Patent Publication Number: US-2012026032-A1

Title: Cross-polarization component cancellation

Description:
BACKGROUND 
     Telecommunications providers transmit signals with different polarity components (e.g., horizontal and vertical components) as a way to differentiate between signals with the same or similar frequencies. This gives the telecommunications provider more options for transmitting information at a particular frequency. The intended polarization component is known as the co-polarization component and the unintended polarization component is known as the cross-polarization component. Ideally, a transmitting station transmits only the co-polarization component of the signal to a satellite because the cross-polarization component is received as noise. Furthermore, the satellite ideally only transmits the co-polarization component of the signal to a monitoring station. In reality, however, both the co-polarization component and the cross-polarization component are transmitted from the transmitting station to the satellite and from the satellite to the monitoring station. Additionally, the monitoring station is unable to completely isolate the co-polarization and cross-polarization components from the signals received from the satellite, causing further noise. Accordingly, a system is needed that reduces the noise caused by the monitoring station. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary system having a remote station, a satellite, and a monitoring station that is configured to reduce the noise created by a cross-polarization component of a signal. 
         FIG. 2  illustrates an exemplary diagram of the components of the remote station, the satellite, and the monitoring station. 
         FIG. 3  illustrates an exemplary circuit diagram of the monitoring station that is configured to reduce noise created by the cross-polarization component of the signal. 
         FIG. 4  illustrates an exemplary process flow diagram implemented by the system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     A system includes a remote station configured to transmit a first signal having a co-polarization component and a first cross-polarization component to a satellite. The co-polarization component is the component of the signal transmitted at the intended polarity (e.g., a horizontal or vertical polarity). The cross-polarization component is the component of the signal transmitted at the unintended polarity and is received at the satellite as noise. Various factors contribute to cross-polarization. For instance, the alignment of the remote station relative to the satellite can cause cross-polarization. The satellite receives the first signal and transmits a repeated signal that substantially includes the first signal to a monitoring station. The monitoring station receives and isolates the repeated signal received from the satellite. That is, the monitoring station separates the co-polarization component and the cross-polarization component from the repeated signal. Doing so, however, generates a second signal having the co-polarization component, the first cross-polarization component, and a second cross-polarization component (e.g., noise from the monitoring station). The monitoring station is further configured to substantially reduce the second cross-polarization component of the second signal. For example, the monitoring station includes a tuning circuit that substantially reduces the cross-polarization component of the signal and a feedback circuit that iteratively adjusts the tuning circuit until the second cross-polarization component of the signal is substantially reduced. Accordingly, a process implemented by the system disclosed herein includes receiving a signal having a co-polarization component and a plurality of cross-polarization components, manipulating the co-polarization component, and introducing the manipulated co-polarization component to the plurality of cross-polarization components to substantially reduce at least one of the cross-polarization components. 
       FIG. 1  illustrates an exemplary system  100  that is configured to substantially reduce noise generated by a cross-polarization component of a signal. The system  100  may take many different forms and include multiple and/or alternate components and facilities. While an exemplary system  100  is shown in  FIG. 1 , the exemplary components illustrated in the figures are not intended to be limiting. Indeed, additional or alternative components and/or implementations may be used. 
     As illustrated in  FIG. 1 , the system  100  includes a remote station  105 , a satellite  110 , and a monitoring station  115 . The remote station  105  acts as a signal source configured to transmit a test signal  120  to the satellite  110 , and the satellite  110  also acts as a signal source configured to transmit a repeated signal  125  to the monitoring station  115 . Both the test and repeated signals  120 ,  125  may have components of different polarities. For instance, both the test and repeated signals  120 ,  125  may have horizontal and vertical components. The remote station  105  and satellite  110 , therefore, may be configured to transmit signals with either or both polarity components. The satellite  110  and monitoring station  115  may be configured to receive signals with either or both polarity components. 
     While the remote station  105  may be configured to transmit the test signal  120  with an intended polarity component (e.g., a co-polarization component), the remote station  105  may additionally transmit the test signal  120  with an unintended polarity component (e.g., a first cross-polarization component). The first cross-polarization component is received as noise by the satellite  110 . The satellite  110  transmits the repeated signal  125  with the co-polarization component and the first cross-polarization component from the test signal  120  to the monitoring station  115 . Therefore, the monitoring station  115  receives the repeated signal  125 , which includes the co-polarization component and the first cross-polarization component (e.g., noise from the remote station  105 . 
     The monitoring station  115 , in one exemplary approach, may be used to monitor the signals transmitted by the remote station  105  to, for instance, determine whether the remote station  105  is operating properly. The monitoring station  115 , therefore, is configured to differentiate noise transmitted by the remote station  105  from other types of noise (e.g., noise transmitted by the satellite  110  or caused by the monitoring station  115  itself). Unless accounted for, noise caused by the monitoring station  115  is unfairly attributed to the remote station  105 . The monitoring station  115  is configured to polarize the repeated signal  125 . Doing so, however, generates a signal with the co-polarization component, the first cross-polarization component, and a second cross-polarization component. The second cross-polarization component represents noise generated by the monitoring station  115 . The monitoring station  115  is configured to identify the second cross-polarization component of the repeated signal  125  as noise and substantially reduce the second cross-polarization component so that the monitoring station  115  can properly monitor the quality of the test signal  120  transmitted by the remote station  105 . 
       FIG. 2  illustrates an exemplary diagram of the components of the remote station  105 , the satellite  110 , and the monitoring station  115 . The remote station  105  includes a signal generator  130  and a transmitter  135 . The signal generator  130  may include any device configured to generate the test signal  120 . The signal generator  130  may be configured to generate the test signal  120  at a particular frequency. For instance, the signal generator  130  may generate the test signal  120  at a frequency of 11.7 to 12.2 GHz or 140.-14.5 GHz for the Ku band. Of course, the signal generator  130  may generate the test signal  120  at another frequency or range of frequencies. The signal generator  130  may be configured to generate the test signal  120 . The rotation of the antenna feed system of the remote station  105  may set the desired polarity. However, the feed system may have a limited ability to polarize the signal to the intended polarity (e.g., the co-polarization component) resulting in some isolation component (e.g., the cross-polarization component). The azimuth and elevation alignment of the antenna of the remote station  105  to the satellite  110  may also contribute to this isolation. Accordingly, the remote station  105  may transmit the test signal  120  to have the co-polarization component, the first cross-polarization component, or both. In one particular approach, the remote station  105  is configured to generate the test signal  120  with more power directed to the co-polarization component than directed to the first cross-polarization component. The transmitter  135  may include any device configured to transmit the test signal  120  to the satellite  110 . The transmitter  135  may, for instance, include an antenna that is configured to propagate an electromagnetic signal to the satellite  110 . 
     The satellite  110  may include any device configured to receive the test signal  120  transmitted by the remote station  105 . The satellite  110  may orbit the Earth and receive signals from the remote station  105  when the satellite  110  and remote station  105  are visually aligned. The satellite  110  may include a plurality of transponders that are configured to receive a polarity component of the test signal  120  and transmit the received polarity component to the monitoring station  115  as the repeated signal  125 . In one exemplary approach, each transponder may be dedicated to a specific polarity component of received signals. For instance, a first transponder  140  may be dedicated to a vertical component of received signals while a second transponder  145  may be dedicated to a horizontal component of received signals. Therefore, the first transponder  140  may receive the co-polarization component of the test signal  120  while the second transponder  145  may receive the first cross-polarization component of the test signal  120 . The transponders  140 ,  145  act as repeaters to transmit the co-polarization component and first cross-polarization component of the test signal  120  to the monitoring station  115  as part of the repeated signal  125 . Due to imperfections with alignment between the satellite  110  and the monitoring station  115  such as azimuth, elevation, and rotation, the satellite  110  may further transmit its own cross-polarization component to the monitoring station  115  as part of the repeated signal  125 . However, this cross-polarization component may be relatively small and not add a significant amount of noise to the cross-polarization component of the test signal  120 . 
     The monitoring station  115  may include any device configured to monitor the signals transmitted by the remote station  105 . For instance, the monitoring station  115  may include an antenna  150  configured to receive the repeated signal  125  generated by the satellite  110 . The monitoring station  115  may further include a polarizer (not shown) that is configured to isolate the co-polarization component and the first cross-polarization component of the repeated signal  125 . However, the antenna may generate noise when isolating the repeated signal  125 . This noise is represented as the second cross-polarization component. Therefore, the output of the antenna includes the co-polarization component and the first and second cross-polarization components. The monitoring station includes a tuning circuit  155  configured to substantially remove the noise (e.g., the second cross-polarization component) created by the monitoring station  115 , and a feedback circuit  160  configured to control the tuning circuit  155 . 
       FIG. 3  illustrates the exemplary components of the antenna  150 , the tuning circuit  155 , and the feedback circuit  160 . The antenna  150  receives the repeated signal  125  from the satellite  110  and outputs a signal with the co-polarization component and the first and second cross-polarization components. The tuning circuit  155  generates a cancelling signal, which is coupled to the cross-polarization components of the repeated signal  125  resulting in a filtered signal. Thus, the filtered signal includes the first cross-polarization component and a substantially reduced second cross-polarization component. The feedback circuit  160  monitors the filtered signal and controls the tuning circuit  155  to substantially reduce the second cross-polarization component from the filtered signal. 
     The antenna  150  includes a first portion  165  configured to receive the co-polarization component of the repeated signal  125  from the polarizer (not shown). The co-polarization component of the repeated signal  125  is representative of the co-polarization component of the test signal  120 . The antenna  150  further includes a second portion  170  configured to receive the first and second cross-polarization components of the repeated signal  125  from the polarizer (not shown), which includes the first cross-polarization component of the test signal  120  received at the second transponder  145  from the remote station  105  and transmitted to the monitoring station  115  (e.g., noise from the remote station  105 ) and the second cross-polarization component caused by the polarizer in the antenna  150  (e.g., noise from the monitoring station  115 ). 
     The tuning circuit  155  is configured to detect the noise from the monitoring station  115  and substantially reduce the noise. In one exemplary approach, the noise from the monitoring station  115  has the same frequency as the co-polarization component of the repeated signal  125  since the co-polarization component and the noise (e.g., the second cross-polarization component) were transmitted from the same transponder (e.g., the first transponder  140 ) of the satellite  110 . Because the monitoring station  115  generates the second cross-polarization component from the co-polarization component, both the co-polarization component and the cross-polarization component have the same frequency because both were transmitted by the first transponder  140 . 
     Accordingly, the tuning circuit  155  may use the frequency of the co-polarization component to cancel the second cross-polarization component. For instance, the tuning circuit  155  may be configured to cancel the second cross-polarization component by coupling the cancelling signal to the second portion  170  of the antenna  150  since, in one exemplary approach, the cancelling signal has the same frequency and magnitude, but opposite phase, as the second cross-polarization component. Thus, coupling the cancelling signal to the second portion  170  of the antenna  150  substantially cancels the second cross-polarization component, leaving only the first cross-polarization component. 
     The tuning circuit  155  may include a variable attenuator  175  and a phase shifter  180 . The variable attenuator  175  may be in communication with the first portion  165  of the antenna  150  and may include any device configured to attenuate a signal. The output of the variable attenuator  175  may be a signal with the same frequency but different magnitude as the co-polarization component of the repeated signal  125 . The amount of the attenuation may be variable. As discussed in greater detail below, the feedback circuit  160  may control the amount of the attenuation. 
     The phase shifter  180  may also be in communication with the first portion  165  of the antenna  150  and include any device configured to shift a phase of the co-polarization component of the repeated signal  125 . The phase of an oscillating signal is the fraction of a complete cycle corresponding to an offset in the displacement from a specified reference point. Phase may be represented as an angle or radians. The phase shifter  180  can be used to substantially cancel a signal or a portion of a signal. A complete cycle of an oscillating signal is 360 degrees or  27   c  radians. Therefore, two signals with the same magnitude and frequency will cancel each other if they are 180 degrees or π radians out of phase. The phase shifter  180  may be configured to shift the signal received from the variable attenuator  175  by 180 degrees to generate the cancelling signal, which has the same frequency and magnitude, but opposite phase, of the second cross-polarization component. Adding the cancelling signal to the second portion  170  of the antenna  150  results in the filtered signal that includes the first cross-polarization component and a substantially reduced second cross-polarization component. 
     The feedback circuit  160  includes a closed-loop control system that may be configured to control the tuning circuit  155 . In particular, the feedback circuit  160  may be configured to measure the filtered signal on the second portion  170  of the antenna  150  and adjust the elements of the tuning circuit  155 , such as the variable attenuator  175 , phase shifter  180 , or both until the second cross-polarization component is substantially reduced. The feedback circuit  160  may include a down converter  190 , an amplifier  205 , a power detector  195 , and a controller  200 . 
     The down converter  190  may be in communication with the second portion  170  of the antenna  150  to measure the filtered signal. The down converter  190  may be used to convert the frequency of the filtered signal, for instance, to make processing easier. The filtered signal may have a frequency of between approximately 11.7 and 12.2 GHz, and the down converter  190  may be configured to reduce the frequency to approximately 1 GHz or below. The down converter  190  may include an amplifier  205 , a mixer  210  and oscillator  215 , and a filter  220 . 
     The amplifier  205  may be configured to change the magnitude of the filtered signal. For instance, the magnitude of the filtered signal may be relatively low, so the amplifier  205  may increase the magnitude to make processing the filtered signal easier. The amplifier  205  may include any device, such as an operational amplifier, configured to amplify the filtered signal. 
     The mixer  210  and oscillator  215  may be configured to change the frequency of the filtered signal. Again, the filtered signal may have a frequency between approximately 11.7 and 12.2 GHz. It may be difficult to process signals in this frequency range. Accordingly, the mixer  210  and oscillator  215  may be configured to reduce the frequency to approximately 1 GHz or below. 
     The filter  220  may be configured to isolate the first and second cross-polarization components from the filtered signal. As discussed above, the filtered signal includes the first cross-polarization component and the substantially reduced second cross-polarization component. The tuning circuit  155  is configured to remove noise caused by the monitoring station  115  based on the peak-to-peak power of the first and second cross-polarization components. The filter  220 , therefore, is configured to remove most signals other than the first and second cross-polarization components from the filtered signal. This is so the feedback circuit  160  can control the tuning circuit  155  based on the sum of the powers of the first and second cross-polarization component. 
     Another amplifier  225  may be configured to amplify the signal received from the down converter  190 . The signal from the down converter  190  may have a relatively low magnitude, so this amplifier  225  may be used to increase the magnitude to make processing easier. Like the amplifier  205  in the down converter  190 , this amplifier  225  may include any device, such as an operational amplifier, configured to amplify the signal received from the down converter  190 . 
     The power detector  195  is any device configured to receive the amplified signal from the down converter  190  and determine the power of the first and second cross-polarization components from that amplified signal. The power detector  195  outputs a voltage signal that is proportional to the measured power. The power of the filtered signal will change over time if the tuning circuit  155  is not properly tuned. Therefore, any oscillations in the voltage signal indicate the additional tuning may be necessary to substantially cancel the second cross-polarization component. Of course, the feedback circuit  160  may be configured to allow a small variation in peak-to-peak power. Even though this small variation indicates that the second cross-polarization component is not completely eliminated, it may be made small enough to be insignificant. 
     The controller  200  is in communication with the power detector  195  and is configured to control the tuning circuit  155  based on the signal received from the power detector  195 . For instance, the controller  200  may receive the signal representing the peak-to-peak power from the power detector  195  and, depending on the value represented by the signal, adjust the variable attenuator  175  and phase shifter  180  accordingly. In one exemplary approach, a high peak-to-peak power indicates that the second cross-polarization component has not been substantially reduced and that further tuning is required. On the other hand, the controller  200  may interpret a DC voltage signal (e.g., a signal representing a peak-to-peak power of zero) as an indication that the second cross-polarization component has been completely or substantially cancelled. Of course, the controller  200  may interpret other signals with non-zero peak-to-peak voltage as an indication that the second cross-polarization component has been substantially cancelled. 
     The controller  200  may be configured to iteratively adjust the variable attenuator  175 , the phase shifter  180 , or both using, for instance, digital signal processing. In one exemplary implementation, the controller  200  may hold the settings of the phase shifter  180  constant and change the settings of the variable attenuator  175  until the peak-to-peak voltage signal output by the power detector  195  is minimized. The controller  200  may further hold the settings of the variable attenuator  175  constant and cycle through the various settings of the phase shifter  180  until the minimum peak-to-peak voltage is reached. The controller  200  may repeat this sequence until the second cross-polarization signal is substantially reduced. Of course, the controller  200  may begin by changing the settings of the phase shifter  180  instead of the variable attenuator  175 . 
     The monitoring station  115  may include additional components such as one or more directional couplers  230 , a disable switch  235 , and one or more spectrum analyzers  240 . For instance, a first coupler  230 A may be used to sample the co-polarization component from the first portion  165  of the antenna  150 . A second coupler  230 B may be used to couple the cancelling signal to the second portion  170  of the antenna  150 . A third coupler  230 C may be used to sample the filtered signal. 
     The switch  235  may be used to disable the tuning circuit  155 , for instance, upon command from the controller  200 . For instance, the controller  200  may determine that it is unable to decrease the second cross-polarization component or that its attempts to reduce the second cross-polarization component have actually increased the amount of noise. Therefore, the controller  200  may be configured to disable the tuning circuit  155  by opening the switch  235 . Moreover, the switch  235  may further represent a manual switch  235  that may be opened by a technician to disable the tuning circuit  155 . 
     The spectrum analyzers  240 A and  240 B may include any device configured to measure the frequency, magnitude, or any other characteristic of the repeated signal  125 . The spectrum analyzers  240 A and  240 B may be in communication with the first and second portions  165 ,  170  of the antenna  150  and receive the co-polarization component of the repeated signal  125  and the filtered signal representing the first cross-polarization component and the substantially reduced second cross-polarization component of the repeated signal  125 . 
     In general, computing system and/or devices, such as the controller  200 , the power detector  195 , the spectrum analyzers  240 A and  240 B, etc. may employ any of a number of well known computer operating systems, including, but by no means limited to, known versions and/or varieties of the Microsoft Windows® operating system, the Unix operating system (e.g., the Solaris® operating system distributed by Sun Microsystems of Menlo Park, Calif.), the AIX UNIX operating system distributed by International Business Machines of Armonk, N.Y., and the Linux operating system. Examples of computing devices include, without limitation, a computer workstation, a server, a desktop, notebook, laptop, or handheld computer, or some other known computing system and/or device. 
     Computing devices generally include computer-executable instructions, where the instructions may be executable by one or more computing devices such as those listed above. Computer-executable instructions may be compiled or interpreted from computer programs created using a variety of well known programming languages and/or technologies, including, without limitation, and either alone or in combination, Java™, C, C++, Visual Basic, Java Script, Perl, etc. In general, a processor (e.g., a microprocessor) receives instructions, e.g., from a memory, a computer-readable medium, etc., and executes these instructions, thereby performing one or more processes, including one or more of the processes described herein. Such instructions and other data may be stored and transmitted using a variety of known computer-readable media. 
     A computer-readable medium (also referred to as a processor-readable medium) includes any non-transitory (e.g., tangible) medium that participates in providing data (e.g., instructions) that may be read by a computer (e.g., by a processor of a computer). Such a medium may take many forms, including, but not limited to, non-volatile media and volatile media. Non-volatile media may include, for example, optical or magnetic disks and other persistent memory. Volatile media may include, for example, dynamic random access memory (DRAM), which typically constitutes a main memory. Such instructions may be transmitted by one or more transmission media, including coaxial cables, copper wire and fiber optics, including the wires that comprise a system bus coupled to a processor of a computer. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, an EPROM, a FLASH-EEPROM, any other memory chip or cartridge, or any other medium from which a computer can read. 
     In some examples, system elements may be implemented as computer-readable instructions (e.g., software) on one or more computing devices (e.g., servers, personal computers, etc.), stored on computer readable media associated therewith (e.g., disks, memories, etc.). A computer program product may comprise such instructions stored on computer readable media for carrying out the functions described herein. 
       FIG. 4  illustrates an exemplary process  400  that may be implemented by the system  100  illustrated in  FIGS. 1-3 . 
     Block  405  includes receiving a signal such as the repeated signal  125  having the co-polarization component and the first cross-polarization components from the satellite  110 . The repeated signal  125  may be transmitted by the first and second transponders  140 ,  145  of the satellite  110  and be received at the antenna  150  of the monitoring station  115 . The antenna  150  may isolate the co-polarization component and the first cross-polarization component of the repeated signal  125  using a polarizer. Doing so, however, may generate the second cross-polarization component as noise. The first portion  165  of the antenna  150  may receive the co-polarization component and the second portion  170  of the antenna  150  may receive the first and second cross-polarization components. 
     Decision block  410  may include determining whether one of the cross-polarity components has the same frequency as the co-polarization component. If not, no noise was generated by the polarizer of the monitoring station  115  and the process  400  repeats block  410  until one of the cross-polarity components has the same frequency as the co-polarization component. If so, the process  400  may continue with block  415 . 
     Block  415  may include manipulating the co-polarization component of the repeated signal  125  with a tuning circuit  155 . The tuning circuit  155  may include the phase shifter  180  to shift the phase of the co-polarization component and the variable attenuator  175  to attenuate the co-polarization component. The output of the tuning circuit  155  is the cancelling signal. The cancelling signal is a manipulated version of the co-polarization component. For instance, the cancelling signal has the same frequency, but opposite phase, as the co-polarization component. The cancelling signal also has the same frequency and magnitude as the second cross-polarization component, but opposite phase. 
     Block  420  includes introducing the manipulated co-polarization component to the plurality of cross-polarization components to substantially reduce at least one of the cross-polarization components. The manipulated co-polarization component is represented as the cancelling signal. Again, the cancelling signal has the same frequency and magnitude, but opposite phase, as the second cross-polarization component. Therefore, when added to the second portion  170  of the antenna  150 , the cancelling signal cancels the second cross-polarization component. 
     Decision block  425  includes determining whether the second cross-polarization component is substantially reduced. For instance, the feedback circuit  160  may determine whether the cancelling circuit has substantially reduced the second cross-polarization component. If not, the process  400  may go to block  415 . The controller  200  of the feedback circuit  160  may iteratively adjust the parameters of the phase shifter  180  and variable attenuator  175  until the second cross-polarization signal is substantially reduced. Once substantially reduced, the process  400  may end after block  425 . 
     CONCLUSION 
     With regard to the processes, systems, methods, heuristics, etc. described herein, it should be understood that, although the steps of such processes, etc. have been described as occurring according to a certain ordered sequence, such processes could be practiced with the described steps performed in an order other than the order described herein. It further should be understood that certain steps could be performed simultaneously, that other steps could be added, or that certain steps described herein could be omitted. In other words, the descriptions of processes herein are provided for the purpose of illustrating certain embodiments, and should in no way be construed so as to limit the claimed invention. 
     Accordingly, it is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments and applications other than the examples provided would be apparent upon reading the above description. The scope of the invention should be determined, not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. It is anticipated and intended that future developments will occur in the technologies discussed herein, and that the disclosed systems and methods will be incorporated into such future embodiments. In sum, it should be understood that the invention is capable of modification and variation. 
     All terms used in the claims are intended to be given their broadest reasonable constructions and their ordinary meanings as understood by those knowledgeable in the technologies described herein unless an explicit indication to the contrary in made herein. In particular, use of the singular articles such as “a,” “the,” “said,” etc. should be read to recite one or more of the indicated elements unless a claim recites an explicit limitation to the contrary.