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Due to the forecasted fast increasing cellular traffic and the already highly congested licensed spectrum, it is critical to exploit and utilize the unlicensed spectrum resources for the fifth-generation (5G) and beyond networks. A challenging problem is the coexistence of 5G and other networks with fair, reliable, and efficient sharing of the unlicensed spectrum. In this paper, we propose a blockchain-enhanced distributed spectrum sharing scheme for coexisting multiple operators and multiple WiFi APs. We design a novel lightweight and efficient consensus mechanism, named Proof of Strategy (PoG). In this consensus mechanism, the problem of spectrum sharing is used as a consensus puzzle, and the part of the unlicensed spectrum is used as the ‘fee’ of miners. With such a design, the computing overhead of the consensus process is expected to be reduced significantly. We develop a non-cooperative game to analyze the behavior of the miners and obtain a symmetric Bayesian Nash equilibrium under the uniform distribution of mining cost estimation. It can be found mathematically and experimentally that the strategy of the winner tends to maximize the system revenue by sharing the unlicensed spectrum resource. Furthermore, to reduce the impact of heavy interactions on system throughput, the operation of WiFi APs in the proposed scheme can be adaptively switched between ‘contention mode’ and ‘blockchain mode’ according to the network traffic load. The dynamic behavior is constructed as an evolutionary game, and the existence and uniqueness of equilibrium points are proved by theoretical analysis. Simulations demonstrated the fairness and effectiveness of the proposed blockchain-based scheme and the mode switching method for distributed spectrum sharing by heterogeneous wireless networks. [ABSTRACT FROM AUTHOR]

This paper investigates the outage and throughput performance of full-duplex (FD) cooperative relaying (CR) based non-orthogonal multiple access system (NOMA) with energy harvesting (EH) i.e., FD-CR-EH-NOMA system. We consider a network scenario, where the base station (BS) serves two downlink users, with the near user configured as a FD relay to deliver messages to the far user. We derive analytical expressions for the outage probabilities experienced by the users and the system outage probability of FD-CR-EH-NOMA network under time switching relaying (TSR) protocol in the presence/absence of direct link from BS to the far user. Assuming imperfect successive interference cancellation (i-SIC), we derive analytical expressions for (i) optimal power allocation (OPA) factor at the BS and (ii) optimal time switching (OTS) factor at the relay that independently minimizes the system outage probability. Further, we use the alternating optimization technique to determine the jointly optimal power allocation and time switching factors that minimize the system outage probability. Furthermore, we determine the OTS factor that maximizes the asymptotic throughput of the system in the delay-limited transmission mode. With the help of numerical and simulation investigations, we show that the system outage and throughput of the considered network improve significantly under the proposed schemes. [ABSTRACT FROM AUTHOR]

For search and rescue (SAR), the group unmanned aerial vehicle (GUAV) can rapidly cover the disaster area, and it can provide reliable connectivity to victim by aerial backbone network (ABN). However, existing 3D aerial mobility model (3D AMM) cannot capture unique features of GUAV in SAR, especially smooth 3D trajectory and collision avoidance. In this paper, we develop realistic 3D aerial group mobility model based on spiral line (3D SLGM) for SAR. Firstly, we review some related works. Then, we introduce the mechanism of 3D SLGM, such as Z-Or-SLGM and Z-Non-SLGM. Furthermore, we analyze some mathematical features of 3D SLGM. In addition, we investigate key mobility features of 3D SLGM. Finally, we evaluate the network performance under 3D SLGM. The result shows that 3D SLGM has smooth 3D trajectory and uniform distribution of spatial nodes in 3D space. With the collided rate of 0%, 3D SLGM merely takes about 1.4 minutes to cover 100% of the target area of 200 m*200 m. Besides, the network under 3D SLGM can approach the throughput of 0.45 Mb/s, the end-to-end delay of 3.2 ms and the loss packets rate of 0%. We believe that 3D SLGM, as a significant supplement of 3D AMM, can provide many helpful guidelines in the design and analysis of authentic ABN. [ABSTRACT FROM AUTHOR]

In this paper, we propose a full-duplex (FD) relaying system with multi-input multi-output (MIMO) with simultaneous wireless information and power transfer (SWIPT), where the communication from source to destination is assisted by a full-duplex decode-and-forward (DF) relay. The time switching (TS) protocol is used at the relay to harvest the energy of radio-frequency (RF) signals transmitted from the source. To improve both system performance and the amount of harvested energy, multiple antennas are used at source and destination. Transmit antenna selection (TAS) is employed at the source with an assumption that the feedback of channel state information (CSI) is outdated. Meanwhile, both selection combining (SC) and maximal ratio combining (MRC) techniques are applied at the destination. The closed-form expressions of the outage probability (OP), optimal throughput, and symbol error probability (SEP) are derived subject to the outdated CSI over Rayleigh fading channels. We also make a comparison between the performance of the proposed MIMO-FD relaying system with SWIPT and that of MIMO half-duplex (HD) relaying systems with and without SWIPT. The validity of derived mathematical expressions is verified by Monte-Carlo simulations. Numerical results show that the TAS/MRC scheme gives better system performance than the TAS/SC scheme. Moreover, higher energy harvesting time is needed to maximize the throughput than to minimize the OP. [ABSTRACT FROM AUTHOR]

In this paper, to perform an energy-efficient and high-throughput time-switching (TS)-based energy-harvesting (EH) relaying in a practical block-by-block manner, an adaptive discrete TS-based EH relaying scheme is proposed. Specifically, focusing on both dual-hop amplify-and-forward (AF) and decode-and-forward (DF) systems, we make full use of the channel state information (CSI) at the relay to determine an adaptive relaying power as well as an adaptive TS factor based on the relay's current accumulated energy. For such, an effective analytical framework is proposed to characterize the throughput performance of the proposed scheme, which shows the superiority of the proposed scheme over the conventional one. In particular, the limiting throughput efficiency of the proposed scheme is shown to achieve the limiting/best throughput efficiency of 50% for half-duplex relaying regardless of channel fading types, while the limiting throughput efficiency of the conventional scheme is always less than 50%. Furthermore, simulation results are given to validate our theoretical analysis, showing that for AF mode, the proposed scheme can provide up to 7.4 dB threshold signal-to-noise ratio (SNR) gain over the conventional solution. In addition, a comprehensive comparison between the proposed scheme and other state-of-the-art protocols is also made via representative numerical examples. [ABSTRACT FROM AUTHOR]

The design of an efficient medium access control (MAC) protocol for multichannel ad hoc cognitive radio networks is an important problem and has been the topic of extensive recent research. In this paper, we present the design and performance evaluation of a protocol, group MAC (GMAC), which is customized for a situation that commonly arises in ad hoc networks: The network consists of multiple groups of nodes such that a large fraction of the traffic of each node needs to be sent to other nodes of its own group. Some examples are 1) units (e.g., platoons) in a military ad hoc network; 2) divisions in an emergency or disaster relief network; and 3) departments in a corporate or university network. Our protocol requires each secondary node to have only one narrowband transceiver, does not rely on a control channel, and incorporates a novel technique for dynamically balancing the traffic load of secondary nodes across the set of free channels. We formulate the problem of partitioning the network nodes into groups based on the volumes of data traffic to be sent between different pairs of nodes, which we call the group formation problem (GFP). We show that the GFP is NP-complete and propose a greedy algorithm to solve it. We analyze the stability region of the GMAC protocol using a queuing theoretic framework. Our extensive simulations show that a large fraction of the bandwidth unoccupied by primary users is utilized by the GMAC protocol for data transmissions. [ABSTRACT FROM AUTHOR]

In this paper, we compare the performance of time-switching relaying (TSR) and power-splitting relaying (PSR) protocols in two-hop networks with a battery-assisted energy-harvesting (EH) amplify-and-forward relay. In this battery-assisted relay framework, the EH relay augments the harvested energy with energy drawn from a battery. Using expressions derived for throughput and average battery energy consumption, we investigate maximization of throughput for given battery energy availability per time slot and minimization of battery energy consumption for target throughput requirement. When only statistical channel knowledge is available, PSR results in better throughput performance at practical signal-to-noise ratios. However, in the typical low battery energy and low target throughput regime, it is TSR that is more battery energy efficient. When second-hop instantaneous channel knowledge is available, we observe dramatical energy savings that increases lifetime of nodes. Simulation results are presented to demonstrate accuracy of the derived expressions. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the optimal throughput performance for simultaneous wireless information and power transfer relaying network in the presence of direct link between the source and the destination. By considering the direct link, system performance can be improved when the channel condition is good from source to destination. The cooperative network consists of a source, an amplify-and-forward relay, and a destination, where the relay harvests energy from the source and then uses the harvested energy to forward information to the destination. At the destination node, the signals from the direct link and relay are combined by the maximum ratio combining (MRC) method. The time switching (TS) relaying protocol is applied to enable energy harvesting and information processing simultaneously. At the same time, we made progress on analyzing the throughput of information transmission on the basis of the MRC method with power switching (PS) relaying protocol. Additionally, adaptive-MRC protocol is proposed based on the TS and PS relaying protocols, which can choose better mode to achieve the communication. The numerical analyses provide practical insights into the effect of various system parameters, such as energy harvesting time splitting ratio, source transmission rate, distance between nodes, and noise power at the destination and the relay. [ABSTRACT FROM AUTHOR]

We consider an energy-harvesting cognitive radio (CR) system coexisting with an unslotted primary user (PU) system. The secondary user (SU) either harvests energy from the PU transmissions or transmits when the PU is sensed to be idle. In this paper, we optimize the sensing intervals to balance between energy harvesting and spectrum access, considering the PU traffic statistics that affects both the energy arrival and consumption in addition to the opportunistic spectrum access. We propose to use different sensing intervals if the SU decides to transmit or harvest energy. The harvesting and transmission durations can be used to optimize the tradeoff between maximizing the utilization of PU spectrum opportunities and harvesting sufficient energy to transmit. We determine a closed-form expression for the probability of SU being active as a function of the PU traffic statistics and SU's access and harvest durations. Optimal transmission and harvesting durations have been found to maximize the CR throughput while protecting the PU. Furthermore, we enhance the system capability by considering that the SU can choose to purchase energy from the PU during the discovered PU idle periods in addition to the energy harvested opportunistically. It can further exploit the difference in the PU busy and idle durations as per its energy needs. The average energy cost spent in a time slot is minimized to achieve a given SU transmission rate while adhering to the PU collision constraint. [ABSTRACT FROM AUTHOR]

In this paper, we propose an adaptive medium access control (MAC) solution for a fully connected mobile ad hoc network (MANET), supporting homogeneous best-effort data traffic. The MAC scheme achieves consistently high network performance by adapting to the ever-varying network traffic load. Based on the detection of a current network load condition, nodes can make a switching decision between IEEE 802.11 distributed coordination function (DCF) and dynamic time-division multiple access (D-TDMA), when the network traffic load reaches a threshold, referred to as MAC switching point. The adaptive MAC solution determines the MAC switching point to maximize network performance. Approximate and closed-form performance analytical models for both MAC protocols are established, which facilitate the computation of MAC switching point in a tractable way. Extensive analytical and simulation results demonstrate that the adaptive MAC solution provides consistently maximal network performance in the presence of traffic load dynamics. [ABSTRACT FROM AUTHOR]

The introduction of fourth-generation wireless technologies has fueled the rapid development of cellular networks, significantly increasing the energy consumption and the expenditures of mobile network operators (MNOs). In addition, network underutilization during low-traffic periods (e.g., night zone) has motivated a new business model, namely, infrastructure sharing, which allows the MNOs to have their traffic served by other MNOs in the same geographic area, thus enabling them to switch off part of their network. In this paper, we propose a novel infrastructure-sharing algorithm for multioperator environments, which enables the deactivation of underutilized base stations during low-traffic periods. Motivated by the conflicting interests of the MNOs and the necessity for effective solutions, we introduce a game-theoretic framework that enables the MNOs to individually estimate the switching-off probabilities that reduce their expected financial cost. Our approach reaches dominant strategy equilibrium, which is the strategy that minimizes the cost of each player. Finally, we provide extensive analytical and experimental results to estimate the potential energy and cost savings that can be achieved in multioperator environments, incentivizing the MNOs to apply the proposed scheme. [ABSTRACT FROM AUTHOR]

In a cognitive radio network (CRN), two nodes have a rendezvous when they tune to the same channel simultaneously. Providing rendezvous guarantee between any pair of nodes is essential because a rendezvous is necessary for communication. Some existing works claim that rendezvous guarantee can be provided by using a dedicated common control channel to negotiate the channel being used. A serious problem of these mechanisms is that a globally available channel may not exist. Some channel hopping protocols try to provide a rendezvous guarantee without using a common control channel. However, these solutions may suffer from a poor number of rendezvous or uneven channel utilization. In this paper, we propose a novel distributed channel hopping protocol: Quorum and Latin square channel hopping (QLCH). The QLCH scheme efficiently provides rendezvous guarantee by utilizing the concept of quorum systems and Latin squares. The former is utilized to guarantee balanced rendezvous among nodes, whereas the latter is adopted to share the rendezvous among channels. QLCH efficiently provides fast rendezvous guarantee and can cooperate with other channel hopping protocols to enhance network throughput. Analytical and simulation results verify the improvement of QLCH. For example, when there are 30 flows using 11 channels in a CRN, the achieved time to rendezvous of QLCH is 9.84 times lower than that of the existing protocol SYNC-ETCH, whereas the achieved network throughput of QLCH is 362% higher than that of the existing protocol, i.e., Quorum-based channel hopping (L-QCH). [ABSTRACT FROM PUBLISHER]

This paper proposes a generalized interrelay interference cancelation (gIRIC) scheme for a two-path relay model in multisource systems. Both the sources and the relay adopt complex field network coding (CFNC) to remove the interrelay interference (IRI) caused by the two-path relay. Furthermore, we introduce two detecting modes (gIRIC-noSD and gIRIC-SD) for destination in our scheme. Two switching rules are given to select a suitable detecting mode between treating the signal of a direct link as noise (gIRIC-noSD) and utilizing the direct link to assist signal detection (gIRIC-SD). The bounds of average symbol error probability (SEP) and throughput of our scheme are derived. [ABSTRACT FROM PUBLISHER]

With growing concern about environmental issues and an emerging green communications paradigm, cognitive radio (CR) networks (CRNs) have to be considered from the energy efficiency perspective. In this paper, we focus on scheduling in CRNs, in which a cognitive base station (CBS) makes frequency allocations to the CRs at the beginning of each frame. A cognitive scheduler must consider the diversity among CRs' queues and channel capacities in terms of number of bits and the channel switching cost from one frequency to another. Taking all these into account, we formulate the scheduling problem as an energy efficiency maximization problem, which is a nonlinear integer programming (NLP) problem and is thereby hard to solve. We seek alternate computationally easier solutions. To this aim, we propose a polynomial-time heuristic algorithm, i.e., the energy-efficient heuristic scheduler (EEHS), which allocates each idle frequency to the CR that attains the highest energy efficiency at this frequency. Next, we reformulate the original problem first as a throughput maximization problem subject to energy consumption restrictions and then as an energy consumption minimization problem subject to minimum throughput guarantees. These two schedulers also have the power to provide fairness in resource allocation. We analyze the energy efficiency and successful transmission probability of the proposed schedulers under both contiguous and fragmented spectrum scenarios. Performance studies show that, compared with a pure opportunistic scheduler with a throughput maximization objective, proposed schedulers can attain almost the same throughput performance with better energy efficiency. [ABSTRACT FROM PUBLISHER]

In this paper, the problem of mode switching in multiple-input–multiple-output (MIMO) broadcast channels utilizing the Per-User Unitary Rate Control (PU2RC) transmission scheme is considered. Since there is no mathematical expression for the achievable rate of the PU2RC systems, it is proposed to approximate them using proper bounds. It is shown that certain simple feedback distributions will lead to tight bounds on the achievable rates of the PU2RC systems. The proposed bounds are used for the calculation of mode-switching points and maximization of the system rate under different multiplexing order conditions. The asymptotic behavior of the preferred modes is also studied under high-signal-to-noise-ratio (SNR) and low-SNR conditions, and it is shown that the single-user transmission mode is the preferred mode for both regimes. [ABSTRACT FROM PUBLISHER]

Multistage sensing is a novel concept that refers to a general class of spectrum sensing algorithms that divide the sensing process into a number of sequential stages. The number of sensing stages and the sensing technique per stage can be used to optimize the performance with respect to secondary user (SU) throughput and the collision probability between primary user (PU) and SU. So far, the impact of multistage sensing on network throughput and collision probability for a realistic network model has been relatively unexplored. Therefore, we present the first analytical framework that enables the performance evaluation of different multichannel multistage spectrum sensing algorithms for opportunistic spectrum access (OSA) networks. The contribution of this paper lies in studying the effect of the following parameters on performance: number of sensing stages, physical layer sensing techniques and durations per each stage, single and parallel channel sensing and access, number of available channels, PU and SU traffic, buffering of incoming SU traffic, and medium access control layer sensing algorithms. The analyzed performance metrics include the average SU throughput and the average collision probability between PU and SU. Our results show that when the probability of PU misdetection is constrained, the performance of multistage sensing is, in most cases, superior to the single-stage sensing counterpart. In addition, prolonged channel observation at the first stage of sensing considerably decreases the collision probability while keeping the throughput at an acceptable level. Finally, in realistic PU traffic scenarios, using two stages of sensing provides a good balance between SU throughput and collision probability while meeting successful detection constraints subjected by OSA communication. [ABSTRACT FROM PUBLISHER]