Joint HARQ ACK/NACK Encoding via Convolutional Codes
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Solution Overview
Problem
Current wireless communication systems, such as UMTS and LTE, face inefficiencies due to the presence of two error correction protocols (HARQ and ARQ) which lead to increased complexity, slower error detection, and excessive protocol overhead, particularly due to the high rate of NACK-to-ACK errors that can cause packet loss and throughput degradation.
Innovation Solution
Implementing a novel error protection mechanism where successive HARQ acknowledgement messages are jointly coded using convolutional codes, allowing for improved reliability and reduced delays by decoding feedback signals over multiple epochs, thereby reducing the need for the ARQ protocol and minimizing NACK-to-ACK errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two error correction protocols (HARQ and ARQ) are used, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent extracts and removes the ARQ protocol from the system, retaining only HARQ. By eliminating the redundant ARQ layer and its associated complexity, the system maintains sufficient reliability through HARQ alone, especially when combined with the innovative feedback signal encoding scheme that reduces NACK-to-ACK errors.
Solution Approach 2:
The patent merges the functions of HARQ and ARQ into a single unified HARQ protocol. By combining the error correction capabilities of both protocols into one integrated system with enhanced feedback signaling, the patent achieves comparable reliability to the dual-protocol approach while significantly reducing complexity.
2Reliability
If two error correction protocols (HARQ and ARQ) are used, then reliability is improved, but loss of time increases
Solution Approach 1:
By removing the ARQ protocol and its associated delay mechanisms (gap detection, status reports, retransmission waiting periods), the patent eliminates the time delays inherent in dual-protocol operation. HARQ alone, with improved feedback reliability, provides faster error detection and correction.
3Reliability
If two error correction protocols (HARQ and ARQ) are used, then reliability is improved, but loss of information increases
Solution Approach 1:
The patent removes the ARQ protocol and its associated overhead elements (sequence numbers, cumulative acknowledgments, status reports). The simplified HARQ system uses compact feedback signals with improved encoding to achieve the necessary reliability without the information overhead of a dual-protocol approach.
4Reliability
If feedback signals are sent frequently for HARQ, then reliability is improved, but use of energy increases
Solution Approach 1:
The patent combines multiple feedback signals into a single encoded feedback message using convolutional coding. Instead of transmitting separate ACK/NACK signals for each packet, the system encodes multiple feedback bits into a compact coded sequence, reducing the total number of transmissions required while maintaining high reliability.
Solution Approach 2:
The patent changes the encoding parameters of feedback signals by applying convolutional codes with specific rates (e.g., 1/2, 2/3). This encoding transforms multiple feedback bits into a more efficient coded representation, improving reliability through better error protection while reducing the energy cost of frequent feedback transmissions.
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AI summary
In a packet transmission method, an error protection mechanism for HARQ feedback jointly codes successive acknowledgement messages to improve reliability. Successive acknowledgement messages are channel encoded into feedback signals using a convolutional code with rate k/m (see e.g. Lin & Costello Error Control Coding Prentice Hall 1983). With convolutional codes one input block of k information bits arrives per epoch and is coded into an output block of m>k coded bits. The coded signal at the current epoch depends on the input at the current epoch and the λ-1 previous input blocks (λ is called the code constraint length).The decoder introduces a delay when decoding HARQ acknowledgements messages but this delay is more than compensated the improved performance and the elimination of the large delays due to NACK to ACK errors.