SCMA Precoding for Low PAPR Wideband IoT
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Solution Overview
Problem
Existing SCMA systems face challenges in achieving low peak-to-average power ratio (PAPR) for wide-band transmissions, which is crucial for massive IoT applications with power-limited transmitters, as current low-PAPR codebooks are limited to narrow-band transmissions and result in higher PAPR when multiple blocks are used.
Innovation Solution
The method involves generating precoded SCMA blocks using an IDFT matrix and concatenating them, followed by DFT precoding to produce a precoded output, which is then used for OFDM modulation, allowing for the use of SCMA codebooks with multiple non-zero elements to reduce PAPR across multiple blocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If low-PAPR SCMA codebooks with one non-zero component per codeword are used, then PAPR is reduced for narrow-band transmission, but the system cannot achieve low PAPR for wide-band transmission when multiple blocks are used
Solution Approach 1:
The patent segments the SCMA codeword into multiple blocks, where each block can be independently processed with its own precoding parameters. This allows different blocks to be allocated to different frequency subbands, enabling the system to achieve low PAPR in each narrow band while collectively covering a wide bandwidth. The segmentation of the codeword structure resolves the contradiction by allowing narrow-band low-PAPR properties to be maintained within each segment while achieving wide-band coverage through concatenation of multiple segments.
Solution Approach 2:
The patent introduces a new dimension of frequency-domain precoding by applying DFT-based precoding matrices to the SCMA codewords before OFDM modulation. This transforms the signal from the time domain to the frequency domain, enabling selective allocation of non-zero components across different frequency subbands. This dimensional transformation allows the system to maintain low PAPR properties while achieving wide-band transmission capability, as the energy distribution can be optimized in the frequency dimension.
2Area of stationary object
If multiple SCMA blocks are concatenated to achieve wide-band transmission, then bandwidth coverage is improved, but PAPR increases
Solution Approach 1:
The patent applies local quality by allowing each SCMA block to have its own precoding parameters and frequency subband allocation, optimized for local low PAPR performance. Instead of applying a uniform precoding scheme across the entire wide-band signal, each block is independently precoded and allocated to specific frequency subbands where it can maintain low peak-to-average power ratio. This local optimization approach ensures that PAPR remains low in each local frequency region while collectively achieving wide bandwidth coverage through the concatenation of multiple such blocks.
3Adaptability or versatility
If SCMA codebooks with multiple non-zero elements are used, then wide-band transmission capability is improved, but PAPR increases and power amplifier requirements become more stringent
Solution Approach 1:
The patent applies preliminary action by performing DFT-based precoding on the SCMA codewords before OFDM modulation and transmission. This precoding operation is performed in advance to distribute the energy of each codeword across multiple frequency subbands in a controlled manner. By pre-shaping the frequency-domain representation of the signal, the system enables wide-band transmission capability while maintaining low PAPR, as the energy distribution is optimized before the signal enters the power amplifier stage.
Solution Approach 2:
The patent changes the parameter of energy distribution in the frequency domain by applying DFT precoding with configurable matrix dimensions and subband allocations. Instead of using fixed codebooks with a predetermined number of non-zero elements, the system dynamically adjusts the frequency-domain energy distribution through precoding parameters. This parameter change allows the effective number of non-zero elements to be adapted based on channel conditions and bandwidth requirements, achieving wide-band capability without proportionally increasing PAPR.
Data Source
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AI summary
Systems and methods for DFT-S-SCMA (discrete Fourier Transform-spread-sparse code multiple access) are provided. Input bits are encoded with an SCMA encoder. The output is precoded with a IDFT (inverse DFT) to produce a precoded SCMA block. Multiple precoded SCMA blocks are combined at the input of a DFT. This is done in parallel for multiple sets of SCMA blocks at multiple DFTs. Then, the outputs of the DFTs are combined and OFDM modulated. This approach can be used to improve the PAPR (peak to average power ratio) at the output of the OFDM modulation.