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IEEE Transactions on Vehicular Technology

Physical Layer Key Generation of LEO Satellite Communication Based on OTFS Technology

Ye Fan, Xiaotong Sun, Rugui Yao, Tong-Xing Zheng, Xiaoya Zuo, Jialong Shi

Published Oct 30, 2025• 0 citations
Publisher

Abstract

Low earth orbit (LEO) satellite signals cover extensive areas with high intensity, rendering them vulnerable to interception. However, the rapid movement of LEO satellites leads to severe Doppler frequency shift, making it extremely challenging to generate a consistent key using traditional physical key generation techniques. In response to these issues, we have fully utilized Orthogonal Time Frequency Space (OTFS) in dynamic environments and propose a physical layer key generation (PLKG) scheme based on delay- Doppler (DD) domain signal processing. In the preprocessing stage, we propose a Linearly Weighted Moving Average Coding (LW-MAC) algorithm that dynamically adjusts weights with varying channel response intensities, significantly reducing the inconsistency in channel estimation. Subsequently, to address the reduction in key security caused by insufficient key length, we propose a Maximum of Real and Imaginary parts of channel response Assisted Amplitude Quantization (MRIAAQ) algorithm, which increases the key length and enhances the key entropy value. Simulation results demonstrate that our proposed PLKG scheme has substantial advantages over bidirectional difference quantization (BDQ) and equal probability quantization schemes in terms of key disagreement rate (KDR). Moreover, our PLKG scheme significantly reduces the bit error rate (BER) by approximately 71.37$\%$on average compared to artificial noise-aided physical layer security scheme, thereby greatly enhancing the security of dynamic satellite-to-ground communication.

DOI
10.1109/tvt.2025.3626858

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Low earth orbit (LEO) satellite signals cover extensive areas with high intensity, rendering them vulnerable to interception. However, the rapid movement of LEO satellites leads to severe Doppler frequency shift, making it extremely challenging to generate a consistent key using traditional physical key generation techniques. In response to these issues, we have fully utilized Orthogonal Time Frequency Space (OTFS) in dynamic environments and propose a physical layer key generation (PLKG) scheme based on delay- Doppler (DD) domain signal processing. In the preprocessing stage, we propose a Linearly Weighted Moving Average Coding (LW-MAC) algorithm that dynamically adjusts weights with varying channel response intensities, significantly reducing the inconsistency in channel estimation. Subsequently, to address the reduction in key security caused by insufficient key length, we propose a Maximum of Real and Imaginary parts of channel response Assisted Amplitude Quantization (MRIAAQ) algorithm, which increases the key length and enhances the key entropy value. Simulation results demonstrate that our proposed PLKG scheme has substantial advantages over bidirectional difference quantization (BDQ) and equal probability quantization schemes in terms of key disagreement rate (KDR). Moreover, our PLKG scheme significantly reduces the bit error rate (BER) by approximately 71.37%\%%on average compared to artificial noise-aided physical layer security scheme, thereby greatly enhancing the security of dynamic satellite-to-ground communication.
Physical-layer key generation (PLKG) is a technique that produces symmetric encryption keys by exploiting the inherent characteristics of wireless channels. It offers advantages including high physical-layer security, elimination of pre-shared keys, dynamic upgradability, and resistance to quantum attacks, making PLKG a promising security solution for next-generation (6G) networks. However, satellite communication channels exhibit high dynamics and long propagation delays. Characteristics such as large Doppler shifts, short coherence times, and orbital predictability pose severe challenges to PLKG, including reciprocity degradation, low key generation rate (KGR), and susceptibility to channel-prediction attacks. This work proposes a delay-Doppler domain time-hopping key generation scheme (KE-DD-TH) based on Orthogonal Time Frequency Space (OTFS) modulation for high-speed links between Low-Earth-Orbit (LEO)/Medium-Earth-Orbit (MEO) satellites and ground terminals in Ka/Ku bands. The scheme performs non-uniform sampling on the DD domain grid of OTFS symbols using an ephemeris-driven pseudo-random time-hopping sequence generated by cascaded linear feedback shift registers (LFSRs) and a nonlinear matrix transformation. Both legitimate parties estimate the channel only at time-hopping instants and multiply two adjacent estimates to construct an "equivalent channel" matrix, yielding a random source with high entropy, high reciprocity, and low predictability. The eavesdropper's key disagreement rate (KDR) remains close to 0.5 under all signal-to-noise ratio (SNR) conditions, corresponding to the ideal random-guessing baseline. This indicates that Eve obtains negligible mutual information, i.e., I(KA;KE)≈0. By contrast, the conventional KE-DD scheme allows Eve's KDR to degrade to 0.014 at 30 dB SNR, indicating near-complete key recovery. The generated keys pass all 12 randomness tests of the NIST SP 800-22 statistical test suite.
Physical layer key generation (PLKG) has emerged as a promising strategy for securing wireless communication using shared channel knowledge between two legitimate users. Traditional PLKG systems rely on time-frequency domain channels using metrics such as Received Signal Strength Indicator (RSSI) or Channel State Information (CSI) to generate secure keys. As a result of the rapid variation in the time-frequency domain channels, these systems are prone to error and suffer from a high reconciliation overhead requirement. Conversely, the same channels have a sparse and static representation in the delay-Doppler domain, which is utilized by the recently introduced Orthogonal Time Frequency Space (OTFS) modulation scheme. Furthermore, the channel representation in the delay-Doppler domain is uniquely determined by the scattering environment between the transmitter-receiver pair. In this paper, we leverage the sparsity of the delay-Doppler domain channel as well as the uniqueness of the channel representation to introduce two OTFS based PLKG schemes. We show through extensive simulations that the introduced OTFS schemes can get < 10% bit disagreement ratio (BDR) in scenarios where time-frequency domain based RSSI methods break down.
Low Earth Orbit (LEO) satellite communications are vulnerable to eavesdropping over open wireless links. This paper proposes a simplified artificial noise (AN)-aided physical layer security scheme. A system model with a multi-antenna LEO satellite, a single-antenna ground user, and multiple eavesdroppers is built under shadowed-Rician fading and imperfect channel state information. AN is projected into the null space of the legitimate channel to avoid interference, and fixed power allocation is adopted for low complexity. Simulations show the scheme achieves better secrecy rate and secrecy outage probability than traditional methods, suitable for resource-constrained LEO satellite systems.
Low Earth Orbit (LEO) satellite communications are vulnerable to eavesdropping due to open wireless links. To address this issue, a simplified artificial noise (AN)-aided physical layer security scheme is proposed. A practical system model including a multi-antenna LEO satellite, a single-antenna ground user, and multiple eavesdroppers is established, considering shadowed Rician fading and imperfect channel state information (CSI). The AN is projected into the null space of the legitimate user’s channel to avoid interference, while suppressing eavesdroppers. A fixed power allocation strategy is adopted for easy implementation. Simulation results show that the proposed scheme outperforms traditional methods in secrecy rate and secrecy outage probability (SOP) with low computational complexity, making it suitable for resource-constrained LEO satellite systems.
With the rapid advancement of Low Earth Orbit (LEO) satellite constellations, ensuring the security of satellite-to-ground communication has become a critical concern. Traditional cryptographic techniques, while effective against classical attacks, face increasing threats from quantum computing. This paper proposes a quantum key secure transmission method tailored for LEO satellite-ground communication scenarios. The method integrates quantum key distribution (QKD) with dynamic channel estimation and orbital mobility prediction to support secure and low-latency key handshakes between satellites and ground stations. A hybrid encryption strategy is introduced, where QKD-generated keys are used to refresh symmetric session keys in real time, significantly enhancing resistance to eavesdropping and man-in-the-middle attacks. Simulation results demonstrate that the proposed method ensures stable key distribution under Doppler-shifted and intermittent link conditions, achieving improved secrecy capacity and resilience against quantum-level adversaries. This work provides a viable and scalable quantum-safe communication solution for future secure satellite networks.
Vehicular communication is delay sensitive and demands high security. However, the time for key establishment between node pairs is limited due to the unique features of fast-moving and high dynamics in Vehicular ad hoc networks (VANETs). Moreover, under high-mobility scenarios, the communication performance of Orthogonal Frequency Division Multiplexing (OFDM) signals degrades significantly, while Orthogonal Time Frequency Space (OTFS) signals maintains better performance. Towards this end, considering the time for key establishment, we propose an efficient physical layer secret key generation (PLSKG) scheme utilizing OTFS channel state information (CSI). First, we preprocess the estimated CSI with a moving average coding (MAC) algorithm to improve channel reciprocity. Next, we adopt a bidirectional difference quantization (BDQ) for increased key bit generation and propose a one-way reconciliation protocol to remove bit mismatch. Results from extensive simulations have verified that our scheme achieves random 0-b disagreement keys with a high key generation rate and reduced time for key establishment compared to other schemes.