LDPC HARQ Retransmission Bit Reordering for Self-Decodability
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Solution Overview
Problem
Wireless communication systems using LDPC codes face reduced throughput due to non-self-decodable retransmissions, especially in bursty interference conditions, where retransmissions lack sufficient systematic bits for independent decoding without combining with original transmissions.
Innovation Solution
A wireless device reorders bits in the encoded bit stream before storing them in a circular buffer, ensuring that retransmissions include sufficient systematic bits for self-decodability by allocating bits into a matrix and performing a random circular shift, allowing for independent decoding even without the original transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If retransmissions use mainly parity bits to improve coding efficiency, then code rate is optimized, but self-decodability is lost requiring combination with original transmission
Solution Approach 1:
The patent segments the encoded bit stream into systematic bits and parity bits, then selectively transmits different portions in original transmission versus retransmission. The original transmission sends systematic bits first, followed by parity bits in retransmissions, allowing the receiver to attempt independent decoding of retransmissions containing sufficient systematic bits.
Solution Approach 2:
The patent performs preliminary ordering of bits in the circular buffer such that systematic bits are positioned at specific locations (e.g., beginning portions) before retransmission. This preliminary arrangement ensures that retransmissions automatically include sufficient systematic bits for potential independent decoding without requiring complex real-time processing.
2Reliability
If retransmissions include sufficient systematic bits for independent decoding, then self-decodability is improved, but coding efficiency decreases due to redundant systematic bit transmission
Solution Approach 1:
The patent applies local quality by making different portions of the codeword have different characteristics across transmissions. The original transmission contains full systematic bits, while retransmissions contain selectively ordered bits from the circular buffer that include sufficient systematic bits for self-decodability but minimize redundancy. This localized differentiation optimizes both self-decodability and throughput.
3Loss of information
If retransmissions are designed for independent decoding, then loss of information is reduced in bursty interference, but device complexity increases due to reordering operations
Solution Approach 1:
The patent uses a circular buffer structure that stores encoded bits and allows retransmissions to be generated by copying and reordering stored bits rather than re-encoding the original information bits. This copying approach from the circular buffer significantly reduces computational complexity compared to full re-encoding, while maintaining the ability to provide self-decodable retransmissions.
Data Source
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AI summary
Methods, systems, and devices for wireless communication are described. In some examples, a wireless device (e.g., a user equipment (UE) or a base station) may encode a codeword from a set of information bits using an LDPC code. The wireless device may then transmit multiple versions of the codeword to improve the chances of the codeword being received. In some aspects, the wireless device may use the techniques herein to generate self- decodable redundancy versions of the codeword to be transmitted to the receiving device. Accordingly, a receiving device may be able to identify information bits from one or more redundancy versions of the codeword even if the receiving device failed to receive an original transmission of the codeword. Specifically, the wireless device may re-order bits in an encoded bit stream for a retransmission before storing these bits in a circular buffer. Once the bits are re-ordered and stored in the circular buffer, the wireless device may select bits from the buffer and transmit the selected bits to the receiving device. By re-ordering bits in the encoded bit stream, the wireless device may ensure that sets of information bits are distributed evenly across the selected bits. Accordingly, when the wireless device selects bits from the circular buffer for the retransmission, the retransmission may include sufficient systematic bits to enable the retransmission to be decoded by the receiving device with or without being combined with an original transmission.