Communications methods and apparatus
First Claim
1. A method of transmitting information comprising the steps of:
- buffering at least some information to be transmitted;
selecting different ones of a plurality of communication modes depending upon an amount of information buffered in said buffering step; and
transmitting information using the selected communication mode;
wherein the information to be transmitted comprises data packets and control or response packets, the data packets are buffered, and the selection of the communication mode is dependent upon a number of buffered data packets to be transmitted;
wherein the plurality of communication modes comprise different symbol transmission frequencies and/or different modulation methods and/or bits per symbol providing a plurality of different transmitted bit rates; and
wherein the step of selecting different ones of the plurality of communication modes comprises selecting a communication mode having a relatively low symbol transmission frequency in response to there being no buffered data packets to be transmitted and selecting a determined one of the communication modes when there is at least one buffered data packet to be transmitted.
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Accused Products
Abstract
Ethernet frames are communicated via a telephone line between master and slave modems using half duplex communication of data and control information to avoid collisions, data to be transmitted being buffered in each modem. Different communication modes, involving different transmitted symbol frequencies, modulation methods, and bits per symbol to provide different transmission rates, can be used depending on errors on the line. To reduce signal attenuation and interference both of which increase with increasing frequency, a lowest frequency communication mode is used for transmitting control information when there is no data in the buffer for transmission, whereas a higher transmission rate communication mode is used for transmission of data and control information when the buffer is not empty. The communication mode can also be adjusted in dependence upon signal to noise ratio, signal and noise energies being monitored by the modem receiver respectively during and in a quiet period immediately following each received signal burst. Changes especially to a higher transmission rate communication mode can be made selectively depending upon a monitoring in the quiet period by the modem receiver of noise in the higher communication mode, the relevant signal to noise ratio being determined from this and a stored signal level for this mode.
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Citations
13 Claims
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1. A method of transmitting information comprising the steps of:
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buffering at least some information to be transmitted;
selecting different ones of a plurality of communication modes depending upon an amount of information buffered in said buffering step; and
transmitting information using the selected communication mode;
wherein the information to be transmitted comprises data packets and control or response packets, the data packets are buffered, and the selection of the communication mode is dependent upon a number of buffered data packets to be transmitted;
wherein the plurality of communication modes comprise different symbol transmission frequencies and/or different modulation methods and/or bits per symbol providing a plurality of different transmitted bit rates; and
wherein the step of selecting different ones of the plurality of communication modes comprises selecting a communication mode having a relatively low symbol transmission frequency in response to there being no buffered data packets to be transmitted and selecting a determined one of the communication modes when there is at least one buffered data packet to be transmitted. - View Dependent Claims (2, 3, 4)
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5. A modem for coupling between first and second communications paths, the first communications path providing for communication of data frames in a CSMA/CD (Carrier Sense Multiple Access with Collision Detection) network and the second communications path providing for communication of data of said frames and control information using half duplex communications with a complementary modem, the modem comprising:
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a first buffer for buffering information received via the first path for transmission via the second path;
a control unit;
a transmitter for transmitting data from the first buffer and control information from the control unit via the second path;
a receiver for receiving information from the second path; and
a second buffer for buffering information received by the receiver for supply to the first path;
wherein the transmitter and receiver are operable under the control of the control unit in any of a plurality of communication modes providing different transmission rates in each direction on the second path, and the control unit is responsive to data in the first buffer for controlling the transmitter to use different communication modes providing respectively lower and higher transmission rates in the absence and presence of data to be transmitted from the first buffer.
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6. A method of determining a signal to noise ratio on a communications path of a communications system in which signals are transmitted in bursts, wherein the communications system provides for any of a plurality of communication modes providing different transmission rates for the signal bursts on the communications path, comprising the steps of:
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monitoring signal energy received via the communications path during a signal burst;
monitoring noise energy received via the communications path between successive signal bursts;
determining a signal to noise ratio from the monitored signal and noise energies; and
changing the communication mode for signal bursts in dependence upon the determined signal to noise ratio, wherein the step of changing the communication mode comprises changing to a communicator mode providing a higher transmission rate, in response to the determined signal to noise ratio exceeding a threshold, comprising the steps of;
monitoring noise energy received via the communications path between successive signal bursts for communications using the communication mode providing the higher transmission rate;
determining a signal to noise ratio for the communication mode providing the higher transmission rate from a stored signal energy and the monitored noise energy for this communication mode; and
selectively changing to the communication mode providing the higher transmission rate in dependence upon the determined signal to noise ratio for this communication mode. - View Dependent Claims (7, 8)
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9. In a half duplex communications system having a plurality of communication modes providing different transmitted bit rates using different symbol transmission frequencies and/or different modulation methods and/or bits per symbol, a method of changing the communication mode comprising the steps of:
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monitoring noise energy received using the current communication mode following a received signal and before transmission of a signal;
determining a signal to noise ratio for the current communication mode from the monitored signal and noise energies;
changing the communication mode in dependence upon the determined signal to noise ratio; and
determining and storing signal energy for a new communication mode to which a change may be made from the current communication mode, wherein the step of changing from the current to the new communication mode comprises the steps of;
monitoring noise energy received using the new communication mode following a received signal using the current communication mode and before transmission of a signal;
determining a signal to noise ratio for the new communication mode from the stored signal energy and the monitored noise energy for the new communication mode; and
selectively changing to the new communication mode in dependence upon the determined signal to noise ratio for the new communication mode. - View Dependent Claims (10, 11, 12)
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13. Communications apparatus comprising:
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a receiver for receiving information via a communications path;
a transmitter for transmitting information via the communications path; and
a control unit for controlling half duplex communications of the receiver and transmitter;
wherein the receiver is configurable under the control of the control unit to use any of a plurality of communication modes providing different transmission rates on the communications path, and the control unit and receiver are arranged to;
determine signal energy of a signal received using a current communication mode;
determine noise energy received using the current communication mode following a received signal and before transmission of a signal by the transmitter;
determine a signal to noise ratio for the current communication mode from the determined signal and noise energies, whereby the communication mode can be changed in dependence upon the determined signal to noise ratio;
determine noise energy received using a new communication mode, to which a change may be made, following a received signal using the current communication mode and before transmission of a signal by the transmitter; and
determine a signal to noise ratio for the new communication mode from a stored signal energy for the new communication mode and the determined noise energy for the new communication mode, whereby the current communication mode can be changed to the new communication mode selectively in dependence upon the determined signal to noise ratio for the new communication mode.
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Specification