Orthogonal space-time block codes (OSTBC) from orthogonal designs have both advantages of complex symbol-wise maximum-likelihood (ML) decoding and full diversity. However, their symbol rates are upper bounded by 3/4 for more than two antennas for complex symbols. To increase the symbol rates, they have been generalized to quasi-orthogonal space-time block codes (QOSTBC) in the literature but the diversity order is reduced by half and the complex symbol-wise ML decoding is significantly increased to complex symbol pair-wise (pair of complex symbols) ML decoding. The QOSTBC has been modified by rotating half of the complex symbols for achieving the full diversity while maintaining the complex symbol pair-wise ML decoding. The optimal rotation angles for any signal constellation of any finite symbols located on both square lattices and equal-literal triangular lattices have been found by Su-Xia, where the optimality means the optimal diversity product (or product distance). QOSTBC has also been modified by Yuen-Guan-Tjhung by rotating information symbols in another way such that it has full diversity and in the meantime it has real symbol pair-wise ML decoding (the same complexity as complex symbol-wise decoding) and the optimal rotation angle for square and rectangular QAM constellations has been found. In this paper, we systematically study general linear transformations of information symbols for QOSTBC to have both full diversity and real symbol pair-wise ML decoding. We present the optimal transformation matrices (among all possible linear transformations not necessarily symbol rotations) of information symbols for QOSTBC with real symbol pair-wise ML decoding such that the optimal diversity product is achieved for both general square QAM and general rectangular QAM signal constellations. Furthermore, our newly proposed optimal linear transformations for QOSTBC also work for general QAM constellations in the sense that QOSTBC have full diversity with good diversity product property and real symbol pair-wise ML decoding. Interestingly, the optimal diversity products for square QAM constellations from the optimal linear transformations of information symbols found in this paper coincide with the ones presented by Yuen-Guan-Tjhung by using their optimal rotations. However, the optimal diversity products for (nonsquare) rectangular QAM constellations from the optimal linear transformations of information symbols found in this paper are better than the ones presented by Yuen-Guan-Tjhung by using their optimal rotations. In this paper, we also present the optimal transformations for the co-ordinate interleaved orthogonal designs (CIOD) proposed by Khan-Rajan for rectangular QAM constellations.

For millimeter-wave systems, a low-complexity hybrid precoding method is proposed. Specifically, with the aid of the ordered singular value decomposition of channel matrix, we show that the radio frequency (RF) precoding matrix can be straightforwardly derived based on the right singular vectors (RSVs) of channel matrix by applying the phase angles of entries in the RSVs, and hence, the complicated optimization procedures used to search the near-optimum RF precoding matrix can be avoided. Furthermore, the antenna array response vectors at the transmitter are not required. Simulation results show that the proposed method can achieve the similar performance of that achieved by the fully digital optimum precoding method.

This study investigates the bulk density, sintering behaviour, and microwave dielectric properties of the MgO-2B₂O₃ series ceramics synthesised by solid-state reaction. According to the X-ray diffraction and microstructural analyses, the as-prepared MgO-2B₂O₃ ceramics possess a single-phase structure with a rod-like morphology. The effects of different quantities of H₃BO₃ and BaCu(B₂O₅) (BCB) on the bulk density, sintering behaviour, and microwave dielectric properties of the MgO-2B₂O₃ ceramics were investigated. Accordingly, the optimal sintering temperature was obtained by adding 30 wt% H₃BO₃ and 8 wt% BCB. We also reduced the sintering temperature to 825 °C. Furthermore, the addition of 40 wt% H₃BO₃ and 4 wt% BCB increased the quality factor, permittivity, and temperature coefficient of resonance frequency of MgO-2B₂O₃ to 44,306 GHz (at 15 GHz), 5.1, and −32 ppm/°C, respectively. These properties make MgO-2B₂O₃ a viable low-temperature co-fired ceramic with broad applications in microwave dielectrics.

In this paper we study multiple-input multiple-output (MIMO) systems with a large number of antennas at a base station serving a number of users in a cell. The antennas at the base station are assembled into multiple antenna arrays (MAA), which are well separated to keep independence between the arrays, but in each array antennas are densely installed. The MAA can be viewed as a flexible configuration of multiple antennas to reduce the space for installing the antennas and benefit from beamforming. In order to determine how dense the MAA can be designed, we define an antenna area efficiency, that is the ratio of the achievable rate and the 2D space required by installing the antennas. Then, we analyze the achievable rate of the massive MIMO system with $K$ uplink users and $NM$ antenna elements at the base station placed in $N$ square arrays and each array having $\sqrt{M}\times\sqrt{M}$ antennas densely deployed. Specifically, the analytical uplink sum-rate is first derived. Then, the sum-rate in the low-SNR and high-SNR regimes are respectively studied. A case study is provided to show how dense MAA can be designed in a massive MIMO system. Our analytical and simulations results show that, for $10$ users in low SNR, a single dense antenna array with $11\times 11$ antennas in a square requires only $1/200$ of the area of conventional $100$ independent antennas to achieve the same rate. For $10$ users in high SNR, we find that two $8\times 8$ square arrays can achieve the highest antenna area efficiency in comparison with one $16\times 16$ antenna arrays, four $5\times 5$ antenna arrays and $100$ independent antennas.

In this paper, a multi-cell multiple-input multiple-output (MIMO) uplink system is considered. For uplink transmission, to implement decoding, the base station (BS) generally needs to estimate channels with the aid of training sequences. Obviously, for full frequency reuse systems, training also suffers from inter-cell interference, namely pilot contamination. In this paper, the impact of pilot contamination on the performance of the considered system is studied based on the maximum likelihood (ML) decoder. Specifically, an exact analytical expression of pair-wise error probability (PEP) is derived, and then, a lower bound and an upper bound of PEP are given, to explicitly show the impact of pilot contamination. With the detailed analysis of these bounds, we can discover: (1) pilot contamination can result in error floor, provided that the number of BSs in the considered system is larger than the length of a frame; and (2) if the length of a frame is larger than or equal to the number of BSs, and an appropriate coding scheme is applied, error floor can be removed. Finally, a coding design criterion is proposed. Based on this criterion, it can be shown that the considered system can achieve the same diversity to what can be achieved by a single isolated cell system.

As a strong coupled nonlinear under-actuated system, the balance control of the circular-rail double inverted pendulum system is discussed in this paper. Firstly, the linear quadratic regulator is established based on the mathematical model of the plant which is linearized about the pendulum's upright equilibrium position. In order to obtain the optimal control performance, as well as to avoid repeated adjustment of LQR parameters, artificial bee colony(ABC) algorithm as a new meta-heuristic approach inspired by intelligent foraging behavior of honeybee swarm is introduced for the parameters optimization of Q and R during LQR controller design. The simulation with the circular-rail double inverted pendulum is conducted to demonstrate the effectiveness of the LQR control strategy as well as the ABC optimization algorithm.