Aboulnasr Hassanien

Dual-Function Radar-Communications: Information Embedding Using Sidelobe Control and Waveform Diversity

We develop a new technique for a dual-function system with joint radar and communication platforms. Sidelobe control of the transmit beamforming in tandem with waveform diversity enables communication links using the same pulse radar spectrum. Multiple simultaneously transmitted orthogonal waveforms are used for embedding a sequence of LB bits during each radar pulse. Two weight vectors are designed to achieve two transmit spatial power distribution patterns, which have the same main radar beam, but differ in sidelobe levels towards the intended communication receivers. The receiver interpretation of the bit is based on its radiated beam. The proposed technique allows information delivery to single or multiple communication directions outside the mainlobe of the radar. It is shown that the communication process is inherently secure against intercept from directions other than the pre-assigned communication directions. The employed waveform diversity scheme supports a multiple-input multiple-output radar operation mode. The performance of the proposed technique is investigated in terms of the bit error rate.

A dual function radar-communications system using sidelobe control and waveform diversity

In this paper, we develop a new technique for dual-function radar-communications in a transmit multi-sensor array where information embedding is achieved using sidelobe control in tandem with waveform diversity. A set of Q orthogonal waveforms is exploited to embed a sequence of Q bits during each radar pulse. All waveforms are transmitted simultaneously where one bit is embedded in each waveform. We design two transmit weight vectors to achieve two distinct transmit power distribution patterns which share the same main radar beam but have different sidelobe levels towards the communication direction. The receiver interprets the bit associated with a certain waveform as binary information based on whether that waveform is radiated over the transmit beam associated with the first or the second weight vector. The proposed technique enables information delivering to a single or multiple communication directions located outside the mainlobe of the radar. The communication message has low probability of intercept from directions other than the preassigned communication directions. Additionally, the waveform diversity enables the radar to operate in multiple-input multiple-output (MIMO) mode. The performance of the proposed technique is investigated in terms of the bit error rate (BER).

Signaling strategies for dual-function radar communications: an overview

The last decade witnessed a growing demand on radio frequency that is driven by technological advances benefiting the end consumer but requiring new allocations of frequency bandwidths. Further, higher data rates for faster communications and wireless connections have called for an expanded share of existing frequency allocations. Concerns for spectrum congestion and frequency unavailability have spurred extensive research efforts on spectrum management and efficiency within the same type of service and have led to cognitive radio and cognitive radar. On the other hand, devising schemes for coexistence among different services have eased the competition for spectrum resources, especially for radar and wireless communication systems. Both systems have been recently given a common portion of the spectrum by the Federal Communications Commission.

Transmit Radiation Pattern Invariance in MIMO Radar With Application to DOA Estimation

The desired property of having the same beampattern for different columns of a beamspace transformation matrix (beamforming vectors) often plays a key importance in practical applications. At most 2M - 1 - 1 beamforming vectors with the same beampattern can be generated from any given beamforming vector, where M is the size of the beamforming vector. Thus, one can start with a single (mother) beamforming vector, which gives a desired beampattern, but may not satisfy some other desired properties, and generate all other beamforming vectors, which give the same beampattern, in a computationally efficient way. Then the beamforming vectors, which in addition satisfy other desired properties that the mother beamforming vector may not satisfy, can be selected. Such procedure is developed in this letter in the application to the transmit beamspace design that ensures practically important properties for multiple-input multiple-output radar. A computationally efficient sub-optimal method for selecting best beamforming vectors from a population of vectors that give the same beampattern is also developed.

Dual-function radar-communications using phase-rotational invariance

In this paper, we develop a new technique for dual-function radar-communications in a transmit multi-sensor array where information embedding is achieved using phase-rotational invariance. A sequence of Q bits is first mapped into a dictionary of 2Q phase rotations. Then, one pair of transmit orthogonal waveforms is used in tandem with 2Q pairs of transmit beamforming weight vectors for embedding a certain entry of the phase-rotation dictionary during each radar pulse. The same pair of waveforms is used during all pulses while the pair of transmit beamforming weight vectors changes from pulse to pulse based on which entry of the phase-rotation dictionary is embedded. During each pulse, the receiver detects the embedded phase rotation and employ it to decipher the transmitted bit sequence. The proposed information embedding technique is angle-dependant and, therefore, the communication process is inherently secure against interception from directions other than the desired communication direction. The performance of the proposed technique is investigated in terms of the bit error rate (BER).

Towards a dual-function MIMO radar-communication system

Recently, dual-function radar-communication systems in which the radar platform and resources are used for communication signal embedding have emerged as means to alleviate spectrum congestion and ease competition over frequency bandwidth. In this paper, we introduce a new technique for information embedding specific to multiple-input multiple output (MIMO) radar. We exploit the fact that in a MIMO radar system, the receiver needs to know the association of the transmit waveforms to the transmit antennas. However, this association can change over different pulse repetition periods without impacting the radar functionality. We show that by shuffling the waveforms across the transmit antennas over constant pulse repetition periods, a data rate of megabits per second can be achieved for a moderate number of transmit antennas. The probability of error is analyzed and the bounds on the symbol error rate are derived. Simulation examples are provided for performance evaluation and to demonstrate the effectiveness of the proposed information embedding technique.

Non-coherent PSK-based dual-function radar-communication systems

Dual-function radar-communication (DFRC) systems enable information embedding into the radar signal emission. Existing methods for non-coherent phase-modulation DFRC employ multiple pairs of orthogonal waveforms and embed one communication symbol into each pair. The total number of symbols is equal to one-half of the number of waveforms. In this paper, we propose a new signaling strategy for embedding a higher number of communication symbols. The proposed method implements non-coherent phase-shift keying (PSK) by employing one of the orthogonal waveforms as a common reference and modulating the information in terms of the phase differences between all other waveforms and the reference waveform. The number of communication symbols that can be embedded equals the total number of waveforms minus one. We introduce two schemes for achieving a desired phase constellation. The proposed approach is shown to achieve a two-fold increase in the data rate compared to existing methods for a large number of waveforms.

Capon-based single-snapshot DOA estimation in monostatic MIMO radar

We consider the problem of single snapshot direction-of-arrival (DOA) estimation of multiple targets in monostatic multiple-input multiple-output (MIMO) radar. When only a single snapshot is used, the sample covariance matrix of the data becomes non-invertible and, therefore, does not permit application of Capon-based DOA estimation techniques. On the other hand, low-resolution techniques, such as the conventional beamformer, suffer from biased estimation and fail to resolve closely spaced sources. In this paper, we propose a new Capon-based method for DOA estimation in MIMO radar using a single radar pulse. Assuming that the angular locations of the sources are known a priori to be located within a certain spatial sector, we employ multiple transmit beams to focus the transmit energy of multiple orthogonal waveforms within the desired sector. The transmit weight vectors are carefully designed such that they have the same transmit power distribution pattern. As compared to the standard MIMO radar, the proposed approach enables transmitting an arbitrary number of orthogonal waveforms. By using matched-filtering at the receiver, the data associated with each beam is extracted yielding a virtual data snapshot. The total number of virtual snapshots is equal to the number of transmit beams. By choosing the number of transmit beams to be larger than the number of receive elements, it becomes possible to form a full-rank sample covariance matrix. The Capon beamformer is then applied to estimate the DOAs of the targets of interest. The proposed method is shown to have improved DOA estimation performance as compared to conventional single-snapshot DOA estimation methods.

Computationally efficient beampattern synthesis for dual-function radar-communications

The essence of amplitude-modulation based dual-function radar-communications is to modulate the sidelobe of the transmit beampattern while keeping the main beam, where the radar function takes place, unchanged during the entire processing interval. The number of distinct sidelobe levels (SLL) required for information embedding grows exponentially with the number of bits being embedded. We propose a simple and computationally cheap method for transmit beampattern synthesis which requires designing and storing only two beamforming weight vectors. The proposed method first designs a principal transmit beamforming weight vector based on the requirements dictated by the radar function of the DFRC system. Then, a second weight vectors is obtained by enforcing a deep null towards the intended communication directions. Additional SLLs can be realized by simply taking weighted linear combinations of the two available weight vectors. The effectiveness of the proposed method for beampattern synthesis is verified using simulations examples.

A dual-function MIMO radar-communications system using PSK modulation

In this paper, we develop a new technique for information embedding into the emission of multiple-input multiple-output (MIMO) radar using dual-functionality platforms. A set of orthogonal waveforms occupying the same band is used to implement the primary MIMO radar operation. The secondary communication function is implemented by embedding one phase-shift keying (PSK) communication symbol in each orthogonal waveform, i.e., the number of embedded communication symbols during each radar pulse equals the number of transmit antennas. We show that the communication operation is transparent to the MIMO radar operation. The communication receiver detects the embedded PSK symbols using standard ratio testing. The achievable data rate is proportional to the pulse repetition frequency, the number of transmit elements, and the size of the PSK constellation. The performance of the proposed technique is investigated in terms of the symbol error rate. Simulations examples demonstrate that data rates in the range of several Mbps can be embedded and reliably detected.