Multi-spot satellite system for broadband communication

The present invention relates to the field of two-way satellite communications and in particular, to high capacity multi-purpose satellite communication systems optimized for two-way broadband communications. The two satellites are collocated and utilize a complementary channel arrangement which facilitates full dual pole coverage continuity when one of the satellites fails. Four channels of either inbound or outbound may be associated with each spot-beam area. Two channels may be provided by each of the two co-located satellites and may be configured to have a specific predetermined relationship with each other.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS. 1 and 2 , embodiments of one or more aspects of the present invention may include one or more satellites (e.g., Satellite I identified as element 9 and Satellite II identified as element 10 ) configured to include one or more sets of one or more spot beams (e.g., spot beam A-D) and one or more generic beams (G 1 -Gn). These satellites may direct one or more of a plurality of beams to one or more relatively confined geographic areas (spot beam areas) or to a broader (generic) area. For example, separate spot beams may be directed to Atlanta (spot Beam A), Washington DC(spot beam B), Miami (spot beam C), and Boston (spot beam D). All have different frequency channels which together are covering the whole frequency range in one polarization. We can repeat the same frequency range in second set of beams, e.g., St. Louis (spot Beam A), Chicago (spot beam B), Cincinnati C (spot beam C), and New Orleans (spot beam D) still working in the same polarization. In this example, each one of the four spots in a set takes one quarter of the frequency range. Any particular spot beam uses channels different in frequency and/or polarization from any adjacent spot beam area. Further, it has been found that certain frequency channels and polarization arrangement provide superior performance in two-way communication systems such as those applicable to the present inventions. Specifically, referring to FIGS. 3 A- 3 C, the A-D spot channels may be variously configured. For example, the available frequency spectrum (Ka or Ku) may be divided into a plurality of channels. In this example, the inbound frequencies have been divided into 8 channels and the outbound frequencies have been divided into 8 channels. The channel configuration shown in FIGS. 3 A- 3 C provides an extremely efficient channel arrangement for providing hot backup multi-spot beam area coverage. In alternate embodiments, one or more channels may be reserved for multicast channels directed to generic coverage. The multicast channels may carry any data currently carried by satellite transmission including electronic data such as Internet data, audio data, and video data. Referring to FIG. 7 , satellite I may operate with one polarization for both a-channels and b-channels on both the outbound (OB) direction and the inbound (IB) direction. Similarly, satellite II may operate on the other polarization for both a-channels and b-channels on both the out bound (OB) direction and the in bound (IB) direction. Any number of permutations may be adapted for any one satellite such as only operating in a-channels or b-channels, or a-channels with x-polarization and b-channels with y-polarization, and/or with switching options between any of the foregoing configurations. It is possible for a single satellite to cover all spot beam areas even where the other satellite has failed. As discussed above, each spot beam color area may be serviced by two collocated satellites (e.g., collocation within up to 0.5 degrees of separation). Where satellite 10 has failed, satellite 9 may continue to cover all spot areas A-D. With the frequency spacing discussed herein, it is possible to continue to supply channels to all spot areas in both polarizations with only one satellite. Referring to FIG. 5, a block diagram of an exemplary satellite payload 30 is shown. Telecommand control block 31 represents a conventional interface between the ground control and the satellite payload control 30 . The telecommand control block 31 transfers commands to and from the main control processor 38 . The main control processor 38 controls the satellite communication payload functions as described herein. For example, the main control processor 38 may activate a band selection control block 32 , an unequal capacity allocation control block 39 , a transponder gain control block 33 , a transponder redundancy control 36 and a coverage mode selection control block 37 which enables switching (e.g., using switching of transponders) between a first antenna array 34 (spot beam) and second antenna array (generic beam) 35 . Band selection control block 32 provides frequency band selection between different frequency bands such as Ku or Ka as discussed herein. The unequal capacity allocation control block 39 provides control functions for moving channels between spot beams. The transponder gain control block 33 conventionally provides adjustment of the gain control of the transponder between input and output. Referring to FIG. 6 , the satellites 9 , 10 may include a generic mode coverage in addition to and/or as an alternative to spot beam coverage. The illustrated example uses CONUS (contiguous United States) coverage. The generic coverage may be utilized for any suitable applications. In the example described in FIG. 8 , the outbound channels path going from the Hub (which may work in the Ka or Ku band) via the satellite to four spot beams (one set) to the small terminals (which may work in the Ku band). Additionally, a multicast channel may be associated with coverage of all of the service area. In this figure, a single satellite is shown providing the downlink directed y-polarization channels (color A-D a-channels, color A-D b-channels, and a multicast channel) spanning the full 500 MHz available in the Ku band (lower part of table). In this example, the uplink for the above mentioned downlink channels are similar channels which may be in this or another frequency band (e.g., the Ka frequency band). Thus, also in this figure, the single satellite is shown providing the uplink directed x-polarization channels (color A-D a-channels, color A-D b-channels, and a multicast channel) spanning the full 500 MHz available in the Ka band (upper part of table). Although it is preferred to switch the polarizations between the uplink and the downlink to provide better isolation, other configurations may be utilized with the same polarizations. Thus, FIG. 8 represents the single satellite eight channel half configuration including both the uplink and downlink directed channels for the outbound path only. Referring to FIG. 9, a dual satellite configuration is shown in a manner similar to that shown in FIG. 8 above. In the configuration shown in FIG. 9 , the outbound channels path going from the Hub (which may work in the Ka or Ku band) via the satellites to four spot beams (one set) to the small terminals (which may work in the Ku band). Additionally, a multicast channel may be associated with coverage of all of the service area. In this figure, a dual satellite is shown providing the downlink directed x-polarization and y-polarization channels (color A-D a-channels, color A-D b-channels, and a multicast channel) spanning the full 500 MHz available in the Ku band (lower part of table). In this example, the uplink for the above mentioned downlink channels are similar channels which may be in this or another frequency band (e.g., the Ka frequency band). Thus, also in this figure, the dual satellite is shown providing the uplink directed x-polarization and y-polarization channels (color A-D a-channels, color A-D b-channels, and a multicast channel) spanning the full 500 MHz available in the Ka band (upper part of table). Although it is preferred to switch the polarizations between the uplink and the downlink on any one given satellite to provide better isolation, other configurations may be utilized with the same polarizations. Thus, FIG. 9 represents the dual satellite eight channel full configuration including both the uplink and downlink directed channels for the outbound path only. FIGS. 10 and 11 parallel FIGS. 8 and 9 except that FIGS. 10 and 11 illustrate the inbound path without the multicast channel. Referring to FIG. 10 , in a single satellite is shown providing the uplink directed x-polarization channels (color A-D a-channels and color A-D b-channels) spanning the full 500 MHz available in the Ku band (upper part of table). In this example, the downlink for the above mentioned uplink channels are similar channels which may be in this or another frequency band (e.g., the Ka frequency band). Thus, also in this figure, the single satellite is shown providing the downlink directed y-polarization channels (color A-D a-channels and color A-D b-channels) spanning the full 500 MHz available in the Ka band (lower part of table). Although it is preferred to switch the polarizations between the uplink and the downlink to provide better isolation, other configurations may be utilized with the same polarizations. Thus, FIG. 10 represents the single satellite eight channel half configuration including both the uplink and downlink directed channels for the inbound path only. Referring to FIG. 11, a dual satellite inbound configuration is shown in a manner similar to that shown in FIG. 10 above. In the configuration shown in FIG. 11 , the inbound channels path going to the Hub (which may work in the Ka or Ku band) via the satellites from four spot beams (one set) associated with the small terminals (which may work in the Ku band). In this figure, a dual satellite is shown providing the uplink directed x-polarization and y-polarization channels (color A-D a-channels and color A-D b-channels) spanning the full 500 MHz available in the Ku band (upper part of table). In this example, the downlink for the above mentioned uplink channels are similar channels which may be in this or another frequency band (e.g., the Ka frequency band). Thus, also in this figure, the dual satellite is shown providing the downlink directed x-polarization and y-polarization channels (color A-D a-channels and color A-D b-channels) spanning the full 500 MHz available in the Ka band (lower part of table). Although it is preferred to switch the polarizations between the uplink and the downlink on any one given satellite to provide better isolation, other configurations may be utilized with the same polarizations. Thus, FIG. 11 represents the dual satellite eight channel full configuration including both the uplink and downlink directed channels for the inbound path only. Referring to FIG. 12, a restoration mode is shown which occurs where one of the satellites is disabled and the remaining satellite must switch to single satellite channel configuration having two polarizations covering all four spot beam areas in each set. In this configuration, there are still two channels per spot beam color area in each orthogonal polarization in each direction as well as capacity for continuing to carry the multicast channel. The switching of the satellite as well as the various permutations in the configuration have been discussed above and need not be repeated with respect to FIG. 12 . Referring to FIG. 13, a detailed chart representing unequal allocation of spot beam capacity among different spot beam areas within a set is shown. For example, where one spot (e.g., that covering Washington D.C.) requires extra capacity, it may be possible to borrow capacity from the spot beam area covering Atlanta. As shown in FIG. 13, a channel from spot beam area B (VSAT spot No. 2 in FIG. 13 ) may be allocated to spot beam area C (VSAT spot No. 3 in FIG. 13 ). In this manner, it is possible to transfer inbound channel and one outbound channel in the Ku band from one spot beam area to another within the same set. In some embodiments, it may be desirable to transfer up to four channels in both directions from two spot beams to a third in the same set. As shown in FIGS. 14 and 15 , the color spot donation avoids any conflicts with adjacent sets. For example, while it is permissible to transfer channels from color spot A to color spot B in set 5 (see FIG. 14 ), it would not be permissible to transfer channels from color spot C to color spot B in set 5 (see FIG. 15 ). The reason for the limitation is that the transfer channel carries its original color and may not become adjacent to the same color due to the risk of interference. After channel donation, color spot B has 5 channels while color spot A has 3 channels in each direction. Referring to FIG. 16 , the channel donation and demand load balancing may be applied to all color spot locations by utilizing existing beam spread overlap so that adjacent color spots overlap. Thus, a user may be moved from one set to another or from one color spot to another to balance the load among the various spots in order to avoid high user concentrations in some spots. FIG. 17 illustrates the dramatic improvements in system capacity and cost savings achieved using embodiments of the present invention. As shown in FIG. 17 , the overall capacity of the system has increased more than 12 fold from 1 GHz to 12 GHz with little or no increase in cost of the overall system. This is due to the combination of several mechanisms including embodiments of the present invention. Thus, the use cost per subscriber may be reduced substantially. Thus, two-way VSAT service may for the first time be cost competitive with land lines even in well developed areas.