Pulse-Encoded RF Transitions for Lower ACLR Switching Modulation
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Solution Overview
Problem
Existing DRFM systems face challenges with high-speed switching techniques at the antenna producing aliases and significant ACLR, which are difficult to mitigate without compromising efficiency, and require high digital processing power and narrow-band filter banks.
Innovation Solution
Implementing pulse encoded transitions (PET) to shift transition noise into higher order harmonics, using a digital domain approach with additional pulses to simplify the transmit chain and improve signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-speed switching techniques are used at the antenna, then RF signaling efficiency is improved, but ACLR increases significantly due to aliases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and pre-distorting the signal in the digital domain before transmission. The system computes compensation values that anticipate and counteract the non-linear distortion and aliasing that will occur during high-speed switching, thereby preventing ACLR generation rather than attempting to filter it afterward.
Solution Approach 2:
The patent converts the harmful effect of high-speed switching aliases into a benefit by using digital pre-distortion techniques. The system intentionally introduces controlled inverse distortion that cancels out the expected harmful aliases, transforming what would be a detrimental effect into an opportunity for improved signal quality and efficiency simultaneously.
2Object-generated harmful factors
If bandpass filter banks are used to reduce ACLR, then ACLR is reduced, but insertion loss increases significantly
Solution Approach 1:
The patent substitutes mechanical/electrical filtering systems with digital signal processing. Instead of using physical bandpass filter banks that introduce insertion loss, the system employs digital pre-distortion and alias rejection algorithms that achieve ACLR reduction without the energy losses associated with narrow-band filtering components.
3Object-generated harmful factors
If predistortion is used to control ACLR, then ACLR is reduced, but efficiency and PAPR benefits are counteracted
Solution Approach 1:
The patent replaces analog predistortion mechanisms with digital domain processing. By performing all predistortion calculations and compensations in the digital realm before conversion to RF, the system maintains the efficiency benefits of digital signal processing while achieving ACLR control, avoiding the power losses and complexity of analog predistortion circuits.
4Object-generated harmful factors
If Σ—Δ modulation is used with BPF to reduce ACLR, then ACLR is reduced, but digital processing power and sampling rate requirements increase significantly
Solution Approach 1:
The patent optimizes the sampling rate parameter to be only 2x the bandwidth rather than the 100x+ required by Σ-Δ modulation approaches. This parameter change, combined with selective alias rejection techniques, achieves comparable ACLR reduction with dramatically reduced digital processing requirements and more practical implementation constraints.
Data Source
AI summary
A method for switching interval modulation includes modulating an RF input data signal while generating and inserting additional pulses in transitions of the data signal. The additional pulses are structured to shift transition noise into higher order harmonics. Higher order harmonics are easily filtered. The generating is conducted in the digital domain. The additional pulses can be used to simplify the transmit chain through optical modulators and improve the signal integrity over long distances, can be applied at the output of a transmitter to filter power amplifier distortion, and can be applied to non-linear RF over fiber for a distributed MIMO system.