OFDM Signal Frequency Shifting for SSBI Noise Elimination
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Solution Overview
Problem
Existing direct detection orthogonal frequency division multiplexing (DDOFDM) systems face low bandwidth utilization due to the requirement of double signal bandwidth to eliminate subcarrier-subcarrier beating interference (SSBI) noise, which affects system performance.
Innovation Solution
Shifting the frequency of the OFDM signal by Δf/n on the transmit side, where n is an integer greater than 1, ensures that the OFDM signal and SSBI noise are on different subcarriers, allowing for SSBI noise elimination without doubling the bandwidth, thereby improving bandwidth utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If signals are filled only on a band whose spectrum range is [W, 2W] or data is filled only on odd-numbered subcarriers to eliminate SSBI noise, then SSBI noise is eliminated, but bandwidth utilization becomes low due to double signal bandwidth requirement
Solution Approach 1:
The patent changes the frequency parameter of the OFDM signal by applying a frequency shift of fs = Δf/n, where n is an integer greater than 1. This parameter change relocates the signal spectrum such that SSBI noise falls into different subcarrier positions, eliminating interference without requiring double bandwidth. The frequency shift transforms the spectral distribution to achieve both SSBI elimination and efficient bandwidth utilization.
2Reliability
If the frequency of OFDM signal is shifted by fs = Δf/n, then SSBI noise is eliminated while maintaining original bandwidth, but the signal spectrum distribution changes
Solution Approach 1:
The patent introduces asymmetric frequency shifting by applying a non-zero frequency offset fs = Δf/n to the OFDM signal. This asymmetric shift breaks the original symmetric spectral distribution centered at zero frequency, relocating the signal to an asymmetric position in the frequency domain. The asymmetric distribution ensures that SSBI noise components fall into guard bands or unused subcarrier positions, achieving noise elimination while the signal maintains its structural integrity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively eliminates SSBI noise while minimizing bandwidth wastage, enhancing bandwidth utilization and system performance without the need for double bandwidth, thus improving the efficiency of the DDOFDM system.
Implementation Method 1
multiplying, in a digital domain, a generated orthogonal frequency division multiplexing OFDM signal by a simple harmonic wave whose frequency is fs to obtain a frequency shifted OFDM signal
Data Source
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AI summary
The present invention is applicable to the communications field and provides a processing method for an orthogonal frequency division multiplexing signal and a network device. The processing method includes: obtaining an orthogonal frequency division multiplexing OFDM signal; multiplying, in a digital domain, the obtained OFDM signal by a simple harmonic wave whose frequency is fs to obtain a frequency shifted signal; and outputting and loading the frequency shifted signal by using a DAC to a driver and a modulator to send the frequency shifted OFDM signal. The technical solutions provided in embodiments of the present invention have an advantage of improving bandwidth utilization.