Editorial: Reliable Communication for Emerging Wireless Networks
As many as 50 billion devices will be connected to the Internet by 2020. It is predicted that the number of mobile-connected devices will exceed 11.5 billion by 2019 (nearly 1.5 mobile devices per capita), which poses a huge traffic demand for ubiquitous communications. Data rates are projected to increase by a factor of ten every five years, and with the emerging Internet of Things (IoT) predicted to wirelessly connect trillions of devices across the globe. It is anticipated that we will witness an up to 10,000- fold growth in wireless data traffic by the year 2030. Predictions evidently indicates that the growth in data traffic will cater unprecedented services and applications for machine type communication such as driverless vehicles and drone-based deliveries, smart cities and factories, remote medical diagnosis and surgery, and artificial intelligence- based personalized assistants along with traditional human-centric communications. Coexistence of human-centric and machine-type services as well as hybrids of these will make next generation wireless networks more diverse and complex. Current wireless radio access techniques are not capable of delivering these new applications and services as they are very different from traditional human-centric communications in terms of reliability, latency, energy efficiency, security, flexibility, and connection density. Without novel approaches, future wireless mobile networks (5G and beyond) will grind to a halt unless more capacity is created, on the other hand, to cope with the challenges due to new service categories, a new look on the wireless networks is required to meet performance requirements such as massive connectivity, lower latency, higher reliability, better energy efficiency and security.
To overcome the aforementioned challenges of emerging wireless communications and networks for 5G and Beyond, this special issue focuses on (but are not restricted to) the following topics: Ultra-reliable and low latency communication (URLLC); Massive machine-type communication (mMTC); New air interface design for 5G (New Radio (NR)); QoS/QoE mechanisms for wireless communications and networks; 5G wireless heterogeneous networks: design and optimization; Sensing technologies and applications for 5G; 5G wireless communications and networks for surveillance and management; 5G Cognitive networks and IoT; Experimental results, prototypes, and testbeds of 5G wireless communications and networks; Integration and co-existence of 5G wireless communication and network technologies; Energy efficiency (harvesting and saving) wireless protocols and algorithms for 5G; Security and privacy concerns in 5G wireless communications; NOMA, full-duplex, massive MIMO; Green 5G multimedia wireless networks; AI techniques for Wireless Communication and security; MmWave Massive MIMO; and Hardware impairments affecting wireless communications.
This special issue includes eight high-quality papers. In the first paper entitled “Joint User Association and Power Allocation for Millimeter-Wave Ultra-Dense Networks,” the authors consider millimeter-Wave (mmWave) communication in ultra-dense networks (UDNs), where many small-cell base stations (SBSs) are deployed. The key idea of the proposed scheme is to jointly optimize the SBS-UE association and power allocation to maximize the system energy efficiency while guaranteeing the quality of service (QoS) constraints for each user. Towards a practical application, successive convex approximation is developed to for its solution, where the nonconvex parts are converted into the simple convex quadratic functions at each iteration.
In the second paper, entitled “Coordinated Handover Signaling and Cross-Layer Adaptation in Heterogeneous Wireless Networking,” a cross-layer-based adaptive vertical handoff algorithm to reduce the handover latency and signaling overhead. In this way, the proposed cross-layer scheme is able to provide the sender with prediction of the available bandwidth. Evaluation results demonstrate the achieved improvements over the existing schemes.
In the third paper, entitled “Uplink Resource Allocation for Multi-Cluster Internet-of-Things Deployment Underlaying Cellular Networks,” to enable uplink transmission in multiple IoT groups/clusters, the authors consider Device-to-Device (D2D) communication technology, where the resource block (RB) of each cellular user is reused by multiple IoT devices (IoTDs). The authors formulate the optimization problem of joint resources and power allocation optimization to maximize both the IoTDs connectivity and cell throughput under the interference constraint. A heuristic, but efficient algorithm, namely greedy iterative matching (GIM), is proposed as for its suboptimal solution. Simulations results are provided to demonstrate that the proposed algorithm is capable of enhancing cell throughput gain and accessibility to IoTDs.
To cope with the mass and different communication requirements of tremendous intelligent vehicles, the authors of the fourth paper “Consortium Blockchain-Based Secure Software Defined Vehicular Network” design a decentralized trust management architecture which constitutes of three layers based on consortium blockchain. They propose a joint proof-of-stake and modified practical Byzantine fault tolerance (PoS-mPBFT) algorithm to reduce the confirmation time, where a prediction model is used to estimate trust value of vehicles in the next period. Numerical results show that the proposed trust management architecture and algorithm could provide better safety in SDVN and reduce consensus time.
To improve the efficient data transmission in 5G networks, the fifth paper “PBDT: An Energy-Efficient Posture based Data Transmission for Repeated Activities in BAN” considers a scheme, namely posture based data transmission (PBDT) which is based on the occurrence of potential (best) posture over time in repeated activities. In the proposed PBDT, each node first recognizes the sequence of postures by observing the variation of received signal strength indicator from neighbor nodes over time, and then finds the best posture from posture sequence for data transmission, and maintains a dynamic active/sleep schedule in order to reduce lossy transmission, collision and overhearing.
Motivated to solve the problem of the users’ discovery to timely communicate the emergency information, the sixth paper entitled “Full-Duplex Enabled Time-Efficient Device Discovery for Public Safety Communications” proposes to use the in-band full duplex (IB-FD) communication as an enabler to quickly discover the user due to simultaneous transmission and reception in the same time-frequency resource. In particular, the frame structure for IB-FD system with prioritized public safety (PS) users is proposed. Aiming at spectral efficiency, time-efficient device discovery resource allocation (TE-DDRA) scheme is also proposed, which is capable of switching the transmission mode from HD to IB-FD if the demand exceeds the available resources. Simulation results verify that with PS priority mode around 37% discovery time as compared with random access mode.
The seventh paper is on “Topology Optimizing in FSO-based UAVs Relay Networks for Resilience Enhancement” in which the free space optical (FSO) in unmanned aerial vehicles (UAVs) relay networks is considered. In particular, the authors investigate the network topology formation problem by considering the network resilience, where the resilience is referred to the ability of a network topology to defend against link failures. The network topology formation problem is formulated as a mixed integer nonlinear optimization problem to maximize the network resilience. To this end, two network resilience aware topology formation (NRATF) methods (i.e., centralized-NRATF and distributed-NRATF) are proposed to solve the topology designing problem efficiently.
The last paper in this special issue is “Performance Analysis of Full-Duplex Vehicle-to-Vehicle Relay System over Double-Rayleigh Fading Channels.” In this paper, the authors study the performance of a full-duplex (FD) relay system in vehicle-to-vehicle (V2V) communication, where the communication link from the source to relay node can be modeled by Rayleigh fading or double (cascaded) Rayleigh fading distributions while the link from the relay to the destination is modeled by double Rayleigh fading distribution. They derive the exact analytical expressions for the outage probabilities (OPs) and symbol error rates (SERs) in two cases, i.e. case A (the first hop is the Rayleigh fading channel and the second hop is double Rayleigh fading channel) and case B (two hops are the double Rayleigh fading channels). In addition, the impacts of the distances between the nodes and the residual self-interference at the FD relay are studied. Extensive numerical results are provide to show that the system performance in terms of OP and SER in the case of double Rayleigh fading channels is significant lower than the case of Rayleigh fading channels.