The fifth-generation cellular mobile networks are expected to support mission critical ultra-reliable low latency communication (URLLC) services in addition to the enhanced mobile broadband applications. This article first introduces three emerging mission critical applications of URLLC and identifies their requirements on end-to-end latency and reliability. We then investigate the various sources of end-to-end delay of current wireless networks by taking the 4G Long Term Evolution (LTE) as an example. Subsequently, we propose and evaluate several techniques to reduce the end-to-end latency from the perspectives of error control coding, signal processing, and radio resource management. We also briefly discuss other network design approaches with the potential for further latency reduction.There is a general consensus that the future of many industrial control, traffic safety, medical, and internet services depends on wireless connectivity with guaranteed consistent latencies of 1ms or less and exceedingly stringent reliability of BLERs as low as 10 -9 [3]. While the projected enormous capacity growth is achievable through conventional methods of moving to higher parts of the radio spectrum and network densifications, significant reductions in latency, while guaranteeing an ultra-high reliability, will involve a departure from the underlying theoretical principles of wireless communications. II. Emerging URLLC ApplicationsIn this section, we briefly introduce three emerging mission-critical applications, including telesurgery, intelligent transportation, and industry automation, whose latency and reliability requirements will be identified. Other possible applications of URLLC include Tactile Internet, augmented/virtual reality, fault detection, frequency and voltage control in smart grids, which are not elaborated here due to space limitation. A. Tele-surgeryThe application of URLLC in tele-surgery has two main use cases [4]: (1) remote surgical consultations, and (2) remote surgery. The remote surgical consultations can occur during complex life-saving procedures after serious accidents with patients having health emergency that cannot wait to be transported to a hospital. In such cases, first-responders at an accident venue may need to connect to surgeons in hospital to get advice and guidance to conduct complex medical operations. On the other hand, in a remote surgery scenario, the entire treatment procedure of patients is executed by a surgeon at a remote site, where hands are replaced by robotic arms. In these two use cases, the communication networks should be able to

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Surface deformation behavior of beta solution treated and overaged Ti-6Al-4V during laser shock processingIn laser forming, phase transformations in the heat-affected zone take place under steep thermal cycles, and have a significant effect on the flow behavior of Ti-6Al-4V alloy and the laser-forming process. The flow-stress data of a material are generally provided as only dependent on strain, strain rate, and temperature, while phase transformations are determined by both temperature and temperature history. Therefore, effect of phase transformations on the flow behavior of materials in thermomechanical processing is not given necessary considerations. In the present work, both the ␣ → ␤ transformation during heating and the decomposition of ␤ phase, producing martensite ␣Ј or lamellae ␣ dependent on cooling rate, are numerically investigated. The spatial distribution of volume fractions of phases is obtained by coupling thermal and phase transformation kinetic modeling. Consequently, the flow stress of Ti-6Al-4V alloy is calculated by the rule of mixtures based on the phase ratio and the flow stress of each single phase, which is also a function of temperature, strain, and strain rate. According to the obtained flow-stress data, the laser-forming process of Ti-6Al-4V alloy is modeled by finite element method, and the deformation is predicted. A series of carefully controlled experiments are conducted to validate the theoretically predicted results.

Generalized spatial modulation (GSM) activates nt out of Nt (1 ≤ nt < Nt) available transmit antennas, and information is conveyed through nt modulated symbols as well as the index of the nt activated antennas. GSM strikes an attractive tradeoff between spectrum efficiency and energy efficiency. Linear precoding that exploits channel state information at the transmitter enhances the system error performance. For GSM with nt = 1 (the traditional SM), the existing precoding methods suffer from high computational complexity. On the other hand, GSM precoding for nt ≥ 2 is not thoroughly investigated in the open literature. In this paper, we develop a unified precoding design for GSM systems, which universally works for all nt values. Based on the maximum minimum Euclidean distance criterion, we find that the precoding design can be formulated as a large-scale non-convex quadratically constrained quadratic program (QCQP) problem. Then we transform this challenging problem into a sequence of unconstrained subproblems by leveraging augmented Lagrangian and dual ascent techniques. These subproblems can be solved in an iterative manner efficiently. Numerical results show that the proposed method can substantially improve the system error performance relative to the GSM without precoding, and features extremely fast convergence rate with a very low computational complexity.

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