HARQ Implementation with Air Interface Encryption
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Solution Overview
Problem
The implementation of the Hybrid Automatic Repeat Request (HARQ) mechanism is hindered in radio-electric systems that use Air Interface Encryption (AIE) ciphering before data channel coding, such as in PMR systems like TETRA and P25, due to changes in transmitted data during retransmissions, making it impossible to effectively implement the HARQ protocol.
Innovation Solution
A method that involves linear processing and error coding of data packets, where the receiver modifies and combines packets from different transmissions using different error correcting codes to compensate for processing differences, allowing HARQ implementation even with AIE ciphering, by coding and deciphering key sequences through error detection and correction codes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AIE ciphering is implemented before data channel coding, then data security is improved, but HARQ mechanism cannot be implemented due to changes in transmitted data during retransmissions
Solution Approach 1:
The patent introduces an intermediary compensation mechanism that bridges the conflict between AIE ciphering and HARQ. The receiver compensates for ciphering-induced changes by comparing received packets with expected patterns, enabling HARQ to function despite the presence of AIE ciphering. This intermediary compensation step allows both data security (through AIE) and retransmission capability (through HARQ) to coexist.
2Productivity
If HARQ mechanism is implemented, then effective data flow rate is improved through error correction, but system complexity increases due to additional processing steps
Solution Approach 1:
The patent merges the AIE decryption process with the HARQ compensation and error correction processes into a unified receiver operation. By combining these functions, the system achieves improved effective data flow rate through HARQ while minimizing additional complexity, as the processes share common computational resources and operational frameworks.
3Reliability
If multiple error correcting codes are used for different transmissions, then error correction capability is improved, but decoding complexity increases
Solution Approach 1:
The patent employs parameter changes by selecting different error correcting codes (with varying strength and complexity) for different transmission attempts. The receiver adapts its decoding strategy based on the specific code used, optimizing the balance between error correction capability and decoding complexity for each retransmission scenario.
Data Source
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AI summary
This transmission comprising a first transmission of a packet (52), comprising the steps consisting in: a first processing (54) of said packet (52) to obtain a first packet (56); and a coding (57, 59) of the first packet (56); wherein, when the first coded packet is received erroneous, the method comprises a second transmission of said packet, comprising: the steps implemented in the transmitter, consisting in: a second processing (84) of said packet (52) to obtain a second packet (86); and a coding (87, 89) of the second packet (86); and the steps implemented in the receiver, consisting in: a modification of the first and/or the second coded packets to obtain two packets in which the difference due to the first and second processings is compensated for: a combination (110) of both packets according to a HARQ procedure; and -a decoding (112) of the combined packet.