JPS60134538A - Information transmitting system - Google Patents

Abstract

PURPOSE:To ensure detection of collision of carrier band signals by detecting independently the presence of a different frequency component corresponding to a different signal level of a base band signal or its coded signal to detect that plural frequency components exist at the same time. CONSTITUTION:Plural MODEMs 6 are connected to the network, BPF12, 15 are connected respectively to an FM modulator 11 and an FM demodulator 16 of each MODEM6, a transmission amplifier 13 is connected to the BPF12 and a reception amplifier 14 is connected to the BPF15. A collision detector 17 connected to a collision display signal generating circuit 18 is connected to the BPF15. The detector 17 is provided with BPF20, 21 inputting a signal from the BPF15, each signal level is extracted and envelope detectors 22, 23 detect the signal. The signal is fed to comparators 26, 27, compared with a reference signal from reference signal generators 24, 25, the frequency component to each signal level is detected independently, an output of the comparators 26, 27 is fed to an AND circuit 28 to detect surely the collision of the carrier band signals.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to signal transmission via a carrier band transmission path.
The present invention relates to a practical information transmission system that can reliably detect conflicts.

[Technical background of the invention and its problems]

As a network that does not require a central control station and is highly scalable, it uses a completely distributed peer-to-peer protocol transmission method, that is, C8 Kite D' (Carrier SenseM
ultiple Access with Ce1li
Detection) method is known.

This method performs baseband transmission via a coaxial cable as a transmission path, but recently, in order to use the coaxial cable more efficiently, the baseband signal is converted to a high frequency carrier band signal. The development of a so-called broadband network, which aims to make effective use of bandwidth, is underway.

By the way, on such a carrier band transmission path.

Challenges in realizing the C8MA7CD system include ensuring the same level of collision detection characteristics as conventional baseband transmission paths and ensuring compatibility with higher-level protocols. Regarding the above-mentioned collision detection method, the following methods are being considered.

That is, in the first method, the transmitted data is temporarily stored, and when the data returned via the transmission line and the transmitted data all match, the transmission is performed without causing a collision, and conversely, the data is transmitted without any collision. If there is a 1-bit data difference, it is considered that a conflict has occurred, and this method is called a pit matching method for transmitted and received data. Since it is necessary to store the transmitted data, for example, in order to ensure compatibility with the upper-level protocol, some of the functions that the upper-level protocol originally has must be stored at the physical level, which is the lower-level protocol. This is necessary. For this reason, the configuration of the modem as hardware that realizes all the physical levels becomes complicated, leading to a problem of soaring prices.

Moreover, this system has an inherent problem in that only the transmitting modem can detect the collision, and the receiving modem cannot detect the collision. For this reason,
While the modem that detected the above conflict is executing a random process called backoff, another modem that was in the receiving state acquires the right to transmit and is in a high traffic state. This causes a problem in that modems that once have a conflict are unable to transmit forever. Furthermore, when monitoring traffic on the network, it is not possible to measure the extent to which conflicts are occurring, which poses network management problems.

In the second method, the modem that is about to transmit sends out two pulses at random time intervals before transmitting data, and from the time when the first pulse is sent out, the modem sends out two pulses at random time intervals. There is a so-called random pulse time monitoring method in which the transmission path is monitored for a period of time, and if only two pulses are received during that time, it is assumed that there is no conflict and data transmission is started.

However, this method requires time to monitor whether there is a conflict every time a packet of data is sent, so there is a problem that the transmission efficiency of the network and the effective transmission capacity are reduced. . Also, similar to the first method described above, in order to ensure compatibility with the upper level protocol, two random pulses are sent out after receiving the transmission data from the upper level, and while this is monitored, the above transmission Since it is necessary to store data, the modem hardware becomes complicated, which causes problems that lead to soaring costs.

Furthermore, as a third method, if the level of the beat signal generated by overlapping signals sent from two modems is in the same phase, for example, it is detected that the peak value is doubled, and the presence or absence of a collision is detected. There is a so-called signal level detection method that determines the According to this method, the first and 81'! 2
This method often causes problems such as the modem in the receiving state cannot perform collision detection or the efficiency of the network decreases.

However, in the modulation methods such as VSB and deobiner IJ uK's I (such as VSB and IJ uK's I), which have recently been attracting attention from various viewpoints, the carrier frequency does not change in Id, .

The frequency of the beat signal caused by the collision of the signals is very low, and the transmission period of the bucketed data is 1, +
There is no guarantee that twice the peak value will always be generated by one bit of the in-phase signal of each vcl. For this reason.

There is a drawback that the collision cannot be reliably detected for 100 times.

[Purpose of the invention]

The present invention has been made in consideration of these circumstances, and its purpose is to enable each modem to reliably detect collisions on a carrier band transmission path and to improve network efficiency. The objective is to provide a highly practical information transmission method that can be used.

[Summary of the invention]

The present invention provides a baseband signal in a transmission line network in which a plurality of modems that modulate a baseband signal or a signal obtained by encoding this baseband signal into a carrierband signal with a frequency shift are connected to a carrierband transmission line. or the carrier band transmitted from multiple modems by independently detecting the presence of different frequency components corresponding to different signal levels of the encoded signal, and by detecting the simultaneous presence of multiple frequency components. This detects signal imbalance.

〔Effect of the invention〕

Therefore, according to the present invention, if the signal levels of baseband signals or their encoded signals corresponding to two carrier band signals that are in conflict are different, a conflict can be instantly and reliably detected. Moreover, since the frequency component is transmitted over the entire transmission path, all modems connected to the transmission path can detect the collision. Furthermore, since there is no need for processing such as sending out pulses prior to data transmission,
The network efficiency can be improved, and the modem configuration does not become complicated or expensive, which is a great practical effect.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to all the drawings.

FIG. 1 is a schematic configuration diagram of a network to which this method is applied, in which a carrier band transmission line 1 includes a transmission line 2, a reception line 3. and a head end 4 consisting of a directional coupler. The head end 4 transmits the signals sent out on the transmission line 2 via the reception line 3, forming a so-called double cable network. A plurality of modems 6 (6a, 6b to 5n) are connected to such a transmission line (2). It goes without saying that each modem 6 (6a, 6bz6n) is connected to the transmission line 21 and reception line 3 of the transmission path 1 via a directional coupler. Each modem 6 (6, a, 6 b to 6 n) is connected to an upper protocol device such as an information processing device via an interface line.

The modem 6 is configured as shown in FIG. 2, for example. That is, transmission data consisting of a baseband signal or an encoded signal of the baseband signal given from the upper protocol device via the interface line is input to the FM modulator 11 and frequency-modulated, and then sent to the bandpass filter 12 . The signal is sent to the transmission line 2 via the transmission amplifier 13. In other words, the transmission data is modulated into a carrier band signal with all the frequency deviations and is transmitted to the transmission path 1. On the other hand, a carrier band signal (d) inputted from the reception line 3 of the transmission path 1 is inputted via the reception amplifier 14, and is passed through the bandpass filter 15'ea to F
M demodulator 16. The F'M demodulator 16 demodulates the carrier band signal and reproduces the base band received data. This baseband received data is then given to the upper protocol equipment via the interface line.

Also, in this modem 6, a bandpass filter 15
The output signal is also given to the collision detector 17. This equilibrium detector 17, whose configuration is shown in FIG. 3, independently detects frequency components corresponding to each possible signal level of the baseband signal or its encoded signal,
A collision is detected by detecting the simultaneous presence of a plurality of frequency components, and the detection information is provided to the collision display signal generation circuit 18. This equilibrium display signal generation circuit 18 is composed of a pulse generator of 5, for example, 101M1 (z), and is energized by the collision detection by the equilibrium detector 17 to generate an equilibrium display signal consisting of pulses of lQMH2. The above-mentioned upper protocol 4a
is sent to the transmission line 1 to notify that a collision has occurred on the transmission line 1.

By the way, the collision detector 17 which performs collision detection as shown in FIG. 3 is constructed as shown in FIG. The signal given from the bandpass filter 15 is guided to a bandpass filter 20. This bandpass filter 20 passes 3μ of frequency components near the frequency corresponding to the signal level FB of the baseband signal or its encoded signal, and removes frequency components near the frequency corresponding to the signal level "o". . The signal given from the bandpass filter 15 is
The signal is also guided to a band pass filter 21, where only frequency components near the frequency corresponding to the signal level "0" are passed, and frequency components near the frequency corresponding to the signal level "1" are removed. In this way, the bandpass filter 20
, 21 respectively.
'' are detected by envelope detectors 22 and 23, respectively, and the reference signals output from reference signal generators 24 and 25 are detected by comparators 26 and 27, respectively. It is determined whether a frequency component corresponding to the signal levels [1J, [OJ] exists as a threshold value.

These reference signal generators 24 and 25 provide thresholds that are sufficiently higher than the noise level of the transmission line 1, and the comparators 26 and 27 output signals when these values are exceeded. . The outputs of these comparators 26 and 27 are ANDed by an AND circuit 28, and the output is given to a monostable multivibrator 29. As a result, when a collision is detected, the monostable multivibrator 29 outputs a collision detection signal with a constant time width. In the collision detector 17, the signal level "
””.

Collision is detected by detecting the simultaneous presence of frequency components corresponding to "0".

Incidentally, the modem 6 may be constructed as shown in FIG. 4. That is, transmission data &'i consisting of a baseband signal or a coded signal of the baseband signal given from the upper protocol device via the interface line is input to the FM modulator 31, frequency modulated, and then transmitted to the bandpass filter 32°. The transmission line 2 via the transmission amplifier 33
will be sent to. That is, the transmission data is modulated into a carrier band signal with a frequency shift and is transmitted to the transmission path 1. on the other hand,
The non-carrier band signal inputted from the receiving line 3 of the transmission line 1 is inputted via the receiving amplifier 34, passes through the entire bandpass filter 35, and is applied to the EM demodulator/collision detector 36. The carrier band signal is demodulated by the FM demodulator/equilibrium detector 36 and the received data of the base band is reproduced. This baseband received data is then given to the upper protocol device via the interface line. Furthermore, this FM demodulator/equilibrium detector 36 independently detects frequency components corresponding to each possible signal level of the baseband signal or its encoded signal, and detects the simultaneous presence of a plurality of frequency components. A collision is detected, and the detected information is given to the collision display signal generation circuit 37. The collision display signal generation circuit 37 is composed of, for example, a 10 MHz pulse generator, and is connected to the FM demodulator and collision detector 36.
When a collision is detected, the signal is energized to generate a collision indication signal consisting of a pulse of lQ MHz. This conflict indication signal is given to the upper protocol equipment to notify that a conflict has occurred on the transmission line 1.

By the way, F which performs such FM demodulation and collision detection
The M demodulator and collision detector 36 is constructed as shown in FIG. The signal given from the bandpass filter 35 is guided to a tuning circuit 40.41, which selects frequency components corresponding to the signal levels r1J, ro, and J of the baseband signal or its encoded signal, respectively. The output signals of the tuning circuits 40 and 41 are respectively detected by envelope detectors 42 and 43, and a comparator 44 detects the rl and J of the received data depending on which of the two frequency components is larger.
, determine roJ. On the other hand, envelope detectors 42 and 43
The outputs of are also given to comparators 45 and 46, respectively, and it is determined whether or not a frequency component corresponding to the signal levels r2J and roj exists using the reference signal output from the reference signal generator 47 as a dark value. This reference signal generator 47 provides a sufficiently high threshold against signal leakage due to over-ramp of the resonance characteristics of the two tuned circuits, and the comparators 45 and 46 output a signal when the threshold is exceeded. It has become a thing. The outputs of these comparators 45 and 46 are ANDed by an AND circuit 48 and then input to a monostable multivibrator 49, which outputs an equilibrium detection signal with a constant time width.

In this way, according to this method, if the signal levels in the baseband of the carrier band signals that conflict in the transmission line network that frequency modulates and transmits the baseband signal or its coded signal are different, it can be instantaneously and extremely easily transmitted. Collision can be detected accurately and reliably. Moreover, since there is no need for processing such as transmitting two pulse signals and monitoring the state of the transmission line 1 prior to data transmission as in the conventional method, network efficiency can be made sufficiently high. Also '471
Since the collision is detected from the frequency components on the transmission line 1 as described above, it is possible to simultaneously detect the collision in all the modems 6 connected to the transmission line 1. As mentioned above, the structure is simple, and it can be realized at low cost, resulting in great practical effects.

The system of the present invention has been described above, but the present invention is not limited to these embodiments and does not include 1. As explained about the K signal, even if the baseband signal is multi-level encoded, it is possible to detect each frequency component corresponding to the signal level and detect that two or more of them exist simultaneously. Collision can be detected.

In addition, in the embodiment, a two-city cable type network will be described, in which a single cable is band-divided so that it is shared by the transmitting line and the receiving line, and the frequency is converted at the head end. Even in the so-called single-cable system, the frequency components on the transmission line are equally frequency-shifted and sent to the reception line, so collisions can be reliably detected in the same way as in the previous embodiment.

Furthermore, transmission line 1. Of course, this can be realized using twisted bare wires or coaxial cables that handle electrical information, but it is also possible to use light as the information medium and configure transmission #1 with an optical fiber cable. In short, the present invention can be modified in various ways without departing from its gist. I'll be able to have a real life

[Brief explanation of drawings]

The figures show an embodiment of the present invention. Figure 1 is a network configuration diagram, Figure 2 is a modem configuration diagram, Figure 3 is a collision detector configuration diagram, and pXJ diagram is another modem configuration example. FIG. 5 is a diagram showing a configuration example of an FM demodulator/collision detector. 1...Carrier band transmission path, 4...Head end, 6.
6a to 6n...Modem, 17...Collision detector, 2
0.21 band pass filter, 22, 23, 42.4
3 - Envelope detector, 24°25, 47... Reference signal generator, 26, 27, 44, 45.46... Comparator, 36... FM demodulator and collision detector, 40.41・・・
Tuned circuit. Agent Patent attorney Kensuke Norichika (and 1 other person) Figure 1 Figure 4 Shiun Figure 5

Claims (1)

[Claims] (1) In a transmission line network in which a plurality of modems that modulate a baseband signal or a signal obtained by converting this baseband signal into a carrierband signal with a frequency shift are connected to a carrierband transmission line, the baseband A plurality of frequency components can be transmitted from a plurality of modems by independently detecting the presence of different frequency components corresponding to different signal levels of the signal or its encoded signal, and detecting the simultaneous presence of the plurality of frequency components. An information transmission method characterized by detecting collisions of carrier band signals.