Multiplex communications – Communication over free space – Using atm as a wireles protocol
Reexamination Certificate
2000-08-23
2004-03-09
Chin, Wellington (Department: 2664)
Multiplex communications
Communication over free space
Using atm as a wireles protocol
C370S323000, C370S325000, C370S316000, C370S349000, C370S522000
Reexamination Certificate
active
06704297
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a communications system and, more particularly, to a downlink order wire integrator and separator for use in a processing satellite and user terminal employed in a satellite based communications system.
2. Discussion of the Related Art
In a satellite based communications system, a central terrestrial control processor or network control center (NCC) generally controls one or more processing satellites operating within the communications system. Each processing satellite within the communications system services multiple users or terminals located in multiple geographic areas, known as ground cells. The processing satellites receive and transmit data signals to and from the multiple users or terrestrial terminals positioned at different locations within the ground cells on a point-to-point manner, via uplinks and downlinks.
Transmission access to the uplinks in each ground cell is typically divided into sub-bands using frequency division multiple access (FDMA). Within each sub-band, the sub-band may again be divided by frequency into multiple channels using FDMA. Transmission access is also divided by time using time division multiple access (TDMA) into slots occupied by the transmission burst. On the downlinks, each ground cell typically operates on a single carrier frequency or channel, which is generally always on. This channel is also divided by time using TDMA.
Typically the data flow in a downlink in a particular ground cell for a satellite based communications system is arranged into three (3) parts. These parts include essential frame controls (operations, administration and maintenance (OA&M) functions for transferring the remaining portion of the frame), a separate fixed orderwire portion and a traffic or data portion. The essential OA&M functions generally include the synchronization fields for delineation of the frame and control directives which must be established in order to process the frame, such as the decoding technique or type. Additionally, this portion of the frame also generally identifies the beginning of the frame, the length and the frame number. The fixed space for orderwire information which includes other OA&M traffic generally includes synchronization feedback information, power control information, assignment of time slots and channels for transmitting data, authorization information, billing and other housekeeping information known in the art. The remaining portion of the frame includes many traffic or data cells that may be formed as asynchronous transfer mode (ATM) cells that actually carry the desired communication or information data.
For example, in the terrestrial SONET transmission system, this terrestrial system sets aside a 27 byte fixed orderwire overhead space or {fraction (1/30)}th of the frame total in every frame for conveyance of OA&M orderwire traffic in this fixed format. Existing satellite communications systems also follow this structure of providing a fixed or distinct orderwire portion of the frame to carry OA&M traffic separate from the payload traffic. While this structure or approach has been used for many years, it is relatively inefficient and inflexible when handling and managing OA&M traffic because of the fixed allocation in the downlink frame assigned to the OA&M process, much of which may be wasted when there is little OA&M traffic. In other words, by providing or allocating a fixed portion of the frame for OA&M traffic, should there be little or no OA&M traffic, the bandwidth for communication and information data may be unnecessarily limited based upon this fixed allocation.
What is needed then is a downlink orderwire integrator and separator for use in a processing satellite and a user terminal in a satellite based communication system. This will, in turn, provide a more efficient use of the overall frame or bandwidth, eliminate a fixed orderwire structure, provide an adaptive approach for transferring OA&M information which is not constrained by a fixed frame allocation, and enable more communication or information data to be transferred when there is little or no OA&M traffic. It is, therefore, an object of the present invention to provide such a downlink orderwire integrator and separator for a processing satellite and user terminal in a satellite based communications system.
SUMMARY OF THE INVENTION
In accordance with the teachings of the present invention, a downlink orderwire integrator and separator for use in a processing satellite and a user terminal in a satellite based communications system is provided. The downlink orderwire integrator and separator is operable to provide a versatile and efficient mechanism for transferring orderwire information or cells in a dynamic fashion. In other words, varying number of orderwire cells may be transferred per frame in a downlink as opposed to providing a fixed dedicated portion of a frame for orderwire information which may reduce the overall bandwidth capability.
In one preferred embodiment, a downlink orderwire integrator for use in a processing satellite in a satellite based communications system includes a formatter and a cell switch. The formatter generates orderwire cells with each orderwire cell having a header and a body. The cell switch receives the orderwire cells from the formatter and traffic cells from at least one uplink. The cell switch further arranges the orderwire cells and the traffic cells in at least one frame to transmit on at least one downlink, where the frame includes a fixed control frame portion and a traffic portion that contains both the traffic cells and the orderwire cells.
In another preferred embodiment, a downlink orderwire integrator and separator for use in a processing satellite and a user terminal in a satellite based communications system include a formatter, a cell switch, and a cell sieve. The formatter generates orderwire cells with each orderwire cell having a header and a body. The cell switch receives the orderwire cells from the formatter and traffic cells from at least one uplink and arranges the orderwire cells and the traffic cells in at least one frame to transmit on at least one downlink. The frame includes a fixed frame portion and a traffic portion that contains both the traffic cells and the orderwire cells. The cell sieve receives the at least one frame from the at least one downlink and separates the traffic cells and the orderwire cells from the traffic portion, such that the formatter and cell switch are positioned within the processing satellite and the cell sieve is positioned within the user terminal.
Use of the present invention provides a downlink orderwire integrator and separator for use in a processing satellite and a user terminal of a satellite based communications system. As a result, the aforementioned disadvantages associated with conventional frame allocations in a satellite based communications system have been substantially reduced or eliminated.
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Robert W. Chang, “Synthesis of Band-Limited Orthogonal Signals for Multichannel Data Transmission”, 1966, pp. 1775-1796.
David McDysan and Darren Spohn, “ATM Theory and Applications”, pp. 299-306, 330-336, and 791-818.
Caso Gregory S.
Linsky Stuart T.
Wright David A.
Chin Wellington
Harness & Dickey & Pierce P.L.C.
Northrop Grumman Corporation
Shew John
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