Joint optimization of Age of Information and Energy Efficiency in IoT Networks

Age of information (AoI) refers to the freshness of data generated by a status-update system. It is a crucial metric in networks such as Internet of things (IoT), specially when the underlying application demands fresh update. In environmental monitoring and smart agriculture, apart from the importance of AoI, energy efficiency (EE) becomes inevitable owing to network longevity. This paper studies an IoT network where the end devices transfer their information to a central gateway residing on a moving platform such as a tractor, which collects information from a large number of sensors in an agri-field. An optimal trajectory of the mobile reader is proposed using a modified nearest neighbor algorithm to gather the information from randomly distributed sensors. A clustering algorithm is also used to cluster the data in such a way that the overall EE of the network is maximized keeping a desired AoI and outage probability

NOMA Enhanced Backscatter Communication for Green IoT Networks

Backscatter communication has recently emerged as a promising technology to enable the passive sensing-based Internet-of-things (IoT) applications. In a backscatter communication network, uplink transmissions of multiple nodes are usually multiplexed in time- or frequency-domain to avoid collisions, yet it is desirable to improve the uplink capacity further. In this paper, we study a wireless-powered backscatter communication system, where the sensors use a hybrid channel access scheme by combining time division multiplexing access (TDMA) with power-domain non-orthogonal multiple access (PD-NOMA) to enhance the system performance in terms of outage probability and throughput. Our analysis shows that the proposed PD-NOMA increases both the spectrum efficiency and the throughput of the system

Utility-oriented optimization for video streaming in UAV-aided MEC network: a DRL approach

The integration of unmanned aerial vehicles (UAVs) in future communication networks has received great attention, and it plays an essential role in many applications, such as military reconnaissance, fire monitoring, etc. In this paper, we consider a UAV-aided video transmission system based on mobile edge computing (MEC). Considering the short latency requirements, the UAV acts as a MEC server to transcode the videos and as a relay to forward the transcoded videos to the ground base station. Subject to constraints on discrete variables and short latency, we aim to maximize the cumulative utility by jointly optimizing the power allocation, video transcoding policy, computational resources allocation, and UAV flight trajectory. The above non-convex optimization problem is modeled as a Markov decision process (MDP) and solved by a deep deterministic policy gradient (DDPG) algorithm to realize continuous action control by policy iteration. Simulation results show that the DDPG algorithm performs better than deep Q-learning network algorithm (DQN) and actor-critic (AC) algorithm

Behind the counter: pharmacies and dispensing patterns of pharmacy attendants in Karachi.

BACKGROUND: There is little literature available on dispensing patterns and unsupervised sale of medicines from pharmacies in developing countries. OBJECTIVE: This study obtained background information on pharmacies assessed the level of training, knowledge and dispensing patterns of pharmacy attendants in Karachi. METHODOLOGY: This is a descriptive cross sectional study with convenient sampling. A structured questionnaire was used to interview pharmacy attendants. RESULTS: Of the 219 pharmacies surveyed, 62% reported more than 50 customers daily and 20% also sold items of general provision. Mean operating hours were 13. Only 24 (11%) had a visible license. On an average 3 attendants were employed per pharmacy. We interviewed one in each. Amongst the 219 interviewed, 77 (35%) were intermediate qualified and only 26 (12%) pharmacologically trained. Correct frequency of ORS administration was not known by 167 (76%) and 21% incorrectly suggested an anti-diarrhoeal preparation for viral diarrhoea in children. The knowledge of those with pharmacological training was significantly better. For respiratory tract infection in children approximately 60% did not know the correct dose of Paracetamol and Amoxicillin. Only 13 (6%) knew that Propanalol was contraindicated in hypertensive asthamatics. For Cotrimoxazole, metronidazole and lomotil only 40%, 21% and 15% respectively, were aware that these could not be dispensed without prescription. CONCLUSION: In the absence of trained pharmacists existing pharmacy attendants should be trained to improve drug-dispensing patterns

Low-complexity detectors for space-time block coded differential spatial modulation

Space-time block coded differential spatial modulation (STBC-DSM) is a recently proposed DSM-based multiple-input-multiple-output (MIMO) transmission technique with high diversity gain. The existing low-complexity detectors for STBC-DSM can be further designed to reduce complexity. In this paper, we propose an ordered antenna index vector detector (OVD) for STBC-DSM, and an OV-low repetition detector (OV-LRD) for further simplification. The OVD detects the symbols in a designed order, and the OV-LRD fully uses the STBC structure to simplify the OVD. Simulation results show that the OVD achieves near-optimal performance, and the OV-LRD significantly reduces complexity with negligible performance loss

Intelligent reflecting surfaces based offset index modulation for MIMO systems

In this paper, we introduce the concept of offset to the field of intelligent reflecting surfaces-based index modulation (IRS-IM) and propose an IRS-based offset IM (IRSOIM) scheme. The IRS-OIM scheme not only divides the IRS elements into several blocks but also introduces an offset at the transmitter while reducing the number of IRS controller operations. Furthermore, we develop three offset IRS block selection (OIBS) approaches to adapt to different numbers of activated IRS blocks for IRS-OIM. Compared with IRS-IM, the IRS-OIM increases the reliability of information transmission and ensures a high effective gain for the IRS while increasing the data transmission rate. In addition, the mathematical expression for the average bit error probability (ABEP) of the IRS-OIM scheme is deduced. Comparison between IRS-OIM and their counterparts in terms of complexity is also provided. Monte Carlo simulation results demonstrate the superiority of the proposed IRS-OIM scheme, and show that IRS-OIM achieves more balanced trade-off among complexity and performance than their counterparts

Enhanced index modulation aided orthogonal time frequency space with variable active grids and multiple constellations

Present orthogonal time frequency space modulation with index modulation (OTFS-IM) techniques activate a given number of grids in the delay-Doppler (DD) domain and employ fixed constellation as changing them would result in ambiguous detection. Motivated by this, we propose a novel enhanced OTFS with index modulation (E-OTFS-IM) scheme which permits changing the number of active grids conveying modulation symbols from any constellation. The proposed E-OTFS-IM scheme alleviates ambiguous detection by jointly mapping information to grid activation pattern in DD domain and 2D modulation symbols. We also propose an efficient encoding method for E-OTFS-IM. In addition, an updated message passing (MP) detection suitable for E-OTFS-IM as well as its low-complexity improvement are developed. We derive a average bit error probability (ABEP) upper bound for our proposed E-OTFS-IM scheme employing the maximum likelihood detector. Additionally, we also propose an enhanced scheme named E-OTFS-IM with in-phase/quadrature (E-OTFS-IM-IQ) to further improve the spectral efficiency and reliability. In E-OTFS-IM-IQ, the principle of E-OTFS-IM is extended to in-phase and quadrature branches independently. The efficient encoding method and MP detector for this modified scheme is also introduced. Simulation results confirm that the derived ABEP upper bound is tight in the high signal-to-noise ratio region, and show that our proposed E-OTFS-IM improves the performance of conventional OTFS and OTFS-IM. The results also indicate the proposed E-OTFS-IM-IQ achieves better bit error rate performance than E-OTFS-IM

Blockchain-based secure and efficient secret image sharing with outsourcing computation in wireless networks

Secret Image Sharing (SIS) is the technology that shares any given secret image by generating and distributing n shadow images in the way that any subset of k shadow images can restore the secret image. However, in the existing SIS schemes, the shadow images will be easily tampered and corrupted during the communication, which will pose serious security issues. Recently, blockchain has emerged as a promising paradigm in the field of data communication and information security. To securely communicate and effectively protect the secret image data in wireless networks, we propose a Blockchain-based Secure and Efficient Secret Image Sharing (BC-SESIS) scheme with outsourcing computation in wireless networks. In the proposed BC-SESIS scheme, the shadow images are encrypted and stored in the blockchain to prevent them from being tampered and corrupted. The identity authentication-enabled smart contract is deployed to achieve the ( k, n ) threshold for secret image restoring. Furthermore, to reduce the computational burden of smart contract and users, an efficient outsourcing computation method is designed to outsource the restoring task, which is securely implemented by agent miners in the encryption domain. Theoretical analysis and extensive experiments demonstrate that the BC-SESIS scheme can achieve desirable communication security and high computational efficiency in the wireless networks

Effect of Substrate Bed Temperature on Solute Segregation and Mechanical Properties in Ti–6Al–4V Produced by Laser Powder Bed Fusion

Titanium alloys are particularly sensitive to temperature during additive manufacturing processes, due to their dual phase microstructure and sensitivity to oxygen uptake. In this paper, laser powder bed fusion (LPBF) was used in conjunction with a heated substrate bed at 100 °C, 570 °C and 770 °C to produce specimens of Ti–6Al–4V, to investigate the change in mechanical properties and segregation of alloying elements. An initial increase in ductility was observed when increasing the temperature from 100 °C to 570 °C, followed by a significant loss in ductility when samples were produced at 770 °C. A suite of multi-scale characterisation techniques revealed that the as-printed microstructure was drastically different across the range of temperatures. At 100 °C, α + α′ phases were identified. Deformation twinning was extensively observed in the a phase, with Al and V segregating at the twin interfaces. At 570 °C (the most ductile sample), α′, α and nano-particles of β were observed, with networks of entangled dislocations showing V segregation. At 770 °C, no martensitic α′ was identified. The microstructure was an α + β microstructure and an increased volume fraction of tangled dislocations with localised V segregation. Thermodynamic modelling based on the Gibbs-free energy of formation showed that the increased V concentration at dislocations was insufficient to locally nucleate β phase. However, b-phase nucleation at grain boundaries (not dislocations) caused pinning of grain boundaries, impeding slip and leading to a reduction in ductility. It is likely that the increased O-content within specimens printed at increased temperatures also played a key role in high-temperature embrittlement. Building operations are therefore best performed below sub-transus temperatures, to encourage the growth of strengthening phases via solute segregation, and the build atmosphere must be tightly controlled to reduce oxygen uptake within the samples