Constant-Envelope FM-OFDM Waveform for Noise Robustness
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current wireless communication technologies, such as OFDM, are vulnerable to Doppler, phase noise, and frequency instability, which affect performance and power efficiency, especially at high frequencies, and lack adequate robustness against additive Gaussian noise.
Innovation Solution
A method using a constant-envelope FM-OFDM waveform with a specific phase representation and calculation of FFT length and active subcarriers to enhance signal-to-noise ratio, protecting against noise, Doppler, phase noise, and carrier frequency offset impairments by selecting an optimal cutoff subcarrier and noise reduction factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If OFDM is used for efficient user and data multiplexing, then throughput is improved, but sensitivity to Doppler, phase noise and frequency offset increases
Solution Approach 1:
The patent changes the fundamental parameter of the waveform structure from traditional OFDM to a constant-envelope waveform with time-varying frequency. This parameter change transforms the signal characteristics to be inherently more robust against Doppler, phase noise and frequency offset while maintaining efficient multiplexing capabilities through frequency modulation of the instantaneous frequency signal.
Solution Approach 2:
The patent substitutes the mechanical/structural approach of OFDM (orthogonal subcarriers in frequency domain) with a frequency modulation approach where information is encoded in the instantaneous frequency. This substitution replaces the vulnerability of fixed frequency subcarriers with the flexibility of time-varying frequency modulation, achieving better robustness against frequency-related impairments.
2Reliability
If power amplifiers operate in linear region to maintain signal quality, then signal fidelity is improved, but power efficiency deteriorates
Solution Approach 1:
The patent changes the signal envelope parameter from variable (in OFDM) to constant. By designing a constant-envelope waveform, the power amplifier can operate at maximum power output without risking signal distortion, thereby achieving high power efficiency while maintaining signal fidelity through the inherent robustness of constant-envelope modulation to non-linear amplification.
3Productivity
If cutoff subcarrier is increased to accommodate more subcarriers, then data rate is improved, but robustness against noise and interference deteriorates
Solution Approach 1:
The patent applies local quality by differentiating the treatment of different frequency regions. The cutoff subcarrier parameter creates a distinction between low-frequency subcarriers (more robust to noise) and high-frequency subcarriers (more susceptible to noise and interference). By strategically mapping information to subcarriers based on their noise robustness characteristics, the system achieves optimal balance between data rate and reliability.
Data Source
AI summary
A method to provide robustness against noise and interference in wireless communications, a transmitter and computer program products, involving sending to a receiver (13), through a wireless channel (12), information using a constant-envelope waveform with complex baseband representation of the form s[n]=Ac exp{jϕ[n]}. The phase ϕ[n] following the expression(ϕ[n]-ϕ[n-1])=2πm·∑k=k0+1k0+Na,FM+-1x[k]exp(j2πknN),and the wireless channel has an Additive White Gaussian Noise component and flat-fading conditions, wherein the transmitter (110) calculates a FFT length, N, and a number of active positive subcarriers, Na,FM+, needed in order to have a given improvement in the signal to noise ratio at the active positive subcarriers of the instantaneous frequency spectrum containing the information; calculates a cutoff subcarrier k0 needed to overcome Doppler, phase noise and carrier frequency offset impairments at the receiver side, and generates a complex baseband signal waveform of the form s[n]=Ac exp{jϕ[n]} carrying information with the FFT length, number of active positive subcarriers and cutoff subcarrier.