Performance Analysis of Directional Modulation with Finite-quantized RF Phase Shifters in Analog Beamforming Structure

TL;DR

This paper analyzes how finite-quantized RF phase shifters impact the performance of directional modulation in analog beamforming, deriving closed-form expressions and showing performance improves with more quantization bits.

Contribution

It provides a closed-form SINR loss expression due to quantization error and demonstrates the performance benefits of increasing quantization bits in directional modulation systems.

Findings

SINR loss decreases with more quantization bits, less than 0.3dB for L≥3.

Performance loss becomes negligible when L exceeds 5 bits.

Secrecy rate loss reduces as quantization bits increase, about 0.1 bits/s/Hz at L=3.

Abstract

The radio frequency (RF) phase shifter with finite quantization bits in analog beamforming (AB) structure forms quantization error (QE) and causes a performance loss of received signal to interference plus noise ratio (SINR) at the receiver (called Bob). By using the law of large numbers in probability theory, the closed-form expression of SINR performance loss is derived to be inversely proportional to the square of sinc (or sin(x)/x) function. Here, a phase alignment method is applied in directional modulation transmitter with AB structure. Also, the secrecy rate (SR) expression is derived with QE. From numerical simulation results, we find that the SINR performance loss gradually decreases as the number L of quantization bits increases. This loss is less than 0.3dB when L is larger than or equal to 3. As L exceeds 5, the SINR performance loss at Bob can be approximately trivial. Similarly, SR performance loss gradually reduces as L increases. In particular, the SR performance loss is about 0.1 bits/s/Hz for L=3 at signal-to-noise ratio of 15dB.