Following successful adoption of cloud computing, many service providers (SPs) are now using high-performance Virtual Machines (VMs) located in large datacenters owned by public cloud infrastructure providers to deploy their virtual network functions (VNFs). Since using these VMs has a cost depending on utilization time, a complex problem of VNF placement and scheduling (VPS) must be addressed to achieve satisfactory network performance (e.g., latency) while minimizing the cost paid to lease VMs. In this study, a cost-efficient VPS scheme (CEVPS) is proposed to address the VPS problem in public cloud networks considering dynamic requests of ordered sequences of VNFs. Our CE-VPS scheme goes beyond existing solutions as it models some important practical aspects such as an additional latency incurred by booting a VM and installing a VNF instance. Also, CE-VPS considers that VNFs can be multi-threaded or single-threaded, and that their throughput as a function of allocated computing resources must be modeled differently. CEVPS is formulated as a mixed inter linear program (MILP) and also as an efficient heuristic algorithm. CE-VPS achieves lower cost and latency than conventional Best-Availability and Cost- Efficient Proactive VNF Placement schemes, and a better tradeoff between resource consumption and latency performance than a conventional Low-Latency scheme.

Na-, K- and Mg-ion batteries (NIBs, KIBs and MIBs) have drawn considerable interest due to their high abundance and excellent safety. However, the lack of high-performance anode materials is a major obstacle to its development. A metallic SnB planar monolayer is predicted by using the two-dimensional global minimum structure search method of swarm intelligence. Based on first-principles calculations, we proved that the metal SnB monolayer has high binding energy and excellent dynamical, thermal and mechanical stability. It is worth noting that the SnB monolayer has several stable adsorption sites for Na-, K- and Mg-ions, so it has a high theoretical capacity of 620.93, 517.44 and 620.93 mA h g⁻¹, respectively. For Na-, K- and Mg-ion batteries, the low diffusion barriers of the SnB monolayer are 0.22, 0.07 and 0.68 eV, and the low average open circuit voltages are 0.42, 0.49 and 0.23 V, which ensure long service life and fast charging in practical applications. In addition, it is proved that the SnB monolayer maintains excellent conductivity and stability during the charge–discharge process. The results show that the SnB monolayer offers innovative advantages for the development of new two-dimensional planar structures that further advance the development of anode materials for metal ion batteries.

Millimeter wave (mmWave) communication is expected to be a key technology for 5G networks, because it can provide high data rates and large available bandwidth. Large antenna array is necessary to be applied to mmWave system to overcome the high path loss. Restricted by power consumption and system complexity, traditional digital precoding cannot be used for mmWave system. Therefore, analog radio frequency signal processing is introduced to simplify the architecture of precoder. In this paper, we propose dominant vector approaching (DVA) searching method for analog precoder design. Assuming that the channel state information is known at both transmitter and receiver sides, we decompose the analog precoding problem into a series of subproblems. For each subproblem, we just need to optimize one column of analog precoding matrix. Then we can apply DVA searching method to solve these subproblems under unit modulus constraint. For the fully-connected structure (FS) and the partially-connected structure (PS), we propose DVA-FS and DVA-PS as our precoding designs, respectively. In addition, we prove that DVA searching method finds the near-optimal solutions for the non-convex subproblems. Through simulation, we show that DVA algorithms achieve near-optimal performance with analog precoder in different scenarios. Besides, we investigate the effect of quantization and the energy efficiency of DVA algorithms, and find that they perform well with rough quantization.

Ultra-wideband impulse radio (UWB-IR) sensors should comply entirely with the regulatory spectral limits for elegant coexistence. Under this premise, it is desirable for UWB pulses to improve frequency utilization to guarantee the transmission reliability. Meanwhile, orthogonal waveform division multiple-access (WDMA) is significant to mitigate mutual interferences in UWB sensor networks. Motivated by the considerations, we suggest in this paper a low complexity pulse forming technique, and its efficient implementation on DSP is investigated. The UWB pulse is derived preliminarily with the objective of minimizing the mean square error (MSE) between designed power spectrum density (PSD) and the emission mask. Subsequently, this pulse is iteratively modified until its PSD completely conforms to spectral constraints. The orthogonal restriction is then analyzed and different algorithms have been presented. Simulation demonstrates that our technique can produce UWB waveforms with frequency utilization far surpassing the other existing signals under arbitrary spectral mask conditions. Compared to other orthogonality design schemes, the designed pulses can maintain mutual orthogonality without any penalty on frequency utilization, and hence, are much superior in a WDMA network, especially with synchronization deviations.

Hybrid precoding has been regarded as a promising technology for millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) systems due to the low hardware cost and power consumption. This paper focuses on digital and analog codebooks design to efficiently quantize the hybrid precoders with arbitrary-resolution analog phase shifters in frequency-division duplex systems. We formulate the codebooks design as a joint optimization problem and propose an iteration algorithm to obtain the enhanced codebooks based on dictionary learning methods. Moreover, this paper shows that the optimal precoders for all data streams exhibit a hidden joint sparsity structure caused by the limited number of scattering clusters with low angular spreads of mmWave MIMO channels. Exploiting the structure, a jointly sparse precoding is proposed as the pursuit method for the proposed codebooks design algorithm. The simulation results demonstrate that the near-optimal performance can be achieved by the joint utilization of the proposed hybrid precoding algorithm and codebooks even when the low-resolution phase shifters are used.