmission/reception apparatus isolates a signal transmission path from a signal reception path using RF switches, a frame synchronization signal of a transmitted signal and a received signal must be extracted to control the RF switches, and then the RF switches must be turned on or off in response to the extracted frame synchronization signal while keeping monitoring the extracted frame synchronization signal. Thus, the structure of the conventional TDD transmission/reception apparatus may become too much sophisticated. In addition, since there is a need to realize a synchronization signal extraction algorithm, the manufacturing cost of the conventional TDD transmission/reception apparatus may increase.  
         [0014]     Conventionally, as indicated in Table 1 below, the switching time of RF switches must be controlled within several dozens of usec, and thus, a high precision switching control technique is required. In addition, the control of the RF switches must be performed at intervals of 5 msec, and thus, a high precision switching control technique which can ensure a high durability against a considerable number of switching control repetitions is required. Repetitive RF switch controls, however, deteriorate the performance of RF switches over time, and eventually reduce the lifetime of transmission/reception apparatuses considerably.  
                           TABLE 1                                   Variables   Values                           Channel Bandwidth   10 MHz           Sampling Frequency (F s )   10 MHz           Sampling Interval (1/F s )   100 nsec           FFT Size (N FFT )   1024           Quantity of Sub-Carriers Used   864           Quantity of Data Sub-Carriers   768           Quantity of Pilot Sub-Carriers   96           Sub-Carrier Frequency Interval   9.765625 KHz           Valid Symbol Time (T b  = 1/Δ f)   102.4 μs           CP Time (T g  = T b /8)   12.8 μs           OFDMA Symbol Time (T s  = T b  + T g )   115.2 μs           TDD Frame Length   5 ms                      
 
       SUMMARY OF THE INVENTION  
       [0015]     The present invention provides a TDD transmission/reception apparatus and method which can enhance the efficiency of transmission/signal reception path isolation without using RF switches by polarizing transmitted signals and received signals with the aid of a polarized duplexer having an inclined surface such that the directivity of the transmitted signals is perpendicular to the directivity of the received signals.  
         [0016]     According to an aspect of the present invention, there is provided a time division duplexing (TDD) transmission/reception apparatus. The TDD transmission/reception apparatus includes: a transmitter which generates a transmitted signal; an antenna which transmits the transmitted signal to an external device and receives a received signal from an external device; a receiver which restores source data by demodulating the received signal; and a polarized duplexer which has a first end connected to the transmitter and the receiver and a second end connected to the antenna and comprises an inclined surface, the inclined surface polarizing the transmitted signal and the received signal such that the directivity of the transmitted signal and the directivity of the received signal are perpendicular to each other.  
         [0017]     The transmitter and the receiver may be connected to the first end of the polarized duplexer such that they can be perpendicular to each other.  
         [0018]     The polarized duplexer may include 2 inclined surfaces which polarize the transmitted signal and the received signal such that the directivity of the transmitted signal and the directivity of the received signal are perpendicular to each other, wherein the 2 inclined surfaces are symmetrical.  
         [0019]     The transmitter may include a polarization filter which filters the transmitted signal, and the receiver may include a polarization filter which filters the received signal.  
         [0020]     The polarized duplexer may be a polarized waveguide.  
         [0021]     The polarized duplexer may include: a first polarized rectangular waveguide which is connected to the transmitter; a second polarized rectangular waveguide which is connected to the receiver; and a circular waveguide which is connected to the antenna.  
         [0022]     The inclination angle of the inclined surface may be determined according to a frequency band used by the TDD transmission/reception apparatus.  
         [0023]     According to another aspect of the present invention, there is provided a TDD transmission/reception method. The TDD transmission/reception method includes: generating a transmitted signal; receiving a received signal from an external device via an antenna; polarizing the transmitted signal and the received signal such that the directivity of the transmitted signal and the directivity of the received signal are perpendicular to each other; restoring source data by demodulating the received signal; and transmitting the polarized transmitted signal to an external device via the antenna.  
         [0024]     The polarizing may include making the transmitted signal and the received signal incident upon an inclined surface in perpendicular directions such that they can be perpendicular to each other.  
         [0025]     The polarizing may include making the transmitted signal and the received signal incident upon 2 inclined surfaces in perpendicular directions such that the directivity of the transmitted signal and the directivity of the received signal are perpendicular to each other, wherein the 2 inclined surfaces are symmetrical.  
         [0026]     The inclination angle of the inclined surface may be determined according to a frequency band used for transmitting/receiving signals. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
         [0028]      FIG. 1  is a block diagram of a conventional time division duplexing (TDD) transmission/reception apparatus using RF switches;  
         [0029]      FIGS. 2A and 2B  are diagrams illustrating examples of the format of a frame of a conventional TDD transmission/reception apparatus;  
         [0030]      FIG. 3  is a block diagram of a TDD transmission/reception apparatus using a polarized duplexer according to an exemplary embodiment of the present invention;  
         [0031]      FIG. 4  is a perspective view of a polarized duplexer according to an exemplary embodiment of the present invention;  
         [0032]      FIG. 5  is a cross-sectional view of a polarized duplexer according to another exemplary embodiment of the present invention;  
         [0033]      FIG. 6  is a perspective view of a polarized duplexer to which an antenna is connected, according to an exemplary embodiment of the present invention; and  
         [0034]      FIG. 7  is a graph illustrating experimental results obtained by measuring S parameters of a TDD transmission/reception apparatus using a polarized duplexer according to an exemplary embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     The present invention will now be described more fully with reference to the accompanying drawings in which exemplary embodiments of the invention are shown.  
         [0036]      FIG. 3  is a block diagram of a TDD transmission/reception apparatus using a polarized duplexer  315  according to an exemplary embodiment of the present invention. Referring to  FIG. 3 , the TDD transmission/reception apparatus includes a transmitter  300 , a receiver  305 , an HPA  310 , the polarized duplexer  315 , a BPF  320 , and an antenna  325 . The transmitter  300  includes a modulator  330 , an up converter  335 , an RF amplifier  340 , and a step attenuator  345 . The receiver  305  includes a demodulator  365 , a down converter  360 , a step attenuator  355 , and an LNA  350 .  
         [0037]     The modulator  330  generates a transmitted signal to be transmitted. The up converter  335  up-converts the frequency of the transmitted signal such that the transmitted signal can be readily transmitted. The RF amplifier  340  amplifies the transmitted signal. The step attenuator  345  attenuates the power of the transmitted signal in steps. The HPA  110  amplifies the transmitted signal to have a very high power and outputs the amplified result.  
         [0038]     The antenna  325  receives signals transmitted by an external device (not shown) from the air. Of the received signals, the BPF  320  filters the received signals corresponding to a frequency band used by the TDD transmission/reception apparatus.  
         [0039]     The polarized duplexer  315  polarizes a transmitted signal output by the HPA  310  and a received signal BPF  320  using an inclined surface such that the directivity of the transmitted signal is perpendicular to the directivity of the received signal. The transmitted signal which has been polarized so as to be perpendicular to the received signal and to have a high power by the inclined surface of the polarized duplexer  315  does not interfere with the received signal. Thus, the transmitted signal passes through the polarized duplexer  315 , and the received signal which is input to the receiver  305  is neither flawed by nor mixed with the transmitted signal or a noise signal.  
         [0040]     The LNA  350  of the receiver  305  amplifies the received signal while minimizing noise. The step attenuator  355  attenuates the power of the received signal in steps. The down converter  360  down-converts the frequency of the received signal. The demodulator  365  demodulates the received signal down-converted by the down converter  360 , thereby restoring desired source data.  
         [0041]      FIG. 4  is a perspective view of a polarized duplexer according to an exemplary embodiment of the present invention. Referring to  FIG. 4 , the polarized duplexer includes a first waveguide  400 , a second waveguide  410 , and a third waveguide  420 . The third waveguide  420  is cylindrical. A first end of the third waveguide  420  is connected to an antenna (not shown), and a second end of the third waveguide  420  is connected to the first and second waveguides  400  and  410 . The third waveguide  420  includes an inclined surface  430 . The first and second waveguides  400  and  410  may be located so that they can make the directivity of a transmitted signal and the directivity of a received signal perpendicular to each other.  
         [0042]     The first waveguide  400  is connected to the transmitter  300  of  FIG. 3 . Thus, a transmitted signal generated by the transmitter  300  can be incident upon the inclined surface  430  of the third waveguide  420 . Then, the transmitted signal is polarized toward a first direction which is determined according to the inclination angle of the inclined surface  430  and the angle at which the transmitted signal is incident upon the inclined surface  430 . Thereafter, the polarized transmitted signal passes through the third waveguide  420  and is output to the antenna to which the third waveguide  420  is connected.  
         [0043]     Signals having arbitrary directivities are received via an antenna, pass through the polarized duplexer  315 , and are transmitted to the receiver  305  of  FIG. 3 . The received signals having arbitrary directivities are mixed with transmitted signals having very high powers in the third waveguide  420 . However, of the received signals, only the received signal which is directed toward a second direction which is perpendicular to the first direction can pass through the third waveguide  420  without being interfered by the polarized transmitted signal.  
         [0044]     Thereafter, the received signal which is directed toward the second direction and is thus prevented from being interfered by the polarized transmitted signal is incident upon the inclined surface  430  and is output to the receiver  305  via the second waveguide  410 . Thereafter, the receiver  305  can restore source data which is not affected by the polarized transmitted signal, by modulating the received signal which is directed toward the second direction.  
         [0045]      FIG. 5  is a cross-sectional view of a polarized duplexer according to another exemplary embodiment of the present invention. Referring to  FIG. 5 , a third waveguide  500  may include 2 inclined surfaces  510  and  520  which are symmetrical. The inclined surfaces  510  and  520  may be formed to connect a connection area between the third waveguide  500  and a second waveguide  410  and a connection area between the third waveguide  500  and a first waveguide  400 . The sizes of the first through third waveguides  400 ,  410 , and  500  may be altered according to a frequency band used for transmitting/receiving signals and the specifications of a transmission/reception apparatus used for transmitting/receiving signals. Therefore, the inclination angles and length of the inclined surfaces  510  and  520  may be also altered according to a frequency band used for transmitting/receiving signals and the specifications of a transmission/reception apparatus used for transmitting/receiving signals.  
         [0046]      FIG. 6  is a perspective view of a polarized duplexer which has 2 inclined surfaces and is connected to an antenna according to an exemplary embodiment of the present invention.  
         [0047]      FIG. 7  is a graph illustrating experimental results obtained by measuring S parameters of the TDD transmission/reception apparatus of  FIG. 3  when using a terminal of the antenna  326 , a terminal of the transmitter  300 , and a terminal of the receiver  305  as port  1 , port  2 , and port  3 , respectively.  
         [0048]     Referring to  FIG. 7 , a curve  700  illustrates the variation of an S 13  parameter, a curve  710  illustrates the variation of an S 33  parameter, a curve  720  illustrates the variation of an S 12  parameter, and a curve  730  illustrates the variation of an S 22  parameter. As indicated by the curves  700  through  730 , transmitted signals and received signals belonging to a desired frequency band transmit through the TDD transmission/reception apparatus using a polarized duplexer according to an exemplary embodiment of the present invention with the same resonance frequencies.  
         [0049]     A curve  740  illustrates the variation of an S 23  parameter measured at the receiver  305  of the TDD transmission/reception apparatus, a curve  750  illustrates the variation of the S 23  parameter measured at the transmitter  300  of the TDD transmission/reception apparatus. Values of the S 23  parameter represented by the curves  740  and  750  are a factor for determining the efficiency of isolating a signal transmission path of the transmitter  300  from a signal reception path of the receiver  305 . Therefore, as indicated by the curves  740  and  750 , the TDD transmission/reception apparatus using a polarized duplexer according to an exemplary embodiment of the present invention can achieve a high transmission/signal reception path isolation of −60 dB or greater.  
         [0050]     As described above, according to the present invention, transmitted signals and received signals are polarized with the aid of a polarized duplexer having one or more inclined surfaces such that the directivity of the transmitted signals is perpendicular to the directivity of the received signals. Therefore, it is possible to protect a receiver from transmitted signals without using RF switches, which complicate the structure of a TDD transmission/reception apparatus and increase the manufacturing cost of the TDD transmission/reception apparatus, by enhancing the efficiency of transmission/signal reception path isolation. In addition, it is possible to minimize the noise level of transmitted signals input to the receiver.  
         [0051]     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.