SCMA Decoding Complexity Reduction via Dimension Segmentation
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Solution Overview
Problem
The decoding complexity of Sparse Code Multiple Access (SCMA) becomes prohibitive for very high rates due to large constellations or a combination of large constellations and layers, which is a challenge in achieving high data rates for next-generation wireless networks.
Innovation Solution
The method involves modulating a data stream using a codebook with codewords that map data to transmission resources, where N non-zero values represent projections on N complex constellations, and independent real and imaginary components are used for decoding, reducing complexity by using a layer-specific signature with a consistent phase and applying a change of power level to non-zero transmission resources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional SCMA encoding with large constellations or many layers is used, then data rate is improved, but decoding complexity becomes prohibitive
Solution Approach 1:
The patent segments the complex N-dimensional constellation into multiple lower-dimensional constellations (e.g., two 2D constellations for a 4D constellation). Each dimension is independently modulated and decoded, breaking down the prohibitive decoding complexity into manageable segments while maintaining high data rates through the combined capacity of all dimensions.
Solution Approach 2:
The patent transitions from treating the N-dimensional constellation as a single complex entity to processing it as multiple independent lower-dimensional constellations. This dimensional decomposition allows the receiver to decode each dimension separately, dramatically reducing computational complexity while preserving the high data rate capability of the overall N-dimensional system.
2Productivity
If the number of layers or constellation size is increased to achieve very high rates, then productivity is improved, but the decoding complexity becomes prohibitive
Solution Approach 1:
The patent applies segmentation by dividing the high-dimensional constellation space into multiple independent lower-dimensional sub-constellations. Each layer or dimension is processed separately through its own modulation and decoding chain, enabling the system to support many layers and high data rates without exponentially increasing decoding complexity at the receiver.
Solution Approach 2:
The patent changes the fundamental parameter of how constellations are represented and processed. Instead of using a single large N-dimensional constellation that requires complex joint decoding, the system uses multiple independent lower-dimensional constellations with simpler individual decoding requirements, thereby achieving high data rates with manageable complexity.
3Device complexity
If independent real and imaginary components are used for constellation points, then decoding complexity is reduced, but the number of points in the constellation is limited
Solution Approach 1:
The patent segments the constellation into independent real and imaginary components, each being a separate lower-dimensional constellation. This segmentation reduces decoding complexity because each component can be decoded independently using simpler algorithms, while the total number of constellation points is maintained through the combination of all component points across all dimensions.
Solution Approach 2:
The patent exploits the dimensional structure by treating real and imaginary parts as independent dimensions that can be processed separately. This dimensional independence allows for reduced decoding complexity in each dimension while the overall system capacity (number of constellation points) is preserved through the product of the capacities of individual dimensions.
Data Source
AI summary
Higher rates of data communication may be utilized for downlink than for uplink. However, the decoding complexity of Sparse Code Multiple Access (SCMA) may become prohibitive for very high rates, resulting from, for example, a large number of layers, for very large constellations, or a combination of the two. Methods and transmitters are provided herein for transmitting that has been generated to reduce complexity at the receiver and methods and receivers are provided herein for receiving and decoding a received signal with reduced complexity. The reduced complexity in part is provided by the ability to maintain real and imaginary parts of a transmitted signal independent from one another.