[Paper Review] Secure M-PSK Communication via Directional Modulation

Ashkan Kalantari, Mojtaba Soltanalian+3 more|arXiv (Cornell University)|Apr 10, 2016

Wireless Communication Security Techniques28 references4 citations

TL;DR

This paper proposes a directional modulation beamforming technique for secure M-PSK communication using multi-antenna transmitters, steering the array beam so that the received signal phase at the legitimate receiver matches intended M-PSK symbols, while inducing a different phase at the eavesdropper, thereby increasing its symbol error rate (SER) without requiring eavesdropper channel state information (CSI). The method achieves lower power consumption and significantly higher SER at the eavesdropper compared to zero-forcing precoding, demonstrating improved physical layer security for finite-alphabet signals.

ABSTRACT

In this work, a directional modulation-based technique is devised to enhance the security of a multi-antenna wireless communication system employing M-PSK modulation to convey information. The directional modulation method operates by steering the array beam in such a way that the phase of the received signal at the receiver matches that of the intended M-PSK symbol. Due to the difference between the channels of the legitimate receiver and the eavesdropper, the signals received by the eavesdropper generally encompass a phase component different than the actual symbols. As a result, the transceiver which employs directional modulation can impose a high symbol error rate on the eavesdropper without requiring to know the eavesdropper's channel. The optimal directional modulation beamformer is designed to minimize the consumed power subject to satisfying a specific resulting phase and minimal signal amplitude at each antenna of the legitimate receiver. The simulation results show that the directional modulation results in a much higher symbol error rate at the eavesdropper compared to the conventional benchmark scheme, i.e., zero-forcing precoding at the transmitter.

Motivation & Objective

• To enhance physical layer security in multi-antenna M-PSK systems without requiring eavesdropper channel state information (CSI).
• To design an optimal beamformer that minimizes transmit power while ensuring correct phase alignment at the legitimate receiver and minimum signal amplitude at each transmit antenna.
• To evaluate the performance of directional modulation against conventional zero-forcing (ZF) precoding in terms of symbol error rate (SER) and power efficiency.
• To demonstrate that directional modulation can induce high SER at the eavesdropper due to phase misalignment, even when the eavesdropper has global CSI and full knowledge of system configuration.

Proposed method

• The beamformer weights are optimized to align the phase of the received signal at the legitimate receiver with the desired M-PSK symbol phase, while minimizing total transmit power.
• The beamforming design enforces a minimum signal amplitude at each transmit antenna to ensure reliable reception at the legitimate receiver.
• The method exploits the difference in channel responses between the legitimate receiver and the eavesdropper to induce phase mismatch at the eavesdropper, increasing its SER.
• The technique does not require zero-forcing or MMSE processing at the legitimate receiver, simplifying receiver design.
• The beamformer is designed under the assumption that the eavesdropper has global CSI and knowledge of system parameters, including number of antennas and modulation order.
• The performance is evaluated via simulations comparing SER and power consumption against zero-forcing precoding, a conventional benchmark scheme.

Experimental results

Research questions

• RQ1 Can directional modulation achieve secure M-PSK communication without requiring eavesdropper CSI?
• RQ2 How does the symbol error rate (SER) at the eavesdropper compare between directional modulation and zero-forcing precoding?
• RQ3 What is the power efficiency of the directional modulation beamformer compared to conventional ZF precoding?
• RQ4 How does the number of transmit and receive antennas affect the security and performance of directional modulation?
• RQ5 Under what conditions can the eavesdropper successfully decode signals in the directional modulation scheme?

Key findings

• The directional modulation scheme achieves significantly higher symbol error rate (SER) at the eavesdropper compared to zero-forcing precoding, especially when the eavesdropper has more antennas than the legitimate receiver.
• For L = 9 and N = 8, the SER difference between directional modulation and ZF at the eavesdropper exceeds that when N = 6, indicating enhanced security with larger eavesdropper arrays.
• The average consumed power of directional modulation is lower than that of zero-forcing precoding for a specific range of transmit antennas L, with the power advantage increasing as L grows.
• When L = 8 and N = 6, the SER at the eavesdropper remains high and does not decrease with increasing signal level √γ in directional modulation, unlike in ZF, where SER decreases as √γ increases.
• The eavesdropper cannot reliably estimate the beamformed signal in directional modulation when N < L, due to phase mismatch, even with full CSI knowledge.
• The legitimate receiver does not require zero-forcing or MMSE processing, simplifying receiver implementation and reducing complexity.