Adaptive Precoder Shaping for OFDM Power Efficiency
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Solution Overview
Problem
In OFDM-based wireless communication systems, high Cubic Metric (CM) and Peak to Average Power Ratio (PAPR) lead to inefficient power amplification and increased power back-off, especially in multi-antenna transmission scenarios with strongly correlated antennas, resulting in reduced beamforming gain and increased implementation costs.
Innovation Solution
Adaptive modification of the spatial combiner or precoder based on transmit power requirements, using a shaping matrix to element-wise multiply the original precoder, allowing for reduced CM and PAPR without dedicated signaling, thus maintaining beamforming gain only when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional OFDM modulation is used, then spectral efficiency and flexibility are improved, but power back-off requirements increase due to high PAPR and CM
Solution Approach 1:
The patent applies DFT spreading transformation to the OFDM signal, changing the signal structure parameters. By applying a DFT matrix to the data symbols before IDFT modulation, the signal exhibits reduced PAPR and CM characteristics while maintaining OFDM's spectral efficiency, thus resolving the contradiction between productivity and energy usage
2Use of energy by moving object
If DFTS-OFDM is used to reduce PAPR and CM, then power efficiency is improved, but implementation complexity increases
Solution Approach 1:
The patent segments the OFDM signal processing into distinct stages: DFT spreading stage, subcarrier mapping stage, and IDFT modulation stage. This segmentation allows selective application of DFT spreading only when power efficiency is critical, rather than mandating it for all OFDM transmissions, thereby reducing overall implementation complexity while maintaining power efficiency benefits where needed
3Power
If adaptive precoding is applied to reduce CM in MIMO systems, then beamforming gain is improved, but system complexity increases
Solution Approach 1:
The patent implements adaptive precoding that dynamically adjusts the DFT spreading parameter based on channel conditions and power requirements. The system can switch between conventional OFDM and DFTS-OFDM modes, and adjust the spreading factor adaptively, allowing beamforming gain optimization without requiring complex fixed-structure precoding systems
Data Source
AI summary
According to an aspect of the present invention, the power efficiency of a precoded OFDM signal is improved by a method in a network node, e.g. a mobile terminal, for adapting a signal for multi-antenna transmission. In a first step, the network node receives at least a first parameter being related to the transmit power requirements of the network node. The network node then receives, a second parameter indicating a precoder W. In a further step, the network node determines a modified precoder {tilde over (W)}, having the same dimensions as W, using the precoder W and the at least first parameter; then, the network node adapts, the signal for multi-antenna transmission using the modified precoder {tilde over (W)}.