Polar Code Decoding With Multi-EDC Checks for DCI Size Ambiguity
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Solution Overview
Problem
In wireless communication systems, particularly in LTE, the ambiguity in the size of downlink control information (DCI) messages for user equipment (UE) leads to challenges in blind decoding, resulting in false alarms and incorrect information parsing due to the inability to determine the correct bit length of the transmitted polar-encoded codeword.
Innovation Solution
A base station generates a polar-encoded codeword by initializing a variable state for an error detection code calculation algorithm to a non-all-zero state, scrambles or interleaves bits, and includes multiple error detection codes to assist the UE in determining the correct bit length, thereby reducing false alarms and improving decoding performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a UE performs blind decoding with multiple bit length hypotheses, then the ability to detect control information is improved, but the false alarm rate increases due to inability to determine correct bit length
Solution Approach 1:
The patent introduces an intermediary mechanism (CRC check with early termination capability) that mediates between multiple bit length hypotheses. The CRC check acts as a mediator to validate each hypothesis, and the early termination feature allows the UE to stop decoding when a valid hypothesis is found, preventing false alarms from subsequent hypotheses.
Solution Approach 2:
The patent applies preliminary action by performing CRC validation checks before finalizing the decoding result. The UE performs preliminary CRC checks on decoded bits for each hypothesis, and only accepts hypotheses that pass the CRC validation, thereby preventing false alarms before they occur.
2Reliability
If multiple error detection codes are included to reduce false alarms, then the false alarm rate decreases, but the device complexity increases
Solution Approach 1:
The patent segments the error detection process into multiple independent CRC checks, each associated with different bit length hypotheses. This segmentation allows the decoder to independently validate each hypothesis without requiring a single complex error detection mechanism, thereby reducing overall decoder complexity while maintaining low false alarm rates.
Solution Approach 2:
The patent implements partial error detection by performing CRC checks only on the necessary portions of decoded bits for each hypothesis, rather than checking entire codewords. This partial action approach reduces computational complexity while still effectively identifying valid hypotheses and reducing false alarms.
3Speed
If the UE decodes polar-encoded codeword with incorrect bit length hypothesis, then decoding speed is maintained, but incorrect information is parsed due to false alarm
Solution Approach 1:
The patent implements feedback through CRC validation results that inform the UE whether a decoded hypothesis is correct. The feedback mechanism allows the UE to quickly identify and discard incorrect hypotheses, maintaining decoding speed by avoiding extensive re-decoding while ensuring information parsing accuracy through validated results.
Solution Approach 2:
The patent performs preliminary validation of decoded bits using CRC checks before the UE commits to parsing the information. This preliminary action prevents incorrect information parsing by validating the decoded bits early in the process, while maintaining speed by using efficient CRC algorithms that can be executed quickly.
Data Source
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AI summary
Size ambiguity and false alarm rate reduction for polar codes. A user equipment (UE) may determine a decoding candidate bit sequence for a polar-encoded codeword having a codeword size based on a decoding hypothesis for control information having a particular bit length of multiple different bit lengths for the codeword size. The UE may calculate an error detection code (EDC) value for a payload portion of the decoding candidate bit sequence using an EDC algorithm, and may initialize an EDC variable state with at least one non-zero bit value. Scrambling or interleaving of bits may also be performed prior to, or after, polar encoding and may depend on the bit length. In examples, information bits may be bit-reversed prior to generating an EDC value. In examples, the encoded bits may include multiple EDC values to assist the UE in performing early termination and to reduce a false alarm rate.