In this letter, we investigate whether the use of artificial noise (AN) is helpful to enhance the secrecy rate of an intelligent reflecting surface (IRS) assisted wireless communication system. Specifically, an IRS is deployed nearby a single-antenna receiver to assist in the transmission from a multi-antenna transmitter, in the presence of multiple single-antenna eavesdroppers. Aiming to maximize the achievable secrecy rate, a design problem for jointly optimizing transmit beamforming with AN or jamming and IRS reflect beamforming is formulated, which is however difficult to solve due to its non-convexity and coupled variables. We thus propose an efficient algorithm based on alternating optimization to solve the problem sub-optimally. Simulation results show that incorporating AN in transmit beamforming is beneficial under the new setup with IRS reflect beamforming. In particular, it is unveiled that the IRS-aided design without AN even performs worse than the AN-aided design without IRS as the number of eavesdroppers near the IRS increases.
In this paper, we consider simultaneous wireless information and power transfer (SWIPT) in orthogonal frequency division multiple access (OFDMA) systems with the coexistence of information receivers (IRs) and energy receivers (ERs). The IRs are served with best- effort secrecy data and the ERs harvest energy with minimum required harvested power. To enhance physical- layer security and yet satisfy energy harvesting requirements, we introduce a new frequency-domain artificial noise based approach. We study the optimal resource allocation for the weighted sum secrecy rate maximization via transmit power and subcarrier allocation. The considered problem is nonconvex, while we propose an efficient algorithm for solving it based on Lagrange duality method. Simulation results illustrate the effectiveness of the proposed algorithm as compared against other heuristic schemes.
This paper is concerned with dynamic resource allocation in a cellular wireless network with slow fading for support of data traffic having heterogeneous transmission delay requirements. The multiple-input single-output (MISO) fading broadcast channel (BC) is of interest where the base station (BS) employs multiple transmit antennas to realize simultaneous downlink transmission at the same frequency to multiple mobile users each having a single receive antenna. An information-theoretic approach is taken for characterizing capacity limits of the fading MISO-BC under various transmission delay considerations. First, this paper studies transmit optimization at the BS when some users have delay-tolerant ldquopacketrdquo data and the others have delay-sensitive ldquocircuitrdquo data for transmission at the same time. Based on the convex optimization framework, an online resource allocation algorithm is derived that is amenable to efficient cross-layer implementation of both physical (PHY) - layer multi-antenna transmission and media-access-control (MAC) - layer multiuser rate scheduling. Secondly, this paper investigates the fundamental throughput-delay tradeoff for transmission over the fading MISO-BC. By comparing the network throughput under completely relaxed versus strictly zero transmission delay constraint, this paper characterizes the limiting loss in sum capacity due to the vanishing delay tolerance, termed the delay penalty, under some prescribed user fairness for transmit rate allocation.
The user plane is one of the most important issues of LTE (Long Term Evolution) system design. The implementation of the user plane data transmission is directly related to the real-time performance and efficiency of the system. Based on the research of the protocol stack data processing, the software architecture of the user plane and data transmission submodules are designed in this paper. Then the solution of the interface between L1C (L1 Layer Control Plane) and physical layer are put forward and implemented on the hardware platform of BCM (Broadcom). At last, the performance of the whole system tested on the hardware is given, and the results show that the designed architecture and interface can meet the demand of LTE system.
This letter studies a wireless-powered amplify-and-forward relaying system, where an energy-constrained relay node assists the information transmission from the source to the destination using the energy harvested from the source. We propose a novel two-phase protocol for efficient energy transfer and information relaying, in which the relay operates in full-duplex mode with simultaneous energy harvesting and information transmission. Compared with the existing protocols, the proposed design possesses two main advantages: i) it ensures uninterrupted information transmission since no time switching or power splitting is needed at the relay for energy harvesting; ii) it enables the so-called self-energy recycling, i.e., part of the energy (loop energy) that is used for information transmission by the relay can be harvested and reused in addition to the dedicated energy sent by the source. Under the multiple-input single-output (MISO) channel setup, the optimal power allocation and beamforming design at the relay are derived. Numerical results show a significant throughput gain achieved by our proposed design over the existing time switching-based relay protocol.
We consider a two-way relay network, where two source nodes, S1 and S2, exchange information through a cluster of relay nodes. The relay nodes receive the sum signal from S1 and S2 in the first time slot. In the second time slot, each relay node multiplies its received signal by a complex coefficient and retransmits the signal to the two source nodes, which leads to a distributed two-way beamforming system. By applying the principle of analog network coding, each receiver at S1 and S2 cancels the ``self-interference'' in the received signal from the relay cluster and decodes the message. This paper studies the 2-dimensional achievable rate region for such a two-way relay network with distributed beamforming. With different assumptions of channel reciprocity between the source-relay and relay-source channels, the achievable rate region is characterized under two setups. First, with reciprocal channels, we investigate the achievable rate regions when the relay cluster is subject to a sum-power constraint or individual-power constraints. We show that the optimal beamforming vectors obtained from solving the weighted sum inverse-SNR minimization (WSISMin) problems are sufficient to characterize the corresponding achievable rate region. Furthermore, we derive the closed form solutions for those optimal beamforming vectors and consequently propose the partially distributed algorithms to implement the optimal beamforming, where each relay node only needs the local channel information and one global parameter. Second, with the non-reciprocal channels, the achievable rate regions are also characterized for both the sum-power constraint case and the individual-power constraint case. Although no closed-form solutions are available under this setup, we present efficient algorithms to compute the optimal beamforming vectors, which are attained by solving SDP problems after semi-definite relaxation.
We consider the use of energy harvesters, in place of conventional batteries with fixed energy storage, for point-to-point wireless communications. In addition to the challenge of transmitting in a channel with time selective fading, energy harvesters provide a perpetual but unreliable energy source. In this paper, we consider the problem of energy allocation over a finite horizon, taking into account a time varying channel and energy source, so as to maximize the throughput. Two types of side information are assumed to be available: causal side information of the immediate past channel condition and harvested energy, and full side information. We obtain structural results for the optimal energy allocation, via the use of dynamic programming and convex optimization techniques. In particular, if unlimited energy can be stored in the battery with harvested energy, we prove the optimality of a water-filling energy allocation solution with multiple, non-decreasing water levels.
With the construction of HVDC (high voltage direct current) transmission project, the operation personnel have increasingly strong demand. At the same time, due to the requirements of the reliability of the power grid, the new operators need to go through a training to perform their work well. The paper briefly investigates a realization method of UHVDC (ultra high voltage direct current) simulation training system. The training system simulation is based on MATLAB implementation and combined with the already client system meets the demand of training well. Compared with the other methods, the method is based on MATLAB and combines with the XPC real time operating system. It has the good simulation results.
The study of the movement of pollutants through ducts facilitates the assessment and control of ambient air quality problems (AQ). Among other things, understanding the deposition and distribution of particulate matter in elbows is important for practical engineering applications. In this study, the turbulent flow field and particle deposition in a 90° bend is investigated using RANS simulation. The RNG k-ε turbulence model was employed to calculate the airflow flow field and the discrete phase model (DPM) was used to simulate the particle phase motion. Where for the discrete phase, the Discrete Random Wander (DRW) model was considered and the deposition of particles with sizes of 1, 3, 5, 10, 20, and 40 μm in the flow field was investigated separately. Grid-independent validation of the models used in the simulations was performed. The effects of inlet velocity, particle size, and direction of gravity on the flow field and particle deposition in the elbow were considered. The results show that the flow field in the bend is strongly influenced by the above parameters. Among them, the turbulent disturbance in the bend section is the most intense, with high turbulent energy value, and it is also the region with the largest energy loss. The inlet velocity is negatively correlated with the deposition rate, and the particle size is positively correlated with the deposition rate.
This paper proposes a novel antenna architecture called movable antenna (MA) to improve the performance of wireless communication systems. With the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ca</sup> pability of flexibl <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sup> movement, MAs can be deployed at positions with more favorable channel conditions to achieve higher spatial diversity gains. Based on our proposed field-response channel model, we analyze the maximum channel gain achieved by a single receive MA as compared to its fixed-position antenna (FPA) counterpart in both deterministic and stochastic channels. In the deterministic channel case, we show the periodic behavior of the multi-path channel gain in a given spatial field. In the stochastic channels, the expected value and the approximate cumulative distribution function of an upper bound on the maximum channel gain of the MA are derived. Numerical examples validate our analytical results and demonstrate that a single MA can reap considerable performance gains over the conventional FPA systems with/without antenna selection, and even achieve comparable performance to the single-input multiple-output beamforming system.
This letter considers spectrum sharing between a multiuser multiple-input multiple-output (MIMO) wireless energy transfer (WET) system and a coexisting point-to-point MIMO wireless information transmission (WIT) system, where WET generates interference to WIT and degrades its throughput performance. We show that due to the interference, the WIT system suffers from a loss of the degrees of freedom (DoF) proportional to the number of energy beams sent by the energy transmitter (ET), which, in general, needs to be larger than one to optimize the multiuser WET with user fairness consideration. To minimize the DoF loss in WIT, we further propose a new single-beam energy transmission scheme based on the principle of time sharing, where the ET transmits one of the optimal energy beams at each time. This new scheme achieves the same optimal performance for the WET system, and minimizes the impact of its interference to the WIT system.
A scheme of wind-solar complementary power system based on energy storage is proposed in this paper, taking the operating characteristics of wind and photovoltaic power system into consideration. The BUCK circuit, tracking the voltage variation of DC BUS, is adopted in the pre-stage system to drive the conversion of the wind and solar power. Push-pull topology, with a high frequency flux, and H4 full bridge topology structure are employed in the backward-stage system, which accomplished high-gain conversion of electrical energy, realized DC boosting and inverter discharging. This paper fully considers the practical application in the remote region, where the power grid is usually less developed. On the basis of the electrical parameters of the system and the lead-acid battery taking as storage unit, the energy management strategy is designed and analyzed, and a prototype is made successfully. Finally, according to the actual operating conditions, a variety of conditions are simulated, and the electrical performance of the prototype is verified according to the relevant standards of the distributed system.
Intelligent reflecting surface (IRS) can bring significant performance enhancement for wireless communication systems by reconfiguring wireless channels via passive signal reflection. However, such performance improvement generally relies on the knowledge of channel state information (CSI) for IRS-associated links. Prior IRS channel estimation strategies mainly estimate IRS-cascaded channels based on the excessive pilot signals received at the users/base station (BS) with time-varying IRS reflections, which, however, are not compatible with the existing channel training/estimation protocol for cellular networks. To address this issue, we propose in this paper a new channel estimation scheme for IRS-assisted communication systems based on the received signal power measured at the user, which is practically attainable without the need of changing the current protocol. Specifically, due to the lack of signal phase information in power measurements, the autocorrelation matrix of the BS-IRS-user cascaded channel is estimated by solving equivalent matrix-rank-minimization problems. Simulation results are provided to verify the effectiveness of the proposed channel estimation algorithm as well as the IRS passive reflection design based on the estimated channel autocorrelation matrix.
Aiming at the problems of high energy consumption and packet loss rate, long delay and poor fault tolerance of existing information transmission rate control methods, a practical vehicle-based passive vehicle communication information transmission rate control method is proposed. The average relative speed of vehicles and the number of neighbour vehicle nodes are selected as input parameters. The cluster head is selected by using fuzzy logic, and the cluster stability is set to the long duration of the cluster. The effective connection time model of the cluster vehicles' communication link is constructed. Taking the effective connection time model and channel capacity as constraints, the Shannon information concept and the maximum utility function are used to obtain the optimal information transmission rate of the current node. Experimental results show that the proposed method has lower-energy consumption and delay, less packet loss, and better fault-tolerant performance than the current research results.
