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Ep 1130919 A2 Europäisches Patentamt *EP001130919A2* (19) European Patent Office Office européen des brevets (11) EP 1 130 919 A2 (12) EUROPEAN PATENT APPLICATION (43) Date of publication: (51) Int Cl.7: H04N 7/173, H04L 12/28, 05.09.2001 Bulletin 2001/36 H04J 11/00, H04J 13/02, H04J 3/06, H04B 1/707, (21) Application number: 01104541.6 H04L 5/02, H04L 27/38 (22) Date of filing: 25.07.1996 (84) Designated Contracting States: (72) Inventors: AT BE CH DE DK ES FI FR GB GR IE IT LI LU MC • Rakib, Selim Shlomo, Dr. NL PT SE Cupertino, California 95014 (US) • Azenkot, Yehuda (30) Priority: 25.08.1995 US 519630 San Jose, California 95129 (US) 19.01.1996 US 588650 19.07.1996 US 684243 (74) Representative: Brax, Matti Juhani Berggren Oy Ab, (62) Document number(s) of the earlier application(s) in P.O. Box 16 accordance with Art. 76 EPC: 00101 Helsinki (FI) 96927270.7 / 0 858 695 Remarks: (71) Applicant: Terayon Communication Systems, Inc. This application was filed on 05 - 03 - 2001 as a Santa Clara, CA 95054 (US) divisional application to the application mentioned under INID code 62. (54) Apparatus and method for digital data transmission (57) A method and apparatus for carrying out syn- energy of each channel data over a frame of data trans- chronous co-division multiple access (SCDMA) commu- mitted in a code domain. Frames are synchronized as nication of multiple channels of digital data over a between remote (1164) and central units (1160) using a shared transmission media (1162). The system includes ranging scheme which is also useful in any other system modems at remote units (1164) and a central unit (1160) transmitting data by frames in a distributed system to receive time division multiplexed digital data arranged where synchronizing the frames as between all units re- into timeslots or channels and uses orthogonal codes to gardless of differences in propagation delays is neces- encode each channel of multiple data and spread the sary. Each frame in the SCDMA modulation scheme in- cludes a gap or guardband containing no other data. EP 1 130 919 A2 Printed by Jouve, 75001 PARIS (FR) EP 1 130 919 A2 Description [0001] This application relates to the applicant's granted U.S. patents 5,793,759, issued 11 August 1998, and 5,768,269, issued 16 June 1998, which existed as U.S. patent applications Serial No. 08/588,650 and Serial No. 5 08/519,630 respectively, and correspondingly were not available to the public, at the filing date of this application. Field of the Invention [0002] The invention pertains to the field of bidirectional communication of digital data over coaxial cable or other 10 transmission media. More particularly, the invention pertains to the field of provision of multiple channels of digital data including interactive TV services, digital telephony, video teleconferencing, video on demand, intemet access at 10 megabit/second or media data rates etc., all provided to home or business establishments over cable TV coax or combinations of coaxial cable, fiber optic links, microwave or satellite links or other wireless systems using synchronous COMA system technology. These new services delivered over the CATV system will hereafter be called supplemental 15 services. Background of The Invention [0003] In order to provide bidirectional digital data communication over a cable TV coaxial network to multiple sub- 20 scribers with multiple digital services including data, digitized video and digitized audio, all made available over a single cable TV hybrid fiber coax (hereafter HFC) network (hereafter called CATV systems), several problems have to be solved. First, video applications such as video teleconferencing and video on demand movies require that a flexible amount of bandwidth be awarded to support the digitized video transmissions and that the amcunt of bandwidth award- ed be guaranteed, i.e., the awarded bandwidth will be made available continuously without interruption until the video 25 service is completed. These requirements force the use in the CATV environment of higher level protocols that have been developed or which are in the process of development for local area networks such as ATM or ISON that are designed for delivery of digitized video, digitized audio and digital data over point to point LAN connections. Thus, the a major problem exists in adapting these point to point LAN protocols to the point-to-multipoint CATV environment. [0004] Second. there is the problem of bandwidth availability and sharing the available bandwidth among a plurality 30 of users who are physically distributed and all of whom have changing bandwidth needs over time. In CATV systems, typically only 6 mHz of bandwidth is available for communications of digital data downstream from the head end to the subscribers and another 6 mHz elsewhere on the spectrum of the CATV media is made available for upstream com- munications. These 6 mHz bands must be shared by all the users to carry data for all the services provided. Since video is a high bandwidth demand application which requires continuous availability, the available bandwidth must be 35 fully utilized with maximum efficiency so as to provide bandwidth capacity to as many users as possible. [0005] Third, there is the problem of noise and interference on the CATV system which could degrade the supple- mental services to the point of unacceptability if techniques are not employed to lessen the affect of the noise on reception or otherwise deal with the problem. Cable TV media are high noise environments because of numerous reasons which are well known to those skilled in the art. 40 [0006] A fourth major problem, but related to the second problem, is synchronization of data transmission. Synchro- nization must be maintained between all remote units and the central unit for maximum efficiency use of the available bandwidth. If synchronization is not maintained. the number of users which can simultaneously share the available bandwidth is reduced. [0007] In addition, there is the problem of eliminating the intersymbol interference and partial cross correlation be- 45 tween codes of code division multiple access (herafter CDMA) technology. CDMA technology is used in the genus of the invention to support multiple user with simultaneous pseudo point-to-point connections to the head end. CDMA is known in the prior art and has the advantage of not requiring the bandwidth allocation of frequency-division multiplexing nor the time synchronization of time-divsion multiplexing. However. it has the problems mention above which must be solved for a system acceptable to a user to exist. In addition, to maximize the number of users supported, frame 50 synchronization is used in the invention and one of the problems solved by the inventors is how to achieve this frame synchronization in a physically distributed system of transmitters. [0008] Of course all nonbaseband COMA systems require two additional forms of synchronization as is well known in the art: first, there must be synchronization in phase and frequency between the transmitting carrier and the local oscillator in the receiver which feeds the demodulator. Also, as is known in the art all COMA systems require clock 55 recovery synchronization so that the pseudonoise code (hereafter PN code) sequence fed into the despreading circuitry is not only identical to the PN code fed into the spreading circuitry of the transmitter, but also exactly in phase therewith. Further. clock recovery is necessary in CDMA systems so as to know symbol boundaries so as to be able to correctly sample the baseband data stream exiting the despreading circuitry. How to achieve these forms of synchronization in 2 EP 1 130 919 A2 a CATV CDMA system are another set of problems that must be solved. [0009] Further, in CDMA systems with multiple transmitters which are physically distributed each using different spreading codes, it is possible for signals from different transmitters to arrive at the central unit at different power levels. This causes nonzero cross-correlations between the different codes, and gives rise to a problem known as the "near- 5 far" problem. To prevent high error rates from strong signals overwhelming weaker ones, the near-far problem must be solved. [0010] An example of one attempt to transmit digital data bidirectionally over a CATV system is the technology dis- closed in U.S. patents 4,912,721 and 5,235,619 assigned to Scientific Atlanta. In these systems, direct sequence spread spectrum technology is used to overcome the noise problem in CATV systems, but no support of multiple users 10 by code division multiple access is sought. The Scientific Atlanta patents are single user direct-sequence spread spec- trum systems, and there is no teaching of how to achieve frame synchronization which is necessary to maximize the number of users in a CDMA multiuser system. In the Scientific Atlanta patents, each user sends billing and request data to the head end and the head end sends data related to supplemental services other than the cable TV program- ming to the remote units at the sites of users during a timeslot assigned to that user. The transmission of data is 15 accomplished on a one user per timeslot basis using a pseudonoise spreading code. No teaching of the use of orthog- onal codes is present in U.S. patent 4,912,721. Therefore, only one user can use the available bandwidth devoted to the supplemental services at any particular time. Accordingly, for all users to share the available bandwidth, a time division multiplexing scheme must be used and the direct-sequence, spread spectrum technology is used only to overcome the noise and other impairments on the CATV channel.
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