Sub-thermal Spread Spectrum Data-link for Secure Communication
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Solution Overview
Problem
Existing communication systems using silicon-based millimeter-wave datalinks struggle to maintain security and concealment due to the detectability of signals above the thermal noise floor, making them vulnerable to eavesdropping and interference.
Innovation Solution
A communication system that leverages wide mm-wave channel bandwidths by spreading low-data rate signals across large bandwidths, rendering them undetectable below the thermal noise floor, using a cyclic de-spreader to restore the signal without pre-detection timing knowledge, and employing analog mixers for parallel processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If signals are transmitted above the thermal noise floor to ensure detectability, then communication reliability is improved, but security and concealment deteriorate because signals become vulnerable to eavesdropping and interference
Solution Approach 1:
The patent changes the fundamental parameter of signal power spectral density by spreading the signal across a wide bandwidth, reducing the PSD below the thermal noise floor. This allows the signal to be undetectable to conventional receivers while remaining recoverable by the intended receiver through correlation processing
Solution Approach 2:
The patent transitions from narrowband communication to wideband communication, spreading the signal across a large bandwidth dimension. This dimensional expansion allows the signal to conceal itself within the thermal noise floor while maintaining communicability through spread spectrum processing
2Object-affected harmful factors
If spread spectrum techniques are used to reduce signal PSD below thermal noise floor, then security and concealment are improved, but signal detection and timing synchronization become more difficult
Solution Approach 1:
The patent applies preliminary action by using a known spreading sequence at the transmitter that is replicated at the receiver. This pre-established code allows the receiver to correlate with the spread signal and achieve timing synchronization without needing to detect or estimate the signal timing beforehand
Solution Approach 2:
The patent employs feedback through the correlation process where the receiver continuously correlates the received spread signal with locally generated spreading sequences at different time offsets, using the correlation output to identify the correct timing and synchronize the signal recovery
3Object-affected harmful factors
If wide bandwidth is used for spread spectrum signaling, then security and concealment are improved, but device complexity increases due to parallel processing requirements
Solution Approach 1:
The patent segments the de-spreading operation into multiple parallel correlators, each processing a different time offset of the spreading sequence. This segmentation allows simultaneous processing of all possible timing offsets, simplifying the overall architecture by eliminating the need for sequential search
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
The system ensures secure communication by making signals invisible to unintended receivers, reducing radio frequency interference, and achieving bit error rates better than 1e-8, with data transmission below the thermal noise floor, allowing only intended receivers to decode the message.
Implementation Method 1
the spreading sequence spreading a signal bandwidth of the signal to form the spread signal having a spread PSD smaller than the thermal noise PSD for all frequencies in the spread signal
Implementation Method 2
a demodulator demodulating the carrier electromagnetic radiation to obtain a demodulated signal comprising a spread signal combined with thermal noise
Implementation Method 3
comparing the demodulated signal with a plurality of de-spreading sequences representing different timings of the spreading sequence with respect to the demodulated signal, to find or obtain a correlated signal comprising a correlation between the demodulated signal and one of the de-spreading sequences
Data Source
AI summary
We have demonstrated that the bandwidth millimeter wavelengths offer can be leveraged to deeply spread a low-data rate signal below the thermal floor of the environment (sub-thermal) by lowered transmit power combined with free space losses, while still being successfully received through a novel dispreading structure which does not rely on pre-detection to extract timing information. The demonstrated data link ensures that it cannot be detected beyond a designed range from the transmitter, while still providing reliable communication. A demonstration chipset of this sub-thermal concept was implemented in a 28 nm CMOS technology and when combined with an InP receiver was shown to decode signals up to 30 dB below the thermal noise floor by spreading a 9600 bps signal over 1 GHz of RF bandwidth from 93 to 94 GHz using a 64 bit spreading code. The transmitter for this chipset consumed 62 mW while the receiver consumed 281 mw.