Alphanumeric terminal for a communications system

• US 3,906,445 A
• Filed: 10/21/1974
• Issued: 09/16/1975
• Est. Priority Date: 10/21/1974
• Status: Expired due to Term

• Current Assignee: Donald J. Nieglos, Gary R. Reynolds, James A. Lamb, Robert M. Beckmann
• Original Assignee: Donald J. Nieglos, Gary R. Reynolds, James A. Lamb, Robert M. Beckmann
• Inventors: Reynolds, Gary R., Beckmann, Robert M., Lamb, James A., Nieglos, Donald J.
• Primary Examiner(s): Dildine, Jr., R. Stephen
• Application Number:
  US05/516,325
• Time in Patent Office: 330 Days
• Field of Search: 179/15A,15AE 340/146.1BA
• US Class Current: 714/822
• CPC Class Codes: H04L 1/00 Arrangements for detecting or preventing errors in the information received correcting synchronisation H04L7/00

Abstract

An alphanumeric terminal providing a digital message having a fixed portion consisting of the address of the receiver in sixteen bits, followed by a repeat of the address in sixteen bits, a status indication in four bits, a request in four bits and an acknowledge plus an indication of whether text follows in two bits; and a variable portion consisting of a text message of zero to 384 bits, which fixed and variable portions of the message have parity bits inserted after each digital word and are delayed and interleaved (every other bit) with a similar undelayed message to form a composite message, which composite message is preceded by a pseudo random code of 127 bits. The terminal also includes noise and error detection circuitry, associated with the receiver, which separates the two interleaved messages and compares them for similarity, checks the parity bits for correctness and compares the amplitude of each bit to a predetermined upper and lower level to determine whether the bit is noise or a portion of the signal. From the various noise and error checks the terminal then provides a decision as to whether a digital word is good or bad and, if the digital word is in error and comes within the text portion of the message, an asterisk appears in the visual display so that the operator can mentally determine what the character should be.

Claims

1. In a communications system utilizing digitally encoded messages and including a transmitter and receiver, a terminal with the capability of sending predetermined messages comprising:

a. keyboard means providing text signals representative of alphanumeric characters and control signals in response to operation of keys thereon;

b. a text memory connected to receive and store the text signals from said keyboard means;

c. a fixed message memory having therein predetermined messages and connected to receive control signals from said keyboard means for selecting predetermined messages therein in response to operation of control keys on said keyboard means;

d. an address memory having therein an address code of said transmitter and receiver;

e. logic circuitry connected to receive the text signals from said text memory, the selected predetermined messages from said fixed message memory and the address code from said address memory and providing a first digital message serially including the text signals, the selected predetermined messages and the address code;

f. a parity generator and interleaving circuit connected to receive the first digital message from said logic circuitry and periodically generate and insert parity bits therein, said parity generator and interleaving circuit developing a second digital message serially including the text signals, the selected predetermined messages, the address code and the parity bits and interleaving the first and second digital messages into a composite message; and

g. means connecting the composite message to said transmitter.

2. A communications system as claimed in claim 1 including a psuedo random code generator connected to the connecting means and providing a pseudo random code serialLy preceding the composite message.

3. A communications system as claimed in claim 2 wherein the pseudo random code generator includes circuitry for providing several pseudo random codes each of which is an indication of the type of message to follow.

4. A communications system as claimed in claim 1 wherein the connecting means includes an encoder and modulator for differentially encoding the composite signal and modulating the differentially encoded signal at a predetermined frequency.

5. A communications system as claimed in claim 1 wherein the parity generator and interleaving circuit includes delay means for delaying the second digital message for a short period relative to the first digital message prior to interleaving the two messages.

6. A communications system as claimed in claim 1 wherein the logic circuitry includes means for inserting the address code twice in each of the first and second digital messages.

7. A communications system as claimed in claim 6 wherein the logic circuit and the parity generator and interleaving circuit are connected to provide each of the first and second digital messages in the following form, the address code, followed by a repeat of the address code, followed by at least one predetermined message, followed by any signals stored in the data memory, and followed by a stop indicating signal.

8. A communications system as claimed in claim 7 wherein the fixed message memory includes an acknowledge memory and an acknowledge code is serially included in the first digital message by said logic circuitry.

9. A communications system as claimed in claim 8 wherein the parity generator and interleaving circuit, the acknowledge memory, the address memory and the fixed message memory are all constructed so that the first and second digital messages each are serially composed of a first portion having a fixed length including a 16 bit address, a repeated 16 bit address, a first four bit predetermined message, a second four bit predetermined message and a two bit acknowledgment code and a second text portion variable in length with both the fixed and variable portions having a parity bit inserted after every sixth information bit.

10. A communications system as claimed in claim 9 wherein the pseudo random generator is constructed to provide approximately 127 bits serially preceding the first address.

11. A communications system utilizing digitally encoded messages comprising:

a. a base station including a transmitter, a receiver and means for processing messages; and

b. a plurality of mobile stations each including a transmitter and receiver and a terminal including keyboard means providing text signals representative of alphanumeric characters and control signals in response to operation of keys thereon, a text memory connected to receive and store the text signals from said keyboard means, a fixed message memory having therein predetermined messages and connected to receive control signals from said keyboard means for selecting predetermined messages therein in response to operation of control keys on said keyboard means, an address memory having therein an address code of said mobile transmitter and receiver, logic circuitry connected to receive the text signals from said text memory, the selected predetermined messages from said fixed message memory and the address code from said address memory and providing a first digital message serially including the text signals, the selected predetermined messages and the address code, a parity generator and interleaving circuit connected to receive the first digital message from said logic circuitry and periodically generate and insert parity bits therein, said parity generator and interleaving circuit developing a second digital message serially including the text signals, the selected predetermined messages, the address code and the parity bits and interleaving the first and second digital messages into a composite message, means connecting the composite message to said transmitter of the associated mobile station, signal processing circuitry connected to said associated mobile receiver and said logic circuitry for converting received signals including interleaved first and second messages into a usable message, comparing means connected to said logic circuitry and said address memory for identifying messages received by said associated mobile receiver which contain the address code thereof, and display means connected to said logic circuitry for displaying text messages supplied to said text memory and for displaying messages identified by said comparing means.

12. A communications system utilizing digitally encoded messages as claimed in claim 11 wherein the signal processing circuitry includes parity checking means supplying an output signal indicative of an error in the portion of the received signal associated with each of the parity bits checked and gating means connected to receive the output signal and connect the portions of one of the first and second messages in the received signal which do not contain errors to said logic circuitry.

13. A communications system utilizing digitally encoded messages as claimed in claim 11 wherein the signal processing circuit includes noise indication means for comparing the amplitude of each bit in the received signal to predetermined high and low levels and providing output signals indicating bits not exceeding said levels, and gating means connected to receive the output signals and connect the bits of one of the first and second messages in the received signal which exceed said levels to said logic circuitry.

14. A communications system utilizing digitally encoded messages as claimed in claim 13 wherein the signal processing circuit includes means for separating the first and second messages in the received signal and means for matching each word in the first message to the words in the second message representing the same portion of the message, said matching means providing an output signal indicative of matches, the output signal of said matching means being supplied to said gating means and operating said gating means to connect the words of one of the first and second messages in the received signal to said logic circuitry when a match is indicated.

15. In a communication system including a receiver for receiving a signal composed of a first digital message interleaved with a second digital message, which is the first digital message repeated, and periodic parity bits, signal processing circuitry comprising:

a. parity checking means having applied thereto the received signal and providing an output signal indicative of an error in the portion of the received signal associated with each of the parity bits checked;

b. noise indication means having applied thereto the received signal for comparing the amplitude of each bit in the received signal to predetermined high and low levels and providing output signals indicating bits not exceeding said levels;

c. separating means having applied thereto the received signal and separating the first and second messages therein;

d. matching means connected to said separating means and matching each word in the first message to each word in the second message, said matching means providing an output signal indicative of matching words; and

e. gating means connected to receive the output signals from said parity checking means, said noise indication means and said matching means, said gating means including circuitry for passing digital words in one of said first and second messages which do not have parity errors and which contain bits that exceed the high and low levels of the noise indication means, said gating means further including circuitry for passing digital words in one of said first and second messages which do not have parity errors, which contain bits that do not exceed the high and low levels of the noise indication means and which match, and said Gating means further including circuitry providing a flag signal when the same digital word in both the first and second messages contains one of a parity error, a parity error and bits which do not exceed the levels in the noise indication means, and a mismatch and bits which do not exceed the levels in the noise indication means.

16. In a communications system a receiver for receiving a signal composed of a first digital message interleaved with a second digital message, which is the first digital message repeated, and parity bits, signal processing circuitry as claimed in claim 15 including in addition display means connected to receive the digital words passed by said gating means and providing a visual display of characters representative of the digital words, said display means providing a visual display of a special character in response to a flag signal from said gating means.