Exploiting Amplitude Control in Intelligent Reflecting Surface Aided Wireless Communication with Imperfect CSI

Intelligent reflecting surface (IRS) is a promising new paradigm to achieve high spectral and energy efficiency for future wireless networks by reconfiguring the wireless signal propagation via passive reflection. To reap the potential gains of IRS, channel state information (CSI) is essential, whereas channel estimation errors are inevitable in practice due to limited channel training resources. In this paper, in order to optimize the performance of IRS-aided multiuser systems with imperfect CSI, we propose to jointly design the active transmit precoding at the access point (AP) and passive reflection coefficients of IRS, each consisting of not only the conventional phase shift and also the newly exploited amplitude variation. First, the achievable rate of each user is derived assuming a practical IRS channel estimation method, which shows that the interference due to CSI errors is intricately related to the AP transmit precoders, the channel training power and the IRS reflection coefficients during both channel training and data transmission. Then, for the single-user case, by combining the benefits of the penalty method, Dinkelbach method and block successive upper-bound minimization (BSUM) method, a new penalized Dinkelbach-BSUM algorithm is proposed to optimize the IRS reflection coefficients for maximizing the achievable data transmission rate subjected to CSI errors; while for the multiuser case, a new penalty dual decomposition (PDD)-based algorithm is proposed to maximize the users' weighted sum-rate. Simulation results are presented to validate the effectiveness of our proposed algorithms as compared to benchmark schemes. In particular, useful insights are drawn to characterize the effect of IRS reflection amplitude control (with/without the conventional phase shift) on the system performance under imperfect CSI.Comment: 15 pages, 10 figures, accepted by IEEE Transactions on Communication

4-Bromo­anilinium perchlorate 18-crown-6 clathrate

The reaction of 4-bromo­aniline, 18-crown-6, and perchloric acid in methanol yields the title compound, C6H7BrN+·ClO4 −·C12H24O6, in which the protonated –NH3 + group forms three bifurcated N—H⋯O hydrogen bonds to the O atoms of the crown ether

1-Cyano­methyl-1,4-diazo­niabicyclo­[2.2.2]octane tetra­chloridomanganate(II)

In the crystal structure of the title compound, (C8H15N3)[MnCl4], the Mn atom is coordinated by four chloride ligands in a slightly distorted tetra­hedral geometry. Each [MnCl4]2− anion is connected to the 1-cyano­methyl-1,4-diazo­niabicyclo­[2.2.2]octane dications by N—H⋯Cl hydrogen bonds, forming chains parallel to [001]

4-Methoxy­anilinium chloride

The crystal structure of the title compound, C7H10NO+·Cl−, was synthesized by the reaction of 4-methoxy­aniline and hydro­chloric acid. In the crystal structure, the ions are involved in inter­molecular N—H⋯Cl hydrogen bonds

Triaqua­chlorido(18-crown-6)barium chloride

In the title compound, [BaCl(C12H24O6)(H2O)3]Cl, the BaII atom, the coordinating and free Cl− anions, one coordinating water mol­ecule and two O atoms of an 18-crown-6 mol­ecule lie on a mirror plane. The environment of the ten-coordinate Ba2+ ion is defined by one Cl atom, three water mol­ecules and six O atoms from the macrocyclic ether. The macrocycle adopts a conformation with an approximate D 3d symmetry. In the crystal, O—H⋯Cl hydrogen bonds link the complex cations and Cl− anions into a two-dimensional network parallel to (010). An intra­molecular O—H⋯Cl hydrogen bond is also present

N-(4-Methyl­phen­yl)formamide

In the title compound, C8H9NO, the amide group makes a dihedral of 32.35 (1)° with the benzene ring. In the crystal, pairs of strong N—H⋯O hydrogen bonds link the mol­ecules into inversion dimers. Weak C—H⋯O inter­actions further connect the mol­ecules into chains along the a axis

Robust Transceiver Design for MISO Interference Channel with Energy Harvesting

In this paper, we consider multiuser multiple-input single-output (MISO) interference channel where the received signal is divided into two parts for information decoding and energy harvesting (EH), respectively. The transmit beamforming vectors and receive power splitting (PS) ratios are jointly designed in order to minimize the total transmission power subject to both signal-to-interference-plus-noise ratio (SINR) and EH constraints. Most joint beamforming and power splitting (JBPS) designs assume that perfect channel state information (CSI) is available; however CSI errors are inevitable in practice. To overcome this limitation, we study the robust JBPS design problem assuming a norm-bounded error (NBE) model for the CSI. Three different solution approaches are proposed for the robust JBPS problem, each one leading to a different computational algorithm. Firstly, an efficient semidefinite relaxation (SDR)-based approach is presented to solve the highly non-convex JBPS problem, where the latter can be formulated as a semidefinite programming (SDP) problem. A rank-one recovery method is provided to recover a robust feasible solution to the original problem. Secondly, based on second order cone programming (SOCP) relaxation, we propose a low complexity approach with the aid of a closed-form robust solution recovery method. Thirdly, a new iterative method is also provided which can achieve near-optimal performance when the SDR-based algorithm results in a higher-rank solution. We prove that this iterative algorithm monotonically converges to a Karush-Kuhn-Tucker (KKT) solution of the robust JBPS problem. Finally, simulation results are presented to validate the robustness and efficiency of the proposed algorithms.Comment: 13 pages, 8 figures. arXiv admin note: text overlap with arXiv:1407.0474 by other author

Joint Transceiver Design Algorithms for Multiuser MISO Relay Systems with Energy Harvesting

In this paper, we investigate a multiuser relay system with simultaneous wireless information and power transfer. Assuming that both base station (BS) and relay station (RS) are equipped with multiple antennas, this work studies the joint transceiver design problem for the BS beamforming vectors, the RS amplify-and-forward transformation matrix and the power splitting (PS) ratios at the single-antenna receivers. Firstly, an iterative algorithm based on alternating optimization (AO) and with guaranteed convergence is proposed to successively optimize the transceiver coefficients. Secondly, a novel design scheme based on switched relaying (SR) is proposed that can significantly reduce the computational complexity and overhead of the AO based designs while maintaining a similar performance. In the proposed SR scheme, the RS is equipped with a codebook of permutation matrices. For each permutation matrix, a latent transceiver is designed which consists of BS beamforming vectors, optimally scaled RS permutation matrix and receiver PS ratios. For the given CSI, the optimal transceiver with the lowest total power consumption is selected for transmission. We propose a concave-convex procedure based and subgradient-type iterative algorithms for the non-robust and robust latent transceiver designs. Simulation results are presented to validate the effectiveness of all the proposed algorithms