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Most of the existing works in millimeter wave (mmWave) and non-orthogonal multiple access (NOMA) communications (mmWave NOMA) employs phased array (PA) antennas which yield only angle beamspace without range dependent, range-interference suppression and “dot-shaped” array resolution. In this paper, we propose a collocated transmitter (Tx) - receiver (Rx) mmWave NOMA system where frequency diverse array (FDA) antennas are utilized. FDA employs small frequency increments across the element indices which yields angle-range dependent beamspace. Herein, an equivalent radiate beamspace is designed to serve the users. Further, to ensure user equity, we formulate objective function to max-min achievable sum rate subject to power allocation and BS equivalent FDA transmit beamspace along the users. Since the problem is not convex, a boundary-compressed Bat meta-heuristic optimization algorithm is devised to provide a sub-optimal solution by optimizing the frequency increments to synthesis the BS beamspace along the users. The achievable secrecy rate, cost efficiency (CE), economic efficiency (ECE), and secrecy energy efficiency (SEE) are derived for the users. Both theoretical analysis and simulation results indicate that the proposed scheme would constitute an excellent nominee for 5G mmWave NOMA communication applications. [ABSTRACT FROM AUTHOR]

Quadrature spatial modulation (QSM) based millimeter wave (mmWave) communication system design using frequency diverse array (FDA) is proposed in this article. Since spatial modulation techniques (SMT) employ maximum likelihood (ML) based detector at receiver, the computational complexity increases vastly. Moreover, numerous existing SMT methods utilize phased array (PA), where only angle dependent communication is possible. In this article, we propose to use a standard FDA that exploits a small linearly increasing frequency offset across the array for range-angle dependent QSM wireless communications. That is, the in-phase and quadrature components of transmission vector utilize slightly different frequencies to deliver the information. Furthermore, we propose a suboptimal multi-stage (MS) detector in the receiver, which applies a matched filtering (i.e., bandpass filters matched to the corresponding frequency offsets) approach to decode the index bits at first step, whereas, merely, two most probable estimated indices are utilized further to decode associated data bits using a standard ML method. Adhering an improved signal to noise ratio (SNR) due to an FDA based range-angle dependent transmission, simulation and numerical results show the improved performance of the proposed design over existing SM and QSM based schemes, while MS approach reduces the receiver’s computational complexity. [ABSTRACT FROM AUTHOR]

Designing energy-efficient security techniques for Internet of Things (IoT) networks is particularly vital due to its limited battery capacity and the flow of information via broadcasting. In this article, we propose retrodirective frequency diversity array (RDFDA) based on directional modulation (DM) concept in a time-modulated way to enhance security in IoT. Different from the existing IoT security, in the proposed scheme, the prior knowledge of the intended receivers’ location is not required for the transmitter and no need of channel state information. Leveraging on this feature, we design time controlling switch sequences, which require a single radio frequency chain. To facilitate the DM operation in the proposed RDFDA, the connecting–disconnecting switching functionality for each element branch needs to be judiciously selected. Furthermore, we give insights on how the useful messages can be leaked along the eavesdropper (Eve) direction when an outage has occurred as well as Eve error detectability by analyzing the following metrics such as secrecy outage probability, Eve detecting error probability, and leakage rate of noncolluding Eves. Other metrics, such as secrecy energy efficiency, economic efficiency, and cost efficiency were also analyzed. We give numerical results to disclose the proposed scheme achievements. [ABSTRACT FROM AUTHOR]

In multicast communication scenario, the desired users are decomposed into M groups to receive private M useful data from the transmitter, while eavesdroppers (Eves) group tries to intercept. Since wireless security system consists of authentication and secure transmission, we propose directional modulation (DM) artificial noise (AN) matrix-aided Costas sequence (CS) matrix frequency diverse array (FDA) in multicast precoding systems in this paper. Specifically, we utilize the CS matrix for desired groups authentication (i.e., group identity), and it is shared via a low-speed forward link in advance. Next, we design AN matrix-aided FDA to offer robust antieavesdropping method based on leakage concept. Furthermore, we devise secrecy metrics, namely, secrecy outage probability (SOP), asymptotic Eve's detectability error probability, and average useful data leakage rate, based on the scenario where Eve's instantaneous channel state information (CSI) is unavailable. In addition, we numerically analyze the proposed energy beamforming focusing and evaluate the secrecy energy efficiency. Via simulation results, the proposed scheme gives important insights into how to design and measure secrecy performances in multicast scenarios. [ABSTRACT FROM AUTHOR]

Millimeter-wave (mmWave) networks with the frequency spectrum ranging from 30 GHz (with wavelength 10 mm) to 300 GHz (with wavelength 1 mm), can support massive wireless data in fifth-generation (5G) systems. Importantly, large colocated antenna elements can be exploited at the base station (BS) to facilitate beam-steering synthesis along the users' directions. This paper proposes the Butler matrix (BM) frequency diverse retrodirective array (BM-FDRA) beamforming network at the BS for multiuser communications in mmWave networks. We utilize the orthogonal feature of the M × M BM with M elements of the FDRA to create directional beams for concurrent transmission towards different users in range-angle locations. The proposed scheme has the following merits: (a) there is beam-steering orthogonality without beam interferences and (b) there is automatic tracking functionality, i.e., the prior knowledge on the user location is not required by the proposed BM-FDRA at the BS. The proposed method can serve multiple users concurrently using the beam-steering orthogonality property. Furthermore, performance metrics such as the multiaccess secrecy sum rate (SSR) model, bit error rate (BER), system capacity, and energy efficiency are examined. The proposed BM-FDRA scheme achievements are highlighted via simulation results. [ABSTRACT FROM AUTHOR]

In this letter, we present an analytical method to design a range-angle-dependent beampattern using frequency diverse array (FDA) with null depth control (NDC) for joint radar and communication applications. A slow time-dependent nonuniform frequency offset is used to lock the phase of transmitted signal at a specific time instant to achieve the objective. Moreover, we introduce range-angle-dependent NDC for the joint radar and communication functionalities. That is, we design two transmit beamspace matrices for the subaperturing FDA to generate a similar main lobe toward the target for radar functionality but distinct null depth levels for communication purpose, so that the transmitted information can be efficiently detected by the intended communication receiver. The performance of the proposed design is evaluated using the bit error rate for communication and using the signal-to-interference-plus-noise ratio for radar. [ABSTRACT FROM AUTHOR]

Quadrature spatial modulation (QSM) using frequency modulated diverse retrospective array (FMD-RDA) is put forward to achieve green transmission paradigm shift from phased-array-based arrangement. Up to date, the QSM techniques have employed phased-array, but only angular focusing direction is possible without range focusing direction. On the other hand, millimeter-wave (mmWave) scheme is suggested as an alternative approach for fifth-generation because of large bandwidth spectrum. Therefore, this paper studies green secure communication range-angle focusing QSM FMD-RDA in mmWave wireless communication. In FMD-RDA, a small frequency increment is included across the RDA elements to decouple range-angle focusing. More importantly, an attractive advantage of using FMD-RDA is the automatic self tracking feature which alleviate transmitter/receiver's channel state information (CSI) requirement. To ensure secure transmission, we exploit physical layer security to degrade the channel quality of the eavesdropper. Furthermore, low complexity greedy detector is devised to retrieved the information bits at the receiver. We also derived pair-wise error probability, and analyze secrecy sum rate and energy transfer capability. The reported simulation results demonstrate that the proposed scheme is effective in improving the spectral efficiency with low complexity and no CSI requirement. [ABSTRACT FROM AUTHOR]

With the massive growth of wireless data in mobile broadband communications, millimeter-wave (mm-wave) communication is an alternative enabling technique for fifth generation (5G) wireless communication systems. More importantly, mm-wave offers large frequency spectrum bands ranging from 30GHz to 300GHz that can be utilized to provide very high capacity (i.e., multigigabits per-second data rates). Moreover, because of the small wavelength at mm-wave frequencies, we can exploit large antenna elements in a small physical area, meaning beamforming schemes are feasible. Nevertheless, high directional antennas should be used due to overcoming the severe path loss and absorption in mm-wave frequencies. Further, the antennas should be steerable in angle and range directions to support point-to-point (multipoint) communications. So far, mm-wave communication has utilized phased-array antennas arrangement which is solely angle dependent. This review paper presents recent array technology, namely, frequency modulated frequency diverse array (FDA) for mm-wave communication applications with an emphasis on beamforming. In FDA, small frequency increment is added across the elements. In doing so, an array beam is generated which is angle-range-time dependent without the need of phase shifters. This feature has several promising potentials in mm-wave communications. In this review, the object is to bring to the fore this advance FDA technology to mm-wave communications community to call for more investigations. We review FDA research progress up to date and highlight the potential applications in mm-wave communications. [ABSTRACT FROM AUTHOR]

Dual-function radar-communication (DFRC) system has evolved as a solution for frequency-spectrum congestion in recent years. In this letter, we propose a DFRC strategy by employing the concept of sidelobe manipulation. Specifically, we exploit the beam orthogonality associated with $N \times N$ Butler matrix (BM) connected with an $N$ -element frequency diverse array. The proposed scheme utilizes BM parallel excited by radar signals while communication signal is injected into the system alongside the radar signal. In doing so, the communication signal is projected along the null radiation direction of the radar main beam concurrently. Furthermore, because of the beam orthogonality feature of the BM, there is no cross-interference between the communication signal and radar target detection. Numerical examples are provided for performance evaluations and to demonstrate the effectiveness of the proposed system. [ABSTRACT FROM AUTHOR]

An evolution of antenna selection scheme, namely spatial modulation (SM) using phased-array for wireless communications has received much attention, because the spatial index of each phased-array element can be exploited as an additional source for information transmission. However, only angle-dependent SM can be achieved for phased-array. This means that SM in range-dimension cannot achieve in the SM literature. In this paper, we propose both angle- and range-dependent SM using frequency diverse array antenna for orthogonal frequency division multiplexing (OFDM) wireless communications. The proposed scheme can operate in twofold: One is that only one array element is chosen for transmission at each instant, and the other one uses multiple array elements to transmit simultaneously, which enhances the spectral efficiency. In the receiver, an optimal detector is adopted to jointly estimate the transmitted information symbols and the index of the transmitting elements. Specifically, if the array elements simultaneously transmit at slightly distinct carrier frequencies, their coherent summation will give rise to both angle- and range-dependent receiving signal, which provides a possibility to recover the transmitted information. Simulation results show that the proposed approach achieves better averaged bit error probability and system capability than phased-array SM schemes for OFDM wireless communications. [ABSTRACT FROM AUTHOR]

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 Earth's 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. [ABSTRACT FROM AUTHOR]

In this letter, we explore time-modulated frequency diverse multiple-input–multiple-output (TMFD-MIMO) array for integrated radar and communications, where the communication information bits are embedded via spread sequence technique during each radar pulse. Orthogonal waveforms are adopted in the TMFD-MIMO array for radar functionality, and a switching time-modulation scheme is applied according to the information bits, i.e., binary phase-shift keying (BPSK) associated spreading sequences. Thus, the number of embedded information bits during each radar pulse equals the number of spread sequences. In doing so, the communication receiver interprets the bits associated with a particular waveform as binary information with prior knowledge of the spread sequences. When compared with existing radar-communications, the achievable data rate is then proportionally increased with the pulse repetition frequency, spreading sequence, and size of the BPSK constellation. Moreover, satisfactory probability of target resolution and signal-to-interference-plus-noise ratio for radar functionality and symbol error rate for communication functionality are achieved. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this study, the authors propose a time‐modulated frequency diverse array (FDA) by combining time‐modulated array (TMA) and FDA for physical‐layer security. The proposed scheme has two‐folds: first, the information codes are specifically designed for the FDA elements switching alternatively, which produces a specified directional pattern projecting the phase‐modulation signal as a constellation in the desired range–angle section while distorting in other areas. Second, a switching scheme is adapted for the TMA according to the spreading sequence associated with the transmitted signal and the desired receiver position. In such a fashion, only the receiver located at the pre‐specified range–angle position can demodulate the received signal successfully but the distorted signals radiated to other undesired range–angle positions will be difficult to demodulate by the eavesdroppers even if with the knowledge of the spread sequence. Numerical results show that, due to the range–angle‐dependent characteristics, the proposed method offers more secure transmission performance and outperforms the traditional phased‐array‐based directional modulation method. [ABSTRACT FROM AUTHOR]