The vision of battery-free communication has made backscatter a compelling technology for on-body wearable and implantable devices. Recent advances have facilitated the communication between backscatter tags and on-body smart devices. These studies have focused on the communication dimension, while the security dimension remains vulnerable. It has been demonstrated that wireless connectivity can be exploited to send unauthorized commands or fake messages that result in device malfunctioning. The key challenge in defending these attacks stems from the minimalist design in backscatter. Thus, in this paper, we explore the feasibility of authenticating an on-body backscatter tag without modifying its signal or protocol. We present SecureScatter, a physical-layer solution that delegates the security of backscatter to an on-body smart device. To this end, we profile the on-body propagation paths of backscatter links, and construct highly sensitive propagation signatures to identify on-body backscatter links. We implement our design in a software radio and evaluate it with different backscatter tags that work at 2.4 GHz and 900 MHz. Results show that our system can identify on-body devices at 93.23% average true positive rate and 3.18% average false positive rate.

Recent years have seen proliferation in versatile mobile devices and an upsurge in the growth of data-consuming application services. Orthogonal multiple access (OMA) technologies in today's mobile systems fall inefficient in the presence of such massive connectivity and traffic demands. In this regards, non-orthogonal multiple access (NOMA) has been advocated by the research community to embrace unprecedented requirements. Current NOMA designs have been demonstrated to largely improve conventional system performance in terms of throughput and latency, while their impact on the end users' perceived experience has not yet been comprehensively understood. We envision that qualityof-experience (QoE) awareness is a key pillar for NOMA designs to fulfill versatile user demands in the 5th generation (5G) wireless communication systems. This article systematically investigates QoE-aware NOMA designs that translate the physical-layer benefits of NOMA to the improvement of users' perceived experience in upper layers. We shed light on design principles and key challenges in realizing QoE-aware NOMA designs. With these principles and challenges in mind, we develop a general architecture with a dynamic network scheduling scheme. We provide some implications for future QoE-aware NOMA designs by conducting a case study in video streaming applications.Recent years have witnessed a boom in versatile wireless devices and data-consuming mobile services. In the coming wave of a large number of new generation mobile Internet devices, including tablets, smartphones, smart wearables and so on, future 5th generation (5G) mobile networks need to support the massive connectivity of wireless devices. Additionally, the emergence of new data-consuming services, such as virtual reality (VR), augmented reality (AR), high-definition (HD) video streaming, cloud and fog computing services, have elevated the traffic demands. The ever-increasing traffic demands have raised the stakes on developing new access technologies to utilize limited spectrum resources. Non-orthogonal multiple access (NOMA), as an emerging multiple access (MA) technology for improving spectral efficiency, has recently obtained remarkable attention [1], [2]. The innovative concept of NOMA is to serve multiple users in a single resource block, and thus is fundamentally different from conventional orthogonal multiple access (OMA) technologies, such as time division multiple access (TDMA) and orthogonal frequency division multiple access (OFDMA). Recently, a downlink version of NOMA, termed multiuser superposition transmission (MUST), has been included for the 3rd generation partnership project (3GPP) long term evolution (LTE) initiative [3]. Another NOMA technology, namely layer-division-multiplexing (LDM) has been accepted by the digital TV standard advanced television systems committee (ATSC) 3.0 [4] for its efficiency in delivering multiple services in one TV channel.Despite growing attempts and extensive efforts on NOMA, most studies have focused on the physical layer (PHY)...

An estimation method of plasma density based on surface plasmons theory for surface-wave plasmas is proposed. The number of standing-wave is obtained directly from the discharge image, and the propagation constant is calculated with the trim size of the apparatus in this method, then plasma density can be determined with the value of 9.1 × 1017 m−3. Plasma density is measured using a Langmuir probe, the value is 8.1 × 1017 m−3 which is very close to the predicted value of surface plasmons theory. Numerical simulation is used to check the number of standing-wave by the finite-difference time-domain (FDTD) method also. All results are compatible both of theoretical analysis and experimental measurement.

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