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Directional Modulation Using Frequency Diverse Array For Secure Communications

In this paper, to obtain a better physical layer security for wireless communications, a directional modulation (DM) using frequency diverse array (FDA) is proposed. Different from the traditional directional modulation that achieves only angle dependent directional modulation, our proposed scheme achieves DM in both angle and range dimensions. The transmitted signal symbols only could be recovered successfully at the desired receiver, while they are distorted to be unrecoverable at the undesired receivers. Therefore, it will increases the security of data transmission to against the eavesdroppers. This FDA-based DM scheme can be potentially applied in the point-to-point security communications and the effectiveness is validated by numerical results.

Secure directional modulation using frequency diverse array antenna

Inspired by the frequency diverse array (FDA) producing range and angle dependent beampattern due to the employment of frequency increments across the array elements, this paper proposes a direction-dependent communications using 2-bit phase control across a two-element FDA antenna. The produced directional pattern projects the phase modulation signal as a constellation, which offers physical-layer security for wireless communications. This is because the transmitted symbols can be purposely distorted in other positions, but they could be successfully decoded at the intended range and angle position. The effectiveness of the proposed method is verified by numerical results.

Frequency Diverse Array Antennas: From Their Origin to Their Application in Wireless Communication Systems

Wireless communication systems have gained considerable growth rate nowadays, with the anticipation that communications will be available everywhere and anywhere in the near future. Phased array antenna whose beam steering is fixed in an angle for all range cells has been utilized for wireless communications. To mitigate this problem, a new array concept, namely, frequency diverse array (FDA), was proposed. This paper presents how FDA technology could be useful in today’s wireless communication technology. FDA is distinct from phased array in a sense that it employs frequency increment across array elements. The use of a frequency increment creates a beam steering that is a function of angle, time, and range which allows the FDA antenna to transmit the energy along the prespecified range and angle direction. In addition, we consider the time-variant beampattern aspect of an FDA, which has normally been ignored in the literature. In this study, we present the mathematical fundamentals of FDA antenna and why it could be exploited for wireless communication systems. Furthermore, FDA using Butler matrix for communication has been discussed. Performance analysis in terms of transmit beampattern, signal-to-interference-and-noise ratio (SINR), and direction of arrival has been presented and compared with that of phased array antenna.

OFDM Chirp Radar for Adaptive Target Detectionin Low Grazing Angle.

Low-altitude target detection is of great importance in radar applications, especially for military radar to counter the targets penetrated from low grazing angles. However, it is a challenge to detect the targets in low grazing angle area due to severe multipath reflection effects. In this study, the authors propose orthogonal frequency division multiplexing (OFDM) chirp waveform for target detection in low grazing angle region. The OFDM chirp waveform has better peak-to-average-power ratio level and provides larger time-bandwidth product than that of conventional OFDM waveform, which is beneficial for target detection. Two different radar schemes, namely, OFDM chirp radar and OFDM chirp multiple-input multiple-output (MIMO) radar, are studied under the Earths curvature geometry model with the consideration of realistic multipath reflection effects. The generalised likelihood ratio test algorithm is developed by jointly exploiting the advantages of OFDM chirp waveform and MIMO configuration in increased degrees of freedom. In addition, an adaptive algorithm is further applied to enhance the target detection performance. All proposed schemes are verified by numerical results.

FDA radar using Costas sequence modulated frequency increments

Frequency diverse array (FDA) radar provides new application capabilities and potentials due to its range-dependent transmit array beampattern, but the FDA using linearly increasing frequency increments produces a range and angle coupled beampattern. This paper proposes a uniform linear array (ULA) FDA using Costas sequence modulated frequency increments to produce random-like energy distribution in the transmit beampattern to decouple the range-angle-dependent of targets. In doing so, the range and angle of targets can be solely estimated through matched filtering and subspace decomposition algorithms in the receiver signal processor. Numerical results show that the proposed scheme outperforms the standard FDA in focusing the transmit energy, especially in the range dimension.