Abstract:
A system for distributing separate multiple satellite communication services signals to receivers at a local earth site on a single cable line. A dual satellite antenna receives the signals from two separate satellites, each of which can correspond to a respective satellite communication service. The received satellite signals are processed into two separate frequency bands. A frequency converter using frequency division multiplexing converts at least one of the received frequency bands so as to position both of the frequency bands adjacent to each other. A summer receives the adjacent frequency bands and distributes them on a single cable line to receivers so that the receivers have access to the separate multiple satellite communication service signals on a single cable line. A demultiplexer coupled to the adjacent frequency bands from the summer enables the plurality of receivers at the output of the demultiplexer lines to obtain simultaneous access to both satellite communication services distributed over the single cable line to the receiver.

Description:
BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates in general to satellite receive earth stations and, more particularly, to a system for receiving satellite signals from separate and multiple satellites and distributing the signals received from the satellites on a single cable line. 
     (b) Description of Related Art 
     Satellite-based communication systems typically beam signals from a terrestrial antenna to a geostationary satellite. The satellite processes and “downlinks” the signals to terrestrial satellite receive antennas located within the satellite&#39;s coverage area or footprint. On-board transponders modulate signals to an assigned carrier frequency and polarity, then send the signals to an on-board antenna for transmission (downlinking) the satellite signals to earth for reception at individual receiver units. 
     At the individual receiver units at a local earth site, such as a household, a satellite receive antenna, typically comprising a parabolic dish antenna, reflects and concentrates the received satellite signals to a focal point. 
     Typically, such antennas include a low noise block (LNB) which amplifies, filters and shifts the incoming satellite signal to an intermediate frequency band for coupling to a set-top box or other integrated receiver and detector (IRD) associated with the receiver unit at the local earth site. 
     At present, there are several different satellite communication services available. For instance, one known direct-to-home digital satellite system now in operation uses an uplink signal modulated onto frequency bands between about 17.2 GHz and about 17.7 GHz. The satellites associated with this system shift the uplink signals to carrier frequencies ranging from approximately 12.2 GHz to approximately 12.7 GHz and transmit these frequency shifted transponder signals back to earth for reception at each of a plurality of individual receiver units in what may be termed a digital television broadcast satellite system or “DTV”. Other satellite communication systems are presently available for transmitting digital information to a local earth site for reception and use in a personal computer at the local earth site. For present purposes, such a communication satellite service system is hereinafter identified as a digital personal computer system or “DPC”. A DPC satellite communication service system may for instance supply satellite signals at carrier frequencies ranging from approximately 11.7 GHz to approximately 12.2 GHz, which DPC satellite signals are transmitted back to earth for reception at a receiver at the local site. 
     Accordingly, if a household for instance wishes to subscribe to more than one satellite service, this normally requires the installation of a separate antenna for each satellite service as well as a separate coaxial cable line for distributing the respective satellite service signals to the respective receivers at the local site. A household subscribing to several satellite services thus may require not only an array of satellite receive antennas which is very costly, but also requires the additional expenditures for installing more than the usual single coaxial cable line supplied to one or more rooms in the house. 
     In a pending application, U.S. Ser. No. 08/544,423 filed Oct. 10, 1995, assigned to the same assignee as herein, there is described a satellite receive antenna capable of simultaneously receiving signals from satellites at different geostationary positions. The aforementioned application Ser. No. 08/544,423 is incorporated herein by reference. This enables one to receive separate multiple satellite communication services signals on a single antenna which therefor eliminates the requirement for a costly antenna array for a household desiring to subscribe to more than one satellite communication service. 
     However, there is still a need to address the problems in distributing the received separate satellite signals at the outputs of such a dual satellite antenna. In particular, it is desired to distribute the satellite signals from separate multiple satellites on a signal cable line. Further, it is particularly desired to enable a user to access the communication signals from separate multiple satellites simultaneously at for instance different rooms within the household, while only using a single cable to each receiving device. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a system for distributing satellite communication signals from separate multiple satellites on a single cable line. According to one aspect of the present invention, a dual satellite receiving antenna receives a first broadband signal at a first set of frequency bands corresponding to first satellite service signals, and a second broadband signal at a second set of frequency bands corresponding to second satellite service signals. A frequency converter using frequency division multiplexing receives and converts at least one of the sets of frequency bands to position the converted set of frequency bands adjacent to the other frequency band. A combiner receives the two adjacent frequency bands and distributes them on a single cable line to one or more receivers at the local site for access of the separate multiple satellite communication service signals by the receivers. 
     According to another aspect of the present invention, a dual mode or two-channel LNB provides both the right-hand polarized and the left-hand polarized signals of a DTV satellite system signal to be provided via separate lines. A frequency converter, utilizing frequency division multiplexing frequency converts the signals from a second satellite system, such as, DPC with each of the separate DTV-left-hand polarization and right-hand polarization signals to provide two adjacent bands of frequency signals, each of which is separately combined in a respective summer unit and distributed on a single coaxial line. A demultiplexer and switch selection circuitry is provided for receiving the two separate lines from the respective summer units and provides a plurality of single cable output lines on which each coupled receiver may simultaneously access any of the received separate satellite signals from the multiple satellites and on a single cable line supplied to the respective receiver. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a satellite system capable of using the present invention; 
     FIG. 2 is a diagram of a satellite receive antenna useful in connection with the present invention; 
     FIG. 3 is a top view diagram showing the satellite receive antenna shown in FIG. 2; 
     FIG. 4 is a schematic diagram illustrating a local earth site system for distributing separate multiple satellite communication services signals on a single cable line in accordance with the present invention; 
     FIG. 5 is a block diagram of the low noise block (LNB) shown in FIGS. 2 and 4; 
     FIG. 6 is a block diagram illustrating the combiner of FIG. 4; 
     FIGS.  7 ( a ),  7 ( b ),  7 ( c ) is a frequency distribution chart illustrating representative options for combining and frequency division multiplexing of the satellite signals from separate multiple satellites; and 
     FIG. 8 is another embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a satellite system  100  capable of utilizing the present invention. The system  100  includes ground-based uplink transmitters  101 ,  102 , a ground-based satellite receiver  130 , and a space segment  103  consisting of orbiting satellites  104 ,  105   a ,  105   b . In a typical application, the satellites  104 ,  105   a ,  105   b  are positioned at geostationary positions spaced approximately 2° of arc apart. For example, satellite  104  may be the Galaxy  4  satellite at 99.0° W longitude, and satellites  105   a ,  105   b  may be satellites DBS-1 and DBS-2, located at 101.2° W longitude and 100.8° W longitude. 
     Preferably, uplink transmitter  102  modulates a digital signal onto the assigned frequency carriers for uplink to satellites  105   a ,  105   b . Satellites  105   a ,  105   b  translate the uplink carriers to the assigned Ku2-band downlink frequency carriers, (over 12 GHz), for downlink to the satellite receiver  130 . The satellites  105   a ,  105   b  ordinarily transmit carrier signals with alternating left-hand circularly polarized (LHCP) and right-hand circularly polarized (RHCP) signals. Preferably, satellites  105   a ,  105  are high-power satellites that transmit downlink signals in a focused beam pattern  108 . Similarly, the uplink transmitter  101  uplinks signals to satellite  104 . The satellite  104  translates the carrier signals to the assigned C-band or Ku-band downlink frequencies for subsequent demodulation and downlink to the satellite receiver  130 . The satellite  104 , ordinarily transmits carriers with alternating vertical and horizontal polarity. 
     Referring to FIG. 2, a preferred embodiment of the satellite receiver  130  as described in the aforementioned pending application Ser. No. 08/544,423 incorporated by reference herein, has a small aperture antenna  131 , a siamese feedhorn  132 , two low noise blocks (LNB)  133 ,  134 , and a feedhorn support arm  135 . The antenna  131  has a boresight line  137 , from which the antenna  131  receives signals with maximum gain, and a beamwidth  138  along the boresight. Signals  144  within the beamwidth  138  are reflected and focused by the antenna  131  to a focal point  140 . Siamese feedhorn  132  and LNBs  133 , are mounted on a feedhorn support arm  135  and positioned at the focal point  140 . 
     When satellite services are desired from two satellites broadcasting at different power levels, the antenna  131  is most preferably aimed or boresighted at the satellite with the lower-power signal. For example, to receive signals from the satellite  104  at 99.0° W longitude and the higher-power satellites  105   a ,  105   b  at 100.8° W longitude and 101.2° W longitude, the antenna  131  is boresighted at the lower-power satellite  104  and 99.0° W longitude. 
     FIG. 3 is a top view diagram of the antenna  131  illustrating a typical focal point and offset region. The antenna  131  focuses satellite signals  144  from within its beamwidth  138  to a focal point  140 . The antenna  131  has a beamwidth  138  of approximately 2.8° at the Ku-band. With the boresight  137  of the antenna  131  aimed at the 99.0° W location, the focal point  140  receives signals from 1.4° (2.8°/2) to either side of 99.0° W longitude, i.e., from 97.6° W to 100.4° W longitude. Signals  145  from the satellites  105   a ,  105   b  at approximately the 101° W longitude position are therefore not of sufficient strength to be seen by the focal point  140 . 
     Signals  145  from a satellite outside the antenna beamwidth  138  are generally reflected by the antenna  131  to an offset region, and more particularly to an offset location  141 . The offset location  141  may be chosen according to the separation between the satellites and the terrestrial antenna. Satellites  104  and  105   a ,  105   b  have different azimuth and elevation separation angles according to the terrestrial location of the antenna observing the satellites. 
     For all geographic locations in the continental United States, the difference in the observed azimuth angle  142  between the 99.0° W longitude satellite  104  and the 101° W.longitude satellites  105   a ,  105   b  ranges from a minimum of 2.82° to a maximum of 4.60°. For example, from Los Angeles, Calif., the satellites  105   a ,  105   b  appear about 2.65° apart from the satellite  104 . From Laredo, Tex., the satellites  105   a ,  105   b  appear to be about 4.14° apart from the satellite  104 . Because the difference in azimuth angles between the satellite  104  and the satellites  105   a ,  105   b  varies from Los Angeles to Laredo, the offset location  141  varies. However, a single azimuth angle difference  142  can be used by choosing a fixed distance  143  between focal point  140  and offset location  141 , resulting in an azimuth angle  142  approximately halfway between the range of the possible azimuth angles. 
     Preferably, the offset location  141  is a distance  143  between 1.5 to 2.5 cm from the focal point  140 . Providing an offset location  141  at a fixed 1.5 to 2.5 cm distance from the focal point  140  results in an azimuth angle  142  suitable for simultaneously receiving both the 99.0° W satellite  104  and the 101.0° W satellites  105   a ,  105   b  from most terrestrial locations throughout the continental United States. One skilled in the art can readily calculate the range of azimuth angle differences  142  and corresponding offset distances for other geostationary satellite positions and terrestrial locations. A suitable fixed offset distance  143  can thus be selected from the calculated range. 
     Referring now to FIG. 4, there is illustrated the ground-based satellite receiver  130  at a local earth site, such as a household, with the receiving antenna  131  capable of receiving satellite signals from the separate satellites  105   a ,  105   b  as well as from the satellite  104 . The downlink satellite signals from satellites  105   a ,  105   b  are typically between 12.2 GHz-12.7 GHz, and between about 11.7 GHz-12.2 GHz from satellite  104 . For convenience, the satellite signals received from satellites  105   a ,  105   b  are referred to hereinafter as DTV communication signals which are the aforementioned Ku-band carrier signals with alternating left-hand circularly polarized (LHCP) and right-hand circularly polarized (RHCP) signals. The second satellite communication service signals received from satellite  104  will be hereinafter identified as DPC communication signals which are ordinarily in the aforementioned lower Ku-band of carrier signals with alternating vertical polarity (VP) and horizontal polarity (HP). 
     As shown in FIG. 4, each of the respectively received separate satellite signals from the separate satellites are focused by antenna  131  at a focal point where there the LNBs  133 ,  134  are located as previously described. An LNB is preferably comprised of an integrated low noise amplifier and a low noise frequency converter, and such devices are well-known to those skilled in the art. Reference may be made for instance to FIG. 5 where there is illustrated a representative LNB with an input  220  receiving signals from the antenna, and an output  229  coupling the intermediate frequency band to a receiver. Bandpass filters (BPF)  221 ,  222 ,  223  remove unwanted frequency signals while allowing desired signals to pass. Preferably, a field effect transistor (FET) amplifier  224 , pre-amplifies the signal before it is mixed to the desired frequency. FET amplifier  224  is preferably a GaAs amplifier that provides a gain of 10 dB with a noise figure of 0.9 dB or less. Preferably, FET amplifier  224  provides a gain of 30 dB to 60 dB. 
     Local oscillator (LO)  225  and Schottky diode  226  mix the signal to the desired frequency. The signal is then amplified by amplifier stage  227  before being sent but on a shielded coaxial line  229  to an indoor receiver. A voltage regulator  228  preferably regulates the voltage provided by the LNB to the indoor receiver and incorporates a voltage level switch control for selecting either the right-hand or left-hand polarized signals in response to a switch control signal from the indoor receiver in a manner well-known to those skilled in the art. 
     The LNBs  133 ,  134  detect signals relayed from the feedhorn  132 , convert the signals to an electrical current, amplify the signals, and downconvert the signals to a lower frequency. LNBs typically downconvert signals from the received satellite carrier frequencies to intermediate frequencies between 900 MHz and 2000 MHz. In the preferred embodiment, the LNB downconverts the satellite carrier signals to the intermediate frequency range of 950 to 1450 MHz. 
     Typically, only the RHCP signals or the LHCP signals are converted down to the intermediate frequency, depending on which particular receiver channel a DTV user is viewing. That is, when the viewer selects a particular DTV channel, an appropriate voltage switch control level is supplied to the LNB in a known manner to control the local oscillator  225  so as to provide either the RHCP or the LHCP signals for return to the indoor receiver. However, in systems having a dual mode or two-channel LNB, as well-known to those skilled in the art, both RHCP LHCP signals may be individually shifted down to a 500 MHz portion of L-Band (e.g. between 950 MHz and 1450 MHz) and provided, via separate lines, each like output line  229 , to a set-top box or other integrated receiver and detector (IRD) associated with the receiver unit. 
     Accordingly, in FIG. 4, the output on line  302  is a DTV-left-hand or right-hand polarized signal in the frequency range 950-1450 MHz. On an output line  304  from the LNB  134 , there is provided the DPC satellite signals at the intermediate frequency range also of 950-1450 MHz. A combiner  306  provides frequency division multiplexing to the two input signals on lines  302 ,  304  and locates the band of frequencies together so that they are adjacent and consecutive, thereby enabling them to be placed on a single coaxial cable line  308  for distribution to respective IRD and DPC units at respective terminals  310 ,  312 , each of which is connected to a respective single coaxial line ultimately connected through a splitter  314  to the single coaxial line  308 . 
     Referring to FIG. 6, there is illustrated the details of the combiner  306 . Input line  302  containing the DTV, either left-hand or right-hand polarized signals is coupled to a buffer amplifier  316  and then supplied to a summer  318 . Input line  304  containing the DPC frequency band also at 950-1450 MHz is coupled to a buffer amplifier  320  and thereafter coupled to a frequency converter  322  for upconverting the 95014 1450 MHz band to a band between about 1550-2050 MHz. 
     Reference may be made to FIG.  7 ( a ) wherein the frequency distribution at the output of summer  318  on output line  308  is illustrated for convenience. As can be seen from this frequency distribution chart, the DPC band of frequencies has been located adjacent and consecutive with the DTV left-hand or right-hand polarized signals. For purposes of illustration, the lower band of frequencies between about 50 MHz to 850 MHz is illustrated as reserved for CATV or VHF/UHF cable signals which provide VHF/UHF broadcast channel signals in a known manner. 
     Reference may be made now to FIG. 8 wherein there is illustrated a local earth site distribution system  330  which enables each of the users at terminals  332 ,  334  . . .  340  to have access to both the left-hand as well as the right-hand DTV signals from satellites  105   a ,  105   b , as well as having access to the DPC signals from satellite  104 . In the embodiment  330  shown in FIG. 8, the receiving antenna  331  includes an LNB with three outputs. One of the LNB outputs is a downconverted intermediate frequency from satellite  105   a ,  105   b  representing the left-hand polarized signals in the range 950 MHz to 1450 MHz, and is labelled DTV-L and is supplied on output line  342 . Similarly, output line  344  contains the downconverted right-hand polarized portion of the 950 MHz to 1450 MHz signals from satellites  105   a ,  105   b  and is indicated in FIG. 8 as DTVR. The third output line  346  of the LNB provides the downconverted intermediate frequencies received from satellite  104 , and this output line is accordingly labelled DPC. 
     The three LNB output lines  342 ,  344 ,  346  are coupled to a combiner  348  which includes frequency converters and summers for providing frequency division multiplexing of the input signals. Reference may be made to FIG.  7 ( c ) wherein there is illustrated the results of the frequency division multiplexing supplied by combiner  348 . In particular, it can be seen from FIG.  7 ( c ) that the DTV left-hand and right-hand polarized signals are available in the frequency range 950 MHz to 1450 MHz, whereas all of the DPC signals have been frequency converted and positioned in the 1550 MHz to 2050 MHz frequency band. The DTV-left-hand polarized signals and the DPC vertical polarized signals are provided on combiner  348  output line  350 . The DTV right-hand polarized signals and the DPC horizontally polarized signals are provided on combiner  348  output line  352 . FIG.  7 ( b ) shows an alternative distribution of the DTV and DPC signals using frequency division multiplexing. 
     A demultiplexer  354  includes respective inputs for receiving output lines  350  and  352 , and also an input line  356  containing VHF/UHF broadcast signals. Demultiplexer  354  includes output lines  358  each of which can supply any of the signals from input lines  350 ,  352  and  356  for coupling to the respective terminals  332 ,  334  . . .  340 . For instance, the IRD  1  unit coupled to terminal  332  has access to all of the signals received from both of the separate satellites  105   a ,  105   b  as well as from satellite  104 . Coupling of the selected signals is accomplished automatically in a well-known manner, such as by using voltage biased levels supplied from IRD  1  to a switch selector in the multiplexer  354  to accomplish the selection of the particular signal desired. This switch selection may be accomplished in a manner similar to that previously described with respect to existing LNBs. Demultiplexer  354  is a standard commercially available unit, such as Channelmaster model 63141FD, or similar available units such as. 
     Accordingly, it can be seen that in either of the illustrated embodiments, separate multiple satellite communication service signals are supplied on a single cable line at the local earth receiver site. Secondly, with respect to the embodiment shown in FIG. 8, all of the communication satellite signals from each of the separate satellites is available simultaneously on each of the single cable lines connected, for instance, to terminals  332 ,  334 ,  336 ,  338 ,  340 . 
     The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.