Passive Multiple-input Multiple-output Research Articles

Passive MIMO Radar Detection with Unknown Colored Gaussian Noise

The target detection of the passive multiple-input multiple-output (MIMO) radar that is comprised of multiple illuminators of opportunity and multiple receivers is investigated in this paper. In the passive MIMO radar, the transmitted signals of illuminators of opportunity are totally unknown, and the received signals are contaminated by the colored Gaussian noise with an unknown covariance matrix. The generalized likelihood ratio test (GLRT) is explored for the passive MIMO radar when the channel coefficients are also unknown, and the closed-form GLRT is derived. Compared with the GLRT with unknown transmitted signals and channel coefficients but a known covariance matrix, the proposed method is applicable for a more practical case whenthe covariance matrix of colored noise is unknown, although it has higher computational complexity. Moreover, the proposed GLRT can achieve similar performance as the GLRT with the known covariance matrix when the number of training samples is large enough. Finally, the effectiveness of the proposed GLRT is verified by several numerical examples.

Passive MIMO radar detection in the presence of clutter or multi‐path without reference channel

Target detection problem in a multiple-input multiple-output (MIMO) radar which includes non-cooperative illuminators of opportunity (IOs) and spatially distributed receivers is discussed. The receivers utilize only one processing channel and discard the difficulties in providing an ideal version of the transmitted waveforms. The signal model, in addition to the receiver noise and the possible echo from the target of interest, considers the direct-path and clutter/multi-path interferences (DPI and MPI). A Rao test and an approximated GLR test detectors are proposed to solve the problem and an innovative recursive algorithm is proposed to simultaneously estimate the nuisance parameters in the test. Then, by regarding some matrix properties in the proposed Rao detector expression, a low complexity version of the Rao detector is proposed. Besides, two detectors based on Rao and GLR principles in the case of active MIMO radar are introduced as the performance upper-bounds for the proposed detectors. The convergence and suitable performance of the proposed detectors are verified by numerical simulations.

Improving Detection Performance of Passive MIMO Radar by Exploiting the Preamble Information of Communications Signal

In passive multiple-input multiple-output (MIMO) radar, the transmit signals of the noncooperative illuminators of opportunity are usually not completely known. They are usually standard communications signals following specific protocols which stipulate the preamble format. In this article, we show that the preamble information can be exploited to improve the performance of passive MIMO radar. We have derived two generalized likelihood ratio tests (GLRTs) for passive MIMO radar detection, one for the case where the noise variance is known, and the other for the case where the noise variance is unknown. Our analysis shows that the derived two GLRTs have constant false alarm rate. Simulation results show that under the same condition the derived GLRTs outperform the GLRTs without using the preamble information. Moreover, the derived GLRTs are also compared with the GLRTs for active MIMO radar that totally knows transmit signals. These comparisons show that the performance of the derived GLRTs vary between the GLRTs for active MIMO radar and those for the passive MIMO radar with the transmit signals completely unknown.

Passive MIMO radar detection exploiting known format of the communication signal observed in colored noise with unknown covariance matrix

In passive multiple input multiple output (MIMO) radar, the transmit signals of the noncooperative illuminators of opportunity are usually not completely known. However, they are often standard communication signals with some specific signal structure. Exploiting such information, the detection performance of passive MIMO radar can be improved. In this paper we derive a generalized likelihood ratio test (GLRT) for passive MIMO radar detection when the covariance matrix of the colored Gaussian noise is unknown and the structure of the transmit signal is known but it contains some unknown information bits. Moreover, a model which employs a reasonable approximation for some practical scenarios while requiring only a limited number of training samples is also considered, and a GLRT for this model is also derived. Our tests are shown to be constant false alarm rate (CFAR), and their performance approaches the optimum performance with known signal structure and known covariance matrix when the number of training samples is increased. Finally, several numerical examples are presented to demonstrate the effectiveness of the proposed method.

Rao Detector for Passive MIMO Radar With Direct-Path Interference

This article deals with the problem of target detection in a passive multiple-input multiple-output (MIMO) radar network involving noncooperative illuminators of opportunity (IOs) and geographically dispersed multichannel receivers. The signal model considers the direct-path interference (DPI). We employ the Rao test to solve the problem and derive a closed-form detector. Then, by considering the properties of the ambiguity functions of most IO waveforms, an approximated version of the detector with a simpler form is derived. Two detectors in the case of an active MIMO network are also provided as the upper bounds of the passive situations. Moreover, considering target echo signal fluctuation, we have analyzed the performance of the detectors in terms of probability of miss-detection when being used in a multistatic configuration and have specified the conditions under which the full diversity gain is achieved. Numerical results verify the effectiveness of the proposed detectors and demonstrate that the proposed detectors have performance very close to the active situation.

Antenna Measurements in Reverberation Chamber Using USRP

This paper shows that a universal software radio peripheral (USRP) can be used to measure the complete passive over-the-air (OTA) performance of multiport antennas for multiple-input multiple-output (MIMO) systems. The passive MIMO OTA measurements are performed in a reverberation chamber using the USRP as a measurement instrument. The total embedded radiation efficiencies, the correlation, and the resulting diversity gain are extracted from transmission measurements only. These are in good agreement with S-parameter measurements (both transmission and reflection) obtained with a vector network analyzer (VNA). The proposed measurement approach involving USRPs provide an economical alternative to these type of measurements as compared to high-end equipment.

Cramér–Rao bounds for L‐band digital aeronautical communication system type 1 based passive multiple‐input multiple‐output radar

In this study, of concern is the achievable estimation accuracy for a non-coherent passive multiple-input multiple-output (MIMO) radar employing orthogonal frequency-division multiplexing (OFDM) based signals of opportunity. The motivation behind this investigation is the surveillance aspect of the air trac management modernisation process currently taking place in civil aviation. To this end, the surveillance capability of the OFDM-based L-band digital aeronautical communication system type 1 (LDACS1) is analysed. The extension of the LDACS1 communication system towards surveillance is of great importance since it would enable an alternative, non-cooperative surveillance application, and, together with the already validated navigation extension, establish a fully integrated LDACS1-based communication, navigation, and surveillance technology. The modied Cramer-Rao bound on the joint estimation of target location and velocity for a non-coherent passive MIMO radar, employing the OFDM-based LDACS1 signals as signals of opportunity, is investigated. The analysis is carried out assuming one target, multiple and widely separated transmit and receive antennas, orthogonal waveforms, independent reection coecients, and zero-mean white Gaussian noise. Closed-form expressions for the relevant elements of the modied Fisher information matrix are obtained. The results can be used to assess the estimation accuracy of a multiple antenna passive radar system employing any OFDM-based signals of opportunity.

Detection in Passive MIMO Radar Networks

This paper addresses target detection in passive multiple-input multiple-output (MIMO) radar networks comprised of non-cooperative transmitters and multichannel receivers. A generalized likelihood ratio test is derived, and approximate test statistic distributions are presented for both hypotheses under common scenario conditions. Analysis and simulation results show that this detector outperforms other passive MIMO radar detectors because it exploits more correlations within the measurement data. This detector is also compared against related detectors for active MIMO radar and passive source localization sensor networks. These comparisons reveal that passive MIMO radar detection performance varies between active MIMO radar and passive source localization detection performance as a function of direct-path signal quality. Therefore, passive MIMO radar unifies active MIMO radar and passive source localization sensor networks in a common theoretical framework.

Centralized Passive MIMO Radar Detection Without Direct-Path Reference Signals

This work addresses the problem of target detection in passive multiple-input multiple-output (MIMO) radar networks without utilization of direct-path reference signals. A generalized likelihood ratio test for this problem is derived, and the distribution of the test statistic is identified under both hypotheses. Equivalence is established between passive MIMO radar networks without references and passive source localization networks. Numerical examples demonstrate important characteristics of the detector, namely, the asymmetric contributions to detection performance from transmitters and receivers, and non-coherent integration gain as a function of signal length. The ambiguity properties of this detector are also investigated, and it is shown that the salient ambiguities can be explained in terms of the time-difference of arrival, frequency-difference of arrival, and angle-of-arrival of the target signals.