Optimisation of server selection for maximising utility in Erlang-loss systems

This paper undertakes the challenge of server selection problem in Erlang-loss system (ELS). We propose a novel approach to the server selection problem in the ELS taking into account probabilistic modelling to reflect a practical scenario when user arrivals vary over time. The proposed framework is divided into three stages, including i) developing a new method for server selection based on the M/M/n/n queuing model with probabilistic arrivals; ii) combining server allocation results with further research on utility-maximising server selection to optimise system performance; and iii) designing a heuristic approach to efficiently solve the developed optimisation problem. Simulation results show that by using this framework, Internet Service Providers (ISPs) can significantly improve QoS for better revenue with optimal server allocation in their data centre networks

Decomposing definiteness in vietnamese

This paper provides a detailed description of how Vietnamese encodes definiteness in the nominal phrase in the context of the crosslinguistic debate about the existence of lexical articles in classifier languages. We first show that so-called lexical determiners in Vietnamese are not genuine articles in the technical sense. We then scrutinize six different referring expressions in Vietnamese including bare nouns, classifier – nouns, numeral – classifier – nouns, plural – classifier – nouns, focus cái – classifier – nouns while pointing out how Vietnamese differs from other better-studied classifier languages. Based on this thorough investigation, we posit that Vietnamese systematically differentiates six levels of the givenness hierarchy in the sense of Gundel et al. (1993); therefore, Vietnamese contributes to a better understanding of the nature of definiteness and the structure of the nominal phrase

A power-splitting relaying protocol for wireless energy harvesting and information processing in NOMA systems

Non-orthogonal multiple access (NOMA) along with cooperative communications have been recognized as promising candidates for the fifth generation (5G) wireless networks and have attracted many researchers. Every networked device however has its own limited power supply. To this extent, this paper investigates a power-splitting relaying (PSR) protocol for wireless energy harvesting and information processing in the NOMA systems to prolong the lifetime of the energy-constrained relay nodes in wireless networks so as to avail the ambient radio-frequency (RF) signal as well as to simultaneously harvest the energy and process the information. Decode-and-forward relaying is employed at the relay node where the energy from the received RF signal is harvested and exploited to forward the information to the destination. Specifically, the outage probability and ergodic rate of the PSR protocol are derived to realize the impacts of energy harvesting time, energy harvesting efficiency, power splitting ratio, source data rate, and the distance between nodes. It is also shown that an increased energy harvesting efficiency results in an enhanced performance and an outperformance in terms of the energy efficiency is achieved with the employment of the NOMA when compared to the conventional orthogonal multiple access. Numerical results are provided to verify the findings

Optimising energy efficiency of non-orthogonal multiple access for wireless backhaul in heterogeneous cloud radio access network

This paper studies the downlink problem of a cloud-based central station (CCS) to multiple base stations (BSs) in a heterogeneous cellular network sharing the same time and frequency resources. We adopt non-orthogonal multiple access (NOMA) and propose power allocation for the wireless downlink in the heterogeneous cloud radio access network (HCRAN). Taking into account practical channel modelling with power consumptions at BSs of different cell types (e.g. macro-cell, micro-cell, etc.) and backhauling power, we analyse the energy efficiency (EE) of the practical HCRAN utilising NOMA. Simulation results indicate that the proposed NOMA for the HCRAN outperforms the conventional orthogonal frequency division multiple access (OFDMA) scheme in terms of providing higher EE of up to four times. Interestingly, the results reveal a fact that the EE of the NOMA approach is not always an increasing function of the number of BSs but varies as a quasiconcave function. This motivates us to further introduce an optimisation problem to find the optimal number of BSs that maximises the EE of the HCRAN. It is shown that, with a low power supply at the CCS, a double number of micro BSs can be served by HCRAN providing an improved EE of up to 1.6 times compared to the macro BSs and RRHs, while they achieve the same EE performance with high-power CCS

A secure network coding based modify-and-forward scheme for cooperative wireless relay networks

This paper investigates the security at the physical layer of cooperative relay communications. Inspired by the principle of physical-layer network coding (PNC), we propose a new secure relaying scheme, namely secure PNC-based modify-and-forward (SPMF). In the proposed scheme, the relay node linearly combines the decoded data from the source node with an encrypted key before conveying the mixed data to the destination node. As both the linear PNC operation and encrypted key at the relay are unknown to the eavesdropper, the SPMF scheme provides a double security level in the system. Particularly, taking into account the practical scenario of the imperfect knowledge shared between the relay and destination, the secrecy outage probability (SOP) of the proposed SPMF scheme is analysed and evaluated in comparison with modify-and-forward, cooperative jamming, decode-and-forward and direct transmission schemes. The proposed scheme is shown to achieve a performance improvement of up to 3 dB when compared to the conventional schemes under imperfect knowledge of shared information between the nodes

On the performance of NOMA in SWIPT systems with power-splitting relaying

This paper presents a decode-and-forward (DF) relaying protocol, namely power-splitting relaying (PSR), employed at relay nodes in NOMA technique. The PSR is considered for simultaneous wireless information and power transfer (SWIPT) systems. The relaying node is both energy harvesting from the received radio frequency (RF) signal and information forwarding to the destination. The outage performance and ergodic rate of the PSR are analyzed to realize the impacts of energy harvesting time, energy harvesting efficiency, power splitting ratio, source data rate, and the distance between the source and relay nodes. The simulation results show that NOMA schemes have the lower outage probability compared to the that of the conventional orthogonal multiple access (OMA) schemes at the destination node. Numerical results are provided to verify the findings

Mechanical Attributes of Fractal Dragons

Fractals are ubiquitous natural emergences that have gained increased attention in engineering applications, thanks to recent technological advancements enabling the fabrication of structures spanning across many spatial scales. We show how the geometries of fractals can be exploited to determine their important mechanical properties, such as the first and second moments, which physically correspond to the center of mass and the moment of inertia, using a family of complex fractals known as the dragons