OFDM Transmitter Adaptive Back-Off for EVM and Power Efficiency
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Solution Overview
Problem
OFDM transmitters face inefficiencies due to high peak-to-average power ratio (PAPR), leading to amplifier non-linearity, clipping, spectral regrowth, and transmit errors, which compromise power efficiency and error vector magnitude (EVM) requirements.
Innovation Solution
A transmitter that dynamically adjusts the back-off level of the power amplifier for each symbol by computing and selecting optimal candidate back-off values based on error vector magnitude (EVM) and signal-to-noise ratio (SNR) to minimize clipping and maximize power efficiency, using a symbol processor to apply the selected back-off level to the amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a significant back-off is applied to the amplifier to operate in its linear region for peak power symbols, then amplifier linearity is improved, but power efficiency deteriorates
Solution Approach 1:
The patent applies dynamics by making the back-off level adjustable and adaptive rather than fixed. The system dynamically selects from multiple candidate back-off levels (e.g., 3 dB, 6 dB, 9 dB) based on the actual signal conditions and EVM requirements, allowing the amplifier to operate optimally for each transmitted symbol rather than being constrained by a static back-off setting
Solution Approach 2:
The patent changes the back-off parameter from a fixed value to a variable that can be selected from multiple candidate levels. The symbol processor computes EVM values for different back-off levels and selects the appropriate level, effectively changing the operating parameter of the amplifier based on signal characteristics and performance requirements
2Reliability
If a fixed back-off level is used to ensure amplifier linearity, then transmit errors are reduced, but power efficiency deteriorates
Solution Approach 1:
The system transitions from a static back-off level to a dynamic selection mechanism where the back-off level is adapted for each symbol based on computed EVM values. This allows the system to maintain low transmit errors when needed while improving power efficiency when the signal conditions permit
Solution Approach 2:
The back-off level parameter is changed from a fixed value to a selectable variable with multiple candidate levels. The symbol processor evaluates different back-off levels and selects the optimal one, changing the parameter based on actual performance requirements rather than using a conservative fixed value
3Productivity
If higher order modulation schemes are used to increase spectral efficiency, then data rate is improved, but EVM requirements become more stringent
Solution Approach 1:
The system dynamically adjusts the back-off level based on the modulation scheme being used and the resulting EVM requirements. For higher order modulations like 256QAM that require lower EVM, the system can select more conservative back-off levels to ensure linearity, while adapting to less stringent requirements when using lower order modulations
Data Source
AI summary
A transmitter for transmitting data symbols using an orthogonal frequency division multiplexing (OFDM) scheme, the transmitter comprising: a modulator for generating a plurality of mutually orthogonal sub-carriers, each of the plurality of sub-carriers being modulated with a stream of data symbols to be transmitted; an amplifier for amplifying a signal containing the plurality of modulated sub-carriers for transmission of the signal; and a symbol processor for processing the data symbols of the plurality of sub-carriers, the symbol processor being configured to compute a plurality of EVM values for each data symbol to be transmitted, each of the plurality of EVM values being computed based on a different one of a plurality of candidate back-off values for the amplifier, and to select one of the plurality of candidate back-off values to apply to the transmitter for the data symbol based on the computed EVM values.