Dual DFT Spreading for Low PAPR in FDMA Systems
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current mobile communication systems, such as LTE and LTE-Advanced, face limitations in reducing inter-user interference and maximizing user access in systems with limited capacity due to high Peak-to-Average Power Ratio (PAPR) in OFDMA and complexity in scheduling caused by restricted DFT sizes.
Innovation Solution
The use of a dual discrete Fourier transform (DFT) approach in transmitting and receiving apparatuses, where the first DFT processes resource blocks factorized into prime numbers 2, 3, and 5, and the second DFT handles remaining blocks, allowing for flexible DFT spreading and inverse DFT operations, thereby reducing inter-user interference and enhancing frequency spectrum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If OFDMA is used for downlink multiple access, then system capacity and user access capability are improved, but power consumption increases due to high PAPR
Solution Approach 1:
The patent segments the DFT processing into multiple smaller DFT units (first DFT and second DFT) that can be independently configured. This allows the system to process resource blocks in manageable segments rather than requiring a single large DFT, thereby reducing the PAPR while maintaining system capacity. The segmentation enables flexible allocation of resource blocks to users without being constrained by a fixed large DFT size.
Solution Approach 2:
The patent introduces dynamic adaptability by allowing the DFT size to be flexibly configured based on the number of resource blocks allocated. The system can dynamically adjust the DFT size to match the actual resource allocation, avoiding the need to use a fixed large DFT size that would increase PAPR. This dynamic configuration maintains system capacity while optimizing power consumption.
2Device complexity
If DFT size is restricted to factorized prime numbers (2, 3, 5) to reduce hardware complexity, then hardware complexity is reduced, but scheduling flexibility and resource block allocation capability deteriorate
Solution Approach 1:
The patent divides the DFT processing into multiple smaller DFT units (first DFT and second DFT), each with sizes factorized into prime numbers 2, 3, and 5. This segmentation allows the system to maintain hardware complexity constraints while achieving greater scheduling flexibility. By combining results from multiple smaller DFTs, the system can effectively handle resource block allocations that would require larger non-factorizable DFT sizes.
Solution Approach 2:
The patent merges the outputs from multiple smaller DFT units (first DFT and second DFT) to achieve the equivalent functionality of a larger DFT. This combining approach allows the system to support flexible resource block allocations without requiring a single large DFT with non-factorizable size, thus maintaining both hardware simplicity and scheduling versatility.
3Productivity
If a single large DFT processes all resource blocks, then processing efficiency is improved, but hardware complexity and PAPR increase
Solution Approach 1:
The patent segments the processing of resource blocks into multiple parallel DFT operations (first DFT and second DFT) rather than using a single large DFT. This segmentation maintains processing efficiency by distributing the workload across multiple units while reducing the complexity and PAPR associated with a single large DFT. The segmented approach allows independent optimization of each DFT unit.
Solution Approach 2:
The patent applies partial DFT processing by dividing resource blocks into groups that are processed by different DFT units. Rather than requiring all resource blocks to be processed by a single large DFT, the system performs partial processing in parallel, achieving the necessary processing efficiency without the overhead of a single excessive large DFT.
Data Source
AI summary
A transmitting apparatus may comprise a symbol mapper; a first DFT and a second DFT performing DFT spreading on symbols mapped in the symbol mapper; and a subcarrier mapper mapping symbols which are DFT-spread in the first DFT and the second DFT to subcarriers, wherein the first DFT performs DFT spreading on all resource blocks to be transmitted when a total size of the resource blocks to be transmitted is a size which can be processed by the first DFT, or the first DFT performs DFT spreading on as many resource blocks among the resource blocks to be transmitted as the first DFT can process and the second DFT performs DFT spreading on the rest of the resource blocks to be transmitted when a total size of the resource blocks to be transmitted is not a size which can be processed by the first DFT.