Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/14—Relay systems
  • H04B7/15—Active relay systems
  • H04B7/185—Space-based or airborne stations; Stations for satellite systems
  • H04B7/19—Earth-synchronous stations
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/14—Relay systems
  • H04B7/15—Active relay systems
  • H04B7/185—Space-based or airborne stations; Stations for satellite systems
  • H04B7/1853—Satellite systems for providing telephony service to a mobile station, i.e. mobile satellite service
  • H04B7/18532—Arrangements for managing transmission, i.e. for transporting data or a signalling message
  • H04B7/18534—Arrangements for managing transmission, i.e. for transporting data or a signalling message for enhancing link reliablility, e.g. satellites diversity
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/14—Relay systems
  • H04B7/15—Active relay systems
  • H04B7/204—Multiple access
  • H04B7/212—Time-division multiple access [TDMA]
  • H04B7/2125—Synchronisation
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
  • Y02D30/00—Reducing energy consumption in communication networks
  • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

Definitions

• This invention is related to co-filed application Serial No. to the present inventors, entitled Timing Systems and Methods for Forward Link Diversity in Satellite Radiotelephone Systems and assigned to the assignee of the present invention (Attorney Docket 8194-379), the disclosure of which is hereby incorporated herein by reference.
• This invention relates to radiotelephone systems and methods, and more particularly to satellite radiotelephone systems and methods.
• Satellite radiotelephone systems are being developed and deployed at many locations around the world.
• a satellite radiotelephone system generally includes at least one satellite and at least one gateway that interfaces the satellite radiotelephone system to other telephone systems, such as wire telephone systems and/or cellular radiotelephone systems.
• a plurality of user terminals communicate with the at least one satellite, to provide satellite communications.
• the user terminals may be mobile or fixed. It will be understood that the user terminal may be a satellite radiotelephone, a combined cellular and satellite radiotelephone, a high functionality terminal including Personal
• PCS Communications Systems
• satellite radiotelephone modem a satellite radiotelephone system
• the basic principles regarding a satellite radiotelephone system are described in the publication entitled Dual-Mode Cellular/Satellite Hand- Held Phone Technology by coinventor Karabinis et al, WESCON/96, pp. 206-222, October 22, 1996, and need not be described in further detail herein.
• a user terminal can communicate with more than one satellite Accordingly, satellite diversity may be provided so that the user terminal communicates with two satellites, to thereby allow reduced shadowing and/or blockage problems
• uplink or return link signal bursts such as uplink Time Division Multiple Access (TDMA) bursts
• TDMA Time Division Multiple Access
• a gam of 3dB in signal to noise ratio is obtainable when two satellites receive the same burst of equal quality and relay it to the ground station
• significant statistical benefits in link quality may be obtained Improved reception of the uplink signal bursts by the satellites and/or reduced power consumption by the transmitter of the
• the present invention can provide systems, methods, user terminals and satellites in which a single uplink or return link signal burst from a user terminal in an uplink region of a satellite radiotelephone system is received dunng an uplink signal frame at two or more visible satellites in the uplink region
• the single received signal burst from the user terminal that is received at the two or more visible satellites is diversity combined
• the two or more satellites preferably receive a single uplink signal burst from a plurality of, and preferably all of, the user terminals in the uplink region dunng the uplink signal frame without time overlap, so that diversity combining can be performed
• all of the visible satellites in the uplink region receive a single uplink signal burst from each of the user terminals in the uplink region during the uphnk signal frame without time overlap, so that diversity combining using all of the visible satellites in the uplink region may be obtained
• Improved reception of uplink signal bursts and/or reduced power consumption in the user terminals thereby may be obtained
• Vanable guard times may be incorporated, according to the present invention, between adjacent uplink signal bursts that are transmitted from the user terminals located m the same uplmk region and using the same uphnk earner frequency
• the vanable guard time preferably corresponds to a time of arnval difference between adjacent in time uplink signal bursts from the corresponding pair of user terminals to one of the visible satellites, preferably the visible satellite having lowest elevation angle or a real or fictitious satellite at the honzon
• a guard time may be computed between each pair of adjacent uplink signal bursts based on the actual position in the uplink region ot the corresponding pair of user terminals
• Improved efficiency thereby may be obtained compared to a fixed guard time, because the guard time between each pair of adjacent signal bursts may be based on the actual position of the user terminal rather than a worst case separation.
• Increased complexity may be produced however, because the guard time may need to be computed and separately transmitted to each user terminal and may change as the
• signal bursts from user terminals in an uplink region may be received at two or more, preferably all, of the visible satellites in the uplink region.
• the satellite radiotelephone system preferably can utilize all of the transmitted signal bursts from the user terminals, to allow improved reception by the radiotelephone system and/or reduced power consumption by the user terminals.
• Satellite user terminals include a transmitter that transmits an uplink signal burst for reception by a plurality of satellites that receive transmissions from an uplink region in which the user terminal is located.
• the uplink signal is transmitted a guard time after an immediately preceding uplink signal burst from another user terminal in the uplink region.
• the guard time is based upon a time of arrival difference for the adjacent uplink signal bursts to one of the plurality of visible satellites, for example having lowest elevation angle or a real or fictitious satellite at the horizon.
• the satellite user terminals also may include a user interface that receives user inputs including voice and/or data and provides the user inputs to the transmitter for transmission.
• Satellite user terminals may use a fixed guard time that corresponds to maximum time of arrival difference between adjacent uplink signal bursts from a pair of user terminals that are a maximum distance apart in the uplink region, to one of the plurality of visible satellites, preferably the visible satellite having lowest elevation angle or a real or fictitious satellite at the horizon.
• satellite user terminals may use a variable guard time that corresponds to a time of arrival difference between adjacent uplink signal bursts from the user terminal and another user terminal, to one of the plurality of visible satellites, preferably a visible satellite having lowest elevation angle or a real or fictitious satellite at the horizon.
• the uplink or return signal bursts and downlink or forward signal bursts are communicated in a plurality of repeating uplink and downlink burst frames.
• two downlink signal bursts are received from two satellites in a downlink burst frame. More preferably, the two downlink signal bursts arrive at the center of the downlink region one half a downlink burst frame apart.
• a first downlink signal burst is received from a first one of the visible satellites at a first carrier frequency
• a second downlink signal burst is received from a second one of the visible satellites at a second carrier frequency, during a single downlink signal burst frame.
• a first downlink signal burst is received from a first one of the visible satellites at a first carrier frequency
• a second downlink signal burst is received from a second one of the visible satellites at the first carrier frequency, during a single downlink signal burst frame.
• Figure 1A is an overall block diagram of satellite radiotelephone systems and methods according to the present invention.
• Figure IB is a timing diagram of transmitted and received signal bursts for satellite radiotelephone systems and methods of Figure 1 A.
• FIGS 2A and 2B conceptually illustrate calculation of guard times according to the present invention.
• Figure 3 is a timing diagram that illustrates integration of downlink and uplink timing according to the present invention.
• Figures 4A and 4B are timing diagrams that illustrate alternate embodiments of forward link burst timing according to the present invention.
• Figure 5 illustrates preferred embodiments of the present invention for an eighth rate GSM mode satellite radiotelephone system.
• the present invention may be embodied as methods and/or devices.
• the present invention may take the form of an entirely hardware embodiment or an embodiment combining software and hardware aspects.
• blocks of the drawings support combinations of means for performing the specified functions, combinations of steps for performing the specified functions and computer program instruction means for performing the specified functions. It will also be understood that each block, and combinations of blocks, can be implemented by special purpose hardware-based systems which perform the specified functions or steps, or by combinations of special purpose hardware and computer instructions.
• a satellite radiotelephone communications system 100 such as a LEO or MEO satellite radiotelephone communications system, includes a plurality of visible satellites HOa-l lOn that receive transmissions from a plurality of user terminals 120a-120m in an uplink region 130. It will be understood that although only three visible satellites 110, three user terminals 120 and a single uplink region 130 is shown, a satellite radiotelephone communications system may include many more satellites, user terminals and uplink regions. The user terminals may be mobile or fixed.
• uplink or return link signal bursts such as TDMA bursts, from a user terminal 120 and preferably from all of the user terminals 120a- 120m in the uplink region 130 are received at two or more, preferably all of the visible satellites l lOa-HOn in the uplink region 130 More specifically, as shown in Figure 1 A, an uplink signal burst 140a from user terminal 120a is received at each of the visible satellites 1 lOa-l 1 On An uplink signal burst 140b from user terminal 120b is received at all of the visible satellites HOa-llOn An uplink signal burst 140m from user terminal 120m is received at all of the visible satellites llOa-HOn
• each visible satellite 110 transmits to a ground station 150 a sequence of received uplink signal bursts without time overlap
• satellite 110a transmits to the ground station 150 a sequence 160a of received uplink signals bursts without time overlap
• Satellite 110b transmits to the ground station 150 a sequence 160b of received uplink signal bursts without time overlap
• satellite 11 On transmits to the ground station 150 a sequence 160n of received signal bursts without time overlap
• a diversity combiner 170 combines the received signals from the satellites 1 lOa-l lOn It will be understood by those having skill in the art that more than one ground station 150 may be provided, and the diversity combiner 170 need not be included in the ground station 150 Moreover, cont ⁇ butions from a plurality of ground stations 150 may be provided to a single diversity combiner 170 In order to allow the satellites 110 to receive the up
• the received uplink signal bursts at the satellite 1 lOn having lowest elevation angle (or at the horizon) also will have no time overlap, although adjacent signals may abut one another. Burst collisions therefore may be avoided.
• the fixed guard time G f since the fixed guard time G f is fixed for every user terminal 120, it may be preprogrammed into the user terminal or provided to the user terminal upon initialization or at other times. Accordingly, simplified user terminals may be obtained. However, since the worst case guard time G f is used regardless of the position of the user terminal, the number of user terminals that may be accommodated within an uplink region may be reduced.
• Timing diagram (2) of Figure IB illustrates another embodiment of the invention, wherein a variable guard time Gi-G m -i is used that corresponds to a time of arrival difference between adjacent uplink signal bursts from a conesponding pair of user terminals to one of the satellites HOa-l lOn, preferably the satellite HOn having lowest elevation angle or a real or fictitious satellite at the horizon.
• a variable guard time Gi-G m -i is used that corresponds to a time of arrival difference between adjacent uplink signal bursts from a conesponding pair of user terminals to one of the satellites HOa-l lOn, preferably the satellite HOn having lowest elevation angle or a real or fictitious satellite at the horizon.
• two, preferably three, and most preferably all of the satellites 110 may receive the sequence of uplink signal bursts without time overlap.
• variable guard time G ⁇ -G m - ⁇ is individually selected based on the positional relationship in the uplink region between corresponding pairs of user terminals that transmit adjacent uplink signal bursts, an increased number of signal bursts may be accommodated compared to the fixed guard time of timing diagram ( 1) of Figure IB.
• the guard times may need to be computed and supplied to the individual terminals 120a-120m upon initialization, and may need to change as the position of a user terminal 120 changes. Accordingly, complexity of the user terminals and/or the satellite radiotelephone communications system 100 may increase.
• Figures 2A and 2B conceptually illustrate calculation of guard times according to the present invention.
• Figures 2A and 2B assume that a GSM TDMA architecture is used in a satellite radiotelephone system.
• the uplink region 130 is 250 km by 250 km in size.
• Four user terminals, designated User #1-User #4 are shown in the uplink region 130.
• User #1 and User #2 are very close to each other and a guard time need not be provided.
• User #2 is separated from User #3, and User #3 is separated from User #4 by a distance of about 173 km.
• the guard time ⁇ t may be computed by the distance between the users ⁇ d divided by the speed of light c (3 x 10 m/s).
• the guard time between User #2 and User #3, and the guard time between User #3 and User #4 is about one forward link slot in the GSM TDMA architecture or about 0.577 msec.
• Figure 2B illustrates an example where User #1 and User #2 are adjacent one another and User #3 and User #4 are adjacent one another, but User #2 and User #3 are separated by a maximum amount in an uplink region 130 of about 700 km.
• the guard time G between User #2 and User #3 is about 4 GSM forward link slots or about 2.3 msec. It also will be understood by those having skill in the art that the guard time G of Figure 2B may be used as a fixed guard time between each adjacent uplink signal burst, because it represents the worst case scenario of maximum separation between users corresponding to adjacent uplink signal bursts.
• Figure 3 illustrates integration of downlink (forward) and uplink (return) timing according to the present invention.
• first and second downlink bursts may be provided from first and second satellites at first and second carrier frequencies fl and f2. Each burst may occupy one slot of 64 slots in an eighth rate GSM TDMA forward link frame architecture.
• the uplink bursts may be provided for each user using four separate frequencies and received by all satellites that are in view.
• Figures 4A and 4B illustrate alternate embodiments of forward link burst timing.
• Figure 4A corresponds to timing diagrams (a) and (b) of Figure 3, wherein two downlink bursts are provided per frame using two separate carrier frequencies from two separate satellites.
• one carrier frequency may be used by two satellites.
• a guard time should be provided between the last burst in the first part of the TDMA frame and the first burst in the second part of the TDMA frame. In a GSM TDMA architecture, this may reduce the capacity by about 18.75%, assuming one forward link carrier is serving a 1000 km area.
• the forward link utilizes two carriers to serve each user in a diversity mode.
• the forward link carrier frame contains 64 slots or signal bursts. This may be referred to as eighth rate GSM mode, wherein full rate GSM denotes 8 slots per frame, half rate GSM denotes 16 slots per frame, quarter rate GSM denotes 32 slots per frame and eighth rate GSM denotes 64 slots per frame.
• each forward link carrier of 200 kHz, four corresponding 50 kHz return link carriers are provided.
• each forward link carrier can support 64 users, while each return link carrier can support 16 users.
• two forward link carriers are used to serve 64 users in diversity mode.
• Corresponding to these two forward link carriers are eight return link carriers.
• the return link can achieve diversity with only one transmitted burst.
• Figure 5 illustrates the use of eight return link carriers for each set of two forward link carriers. A guard time of one return link slot or four forward link slots, corresponding to about 2.3 msec also is shown.
• timing diagrams The analysis of timing diagrams has revealed that as long as users who are being served by the same return link carrier, and are using adjacent in time return link slots, are within a physical distance of about 345 km, then a fixed guard time of 2.3 msec (one return link slot, or four forward link slots, or 4 ⁇ ) between adjacent user bursts can suffice to preclude any burst collisions at any one of the visible satellites, including those that may be at the horizon.
• Each return link carrier can support eight users subject to the maximum fixed guard time of 2.3 msec between adjacent user bursts.
• a single forward link region can conespond to four return link regions, i.e. a region of 1000 km x 1000 km, and can be served by two 200 kHz forward carriers, one from each of two visible satellites.
• 64 users can be served in diversity mode over a 1000 km x 1000 km region via two forward link carriers when the system is operating in eighth rate GSM mode, while the eight return link carriers (as shown in Figure 5) are providing return link diversity for the same 64 users.
• the transmission time for each return link burst for the variable guard time case may be calculated as follows.
• the transmission time may be given as follows: where is the transmission time for user 1 ; t R is the receive time for user 1 ; ⁇ is a forward link slot time; and is the receive time for the user's downlink burst at a reference point in the region.
• the transmit time for user 2 may be calculated as follows:
• ⁇ D ⁇ _ 2 denotes the physical distance between users 1 and 2.
• the transmission time for any arbitrary user n corresponds to:
• the forward link earner contains 64 slot frames
• the return link earner utilizes 16 slot frames, with four return link earners used to support the capacity provided by one forward link earner. Further details on the pnnciple of using non-symmetncal forward and return link earners can be found in the aforementioned publication Dual Mode Cellular Satellite Hand-Held Phone Technology by coinventor Karabinis et al, WESCON/96, October 22, 1996, pp. 206-222.
• the quantity 14 ⁇ in the above expressions is chosen as specified so that the return link pulse occurs at the terminal substantially midway between the two forward link pulses (see Figure 3)
• other values ranging from about 2 ⁇ to about 28 ⁇ may be used instead of 14 ⁇ in Equations (1 ), (2), (3), (4), (6) and (8)
• the system mode of operation may be one other than eighth rate GSM.

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• Aviation & Aerospace Engineering (AREA)
• General Physics & Mathematics (AREA)
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  • 2001-01-18 AU AU2001234488A patent/AU2001234488A1/en not_active Abandoned
  • 2001-01-18 EP EP01906597A patent/EP1250769A1/de not_active Withdrawn
  • 2001-01-18 KR KR1020027009213A patent/KR20020067933A/ko not_active Withdrawn
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