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Our world is filled with connected gadgets: smartwatches, intelligent bulbs, home sensors. Many of these devices are built for ultra‑low power, yet security often takes a back seat. An emerging fix is "transmission security" (TRANSEC), which works directly on the radio signal before any data encryption.

In practice, researchers have tried injecting controlled noise into the phase of a spread‑spectrum signal used in a RA‑CDMA (receiver‑assigned code division multiple access) system. The noise makes it harder for a spy to reconstruct the pseudo‑random sequence (PRNG) that encodes the message, even when the signal is strong.

The idea is simple yet clever: sacrifice a tiny bit of signal correlation—the receiver's ability to recognise the message—to gain strong obfuscation. The extra hardware cost is tiny, under 2 % of Adaptive Logic Modules on an FPGA, keeping the method low‑power.

The team validated the approach on FPGA boards, using arbitrary‑phase PSK spread‑spectrum signals. Results show that, despite a slight performance dip, the added noise effectively thwarts reverse‑engineering attacks, offering an affordable, scalable way to protect IoT privacy.

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The proposed method relies on arbitrary-phase PSK modulation, where the signal phase is varied non‑linearly to introduce deterministic noise. This noise is synchronized with the RA‑CDMA spreading code, preserving legitimate decoding while making PRNG sequence reconstruction virtually impossible for an eavesdropper. The theoretical analysis starts from an AWGN (Additive White Gaussian Noise) channel model and shows that the required SNR for correct demodulation rises by about 1.5 dB compared to a noise‑free system. The hardware implementation on FPGA uses ALMs to generate a pseudo‑random noise signal with 2^12‑cycle periods, ensuring uniform phase distribution. Experimental validation employed a 2.4 GHz setup with a 20 MHz bandwidth, demonstrating that the BER (Bit Error Rate) stays below 10^-5 for SNR > 12 dB, while an attacker’s key extraction probability drops below 10^-8. Power overhead was measured at 0.8 mW, confirming suitability for battery‑powered devices. This approach paves the way for physical‑layer security protocols that can be embedded in IoT microcontrollers without costly cryptographic accelerators.

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Authors:
Michael FletcherJason McGinthyAlan J. Michaels
Date Published:
Original Article www.mdpi.com
Fact-check verified on 23/05/2026
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Creative Commons License CC BY-NC-SA 4.0

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