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The existing expectation maximization (EM) and space-alternating generalized EM (SAGE) algorithms are only applied to direction of arrival (DOA) estimation in known noise. In this paper, the two algorithms are designed for DOA estimation in unknown uniform noise. Both the deterministic and random signal models are considered. In addition, a new modified EM (MEM) algorithm applicable to the noise assumption is also proposed. Next, these EM-type algorithms are improved to ensure the stability when the powers of sources are not equal. After being improved, simulation results illustrate that the EM algorithm has similar convergence with the MEM algorithm, the SAGE algorithm outperforms the EM and MEM algorithms for the deterministic signal model, and the SAGE algorithm cannot always outperform the EM and MEM algorithms for the random signal model. Furthermore, simulation results show that processing the same snapshots from the random signal model, the SAGE algorithm for the deterministic signal model can require the fewest computations. [ABSTRACT FROM AUTHOR]

The maximum likelihood (ML) technique plays an important role in direction-of-arrival (DOA) estimation. In this paper, we employ and design the expectation–conditional maximization either (ECME) algorithm, a generalization of the expectation–maximization algorithm, for solving the ML direction finding problem of stochastic sources, which may be correlated, in unknown nonuniform noise. Unlike alternating maximization, the ECME algorithm updates both the source and noise covariance matrix estimates by explicit formulas, and can guarantee that both estimates are positive semi-definite and definite, respectively. Thus, the ECME algorithm is computationally efficient and operationally stable. Simulation results confirm that the ECME algorithm can efficiently obtain the ML based DOA estimate of each stochastic source. [ABSTRACT FROM AUTHOR]

The classic expectation-maximization (EM) algorithm in maximum-likelihood direction finding updates the complete-data sufficient statistics by finding their conditional expectations. Besides, from the perspective of alternating maximization (AM) these sufficient statistics can also be updated by maximizing the complete-data log-likelihood function with respect to only the complete data, based on which both deterministic and stochastic signal models are considered. Theoretical analysis indicates that the proposed AM algorithm is equivalent to the EM algorithm for the deterministic signal model while outperforming the EM algorithm for the stochastic signal model. On this foundation, a sequential AM (SAM) algorithm and two iterative weighting schemes are proposed to improve the convergence of the AM algorithm. Numerical results show that the SAM algorithm yields faster convergence and the two iterative weighting schemes can be used to avoid the convergence of the EM and AM algorithms to an unwanted limit point efficiently. [ABSTRACT FROM AUTHOR]

In this paper, antenna diversity is used to improve the outage performance of downlink non-orthogonal multiple access (NOMA) systems combined with single-user multiple-input multiple-output (SU-MIMO) due to the statistical channel state information (CSI), that the transmitter only knows the statistical characteristic associated with each user's channel matrix. We design the precoding and detection vectors, which makes the proposed MIMO-NOMA system reduce to a single-antenna NOMA system with statistical CSI. Next, a dynamic power allocation scheme is proposed to maximize the ergodic sum rate of the considered NOMA group with the minimum ergodic rate constraints of the weaker users. Under this power allocation, we analyze the impact of user clustering and then develop a novel user clustering algorithm. Also, the outage analysis indicates that the proposed system only obtains receive diversity and under the proposed power allocation, the users’ diversity gains are linear with their successive interference cancellation decoding orders. Simulation results confirm our proposed analysis. [ABSTRACT FROM AUTHOR]

In this letter, antenna diversity is used to improve the outage performance of downlink multiple-input multiple-output non-orthogonal multiple access systems with partial channel state information, of which the transmitter only knows the distance and channel direction information associated with each user. We analyze the ergodic rate and the outage probability of the proposed system. Moreover, we derive the closed-form expression of each user’s outage probability. Numerical results confirm the accuracy of our analysis. [ABSTRACT FROM AUTHOR]

The interaction potential of a He-BH complex is investigated by the coupled-cluster single-double plus perturbative triples (CCSD (T)) method and an augmented correlation consistent polarized valence (aug-cc-pV)5Z basis set extended with a set of (3s3p2d1f1g) midbond functions. Using the five two-dimensional model potentials, the first threedimensional interaction potential energy surface is constructed by interpolating along (r-re) by using a fourth-order polynomial. The cross sections for the rovibrational relaxation of BH in cold and ultracold collisions with 3He atom are calculated based on the three-dimensional potential. The results show that the δv =-1 transition is more efficient than the δv =-2 transition, and that the process of relaxation takes place mainly between rotational energy levels with the same vibration state and the δj =-1 transition is the most efficient. The zero temperature quenching rate coefficient is finite as predicted by Wigner's law. The resonance is found to take place around 0.1-1 cm-1 translational energy, which gives rise to a step in the rate coefficients for temperatures around 0.1-1 K. The final rotational distributions in the state v = 0 resulting from the quenching of state (v = 1, j = 0) at three energies corresponding to the three different regimes are also given. [ABSTRACT FROM AUTHOR]