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In this paper, we study a cognitive radio wireless-powered communication network with an integrated intelligent reconfigurable surfaces system. Actually, massive connectivity and limited energy are the primary challenges to implementing ultra-reliable and low-latency services, as it is extremely difficult to maintain the quality of service and manage the connection of a huge number of users to small cells. So, this paper investigates the application of NOMA-based simultaneous wireless information and power transfer (SWIPT) for massive mobile systems in which the underlay spectrum sharing network is designed to mitigate the interlayer interference such that interference with the primary network is kept less than a predefined level. Problem modeling takes into account residual hardware impairments and channel estimation errors under practical conditions. The communications between the servers and users of NOMA-based small cells are accomplished via an interference-limited multihop connection through intermediate relays. Based on the partial relay selection (PRS) protocol, an optimal relay is selected from K relays to transmit the received signal to multiple user equipment, namely, the far users (FU) and the near users (NU). In addition, to maximize the system total throughput, we formulate the transmitter (Tx)-relay-receiver (Rx) matching problem, which is a mixed-integer nonlinear programming (MINLP) problem. To address this nondeterministic polynomial-time NP-hard problem, we applied a gradient algorithm to obtain a stable matching. The impact of the transmission power, the number of Tx/Rx pairs, and the number of intermediate relays on the sum rate are investigated. Based on the simulation results, the hardware failure parameter has a negative impact on system performance, whereas the channel estimation index is always advantageous to outage probability (OP). Also, the analysis of the energy efficiency and key performance indicators proves that the proposed approach outperforms other similar schemes from the power saving and QoS assurance perspectives. [ABSTRACT FROM AUTHOR]

Multiple-input multiple-output (MIMO) communications are believed as one of the key enabling technologies to fulfill the increasing requirements of future wireless networks. However, the asymptotic performance limits of MIMO vehicular ad hoc network (VANET) systems are not thoroughly investigated. All the related works on MIMO VANETs mainly focused on measurement and geometry based channel analyzing and modeling. In this paper, we present a framework for ergodic capacity analysis on MIMO communications among multi-antenna mounted vehicles. We model a Rayleigh fading channel with standard path-loss and lognormal shadowing, then adopt the tools of stochastic geometry to characterize the MIMO geocast channels. After analyzing the co-channel interference among MIMO geocast sessions, the upper and lower bounds on ergodic capacity of single link MIMO and MIMO geocast channels are derived with careful consideration of the important issues like antenna number, shadow fading, and transmission radius. Results reveal that ergodic capacity of MIMO VANETs can be significantly improved by appropriately mounting multiple transmit and receive antennas on vehicles. As the space for antenna mounting in a vehicle is rather limited, we further give a method to calculate the minimum number of antennas for each vehicle to guarantee the quality of service (QoS) requirements in safety oriented applications of IoV. [ABSTRACT FROM AUTHOR]

In a cellular network (CN), cellular users (CUs) located nearby machine type communications (MTC) devices (MTC-Ds) may act as uplink gateways to relay data to the base station (BS). We consider non-orthogonal multiple access (NOMA) and successive interference cancellation (SIC) at the receiver to increase the number of connected devices and the spectrum efficiency. Both underlay and overlay spectrum access modes (SAMs) are considered. We introduce a dynamic user grouping (UG) concept as a practical constraint for SIC, in order to decrease the receiver complexity. Moreover, SIC constraints are introduced based on a minimum signal-to-noise-plus-interference ratio (SINR) at the receiver. We formulate a joint dynamic UG, power allocation, and resource block (RB) assignment problem, aiming at maximizing the total sum-rate of both CUs and MTC-Ds. We transform the obtained non-convex mixed-integer programming problem into a convex problem by using a quadratic fractional programming (FP). A heuristic method is also proposed to reduce complexity. Simulation results demonstrate that the proposed solution outperforms the conventional CN (C-CN) method and the results of the proposed optimization methods are close to optimal solution obtained by the exhaustive search (ES) algorithm in terms of total average sum-rate and network connectivity, while requiring less transmit power. The heuristic method decrease the computational complexity of the FP method at the expense of a small reduction in spectrum efficiency. [ABSTRACT FROM AUTHOR]

In 5G networks, a massive number of connections of high data rate services, e.g., video streaming services, certainly make the networks deteriorated because of extreme traffic congestion at the backhaul links of macro base stations (MBSs). Although ultra-dense networks (UDNs) have been considered as a promising architecture to stimulate the 5G networks, the congestion problem hampers the UDNs to provide mobile users (MUs), i.e., represented by device-to-device (D2D) pairs and shared downlink resource users (SUs), with high video delivery capacity. In this paper, we propose a social-aware caching and resource sharing (SCS) strategy for video streaming services in 5G UDNs. Particularly, we formulate the SCS problem by taking into account the social relationship of each D2D pair, the available storage of femtocell base stations (FBSs) and transmitters (TXs) of D2D pairs, the target signal to interference plus noise ratio (SINR) of SUs, and the popularity of videos. The SCS problem is then solved for 1) optimal number of caching copies of each video and optimal caching placements in the FBSs and 2) optimal resource sharing allocation between the SUs and the D2D pairs for D2D communications. This way, the workload at the backhaul links of the MBSs can be reduced. Simultaneously, an arbitrary MU can retrieve the videos alternately from the MBSs, FBSs, and TXs at high cache-hit ratio and maximum delivery capacity. Simulation results are analyzed to show the benefits of the proposed SCS strategy compared to other conventional schemes. [ABSTRACT FROM AUTHOR]

Interference from primary transmitters in underlay cognitive networks is practically neither neglected nor integrated into noise terms although most literature inversely addressed. This paper firstly employs a helpful jammer to secure information transmission of a secondary transmitter. Then, its efficacy through secrecy outage probability under practical considerations consisting of exponentially distributed interference from primary transmitter, peak transmission power limitation, interference power limitation, and Rayleigh fading channels are analytically assessed. Finally, results are provided to illustrate significant security performance improvement thanks to exploiting the jammer while considerable security performance degradation due to interference from primary transmitter. [ABSTRACT FROM AUTHOR]

To enhance the spectrum scarcity of cooperative heterogeneous networks (HetNets) with unreliable backhaul connections, we examine the impact of cognitive spectrum sharing over multiple small-cell transmitters in Nakagami-m fading channels. In this system, the secondary transmitters are connected to macro-cell via wireless backhaul links and communicate with the secondary receiver by sharing the same spectrum with the primary user. Integrating cognitive radio (CR) network into the system, we address the combined power constraints: 1) the peak interference power at the primary user and 2) the maximal transmit power at the secondary transmitters. In addition, to exclude the signaling overhead for exchanging channel-state-information (CSI) at the transmitters, the selection combining (SC) protocol is assumed to employ at the receivers. To evaluate the performance, we first derive the closed-form statistics of the end-to-end signal-to-noise (SNR) ratio, from which the exact outage probability, ergodic capacity and symbol error rate expressions are derived. To reveal further insights into the effective unreliable backhaul links and the diversity of fading parameters, the asymptotic expressions are also attained. The two interesting non-cooperative and Rayleigh fading scenarios are also investigated. Numerical results are conducted to verify the performance of the considered system via Monte-Carlo simulations. [ABSTRACT FROM AUTHOR]

Device-to-Device (D2D) communication and wireless small cell networks (SCNs) are two of the most promising paradigms in next generation cellular technologies. However, interference management is a major issue in regard to the use of either or both technologies. In this paper, we propose a D2D pair underlying SCNs using Wireless Power Transfer (WPT) technology. In particular, we have a D2D transmitter and D2D receiver underlying SCNs and operate in close proximity to a SCN primary user (PU). Two scenarios are proposed. The first scenario is when the best base station (BS) link is chosen to harvest energy from, and a second scenario where energy is harvested from all available SCN BSs. The transmission between the D2D pair is kept under a certain threshold so it could not have any harmful effects on the transmission link of PU. The results reveal that the number of interference users shows negative effect on the performance of the considered system. Besides, the primary network's peak interference constraint has significant influence on the optimal value of energy harvesting time at the D2D transmitter. [ABSTRACT FROM AUTHOR]

In this paper we study the spectrum coexistence of secondary wireless networks with contention control and TV services. We propose to use the carrier sensing threshold as a parameter to control the density of secondary transmitters and through that the generated secondary interference to the TV system. For the calculated threshold we propose a simple method to assess the data rate of the secondary system. Using this method one can study whether the secondary performance is limited due to the TV protection requirements or not. Also, the method can be used to study the trade-off between the secondary performance and the TV protection requirement. [ABSTRACT FROM AUTHOR]

Vehicular communications are receiving considerable attention due to the introduction of the intelligent transportation system (ITS) concept, enabling smart and intelligent driving technologies and applications. To design, evaluate and optimize ITS applications and services oriented to improve vehicular safety, but also non-safety applications based on wireless systems, the knowledge of the propagation channel is vital. In particular, the mean path loss is one of the most important parameters used in the link budget, being a measure of the channel quality and limiting the maximum allowed distance between the transmitter (Tx) and the receiver (Rx). From a narrowband vehicular-to-vehicular (V2V) channel measurement campaign carried out at 5.9 GHz in three different urban environments characterized by high traffic density, this paper analyzes the path loss in terms of the Tx-Rx separation distance and fading statistics. Based on a linear slope model, values for the path loss exponent and the standard deviation of shadowing are reported. We have evaluated the packet error rate (PER) and the maximum achievable Tx-Rx separation distance for a PER threshold level of 10 % according to the digital short-range communications (DSRC) specifications. The results reported here can be incorporated in an easy way to vehicular networks (VANETs) simulators in order to develop, evaluate and validate new protocols and systems architecture configurations under realistic propagation conditions. [ABSTRACT FROM AUTHOR]