US1744992A

US1744992A - Communication of intelligence

Info

Publication number: US1744992A
Application number: US24037A
Authority: US
Inventors: Duncan J Stewart
Original assignee: Individual
Current assignee: Individual
Priority date: 1925-04-18
Filing date: 1925-04-18
Publication date: 1930-01-28
Anticipated expiration: 1947-01-28

Description

Jap. 28, 1930. D. J. STEWART 1,744,992

COMMUNICATION 0F INTELLIGENCE I Original Filed April 18. 1925 Bfiupor c005.

- 30 UNITS.

W WWW'VUP' O U 5 E amaze STHNDHRD CHBLE CODE.

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7 UNITS- HOUSE DQ QQ WORD 5/!765.

NW Hm \J v wu-u lnven'ior ylk Patented Jan. 28, 1930 UNITED STATES PATENT @FFHCE DUNCAN J. STEW'ART, OF ROCKFORD, ILLINOIS, ASSIGNOR TO HOWARD D. GOLMAN, OF

ROCKFORD,

ILLINOIS COMMUNICATION OF IIITELLIGENCE Application filed. April 18, 1925, Serial No.'24,037.

The invention relates to the communication of intelligence, and more especially to communication over long distances as in submarine cable telegraphy.

The object of the invention, generally stated, is to provide a code whereby the transmission of intelligence may be accomplished at a substantially greater speed than has heretofore been possible.

In the accompanying drawings I have shown diagrammatically examples of prior codal systems and also an example of the present system, as an aid to a clear understanding of the invention. Figure 1 is an example of a word as transmitted in accordance with the well known Baudot code shown graphically in a manner analogous to the usual graphic representation of the standard cable code shown in Fig. 2. Fig. 3 is a similar example illustrating the use of my code. Fig. 4 illustrates graphically the number of different combinations obtainable by variously arranging a plurality of signal units.

The communication of intelligence as now practiced consists in the transmission of signals electrically to represent the individual letters or characters of the alphabet. In the case of land telegraphy automatically operating mechanism is frequently employed, using what is known as the Baudot code. In this code each letter or character signal is composed of a combination of live units, each of which units is represented by either a positive or a negative current impulse and hence has one of two differentiating characteristics. Thirty-two of such five-unit signal combinations are provided, and these are distributed amon the letters of the alphabet and other characters. There are no spaces between the letter signals composing a word, but spaces between words are represented by a five-unit space signal having certain positive and negative characteristics. The auto matic mechanism employed includes printing devices controlled by the electric current impulses. Herein I have shown in Fig. 1 the positive and negative impulses as being characterized by waves or loops a and b positioned respectively above and below a Zero 0 line 0. Inasmuch as each wave unit may be Renewed November 16, 1928.

said to occupy either of two difierent positions, this code is commonly referred to as a two position code.

In cable or submarine telegraphy, the standard cable code, also known as the modified continental code is now employed. In this code, the letter or character signals are composed of varying numbers of units each having three possible characteristics instead of two as in the Baudot code. Thus the units are represented by current impulses of either positive, negative or Zero polarity, the latter being effected by a neutral line condition. Referring to Fig. 2, the positive and negative characteristics a and Z) are employed to represent the units composing letter or character signals, and the zero characteristic 0 is employed to represent space units between letter or character signals. This code is therefore referred to as a three-positioned code, having reference to the two positions above or below the zero line in the recorded message and the third position coincident with the Zero line.

It will be apparent from the foregoing that in both the Baudot code and in the standard cable code, letter or character Sig-- nals are en'lployed each consisting of units having differentiating characteristics and arranged in predetermined combinations. In each case the units are represented by electric current variations and such variations require in the actual transmission a certain time interval depending upon the speed of the apparatus. Thus, it will be seen that the rate of communication is directly proportional to the number of units which must be employed in transmitting a given message. In the sense herein employed, a unit is the time required for the transmission of either a positive, negative or zero potential impulse.

As is well known, the cost of long telegraphic lines and associated equi )ment, including the initial cost, the interest, depreci: "on and maintenance cost is very great; ano. obviously the cost increases in proportion to the number of signal impulses which it is necessary to transmit to represent a given message. In the case of submarine telegraphy, it has been estimated authoritatively (see Milnor, Journal A. I. E. E. February, 1922) that the cost in the case of each trans- Atlantic cable is approximately 400,000 per year for a cable 2000 miles in length. Furthermore, the same authority estimates that the standard cable code requires'the use of twenty-twounlt-s inspelling out the average word. The use 0]": such a large number or" units per word constitutes a serious limitation on the speed orrate of communication, and when the cost of the equipment i'sconsidered it is readily apparent that this is one of the chief causes of the high cost of cable communication;

It is the aim of the present invention, therefore, to reduce the cost oftelegraphic communication through the mediumof a novel code which is capableot use with the present cable equipment,- and which renders possible. a. substantial reductionv in the time required for transmission by employing a substantially reducednumber of units for the average word: This method consists essentially in providing for each word-of a given vocabulary an individual preconcerted signal;

Proceeding now to a: more detailed consideration of: the method or system constitutingmy inventioml utilize, in providingthe desired number of signals, that principle of mathematics by which'it is established that while a relatively smallnumber of units having different possible characteristics may be arranged ina relatively small number of dis tinct combinations, the number of possible combinations increases very rapidly as the number of units employed increases, and as thenumber of possible characteristics of theunits increases.

In thepresent instance I- employ a threeposition codeso that each signal may represent awor-d and' also a: space. The units employed for the word have two possible'ditlerentcl1aracteristics,viz, positive and negative polarity, and' t-he space unit has only one possible characteristic, viz, a neutral linecondition. The space unit, being-thus specificallydifierent from the word units, serves to separate the word signals ellectually regardless of the length of the latter. This is an important feature of the invention because it renders possible the use of short'signals for frequently used words and". thusgreatly reduces thenumbel of units necessary for the average word.

In Fig. 4 I have shown'the various-possible combinationswhich' may be obtained by the use of one unit, two units, andthree units. where each unit is represented by, a positive or negative current impulse and hence has two different possible characteristics.

lfhe following" table by way of illustration indicates thenumber ofcombinations obtainable-from one. unit up to a relatively large mmiberof units, as for example, seven teen, where each unit may have either of two positions or characteristics.

Combinations (C of two difierent kinds of signal units taken 12 at a time.

It will, be seen-that the number of combinations obtainable from a maximum number of five units where all rnust be'use'dis thirty-two.

But since si nals havin one two three and tour units respectively may also be-used, t-he number of combinations.- which becomes available is equal to the sum of the combinations of one, two, three, four and five. Thus in addition tothe thirty-two combinationsobtainable from a maximum number of five units,-it would also be possible touse sixteen additional combinations: obtainable from four units; eight additional combinations from three units; four additional combinations from two units, and two: additional combinations from one unit, a total of sixtytwo' combinations;

It can be shown mathematically that the total number of combinations available for assignment to signals of varying lengths from a' given maximum number of units, is

equal to 2 PM '2. In such a case, nis the number ot units employed for the word and the added 1- is-for the spaces. Thusif n is'5, 2 2=62. That the: number of combinations available increases rapidly as thenumber of units employed increases will be seen from the fact that where n is 9, 2 '2= 1022; and where 'n is 17, 2" 1) 2=262,1a2. By further increasing the numberof units the number of combinations available may be made large enough to meet any, requirements.

In practicing my'invention the number of units to be employed may obviously be varied as desired, but it is believed that a maximum number of eighteen (seventeen plus one for the space) will in any case be ample,- the number of combinations available in such a. case being 262,142. However,

since the signals vary inlengtlnthe average number ofunitsnecessary to be employed per word would in any case be' obviously somewhat lessthan eighteen. Furthermore,

advantage is taken of the fact that a com paratively small number of words form' a large proportion of the words in common use. Thus by assigning to the words of the vocabulary which occur most frequently the shorter combinations, that is to say, those containing the smaller number of units, the average length, or the average number of units employed per word, is greatly reduced.

Probably the preferred method will in practice provide signal combinations for all comparatively common words, while words occuring rarely may be spelled out letter by letter. In such event, the combinations of two units, three units, four units and five units would be reserved for the letters of the alphabet.

An investigation made for the purpose of determining the approximate number of words in common use disclosed that in a file of ordinary incoming business correspondence containing approximately 60,000 words thirty-two words occurred 28,300 times and one thousand words occurred 5-1,- 300 times. Accordingly. assuming that the signal combinations involving up to five units be reserved for the letters of the alphabet, the signal combinations involving six units would provide for the thirty-two words which are used approximately 47% of the time; and the signal combinations involving from six to ten units would provide for the thousand words which are used approximately 91% of the time. From this it may be estimated that the average length of word in the case of plain or ordinary English is in the neighborhood of seven units, .and since, as above indicated, the average number of units required per word in the case of the present cable code is about twenty-two, the saving effected by my invention is very substantial, being in the neighborhood of three to one. This saving is clearly appar ent from the examples shown in Figs. 1 to 3. The word house is taken in each case as representing an average length word. As spelled out by the standard cable code (Fig. 2) it is shown as consisting of five letter signals employing with the spacing signals twenty-one units. As spelled out by the Baudot code it consists of five signals for the letters and one for the space or a total of thirty units. As represented by a single signal combination (including the space) in accordance with my invention, it may consist of, say, seven units.

From the analysis which has been made it is estimated that less than onetenth of one per cent of the words used would fall outside a vocabulary of 60,000 words. Accordingly if the signal combinations available from sixteen units are assigned to the words of such a vocabulary of 60,000 words, a maxi mum number of eighteen units gives in addition approximately 200,000 signal combinations which are available for assignment to code words as distinguished from plain English words, there being 262,142 signal combinations available for use with all eighteen units, according to the formula 2 1) 2, as above set forth. Any words falling outside such a vocabulary of 260,000 signal combinations may be spelled out letter by letter. It should be noted, however, that each signal, whether representing a Word or a letter, includes a space unit so that no space signal need be used except where two worcs to be spelled out follow in succession.

Obviously signal combinations devised in accordance with my method may be assigned to the most frequently used words up to any desired number, the remaining words being spelled out in accordance with any preferred code. Thus in view of the fact that a comparatively small number of words form a large proportion of every-day language, it may be desirable to limit the assignment of word signals to a maximum of, say, fifty words which in the analysis of plain or ordinary English above referred to were found to occur 31,700 times among 60,000 words. This would represent a substantial saving over the system now in use of approximately fifty per cent. For example, according to the standard cable code, fortyfour units would be required for two words (twenty-two being the average number of units per word), whereas if one of these words were represented by a codal combination according to this invention and the other spelled out by the standard cable code system, a total of only twenty-nine units would be required.

In the use of my method of communication, coding and decoding mechanisms, either partially or wholly automatic, maybe provided or various mechanical aids employed. It is only necessary, however, to employ apparatus which is now available together with a suitable index or file containing the various codal combinations and the words represented thereby. Positive and negative impulses may be transmitted by the use of apparatus such as is in common use to represent the two kinds or characteristics of the units composing the words, and the neutral line condition may be efiected also in accordance with known apparatus to represent spaces. It should be understood, however, that my code is not limited to use in line signaling. Thus it may readily be employed in radio communication. Also, the number of differentiating characteristics for the units may vary. For example, if transmission is effected by the well known carrier current method, different frequencies may be employed to indicate various characteristics and the number of such frequencies and hence characteristics may readily be more than three. This would greatly increase the number of possible combinations available from a small number of units.

s toa-ny written language whatever;

- 'Ilhe message mayiberrecei-vedf and grapl1.-- ioally-recordedby the use ofitheiwell know-n siphon recorder;.and: by the use ot the? indexpnovidedi an operator. decodes the message, translatingthe message represented graphicalliy byaline (see-Fig.3) int'oa wor-d' mes- As' an aidf to the decoding operation,

sa e; apparatus operating Whollyor partially automatically mayhere, too; be employed-,buti

inasmuch as-such coding and decoding apparatus form no part of this invention it. is deemedi unnecessary herein; to describe the same; s

It will'beiappa-nent that because: at the substantial saving intime eifectedaby the: transmissionl of intelligence acconding tomy; in vention: asi compared: to the method now in common? use the.= timerequired for the; decode lHQ'f operation, even though: purely manual,.

offers no SBElbllSiObSffiClfii. Thus it isprob;- able that the additional coding and decoding cost: pBIi'WOE-Cla ELS COlIlPfiI'Bd to the costof. presentmetlio'ds; would be n0minal= and this cost cani bei-veny greatly. reduced by,- theaid ofthecoding?" and decoding apparatus. aloovereferried; to; V

- 'llar reduceto aa mini-mum: errors:- dueto: the failure of the transmitting? operator; 1nes+ sages to: be" transmitted; may, if desined, be-

checked: before sending: out: without substantial'lzy increasing; the cost; and: to insure; ac

cunacyzin: thetransmitting apparatus, itmay be desirable to: neduce slightly the: speech of actualiti'ansmission; This may. bedonewith out aniateria'le nedluction in: the? total sawingter of. code=employed,;that is to say, whether one or: another. of the common commercial codes is beingused I claim asmy invention;

In telegraphic communication system in which signalseach composed of a direct suecession-of unitshaving two or more diflerem tiating, characteristics are transmitted elec+ trically, the method: of signalling which con;

sists in transmitting. word signals individl ually representing such'wonds as fall withinal given; vocabulary, and. transmitting: letter signals; individually representing let-tiers, ofthe-alphabet andlspellingzoutletter by letter such; Words as fall; outside the. given; vocabu:-- larp while composing all of said: signals of code combinations/of a. variable number of units. each: including an! invariable; tenminal; unit so that as thesignals occurlILCllllGOl? suc cession. with; no? space; signals; between them they are capable of being distinguished from;

maeea each other,, and sending a. space signal between; the adjacent terminal letter signals of successive non-vocabulary words.

In testimony whereof I have hereunto. at.- fixed my-signature.

DUNCAN J STEWART.

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