Patent Publication Number: US-7917135-B2

Title: Satellite communications apparatus and methods using asymmetrical forward and return link frequency reuse

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 11/458,754, filed Jul. 20, 2006, entitled Satellite Communications Apparatus and Methods Using Asymmetrical Forward and Return Link Frequency Reuse, and claims the benefit of U.S. Provisional Application Ser. No. 60/703,842, filed Jul. 29, 2005 entitled Satellite Communications Apparatus And Methods Using Asymmetrical Forward And Return Link Frequency Reuse, assigned to the assignee of the present application, the disclosures of both of which are hereby incorporated herein by reference in their entirety as if set forth fully herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to wireless communications systems and methods, and more particularly to satellite and terrestrial wireless communications systems and methods. 
     BACKGROUND OF THE INVENTION 
     Satellite radiotelephone communications systems and methods are widely used for radiotelephone communications. Satellite radiotelephone communications systems and methods generally employ at least one space-based component, such as one or more satellites, that is/are configured to wirelessly communicate with a plurality of satellite radiotelephones. 
     A satellite radiotelephone communications system or method may utilize a single satellite antenna pattern (beam or cell) covering an entire service region served by the system. Alternatively or in combination with the above, in cellular satellite radiotelephone communications systems and methods, multiple satellite antenna patterns (beams or cells) are provided, each of which can serve a substantially distinct service region in an overall service region, to collectively provide service to the overall service region. Thus, a cellular architecture that is similar to that used in conventional terrestrial cellular radiotelephone systems and methods can be implemented in cellular satellite-based systems and methods. The satellite typically communicates with radiotelephones over a bidirectional communications pathway, with radiotelephone communications signals being communicated from the satellite to the radiotelephone over a downlink or forward link (also referred to as forward service link), and from the radiotelephone to the satellite over an uplink or return link (also referred to as return service link). In some cases, such as, for example, in broadcasting, the satellite may communicate information to one or more radioterminals unidirectionally. 
     The overall design and operation of cellular satellite radiotelephone systems and methods are well known to those having skill in the art, and need not be described further herein. Moreover, as used herein, the term “radiotelephone” includes cellular and/or satellite radiotelephones with or without a multi-line display; Personal Communications System (PCS) terminals that may combine a radiotelephone with data processing, facsimile and/or data communications capabilities; Personal Digital Assistants (PDA) that can include a radio frequency transceiver and/or a pager, Internet/Intranet access, Web browser, organizer, calendar and/or a global positioning system (GPS) receiver; and/or conventional laptop and/or palmtop computers or other appliances, which include a radio frequency transceiver. A radiotelephone also may be referred to herein as a “radioterminal,” a “mobile terminal,” a “user device,” or simply as a “terminal”. As used herein, the term(s) “radioterminal,” “radiotelephone,” mobile terminal,” “user device” and/or “terminal” also include(s) any other radiating user device, equipment and/or source that may have time-varying or fixed geographic coordinates and/or may be portable, transportable, installed in a vehicle (aeronautical, maritime, or land-based) and/or situated and/or configured to operate locally and/or in a distributed fashion over one or more terrestrial and/or extra-terrestrial location(s). Furthermore, as used herein, the term “space-based component” or “space-based system” includes one or more satellites at any orbit (geostationary, substantially geostationary, medium earth orbit, low earth orbit, etc.) and/or one or more other objects and/or platforms (e.g., airplanes, balloons, unmanned vehicles, space crafts, missiles, etc.) that has/have a trajectory above the earth at any altitude. 
     Terrestrial networks can enhance cellular satellite radiotelephone system availability, efficiency and/or economic viability by terrestrially using/reusing at least some of the frequencies that are allocated to cellular satellite radiotelephone systems. In particular, it is known that it may be difficult for cellular satellite radiotelephone systems to reliably serve densely populated areas, because satellite signals may be blocked by high-rise structures and/or may not penetrate into buildings. As a result, satellite spectrum may be underutilized or unutilized in such areas. The terrestrial use/reuse of at least some of the satellite system frequencies can reduce or eliminate this potential problem. 
     Moreover, the capacity of an overall hybrid system, comprising space-based (i.e., satellite) and terrestrial communications capability, may be increased by the introduction of terrestrial frequency use/reuse of frequencies authorized for use by the space-based component, since terrestrial frequency use/reuse may be much denser than that of a satellite-only system. In fact, capacity may be enhanced where it may be mostly needed, i.e., in densely populated urban/industrial/commercial areas. As a result, the overall system may become more economically viable, as it may be able to serve more effectively and reliably a larger subscriber base. 
     One example of terrestrial reuse of satellite frequencies is described in U.S. Pat. No. 5,937,332 to inventor Karabinis entitled Satellite Telecommunications Repeaters and Retransmission Methods, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein. As described therein, satellite telecommunications repeaters are provided which receive, amplify, and locally retransmit the downlink/uplink signal received from a satellite/radioterminal thereby increasing an effective downlink/uplink margin in the vicinity of the satellite telecommunications repeater and allowing an increase in the penetration of uplink and downlink signals into buildings, foliage, transportation vehicles, and other objects which can reduce link margin. Both portable and non-portable repeaters are provided. See the abstract of U.S. Pat. No. 5,937,332. Satellite radiotelephones for a satellite radiotelephone system or method having a terrestrial communications capability by terrestrially using/reusing at least some frequencies of a satellite frequency band and using substantially the same air interface for both terrestrial and satellite communications may be more cost effective and/or aesthetically appealing compared to other alternatives. Conventional dual band/dual mode radiotelephone alternatives, such as the well known Thuraya, Iridium and/or Globalstar dual mode satellite/terrestrial radiotelephones, duplicate some components (as a result of the different frequency bands and/or air interface protocols between satellite and terrestrial communications), which leads to increased cost, size and/or weight of the radiotelephone. See U.S. Pat. No. 6,052,560 to inventor Karabinis, entitled Satellite System Utilizing a Plurality of Air Interface Standards and Method Employing Same. 
     Satellite radioterminal communications systems and methods that may employ terrestrial use and/or reuse of satellite frequencies by an Ancillary Terrestrial Network (ATN) comprising at least one Ancillary Terrestrial Component (ATC) are also described in U.S. Pat. No. 6,684,057 to Karabinis, entitled Systems and Methods for Terrestrial Reuse of Cellular Satellite Frequency Spectrum; U.S. Pat. No. 6,785,543 to Karabinis, entitled Filters for Combined Radiotelephone/GPS Terminals; U.S. Pat. No. 6,856,787 to Karabinis, entitled Wireless Communications Systems and Methods Using Satellite-Linked Remote Terminal Interface Subsystems; U.S. Pat. No. 6,859,652 to Karabinis et al., entitled Integrated or Autonomous System and Method of Satellite-Terrestrial Frequency Reuse Using Signal Attenuation and/or Blockage Dynamic Assignment of Frequencies and/or Hysteresis; and U.S. Pat. No. 6,879,829 to Dutta et al., entitled Systems and Methods for Handover Between Space Based and Terrestrial Radioterminal Communications, and For Monitoring Terrestrially Reused Satellite Frequencies At a Radioterminal to Reduce Potential Interference, and in U.S. Pat. Nos. 6,892,068, 6,937,857, 6,999,720 and 7,006,789; and Published U.S. Patent Application Nos. US 2003/0054761 to Karabinis, entitled Spatial Guardbands for Terrestrial Reuse of Satellite Frequencies; US 2003/0054814 to Karabinis et al., entitled Systems and Methods for Monitoring Terrestrially Reused Satellite Frequencies to Reduce Potential Interference; US 2003/0073436 to Karabinis et al., entitled Additional Systems and Methods for Monitoring Terrestrially Reused Satellite Frequencies to Reduce Potential Interference; US 2003/0054762 to Karabinis, entitled Multi-Band/Multi-Mode Satellite Radiotelephone Communications Systems and Methods; US 2002/0041575 to Karabinis et al., entitled Coordinated Satellite-Terrestrial Frequency Reuse; US 2003/0068978 to Karabinis et al., entitled Space-Based Network Architectures for Satellite Radiotelephone Systems; US 2003/0153308 to Karabinis, entitled Staggered Sectorization for Terrestrial Reuse of Satellite Frequencies; and US 2003/0054815 to Karabinis, entitled Methods and Systems for Modifying Satellite Antenna Cell Patterns In Response to Terrestrial Reuse of Satellite Frequencies, and in Published U.S. Patent Application Nos. 2004/0121727, 2004/0142660, 2004/0192395, 2004/0192200, 2004/0192293, 2004/0203742, 2004/0240525, 2005/0026606, 2005/0037749, 2005/0041619, 2005/0064813, 2005/0079816, 2005/0090256, 2005/0118948, 2005/0136836, 2005/0164700, 2005/0164701, 2005/0170834, 2005/0181786, 2005/0201449, 2005/0208890, 2005/0221757, 2005/0227618, 2005/0239457, 2005/0239403, 2005/0239404, 2005/0239399, 2005/0245192, 2005/0260984, 2005/0260947, 2005/0265273, 2005/00272369, 2005/0282542, 2005/0288011, 2006/0040613, 2006/040657 and 2006/0040659; all of which are assigned to the assignee of the present invention, the disclosures of all of which are hereby incorporated herein by reference in their entirety as if set forth fully herein. 
     SUMMARY OF THE INVENTION 
     Some embodiments of the present invention provide methods of operating wireless communications systems. In some embodiments, communications are conducted between a space-based component of the wireless communications system and radioterminals using a plurality of forward link cells and a plurality of return link cells, the return link cells having a greater number of cells per frequency reuse cluster than the forward link cells. Forward links of the forward link cells may have a greater link bandwidth than return links of the return link cells. 
     In some embodiments of the present invention, at least some of the forward and return link cells use at least some frequencies of a terrestrial wireless communications system having an adjacent and/or overlapping coverage area. Forward links of the at least some of the forward and return link cells may have a greater link bandwidth than return links of the at least some of the forward and return link cells. Service links of the terrestrial wireless communications system using forward link frequencies of the at least some of the forward and return link cells may have substantially the same link bandwidth as forward links of the at least some of the forward and return link cells using the forward link frequencies, and service links of the terrestrial wireless communications system using return link frequencies of the at least some of the forward and return link cells may have substantially the same link bandwidth as return links of the at least some of the forward and return link cells using the return link frequencies. 
     Communications on forward and return links of the at least some of the forward and return link cells may be frequency-division duplexed and communications on service links of the terrestrial wireless communications system may be time-division duplexed. Communications on service links of the terrestrial wireless communications system may be orthogonal frequency division multiplexed. 
     In some embodiments, the space-based component and radioterminals may communicate using a first air interface protocol, and the terrestrial wireless communications system and radioterminals may communicate using a second air interface protocol substantially different than the first air interface protocol. In some embodiments, the space-based component and the terrestrial wireless communications system may communicate with radioterminals using substantially the same air interface protocol. For example, the space-based component and radioterminals may communicate using a time division multiplexed (TDM) air interface protocol, a time division multiple access (TDMA) air interface protocol, a code division multiplexed (CDM) air interface protocol, a code division multiple access (CDMA) air interface protocol, an orthogonal frequency division multiplexed (OFDM) air interface protocol, and/or an orthogonal frequency division multiple access (OFDMA) air interface protocol, and the terrestrial wireless communications system and radioterminal may communicate using a time division multiplexed (TDM) air interface protocol, a time division multiple access (TDMA) air interface protocol, a code division multiplexed (CDM) air interface protocol, a code division multiple access (CDMA) air interface protocol, an orthogonal frequency division multiplexed (OFDM) air interface protocol, and/or an orthogonal frequency division multiple access (OFDMA) air interface protocol. 
     According to further aspects of the present invention, transmissions of radiators of the terrestrial wireless communications system located proximate a boundary of the coverage area of the terrestrial wireless communications system may be directed away from a portion of a coverage area of the space-based component outside of the coverage area of the terrestrial wireless communications system. For example, transmissions of the radiators of the terrestrial wireless communications system located proximate the boundary of the coverage area of the terrestrial wireless communications system may directed toward an inner portion of the coverage area of the terrestrial wireless communications system. 
     According to additional aspects, multiple ones of the return link cells overlap a single one of the forward link cells. For example, the forward link cells may have a unity frequency reuse cluster size and the return link cells may have a frequency reuse cluster size greater than one. In some embodiments, respective frequency reuse clusters for the return link cells may be substantially spatially coextensive with respective ones of the forward link cells. 
     In additional embodiments of the present invention, a wireless communications system includes a space-based component configured to communicate with radioterminals using a plurality of forward link cells and a plurality of return link cells, the return link cells having a greater number of cells per frequency reuse cluster than the forward link cells. Forward links of the forward link cells may have a greater link bandwidth than return links of the return link cells. 
     In some embodiments, at least some of the forward and return link cells use at least some frequencies of a terrestrial wireless communications system having an adjacent and/or overlapping coverage area. Forward links of the at least some of forward and return link cells may have a greater link bandwidth than return links of the at least some of the forward and return link cells. Service links of the terrestrial wireless communications system using forward link frequencies of the at least some of the forward and return link cells may have substantially the same link bandwidth as forward links of the at least some of the forward and return link cells using the forward link frequencies, and service links of the terrestrial wireless communications system using return link frequencies of the at least some of the forward and return link cells may have substantially the same link bandwidth as return links of the at least some of the forward and return link cells using the return link frequencies. 
     In further embodiments, a wireless communications system includes a space-based component configured to communicate with radioterminals using a plurality of forward link cells and a plurality of return link cells, the return link cells having a greater number of cells per frequency reuse cluster than the forward link cells, and an ancillary terrestrial component adjacent and/or overlapped by at least some of the forward link cells and the return link cells and configured to communicate with radioterminals using at least some frequencies used by the at least some of the forward and return link cells. 
     Additional embodiments of the present invention provide a terrestrial wireless communications system including at least one station configured to communicate with radioterminals in a coverage area adjacent and/or overlapped by forward link cells and return link cells served by a space-based component of a wireless communication system. The return link cells have a greater number of cells per frequency reuse cluster than the forward link cells and the at least one station is configured to use at least some frequencies used by the forward and return link cells. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating wireless communications systems and methods according to some embodiments of the present invention. 
         FIG. 2  is a schematic diagram illustrating an example of a forward and return link cell reuse pattern according to further embodiments of the present invention. 
         FIG. 3  is a schematic diagram illustrating an example of a link bandwidth assignment according to further embodiments of the present invention. 
         FIG. 4  is a schematic diagram illustrating directed transmission from peripheral radiators of terrestrial wireless communications system according to some embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Specific exemplary embodiments of the invention now will be described with reference to the accompanying drawing. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. Furthermore, “connected” or “coupled” as used herein may include wirelessly connected or coupled. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms “includes,” “comprises,” “including” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     It will be understood that although the terms first and second are used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. Thus, a first radioterminal below could be termed a second radioterminal, and similarly, a second radioterminal may be termed a first radioterminal without departing from the teachings of the present invention. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. The symbol “/” is also used as a shorthand notation for “and/or”. 
       FIG. 1  illustrates a wireless communications system comprising a Space-Based Component (SBC)  110  and an Ancillary Terrestrial Component (ATC)  120 . The SBC  110  may comprise at least one satellite  112 , which may be a geo-stationary or substantially geo-stationary satellite. The at least one satellite  110  is configured to communicate with radioterminals  10  and may also be configured to communicate with at least one satellite gateway  130 . The ATC  120  may comprise at least one infrastructure element, e.g., one or more base stations  122 , each of which are configured to communicate with radioterminals  20 . It will be understood that although  FIG. 1  illustrates the ATC  120  as including five base stations  122 , a larger or smaller number of base stations may be provided. As shown, a service footprint  125  of the ATC  120  overlaps a service footprint  115  of the SBC  110 . It will be appreciated that, generally, service footprints of an SBC and ATC may be adjacent and/or overlapping, e.g., coextensive, partially overlapping or mutually exclusive. It will be further understood that the radioterminals  10 ,  20  may be single mode and/or dual-mode terminals, i.e., terminals that are configured to communicate with only one of the SBC  110  or the ATC  120  and/or terminals that are configured to communicate with both the SBC  110  and the ATC  120 . It will be understood that the space-based infrastructure and the terrestrial infrastructure shown in  FIG. 1  may be components (subsystems) of an integrated system or may be separate systems, e.g., a mobile satellite communications system having a coverage area adjacent to and/or overlapped by a terrestrial wireless communications system, which may be operated in coordination and/or independently and autonomously. 
     Referring to  FIGS. 1 and 2 , the SBC  110 , at least one satellite gateway  130  and/or other system element that is connected to the SBC  110  and/or the at least one satellite gateway  130  may be configured to form a plurality of forward service link beams (cells, or antenna patterns)  210  and a plurality of return service link beams (cells, or antenna patterns)  220  using respective pluralities of forward and return service link SBC antenna feed elements. The SBC  110  may be configured to provide forward service link communications to a first plurality of radioterminals that are geographically distributed over a plurality of SBC forward service link beams by using a first set of frequencies F 1  (at least some of which may be used by an adjacent and/or overlapping terrestrial wireless communications system) over each of the forward service link beams  210  to thereby provide immediate frequency reuse over the forward service link beams  210 , i.e., a reuse factor of one (1). The SBC  110  may be further configured to provide return service link communications to a second plurality of radioterminals that are geographically distributed over a plurality of the SBC return service link beams  220  by selectively using a second set of frequencies F 2 , e.g., frequency subsets F 2a , F 2b , F 2c  of the set F 2  (at least some of which may be used by an adjacent and/or overlapping terrestrial wireless communications system), to thereby provide frequency reuse that is based on a frequency reuse cell cluster size comprising more than one return service link beam  220 , i.e., a frequency reuse factor greater than one. Accordingly, in some embodiments of the invention, an SBC is configured to communicate with radioterminals using immediate forward service link frequency reuse and communicate with radioterminals using a return service link frequency reuse comprising a cell cluster size that contains more than one cell. 
     It will be understood that “selectively using” means selectively using the frequencies on a geographic basis and that, in some embodiments, the first and second plurality of radioterminals may be the same plurality of radioterminals. It will be further understood that the arrangement of beams  210 ,  220  shown in  FIG. 2  is provided for purposes of illustration, and that embodiments of the invention may use any of a number of different arrangements of forward and return link beams or cells. For example, the forward link and/or return link cells may have different footprint shapes/contours than those shown in  FIG. 2 . In some embodiments, at least some forward link beams (cells or antenna patterns) may have substantially similar geographic footprints and/or may be substantially geographically congruent with at least some return link beams (cells or antenna patterns).  FIG. 2  illustrates a three-cell cluster size for the return link beams  220 , but in other embodiments of the invention, greater or lesser cluster sizes may be used. It will also be understood that, while  FIG. 2  illustrates forward link cells  210  and return link cells that are aligned such that each return link cell  220  does not overlap more than one forward link cell  210 , in other embodiments of the invention, different alignments of forward and return link cells may be used, such as arrangements wherein return link cells overlap multiple forward link cells. 
     Embodiments of the invention may allow for higher forward service link (i.e., SBC to radioterminal(s)) data throughput by allowing the SBC to use, with a frequency reuse factor of one (1) (i.e., immediate frequency reuse), a maximum available frequency range and/or a maximum number of available carrier frequencies in forward link cells as needed and/or subject to at least one predetermined communications performance/service measure, such as, for example, a Bit Error Rate (BER), an interference level and/or a user profile, to thereby provide increased forward service link data throughput to one or more radioterminals while providing reduced inter-cell return service link interference by providing non-unity (non-immediate) frequency reuse among return link beams. Immediate frequency reuse on forward service links and non-immediate frequency reuse on return service links may not substantially reduce a capacity of the SBC compared to using an identical frequency reuse (immediate or non-immediate) on the forward and return service links. In some embodiments, immediate frequency reuse on forward service links and non-immediate frequency reuse on return service links may even increase a capacity of the SBC compared to using immediate frequency reuse on the forward and return service links, as interference to the ATC and/or the radioterminals communicating therewith due to the immediate downlink frequency reuse by the SBC may be kept to an acceptable level owing to the signal strength associated with an SBC forward link(s) being relatively small at or near the earth compared to a signal strength associated with the ATC. As shown, in  FIG. 4 , in order to reduce a level of interference to a radioterminal  10  that is receiving communications from the SBC in a coverage area  410  outside a geographic area  420  that is served by the ATC, at least some ATC infrastructure radiators  422  (i.e., base station antenna(s)), that may be proximate to a perimeter of the service area of the ATC, may provide attenuated radiation in directions that point substantially away from an inner location of the ATC coverage area. 
       FIG. 3  illustrates asymmetric forward and return link bandwidths that may be provided using asymmetric frequency reuse along the lines described above with reference to  FIG. 2  (symmetric forward and return link bandwidths may also be provided in some embodiments of the invention). An SBC  310  and an ATC  320  may be configured to use an Orthogonal Frequency Division Multiplexed (OFDM) and/or Orthogonal Frequency Division Multiple Access (OFDMA) air interface protocol to communicate with radioterminals. In some embodiments, the air interface protocol used on service links of the ATC  320  may be based on a Time Division Duplex (TDD) mode and the air interface protocol of the SBC  310  may be based on a Frequency Division Duplex (FDD) mode. In some embodiments, for example, the SBC  310  provides a 10 MHz forward link  313  and a 3.3 MHz return link  315  within the geographic area of a SBC cell (beam or antenna pattern) to thereby provide communications to one or more radioterminals and the ATC  320  provides a 10 MHz forward/return TDD service link  323  based on forward/return service link frequencies of the SBC and/or a 3.3 MHz forward/return TDD service link  325  based on forward/return service link frequencies of the SBC to thereby provide communications to one or more radioterminals within a service region of the ATC. 
     It will be understood that an SBC and ATC may use any of a number of different types of air interface protocols in various embodiments of the invention. An air interface protocol used by the SBC to communicate with radioterminals may be the same, substantially the same or different compared to an air interface protocol that is used by the ATC to communicate with radioterminals (i.e., the SBC may use a Time Division Multiplexed (TDM) and/or Time Division Multiple Access (TDMA) air interface protocol and the ATC may use a Code Division Multiplexed (CDM) and/or Code Division Multiple access (CDMA) air interface protocol or vice versa, for example). It will be further understood that the carrier bandwidths shown in  FIG. 3  are provided for illustrative purposes only, and that other carrier bandwidths may be used. 
     It will be appreciated that the apparatus and operations described above are illustrative examples, and that other architectures and operations fall within the scope of the present invention. More generally, in the drawings and specification, there have been disclosed exemplary embodiments of the invention. Although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being defined by the following claims.