Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Utility Patent
1997-09-08
2001-01-02
Olms, Douglas W. (Department: 2732)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
C370S253000, C370S458000, C370S462000
Utility Patent
active
06169728
ABSTRACT:
FIELD OF THE INVENTION
This invention relates, in general, to data communications and data communications systems and devices and, more specifically, to an apparatus and method for spectrum management in a multipoint communication system.
BACKGROUND OF THE INVENTION
With the advent of multimedia communications, data transmission has become increasingly complex. For example, multimedia communications applications such as real time transmission of digitally encoded video, voice, and other forms of data, may require new forms and systems for data communication and data transmission. One such new communication system is the CableComm™ System currently being developed by Motorola, Inc. In the CableComm™ System, a hybrid optical fiber and coaxial cable is utilized to provide substantial bandwidth over existing cable lines to secondary stations such as individual, subscriber access units, for example, households having new or preexisting cable television capability. These coaxial cables are further connected to fiber optical cables to a central location having centralized, primary (or “head end”) controllers or stations having receiving and transmitting capability. Such primary equipment may be connected to any variety of networks or other information sources, from the Internet, various on line services, telephone networks, to video/movie subscriber service. With the CableComm™ System, digital data may be transmitted both in the downstream direction, from the primary station or controller (connected to a network) to the secondary station of an individual user (subscriber access unit), and in the upstream direction, from the secondary station to the primary station (and to a network).
In the CableComm™ System, downstream data is currently intended to be transmitted using 64 quadrature amplitude modulation (“QAM”) at a rate of 30 M bps (megabits per second), at 5 M symbols/second utilizing 6 bits/symbol, over channels having 6 MHz bandwidth in the frequency spectrum of 50-750 MHz. Anticipating asymmetrical requirements with large amounts of data tending to be transmitted in the downstream direction rather than the upstream direction, less capacity is provided for upstream data transmission, using &pgr;/4 differential quadrature phase shift keying (&pgr;/4-DQPSK) modulation in the frequency band from 5-42 MHz with a symbol rate of 384 k symbols/sec with 2 bits/symbol. In addition, the communication system is designed to have a multipoint configuration, i.e., many end users (secondary stations, also referred to as subscriber access units) transmitting upstream to a primary station, with one or more primary stations transmitting downstream to the secondary stations. The communication system is also designed for asynchronous transmission, with users transmitting and receiving packets of encoded data, such as video or text files. In addition, it is also highly likely that transmission may be bursty, with various users receiving or transmitting data at indeterminate intervals over selected channels in response to polling, contention, or other protocols from the primary station, rather than transmitting a more continuous and synchronous stream of information over a dedicated or circuit switched connection.
For such a communication system having a multipoint configuration, with multiple upstream and downstream channels, it is highly desirable to provide for appropriate or optimal spectrum management, providing for load balancing across various transmit and receive channels, channel (or spectrum) allocation under various types of noise or other error conditions, and for channel (or spectrum) allocation under various types of congestion conditions. Prior art in other fields, such as telephone networks and wireless voice networks, have not been concerned with such spectrum management because these issues typically do not arise for such networks. For example, noise conditions may typically be tolerated in a voice (rather than data) environment. Other fields, such as typical wireline data, are not concerned with channel assignment issues. Wireless voice and data fields, moreover, tend to be concerned about overall system capacity and are not concerned about congestion management and load balancing within channels, as those channels are circuit switched, dedicated channels. Accordingly, a need has remained to provide for spectrum management in emerging multipoint communications systems, such as the CableComm™ system, providing for load balancing, channel assignment, and congestion management within the multipoint communication system.
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Menon Sunil K.
Perreault John A.
Picker Dennis J.
Klayman Jeffrey T.
Motorola Inc.
Olms Douglas W.
Pappas Joanne N.
Vanderpuye Ken
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