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) 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. While compared to 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.

Dual-function radar-communication (DFRC) systems is a promising technology that has been evolved as a solution for frequency spectrum congestion in recent years. In this paper, we propose DFRC strategy by employing the concept of sidelobe manipulation. Specifically, we exploit the beam orthogonality associated with N × N Butler matrix (BM) connected with N element frequency diverse array (FDA). 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, due to 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 efiectiveness of proposed system.

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.

In this paper, we propose a cognitive frequency diverse array multiple input multiple output (FDA-MIMO) design by utilizing channel uncertainty information. Time-variant non-uniform frequency offsets are utilized to decouple FDA range-angle dependent beampattern and a design strategy is proposed to maximize the transmit energy towards the desired range-angle region by steering the beam to match the channel uncertainty for enhanced target detect and tracking performance. To unambiguously estimate target parameters, we divide the FDA elements into multiple fully overlapped subarrays using orthogonal waveforms. Furthermore, we adaptively update the transmit beamspace matrix with two optimization criterions, namely, signal-to-noise ratio maximization and Cramér Rao bound minimization. All proposed approaches are verified by numerical results.

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, phased-array SM only achieves angle-dependent SM. 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 (FDA) 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.