Gray-Mapped Constellation for More Accurate NOMA Decoding
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Solution Overview
Problem
In signal processing using non-orthogonal resources like Superposition Coding (SPC), there is a need for improved decoding accuracy in multiplexed signals at the reception device, as existing methods do not effectively mitigate bit errors caused by interference between signals.
Innovation Solution
Implementing a mechanism in the base station to select and apply a gray-mapped constellation for each signal, ensuring that bit strings corresponding to adjacent symbols differ by at most 1 bit, both before and after SPC multiplexing, to minimize bit errors during decoding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If non-orthogonal multiple access (NOMA) with superposition coding is used to increase user capacity and spectral efficiency, then more users can be multiplexed on the same radio resources, but signal interference between users increases causing degraded decoding accuracy
Solution Approach 1:
The patent applies preliminary action by pre-processing the bit strings through gray mapping before modulation and superposition coding. This ensures that adjacent constellation points differ by only one bit, so that when interference causes decoding errors, the receiver is more likely to decode to an adjacent constellation point rather than a distant one, limiting the bit error to at most one bit even under interference conditions
Solution Approach 2:
The patent converts the harmful effect of signal interference into a beneficial outcome by using gray mapping. Instead of trying to eliminate interference, the system accepts that interference may cause constellation point misinterpretation, but the gray mapping structure ensures that such misinterpretations result in minimal bit errors (at most one bit), thereby converting the harmful interference into a controlled error scenario
2Device complexity
If conventional modulation schemes are used without gray mapping in superposition coding, then the modulation process is simpler, but bit errors increase when signals interfere during reception
Solution Approach 1:
The patent applies parameter changes by modifying the constellation mapping parameters to satisfy the gray mapping condition. Specifically, it changes the bit-to-symbol assignment such that adjacent constellation points (in terms of Euclidean distance) correspond to bit strings that differ by only one bit position. This parameter modification increases robustness against interference while maintaining the same modulation order and spectral efficiency
Data Source
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AI summary
[Object] To provide a device, a method, and a program which are capable of further improving decoding accuracy in a case in which multiplexing/multiple-access using non-orthogonal resources is performed. [Solution] A device includes: a processing unit configured to apply a second constellation corresponding to a symbol position of a first bit string in a first constellation applied to the first bit string, to a second bit string in regard to a plurality of bit strings to be multiplexed for each of transmission signal sequences to be multiplexed in resource blocks for which at least a part of frequency resources or time resources overlap.