Pilot Spoofing Attack on the Downlink of Cell-Free Massive MIMO: From the Perspective of Adversaries
arxiv(2024)
摘要
The channel hardening effect is less pronounced in the cell-free massive
multiple-input multiple-output (mMIMO) system compared to its cellular
counterpart, making it necessary to estimate the downlink effective channel
gains to ensure decent performance. However, the downlink training
inadvertently creates an opportunity for adversarial nodes to launch pilot
spoofing attacks (PSAs). First, we demonstrate that adversarial distributed
access points (APs) can severely degrade the achievable downlink rate. They
achieve this by estimating their channels to users in the uplink training phase
and then precoding and sending the same pilot sequences as those used by
legitimate APs during the downlink training phase. Then, the impact of the
downlink PSA is investigated by rigorously deriving a closed-form expression of
the per-user achievable downlink rate. By employing the min-max criterion to
optimize the power allocation coefficients, the maximum per-user achievable
rate of downlink transmission is minimized from the perspective of adversarial
APs. As an alternative to the downlink PSA, adversarial APs may opt to precode
random interference during the downlink data transmission phase in order to
disrupt legitimate communications. In this scenario, the achievable downlink
rate is derived, and then power optimization algorithms are also developed. We
present numerical results to showcase the detrimental impact of the downlink
PSA and compare the effects of these two types of attacks.
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