GB2105553A

GB2105553A - Communications system and method

Info

Publication number: GB2105553A
Application number: GB08222953A
Authority: GB
Inventors: Brinker Carl Siegmund Den
Original assignee: REDIFFUSION RADIO SYSTEM LIMIT
Current assignee: REDIFFUSION RADIO SYSTEM LIMIT
Priority date: 1981-08-10
Filing date: 1982-08-10
Publication date: 1983-03-23

Abstract

A digital communications system comprises a transmitter, a receiver, and two memories located one at the transmitter and one at the receiver, each memory storing an identical vocabulary of words in the form of binary codes. An entered binary word is compared with the stored binary words, and an abbreviated form of an entered binary word is transmitted when the entered binary word is identical to one of the stored binary words. The abbreviated form may comprise the binary code representing the first two letters of the word. If there is no identity, the entered binary word is transmitted in full. At the receiver the reverse takes place.

Description

SPECIFICATION Communications system and method The present invention relates to a communications system and method.

In many situations, both commercial and military, it is desirable to reduce the time for which a communications system is occupied in carrying a message. Similarly, in many situations it is desirable to encode a message to prevent a competitor or enemy from monitoring the message. It is however also very important for the system to be easy to use so that messages are decoded quickly and operators do not have to be highly trained.

British Patent Specification No. 2 057 821 describes a communications system for transmitting words each of which is composed of a series of characters. The system transmitter and receiver each comprise a read only memory in which a vocabulary of words to be transmitted is stored each work being allocated to a predetermined address which is related to the stored word in accordance with a predetermined hashing algorithm. When a word is entered for transmission, an address is generated from the word itself on the basis of the hashing algorithm and the word stored at the generated address is read out and compared with the entered word. If identity is found, the generated address is transmitted and the word stored in the transmitted address is read out at the receiver. If no identity is found, the word is transmitted in full text.

Thus the system operates in accordance with the following: 1. Enter word in binary code 2. Generate address from binary code 3. Look up binary code stored at generated address 4. Check stored binary code identical to entered binary code 5. If identical, transmit address 6. Read out binary code stored at received address The system of Specification No. 2 057 821 is advantageous in that it provides considerable data compression. It is however complex and clearly concerned with communications which are expected to be made up from a large number of possible words. Such a complex system may find application in situations where large volumes of information are to be communicated but would be too costly and bulky for many applications such as military radiotelephones.The military requirement for data compression is primarily to reduce the transmission time of simple messages rather than to handle large volumes of information.

It is an object of the present invention to provide an improved communications system and method.

According to the present invention, there is provided a communications system for transmitting words comprising a transmitter, a receiver, two memories located one at the transmitter and one at the receiver, each memory storing an identical vocabulary of words in the form of binary codes, means at the transmitter for entering a word to be sent in the form of a binary code, the relationship between the stored binary codes and the words they represent being the same as the relationship between the entered binary code and the word it represents, means for comparing an entered binary code with the stored binary codes, means at the transmitter for transmitting an abbreviated form of an entered binary code when the entered binary code is identical to one of the stored binary codes, and for transmitting the entered binary codes in full when the entered binary code is not identical to any of the stored binary codes, means at the receiver for correlating a received abbreviated binary code with the associated stored binary code, and means for reading out received entered codes and the stored binary code associated with a received abbreviated binary code to reconstitute a message made up from a series of entered binary codes.

Preferably the abbreviated form of an entered binary code comprises the binary code representative of the first in letters of the entered word, for example the first two letters. Even in the case wherein only the first two letters are transmitted a vocabulary of several hundred often used words can be built up. A vocabulary of only three or four hundred words can account for a high proportion of words used in military applications.

In a few cases it might be desired to abbreviate two or more words having the same two first letters. e.g. "enemy", "encompass" and "engage". To enable this to be done, the system can be arranged to abbreviate the words "encompass" and "engage" to their first and third letters, that is EC and EG. This retains the phonetic similarity between the full and abbreviated forms of the words.

In contrast with the arrangement of Specification No. 2 057 821, it is not necessary to generate a memory address from an entered binary code and the transmitted signal is made up from full or abbreviated forms of the entered binary codes. The system is therefore very simple and can be implemented in a small, light form suitable for fitting to a mobile radiotelephone. The system can be operated by personnel without special skills or training as its input and output are in the form of full text. All that is required is an ability to read and write. By providing a message store into which words are loaded prior to transmission, messages can be transmitted in a very short time by reading out the stored message as a single transmission. This makes detection by an enemy difficult.Furthermore the signals which are transmitted are effectively coded in a way which breaks up the normal letter frequency in any language and therefore makes rapid decyphering difficult. Further encryption can be readily achieved by the use of a relatively simple cypher on the "coded" text prior to transmission.

The invention also provides a method of communicating words from a transmitter to a receiver each of which comprises a memory, wherein an identical vocabulary of words is stored in the form of binary codes in each memory, a word to be transmitted is entered in the form of a binary code, the relationship between the stored binary codes and the words they represent being the same as the relationship between the entered binary code and the word it represents, an entered binary code is compared with the stored binary codes, an abbreviated form of an entered binary code is transmitted when the entered binary code is identical to one of the stored binary codes and the entered binary code is transmitted in full when the entered binary code is not identical to any of the stored binary codes, a received abbreviated binary code is correlated with the associated stored binary code, and received entered codes and the stored binary code associated with a received abbreviated binary code are read out to reconstitute the message made up from a series of entered binary codes.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figs. 1 and 2 are flow diagrams of the operation of a system according to the invention when preparing a message for transmission and reconstituting a received message respectively; and Fig. 3 is a schematic diagram of transmitter components of the system.

in the embodiment of the invention described below, each transmitter/receiver unit is provided with a read only memory (ROM) containing exactly the same word information. This formation is organised into columns identified by the first letter of the stored word and rows identified by the second letter of the stored word.

The third and subsequent letters are stored at the location identified by the appropriate column and row. In the case of the word ENEMY for example, this would be stored in column E, row N, and reading out information from this location will result in the read out of E, M and Y in turn.

Referring now to Fig. 1, this is a flow diagram of the transmit sequence followed by the unit. At START, a word which it is desired to transmit is entered via a keyboard, the end of the word being identified by pressing a SPACE key as on a conventional keyboard. In the case of the word ENEMY for example, six binary words identifying E, N, E, M, Y and SPACE are entered and the unit recognises the fact that it has five letter word to process by virtue of the entry of the SPACE. No more than six letters can be entered.

After entry of the word, the unit locates the column and then the row specific to the first two letters. There will always be such a location and therefore this is a simple "look up" operation. The information stored at the location is then read out letter by letter and checked (compared) with the corresponding letter of the entered word. In the event of identity being found on each comparison, the unit continues the sequential comparison until it has compared all the letters of the entered word. The code associated with the entered word, that is the letters EN in the case of ENEMY, is then transmitted.

In the event that identity is not found on any comparison, the entered word is transmitted in full text preceded and followed (after the SPACE) by a binary word representing NUL to identify that transmission as being in full text rather than code.

For example, suppose the word ENEMY is stored in the memory but the word ENERGY is entered.

At the fourth letter check on the information stored at location EN, the letters M and R are compared, found to be non-identical, and the unit transmits NUL-E-N-E-R-G-Y-NUL.

To accommodate more than one word having the same two first letters, e.g. "enemy", "encompass" and "engage", these words could be abbreviated to EN, EC and EG respectively. As the word "encompass" is entered for example, the EN location is looked up at which EMY is stored. This does not check, but the system then executes a sub-routine (not shown in Fig. 1) which follows the steps: If word begins EN, but does not check, then check against "encompass"; If word checks with "encompass", abbreviate to EC; If word does not check with "encompass", then check against "engage"; If word checks with "engage", abbreviate to EG; If word does not check with "engage", transmit nul-word in fullnul. Obviously if EC and EG are used in this way, it is not possible to use these two letter combinations as abbreviations of words in which they appear as the first two letters.

Fig. 2 is a flow diagram of the receive sequence followed by the unit. A received full text or coded word is entered, full text words being identified by their preceding NUL. If there is a NUL, the full text is simply read out. If there is no NUL, the word stored at the location identified by the two received letters is read out. Thus the decoded message is automatically read out.

A series of words making up a message to be transmitted is assembled in a message store and the content of the message store is displayed.

This enables the message to be checked before transmission. To assist in user familiarisation with the unit, the displayed message will highlight those words which much be sent full text as they are not in the store, and will indicate the code letters for those words which are in the store. For example, suppose the message to be sent is "Energy position coordinates" and these three words (or their first six letters) are present in the store, the message sent will be EN PO CO and the display could indicate this by displaying the message in full text but highlighting the code letters EN, PO and CO. if a word not in the store is sent, this can be identified by displaying a character corresponding to Nul. This makes it clear to the user which words are in the store and encourages the use of such words.When the user becomes experienced with the unit he can enter the message directly for example EN PO CO, thereby saving the keying-in time. Thus the unit can be operated by inexperienced personnel but also enables experienced personnel to use it with greater efficiency.

Referring now to Fig. 3, this shows a schematic block diagram of the unit components required for processing a word to be transmitted. It will be appreciated that many of the components will also be used for processing an incoming two letter code but this operation will not be described in detail.

The user enters a word to be transmitted via a keyboard (not shown). Each key he presses applies a serial n-bit binary word to input 1. This binary word identifies a letter or a space is entered into a shift register 2 via AND function 3.

The shift register has a total of six sections 4 to 9 each of which is capable of holding one letter.

The entry of each binary word representing a letter or a space is detected by a space and letter recogniser circuit 10. When a SPACE is entered, or when a sixth letter is entered, the recogniser circuit 10 signals this to a programme counter and controller circuit 11. The programme counter 11 then prevents further entry of letter into the register 2 by inhibiting the AND function 3 and prevents any output of the shift register 2 reaching a message store 1 2 by providing an input to AND function 13.The programme counter 11 also closes one of the switches 14, 15, 1 6 or 17 dependent upon the number of letters in the word in register 2 such that when the register is clocked the first letter of the word is shifted into a second shift register 18, as well as being shifted into section 4 of the register 2, the register 2 being configured into a circulation register by the closed one of the bank of switches 14to 17.

The space and letter recogniser circuit 10 also enables the programme counter and controller 11 to initiate the selection of the first two letters of the entered words by controlling a stepping clock 1 9. This is achieved by arranging that, when the first letter of the word to be transmitted is entered into the register 2, the stepping clock 19 applies stepping pulses to a ROM 20 to read out the contents of the ROM until the start of the column of information identified by that letter is reached.

When the second letter of the word is entered, in the same way the ROM 20 is read out until the start of information stored in the row of information identified by the second letter is reached. At this stage the content of a comparison register 21 connected to the output of the ROM 20 corresponds to the third letter of the word stored in the ROM and having its first two letters identical to the first two letters of the word entered into the register 2. No further stepping of the ROM occurs until the whole word to be transmitted is entered into the register 2.

When the selected one of the switches 14 to 1 7 is closed, the programme counter 11 causes clock 22 to apply clock pulses to the register 2 such that its contents are circulated until the binary word corresponding to the third letter of the entered word is entered into register 18. If the contents of registers 1 8 and 21 are identical, an AND function 23 indicates this to be programme counter and controller 11 which causes another clock pulse to be applied to the register 2 and causes a further stepping pulse to be applied to the ROM 20 by stepping clock 1 9. In this way each letter of the entered word is compared with the stored letters.If identity is found, programme counter and controller 11 opens gate 13 and applies clock pulses to the register 2 so that only the first two letters of the entered word are transmitted to the message store. If identity is not found, programme counter and controller 11 causes a nul to be entered in the message store 12 and then opens gate 13 and applies clock pulses to the register 2 so that all the entered letters are read into the message store 12. A further nul is entered into the message store before the next subsequent coded word.

When operating in the receive mode, letters which appear between a pair of nuls are automatically passed directly to the message store. Coded words are registered and the content of the ROM location identified by the two letters of the coded word are read out to reconstitute the full text message. This is the case even if the sender entered the code words directly rather than the full word so than an inexperienced operator can safely receive messages which are initially generated in coded form.

Claims

1. A communication system for transmitting words comprising a transmitter, a receiver, two memories located one at the transmitter and one at the receiver, each memory storing an identical vocabulary of words in the form of binary codes, means at the transmitter for entering a word to be sent in the form of a binary code, the relationship between the stored binary codes and the words they represent being the same as the relationship between the entered binary code and the word it represents, means for comparing an entered binary code with the stored binary codes, means at the transmitter for transmitting an abbreviated form of an entered binary code when the entered binary code is identical to one of the stored binary codes, and for transmitting the entered binary code in full when the entered binary code is not identical to any of the stored binary codes, means at the receiver for correlating a received abbreviated binary code with the associated stored binary code, and means for reading out received entered codes and the stored binary code associated with a received abbreviated binary code to reconstitute a message made up from a series of entered binary codes.

2. A communications system according to claim 1, wherein the transmitting means is arranged to transmit only the portion of the binary code representative of the first n letters of an entered word when the entered binary code is identical to a stored binary code.

3. A communications system according to claim 2, wherein n is equal to 2.

4. A communications system according to any preceding claim, wherein the word entering means automatically determines the maximum number of letters which may be entered as a single word.

5. A communications system according to claim 4, wherein the maximum number is six.

6. A communications system according to any preceding claim, comprising means for initiating a search of the transmitter memory immediately upon entry of the first letter of a word being entered.

7. A communications system according to any preceding claim, wherein the transmitter and receiver each comprise a message store into which successive words of a message to be transmitted or a message received are entered and stored.

8. A communications system according to any preceding claim, comprising means for distinguishing between entered binary codes which are transmitted in full from abbreviated entered binary codes.

9. A communications system according to claim 8, wherein the distinguishing means comprises means for introducing a nul code before and after each code or group of codes which are transmitted in full.

10. A communications system according to any preceding claim, comprising means for displaying to system users those words which are transmitted in full.

11. A communications system according to any preceding claim, comprising means for displaying to system users the abbreviated form in which words which are stored in the transmitter memory are transmitted.

12. A communications system according to any preceding claim, comprising a first shift register into which the binary code representative of an entered word is entered, means for ciculating the content of the first shift register into a second shift register, means for applying stepping pulses to the memory to sequentially read out the stored binary codes into a third shift register, means for detecting identity between the contents of the second and third shift registers, and means for indicating to the transmitting means whether or not identity has been established.

1 3. A method of communication words from a transmitter to a receiver each of which comprises a memory, wherein an identical vocabulary of words is stored in the form of binary codes in each memory, a word to be transmitted is entered in the form of a binary code, the relationship between the stored binary codes and the words they represent being the same as the relationship between the entered binary code and the word it represents, an entered binary code is compared with the stored binary codes, an abbreviated form of an entered binary code is transmitted when the entered binary code is identical to one of the stored binary codes and the entered binary code is transmitted when the entered binary code is not identical to any of the stored binary codes, a received abbreviated binary code is correlated with the associated stored binary code, and received entered codes and the stored binary code associated with a received abbreviated binary code are read out to reconstitute the message made up from a series of entered binary codes.

14. A communications system substantially as hereinbefore described with reference to the accompanying drawings.

1 5. A method of communicating substantially as hereinbefore described with reference to the accompanying drawings.