Patent Publication Number: US-2010124187-A1

Title: Communication system and method of communicating signals

Description:
TECHNICAL FIELD 
     The present invention generally relates to a communication system and method of communicating signals, and more particularly, a communication system and method of communicating signals having different content on the same frequency. 
     BACKGROUND OF THE INVENTION 
     Generally, vehicles can be equipped with satellite radio receivers as an alternative to, or in combination with, common traditional terrestrial radio receivers. Additionally, satellite radio receivers can be used in places other than vehicles, such as handheld devices. Generally, satellite radio systems are designed, such that the receiver receives a satellite radio frequency (RF) signal from a satellite and a terrestrial RF signal from a terrestrial repeater or a transponder, which typically provides system redundancy. 
     The current systems in operation in the U.S. generally use double redundant information to enable high signal availability to receivers. These systems typically use time and spatial redundancy for the satellite signals, such that the signal is transmitted from two sources. Typically, in urban areas, terrestrial repeaters can provide a third signal source. Generally, such systems use different frequencies for the satellite signal and the terrestrial repeater signal. This architecture generally reduces the bandwidth efficiency of the system by one-third (⅓), while increasing overall availability. 
     Due to current European regulations, the European satellite radio system currently has twenty-three (23) contiguous frequencies across a forty megahertz (40 MHz) frequency band. Generally, there are seven (7) frequencies that are designated for hybrid systems only, which include the transmission of the satellite RF signal and the terrestrial RF signal. Typically, the current European satellite radio system is constrained to frequency bandwidths of 1.712 MHz. 
     With multiple satellites, it can be a problem to receive signals from one satellite and then receive signals from another satellite at the same frequency due to the differing locations of the satellites with respect to the receiver. One exemplary system generally includes a receiver having an antenna element that receives signals at the same frequency, wherein the antenna element has a very high gain (e.g., beam steered). By including such a high gain antenna element, the signals can be separated, along with polarization. Typically, such an exemplary system transmits satellite television signals that are received by the antenna element. 
     Generally, a satellite that communicates a signal to a receiver from a service provider transmits the signal at a particular frequency, and a second satellite communicates another signal to another receiver from another service provider, wherein the signal is transmitted from the second satellite at another particular frequency different that the frequency used by the first satellite. Thus, two frequencies of the frequency spectrum are utilized to transmit different content. Further, if additional signals are to be transmitted with different content at different frequencies, more frequencies of the limited frequency spectrum are occupied, and cannot be utilized for other uses. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a communication system includes a first satellite orbiting in a first orbital path that communicates a first signal having a first content at a transmitting frequency while at a first elevation angle, a second satellite orbiting in a second orbital path that communicates a second signal having a second content at the transmitting frequency while at a second elevation angle, wherein the first elevation angle is greater than the second elevation angle, and at least one terrestrial repeater that communicates a hierarchical modulated signal, wherein a hierarchical primary of the hierarchical modulated signal corresponds to the second signal communicated from the second satellite, and a hierarchical secondary of the hierarchical modulated signal corresponds to the first signal communicated from the first satellite, such that the first and second signals are communicated at the same transmitting frequency. 
     According to another aspect of the present invention, a communication system includes a highly elliptical orbiting (HEO) satellite orbiting in a highly elliptical orbiting path that communicates a first signal having a first content at a transmitting frequency while at a first elevation angle, a geo-stationary (GEO) satellite orbiting in a GEO orbital path that communicates a second signal having a second content at a transmitting frequency while at a second elevation angle, wherein the first elevation angle is greater than the second elevation angle, and at least one terrestrial repeater that communicates a hierarchical modulated signal, wherein a hierarchical primary of the hierarchical modulated signal corresponds to the second signal communicated from the GEO satellite, and a hierarchical secondary of the hierarchical modulated signal corresponds to the first signal communicated from the HEO satellite, such that the first and second signals are communicated at the same frequency. 
     According to yet another aspect of the present invention, a method of communicating signals having different content on the same transmitting frequency includes the steps of communicating a first signal having a first content at a transmitting frequency from a first satellite at a first elevation angle, communicating a second signal having a second content at the transmitting frequency from a second satellite at a second elevation angle, wherein the second elevation angle is lower than the first elevation angle, and communicating a hierarchical modulated signal from at least one terrestrial repeater, wherein a hierarchical primary of the hierarchical modulated signal corresponds to the second signal communicated from the second satellite, and a hierarchical secondary of the hierarchical modulated signal corresponds to the first signal communicated from the first satellite, such that the first and second signals are communicated at the same frequency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is an environmental view of a communications system that includes a communication device, in accordance with one embodiment of the present invention; 
         FIG. 2  is a diagram illustrating an exemplary orbital path of highly elliptical orbiting satellites, in accordance with one embodiment of the present invention; 
         FIG. 3  is a chart illustrating QPSK signals transmitted from satellites having different orbital paths, in accordance with one embodiment of the present invention; 
         FIG. 4  is a block diagram of a communication device, in accordance with one embodiment of the present invention; 
         FIG. 5  is a diagram illustrating the reception characteristics of signals having different polarizations and being received at different reception elevation angles with respect to at least one antenna element, in accordance with one embodiment of the present invention; and 
         FIG. 6  is a flow chart illustrating a method of communicating signals having different content on the same transmitting frequency, in accordance with one embodiment of the present invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     In regards to both  FIGS. 1 and 2 , a communication system is generally shown at reference identifier  10 . The communication system  10  includes a first satellite  12 A, a second satellite  12 B, and at least one terrestrial repeater  14  ( FIG. 1 ). The first satellite  12 A orbits in a first orbital path  16 A, as shown in  FIG. 2 , and communicates a first signal having a first content at a transmitting frequency while at a first elevation angle. The second satellite  12 B orbits in a second orbital path  16 B, as shown in  FIG. 2 , and communicates a second signal having a second content at the transmitting frequency while at a second elevation angle. Typically, the first elevation angle is greater than the second elevation angle. Also, the first content is different than the second content, such that the first signal communicated from the first service provider  17 A differs from a second signal communicated from a second service provider  17 B, according to one embodiment. 
     The terrestrial repeater  14  communicates a hierarchical modulated signal, wherein a hierarchical primary of the hierarchical modulated signal corresponds to the second signal communicated from the second satellite  12 B, and a hierarchical secondary of the hierarchical modulated signal corresponds to the first signal communicated from the first satellite  12 A, such that the first and second signals are communicated at the same transmitting frequency, as described in greater detail herein. 
     The communication system  10  typically includes a receiver, generally indicated at  18 , in communication with one of the first and second satellites  12 A,  12 B, wherein the receiver  18  is configured to reject the signal communicated from the other of the first and second satellites  12 A,  12 B. Thus, the first service provider  17 A can provide content utilizing the first satellite  12 A, while the second service provider  17 B can provide different content utilizing a second satellite  12 B, wherein the receiver  18  is configured to receive content from one of the service providers  17 A,  17 B. Therefore, multiple service providers ( 17 A, 17 B, . . .  17   N ) can provide different content utilizing the same transmitting frequency, and thus, expanding the amount of content that can be communicated in the frequency spectrum. According to one embodiment, the receiver  18  can be used with a vehicle generally indicated at  19 . 
     According to one embodiment, the receiver  18  rejects the signal communicated from the other of the first and second satellites  12 A,  12 B as a function of the first and second elevation angles. By way of explanation and not limitation, the first satellite  12 A can be a highly elliptical orbiting (HEO) satellite having an elliptical orbiting path (e.g., the first orbital path  16 A), and the second satellite  12 B can be a geo-stationary (GEO) satellite having an orbital path substantially along the equator (e.g., the second orbital path  16 B) ( FIG. 2 ). In such an embodiment, there can be three first satellites  12 A orbiting in the HEO orbital path  16 A, wherein the first satellite  12 A that is in the high position above the reception area is transmitting the signal, while the other satellites in the HEO orbital path  16 A are turned off, so that the first satellite  12 A transmitting the first signal has a higher elevation angle than the other satellites  12 A in the HEO orbital path  16 A and the transmitting second satellite  12 B in the GEO orbital path  16 B. 
     Due to the GEO orbital path  16 B having a lower elevation angle for communicating the signal, typically more terrestrial repeaters  14  are utilized to retransmit the signal than the number of terrestrial repeaters  14  that are utilized for retransmitting the signal retransmitted from the first satellite  12 A. Typically, the signals transmitted from the second satellite  12 B in the GEO orbital path  16 B have more obstructions in the signal path, such as mountainous terrain and buildings in urban areas, which do not have such an effect on the signal transmitted from the first satellite  12 A in the HEO orbital path  16 A, which is at the higher elevation angle. 
     Since more terrestrial repeaters  14  are typically utilized to retransmit the signal from the second satellite  12 B than the first satellite  12 A, due to the lower elevation angle of the second satellite  12 B, the hierarchical primary of the hierarchical modulated signal corresponds to the second signal communicated from the second satellite  12 B, and the hierarchical secondary of the hierarchical modulated signal corresponds to the first signal communicated from the first satellite  12 A. According to one embodiment, the hierarchical modulated signal communicated from the terrestrial repeater  14  appears as a sixteen (16) quadrature amplitude modulation (QAM) orthogonal frequency-division multiplexing (OFDM) constellation ( FIG. 3 ). However, it should be appreciated by those skilled in the art that other suitable types of hierarchical modulated signals can be utilized for retransmission of signals from the first and second satellites  12 A,  12 B and the terrestrial repeater  14 . 
     In regards to both  FIGS. 1 and 4 , the receiver  18  can include at least one antenna element A 1  and circuitry generally indicated at reference identifier  24  ( FIG. 4 ) that is in communication with the antenna element A 1 , according to one embodiment. Exemplary communication systems having exemplary antenna elements are disclosed in U.S. patent application Ser. No. ______ (Attorney Docket No. DP-317186), entitled “COMMUNICATIONS SYSTEM AND METHOD OF COMMUNICATING DATA,” and U.S. patent application Ser. No. ______ (Attorney Docket No. DP-317237), entitled “RECEIVER DEVICE AND METHOD OF RECEIVING A PLURALITY OF SIGNALS,” the entire disclosures being hereby incorporated herein by reference. 
     For purposes of explanation and not limitation, in operation, the antenna element A 1  receives at least the first signal having a first polarization, while rejecting the second signal received from the second elevation angle having a second polarization, and the circuitry  24  is configured to process and emit an output  26  based upon the received first signal. In such an embodiment, the antenna element A 1 , the circuitry  24 , or a combination thereof, rejects one of the first and second signals as a function of the elevation angle and the polarization of the signal. Exemplary polarizations that may be utilized are right hand circular polarization (RHCP), left hand circular polarization (LHCP), linear polarization, the like, or a combination thereof, according to one embodiment. It should be appreciated by those skilled in the art that other suitable polarizations may be utilized when transmitting one or more signals. 
     Generally, an elevation angle can be the angle that a signal is received from the satellite (e.g., the first and second satellites  12 A,  12 B) with respect to the antenna element A 1 , according to one embodiment. By way of explanation and not limitation, the output  22  can be a video output, an audio output, the like, or a combination thereof. It should be appreciated by those skilled in the art that the at least one antenna element can include any number of suitable antenna elements (i.e., A 1 ,A 2 , . . . A N ,). 
     The receiver  18  can further include a polarization selector  28  in communication with the antenna element A 1 , wherein the polarization selector  28  alters the polarization of the antenna element A 1 , such that the antenna element A 1  is adapted to receive either the first signal having the first polarization received from the first elevation angle or the second signal having the second polarization received from the second elevation angle. Thus, a single receiver  18  can be configured to receive different content provided from different source providers  17 A,  17 B. 
     Additionally, the receiver  18  can include at least one down converter  29  and at least one analog-to-digital (A/D) converter  30 . Typically, the down converter  29  down converts or reduces a frequency of a radio frequency (RF) signal that is received by the antenna element A 1  to a lower frequency for transmission through the receiver  18 , and the A/D converter  30  converts the analog signal received by the antenna element A 1  to a digital signal. The receiver  18  can further include a demodulator  32  in communication with A/D converter  30  that is configured to demodulate the signal received by the antenna element A 1 . Further, a decoder  34  can be in communication with the demodulator  32  and be configured to decode an output received from the demodulator  32 , and a source decoder  36  can receive a decoded output of the decoder  34 , such that the output  26  is emitted based upon the signal received by the antenna element A 1 . 
     With respect to  FIG. 5 , this figure illustrates reception characteristics of signals having different polarizations and having different reception angles with respect to the at least one antenna element (A 1 ,A 2 , . . . A N ). 
     In regards to  FIGS. 1 ,  2 , and  6 , a method of communicating signals having different content on the same transmitting frequency is generally shown in  FIG. 6  at reference identifier  100 . The method  100  starts at step  102 , and proceeds to step  104 , wherein a first signal is communicated at a transmitting frequency. At step  106 , a second signal is communicated at the transmitting frequency. Typically, the first and second signals have different content and are transmitted at different elevation angles, but are transmitted at the same transmitting frequency. 
     The method  100  then proceeds to step  108 , wherein a hierarchical modulated signal is communicated from the terrestrial repeater  14  at the transmitting frequency. At step  110 , one of the first and second signals is received by the receiver  18 . At step  112 , the other of the first and second signals is rejected by the receiver  18 . Typically, the other of the first and second signals is rejected based upon the elevation angle of the transmitted signal, the polarization of the transmitted signal, or a combination thereof. The method  100  then ends at step  114 . 
     Advantageously, the communication system  10  and method  100  allow for different service providers to provide different content on first and second signals, which are transmitted at the same frequency, and thus, expanding the use of the frequency spectrum. Since the first and second signals are communicated from first and second satellites  12 A,  12 B, respectively, the signals can be rejected by the receiver  18  based upon the elevation angle. Thus, the signal to be rejected causes minimal interference to the signal that is to be received to produce the output  26 . It should be appreciated by those skilled in the art that initial or alternative advantages may be present from the communication system  10  and method  100 . It should further be appreciated by those skilled in the art that the above components can be combined in additional or alternative ways. 
     The above description is considered that of preferred embodiments only. Modifications of the invention will occur to those skilled in the art and to those who make or use the invention. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and not intended to limit the scope of the invention, which is defined by the following claims, as interpreted according to the principles of patent law, including the doctrine of equivalents.