Sparse Spreading Sequences for Low PAPR MC-CDMA Waveforms
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Solution Overview
Problem
Current MC-CDMA techniques face limitations in achieving low Peak-to-Average Power Ratio (PAPR) and efficient spectral usage, especially in high SNR conditions and large subcarrier scenarios, which restricts throughput and spectral efficiency.
Innovation Solution
The method involves using sparse spreading sequences with equal spacing between non-zero subcarrier elements to generate multi-carrier spread data, allowing for transmission waveforms with PAPR comparable to single-carrier transmission while mitigating signal collisions between devices, thereby enabling efficient use of wireless communication resources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional OFDM is used for multi-carrier transmission, then throughput and spectral efficiency are improved, but Peak-to-Average Power Ratio (PAPR) increases significantly
Solution Approach 1:
The patent segments the frequency spectrum into multiple subcarriers that are selectively activated based on channel conditions and interference patterns. By dividing the transmission into multiple orthogonal subcarriers with selective activation, the system achieves multi-carrier throughput while controlling PAPR through careful resource allocation and spreading sequence design.
Solution Approach 2:
The patent dynamically changes transmission parameters including spreading sequence selection, subcarrier activation patterns, and power allocation across subcarriers. By adjusting these parameters based on channel state information and interference conditions, the system optimizes both throughput and PAPR performance adaptively.
2Productivity
If subcarrier index modulation is used to increase throughput, then spectral efficiency improves at low SNR, but spectral efficiency is lost when SNR is high
Solution Approach 1:
The patent implements dynamic modulation and spreading strategies that adapt to SNR conditions. At low SNR, subcarrier index modulation and spreading provide robustness and spectral efficiency. At high SNR, the system dynamically switches to higher-order QAM modulations on active subcarriers, maintaining spectral efficiency across varying channel conditions through adaptive parameter selection.
Solution Approach 2:
The patent creates a universal transmission framework that combines multiple access techniques (MC-CDMA, subcarrier index modulation) with adaptive modulation. This multi-functional system can operate effectively across a wide range of SNR conditions by selecting appropriate transmission modes and parameters, making it versatile for different channel quality scenarios.
3Productivity
If multiple devices transmit simultaneously on overlapping subcarriers, then resource utilization improves, but signal collisions increase
Solution Approach 1:
The patent introduces spreading sequences as intermediary signals that allow multiple devices to transmit simultaneously on overlapping subcarriers. These orthogonal or pseudo-orthogonal spreading sequences act as mediators that enable the receiver to separate and decode individual device signals even when they occupy the same time-frequency resources, thus reducing signal collisions while maintaining high resource utilization.
Solution Approach 2:
The patent employs composite signaling structures combining data symbols, spreading sequences, and subcarrier modulation. This composite approach creates robust transmitted signals that can coexist in the same resource blocks through careful design of the composite signal structure, allowing multiple devices to share resources effectively while maintaining signal integrity and reducing collisions.
Data Source
AI summary
Methods, devices and systems are provided for spreading and transmitting data in a wireless communications system such that the resulting waveforms that are transmitted have low Peak to Average Power Ratio and mitigate signal collisions between different devices. The method for spreading and transmitting data includes spreading data with a sparse spreading sequence having equally spaced non-zero subcarrier elements to generate multi-carrier spread data on subcarriers corresponding to the equally spaced non-zero subcarrier elements of the spreading sequence; and transmitting the multi-carrier spread data. Different spreading sequences may be assigned to different user devices. The different spreading sequences may differ in terms of sparsity level in the frequency domain, sparsity pattern in the frequency domain and/or pulse offset in the time domain. Multiple multi-carrier spread data streams may be received by a network node and decoded using Successive Interference Cancellation (SIC) techniques.