Abstract:
Methods are provided for operating a mobile satellite telecommunications system, as is a system that operates in accordance with the methods. A first method has steps of providing at least one user terminal, at least one satellite in earth orbit and at least one gateway bidirectionally coupled to a data communications network and, responsive to applications, selecting with the user terminal individual ones of a plurality of Quality of Service (QoS) modes for servicing different application requirements. The method further includes communicating a request for a selected one of the QoS modes at least to the gateway. Another method operates in response to stored satellite ephemeris information for selecting a path through the satellite constellation to a destination gateway for routing a communication to or from the data communication network and the user terminal, and for transmitting a description of the selected path from the user terminal to at least one of the constellation of satellites. Another method operates so as to reduce an amount of information contained within a packet header after transmitting a first packet to at least one satellite of the constellation of satellites. Preferably the packet header of the first packet contains information that is descriptive of at least an identification of a source address and a destination address of the packet, and a connection identifier identifying a communication connection to which the packet belongs, whereas headers of subsequent packets of the communication connection contain only the connection identifier. The method further extracts and stores the information from the header of the first packet in the satellites, and routes subsequent packets based on the stored information and on the connection identifier. The method further expands the subsequently transmitted packet headers to contain the stored information prior to being transmitted to the data communication network.

Description:
CLAIM OF PRIORITY FROM COPENDING PROVISIONAL PATENT APPLICATION  
       [0001]    This application claims priority under 35 U.S.C. 119(e) and 120 from provisional patent application No. 60/201,111, filed on May 2, 2000, the disclosure of which is incorporated by reference herein in its entirety. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    These teachings relate generally to satellite-based communication systems and, more particularly, relate to non-geosynchronous orbit satellite communication systems, such as Low Earth Orbit (LEO) and Medium Earth Orbit (MEO) satellite communication systems.  
         BACKGROUND OF THE INVENTION  
         [0003]    In U.S. patent application Ser. No. 09/334,386, filed Jun. 16, 1999, entitled “ISP System Using Non-Geosynchronous Orbiting Satellites,” by Robert A. Wiedeman, there are disclosed embodiments of satellite-based communication systems that extend the Internet using non-geosynchronous orbit satellites. A user in a remote location can use the LEO constellation to access the Internet. The satellites in this system become part of the Internet and act as access points for User Terminals (UTs) in remote areas. This U.S. patent application is incorporated by reference in its entirety, insofar as it does not conflict with these teachings.  
           [0004]    In general, a UT may have the capability to use a circuit-switched or a packet-switched mode to connect to a device at the other end, either on the Public Switched Telephone Network (PSTN) or on the Public Data Network (PDN). However, due to various Quality of Service (QoS) requirements and constraints, one particular mode of operation may be better than another at a particular time. Other considerations also exist, such as a best path for routing a communication, and the conservation of system bandwidth to maximize system capacity and reduce cost.  
           [0005]    As such, a need exists to enable some type of UT selectivity, control and autonomy over the operational modes and other aspects of the communications of the UT during data transfer and other types of communication operations.  
         SUMMARY OF THE INVENTION  
         [0006]    The foregoing and other problems are overcome by methods and apparatus in accordance with embodiments of these teachings.  
           [0007]    In a first aspect of these teachings a method is provided for operating a mobile satellite telecommunications system, as is a system that operates in accordance with the method. The method has steps of providing at least one user terminal, at least one satellite in earth orbit and at least one gateway bidirectionally coupled to a data communications network and, responsive to applications, selecting with the user terminal individual ones of a plurality of Quality of Service (QoS) modes for servicing different application requirements. The method further includes communicating a request for a selected one of the QoS modes at least to the gateway, and in response allocating resources to accommodate the requested QoS mode. The method may select one of a circuit switched or a packet switched mode of operation with the user terminal. Preferably the user is billed a greater amount for use of a QoS of higher quality.  
           [0008]    The QoS modes include a Highest Quality of Service mode, a Medium Quality of Service mode, a Best Available Quality of Service mode, and a Guaranteed Data Rate Packet Data Service mode.  
           [0009]    In a further aspect of these teachings a method provides at least one user terminal, a constellation of satellites in earth orbit and at least one gateway bidirectionally coupled to a data communications network and, in response to at least stored satellite ephemeris information, selects a path through the satellite constellation to a destination gateway for routing a communication to or from the data communication network and the user terminal, and transmits a description of the selected path from the user terminal to at least one of the constellation of satellites. The selection of the path is further responsive to stored gateway location information for selecting the path through the satellite constellation to the destination gateway.  
           [0010]    In a further aspect of these teachings a method provides at least one user terminal, a constellation of satellites in earth orbit and at least one gateway bidirectionally coupled to a data communications network, and operates so as to reduce an amount of information contained within a packet header after transmitting a first packet to at least one satellite of the constellation of satellites. Preferably the packet header of the first packet contains information that is descriptive of at least an identification of a source address and a destination address of the packet, and a connection identifier identifying a communication connection to which the packet belongs. Headers of subsequent packets of the communication connection may contain only the connection identifier. The method further extracts and stores the information from the header of the first packet in the satellites, and routes subsequent packets based on the stored information and on the connection identifier. The method further expands the subsequently transmitted packet headers to contain the stored information prior to being transmitted to the data communication network. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The above set forth and other features of these teachings are made more apparent in the ensuing Detailed Description of the Preferred Embodiments when read in conjunction with the attached Drawings, wherein:  
         [0012]    [0012]FIG. 1 is a simplified block diagram of a mobile satellite telecommunications system (MSTS) that is suitable for practicing these teachings;  
         [0013]    [0013]FIG. 2 is a logical diagram of the UT of FIG. 1, showing the relationship between UT applications, an applications interface and an air interface; and  
         [0014]    [0014]FIG. 3 shows a first type of packet and a second type of packet, having a reduced header size, in accordance with an aspect of these teachings. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    Reference is made to FIG. 1 for illustrating a simplified block diagram of a digital wireless telecommunications system, embodied herein as a mobile satellite telecommunications system (MSTS)  1 , that is suitable for practicing these teachings. While described in the context of the MSTS  1 , those skilled in the art should appreciate that certain of these teachings may have application to terrestrial telecommunications systems as well.  
         [0016]    The MSTS  1  includes at least one, but typically many, wireless user terminals (UTs)  10 , at least one, but typically several, communications satellite  40 , and at least one, but typically several, communications ground stations or gateways  50 . In FIG. 1 three satellites are shown for convenience, with one being designated satellite  40 A, one satellite  40 B and one satellite  40 C, hereafter collectively referred to as satellite or satellites  40 . The satellites  40  preferably contain an on-board processor (OBP)  42  and an on-board memory (MEM)  43 . An Inter-Satellite Link (ISL)  44  is shown between satellites  40 A,  40 B and  40 C. The ISL  41  could be implemented using an RF link or an optical link, and is modulated with information that is transferred between the satellites  40 , as described in further detail below. More than three satellites  40  can be coupled together using ISLs  41 .  
         [0017]    Reference with regard to satellite-based communications systems can be had, by example, to U.S. Pat. No. 5,526,404, “Worldwide Satellite Telephone System and a Network Coordinating Gateway for Allocating Satellite and Terrestrial Resources”, by Robert A. Wiedeman and Paul A. Monte; to U.S. Pat. No. 5,303,286, “Wireless Telephone/ Satellite Roaming System”, by Robert A. Wiedeman; to U.S. Pat. No. 5,619,525, “Closed Loop Power Control for Low Earth Orbit Satellite Communications System, by Robert A. Wiedeman and Michael J. Sites; and to U.S. Pat. No. 5,896,558 “Interactive Fixed and Mobile Satellite Network”, by Robert A. Wiedeman, for teaching various embodiments of satellite communications systems, such as low earth orbit (LEO) satellite systems, that can benefit from these teachings. The disclosures of these various U.S. patents are incorporated by reference herein in their entireties, in so far as they do not conflict with the teachings of this invention.  
         [0018]    The exemplary UT  10  includes at least one antenna  12 , such as an omni-directional antenna or a directional antenna, for transmitting and receiving RF signals over service links  39 , and further includes an RF transmitter (TX)  14  and an RF receiver (RX)  16  having an output and an input, respectively, coupled to the antenna  12 . A controller  18 , which may include one or more microprocessors and associated memories  18   a  and support circuits, functions to control the overall operation of the UT  10 . An input speech transducer, typically a microphone  20 , may be provided to input a user&#39;s speech signals to the controller  18  through a suitable analog to digital (A/D) converter  22 . An output speech transducer, typically including a loudspeaker  26 , may be provided to output received speech signals from the controller  18 , via a suitable digital to analog (D/A) converter  24 . The UT  10  may also include some type of user interface (UI)  36  that is coupled to the controller  18 . The UI  36  can include a display  36 A and a keypad  36 B. The UT  10  may also be coupled with a computing device, such as a laptop computer or a PC  37 , and may thus function as a wireless modem for the PC  37 .  
         [0019]    A transmit path may include a desired type of voice coder (vocoder)  28  that receives a digital representation of the input speech signals from the controller  18 , and includes voice coder tables (VCT)  28   a  and other required support circuitry, as is well known in the art. The output of the vocoder  28 , which is a lower bit rate representation of the input digital speech signals or samples, is provided to a RF modulator (MOD)  30  for modulating a RF carrier, and the modulated RF carrier is upconverted to the transmission frequency and applied to the input to the RF transmitter amplifier  14 . Signaling information to be transmitted from the UT  10  is output from the controller  18  to a signaling path that bypasses the vocoder  28  for application directly to the modulator  30 . Not shown or further discussed is the framing of the transmitted signal for a TDMA type system, or the spreading of the transmitted signal for a CDMA type system, since these operations are not germane to an understanding of this invention. Other operations can also be performed on the transmitted signal, such as Doppler precorrection, interleaving and other well known operations.  
         [0020]    A receive path may include the corresponding type of voice decoder  34  that receives a digital representation of a received speech signal from a corresponding type of demodulator (DEMOD)  32 . The voice decoder  34  includes voice decoder tables (VDT)  34   a  and other required support circuitry, also as is well known in the art. The output of the voice decoder  34  is provided to the controller  18  for audio processing, and is thence sent to the D/A converter  24  and the loudspeaker  26  for producing an audible voice signal for the user. As with the transmitter path, other operations can be performed on the received signal, such as Doppler correction, de-interleaving, and other well known operations. In a manner analogous to the transmit path, received signaling information is input to the controller  18  from a signaling path that bypasses the voice decoder  34  from the demodulator  32 .  
         [0021]    It is pointed out that the above-mentioned voice and audio capability is not required to practice these teachings, as the UT  10  may operate solely as a data communications device. In this mode of operation the vocoder(s) may simply be bypassed, and the data signals modulated/demodulated, interleaved/deinterleaved, etc. In a data-only application the UT  10  may be constructed so as not to include any analog voice capability at all. Furthermore, in a data-only application the user interface  36  may not be required, particularly if the UT  10  is wholly or partially embedded within another device, such as the PC  37 .  
         [0022]    The RF signals transmitted from the UT  10  and those received by the UT  10  over the service links  39  pass through at least one satellite  40 , which may be in any suitable altitude and orbital configuration (e.g., circular, elliptical, equatorial, polar, etc.) In the preferred embodiment the satellite  40  is one of a constellation of non-geosynchronous orbit (non-GEO) satellites, preferably Low Earth Orbit (LEO) satellites, although one or more Medium Earth Orbit (MEO) satellites could be used as well, as could one or more geosynchronous orbit satellites in conjunction with LEO or MEO satellites. In the preferred embodiment the satellite  40  has the on-board processor (OBP)  42 , wherein a received transmission is at least partially demodulated to baseband, processed on the satellite  40 , re-modulated and then transmitted. As will be discussed below, in accordance with an aspect of these teachings the on-board processing conducted by the satellite  40  includes routing a received packet based on stored route information selected by the UT  10 .  
         [0023]    The satellite  40  serves to bidirectionally couple the UT  10  to the gateway  50 . The gateway  50  includes a suitable RF antenna  52 , such as steerable parabolic antenna, for transmitting and receiving a feederlink  45  with the satellite  40 . The feederlink  45  will typically include communication signals for a number of UTs  10 . The gateway  50  further includes a transceiver, comprised of transmitters  54  and receivers  56 , and a gateway controller  58  that is bidirectionally coupled to a gateway interface (GWI)  60 . The GWI  60  provides connections to a Ground Data Network (GDN)  62  through which the gateway  50  communicates with a ground operations control center (not shown) and possibly other gateways. The GWI  60  also provides connections to one or more terrestrial telephone and data communications networks  64 , such as the PSTN. PLMN, and/or PDN, whereby the UT  10  can be connected to any wired or wireless telephone, or to another UT, through the terrestrial telecommunications network. In accordance with an aspect of these teachings the gateway  50  provides an ability to reach the Internet  70 , which provides access to various servers  72 . The gateway  50  also includes banks of modulators, demodulators, voice coders and decoders, as well as other well known types of equipment, which are not shown to simplify the drawing.  
         [0024]    Having thus described one suitable but not limiting embodiment of a mobile satellite telecommunications system that can be used to practice these teachings, a description of the preferred embodiments of these teachings will now be a provided.  
         [0025]    These teachings add the following capabilities to the UT  10 :  
         [0026]    1. a capability to define the QoS required based on the application;  
         [0027]    2. a capability to request a QoS from the air-interface;  
         [0028]    3. a capability to define a path (within the satellite system) to the destination; and  
         [0029]    4. a capability to minimize overhead by reducing header lengths of packets once the connection is established.  
         [0030]    There are potentially at least two types of communication possible.  
         [0031]    Circuit Switched Communication:  
         [0032]    In this type of communication, the UT  10  typically requests a circuit. The circuit may be established between two UT&#39;s or between a UT  10  and some device on a terrestrial voice network (such as the PSTN or the Public Land Mobile Network (PLMN) or on a terrestrial data network (such as the Internet). When the UT  10  makes a request for the circuit, the UT  10  typically also requests some parameters associated with the circuit. Bandwidth of the transfer is one such parameter. When a circuit is granted to the UT  10 , typically a physical channel or path for the transfer is also defined for a period of time.  
         [0033]    Packet Switched Connection:  
         [0034]    The other type of communication is achieved by packet-switching, in which no physical channel is assigned to the UT  10 . Instead, the UT  10  transmits a packet with a destination address for the packet. A satellite  40  receives the packet and decides the next hop based on the destination address, thereby routing the packet. No path is set-up for this type of communication, as the actual path from the UT  10  to the destination can change packet by packet.  
         [0035]    A first aspect of these teachings relates to a UT  10  having a capability to define the QoS.  
         [0036]    In the MSTS  1 , as discussed above, there are the UTs  10 , satellites  40 , gateways  50 , and public/private voice and/or data networks. In a UT  10  originated call, the UT  10  is the entity has knowledge of the application and the application&#39;s requirements. The satellites  40 , the gateway  50  and other nodes in the PSTN  64  or PLMN provide bandwidth and other resources to facilitate this communication. Since the UT  10  knows the application&#39;s requirements, these teachings enable the UT  10  to make the QOS decision.  
         [0037]    The are a variety of QoS modes, examples of which are as follows.  
         [0038]    Highest Quality of Service:  
         [0039]    For voice or data calls, the highest quality may mean that the UT  10  requires a certain data-rate from the circuit established between the UT  10  and the destination. The UT  10  is enabled to define the minimum data-rate that is acceptable to service the application. The amount charged for this type of service will typically be greater than for other services. An example application for this type of service is the real-time transfer of multi-media contents between the UT  10  and the other party to the communication.  
         [0040]    Medium Quality of Service:  
         [0041]    The applications served by this QoS may still use the circuit switched mechanism in the UT  10 . However, the UT  10  may not have the ability to specify the bandwidth requirement. The UT  10  in this case determines the bandwidth based on the current system state. An example of this application is be a typical voice communication application.  
         [0042]    Best Available Quality of Service:  
         [0043]    This service may not establish a circuit at all, and communication is preferably achieved in the packet switched mode. The UT  10  and the satellites  40 , with on-board processing capability, make all routing decisions based on the destination address in each individual packet.  
         [0044]    Guaranteed Data Rate Packet Data Service:  
         [0045]    In this service, although packet switching is used for the communication between the UT  10  and the destination, the path may be defined for packet streams for a period of time, and bandwidth reserved by the satellite  40  on-board processors  42  for the packet streams.  
         [0046]    Referring to FIG. 2, the UT  10  includes an air interface  100  through which data is sent back and forth to the gateway  40  over the service links  39 . The UT  10  also has an application interface  102  through which data is sent back and forth to applications  104 . Examples of typical applications  104  are ftp, http, voice, etc. The UT  10  also has the capability to determine which application  104  is being used. The UT  10  may achieve this by examining the packets that are received by the application interface  102 , and an algorithm in UT  10  uses this information to determine what quality of service (QoS) should be provided to serve the application  104 . Once the UT  10  decides the QoS that the application  104  should receive, the UT  10  negotiates with the gateway  50  for the QoS during the call establishment procedure, using predefined signaling messages and protocols sent over the service links  39 .  
         [0047]    The QoS algorithm run by the UT  10  may be as simple or as complex as desired. For example, the QoS algorithm may maintain a look-up table (LUT) that associates each application  104  with a predetermined QoS. Through the UI  36  the user may request a particular QoS, thereby overriding the UT  10  determined QoS. The QoS may also be a function of the amount of data to be transferred, or of a file extension appended to the data file to be transferred, or may be based on the destination address, where certain destination addresses (e.g., certain servers  72 ) are predetermined to use a certain QoS, while other destination addresses use a different QoS, etc.  
         [0048]    A second aspect of these teachings relates to a UT  10  having a capability to request a QoS from the air-interface  100 .  
         [0049]    The components involved in the operation of the air interface include the UT  10 , the gateway  50 , as well as the number of satellites  40  between the UT  10  and the gateway  50 . When a UT  10  requests a resource, such as bandwidth, a resource allocation protocol (such as RSVP, being developed by IETF, described in IETF RFP  2205 ) may be used to guarantee the availability of that resource on all the components in the air interface.  
         [0050]    For example, assume that the UT  10  requests a bandwidth of X bits/second between its antenna  12  and the PSTN  64  for a particular period of time. The satellite  40  on-board processor  42  and the gateway controller  58  may in this case communicate over a signaling channel so as to reserve sufficient satellite and gateway resources and capacity between themselves to guarantee that the UT  10  bandwidth request will be met.  
         [0051]    A third aspect of these teachings relates to a UT  10  having a capability to define a path (within the MSTS  1 ) to the destination.  
         [0052]    In this regard it can be appreciated that the gateway  50 , the moving non-GEO satellites  40 , and all of the active UTs  10  essentially form a routing network. All of the nodes in the network require a capability to communicate with other nodes. In satellite systems with on-board routing capability, the satellites employ a routing algorithm and ephemeris data of the moving satellite constellation to route the packets and close the circuits. In this case the satellites may have the inter-satellite links (ISLs)  41  for providing communication RF or IR paths between satellites in space, thereby enabling a packet to be routed from one satellite to another until the packet is finally downlinked to either the UT  10  or to the gateway  50 .  
         [0053]    However, having the satellites execute the routing algorithm and route the packets can be expensive. The routing algorithm on the satellites may also demand a large amount of memory  43  usage by the satellite on-board processor  42 .  
         [0054]    To avoid these problems, and referring again to FIG. 1, the UT  10  has the capability to set up connections and route the packets. In this aspect of these teachings the memory  18 A, or an external memory that is accessible to the UT  10 , stores the ephemeris data (ED) of the moving satellite constellation. The memory  18 A also stores information that specifies the locations of the gateways  50  (GWL), including the location of the gateway that the UT  10  is attempting to reach. With this information, and using a routing algorithm (RA) also stored in the memory  18 A, the controller  18  of the UT  10  is enabled to define a path through one or more satellites  40  to the gateway  50  that the UT  10  desires to access. Once a UT  10  has determined the path as defined by the nodes in the path (e.g, satellite  40 A to satellite  40 B to satellite  40 C to gateway X, it establishes a circuit to the desired gateway by transmitting pathing or routing-related information to the satellites  40 , defining which satellite(s)  40  are to participate in the path between the UT  10  and the desired gateway. In this manner the UT  10  essentially establishes a circuit in space between itself and a desired terrestrial termination point for the communication.  
         [0055]    Note that it is within the scope of these teachings to store the ephemeris data, gateway location data and the routing algorithm in the attached PC  37 , to execute the routing algorithm in the PC  37 , and to transmit the selected route to the satellite or satellites  40  using the UT  10  service links  39 .  
         [0056]    Note should also be made that due to movement of the satellites  40  during the communication, it may be necessary to re-specify the participant satellites of the path, either initially or during the communication.  
         [0057]    A fourth aspect of these teachings relates to a UT  10  having a capability to minimize communication overhead by reducing header lengths of the packets once a connection is established.  
         [0058]    Whenever a UT  10  has a well-defined path to the destination, whether the path is determined by the UT  10  or by another router or routers, the UT  10  has the ability to establish the path for the duration of the connection. The satellites  40  in the path recognize the path as belonging to this particular UT  10  connection. The packet headers may then have a “connection identifier” field to identify this connection. This connection identifier field, after the first packet is sent, may then be used to also define the source address, the destination address, the type of connection, the service type, etc. Referring also to FIG. 3, after the UT  10  sends the first packet to the destination successfully (as verified by an acknowledgment, or less preferably by a lack of a non-acknowledgment) for a particular connection, the UT  10  is enabled to reduce the header information substantially by eliminating certain information. The UT  10  may eliminate all of the header information from subsequent packets except for the connection identifier (ID) field, which is used by all the satellites  40  along the defined path to identify the connection and to forward the packets (with reduced headers) appropriately. In this case the packet payload portion may remain the same length or, if desired, the payload portion may be increased by an amount that corresponds to the reduction in the size of the packet header.  
         [0059]    The operation of the MSTS  1  with the connection identifier packet header field can be described as follows. When the UT  10  sends the first packet for the connection to the destination, it includes the connection identifier in the packet. The satellites  40  along the path note and store the header information, along with the connection identifier. In particular, the satellite on-board processors form tables that define the destination points for the connection identifiers. When the UT  10  (or a sender) receives an acknowledgment from the destination, the UT  10  knows that all of the satellites  40  have their tables formed correctly. At this time the UT  10  may eliminate certain fields from the packet header (e.g., one or more, or all, of the source address, the destination address, the type of connection, the service type fields, etc.), with the exception of the connection identifier field. A flag may also be set in the header to identify it to the satellites  40  as being a reduced or minimized packet header. The satellites  40  then use the connection identifier information to route each of the packets to appropriate ports for ISL  41  transmissions, if required, and to eventually downlink the packets to the desired gateway  50 .  
         [0060]    Note that the desired gateway  50  also received the original packet header, and preferably stored the information such as the source address, destination address, etc. As such, upon the receipt of the subsequent packets with minimized headers, the gateway  50  is enabled to add back into the packet header that information that was removed by the UT  10  before forwarding the packets on to the terrestrial communication system, such as the Internet. In this manner the packets with minimized headers are made fully compliant with the terrestrial packet transfer protocol in use, such as TCP/IP. Note that this function could as well be performed by one of the satellites  40 , preferably the last satellite in the path before the packets are downlinked to the gateway  50 .  
         [0061]    The reduction in header size has at least two benefits. First, because the satellites  40  are not required to read all of the header information, the processing time at each satellite  40  is reduced, as the satellites  40  can determine the destination based solely on the connection identifier field in the header. Second, after reducing the header there are fewer bits that are required to be sent from the source to the destination. This results in a reduction in the required bandwidth which, in a satellite communication system, is a valuable resource.  
         [0062]    It can thus be appreciated that this aspect of these teachings increases the overall capacity of the MSTS  1 , as some percentage of each data packet, when transmitted with the minimized or reduced header information, is not required to be sent over the air interface.  
         [0063]    While these teachings have been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that changes in form and details may be made therein without departing from the scope and spirit of these teachings.