# US 9,438,411 B1 · Method and apparatus for synchronizing digital messages > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,438,411 B1 - Document ID: US9438411B1 - Status: Granted - Kind: B1 - Application number: 14/824,330 - Filed: 2015-08-12 - Granted: 2016-09-06 - Earliest claimed: 2015-08-12 - Assignees: The Boeing Company - Applicants: The Boeing Company - Inventors: Brian C Lojeck; Albert A Williams - Web page: https://patentgrep.com/patent/US9438411B1 ## CPC - H04L 7/042: {Detectors therefor, e.g. correlators, state machines (digital correlators in general G06F17/15)} - H04L 7/041: {using special codes as synchronising signal} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract A method and system for synchronizing digital messages. A digital message includes a start-of-message indicator, followed by a key word, followed by the message payload. Before transmitting the digital message, the payload is combined in an exclusive-OR operation with the key word, which is chosen from a pre-designated pool of key words. Each pool represents a message of different type, which is type is related to word length. The key word and start-of-message indicator are appended to the resulting exclusive-OR digital message and transmitted. On receipt, the start-of-message indicator indicates the start of the message, and the key word determines the message word length and, after a second exclusive-OR operation with the key word, restores the original digital message. The start of the message is positively identified without additions to the message payload and without the key word ever appearing in the payload during transmission. ## Claims ### Claim 1 A method for sending a digital message comprising: selecting a digital message having at least one word; selecting a key word; performing an exclusive-OR operation using said key word and said at least one word of said digital message to obtain an exclusive-OR digital message; appending said key word to said exclusive-OR digital message; transmitting said key word and said exclusive-OR digital message; receiving said key word and said exclusive-OR digital message; and performing an exclusive-OR operation using said key word and said exclusive-OR digital message to recreate said digital message from said exclusive-OR digital message. ### Claim 2 (depends on 1) The method as recited in claim 1, wherein said key word is selected so as to not be the same as said at least one word in said message. ### Claim 3 (depends on 1) The method as recited in claim 1, further comprising the step of selecting plural key words into a pool of key words from which said key word can be selected. ### Claim 4 (depends on 3) The method as recited in claim 3, wherein each digital message is a message type characterized by a fixed number of words; and wherein said method further comprises the step of selecting said pool of key words for each message type. ### Claim 5 (depends on 4) The method as recited in claim 4, wherein said key word selecting step further comprises the steps of: determining the number of words in said digital message; determining said message type from said number of word; and selecting, from said pool of key words for said message type, said key word to be appended to said exclusive-OR digital message. ### Claim 6 (depends on 1) The method as recited in claim 1, further comprising the step of selecting a start-of-message word. ### Claim 7 (depends on 6) The method as recited in claim 6, further comprising the step of appending said start-of-message word to said key word and said exclusive-OR digital message before transmitting said key word and said exclusive-OR digital message to a receiver. ### Claim 8 (depends on 6) The method as recited in claim 6, wherein said start-of-message word is an all-zeros word. ### Claim 9 (depends on 7) The method as recited in claim 7, wherein said start-of-message word is not identical to any word in said message. ### Claim 10 (depends on 1) The method as recited in claim 1, wherein said at least one word in said digital message and said key word are the same length. ### Claim 11 (depends on 1) The method as recited in claim 1, wherein said key word is appended to the front of said exclusive-OR digital message. ### Claim 12 A method for sending a digital message comprising: selecting a digital message having one word; selecting a key word that is not the same as said one word; performing an exclusive-OR, operation using said key word and said one word of said digital message to obtain an exclusive-OR digital message; inverting the key word; appending said inverted key word to said exclusive-OR digital message; transmitting said inverted key word and said exclusive-OR digital message without a start-of-message word; receiving said key word and said exclusive-OR digital message; inverting said inverted key word to recover said key word; and performing an exclusive-OR operation using said recovered key word and said exclusive-OR digital message to recreate said digital message from said exclusive-OR digital message. ### Claim 13 (depends on 12) The method of claim 12, wherein, when said key word does not have a value of all ones. ### Claim 14 (depends on 12) The method of claim 12, wherein, when said one word of said digital message does not have a value of all zeros and said key word has a value of all zeros. ### Claim 15 A communication system comprising: a transmitter; a receiver; a first processor configured to receive a digital message having at least one word and to perform an exclusive-OR operation on a key word and said at least one word in said digital message, said first processor connected to said transmitter, said key word selected from a pre-selected pool of key words; and a first memory connected to said processor, said first memory containing said preselected pool of key words, whence said first processor selects said key word, said first processor performing said exclusive-OR operation using said key word and said at least one word of said digital message to form an exclusive-OR digital message, said first processor appending said key word to said exclusive-OR digital message, said transmitter transmitting said exclusive-OR digital message with said appended key word to said receiver; a second processor configured to receive said digital message from said receiver and said key word and to perform an exclusive-OR operation on said message using said key word to obtain said digital message. ### Claim 16 (depends on 15) The communication system of claim 15, wherein said key word is selected to have a value different from the value of said at least one word in said digital message. ### Claim 17 (depends on 15) The communication system of claim 15, further comprising a start-of-message word appended to said exclusive-OR digital message. ### Claim 18 (depends on 15) The communication system of claim 15, further comprising a second memory connected to said second processor, said second memory also containing said pool of key words whereby said key word appended to said exclusive-OR digital message may be verified. ### Claim 19 (depends on 18) The communications system of claim 18, wherein each digital message has a type based on the number of words in said digital message and wherein said pool of key words corresponds to said type. ### Claim 20 (depends on 19) The communication system of claim 19, wherein said key word corresponds to the type of said digital message in said digital message and wherein said second processor determines the number of words in said digital message and processes said message based on said number of words.