REVERSE LINK FOR A SATELLITE COMMUNICATION NETWORK
`
`Classification:
`
`
`Patent Number: EP 0972366 A2 (Appl. Number: EP19980952995)
`Inventor(s): REICHMAN ARIE [IL]; LAUFER SHAUL [IL];
`BARDA AVI [IL]; GOLDENBERG SORIN [IL]
`Applicant(s): SHIRON SATELLITE COMMUNICATION [IL]
`- international: H04B7/185; (IPC1-7): H04B7/185; H04J13/06
`- cooperative: H04B7/1858
`
`
`EP19980952995 19981108
`
`Application
`number:
`Priority
`number(s): US19970970922 19971114; WO1998IL00542 19981108
`Also published
`EP0972366 (A4) WO9926422 (A2) WO9926422 (A3)
`as:
`US6240073 (B1) AU1050999 (A) IL130948 (A)
`
`Abstract not available for EP0972366 (A2)
`Abstract of correspondent: WO9926422 (A2)
`
`The present invention is a return link for a satellite communication system. The return
`link described herein is suitable for use in any type of communications network such
`as networks used for Internet access purposes. The return link in combination with a
`forward link forms a complete two-way communication system via satellite. The
`return link comprises two separate communication schemes used in combination to
`implement the return link of the satellite system. The first communication scheme
`uses a random access method based on a non-synchronous frequency hopping code
`division multiple access technique (NS/FH/CDMA). The second communication
`scheme uses a channel assignment method based on a frequency division multiple
`access (FDMA) technique.; Data generated by a user is transmitted utilizing one of
`the two communication schemes in accordance with the content and amount of data
`generated. Messages requiring a relatively low transmission rate, such as short Sursty
`messages, utilize the random access transmission method. On the other hand,
`messages requiring a higher transmission rate, such as video conferencing utilize the
`channel assignment method.
`
`
`
`Pet., Exh. 1013, p. 1
`
`

`
`Europaisches Patentamt
`
`European Patent Office
`
`Office europeen des brevets
`
`e Veroffentlichungsnummer:
`e Publication number:
`e Numero de publication:
`
`0 972 366
`
`Internationale Anmeldung veroffentlicht durch die
`
`Weltorganisation for geistiges Eigentum unter der Nummer:
`
`WO 99/26422
`
`(art.158 des EPU).
`
`International application published by the World
`
`Intellectual Property Organisation under number:
`
`WO 99/26422
`
`(art.158 of the EPC).
`
`Demande internationale publiee par l 'Organisation
`
`Mondiale de la Propriete sous le numero:
`
`WO 99/26422
`
`(art.158 de la CBE).
`
`Pet., Exh. 1013, p. 2
`
`

`
`PCT
`WORLD INTELLECTUAL PROPERTY ORGANIZATION
`International Bureau
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`WO 99/26422
`
`(11) International Publication Number:
`
`(51) International Patent Classification 6 :
`H04Q
`
`A2
`
`(43) International Publication Date:
`
`27 May 1999 (27.05.99)
`
`(21) International Application Number:
`
`PCT/IL98/00542
`
`(22) International Filing Date:
`
`8 November 1998 (08.11.98)
`
`(30) Priority Data:
`08/970,922
`
`14 November 1997 (14.11.97)
`
`US
`
`(71) Applicant (for all designated States except US): SHIRON
`SATELLITE COMMUNICATIONS (1996) LTD. [IL/IL];
`Kiryat Sefer Street 14, 61520 Tel Aviv (IL).
`
`(72) Inventors; and
`(75) Inventors/Applicants (for US only): REICHMAN, Arie
`[IL/IL]; Bar Ilan Street 3, 44378 Kfar Saba (IL). LAUFER,
`Shaul [IL/IL]; Onkelus Street 7, 62916 Tel Aviv (IL).
`BARDA, Avi [IL/IL]; Magdiel Drive 56, 45342 Hod
`Hasharon (IL). GOLDENBERG, Sorin [IL/IL]; Shimoni
`Street 39, 92623 Jerusalem (IL).
`
`(74) Agent: EITAN, PEARL, LATZER & COHEN-ZEDEK; Ad(cid:173)
`vocates, Notaries and Patent Altorneys, Gav Yam Center 2,
`Shenkar Street 7, 46725 Herzlia (IL).
`
`(81) Designated States: AL, AM, AT, AU, AZ, BA, BB, BG, BR,
`BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, Fl, GB, GD,
`GE, GH, GM, HR, HU, ID, IL, IS, JP, KE, KG, KP, KR,
`KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN,
`MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK,
`SL, TJ, TM, TR, TT, UA, UG, US, UZ, VN, YU, ZW,
`ARIPO patent (GH, GM, KE, LS, MW, SD, SZ, UG, ZW),
`Eurasian patent (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM),
`European patent (AT, BE, CH, CY, DE, DK, ES, Fl, FR,
`GB, GR, IE, IT, LU, MC, NL, PT, SE), OAPI patent (BF,
`BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN,
`TD, TG).
`
`Published
`Without international search report and to be republished
`upon receipt of that report.
`
`(54) Title: REVERSE LINK FOR A SATELLITE COMMUNICATION NETWORK
`
`(57) Abstract
`
`The present invention is a return link for a satellite communication system. The return link described herein is suitable for use in
`any type of communications network such as networks used for Internet access purposes. The return link in combination with a forward
`link forms a complete two-way communication system via satellite. The return link comprises two separate communication schemes
`used in combination to implement the return link of the satellite system. The first communication scheme uses a random access method
`based on a non-synchronous frequency hopping code division multiple access technique (NS/FH/CDMA). The second communication
`scheme uses a channel assignment method based on a frequency division multiple access (FDMA) technique. Data generated by a user
`is transmitted utilizing one of the two communication schemes in accordance with the content and amount of data generated. Messages
`requiring a relatively low transmission rate, such as short Sursty messages, utilize the random access transmission method. On the other
`hand, messages requiring a higher transmission rate, such as video conferencing utilize the channel assignment method.
`
`Pet., Exh. 1013, p. 3
`
`

`
`FOR THE PURPOSES OF INFORMATION ONLY
`
`Codes used to identify States party to the PCT on the front pages of pamphlets publishing international applications under the PCT.
`
`AL
`AM
`AT
`AU
`AZ
`BA
`BB
`BE
`BF
`BG
`BJ
`BR
`BY
`CA
`CF
`CG
`CH
`CI
`CM
`CN
`cu
`CZ
`DE
`DK
`EE
`
`Albania
`Armenia
`Austria
`Australia
`Azerbaijan
`Bosnia and Herzegovina
`Barbados
`Belgium
`Burkina Faso
`Bulgaria
`Benin
`Brazil
`Belarus
`Canada
`Central African Republic
`Congo
`Switzerland
`Ci\te d'Ivoire
`Cameroon
`China
`Cuba
`Czech Republic
`Germany
`Denmark
`Estonia
`
`ES
`FI
`FR
`GA
`GB
`GE
`GH
`GN
`GR
`HU
`IE
`IL
`IS
`IT
`JP
`KE
`KG
`KP
`
`KR
`KZ
`LC
`LI
`LK
`LR
`
`Spain
`Finland
`France
`Gabon
`United Kingdom
`Georgia
`Ghana
`Guinea
`Greece
`Hungary
`Ireland
`Israel
`Iceland
`Italy
`Japan
`Kenya
`Kyrgyzstan
`Democratic People's
`Republic of Korea
`Republic of Korea
`Kazakstan
`Saint Lucia
`Liechtenstein
`Sri Lanka
`Liberia
`
`LS
`LT
`LU
`LV
`MC
`MD
`MG
`MK
`
`ML
`MN
`MR
`MW
`MX
`NE
`NL
`NO
`NZ
`PL
`PT
`RO
`RU
`SD
`SE
`SG
`
`Lesotho
`Lithuania
`Luxembourg
`Latvia
`Monaco
`Republic of Moldova
`Madagascar
`The former Yugoslav
`Republic of Macedonia
`Mali
`Mongolia
`Mauritania
`Malawi
`Mexico
`Niger
`Netherlands
`Norway
`New Zealand
`Poland
`Portugal
`Romania
`Russian Federation
`Sudan
`Sweden
`Singapore
`
`SI
`SK
`SN
`sz
`TD
`TG
`TJ
`TM
`TR
`TT
`UA
`UG
`us
`uz
`VN
`YU
`zw
`
`Slovenia
`Slovakia
`Senegal
`Swaziland
`Chad
`Togo
`Tajikistan
`Turkmenistan
`Turkey
`Trinidad and Tobago
`Ukraine
`Uganda
`United States of America
`Uzbekistan
`Viet Nam
`Yugoslavia
`Zimbabwe
`
`Pet., Exh. 1013, p. 4
`
`

`
`W099/26422
`
`PCT /IL98/00542
`
`REVERSE LINK FOR A SATELLITE COMMUNICATION NETWORK
`
`FIELD OF THE INVENTION
`
`5
`
`The present invention relates generally to satellite communications and
`
`more particularly
`
`relates
`
`to a satellite based multiple access
`
`reverse
`
`communication link suitable for an Internet access network.
`
`BACKGROUND OF THE INVENTION
`
`Currently, communication systems around the world are growing rapidly
`
`10
`
`due to the increasing need for data communication bandwidth.
`
`In particular,
`
`satellite communication systems are currently experiencing rapid growth due to
`
`growing customer demand for satellite based data communications. Most of the
`
`current demand and estimated future demand will be for Internet and other
`
`network based data communication applications. A major factor in these
`
`15
`
`communication systems is the bandwidth capacity demanded by the user.
`
`Applications in widespread use today, such as video conferencing, LAN/WAN and
`
`document delivery require high speed forward and return link data capacities.
`
`Currently, however, these capabilities are not provided by present day Internet via
`
`satellite systems.
`
`20
`
`It is currently estimated that there are approximately 13 million hosts and
`
`25 million users on the Internet. The growth rate has been approximately 3 million
`
`new users a year for the past four years. At the same time, the number of
`
`lntranets (Internet network protocols applied within an enterprise or company for
`
`sharing information) are growing at an even faster rate. Currently, accessing the
`
`25
`
`Internet via satellite has gained recognition as a fast and reliable solution for fast
`
`Internet access. Current commercially available Internet via satellite solutions
`
`such as DirecPC are based on an asymmetrical approach in which the data link to
`
`the user is via satellite while the return link from the user is via telephone lines
`
`Pet., Exh. 1013, p. 5
`
`

`
`W099/26422
`
`PCT/IL98/00542
`
`using commercially available telephony modems. The disadvantages of these
`
`asymmetrical systems are outlined below.
`
`The asymmetric approach via satellite, in which the user receives data
`
`from the Internet via satellite, yet sends data to the Internet via telephone lines,
`
`5
`
`does not take advantage of a major feature of satellite communications: wide area
`
`coverage. The asymmetric link is based on a terrestrial connection and therefore
`
`limits the ability of the fast connection to the Internet to those places in which
`
`telephone lines and Internet service providers are available and have sufficient
`
`grade of service.
`
`10
`
`The data rate of asymmetric Internet via satellite communication systems
`
`enables basically e-mail and browsing applications only. This structure is mainly
`
`targeted to consumer markets where the user is limited to sending data from their
`
`home at relatively low speeds. There are, however, many users such as small
`
`office/home office (SOHO) that desire high speed data communications in both
`
`15
`
`directions yet cannot afford having dedicated lease lines for their Internet
`
`connection.
`
`In the United States alone there are approximately 3.5 million small
`
`businesses of which only 10% can justify an expensive leased line. Thus, there
`
`are a large group of users looking for an on demand economical, fast and reliable
`
`connection to the Internet with a grade of service similar to that of a leased line.
`
`20
`
`Typical applications that require high data rates in both directions include
`
`video conferencing, LAN/WAN systems, Internet applications, document delivery,
`
`audio applications such as Internet Phone, commercial web sites, net gaming,
`
`point of presence, terminal equipment, Net Meeting and collaboration software.
`
`All the above mentioned applications are currently not adequately served by the
`
`25
`
`currently available asymmetric satellite communication solutions.
`
`Spread spectrum communication systems have been used in a variety of
`
`fields for some time now.
`
`In spread spectrum communication systems, the
`
`bandwidth of the transmitted signal is much greater than the bandwidth of the
`
`information to be transmitted. The carrier signal in such systems is modulated by
`
`30
`
`a function that serves to widen or spread the bandwidth of the signal for
`
`transmission. On the receive side, the signal is remapped or decoded into the
`
`original information bandwidth to reproduce the desired output signal.
`
`2
`
`Pet., Exh. 1013, p. 6
`
`

`
`W099/26422
`
`PCT/IL98/00542
`
`Spread spectrum systems can be categorized into direct sequence
`
`systems, frequency hopping systems, time hopping systems and hybrid systems
`
`which are combinations of the above three.
`
`In frequency hopping systems a carrier frequency is shifted or hopped in
`
`s
`
`discrete increments in a pattern dictated by a predetermined code or sequence,
`
`e.g., a pseudo noise sequence or code. The resulting consecutive and time
`
`sequential frequency pattern is called a hopping pattern and the duration of each
`
`hop frequency is called a chip. The transmitted information is embedded in the
`
`codes or embedded within each frequency in the carrier wave by a modulation
`
`10
`
`scheme such as phase shift keying (PSK) or frequency shift keying (FSK).
`
`In reproducing the information signal of the receiver a synchronization
`
`acquisition process is performed in which the code pattern utilized by the receiver
`
`is synchronized with the code pattern generated and used in the transmitter.
`
`Using this, de-spreading and demodulation are performed on
`
`the spread
`
`15
`
`spectrum signal to extract the transmitted data. A local reference signal is used
`
`that has a frequency corresponding to the same code pattern used in the
`
`transmitter for every chip. The received signal and the local reference are mixed
`
`in order to perform a correlation or de-spreading process for converting the
`
`spread spectrum signal into a signal having a frequency bandwidth wide enough
`
`20
`
`to extract the data information. More information describing the operation of
`
`spread spectrum systems can be found in "Spread Spectrum Systems," by R.C.
`
`Dixon published by John Wiley and Sons, Inc., 1976.
`
`Multiple user systems use multiple access techniques to allow users to
`
`share resources such as time and frequency. When the traffic from each user in
`
`25
`
`the network is approximately steady it is possible to divide a single high capacity
`
`multiple access channel
`
`into a plurality of smaller orthogonal channels
`
`corresponding to individual user requirements. This can be accomplished either
`
`on a frequency basis using Frequency Division Multiple Access (FDMA), on a time
`
`basis using Time Division Multiple Access (TOMA) or using Code Division Multiple
`
`30
`
`Access (CDMA). In addition, various combinations of FDMA and TOMA can also
`
`be used to minimize cost in large networks. FDMA and TOMA techniques are
`
`suitable solutions as long the traffic from each user is relatively stable. CDMA is a
`
`3
`
`Pet., Exh. 1013, p. 7
`
`

`
`W099/26422
`
`PCT/IL98/00542
`
`multiple access technique which uses spread spectrum communications. CDMA
`
`communuications can be synchronous if all users are mutually synchronized in
`
`time.
`
`TOMA communication systems are also known for providing multiple
`
`5
`
`access. These systems partition the channel time in a fixed predetermined
`
`manner. They are efficient when the user population includes only a relatively
`
`small number of users having high duty cycles. However, many modern
`
`communication systems need to provide communication among interactive data
`
`terminals which operate in low duty cycle burst modes. Thus, TOMA is not
`
`10
`
`particularly suited to this kind of communication.
`
`In the typical modern interactive network, however, the traffic from
`
`individual terminals in the system varies as a function of time due to random traffic
`
`demands by different users at each terminal.
`
`In addition, the set of terminals
`
`active in the network can vary from moment to moment.
`
`In such systems it may
`
`15
`
`be desirable to assign channel capacity to users on demand by means of a
`
`demand assigned multiple access (DAMA) architecture.
`
`In a DAMA system a
`
`separate channel called the request channel is used by individual users to request
`
`capacity as needed. The capacity can then be allocated in response to requests
`
`by a central master controller implemented by a common algorithm running in
`
`20
`
`each terminal.
`
`A DAMA system however introduces additional overhead into the multiple
`
`access channel due to the process of requesting and assigning capacity.
`
`In
`
`addition, the demand assignment process introduces a delay which can degrade
`
`the performance under the channel.
`
`25
`
`In some DAMA networks the total number of potential data terminals
`
`sharing the request channel is much larger than the number of terminals active at
`
`any given point in time. Thus, subdividing a DAMA request channel into smaller
`
`fixed allocation sub-channels is impractical.
`
`It is thus necessary to design a
`
`request channel architecture based upon a random access technique which
`
`30
`
`allows for the possibility of a small subset of active transmitters selected from a
`
`much larger set of potential transmitters. Two random access techniques are
`
`4
`
`Pet., Exh. 1013, p. 8
`
`

`
`W099/26422
`
`PCT/IL98/00542
`
`currently available for such applications which include ALOHA multiple access
`
`and CDMA.
`The first data network to be based upon a random access protocol was
`
`ALOHANET which went into operation throughout the state of Hawaii in 1970.
`
`5
`
`The ALOHA system was the first random access multi-point packet data
`
`communication system. The system uses a single radio channel shared by
`
`plurality of stations or data terminals. When a station generates a packet, the
`
`ALOHA system transmits the packet on the common radio channel. Since more
`
`than one station may attempt to transmit a packet at the same time several
`
`10
`
`transmissions may overlap. The overlapping transmissions are said to collide if
`
`any portion of two transmissions overlap. When a collision occurs each station
`
`waits a random period of time before attempting to gain access to the channel
`
`again.
`
`To increase the utilization of the radio channel, the slotted ALOHA system
`
`15
`
`was proposed in which the channel is partitioned into time slots equal to a packet
`
`length wherein each station can only transmit a packet at the beginning of a slot.
`
`In this way overlapping transmissions are forced to completely overlap. Using a
`
`slotted approach almost doubles maximum channel utilization compared to the
`
`unslotted ALOHA system.
`
`20
`
`To reduce the effects of collisions in the slotted ALOHA system a slot
`
`reservation scheme was proposed. The channel was partitioned into frames each
`
`containing a reservation slot for transmitting a reservation packet and data slots
`
`for transmitting data packets. Each station transmits a reservation packet on a
`
`random access basis requesting slots needed for data packet transmission. If the
`
`25
`
`request is granted, data slots of a subsequent frame are assigned to the
`
`requesting station which subsequently transmits data packets on its assigned
`
`slots.
`
`Satellite communications can provide point to point channels or broadcast
`
`and multiple access channels. A satellite is well suited to provide one to many
`
`30
`
`i.e., broadcast, channels and many to one, i.e., multiple access, channels from
`
`and to an earth station. The architecture of the network used in very small
`
`aperture terminal 0JSA T) data networks is almost always designed around a
`
`5
`
`Pet., Exh. 1013, p. 9
`
`

`
`W099/26422
`
`PCT/IL98/00542
`
`single large hub earth station transmitting data in a broadcast channel to a large
`
`number of VSATs as shown in Figure 1. Considering Network A, for example, the
`
`VSATs 20 in such a network transmit data in packets to the hub station 18 using
`
`the multiple access capability of the satellite channel 17.
`
`5
`
`The communications from the hub station of a VSA T network to the
`
`VSATs themselves is easily configured using a conventional communication
`
`technique such as Time Division Multiplexing (TOM) or Frequency Division
`
`Multiplexing (FDM). Currently, TOM is widely used for multiplexing the hub to the
`
`VSAT terminals, notwithstanding the fact that there are differences in data rate,
`
`10
`
`modulation techniques and transmission formats among the various VSAT
`
`networks.
`
`The multiple access link from the VSATs to the hub, however, is currently
`
`subjected to a greater degree of variation. The choice of multiple access
`
`technique
`
`from
`
`the VSATs
`
`to
`
`the hub
`
`is currently
`
`the primary
`
`feature
`
`15
`
`distinguishing one network from another.
`
`Recently, however, it has become commonplace to build VSAT networks
`
`composed of hundreds and thousands of more small VSAT terminals. The traffic
`
`in these networks is typically in the form of single data packets originating from
`
`interactive users or bursts of data packets originating from some type of file
`
`20
`
`transcript protocol. As the number of stations in the network increases, the more
`
`the traffic from the single station will appear to fluctuate due to random user
`
`demand. In such networks, the use of FDMA or TOMA becomes impractical while
`
`the use of DAMA would impose an unreasonable amount of overhead in the
`
`network. Thus, to provide multiple access to these types of packet data networks,
`
`25
`
`the access techniques of direct sequence (OS) spread spectrum multiple access,
`
`i.e., OS-CDMA and ALOHA, are used. Both these multiple access techniques
`
`however suffer from disadvantages. Direct sequence spread spectrum systems
`
`require the hub receiving station to have a digital matched filter operating at the
`
`high speed chip rate for each of the possible transmitters with each using a
`
`30
`
`different spreading sequence.
`
`In a network with a large number of VSATs this
`
`becomes unwieldy and expensive to maintain. ALOHA systems suffer from
`
`relatively low capacity and high average power requirements.
`
`6
`
`Pet., Exh. 1013, p. 10
`
`

`
`W099/26422
`
`PCT/IL98/00542
`
`SUMMARY OF THE INVENTION
`
`The present invention is a reverse link for a satellite communication
`
`system. The reverse link described herein is suitable for use in any type of
`
`communications network such as networks used for Internet access purposes.
`
`5
`
`The reverse link in combination with a forward link forms a complete two-way
`
`communication system via satellite. The reverse link comprises two separate
`
`communication schemes used in combination to implement the reverse link of the
`
`satellite system. The first communication scheme uses a random access method
`
`based on a non-synchronous frequency hopping code division multiple access
`
`10
`
`technique (NS/FH/CDMA). The second communication scheme uses a channel
`
`assignment method based on a frequency division multiple access (FDMA)
`
`technique. Data generated by a user is transmitted utilizing one of the two
`
`communication schemes in accordance with the content and amount of data
`
`generated. Messages requiring a relatively low transmission rate, such as short
`
`15
`
`bursty messages, utilize the random access transmission method. On the other
`
`hand, messages requiring a higher transmission rate, such as video conferencing,
`
`utilize the channel assignment method.
`
`There is therefore provided in accordance with the present invention a
`
`multiple access communications system for use in a satellite communication
`
`20
`
`network, comprising a plurality of user terminals for generating data to be
`
`transmitted over the multiple access communication system, at least one hub for
`
`receiving data over the multiple access communication system from the plurality
`
`of user terminals, transmitter means within each user terminal for receiving data to
`
`be transmitted from the user terminal to the hub, the transmitter means including
`
`25
`
`first communication means for transmitting short bursty data in combination with
`
`second communication means for continuous transmission of data, switching
`
`means coupled to the transmitter means for switching transmission between the
`
`first communication means and the second communication means in accordance
`
`with predefined criteria and receiver means within the at least one hub adapted to
`
`30
`
`receive data transmitted by the plurality of terminals utilizing either the first
`
`communication means or the second communication means.
`
`7
`
`Pet., Exh. 1013, p. 11
`
`

`
`W099/26422
`
`PCT/IL98/00542
`
`The first communication means can comprise non-synchronous multiple
`
`access communication means or non-synchronous frequency hopping code
`
`division multiple access communication means. The second communication
`
`means can comprise frequency division multiple access communication means.
`
`5
`
`The receiver means comprises means for receiving data transmitted by the
`
`plurality of user terminals using the first communication means, the first
`
`communication means utilizing non-synchronous frequency hopping code division
`
`multiple access communications, means for receiving data transmitted by the
`
`plurality of user terminals using the second communication means, the second
`
`10
`
`communication means
`
`utilizing
`
`frequency
`
`division multiple
`
`access
`
`communications and means for receiving preamble and synchronization message
`
`data transmitted by the plurality of user terminals precedent to transmissions
`
`utilizing the first communication means.
`
`The switching means comprises means for switching transmission from
`
`15
`
`the first communication means to the second communication means either in
`
`accordance with a source port field within messages received by the transmitter,
`
`when the length of a message received by the transmitter means exceeds a
`
`predetermined threshold, when a continuation flag in a message received by the
`
`transmitter means is turned on, when a user buffer containing a plurality of
`
`20 messages to be sent via the transmitter means fills beyond predetermined level or
`
`in accordance with the type and nature of the software application that initiated a
`
`message to be transmitted via the transmitter means.
`
`The switching means comprises means for switching transmission from
`
`the second communication means to the first communication means either when
`
`25
`
`a source port matching a predetermined criteria ceases to transmit messages,
`
`when the length of a message received by the transmitter means fails to exceed a
`
`predetermined threshold, when a continuation flag in a message received by the
`
`transmitter means is turned off, when a user buffer containing a plurality of
`
`messages to be sent via the transmitter means empties or when the software
`
`30
`
`application meeting a predetermined criteria that initiated a message to be
`
`transmitted via the transmitter means ceases to generate message data.
`
`8
`
`Pet., Exh. 1013, p. 12
`
`

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`WO 99/26422
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`PCT/IL98/00542
`
`In addition, the hub comprises collision detection means for determining
`
`when two frequency hops associated with two independent receivers are utilizing
`
`the same frequency at the same time, thus improving decoding within the receiver
`
`means.
`
`5
`
`There is also provided in accordance with the present invention a multiple
`
`access communication system for use in a satellite communication network, the
`
`satellite communication network including a plurality of user terminals and at least
`
`one hub, the system comprising first transmitter means for transmitting data
`
`utilizing a non-synchronous frequency hopping code division multiple access
`
`10
`
`communication scheme, second transmitter means for transmitting data utilizing a
`
`frequency division multiple access communication scheme, switching means for
`
`switching transmission between the first transmitter means and the second
`
`transmitter means in accordance with predefined criteria, first receiver means for
`
`receiving data transmitted using utilizing the non synchronous frequency hopping
`
`15
`
`code division multiple access communication scheme, second receiver means for
`
`receiving data
`
`transmitted using
`
`the
`
`frequency division multiple access
`
`communication scheme and third receiver means for receiving preamble and
`
`synchronization data transmitted utilizing a non synchronous frequency hopping
`
`code division multiple access communication scheme.
`
`20
`
`The switching means comprises means for switching transmission from
`
`the first transmitter means to the second transmitter means either in accordance
`
`with a source port field within messages received by the transmitter means, when
`
`the length of a message received by the transmitter means exceeds a
`
`predetermined threshold, when a continuation flag in a message received by the
`
`25
`
`transmitter means is turned on, when a user buffer containing a plurality of
`
`messages to be sent via the transmitter means fills beyond predetermined level or
`
`in accordance with the type and nature of the software application that initiated a
`
`message to be transmitted via the transmitter means.
`
`The switching means comprises means for switching transmission from
`
`30
`
`the second transmitter means to the first transmitter means either when a source
`
`port matching a predetermined criteria ceases to transmit messages, when the
`
`length of a message received by the transmitter means fails to exceed a
`
`9
`
`Pet., Exh. 1013, p. 13
`
`

`
`W099/26422
`
`PCT/IL98/00542
`
`predetermined threshold, when a continuation flag in a message received by the
`
`transmitter means is turned off, when a user buffer containing a plurality of
`
`messages to be sent via the transmitter means empties or when the software
`
`application meeting a predetermined criteria that initiated a message to be
`
`5
`
`transmitted via the transmitter means ceases to generate message data.
`
`The system further comprises interface means for interfacing the at least
`
`one hub to an external communications network. The external communications
`
`network can comprise the Internet, a packet switched telephone network (PSTN),
`
`an Integrated Services Digital Network (ISDN), a Community Antenna Television
`
`10
`
`(CATV) network, a Digital Subscriber Loop (xDSL) or a Frame Relay network.
`
`The system further comprises collision detection means for determining
`
`when two frequency hops associated with two independent receivers within the
`
`receiver means are utilizing the same frequency at the same time, thus improving
`
`decoding within the first receiver means.
`
`15
`
`There is also provided in accordance with the present invention a multiple
`
`access communications system for use in a satellite communication network,
`
`comprising a plurality of user terminals for transmitting and receiving data over the
`
`multiple access communication system, at least one hub for transmitting and
`
`receiving data over the multiple access communication system to and from the
`
`20
`
`plurality of user terminals, a forward communication link for transmitting data from
`
`the at least one hub to the plurality of user terminals, a return communication link
`
`for transmitting data from the plurality of user terminals to the at least one hub, the
`
`return communication link including a first communication means for transmitting
`
`short bursty data
`
`in combination with second communication means for
`
`25
`
`continuous transmission of data, switching means within the plurality of user
`
`terminals for switching transmission between the first communication means and
`
`the second communication means in accordance with predefined criteria and
`
`receiver means within the at least one hub adapted to receive data transmitted by
`
`the plurality of terminals utilizing either the first communication means or the
`
`30
`
`second communication means.
`
`Further, each user terminal comprises means for generating a request to
`
`be sent over the return communications link in order to utilize the second
`
`10
`
`Pet., Exh. 1013, p. 14
`
`

`
`W099/26422
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`PCT/IL98/00542
`
`communication means. The hub comprises means for polling each user terminal
`
`over the forward communication link as to whether the transmission of data
`
`should be switched to utilize the second communication means.
`
`11
`
`Pet., Exh. 1013, p. 15
`
`

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`W099/26422
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`PCT/IL98/00542
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The invention is herein described, by way of example only, with reference
`
`to the accompanying drawings, wherein:
`
`Fig. 1 is a high level block diagram illustrating two satellite communication
`
`5
`
`networks coupled to the Internet utilizing both a forward and a reverse link via
`
`satellite;
`
`Fig. 2 is a graph illustrating the relationship between time and frequency
`
`for data packets transmitted by two users;
`
`Fig. 3 is a diagram illustrating a sequence of packets transmitted in time
`1 o making up a message;
`Fig. 4 is a diagram illustrating a frequency band making up the frequency
`
`spectrum of the communication system;
`
`Fig. 5 is a high level block diagram illustrating the random access
`
`transmitter of the communication system of the present invention;
`
`15
`
`Fig. 6 is a high level block diagram illustrating the channel assignment
`
`transmitter of the communication system;
`
`Fig. 7 is a high level block diagram illustrating the software layers making
`
`up the personal computer based transmitter method portion o