Orthogonal OFDM Preamble Interference for Drone Link Disruption
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Solution Overview
Problem
Existing methods to counter unsolicited drone communications via OFDM signals are easily detectable and ineffective against inexperienced users, who can bypass jamming attempts by switching WLAN channels.
Innovation Solution
Retransmitting the succeeding frame preamble of a first data frame concurrently with a succeeding frame preamble of a second data frame, using a second radio power and equalization parameter that are on the same order of magnitude but orthogonal and time-variant, to interfere with the OFDM signal and disrupt communication between drones and their remote controls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a jamming signal is transmitted to counter unsolicited drone communications, then the signal-to-noise ratio of the radio communication is decreased, but the jamming attempt is easily detected by inexperienced users who can switch to a different WLAN channel
Solution Approach 1:
The patent applies parameter changes by modifying the equalization parameters of the retransmitted preamble to differ from the original transmission. Specifically, the equalization parameters are changed to create an orthogonal relationship, making the interference signal appear as legitimate OFDM traffic rather than obvious jamming. This transforms the jamming approach from a detectable noise injection to a subtle parameter manipulation that disrupts communication while evading detection.
Solution Approach 2:
Instead of transmitting a traditional jamming signal that adds noise to the channel, the patent inverts the approach by retransmitting the actual OFDM preamble sequence that was originally received. This inverted approach uses the legitimate signal structure itself as the interference mechanism, combining it with modified equalization parameters to create confusion at the receiver side rather than simple noise addition.
2Power
If a more powerful unmodulated or modulated carrier is transmitted as jamming signal, then the signal-to-noise ratio is decreased, but the jamming can be easily bypassed by switching channels
Solution Approach 1:
The patent changes the equalization parameters of the retransmitted preamble to create an orthogonal relationship with the original signal. This parameter modification causes the combined signal at the drone receiver to have incorrect channel estimation and demodulation, effectively blocking communication without requiring excessive power. The interference is achieved through parameter manipulation rather than brute-force power transmission.
Solution Approach 2:
The patent copies the actual OFDM preamble sequence from the legitimate transmission and retransmits it with modified equalization parameters. This copying approach uses the authentic signal structure as the interference weapon, making it indistinguishable from legitimate traffic to casual observers while still causing functional disruption. The copied preamble is combined with the ongoing transmission to create confusion at the receiver.
3Reliability
If the succeeding frame preamble is retransmitted with orthogonal equalization parameter, then correct channel estimation and demodulation are prevented, but the radio power must be controlled to be no more than 1.5 dB higher than the original
Solution Approach 1:
The patent achieves effective disruption by changing the equalization parameters to an orthogonal relationship with the original signal, rather than increasing power significantly. The orthogonal parameter modification causes the drone receiver to compute incorrect channel estimates and fail to demodulate the signal properly. This parameter-based approach achieves reliable disruption while adhering to the power constraint of no more than 1.5 dB increase over the original transmission power.
Data Source
AI summary
Disclosed are a method of and a system for interference with a transmission of an OFDM signal comprising multiple data frames which respectively comprise a preceding frame preamble and a succeeding frame preamble. The method comprises: receiving a succeeding frame preamble of a first data frame of the multiple data frames; identifying a first radio power and a first equalization parameter associated with the received succeeding frame preamble; determining a second radio power on a same order of magnitude as the first radio power, and a second equalization parameter differing from the first equalization parameter; receiving a preceding frame preamble of a second data frame of the multiple data frames; and retransmitting the succeeding frame preamble of the first data frame concurrently with a succeeding frame preamble of the second data frame. The retransmitted succeeding frame preamble comprises the second radio power and the second equalization parameter.