Fountain HARQ for Low Latency Wireless
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Solution Overview
Problem
Wireless communication systems face latency issues due to the time required for decoding and retransmission in hybrid automatic repeat request (HARQ) processes, particularly in delay-sensitive communications with small payload sizes, where interlaced HARQ can introduce significant delays and decrease link-budget.
Innovation Solution
The implementation of a fountain HARQ scheme, where a transmitter continuously sends redundancy versions of a data block until an acknowledgement (ACK) is received, allowing the receiver to accumulate data symbols, compute log-likelihood ratios, and send an ACK to stop transmission, eliminating the need for NACK signals and enabling efficient multiplexing of packets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional HARQ with ACK/NACK feedback is used, then reliable data transmission is achieved, but latency increases due to decoding time and round trip time for feedback and retransmission
Solution Approach 1:
The transmitter sends multiple redundancy versions of the data block in advance before receiving ACK feedback. This preliminary action allows the receiver to accumulate sufficient redundancy versions and decode the data without waiting for the traditional ACK/NACK round trip, thereby reducing latency while maintaining reliability through progressive redundancy accumulation.
Solution Approach 2:
The transmitter continuously transmits redundancy versions without interruption until the receiver successfully decodes the data. This continuous transmission eliminates the idle waiting period in traditional HARQ where the transmitter must pause for ACK feedback, thereby reducing overall communication latency while ensuring reliable delivery through persistent redundancy provision.
2Reliability
If multiple redundancy versions are transmitted continuously, then decoding success probability increases, but resource overhead increases
Solution Approach 1:
The receiver provides feedback to the transmitter indicating whether successful decoding has been achieved. This feedback mechanism allows the transmitter to stop sending redundancy versions once decoding succeeds, preventing unnecessary resource overhead while maintaining high decoding success probability through adaptive transmission termination based on actual decoding outcomes.
Data Source
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AI summary
Methods, systems, and devices are described for fountain hybrid automatic repeat request (HARQ) for reliable low latency communication. A wireless device may transmit a data block based on a low latency operational mode. The device may then transmit a number of redundancy versions of the data block prior to determining whether an acknowledgement (ACK) has been received. In some examples the ACK may be an augmented ACK, which may be based on the number of redundancy versions received prior to successfully decoding the data block, and which may include an additional resource request. In some examples, the device may select an updated modulation and coding scheme (MCS) based on the augmented ACK. In some examples, the device may increase a number of frequency resources (e.g., component carriers) used for transmission based on the augmented ACK.