Data transmission system with modems coupled to a common communication medium

Claim 2

A data transmission system comprising: a communication medium (1, 2); a plurality of data processors (4a to 4n); modems (5a to 5n) coupling said respective data processors to said communication medium at points thereof for permitting transmission and reception of information signals among said data processors through a predetermined point (3) of said communication medium, each of said modems including a transmitting amplifier (14) for sending out an information signal from the associated data processor to said communication medium and a receiving amplifier (15) for receiving an information signal sent out from other modems to said communication medium; and pilot signal generating means (6) for sending a pilot signal of a predetermined reference level to said communication medium at said predetermined point thereof; each of said modems further including: detector means (18) for detecting the reception level of the pilot signal received by said receiving amplifier (15); and gain adjusting means (19) responsive to the reception level detected by said detecting means to adjust the gain of said transmitting amplifier (14) such that the level of a transmission signal transmitted from said transmission amplifier to said communication medium at said predetermined point of the communication medium becomes a predetermined level of the pilot signal and adjust the gain of said receiving amplifier (5) such that a predetermined reception level is obtained.

Claim 3

The data transmission system according to claim 1, characterized in that the transmission and reception of the information signals among the data processors (4a to 4n) are effected in the form of data packets; and the duration of each data packet is shorter than the duration of the pilot signal; and said gain adjusting means (19) of each of said modems is arranged to effect said adjustment of the gains of said transmitting and receiving amplifiers (14, 15) when the duration of a signal received by said receiving amplifier is longer than the duration of one data packet or when, if the duration of a signal received by said receiving amplifier is shorter than the duration of the pilot signal, the difference between reception levels of successively received two signals is less than a predetermined permissible value.

Claim 4

The data transmission system according to claim 2, characterized in that each of said modems (5a to 5n) further includes means (11, 13) for sending a test signal through said transmitting amplifier (14) to said communication medium after the gain adjustment of said transmitting and receiving amplifiers, said test signal being to be received by said receiving amplifier (15) of the same modem; and said gain adjusting means is arranged to compensate for the gain of said transmitting amplifier (14) according to the difference between the predetermined reception level of said receiving amplifier and the reception level of one of two test signals sent by the same modem if the difference between the reception levels of the two test signals is less than the predetermined value.

Claim 5

The data transmission system according to claim 2, each of said modems further includes means (32) for detecting whether the associated data processor is in a transmitting mode; and said gain adjusting means (19) is arranged to operate, when the associated data processor is not in the transmitting mode, so as to adjust the gain of said transmitting amplifier (14) according to the level of a signal received by said receiving amplifier (15) to make substantially equal the level of signal transmitted through said transmitting amplifier at said predetermined point of said communication medium to the reference level of the pilot signal and increase the gain of said receiving amplifier (15) by an amount corresponding to the difference between said predetermined reception level and the reception level of said received signal if the duration of said received signal is longer than the duration of the data packet, and increase the gains of said transmitting and receiving amplifiers by an amount corresponding to part of the difference between said predetermined reception level and the reception level of said received signal if the duration of said received signal is shorter than the duration of the data packet.

Claim 6

The data transmission system according to claim 4, characterized in that said gain adjusting means (19) is arranged to, when the associated data processor is in the transmitting mode, compensate the gain of said transmitting amplifier by an amount corresponding to the difference between the reception level of a signal which is transmitted from said transmitting amplifier (14) and received by said receiving amplifier (15) through said predetermined point (3) of said communication medium and the predetermined reception level.

Claim 7

The data transmission system according to claim 1, characterized in that said communication medium includes a transmission line (1) and a reception line (2), said transmitting amplifier (14) of each of said modems being coupled to said transmission line, and said receiving amplifier (15) of each of said modems being coupled to said reception line; and a headend (3) is provided at a predetermined point of said communication medium for coupling said transmission line to said reception line.

Claim 8

The data transmission system according to claim 1, characterized in that the transmission and reception of information signals among said modems are effected through a frequency shift keying system.

Claim 9

The data transmission system according to claim 1, characterized in that the predetermined level is the reference level of the pilot signal.

Claim 10

A data transmission system comprising: a communication medium (1, 2); a plurality of data processors (4a to 4n); modems (5a to 5n) for coupling said respective data processors to said communication medium at points thereof to permit transmission and reception of information signals among said data processors through a predetermined point (3) of said communication medium, each of said modems including a transmitting amplifier (14) for sending out an information signal from the associated data processor to said communication medium and a receiving amplifier (15) for receiving an information signal sent out from other modems to said communication medium; and pilot signal supplying means (6) for supplying a non-modulated pilot signal at a predetermined reference level to said communication medium at said predetermined point (3) thereof; each of said modems further including: envelope detecting means (18) for detecting the envelope of a signal received by said receiving amplifier (15); comparing means (191) for comparing an output voltage (V D ) of said envelope detecting means (18) representing the reception level of said received signal to a threshold voltage representing a predetermined reception level; test signal sending means (11, 13) for sending a non-modulated test signal through said transmitting amplifier (14) to said communication medium; non-modulated signal detecting means (32a) for detecting that a signal received by said receiving amplifier (15) is the pilot signal or test signal; and gain adjusting means (19a) responsive to said comparing means (191) and non-modulated signal detecting means (32a) to adjust, when said receiving amplifier (15) receives the pilot signal, the gain of said receiving amplifier so as to make substantially equal the reception level of the pilot signal to the predetermined reception level, and, after the adjustment of the gain of said receiving amplifier, cause said test signal sending means (11, 13) to send the test signal to said communication medium and adjust the gain of said transmitting amplifier (14) to make substantially equal the reception level of the test signal received through said predetermined point of said communication medium to said predetermined reception level.

Claim 11

A data transmission system comprising: a communication medium (1, 2); a plurality of data processors (4a to 4n); modems (5a to 5n) for coupling said respective data processors to said communication medium at points thereof to permit transmission and reception of information signals among said data processors through a predetermined point (3) of said communication medium, each of said modems including a transmitting amplifier (14) for sending out an information signal from the associated data processor to said communication medium and a receiving amplifier (15) for receiving an information signal sent out from other modems to said communication medium; and pilot signal supplying means (6) for supplying a non-modulated pilot signal at a predetermined reference level to said communication medium at said predetermined point (3) thereof; each of said modems further including: envelope detecting means (18) for detecting the envelope of a signal received by said receiving amplifier (15); comparing means (191) for comparing an output voltage (V D ) of said envelope detecting means (18) representing the reception level of said received signal to a threshold voltage representing a predetermined reception level; test signal sending means (11, 13) for sending a non-modulated test signal through said transmitting amplifier (14) to said communication medium; non-modulated signal detecting means (32a) for detecting that a signal received by said receiving amplifier (15) is the pilot signal or test signal; and gain adjusting means (19a) responsive to said comparing means (191) and non-modulated signal detecting means (32a) to adjust, when said receiving amplifier (15) receives the pilot signal, the gain of said receiving amplifier so as to make substantially equal the reception level of the pilot signal to the predetermined reception level, and, after the adjustment of the gain of said receiving amplifier, cause said test signal sending means (11, 13) to send the test signal to said communication medium and adjust the gain of said transmitting amplifier (14) to make substantially equal the reception level of the test signal received through said predetermined point of said communication medium to said predetermined reception level.

Claim 12

The data transmission system according to claim 9, characterized in that said gain adjusting means (19a) is arranged to consecutively effect a coarse gain adjustment of said receiving amplifier, fine gain adjustment thereof, coarse gain adjustment of said transmitting amplifier and fine gain adjustment thereof; each of the coarse gain adjustments being carried out such that the gain is increased or decreased in a coarse gain adjustment step, the gain adjusting step being switched to a finer step every time a relation between the reception level of the pilot signal or test signal and the predetermined reception level is changed, and each of the fine gain adjustments being carried out such that the gain is increased or decreased in a minimum gain adjusting step.

Claim 13

The data transmission system according to claim 9, characterized in that said gain adjusting means is arranged to perform an initial setting routine and a stationary routine, said initial setting routine including consecutive subroutines for a coarse gain adjustment of said receiving amplifier, fine gain adjustment thereof, coarse gain adjustment of said transmitting amplifier and fine gain adjustment thereof, said stationary routine including subroutines for fine gain adjustments of said receiving and transmitting amplifiers and being repeatedly executed during the operation of the modem, and the fine gain adjustment of said transmitting amplifier in the stationary routine being done once for a plurality of times of the fine gain adjustment of said receiving amplifier.

Claim 14

The data transmission system according to claim 9, characterized in that said communication medium includes a transmission line (1) and a reception line (2), and a headend (3) is provided for coupling said transmission line (1) to said reception line (2) at said predetermined point of said communication medium.

Claim 15

The data transmission system according to claim 9, characterized in that the transmission and reception of information signals among said modems are effected through a frequency shift keying system.

Claim 16

A data transmission system comprising: a communication medium (1, 2); a plurality of data processors (4a to 4n); modems (5a to 5n) for coupling said data processors to said communication medium at points thereof to permit transmission and reception of digital information signals among said data processors through a predetermined point (3) of said communication medium, each of said modems including a transmitting amplifier (14) for sending out a digital information signal from the associated data processor to said communication medium and a receiving amplifier (15) for receiving a digital information signal sent out from other modems to said communication medium; and pilot signal sending means (6) for sending out a pilot signal at a predetermined reference level to said predetermined point (3) of the communication medium; each of said modems further including: test signal sending means (11, 13) for sending out a test signal through said transmitting amplifier (14) to said communication medium; envelope detecting means (18) for detecting the envelope of an output signal of said receiving amplifier; and gain adjusting means (19, 19a) for adjusting the gains of said receiving and transmitting amplifiers (14, 15) in response to output voltages of said envelope detecting means (18) when the pilot signal and test signal are received respectively.

Claim 17

A data transmission system comprising: a communication medium (1, 2); a plurality of data processors (4a to 4n); modems (5a to 5n) for coupling said data processors to said communication medium at points thereof to permit transmission and reception of digital information signals among said data processors through a predetermined point (3) of said communication medium, each of said modems including a transmitting amplifier (14) for sending out a digital information signal from the associated data processor to said communication medium and a receiving amplifier (15) for receiving a digital information signal sent out from other modems to said communication medium; and pilot signal sending means (6) for sending out a pilot signal at a predetermined reference level to said predetermined point (3) of the communication medium; each of said modems further including: test signal sending means (11, 13) for sending out a test signal through said transmitting amplifier (14) to said communication medium; envelope detecting means (18) for detecting the envelope of an output signal of said receiving amplifier; and gain adjusting means (19, 19a) for adjusting the gains of said receiving and transmitting amplifiers (14, 15) in response to output voltages of said envelope detecting means (18) when the pilot signal and test signal are received respectively.

Claim 18

A data transmission system comprising: a communication medium (1, 2); a plurality of data processors (4a to 4n); and modems (5a to 5n) coupling said respective data processors to said communication medium at points thereof for permitting transmission and reception of information signals among said data processors through a predetermined point (3) of said communication medium, each of said modems including a transmitting amplifier (14) for sending out an information signal from the associated data processor to said communication medium, a receiving amplifier (15) for receiving an information signal sent out from other modems to said communication medium, detector means (18) for detecting the reception level of a signal received by said receiving amplifier; and gain adjusting means (19) responsive to the reception level detected by said detecting means to adjust the gain of said transmitting amplifier such that the level of a transmission signal transmitted from said transmission amplifier to said communication medium at said predetermined point of the communication medium becomes a predetermined level and adjust the gain of said receiving amplifier such that a predetermined reception level is obtained.

Claim 19

A data transmission system comprising: a communication medium (1, 2); a plurality of data processors (4a to 4n); and modems (5a to 5n) coupling said respective data processors to said communication medium at points thereof for permitting transmission and reception of information signals among said data processors through a predetermined point (3) of said communication medium, each of said modems including a transmitting amplifier (14) for sending out an information signal from the associated data processor to said communication medium, a receiving amplifier (15) for receiving an information signal sent out from other modems to said communication medium, detector means (18) for detecting the reception level of a signal received by said receiving amplifier; and gain adjusting means (19) responsive to the reception level detected by said detecting means to adjust the gain of said transmitting amplifier such that the level of a transmission signal transmitted from said transmission amplifier to said communication medium at said predetermined point of the communication medium becomes a predetermined level and adjust the gain of said receiving amplifier such that a predetermined reception level is obtained.

Claim 20

The data transmission system according to claim 15, characterized in that said gain adjusting means is arranged to adjust the gain of said transmitting amplifier in response to the reception level of a signal transmitted from a predetermined modem.

Claim 21

The data transmission system according to claim 16, characterized in that said gain adjusting means is arranged to adjust the gain of said transmitting amplifier when the difference between the reception levels of successive signals from said predetermined modem is smaller than a predetermined value.