While millimeter-wave (mm-wave) communication can provide abundant spectrum and support high data rate for future 5G systems, its coverage capability in urban environments is a critical issue due to the severe penetration loss. In this letter, we propose a simple scheme to enhance the coverage area of a cell centered with an mm-wave base station. This key idea is to employ multiple passive-reflectors to reflect the mm-wave to the non-lineof-sight (NLOS) regions with low received power levels. In order to improve the received power, a design method for the passivereflector is discussed intensively. Numerical experiment for an outdoor urban environment is presented. The numerical results show that, with the proposed scheme, the coverage radius of an mm-wave cell can be remarkably increased. This indicates that our scheme is an attractive option to alleviate the mm-wave coverage problem for future 5G systems.

This paper investigates the security performance of two relay selection schemes for cooperative non-orthogonal multiple access (NOMA) systems, where K randomly distributed relays are employed with either decode-and-forward (DF) or amplify-and-forward (AF) protocols. More particularly, two-stage relay selection (TRS) and optimal relay selection (ORS) schemes are taken into consideration. To characterize the secrecy behaviors of these RS schemes, new closed-form expressions of both exact and asymptotic secrecy outage probability (SOP) are derived. We confirm that the SOP of the TRS scheme is equal to that of the ORS scheme for DF/AF-based NOMA systems. Based on the analytical results, the secrecy diversity orders achieved by the pair of RS schemes for the DF/AF-based NOMA systems are K , which are equal to the number of relays. It is shown that the secrecy diversity orders for the cooperative NOMA systems are determined by the number of the relays. The numerical results are presented to demonstrate that: 1) the secrecy performance of the AF-based NOMA system outperforms that of the DF-based NOMA system, when not all DF relays successfully decode the received information; 2) with the number of relays increasing, the SOP of these RS schemes for the DF-/AF-based NOMA systems becomes lower, and; 3) the TRS/ORS schemes are capable of achieving better secrecy outage behaviors compared with random RS and orthogonal multiple access-based RS schemes. INDEX TERMS Amplify-and-forward, decode-and-forward, non-orthogonal multiple access, physical layer security, relay selection.

Green areas or parks are the best way to encourage people to take part in physical exercise. Traditional techniques of researching the attractiveness of green parks, such as surveys and questionnaires, are naturally time consuming and expensive, with less transferable outcomes and only site-specific findings. This research provides a factfinding study by means of location-based social network (LBSN) data to gather spatial and temporal patterns of green park visits in the city center of Shanghai, China. During the period from July 2014 to June 2017, we examined the spatiotemporal behavior of visitors in 71 green parks in Shanghai. We conducted an empirical investigation through kernel density estimation (KDE) and relative difference methods on the effects of green spaces on public behavior in Shanghai, and our main categories of findings are as follows: (i) check-in distribution of visitors in different green spaces, (ii) users’ transition based on the hours of a day, (iii) famous parks in the study area based upon the number of check-ins, and (iv) gender difference among green park visitors. Furthermore, the purpose of obtaining these outcomes can be utilized in urban planning of a smart city for green environment according to the preferences of visitors.

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In this paper, we investigate the performance of the non-orthogonal multiple access (NOMA) system with incremental relaying, where the relay is employed with amplify-and-forward (AF) or decode-and-forward (DF) protocols. To characterize the outage behaviors of the incremental cooperative NOMA (ICN) system, new closed-form expressions of both exact and asymptotic outage probability for two users are derived. In addition, the performance of the conventional cooperative NOMA (CCN) system is analyzed as a benchmark for the the purpose of comparison. We confirm that the outage performance of the distant user is enhanced when ICN system is employed. Numerical results are presented to demonstrate that (1) the near user of the ICN system achieves better outage behavior than that of the CCN system in the low signal-to-noise ratio (SNR) region; (2) the outage performance of distant user for the DF-based ICN system is superior to that of the AF-based ICN system when the system works in cooperative NOMA transmission mode; and (3) in the low SNR, the throughput of the ICN system is higher than that of the CCN system. authors of [9] have researched the performance of a downlink single-cell NOMA network when assuming imperfect channel state information (CSI) and second-order statistics. Furthermore, the authors in [10] consider the scenario that each user only feedback one bit of its CSI to a base station (BS) and analyzed the outage performance. Apart from these researches, there are a lot of studies on improving the secrecy performance of multiple users [11,12], where the external and internal eavesdropping scenarios have been considered. Up to now, NOMA has been extended to cooperative communication systems [13, 14], as the higher diversity and extended coverage can be obtained in wireless networks. The authors have analyzed the outage performance of NOMA system with decode and forward (DF) relay employing full-duplex (FD) and half-duplex (HD) mode, where the near user was selected as a relay to deliver information and improve transmission reliability of distance users [15]. Inspired by this, simultaneous wireless information and