Adaptive Tone Reservation for OFDM Peak-to-Average Ratio Reduction
Solution Overview
Problem
Multi-carrier modulation systems, such as OFDM, face challenges with high peak-to-average power ratio (PAPR) in transmit signals, leading to distortion and increased costs for power amplifiers due to the need for larger linear operating ranges, which can result in costly components and higher capacity power supplies.
Innovation Solution
The use of adaptive filtering and tone reservation techniques in multi-carrier transmitters to reduce the peak-to-average power ratio by adjusting filter coefficients and generating adaptive tones, which are then used to mitigate peak power exceedances and nulls in the signal before transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the peak-to-average power ratio of the transmit signal is high, then the signal can carry more data with higher spectral efficiency, but the transmitter power amplifier must operate in a larger linear operating range which increases cost and complexity
Solution Approach 1:
The patent applies preliminary action by reducing the peak-to-average power ratio of the OFDM signal before it reaches the power amplifier. Through signal processing techniques such as clipping and filtering, or tone reservation methods, the signal peaks are mitigated in advance, allowing the power amplifier to operate within a smaller linear operating range without causing distortion, thus reducing cost and complexity while maintaining data transmission capability
Solution Approach 2:
The patent introduces an intermediary signal processing stage between the OFDM modulator and the power amplifier. This intermediary component (such as a peak reduction device or adaptive filter) acts as a mediator that modifies the signal characteristics to be more suitable for the power amplifier, enabling the amplifier to operate efficiently without requiring an oversized linear operating range
2Power
If the peak-to-average power ratio of the transmit signal is high, then more power can be utilized for transmission, but distortion occurs when signal peaks exceed the linear operating range of the transmitter
Solution Approach 1:
The patent applies preliminary anti-action by taking measures to prevent signal peaks from exceeding the linear operating range before they cause distortion. Through techniques such as signal clipping, filtering, or adaptive tone injection, the harmful peak excursions are counteracted in advance, allowing the transmitter to operate at higher power levels without generating distortion that would degrade signal quality
Solution Approach 2:
The patent converts the harmful effect of signal peaks into a benefit by using the peak information to adjust signal characteristics. For example, tone reservation techniques use specific subcarriers to carry peak reduction information, and adaptive filtering uses peak detection to dynamically adjust filter coefficients, thereby transforming the potential harm of high PAPR into a mechanism for improving overall signal quality and power efficiency
Data Source
AI summary
Methods and corresponding systems for reducing a peak-to-average signal ratio include determining peak and null samples of a symbol. Thereafter, an error signal is calculated that is responsive to the peak and null samples. In one embodiment the error signal has values corresponding to differences between the peak samples and a high threshold and the null samples and a low threshold. In response to the error signal, a reserved tone set of time-domain samples are produced and added to a user data set of time-domain samples. The error signal can also be used to adapt a filter for filtering samples of a symbol.