Bi-directional communication channel

Abstract

A communication system using OFDM transmission from a base station to subscriber units, includes means for achieving a bi-directional channel. These means comprise transmitting means in the subscriber units for the transmission of signal synchronous with the guard time interval in the OFDM transmission, and receiving means in the base station for the reception of the transmitted signals. The system also includes signal shaping means in the receiver of the base station and/or the subscriber unit for the application of a window in time to signals received therein. A communication system includes a combination of CDMA modulation codes and OFDM coding/decoding means to achieve orthogonality between signals from the various users in the uplink. A communication system includes a combination of OFDM and channeling means for achieving orthogonality between signals from the various users in the uplink. Automatic Frequency Control is achieved with means in the mobile unit for achieving a frequency-lock to the base station.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] The present application claims priority from the co-pending utility patent application filed by the same inventor, U.S. Ser. No. 09 / 399,109 titled “Bi-Directional Communication Channel”. [0002] The present application is also related to the application No. 129186 filed on Mar. 25, 1999 in Israel and entitled “Bi-Directional Communication Channel”.STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED R&D [0003] There was no Federal sponsoring for the present invention, therefore there are no rights deriving therefrom. FIELD OF THE INVENTION [0004] This invention relates to video, voice and data transmission in wireless or cable communications, and more particularly to improvements in links between base stations and subscriber units. BACKGROUND OF THE INVENTION [0005] Heretofore, Advanced communications today use the Orthogonal Frequency Division Multiplex (OFDM) modulation for efficient transmission of digital signals. Thes...

AI Technical Summary

Benefits of technology

[0084] The performance is further improved with each user including means to be frequency-locked to the base (AFC). Each mobile user locks its frequency to a transmission from the base. The stabilized frequency is then used to transmit back to base, at a known, expected frequency.

[0085] An OFDM/TDD system is disclosed that achieves improved orthogonality between signals for the various users, while allowing for more relaxed timing requirements. This achi

Problems solved by technology

A disadvantage of presently used DVB-T systems is their unidirectional operation.

A system may contain many base stations and subscribers, however there is always an unidirectional flow of information.

An interactive system can be achieved by using a telephone line as a return channel from the set top box, however this method is slow and inconvenient.

To achieve a bi-directional link is a difficult task, that requires an innovative approach as detailed below.

A possible problem with the above modulation method is multipath, that may result in interference between adjacent transmitted frames.

A disadvantage of presently used OFDM channels is the need to reserve a guard interval in order to battle multipath and to enable operation in SFN networks.

Although the guard time is used to address the multipath problem, it is a costly solution, since it reduces the capacity o

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