Power Amplifier Backoff Control Using Cubic Metric Estimation
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Solution Overview
Problem
In CDMA cellular communication systems, the non-linearity of power amplifiers (PAs) causes significant signal quality impairment, particularly when operating close to their maximum power rating, leading to issues like Adjacent Channel Leakage Ratio (ACLR) in 3GPP WCDMA systems, where current methods like power backoff are inefficient due to estimation delays and memory-intensive look-up tables.
Innovation Solution
A method to dynamically calculate a metric related to power amplifier non-linearity using weighting factors for digital signals, allowing real-time control of transmission to prevent non-linear behavior, thereby reducing estimation lag and computational costs, and improving accuracy without relying on cumbersome look-up tables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If power backoff is applied to mitigate PA non-linearity, then signal quality is improved, but transmission power is reduced
Solution Approach 1:
The patent implements dynamic backoff adjustment based on real-time signal characteristics. The backoff value is continuously adapted according to the calculated cubic metric of the current signal, allowing the system to operate at maximum power when signal conditions permit and apply backoff only when necessary to prevent non-linearity, thus resolving the contradiction between maintaining signal quality and maximizing transmission power
Solution Approach 2:
The patent changes the backoff parameter dynamically based on signal parameters. By calculating the cubic metric from signal characteristics and using this to determine the appropriate backoff value, the system adapts the power level to match actual signal conditions, improving efficiency while maintaining signal quality when needed
2Ease of manufacture
If look-up tables are used to determine backoff values, then implementation is simplified, but memory requirements and computational overhead increase
Solution Approach 1:
The patent replaces the mechanical/memory-intensive look-up table approach with a computational method. Instead of storing pre-calculated backoff values in memory, the system calculates the cubic metric in real-time using signal parameters, substituting memory access with mathematical computation that requires minimal storage while maintaining implementation feasibility
Solution Approach 2:
The patent extracts only the essential signal parameters needed for cubic metric calculation, removing the need to store complete signal waveforms or use large look-up tables. By taking out only the necessary weighting factors and signal characteristics, the system achieves accurate backoff determination with minimal memory requirements
3Reliability
If backoff is applied earlier in the transmission chain, then non-linearity is prevented, but estimation lag increases
Solution Approach 1:
The patent performs preliminary calculation of the cubic metric using available signal parameters before the signal reaches the power amplifier. By calculating the metric in advance from weighting factors and signal characteristics that are already available in the digital domain, the system enables early backoff application without introducing additional estimation lag
Solution Approach 2:
The patent uses the cubic metric calculation as an intermediary that bridges early signal processing and power amplifier control. The metric serves as a real-time indicator that enables backoff adjustment at the optimal point in the transmission chain, preventing non-linearity without requiring delayed estimation
Data Source
AI summary
A method of transmitting an RF signal over a wireless communication network is provided. The method comprises determining a respective weighting factor for each of a plurality of digital signals each corresponding to a respective channel, the weighting factors weighting the digital signals to produce a composite signal intended for transmission as an RF signal via a power amplifier. The method further comprises executing instructions on a processor to dynamically calculate a metric related to the non-linearity of the power amplifier's transfer characteristics for the composite signal using the determined weighting factors. The method further comprises supplying to the power amplifier a signal for transmission as an RF signal and amplifying the signal for transmission at the power amplifier to transmit an RF signal over the wireless communication network via at least one antenna. The method further comprises controlling the transmission based on the metric related to the amplifier non-linearity.