Hierarchical 2-D Feature Coding for Secure Pilot Authentication in Multi-User Multi-Antenna OFDM Systems: A Reliability Bound Contraction Perspective

Abstract

Due to the publicly-known and deterministic characteristic of pilot tones, pilot authentication (PA) in multiuser multi-antenna OFDM systems is very suspectable to the jamming/nulling/spoofing behaviors. To solve this, we in this paper develop a hierarchical 2-D feature (H2DF) coding theory that exploits the hidden pilot signal features, i.e., the energy feature and independence feature, to secure pilot information coding which is applied between legitimate parties through a well-designed five-layer hierarchical coding (HC) model to achieve secure multiuser PA (SMPA). The reliability of SMPA is characterised using the identification error probability (IEP) of pilot encoding and decoding, with the exact closed-form upper and lower bounds. However, this phenomenon of nontight bounds brings about the risk of long-term instability in SMPA. Therefore, a reliability bound contraction (RBC) theory is developed to shrink the bound interval and practically, this is done by an easy-to-implement technique, namely, codebook partition within the H2DF code. In this process, a tradeoff between the upper and lower bounds of IEP is identified and a problem of optimal upper-lower bound tradeoff is formulated, with the objective of optimizing the cardinality of sub-codebooks such that the upper and lower bounds coincide. Solving this, we finally derive an exact closed-form expression for IEP, which realizes a stable and highly-reliable SMPA. Numerical results validate the stability and resilience of H2DF coding in SMPA.Index Terms-Physical-layer authentication, anti-attack, multiuser OFDM, channel training, hierarchical 2-D feature coding.

Concatenated Graph Coding on Bandwidth Part for Secure Pilot Authentication in Grant-Free URLLC

“…There are two PLS based research routes to protect pilots, including deterministic-pilot based approach and randompilot based approach. The former is limited to how to detect pilot-aware attack by exploiting the physical layer information, such as auxiliary training or data sequences [19], [20] and some prior known channel information [21]- [23] whereas the latter aims to avoid it by pilot randomization [15], [24], [25]. The importance of pilot randomization on time-frequency resources to avoid pilot aware attack on pilot subcarriers have been stressed in orthogonal frequency-division multiplexing (OFDM) systems [26].…”

“…When pilot aware attack happens, TRP under those schemes highly rely on the coding diversity and spatial fading correlation difference between UE and the attacker. By relaxing the dependence, authors in [25] proposed a scheme of hierarchical 2-D feature coding (H2DF) coding to encode SAPs to realize TRP reliably. Those schemes help answer the question of how to design TRP between UEs and gNB under pilot randomization and pilot-aware attack.…”

“…Authors in [38] have provided a function γ (P f ) Δ = f (N T , K, P f ) for determining on one subcarrier the number of antennas required to achieve a probability P f of false alarm detection. Alice could always flexibly configure γ (ε * ) to make ε * approach zero [25] and precisely detect the number of signals on the jth subcarrier as N j . Then the binary digit corresponding to the j-th pilot subcarrier is "1" when N j ≥ 1 and otherwise when N j = 0, the binary digit is equal to 0.…”

“…Due to the randomness of pilots and SAPs, Ava launches a hybrid attack on SAPs, including wide-band pilot jamming (WB-PJ), partial-band pilot jamming (PB-PJ) and silence cheating (SC) attack [14], [25]. In WB-PJ attack, Ava activates the whole available subcarriers.…”

Fundamental Tradeoffs in Uplink Grant-Free Multiple Access with Protected CSI

“…Previously, it has been mentioned in [6] that attacking channel estimation is with high priority and more powerefficient than the behavior of jamming data packet decoding. Besides, the recent accidents caused by pilot aware attack indicate that the conventional pilot-based channel estimation is suffering significant risks [7]. The commonsense built to resolve this issue is pilot randomization which transforms the pilot-aware attack into a hybrid attack, including silence cheating (SC), wide-band pilot jamming (WB-PJ), and partial-band pilot jamming (PB-PJ) attack.…”