Pulse or digital communications – Repeaters – Testing
Patent
1983-06-07
1986-02-18
Griffin, Robert L.
Pulse or digital communications
Repeaters
Testing
375 19, 371 56, 360 40, 340347DD, H03K 1324
Patent
active
045717354
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to the transmission of binary digital information, and to techniques in the communication of binary digital data between operating entities such as computer processors and remote devices, or between a number of computers where each can obtain direct access to the memory space of another. As will appear below, the invention has many other fields of application, and involves novel aspects both in the communications protocol employed, and in the circuitry by which the system may efficiently be realised.
BACKGROUND ART
Prior art methods of binary digital transmission employed either synchronous or asynchronous transmission, without the ability to change between these modes due to the synchronising characters by which the former is structured, and the start and stop bits employed in the latter, framing each character transmitted for character synchronisation. The use of a unique synchronising character in synchronous data transmission limits the rate of data transmission, due to the requirement that transmitted characters be continuously checked and if necessary modified to preserve the uniqueness of the synchronising character.
DISCLOSURE OF THE INVENTION
The present invention seeks to overcome such disadvantages by employing a novel transmission protocol in a ternary or higher multi-level code, and using the noise-free characteristics of optical fibre links. The invention also provides a novel technique for driving the multi-level signal generator, which not only proivdes advantages in driver operation, but also simplifies the encoding circuitry required.
Using prior art techniques, the maximum transmission bit rate for a given optical fibre link length has been limited by modal and material dispersion. The noise-free properties of optical fibres makes it possible, however, to use ternary or higher multi-level codes to obtain increased data transmission rates for a given bit rate, by trading optical power loss for greater data throughput. When it is considered that a 1 km optical fibre link can achieve -18 dbm optical power at the receiver, and that data can be recovered up to -38 dbm, there is a 20 dbm excess available for the use of a multi-level code. The use of ternary code can give an effective data bit rate equal to the transmitted bit rate. Codes of more levels could be employed to allow the transmitted data bit rate to exceed the transmission bit rate by a factor of 2 or 3, to this end codes of up to 9 levels may be employed to utilise fully the 20 dbm excess previously mentioned.
By providing an approach to multi-level encoding and transmission protocols which simplifies the necessary componentry and achieves very high transmission rates, the present invention enables these properties of fibre optic links to be utilised in achieving very high speed, transparent, and reliable data transfer.
Multi-level encoding of groups of data bits (for example bit pairs) to corresponding voltage level pairs on a transmission line are known. In these techniques the excess states, unused for the encoding of the possible bit pair combinations are used to indicate bit pair synchronisation errors. In paired selected ternary encoding, three such "illegal" states exist. The use of these three illegal states for the purpose of indicating loss of bit pair synchronisation is wasteful, however, as the ability to restore synchronisation during transmission is unnecessary due to the fact that the loss of synchronisation having corrupted the data, the data must be re-transmitted anyway. If only one of the three illegal states is used for pair synchronisation, errors will be identified within a few characters and the transaction aborted.
The invention broadly resides in a method for the transmission of binary sequential data by the multi-level encoding of grouped selected data bits in which a first number of data bit sequences of said grouped data bits are translated into uniquely chosen ones of a first group of differing level pairs of a multi-level signal and the remaining da
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patent: 4048440 (1977-09-01), Peck et al.
patent: 4103234 (1978-07-01), Frazier, Jr.
Dorres, I. et al, "An Experimental 224 Mb/s Digital Repeatered Line", The Bell System Technical Journal, vol. 45, No. 7, Sep. 1966.
"A New Class of Selected Ternary Pulse Transmission Plans for Digital Transmission Lines", J. M. Sipress, IEEE Transactions on Communication Technology, vol. 13, No. 3, pp. 366-372, 9/66.
Greer Timothy K.
Griffin Robert L.
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