Abstract:
An apparatus and method for suppressing interference between a first signal transmitted from an antenna of a first communication system and a second signal received by a second communication system in proximity to the first communication system, including: a reflecting assembly equipped to the transmit antenna of the first communication system and a position adjusting assembly for varying the slope of the reflecting assembly, moving the reflecting assembly right and left, and changing the height of the reflecting assembly. The reflecting assembly includes a plurality of lattices, with a gap between lattices having a width of the wavelength of the first signal divided by a natural number, and further includes two reflecting panes made from aluminum that are symmetric about the adjusting assembly and each have a width equal to the length of the transmit antenna.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for suppressing interference in wireless telecommunications systems, and in particular to an apparatus and method for suppressing frequency interference occurring between a transmitting device and a receiving device in a mobile telecommunication system. 
     2. Description of the Related Art 
     A cellular mobile telecommunication system allows a subscriber to communicate with other subscribers. The entire service area is divided into a plurality of cells having a corresponding base station. The base stations are centralized by a mobile switching center. 
     The cellular mobile telecommunication system is divided into an analog cellular system and a digital cellular system. The AMPS (Advanced Mobile Phone System) functions as the analog cellular system and the CDMA (Code Division Multiple Access) or the FDMA (Frequency Division Multiple Access) system function as the digital cellular system. 
     Due to the rapid and exponentional growth of mobile telecommunications, a plurality of users use limited frequency resources, particularly in cities. Hence, two or more systems using different communication methods may be located adjacent to each other. Therefore, the frequency separation between the systems becomes narrow and frequency interference inevitably occurs between the systems. 
     Consequently, the transmit frequency and receive frequency of two signals adjacent to each other and corresponding to two different systems are not sufficiently apart from each other, thereby causing interference which can significantly affect voice quality. Generally, the output signal and interference signals of a system using one particular communication method or protocol causes degradation in the receiving capability of the other system using a different communication method. The interference condition is typically dealt with by limiting frequency allocation or by adjusting a radiation pattern of the transmitting antenna. Another conventional method is to incorporate a transmit band pass filter (TBPF) in the transmitting system to pass only a transmit frequency band and to incorporate a receive band pass filter (RBPF) in the receiving system to pass only a receive frequency band. 
     However, conventional methods do not completely suppress frequency interference when the transmit frequency of a system is close proximity with the receive frequency of another system, because the TBPF and RBPF can not completely isolate the out-of-band signals. 
     The band pass filters, which are used in the mobile telecommunication system, include a band pass filter to pass the in-band frequency and a notch filter to maximally reduce the out-of-band frequency interference. However, the filter has a larger insertion loss than the band pass filter, and therefore may adversely affect system performance. Additionally, the noise attenuation characteristics in the band where the out-of-band frequency is apart within 1 Mega-Hertz (MHz) cannot obtain effects better than the general band pass filter. Therefore, in circumstances where the transmit frequency of a system is in close proximity with the receive frequency of another system, it has been generally required to do something more than to add a notch filter for solving the problem of frequency interference. 
     U.S. Pat. No. 4,535,476 discloses an offset geometry, interference canceling receiver which performs interference cancellation by the dither signal frequency and a round trip signal delay. The apparatus solves the problem of frequency interference by coupling an antenna to cancellation circuits via several duplexer and amplifier circuit combinations. However, the apparatus cannot suppress frequency interference occurring between different systems in proximity to each other. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus and method for suppressing frequency occurring between different communication systems. An apparatus and method for suppressing frequency occurring between different communication systems are provided. The apparatus and method suppress frequency interference by providing a reflecting assembly in proximity to a transmitting antenna. 
     In the case where frequency of a first signal causes interference with a frequency of a second signal, where the frequency of the first signal is transmitted from a transmit antenna of a first communication system and the frequency of the second signal is received by a receive antenna of a second communication system in proximity to the first communication system, the apparatus of the present invention includes: a reflecting assembly for reducing the incoming interference signal from the transmit antenna to the receive antenna, wherein the reflecting assembly is equipped to the transmit antenna of the first communication system; and an adjusting assembly operatively associated with the reflecting assembly to adjust the position of the reflecting assembly. The position is adjusted by varying the slope of the reflecting assembly, by moving the reflecting assembly right and left, and by changing the height of the reflecting assembly. 
     The reflecting assembly includes a plurality of lattices, where a gap is defined between each of the plurality of lattices having a width of λ/N, where λ is the wavelength of the first signal and N is a natural number. The reflecting assembly includes two reflecting panes made from aluminum and symmetric about the adjusting assembly. The width of each of the reflecting panes is equal to the length of the transmit antenna. 
     The method of the present invention suppresses frequency interference where a frequency of a first signal causes interference with a frequency of a second signal, the first signal being transmitted from a transmit antenna of a first communication system, the second signal being received by a receive antenna of a second communication system in proximity to the first communication system. The method comprises the steps of: providing a reflecting assembly for reducing the incoming interference signal from the transmit antenna to the receive antenna, the reflecting assembly being equipped to the transmit antenna of said first communication system; and adjusting the position of the reflecting assembly to suppress the frequency interference. 
     The present invention suppresses frequency interference when the transmit and receive antennas of a telecommunications system have a narrow frequency separation and are located in proximity to each other. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective top view of a reflector assembly according to the present invention; 
     FIG. 2 is a side view in phantom of the reflecting assembly of FIG. 1 showing movement thereof; 
     FIG. 3 is a perspective side view of the reflecting assembly of FIG. 1; 
     FIG. 4 is a diagram illustrating the reflecting assembly according to the present invention coupled to an antenna; 
     FIG. 5 is a block diagram illustrating the reflecting assembly of FIG. 1 coupled to a transmit antenna; 
     FIG. 6 is a block diagram illustrating a first preferred construction arrangement of the transmit antenna and a receive antenna; 
     FIG. 7 is a table illustrating interference cancellation results of the first preferred construction arrangement of FIG. 6; 
     FIG. 8 is a block diagram illustrating a second preferred construction arrangement of the transmit antenna and the receive antenna; 
     FIG. 9 is a table illustrating interference cancellation results of the second preferred construction arrangement of FIG. 8; 
     FIG. 10 illustrates a third preferred construction arrangement of the transmit antenna and the receive antenna; 
     FIG. 11 is a table illustrating interference cancellation results of the third preferred construction arrangement of FIG. 10; 
     FIG. 12 illustrates a fourth preferred construction arrangement of the transmit antenna and the receive antenna; and 
     FIG. 13 is a table illustrating interference cancellation results of the fourth preferred construction arrangement of FIG.  12 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well known constructions or functions are not described in detail so as not to obscure the present invention. 
     With reference to FIG. 1, there is shown a perspective top view of a reflecting assembly designated generally by reference numeral  5  according to the present invention. The reflecting assembly  5  includes a first reflecting pane  10  having a plurality of lattices  11  and a second first reflecting pane  15  having a plurality of lattices  11 ; and an adjusting mechanism  20  coupled to each reflecting pane  10 ,  15  for adjusting the slope and angle of the reflecting panes  10 ,  15 . 
     FIG. 2 is a side view of the reflecting assembly  5  along the longitudinal axis showing the first reflecting plane  10 , the second reflecting plane  15 , and the adjusting mechanism  20 . The adjusting mechanism  20  is fixed to a pole  30  coupled to a transmit antenna  200  (see FIG.  4 ). The slope, height, position and angles of the first and second reflecting panes  10 ,  15  are adjusted by the adjusting mechanism  20 . FIG. 3 is a perspective side view along the horizontal axis of the reflecting assembly  5  showing the adjusting mechanism  20  fixed to the pole  30  of the transmit antenna  200  and the first and second reflecting planes  10 ,  15  fixed to the adjusting mechanism  20 . 
     The size of the reflecting assembly  5  is determined according to the size of the transmit antenna  200  intended to be connected thereto. Preferably, the length of the reflecting assembly  5  along the longitudinal axis is equal to the length of the transmit antenna  200  and the width of the reflecting assembly  5  along the horizontal axis is maximized accordingly to prevent distortion of the beam pattern of a signal transmitted by the transmit antenna  200 . In addition, the reflecting assembly  5  is constructed from aluminum to be durable to prevent damage from rain, sleet, snow, weight, etc. 
     With reference to FIG. 4, there is shown the reflecting assembly  5  according to the present invnetion coupled to the antenna  200 . As illustrated in FIG. 4, if the signal beam is radiated from the front of transmit antenna  200 , the reflecting assembly  5  is positioned to the side or rear of transmit antenna  200 . Further, according to the position of receive antenna  400  (FIG. 5) interfered with, the slope and angle of the first reflecting pane  10  and the second reflecting pane  15  are adjusted. As shown by FIG. 4, the first reflecting pane  10  and the second reflecting pane  15  are adjusted to positions, A, B or C by adjusting the angle of the panes  10 ,  15  with respect to the horizontal axis. The first reflecting pane  10  and the second reflecting pane  15  are adjacently positioned to the side or rear of transmit antenna  200  to cause a mutual interference when frequency separation of transmit antenna  200  and receive antenna  400  of two different systems is narrow. The reflecting panes  10 ,  15  can be moved into various configurations according to the established configuration of transmit antenna  200  and receive antenna  400  and the level of interference. By the present invention, one can find a point at which the maximum effectiveness is obtained in suppressing the interference by adjusting the position, angle, etc. of one or both of the reflecting panes  10 ,  15 . 
     For example, it is possible to find the optimum slope and angle which greatly minimizes the frequency interference by positioning one or both of the reflecting panes  10 ,  15  at an angle B as shown in FIG.  4 . The panes  10 ,  15  are then gradually moved to change the angle while measuring the level of interference at receive antenna  400  by using measuring means, such as a spectrum analyzer  500  (FIG.  5 ). The reflecting assembly  5  serves as a kind of shield to prevent the interference signal of the transmit antenna  200  from flowing in the receive antenna  400  and also isolates an inflow of a signal contributing to the interference. FIG. 5 illustrates a construction arrangement of transmit antenna  200  coupled to the reflecting assembly  5 ; the receive antenna  400  is also shown. As illustrated in FIG. 5, a signal generator  300  generates a signal to be transmitted by transmit antenna  200 . The signal is received by the transmit antenna  200  from the signal generator  300  via feeder line  350 . The reflecting panes  10 ,  15  are positioned against the transmit antenna  200  and receive antenna  400  is positioned adjacent to the transmit antenna  200 . The spectrum analyzer  500  measures the level of the frequency interference by receiving the signal from the receive antenna  400  via feeder line  550 . 
     Several additional preferred construction arrangements for the reflecting assembly according to the present invention will now be described with reference to FIGS. 6-13. FIG. 6 illustrates a first preferred construction arrangement where transmit antenna  200  is equally as high as receive antenna  400  and the distance of horizontal separation between the antennas  200 ,  400  is 2 meters. The length of each feeder line  350 ,  550  is 3 meters. The transmit frequency is 880 MHz and transmit level is 10 dBm. The transmit and receive antennas are 13 dBd—60° sector antennas having a beam width measuring 60° horizontally and 8° vertically. 
     When the reflecting assembly  5  is arranged with the construction of FIG. 6, the receive isolation level according to a variation in slope and angle of the reflecting panes  10 ,  15  is shown by the table of FIG.  7 . When the slope and angle of the reflecting panes  10 ,  15  are optimized, the signal isolation level via the reflecting assembly  5  becomes about 30.52 dB. Hence, it is possible to decrease the interference signal level by as much as 30.52 dB. 
     FIG. 8 illustrates a second preferred construction arrangement where transmit antenna  200  is higher than receive antenna  400  and the distance of horizontal separation is 2 meters. The distance of vertical separation is 1.7 meters. The length of the feeder line is 3 meters. Transmit frequency is 880 MHz and transmit level is 10 dBm. The transmit and receive antennas are 13 dBd—60° sector antennas having a beam width measuring 60° horizontally and 8° vertically. 
     When the reflecting assembly  5  is arranged with the construction of FIG. 8, the receive isolation level according to a variation in slope and angle of the reflecting panes  10 ,  15  is shown by the table of FIG.  9 . When the slope and angle of the reflecting panes  10 ,  15  are optimized, the signal isolation level via the reflecting assembly  5  becomes about 22.4 dB. Hence, it is possible to decrease the interference signal level by as much as 22.4 dB. 
     FIG. 10 illustrates a third preferred construction arrangement where transmit antenna  200  is equally as high as receive antenna  400  and the distance of horizontal separation is 2 meters. The distance between front and rear is 2 meters. That is, the transmit antenna  200  is positioned in front of the receive antenna  400  by 2 meters. The length of the feeder line is 3 meters. Transmit frequency is 880 MHz and transmit level is 10 dBm. The transmit and receive antennas are 13 dBd—60° sector antennas having a beam width measuring 60° horizontally and 8° vertically. 
     When the reflecting assembly  5  is arranged with the construction of FIG. 10, the receive isolation level according to a variation in slope and angle of the reflecting panes  10 ,  15  is shown by the table of FIG.  11 . When the slope and angle of the reflecting panes  10 ,  15  are optimized, the signal isolation level via the reflecting assembly  5  becomes about 25.68 dB. Hence, it is possible to decrease the interference signal level by as much as 25.68 dB. 
     FIG. 12 illustrates a fourth preferred construction arrangement where transmit antenna  200  is equally as high as receive antenna  400  and the distance of horizontal separation is 2 meters. The distance between front and rear is 4 meters. That is, the transmit antenna  200  is positioned in front of the receive antenna  400  by 4 meters. The length of the feeder line is 3 meters. Transmit frequency is 880 MHz and transmit level is 10 dBm. The transmit and receive antennas are 13 dBd—60° sector antennas having a beam width measuring 60° horizontally and 8° vertically. 
     When the reflecting assembly  5  is arranged with the construction of FIG. 12, the receive isolation level according to a variation in slope and angle of the reflecting panes  10 ,  15  is shown by the table of FIG.  13 . When the slope and angle of the reflecting pages  10 ,  15  are optimized, the signal isolation level via the reflecting assembly  5  becomes about 37.57 dB. Hence, it is possible to decrease the interference signal level by as much as 37.57 dB. 
     As described above in conjunction with the drawings, when the transmit and receive antennas of a telecommunication system have a narrow frequency separation and are positioned adjacent to each other, it is possible to suppress the level of frequency interference by using a reflecting assembly according to the present invention. The reflecting assembly  5  of the present invention is contemplated for use in telecommunication systems operating under various communication protocols, such as CDMA, FDMA and AMPS. 
     While the invention is susceptible to various modification and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and herein described in detail. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modification, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.