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In this paper, we investigate the problem of joint direction of departure (DoD) and direction of arrival (DoA) estimation with bistatic MIMO radar. Specifically, a weaved co-prime array (WCA) bistatic MIMO (WCA-bMIMO) radar is proposed to produce a hole-free sum-difference co-array, which enables to offer significantly increased degrees of freedom (DoFs) and enlarged array aperture. Moreover, the two-dimensional spatial smoothing method is introduced to construct a smoothed received signal, which helps to tackle the rank deduction problem rooted in the equivalent one-snapshot received signal from the sum-difference co-array. Subsequently, the joint DoD and DoA estimates can be obtained by extracting the three-way tensor model. Furthermore, co-array Cramer-Rao Bound (CRB) for the bistatic co-prime MIMO radar is provided. Finally, the superiorities of the proposed bistatic co-prime MIMO radar in accuracy and resolution are proved by numerical simulation results. [ABSTRACT FROM AUTHOR]

Hybrid antenna array consisting of analog subarrays provides a low-cost solution to achieving high beamforming gain in millimeter-wave/terahertz communication systems. For beam adjustment, beam scanning can be readily applied to find the line-of-sight (LoS) path. Conventionally, the beam scanning process is inefficient because the number of grids, together with the scanning period, has to be large to achieve high resolution. To improve the beam scanning efficiency, in this paper we propose an off-gird direction-of-arrival (DoA) estimation method utilizing unequal-sized subarrays. Specifically, we first provide a new solution to overcome the ambiguity problem, i.e., the hybrid antenna array may render the DoA estimate non-unique. That new solution is formed by designing the antenna numbers in the subarrays and can be easily combined with the beam scanning process. We then propose a three-stage beam scanning strategy. At the first stage, coarse scanning is applied to roughly steer the subarrays along the LoS path. At the second stage, a simple DoA estimator is employed to obtain the candidate DoAs. Finally, beam scanning is performed again on the candidate DoAs to obtain the final DoA estimate. Simulation results demonstrate that the proposed method can achieve higher DoA estimation accuracy in shorter scanning period than the conventional beam scanning method; and compared with existing methods developed for equal-sized subarrays, the proposed method is more robust against multi-path interference. [ABSTRACT FROM AUTHOR]

In the scope of vehicular communication networks, the nature of exchanged safety/warning messages renders itself highly location dependent, as it is usually for incident reporting. Vehicles are required to periodically exchange beacon messages that include speed, time, and GPS location information. Reported position information must be accurate and authentic. To mitigate the potential risk of location spoofing/falsifying attack, this paper presents Angle-of-Arrival (AoA) estimation as a physical layer authentication scheme for cross verification of the reported location information. We consider a multi-antenna road side unit under location spoofing attack. Within the considered vehicular communication settings, fundamental limits of AoA estimation are developed in terms of its Cramer–Rao Bound and existence of efficient estimator. The problem of deciding whether the received signal originated from the claimed GPS location is formulated as a two-sided hypotheses testing problem whose solution is given by Wald test statics. We give correct decision $P_D$ and false alarm $P_F$ probabilities in a closed form. To offset the gap between information theoretical studies and practical implementations of physical layer security architectures, theoretical results presented in this paper are further supported by detailed hardware implantation using software-defined radios and field experimental results. We show that the keystone for obtaining reliable AoA measurements is the accurate characterization of the array response vector. Our hardware measurements showed that, unlike idealized models, hardware imperfections leave the actual array response vector of non-structured form. To address this problem, we introduce the method for obtaining the actual array response vector empirically, which led to accurate and stable AoA measurements. Field experimental results shows the feasibility of the proposed AoA authentication scheme. [ABSTRACT FROM AUTHOR]

The performance of the source enumeration with the uniform circular array (UCA) is deteriorated considerably by the colored noise. This effect becomes more obvious especially when the total number of the sources is lower and closed to that of the array sensors. To address this problem, this paper proposes a source enumeration modeling based on a UCA having M antennas (M-UCA). The M-UCA is operated in a narrow band far field environment with the arbitrary azimuth and elevation angles. First, the Hilbert Huang transformation is employed to derive the phase sequence of each selected intrinsic mode function (IMF) of the signal acquired by each antenna of the M-UCA. Then, the phase sequences of the selected IMFs of the signal acquired by all the antennas of the M-UCA are employed to construct an instantaneous phase covariance matrix (IPCM) among the antennas in the UCA. An IPCM is constructed for each order of the selected IMFs. After performing the eigenvalue decomposition of the all IPCMs, a set of eigenvalues carrying useful information for the estimation of the total number of the sources is acquired. This set is served as the training set. Finally, the training set is used to derive the mathematical model via the support vector machine. The trained model can be used to perform the sources number detection. Both the computer numerical simulations and the radio frequency anechoic chamber experiments validate that the source estimation accuracy of the constructed M-UCA mathematical model based on our proposed method has a high robustness to the incident angles variations, the SNR variations, and the snapshot number variations in the colored noise environment in the determined case, especially in the case of that the total number of the signal sources is only one less than the number of the antennas in the UCA. [ABSTRACT FROM AUTHOR]

Impulsive noise (IN) is one of the crucial affecting factors of in-vehicle power line communication (PLC) systems, and therefore an effective IN mitigation scheme is required to enhance the performance significantly. Narrowband interference (NBI) from various nearby radios often has great impact on the IN reconstruction and mitigation. In this paper, IN mitigation over uncoded orthogonal frequency division multiplexing (OFDM) PLC systems is investigated considering the impact of NBI. A null subcarriers assisted IN mitigation scheme is proposed to mitigate IN in the scenarios of NBI absence and NBI presence. The IN vector is reconstructed at the proposed receiver first, and then canceled out from the received signal. Theoretical analysis shows that the proposed scheme outperforms the blanking method. Also, the implementation of pre-joint NBI/IN mitigation with the aid of null subcarriers in the proposed scheme can combat the impact of intensive NBI, and achieve a near-optimal bit error rate performance with no iterations. The effectiveness of the proposed mitigation scheme is validated by simulation results, which is applicable to the vehicular environments under the disturbance of joint IN and NBI. [ABSTRACT FROM AUTHOR]

To ensure link reliability and signal receiving quality, robust adaptive beamforming (RAB) is vital important in mobile communications. In this paper, we propose a new RAB algorithm based on interference-plus-noise covariance (INC) matrix reconstruction and steering vector (SV) estimation. In this method, the INC matrix is reconstructed by estimating all interferences SVs and powers, as well as the noise power. The interference SVs are estimated by using the Capon spatial spectrum together with robust Capon beamforming principle, subsequently the interference powers are estimated based on the orthogonality between different signal SVs. On the other hand, the desired signal SV is estimated via maximizing the beamformer output power by solving a quadratic convex optimization problem. The proposed algorithm only needs to know in advance the array geometry and angular sector, in which the desired signal lies. Simulation results indicate that the proposed algorithm outperforms the existing RAB techniques in terms of the overall performance in cases of various mismatches. [ABSTRACT FROM AUTHOR]

This paper proposes an efficient anti-collision algorithm to improve the read performance of the EPCglobal ultra-high frequency (UHF) Class-1 Generation-2 radio-frequency identification (RFID) standard. Optimal frame length is one of the most important parameters to be adjusted in RFID anti-collision algorithms. Hence, we first derive the optimal frame length by analyzing the maximum of normalized throughput and by taking into account the unequal time intervals of successful, collision, and empty slots. We find that the optimal frame length should be set to 1.89 times of the number of tags when the ratio between collision-slot duration and empty-slot duration is 5. The proposed anti-collision algorithm is based on the mechanism of early adjustment of frame length and examines the fitness of frame length only at an optimal time slot in each read round. The primary advantage of our algorithm is the ability to achieve a good compromise between computation complexity and throughput performance. The results show that the proposed method provides up to 400 tags/s read speed and can obtain 5%–10% time-saving efficiency, as compared with typical dynamic framed-slotted ALOHA. [ABSTRACT FROM AUTHOR]

Recently, wideband orthogonal frequency-division multiplexing (OFDM)-based systems such as Long-Term Evolution (LTE) have been proposed for future railway communication systems. In such high-speed situations, Doppler phenomena, related to the terminal's high speed, affects the use of OFDM systems by producing a loss of orthogonality between different carriers. Thus, the channel estimation and equalization become a challenging problem, particularly when the number of pilot carriers is limited. This paper investigates the use of time-domain channel estimation for OFDM systems in high-speed scenarios and for a sparse pilot distribution. A time-domain linear minimum mean square error (TD-LMMSE) filter is designed for channel estimation. The TD-LMMSE emulates the effect of a sliding window and takes into consideration the interference caused by the data field. The expression of the MSE of linear estimators is also developed. Furthermore, a simple technique for the estimation of the second-order channel statistics is proposed. Simulation results, showing a significant gain in terms of MSE and bit error rate, compared with other state-of-the-art algorithms, are reported over a wide signal-to-noise ratio (SNR) range. [ABSTRACT FROM PUBLISHER]

A mobile relay station (MRS) with soft handover experiences performance degradation because the received signal at the MRS located between two base stations (BSs) is the sum of these two signals with different carrier frequency offsets (CFOs). In this paper, two receive beamforming techniques with CFO compensation (a joint receive beamforming (JB) technique and a spatially separated receive beamforming (SB) technique) are proposed for the MRS with a uniform linear array (ULA) in orthogonal frequency-division multiplexing (OFDM) systems. The SB technique is shown to be robust against CFO errors and can be effectively used for the MRS in a multipath fading channel. The performance of the proposed techniques is evaluated via simulation in a Long Term Evolution (LTE) environment. [ABSTRACT FROM PUBLISHER]