Abstract:
A satellite communications interoperability module and method for frequency down-conversion. The module insertable in-line with an intra-facility link communicating a multiplexed signal between the outdoor unit (ODU) and the indoor unit (IDU). Electrical circuitry of the module transforming and forwarding the multiplexed signal over the intra-facility link, the multiplexed signal including at least direct current, a standard tone, and L-band data signals. Switching means of the module specifies operations performed by the electrical circuitry to transform the multiplexed signal frequencies, waveforms and voltages according to predetermined parameters compatible between the ODU and the IDU. An interoperability method for compatibility with a range of different indoor units applied by the interoperability module and or incorporated into an integral ODU is application of a second frequency shift upon the L-band signal output from the ODU primary down-conversion circuit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/890,533, titled “VIM and FReD VSAT Interoperability Modules”, filed Feb. 19, 2007 by Paul Gareth Lloyd and Ronald P. A. Schiltmans and U.S. Utility patent application Ser. No. 11/779,402, titled Satellite Communications Interoperability Module and Down-Conversion Method by Paul Gareth Lloyd and Ronald P. A. Schiltmans. 
     
    
     BACKGROUND 
       [0002]    The invention relates to satellite communications interoperability modules and Down-Conversion methods. More particularly the invention relates to a satellite communications interoperability module to enable inter-connection and operation of diverse Indoor Unit (IDU) and Outdoor Unit (ODU) satellite communications system components and services. 
         [0003]    Very Small Aperture Terminal (VSAT) Satellite Communication Systems are becoming increasingly common, for example, for broadband internet communications and Direct To Home (DTH) entertainment services. There are multiple standards available, requiring dedicated equipment designed to provide the specified signal parameters of each standard. 
         [0004]    A VSAT network comprises a plurality of terminals. These terminals are designed to handle varying outbound data-rates and bandwidths (to divide the quasi-fixed and finite satellite capacity amongst the plurality of terminals, making maximum use of the satellite capacity). The data-rate requirement differs according to the application. Some applications utilize low data-rate, but “always-on” single channel per carrier (SCPC). Other applications may utilize high data-rates, in intermittent bursts, for example, internet access via satellite. 
         [0005]    A VSAT system includes an ODU mounted at an outside location with a line of sight to the target satellite(s). The ODU typically includes a transceiver coupled to a Low Noise Block (LNB) that illuminates a reflector dish to beam signals between the ODU and target satellite(s). The ODU transceiver inputs and outputs are coupled via an Intra-Facility Link (IFL) to the IDU, which operates as a modem, transferring the desired data from the ODU to consumer terminals such as audio-visual equipment and or personal computers. 
         [0006]    The IFL typically consists of a separate transmit and receive cable. While the satellite communication may take place at C-, Ku- or Ka-frequency bands, information and power is passed between the IDU and ODU over the IFL in a frequency multiplexed manner. 
         [0007]    A typical IFL signal package includes DC power (whose voltage level may be used to provide a polarization selection control signal), a 22 kHz tone (for carrying sub-band selection) and an L-band data signal (a frequency shifted version of the desired, higher frequency, satellite signal). Some IDU also provide a high quality (i.e. stable) local oscillator (LO) reference signal (typically at 10 MHz) to the ODU, whereas most IDU do not. 
         [0008]    Lower data-rates (including SCPC) typically occupy lower bandwidths. Modems operating at lower data-rates are required to “find” the desired signal in amongst a plurality of other signals. Hence, lower data-rate applications require (amongst other parameters) greater frequency stability from the LO (local oscillator), a key subsystem in the LNB. Network designers may specify a minimum level of stability from the LNB for a given terminal, according to the lowest data-rate required. The cost of the frequency reference is exponentially proportional to it&#39;s stability, and the stability is a function of the temperature range over which it is specified for operation. The ODU is typically required to operate in the temperature range −40 C to +55 C, whereas the IDU operates typically between 0 C and +40 C. 
         [0009]    A further problem is that a VSAT modem is designed to receive only a fraction of the total bandwidth available from the satellite. For VSAT applications in the Ku-band for example, the IDU receives only 500 MHz of the 2000 MHz wide Ku-band. The LNB LO frequency is responsible for selecting which sub-band of the Ku-outbound channel is passed to the IDU. 
         [0010]    Previously, a range of similar VSAT components, differentiated for example by locating the frequency reference in the IDU or ODU and having different specific frequency and stability specifications therefore, have been available at corresponding price levels, complicating design marketing, logistics and support issues for equipment manufacturers. Interoperability and regional frequency regulations are another significant limitation. For example, some existing IDU and ODU combinations fail to utilize high quality reference signals generated by the IDU, substituting a lower quality reference signal generated in the ODU. These various issues require an equipment provider to design, forecast and stock LNBs capable of accommodating several different channels/LO frequencies and several different input/output frequencies. 
         [0011]    A highly integrated and cost efficient modular component developed for the ODU is the Fully Integrated Mixer Oscillator Down-converter (FIMOD). As shown in  FIG. 1 , one embodiment of the FIMOD is capable of performing PLL (phase locked loop) functionality, switched between two LO frequencies, KU-low 10.70-11.70 GHz and KU-high 11.70-12.75 GHz, to enable full-band, Phase Locked Loop (PLL) receivers in VSAT outbound/downlink terminals with improved electrical performance and cost efficiency. However, limitations in existing FIMOD based ODU, along with a lack of Intermediate Frequency (IF) bandwidth/performance from many existing IDU limits commercial acceptance of the FIMOD based ODU. 
         [0012]    A typical FIMOD ODU operates with LO frequencies of 9.75 and 10.60 GHz. However, for many standardized VSAT communication system configurations, it is desirable to switch between three frequencies; 10.00 GHz, 10.75 GHz and 11.30 GHz. Because a typical FIMOD ODU is not able to switch between three frequencies or generate the 11.30 GHz frequency, interchangeable use of the FIMOD type ODU with these existing IDU/VSAT communications systems is prevented. 
         [0013]    The specifics of the FIMOD ODU are presented herein for example purposes, other ODU and IDU combinations present similar compatibility problems, requiring equipment manufacturers to design, manufacture, inventory and support a large number of IDU and or ODU models specifically configured for each possible combination. 
         [0014]    Therefore, it is an object of the invention to provide an apparatus that overcomes deficiencies in the prior art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the general and detailed descriptions of the invention appearing herein, serve to explain the principles of the invention. 
           [0016]      FIG. 1  is a frequency band chart for a typical FIMOD IDU. 
           [0017]      FIG. 2  is a schematic view of a VIM positioned in-line between an IDU and an ODU, on the receive signal path. 
           [0018]      FIG. 3  is a schematic view of exemplary Switching Means configuration signals and elements of multi-plexed signals passing along the IFL to and from the VIM port(s). 
           [0019]      FIG. 4  is a signal diagram exemplary of the secondary down-conversion performed upon the L-band according to the switching means input 
           [0020]      FIG. 5  is a flow chart demonstrating one embodiment of VIM configuration and operation. 
           [0021]      FIG. 6  is a table demonstrating an exemplary frequency plan for a VIM. 
           [0022]      FIG. 7  is a graphical representation of the frequency plans of  FIG. 6 . 
           [0023]      FIG. 8  is a schematic view of exemplary FReD Inputs and Outputs. 
           [0024]      FIG. 9  is a schematic view of a FReD positioned in-line between an IDU and an ODU, on the receive signal path. 
           [0025]      FIG. 10  is a schematic view of a FReD positioned in-line between an IDU and an ODU, on the transmit signal path. 
           [0026]      FIG. 11  is a block circuit diagram of an exemplary embodiment of a VIM. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    The inventors have recognized that communications equipment manufacturers desire improved electrical performance from standardized equipment, to simplify product lines and reduce costs. A VSAT Installation Module (VIM) and or Frequency Reference Device (FReD) according to the invention may be installed in-line with the IFL, between the IDU and ODU, either separately or together to enable improved electrical performance and the interconnection/configuration of a wide range of different ODU and IDU equipment that are otherwise incompatible. Alternatively, a series LO down conversion protocol incorporating circuit elements described herein may be implemented to provide multiple band capability/IDU compatibility, for example into a single “universal compatibility” integral ODU. 
         [0028]    Because the sub-bands over which the KU-band receive are divided, without straddling 11.70 GHz and most IDU are capable of handling inverted spectra it is possible to generate signal conversion protocols with respect to the capabilities of, for example, a FIMOD based ODU by selecting either the high or low band output of the FIMOD LO and routing it through an additional mixing stage fed by a second LO to generate the sub bands compatible with the desired IDU. 
         [0029]    As shown for example in  FIG. 2 , the VIM  10  is preferably an electronic, 2 port network with an additional quasi-static user interface configurable during installation. The VIM  10  may be installed in-line with the downlink path  12  and or outbound path  14  of the IFL  16 , between the IDU  18  and the ODU  20 . The VIM  10  may be positioned indoors  22  or outdoors  24 , but typically is located indoors to minimize environmental sealing requirements and exposure to performance degrading temperature extremes. The VIM  10  may be configured as a self contained “dongle” type of accessory module, with input and output port(s)  23  for interconnection with the ends of a break in the IFL  16  or between the IDU  18  and the IFL  16 . Configuration is via one or more switches and or a switch means  26  in a quasi-static user interface to specify signal transformation parameters. Alternatively, the VIM  10  functionality may be incorporated directly into the ODU  20 . The switch means  26  may be any manner of switch apparatus such as a plurality of jumpers, dip switches, slide switches, rotary switches, toggle switches or the like. The switch means  26  may be configured to designate signal transformation parameters, such as, the polarization  27  and or a desired LO frequency  25 , such as 9.75, 10.00, 10.25, 10.60, or 11.30 GHz. Alternatively, the switch means  26  may be a further circuit that is either electronically programmable via commands over the IFL, or auto configuring according to an analysis of IDU responses to test configurations. 
         [0030]    An exemplary version of the VIM  10  contains electronic circuitry  28  comprising a PLL, Voltage Controlled Oscillator (VCO)  29 , frequency reference, 22 kHz tone generator, a voltage variable power supply, a simple microprocessor and additional interconnecting, monitoring, power and or control circuits. As shown in  FIG. 3 , the frequency multiplexed signal elements passing through the IFL  16 , to the VIM  10  port(s)  23  carry both power and data signals at Direct Current (DC)  30 , a standard tone  32 , for example 22 kHz (a standard tone/information carrier frequency in the field of the invention), a reference frequency  34 , for example 10 MHz and L-band  36 , typically 1-2 GHz. The VCO  29  and mixer circuits that apply the selected frequency of the VCO  29  to the L-Band  36  may be incorporated into, for example, a single chip LO integrated circuit, for example the “SaTCR-1” integrated circuit by ST Microelectronics of Geneva, Switzerland, of the electronic circuitry  28 . By passage through the VIM  10  and according to the selected settings of the configuration switches and or switch means  26 , the DC  30 , and L-band  36  voltages and frequencies are adjusted to harmonize the signal characteristics between the selected IDU  18  and ODU  20 . 
         [0031]    As shown in  FIG. 4 , the ODU  20  outputs an L-band  36  component of the multiplexed signal onto the IFL  16  that is a frequency down-converted version of the data signal from the satellite  37 , the down-conversion of the satellite  37  signal performed by the first LO  35  and a first mixer  39  of the ODU  20 . Where the ODU  20  has dual band capability, such as the FIMOD ODU  20 , the ODU  20  can be configured to output the L-band  36  at either the low or high band (see  FIG. 1 ). The PLL and VCO  29  of the VIM  10  electrical circuitry  28  then operate upon the L-band  36  as a second frequency conversion stage via a second mixer  41  to adjust the L-band  36  to a desired L-band  36  sub-band compatible with the IDU  18  for example according to  FIGS. 6 and 7 , as described herein below. 
         [0032]    An exemplary embodiment of the VIM  10  internal circuit interconnections with respect to the single chip LO integrated circuit, for example a SatCR-1, providing the VCO  29  and second mixer  41  functionality is shown in  FIG. 11 . Although the SatCR-1 is marketed as a single chip broadband downconverter for integration within the LNB circuits of an ODU  20  for generation of the L-Band  36  output of the ODU  20 , the inventors have recognized that the control instructions supplied to the on-chip PLL controlled VCO  29  from the IDU  18  to the ODU  20  (assuming the units are frequency band and polarity compatible) can instead be provided with a range of different inputs by a microcontroller  50  of the VIM  10  via an i2C communications link capability of the SatCR-1. The microcontroller  50  receives several inputs such as the polarity and band selections of the selected switch means  26  and is programmed to output control commands (frequency and polarity selections) to the SatCR-1 which in turn drives the VCO  29  (within the SatCR-1) to supply the desired LO frequency to the second mixer  41  (also within the SatCR-1) required for generating an L-band  36  configured for any specific version of a wide range of different indoor unit(s)  18 . 
         [0033]    Within the VIM  10 , a low frequency signal component bypass  51  around the SatCR-1 is coupled at indoor unit  18  and outdoor unit  20  sides of the VIM  10  IFL  16  connections, first passing at each connection through a low pass filter  52 . The low frequency signal component has a further parallel circuit division into a power supply path  54  and a reference signal path  53 . 
         [0034]    The power supply path  54  has a Band Stop Filter  55  tuned to the external reference frequency (typically 10 MHz) at each end. A pre-regulator  56  delivers power to a VIM power supply  57  that in turn supplies operating power to the microcontroller, SatCR-1 and any associated logic and control sub-circuits. Also, the preregulator  56  passes power upstream, to energize the outdoor unit  20 . As any static discharge or other surge coming from the connection to the outdoor unit  20  can be expected to be of low frequency, a surge protection  58  circuit may be included, for example placed at the outdoor unit  20  side of the bypass. 
         [0035]    Depending upon the selected input of the switch means  26  with respect to whether or not the external reference signal or standard tone, if present, or a replacement reference signal is desired, the reference signal path  53  of the bypass provides either a full bypass of the reference signal around the SatCR-1 or a cut-off and replacement of the reference signal with a substitute reference signal generated by a dedicated oscillator  59  of the VIM  10 , depending upon user inputs to the switch means  26 . 
         [0036]    Similar to the filtering applied to the bypass paths to limit the passage of only the desired signals, the input and output of the L-band  36  passing through the SatCR-1 may also be further tuned and or signal conditioned with band pass filter(s)  61 , impedance matching  62  and or precision attenuator arrangement(s)  60 . 
         [0037]    A frequency doubler  63  fed by the 10 Mhz reference frequency is applied to generate and supply a 20 Mhz reference frequency to a reference input of the SatCR-1. 
         [0038]    A 22K modulator  64  controlled by the selected switch means  26  may also be applied in embodiments for use with a FIMOD ODU  20 , where this frequency is used as a control signal for configuring an oscillator present in a specific ODU  20 , such as the FIMOD VCO. 
         [0039]    An exemplary method of operation for the VIM  10  is demonstrated in  FIG. 5 . At start-up  70 , the VIM  10  decodes the quasi-static, user selected configuration of the switch means  26 . At  72 , according to the switch means  26 , the correct DC  30  level and standard tone  32  output to the ODU  20  may be enabled. At  74 , the correct VIM  10  internal LO frequency and architecture is set to suit the applicable IDU  18 /ODU  20  requirements. At  76 , a check is made for the presence of a reference frequency  34 , for example 10 MHz, from the IDU—and if not present, in  78 , a reference frequency  34  is enabled/generated by the VIM  10  and supplied to the ODU  20 . At  80 , the VIM  10  is operating fully configured as a stable receiver taking the universal L-band  36  input from the ODU  20  (LNB/transceiver) and modifying the frequency band frequency limits by performing a mixing operation, filtering and inversion of the spectrum as necessary to supply the IDU with a compatible L-Band  36  signal. Once configuration is complete, VIM  10  operates transparently until powered down, for example by detection of a control signal and or direct current  30  cut-out, at  82 . 
         [0040]    The VIM  10  may be pre-configured to operate according to a wide range of known frequency plans for example as shown in  FIG. 6 . The tabulated figures represent the progression of the adaptive receiver architecture set up, wherein: 
         [0041]    RF Input/GHz: The frequency range, High and Low, transmitted by the satellite and received by the ODU. 
         [0042]    1st LO: The frequency of the LO (local oscillator) used to make the first downconversion step. According to the exemplary embodiment, this is the first LO  35  of the ODU. 
         [0043]    2nd LO: The frequency of the second LO, VCO  29  of the VIM  10 , in the second (optional) downconversion step. 
         [0044]    Effective LO: The net effect of cascading the ODU  20  and VIM  10 . Or in other embodiments, the result of the first and second LO down-conversion, that may alternatively occur in a single device, such as a “universal compatibility” ODU  20 , having the functionality shown for example in  FIG. 4 , but with both down conversion stages resident in the ODU  20 . The IDU  18  does not “know” whether one or two down-conversion steps has taken place. The “effective LO” frequency is the equivalent one step down-conversion LO frequency resulting from the selected frequencies of the first LO  35  and the VCO  29 . 
         [0045]    IF Output/MHz: The occupied bandwidth of the signal transferred from the invention output to the IDU  18 . The bandwidth of the “IF Output” is the same as the “RF Input”, just down-converted to the required frequency for compatibility with the selected IDU  18 . 
         [0046]    As shown by  FIG. 7 , several of the bands require inversion, the sense of spectrum is illustrated by the direction of slope. Hashed areas indicate frequencies of the coarse spectrum that are either filtered by the VIM  10  or discarded by the IDU  18 . To obtain an output according to any of the other bands demonstrated in  FIG. 7 , or others that a specific IDU  18  may require, the VCO  29  of the electrical circuitry  28  is applied in conjunction with a mixer upon the L-band  36  component of the multiplexed signal with the second LO frequency specified by the switch means  26 . The two universal KU-bands (low and high), as shown in  FIG. 1 , may be passed through the VIM  10  without modification, represented by bypass  42  on  FIG. 4 , relying upon the first LO (for example of the FIMOD ODU  20 ) without further manipulation via the VIM  10  VCO, that is the second LO frequency is zero or “off”. 
         [0047]    Depending upon the characteristics of the IDU  18  and or ODU  20  equipment that is being interfaced with, the extended features of the VIM  10  may not be necessary, or alternatively some features may actually conflict with several known IDU  18 . In alternative embodiments, the VIM  10  may be provided with a reduced functionality, for example without the reference frequency capability. Similarly, for configurations where only a high quality reference frequency is desired a simplified embodiment of the invention, a Frequency Reference Dongle (FReD)  38  may be supplied. 
         [0048]    The FReD  38  embodiment, as shown in  FIG. 8 , again inserted inline with the IFL  16  between the IDU  18  and the ODU  20 , may be adapted to allow all signals to pass, bidirectionally, between the IDU  18  and the ODU  20 . The FReD  38  electrical circuitry  28  includes a reference frequency generator sub circuit  40  that supplies a high quality reference frequency  34 , for example, to the ODU  20 . The reference frequency may be, for example crystal based. To prevent the opportunity for unpredictable system behavior, the reference frequency  34  generated and multiplexed into the IFL  16  by the FReD  38  may be shielded from the IDU  18 . As shown in  FIGS. 9 and 10 , the FReD may be alternatively positioned as needed in either the downlink path  12  and or, for example where no original reference frequency is available from the IDU  18  (or the original reference frequency is of insufficient quality), in the outbound path  14 . Where the original reference frequency is of insufficient quality, the FReD  38  may be configured to filter same and inject the reference frequency  34  into the IFL  16  connection to the ODU  20 . 
         [0049]    For a given frequency stability requirement, it is more expensive to realize a given stability using a reference located in the outdoor environment. The corollary of this is that a frequency reference specified over the outdoor temperature range will demonstrate much better stability when operated in the indoor environment. Therefore, the invented architecture offers higher stability systems for the same price, or the same stability for a lower cost. 
         [0050]    One skilled in the art will appreciate that the creation of a low cost, flexible architecture in-line device, that enables use of a VSAT LNB/transceiver, such as a FIMOD ODU  20 , to be used with a wide range of different IDU  18  available in the market enables significant cost and performance improvements. Replacing the, for example eight, VSAT LNB/transceiver ODU  20  configurations described herein by setting up the correct universal VSAT LNB/transceiver configuration (coarse band, polarization etc.), using standard control voltages/tones and adapting the receive architecture dynamically to create the desired emulated IF band provides significant opportunities for ODU  20  manufacturer model consolidation, inventory requirement reduction, supply logistics and field operating band re-configuration. 
         [0051]    In still further embodiment&#39;s the electrical circuitry  28  and switch means  26  described herein may be incorporated into the ODU  20  to provide a single ODU  20  with band shifting capabilities operable in any of the, for example eight, bands shown in  FIG. 6 . Thereby, an ODU  20  is enabled that is interoperable with the majority of known IDU  18 , but that has a total of only two LO, the FIMOD LO, and an additional, for example, SCR integrated circuit VCO incorporated within combined electrical circuitry  28 . 
         [0052]    Further, improvements in electrical performance are realized by enabling wider adoption of FIMOD ODU technology and or via the supply of an external reference with greatly improved stability. 
         [0000]    
       
         
               
             
               
               
             
           
               
                   
               
               
                 Table of Parts 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10 
                 VSAT Installation Module 
               
               
                 12 
                 downlink path 
               
               
                 14 
                 outbound path 
               
               
                 16 
                 intra-facility link 
               
               
                 18 
                 indoor unit 
               
               
                 20 
                 outdoor unit 
               
               
                 22 
                 indoors 
               
               
                 23 
                 port 
               
               
                 24 
                 outdoors 
               
               
                 25 
                 local oscillator frequency 
               
               
                 26 
                 switch means 
               
               
                 27 
                 polarization 
               
               
                 28 
                 circuitry 
               
               
                 29 
                 voltage controlled oscillator 
               
               
                 30 
                 direct current 
               
               
                 32 
                 standard tone 
               
               
                 34 
                 reference frequency 
               
               
                 35 
                 First local oscillator 
               
               
                 36 
                 L-band 
               
               
                 37 
                 satellite 
               
               
                 38 
                 frequency reference dongle 
               
               
                 39 
                 first mixer 
               
               
                 40 
                 reference frequency generator sub circuit 
               
               
                 41 
                 second mixer 
               
               
                 42 
                 bypass 
               
               
                 50 
                 microcontroller 
               
               
                 51 
                 bypass 
               
               
                 52 
                 low pass filter 
               
               
                 53 
                 reference signal path 
               
               
                 54 
                 power supply path 
               
               
                 55 
                 band stop filter 
               
               
                 56 
                 pre-regulator 
               
               
                 57 
                 VIM power supply 
               
               
                 58 
                 surge protection 
               
               
                 59 
                 oscillator 
               
               
                 60 
                 precision attenuator arrangement 
               
               
                 61 
                 band pass filter 
               
               
                 62 
                 impedance matching 
               
               
                 63 
                 frequency doubler 
               
               
                 64 
                 modulator 
               
               
                   
               
             
          
         
       
     
         [0053]    Where in the foregoing description reference has been made to ratios, integers, components or modules having known equivalents then such equivalents are herein incorporated as if individually set forth. 
         [0054]    Each of the patents identified in this specification are herein incorporated by reference in their entirety to the same extent as if each individual patent was fully set forth herein for all each discloses or if specifically and individually indicated to be incorporated by reference. 
         [0055]    While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus, methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of applicant&#39;s general inventive concept. Further, it is to be appreciated that improvements and/or modifications may be made thereto without departing from the scope or spirit of the present invention as defined by the following claims.