Multi-Band RF Digital Predistortion After Upconversion
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Solution Overview
Problem
Conventional digital predistortion techniques, such as Baseband Digital Predistortion (BB-DPD), are not optimal for multi-band transmitters due to high complexity and power consumption, and RF Analog Predistortion (RF-APD) struggles with wide bandwidth and thermal variations, making it difficult to manage non-linear distortion in multi-band signals effectively.
Innovation Solution
The implementation of Radio Frequency Digital Predistortion (RF-DPD) in a multi-band transmitter, which digitally predistorts RF signals after upconversion, reducing sampling rates and complexity by synthesizing intra-band and inter-band distortion products directly at RF, and using separate RF-DPD subsystems for each band to generate predistorted signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Baseband Digital Predistortion (BB-DPD) is used for multi-band transmitters, then non-linear distortion compensation is achieved, but system complexity and power consumption increase significantly
Solution Approach 1:
The patent divides the multi-band signal into separate band-specific paths, with individual digital upconverters and predistortion processors for each band. This segmentation allows each processor to handle only its designated band at a lower effective sampling rate, reducing overall computational complexity while maintaining distortion compensation effectiveness for each band
Solution Approach 2:
The patent changes the operating parameters by performing predistortion at the RF stage rather than baseband, and by using band-specific sampling rates matched to each band's bandwidth requirements. This parameter optimization reduces the sampling rate burden on each predistortion processor while maintaining adequate compensation performance
2Reliability
If Baseband Digital Predistortion (BB-DPD) is used for multi-band transmitters, then non-linear distortion compensation is achieved, but power consumption increases
Solution Approach 1:
By segmenting the signal processing into band-specific paths with dedicated digital upconverters and predistortion processors, each processor operates at a lower sampling rate appropriate to its band's bandwidth. This reduces the computational load and power consumption of each processor compared to a single baseband processor handling all bands simultaneously
Solution Approach 2:
The patent implements dynamic sampling rate adjustment where each band's predistortion processor operates at a sampling rate matched to that band's specific bandwidth requirements. This dynamic adaptation allows the system to consume only the necessary processing power for each band rather than maintaining a high sampling rate for all bands throughout the entire signal chain
3Reliability
If RF Analog Predistortion (RF-APD) is used, then analog predistortion is achieved, but bandwidth coverage is insufficient for wide separation multi-band signals
Solution Approach 1:
The patent segments the wideband multi-band signal into separate band-specific digital paths, each handled by its own digital upconverter and predistortion processor. This segmentation allows each analog RF path to be optimized for a specific band's bandwidth requirements, achieving adequate bandwidth coverage for wide separation multi-band signals while maintaining analog predistortion effectiveness
Solution Approach 2:
The patent introduces digital upconversion as an intermediary step between baseband and RF for each band. This digital intermediary allows precise frequency translation and band-specific signal conditioning before analog predistortion, enabling the system to handle wide separation multi-band signals that would be impossible to cover with a single wideband analog predistortion path
4Reliability
If digital predistortion is performed at baseband prior to digital upconversion, then predistortion is applied, but sampling rate requirements and upconversion complexity increase
Solution Approach 1:
The patent performs predistortion as a preliminary action at the RF stage after digital upconversion, rather than at baseband before upconversion. This reordering allows the predistortion to be applied to the upconverted signal at a lower sampling rate, reducing the computational burden of predistortion while eliminating the need to upconvert high-rate distorted signals
Solution Approach 2:
The patent inverts the conventional signal processing order by performing digital upconversion before predistortion rather than after. This inversion allows the system to work with lower sampling rates throughout the digital signal chain, reducing memory requirements, processing complexity, and power consumption while achieving the same predistortion effect
Data Source
AI summary
Systems and methods for radio frequency digital predistortion in a multi-band transmitter are disclosed. In one embodiment, the multi-band transmitter includes a digital upconversion system configured to digitally upconvert digital input signals to provide digital radio frequency signals. Each digital input signal and thus each digital radio frequency signal corresponds to a different band of a multi-band transmit signal to be transmitted by the multi-band transmitter. The multi-band transmitter also includes a radio frequency digital predistortion system configured to digitally predistort the digital radio frequency signals to provide predistorted digital radio frequency signals, and a combiner configured to combine the predistorted digital radio frequency signals to provide a multi-band predistorted digital radio frequency signal.