Search

In an orthogonal frequency division multiplexing (OFDM) system, cyclic prefix (CP) has to be added to eliminate multipath-induced inter-symbol interference (ISI) with a severely sacrificed bandwidth efficiency. Peak-to-average ratio (PAPR) may impair its performance further if a large number of carriers are used. On the other hand, traditional multi-carrier modulation suffers a prohibitive complexity, which can not be implemented with colorred current available silicon technologies. This work proposes a cost-effective way to implement multi-carrier modulation, namely multi-layer quadrature (MLQ) modulation, which requires only two oscillators. As an application example, we apply MLQ modulation to a complementary coded code division multiple access (MLQ-CC-CDMA) system, whose multi-carrier transmission is based on MLQ modulation to mitigate ISI and multi-user interference (MUI) with ideal auto- and cross-correlations of complementary codes. Compared to a frequency domain (FD) CC-CDMA system, MLQ-CC-CDMA has a lower RF complexity. Compared to OFDM direct sequence (DS) CDMA and single carrier frequency division multiple access (SC-FDMA) CDMA schemes, MLQ-CC-CDMA achieves a higher spectrum efficiency (SE) and a lower bit error rate with Rake and minimum mean square error (MMSE) detection due to its powerful multipath and multi-carrier diversity gains. [ABSTRACT FROM AUTHOR]

Vehicle-to-vehicle (V2V) underlay cellular communication plays an important role in the fifth-generation (5G) and beyond communications and its security issues attract a lot of attention. Physical layer security, which explores channel characteristics to protect wireless communications, is very attractive due to its low latency. This paper focuses on secrecy capacity maximization in V2V underlay cellular communications, where the secrecy capacity of vehicular user equipments (VUEs) is optimized first, followed by sum proportional fairness function optimization for both VUEs and cellular user equipments (CUEs). The optimization problems can be solved in two sub-problems, e.g., power and subcarrier allocation problems. The power allocation can be done with the first strategy using a one-dimensional searching algorithm, whereas a genetic algorithm (GA) is used to solve the second optimization problem. In addition, as VUEs share uplink resources with CUEs, the co-channel interference exists and the subcarrier allocation sub-problem is a 3D search problem, which is solved by a two-step iterative Hungarian algorithm (IHA). Finally, simulations are performed to validate the performance of the proposed schemes. [ABSTRACT FROM AUTHOR]

A traditional direct sequence CDMA (DS-CDMA) system works based on spreading codes, which should have good auto-correlation and cross-correlation properties to eliminate multiple access interference (MAI) and multipath interference (MI). However, to find a large number of good spreading codes is extremely difficult, and thus the capacity of a DS-CDMA system is limited strictly by the number of available spreading codes. This work proposes a downlink DS-CDMA design to enable multiple access using only one spreading code, namely identical code cyclic shift (ICCS) code, where in-phase and quadrature channels are used to transmit data and pilot, respectively. In particular, the ICCS code is used at a transmitter to perform DS modulation for user data, which is then sent to the in-phase channel. At the same time, the pilots are sent over the quadrature channel in a time-division multiplex (TDM) mode to construct a correlation matrix of ICCS code. At a receiver, MAI is removed by so-designed pilots plus a matched filter-bank. Simulation results show that the proposed ICCS multiple access (ICCSMA) can achieve a better performance than a traditional DS-CDMA system in a high signal to noise ratio region. ICCSMA serves as a bridge to turn CDMA to NOMA to enable massive connectivity in 5 G and beyond communications. [ABSTRACT FROM AUTHOR]

Machine-type data traffic volume in 5G networks will grow rapidly with widespread applications of MTC. The MTC devices, including home appliances, sensors, wearable devices, vehicles, and even low-altitude UAVs, will be made smarter with embedded advanced communication modules. However, a massive number of MTCDs with diverse QoS requirements cannot be served well by traditional wireless systems, which were primarily designed for human-type devices. New wireless technologies are needed to support distinct MTC network applications. In this article, five emerging MTC technologies, including Bluetooth 5, WiFi HaLow, LTE-M, NB-IoT, and WURs, are discussed, followed by a survey of 3GPP activities on vehicle-based and UAV-based MTC technologies, such as LTE-V2X and C-UAV for aerial vehicles. In the end, we also address the issues on the new trends for MTC networks with identified research challenges. [ABSTRACT FROM AUTHOR]

Cyclic prefix (CP) is used in OFDM/OFDMA systems for data transmission over multipath channels at a dear price of spectral efficiency degradation. This work aims to design a CP-free OFDM/OFDMA system for futuristic high-speed communications, where data block length can be shorter than channel delay spread. In particular, we utilize a time domain precoding scheme working jointly with a multiblock decision feedback equalization algorithm to mitigate intersymbol interference and intercarrier interference caused by multipath propagation. The satisfactory performance of the scheme is validated by simulation results, showing that the proposed CP-free OFDM/OFDMA scheme with known channel state information at transmitter and receiver offers a significantly higher spectral efficiency than traditional CP-based OFDM/OFDMA schemes. [ABSTRACT FROM AUTHOR]

Global connectivity, low latency, and ready-to-use infrastructure of next generation wireless (NGW) networks provide a platform for machine-to-machine (M2M) communications on a large scale. However, M2M communications over NGW networks pose significant challenges because of different data rates, diverse applications, and a large number of connections. In this paper, we address M2M challenges over NGW networks, and in particular, we focus on random access overload issue and diverse quality-of-service (QoS) requirements to enable M2M communications in the context of NGW networks. To enable massive M2M access while QoS guarantees, we propose group-based M2M communications on the basis of identical transmission protocols and QoS requirements. Furthermore, to guarantee low energy consumption for M2M devices in the same group, we propose a decentralized group-head selection scheme. In addition, a solution is proposed by using an effective capacity concept to provide QoS guarantees for M2M devices with a strict time constraint. A new random access approach based on different lengths super orthogonal codes is proposed to ease massive random access challenges with provisioning diverse QoS requirements of M2M communications in heterogeneous NGW networks. [ABSTRACT FROM AUTHOR]

In traditional orthogonal frequency division multiplexing (OFDM) systems, a cyclic prefix (CP) must be used in every block for intersymbol interference (ISI) suppression in time-dispersive channels at a price of severely impaired spectrum efficiency. To deal with this issue, the symbol cyclic shift equalization (SCSE) algorithm was proposed to implement a CP-free OFDM system. In this paper, we aim to further reduce the computational complexity of the SCSE algorithm. In particular, a pulse amplitude modulation (PAM) is used at a transmitter to construct conjugate symmetric OFDM blocks, while only partial samples in an OFDM block are involved in the SCSE algorithm at the receiver side, leading to a significantly reduced implementation complexity if compared to an SCSE quadratic-amplitude modulation(QAM)/phase-shift keying (PSK)-OFDM system, where all samples in an OFDM block must be involved in the detection process. The performance of the proposed SCSE PAM-OFDM scheme is analyzed and compared to traditional OFDM systems. The results obtained from this paper verify the effectiveness of the proposed scheme. [ABSTRACT FROM PUBLISHER]

A smart utility network (SUN), as defined in the IEEE 802.15.4g standard, is an emerging technology enabling reliable data transmissions in smart grid (SG) neighbourhood area networks. However, a SUN operates on unlicensed bands that are overlapped with most of the channels of wireless local area networks (WLANs). Thus, it is critical to investigate the coexistence issues for SUNs and WLANs in SG. This article aims to propose a dynamic spectrum sharing (DSS) coexistence scheme working with cognitive radio techniques, including the designs of network topology and channel detection/allocation schemes. We also establish Markov chain models based on channel state transitions for the proposed schemes, which are used to analyze network performance from the viewpoint of SUN services. The analytical results show that a channel reservation strategy is critical to ensure satisfactory performance of SUNs. [ABSTRACT FROM AUTHOR]

The use of cyclic prefix (CP) allows all existing orthogonal frequency-division multiplexing or multiple access (OFDM/OFDMA) systems to realize high-data-rate transmission in frequency-selective fading channels at the expense of losses in spectrum efficiency, energy efficiency, and transmission rate (SET). This paper proposes a CP-free OFDM/OFDMA design. Unlike traditional OFDM/OFDMA systems, the proposed CP-free OFDM/OFDMA does not insert CPs between symbols at the transmitter side. The neighboring symbols in frequency-selective fading channels will be overlapped at a receiver, and decision feedback equalization (DFE) is performed before FFT operation for intersymbol interference (ISI) removal. After DFE, each symbol consists of multipath returns with different linear shifts (LSs), which may result in intercarrier interference (ICI). Therefore, the output symbols from the DFE will be sent to a CP restoration unit for LS-to-cyclic-shift (CS) conversion. We call this a CP-free OFDM/OFDMA system symbol CS equalizing OFDM/OFDMA (SCSE-OFDM/OFDMA), whose system design is introduced in detail in this paper. We will show that SCSE-OFDM/OFDMA offers a much higher SET than traditional OFDM/OFDMA systems in frequency-selective fading channels. [ABSTRACT FROM PUBLISHER]

This paper proposes a framework to construct 3-D complementary codes (3DCCs), which enable chip-level space–time coding to integrate multiantenna and multiple-access techniques in a unified platform. The 3DCCs are generated based on an extension method with the help of traditional complementary codes and well-designed matrices. The relationship between the correlation properties and flock size of the constructed 3DCCs is analyzed, and the proposed framework provides a generic way to construct different families of 3DCCs with a controllable tradeoff between their correlation properties and flock sizes. As examples, three families of 3DCCs with different characteristic features are constructed using the framework, and their correlation properties are simulated to validate their properties. The general architecture of the 3DCC-based multiple-input multiple-output (MIMO) system is also proposed in this paper. The simulated bit-error-rate (BER) performance of the corresponding system over both flat and multipath fading channels show that the constructed 3DCCs can eliminate both multiuser and multipath interferences in multiuser MIMO communications. The property to provide both transmit diversity and multiplexing with its uniquely flexible tradeoff between the two also makes it particularly well suited for futuristic wireless communications to fit to varying channel conditions and application requirements. [ABSTRACT FROM PUBLISHER]

In this paper, we consider a multi-cell MISO downlink, where a multi-antenna base station (BS) sends messages to its intended user, while a passive eavesdropper tries to intercept the information in each cell. Physical layer security is employed in order to guarantee information security. Due to incomplete channel state information (CSI) at BSs, residue inter-cell interference exists even with coordinated beamforming, which exerts a great impact on the secrecy performance. In this paper, we conduct a unified performance analysis for physical layer security with incomplete CSI, and derives closed-form expressions of ergodic secrecy rate, secrecy outage probability, and interception probability, considering CSI estimation accuracy, transmit signal to noise ratio (SNR), and channel condition. We reveal some insights on the secrecy performance through asymptotic analysis. Furthermore, based on the derived theoretical results, we propose a CSI exchange amount allocation scheme. Finally, the simulations validate our theoretical claims. [ABSTRACT FROM AUTHOR]

Code-hopping multiple access (CHMA) is a newly emerging multiple-access technique with the potential to offer high capacity. Unfortunately, orthogonality among user signals in existing CHMA schemes can be preserved only in synchronous channels under an assumption that neither multipath interference (MI) nor multiple-access interference (MAI) exists. Exploiting their ideal orthogonality, we apply orthogonal complementary codes to CHMA systems to overcome problems with existing CHMA schemes. In particular, we will show that the application of orthogonal complementary codes can significantly improve the performance of a CHMA system due to its unique collision-resistant capability. To deal with destructive collisions among spreading codes in CHMA systems, convolutional coding is employed in complementary-coded CHMA systems. The properties and bit error rate (BER) performance of the proposed system are analyzed for both uplink and downlink applications, where the system may simultaneously suffer MI and MAI. Simulation results show that the complementary-coded CHMA with channel coding can provide much higher capacity than complementary-coded code-division multiple access (CDMA) systems in varying operational scenarios. [ABSTRACT FROM PUBLISHER]

This paper addresses the issues on spectrum sharing in a cognitive radio network consisting of a primary user and a group of cognitive users. Each cognitive user may occupy a non-overlapped sub-band of the primary spectrum, but it needs to perform spectrum sensing independently before accessing the sub-band. To reduce the complexity of spectrum sensing and thus energy consumption, this paper proposes a scheduled spectrum sensing scheme. First, we consider a single spectrum sensing scenario where only one cognitive user is elected to perform spectrum sensing, and then it broadcasts its sensing results to the other cognitive users. The scheduled spectrum sensing scheme works in both network-centric and user-centric ways. Next, the scheduled spectrum sensing scheme is further generalized to work in a multiple spectrum sensing scenario. The results show the effectiveness of the proposed schemes compared with the traditional schemes where all cognitive users may perform spectrum sensing at the same time. Copyright © 2010 John Wiley & Sons, Ltd. This paper proposes a scheduled spectrum sensing scheme for spectrum sharing in a cognitive radio network consisting of a primary user and a group of cognitive users. Both single and multiple scheduled spectrum sensing schemes are considered. The results show that in general the proposed scheduling schemes are more efficient than the extreme case in terms of the number of sensing operations required with a given sum false alarm probability and the sum-missed detection probability. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The Health Insurance Portability and Accountability Act (HIPAA) has set privacy and security regulations for the US healthcare industry. HIPAA has also established principles for security standards that global e-health industry tends to follow. In this paper, a hybrid public key infrastructure solution (HPKI) is proposed to comply with the HIPAA regulations. The main contribution is the new e-health security architecture that is contract oriented instead of session oriented which exists in most literatures. The proposed HPKI has delegated the trust and security management to the medical service provider during the contract period, which is more realistic. It is much an analogy to existing paper based health care systems in terms of functional structure. The cryptographically strong PKI scheme is deployed for the mutual authentication and the distribution of sensitive yet computational non-intensive data while efficient symmetric cryptographic technology is used for the storage and transmission of high volume of medical data such as medical images. One advantage is that the proposed HPKI can be constructed from existing cryptographic technologies where various relevant security standards, tools and products are available. Discussion has been provided to illustrate how proposed schemes can address the HIPAA privacy and security regulations. [Copyright &y& Elsevier]

An introduction is presented in which the editors discuss various reports within the issue on topics including dynamic spectrum access in cognitive radio systems, a new video-on-demand (VoD) architecture based on mesh-based peer-to-peer (P2P) overlay networks, and sensor scheduling issues in target tracking systems with the use of ultrasonic sensors.

An introduction to the journal is presented in which the editor discusses wireless networking, computer systems, and ad hoc networks.

Growing computation requirements in emerging intelligently connected vehicle (ICV) networks has posed a big challenge for vehicles to process computation-intensive tasks on-board, and thus computation partition and offloading plays a critical role. Owing to broadcast nature of wireless channels, confidential messages without proper security protection in ICVs may be easily exposed to malicious users. In this paper, a mobile crowdsourcing (MCS) based mobile crowd computing framework for ICV networks is proposed, where multiple vehicles act as workers to provide computing services for end user (EU). In particular, artificial noise (AN) assisted physical (PHY) layer security approaches are used to enhance the security in offloading links. Ergodic secrecy rates in different offloading phases in time-varying channels are derived. In addition, an incentive-driven mechanism is introduced to encourage workers to share their idle computing resources, and an optimization problem is formulated to minimize the overall price paid for computing tasks, subject to energy consumption and delay constraints. Finally, Monte Carlo simulations verify the analysis on the ergodic secrecy rates. [ABSTRACT FROM AUTHOR]

With 5G mobile communication systems having been commercially rolled out, research discussions on next generation mobile systems, that is, 6G, have started. On the other hand, vehicular technologies are also evolving rapidly, from connected vehicles called V2X (vehicle to everything) to autonomous vehicles to the combination of the two, that is, the networks of connected autonomous vehicles (CAV). How fast the evolution of these two areas will go hand-in-hand is of great importance, which is the focus of this article. After a brief overview of the technological evolution of V2X to CAV and 6G key technologies, this article explores two complementary research directions, namely, 6G for CAVs versus CAVs for 6G. The former investigates how various 6G key enablers, such as THz, cell free communication and artificial intelligence (AI), can be utilized to provide CAV mission-critical services. The latter discusses how CAVs can facilitate effective deployment and operation of 6G systems. This article attempts to investigate the interactions between the two technologies to spark more research efforts in these areas. [ABSTRACT FROM AUTHOR]

The concept of software defined wireless networks (SDWN) has been rapidly evolving as the solution to meet the demand for dynamic wireless services in ubiquitous computing. In SDWN, the control plane and data plane are decoupled, network intelligence is logically centralized, and the underlying network infrastructure is abstracted from the applications. Thus it highly simplifies network administration and management, which facilitates the dynamic nature of future network functions and intelligent applications while lowering operating costs through simplified hardware, software, and management. This is the second part of the ?Software Defined Wireless Networks (SDWN)? Feature Topic. In Part 1, which was published in November 2015, we provided an overview of the latest major developments and progress in SDWN architecture. In this Part II, we present articles that provide fruitful insights into selected topics such as Cloud-RAN management, flexible spectrum management, SDWN security, and SDN-based self organizing strategies. We believe that it complements Part I, and together they provide a holistic overview of features and trends in future SDWN development. [ABSTRACT FROM PUBLISHER]

The growing popularity of smart phones, tablet computers and mobile cloud services places an increasing demand for dynamic services from wireless networks. This demand creates new requirements for the network architecture, such as flexibility in management and configuration, adaptability and vendor-independence. To meet these requirements, software defined wireless network (SDWN) has been proposed as a cost-effective solution. SDWN decouples the data plane from the control plane, enabling direct programmability of network controls and an abstraction of the underlying infrastructure for wireless applications. With SDWN, we can create a service delivery platform that is adaptable to the users? varying demands. However, issues such as supporting a large number of subscribers, frequent mobility, fine-grained measurement and control, and real-time adaptation need to be addressed by future SDWN architectures. In this Feature Topic, we provide an overview of the latest major developments and progresses in SDWN. [ABSTRACT FROM PUBLISHER]

In a frequency division complementary coded CDMA (FD-CC-CDMA) system, multiple tuners have to be used for multi-carrier modulation, which has a very high complexity and power consumption. In this paper, we propose a CP-free OFDM scheme to implement multi-carrier modulation in an FD-CC-CDMA system, which is named as CP-free OFDM-CC-CDMA system. The transmitter in the CP-free OFDM-CC-CDMA system offers a unique flexibility to adjust the amount of data processed at the same time to ensure that the OFDM block size exceeds the delay spread of a multipath channel, which attributes to effective mitigation of multipath induced inter-symbol interference (ISI). At the receiver of a CP-free OFDM-CC-CDMA system, minimum mean square error (MMSE) equalization and MMSE combining are used to mitigate multi-user interference (MUI) and inter-carrier interference (ICI). The obtained results show that a CP-free OFDM-CC-CDMA system offers a much higher transmission efficiency than FD-CC-CDMA and OFDM-DS-CDMA systems. In addition, the proposed CP-free OFDM-CC-CDMA system outperforms OFDM-DS-CDMA system in terms of bit error rate due to its inherent powerful diversity gain. [ABSTRACT FROM AUTHOR]

This article aims to provide a comprehensive overview on PHY layer security assisted ICV networks. Beginning with a discussion from a general perspective of the ICV network architecture, this work summarizes the major security threats faced by ICV networks. To achieve confidential data transmission with a low latency and a high data rate, several physical layer security schemes are surveyed in this article, which include RRM, cooperative jamming, multi-antenna technologies, and PHY-layer key generation. In addition, the performances of the aforementioned schemes are compared in terms of different aspects, followed by a discussion on some major challenges that need to be tackled in the implementation of ICV networks. [ABSTRACT FROM AUTHOR]

In device-to-device (D2D) underlaying vehicle-to-vehicle (V2V) communications, radio resource blocks (RBs) are allocated to primary cellular users, which yields sub-optimal rates and a long access latency for secondary D2D-enabled vehicles. This work investigates a joint radio resource and power management (RRPM) problem for secure cellular underlaying V2V communications, where cellular users and vehicles have the same priority, giving vehicles more opportunities to access the RBs. Specifically, we aim to maximize secrecy rates of V2V channels under the condition that eavesdropper has an adaptive receiving detection vector to maximize the received signal-to-interference-plus-noise ratio (SINR) from vehicles. For a single pair of a vehicle and a cellular user, the closed-form optimal power allocation expressions are derived for the interference-limited scenario and the noise-limited scenario, respectively. Moreover, for multiple pairs of vehicles and cellular users, a 3-partite hypergraph based 3-dimensional matching approach is proposed to solve a mixed-integer and non-convex problem, which achieves a near-optimal result with an $O(n^4)$ time complexity. Simulations in different scenarios show that the secrecy rate of the proposed scheme can be improved by 50% if compared to existing schemes. [ABSTRACT FROM AUTHOR]

Due to its high speed and low latency, D2D communication plays an important role in providing proximity data services in 5G systems, which may contain privacy sensitive data. Covert communication is useful to protect the privacy of user data against adversaries. In a D2D underlaying cellular network, an antenna array can be used at a base station (BS) to transmit artificial noise to confuse adversaries that try to detect D2D covert signals. Based on the numbers of antennas at BS, two covert schemes are presented in this work and their performances are evaluated in terms of D2D covert throughput, i.e., maximum achievable D2D data rate with the given covertness requirements. As only channel distribution information (CDI) of adversary links is known to the BS, the average minimum error probability (AMEP) is used as a metric to measure the covertness performance. In the proposed schemes, closed-form expressions of the minimum AMEP and achievable D2D data rate are derived. It is shown that the derivation of minimum AMEP can be simplified if either one or massive antennas are allocated for sending artificial noise. The analytical results are compared to Monte-Carlo simulation results to verify the feasibility of the proposed schemes. It is also revealed that covert throughput can be further improved by setting system parameters properly, e.g., the number of antennas at BS and artificial noise transmit power. [ABSTRACT FROM AUTHOR]

Device-to-device (D2D) communication is a promising technique to enhance the spectrum efficiency of a cellular network. However, one of the major challenges in D2D communications is to select appropriate communication modes for all possible D2D pairs in a D2D network. In this paper, we study the mode selection problems in a multi-mode and multi-pair D2D network, where the eNB can assign one of the three D2D communication modes (including local route mode, direct D2D mode, and relay D2D mode) to each D2D pair. To achieve the maximal cell-wise capacity, an optimal mode selection algorithm is proposed in this paper with the aim to share cellular users’ uplink channels. The optimal mode selection problem can be modeled by an integer programming problem. Particularly, in a fully loaded cell, we discover that the optimal mode selection problem can be solved using a linear programming algorithm with a significantly reduced complexity. [ABSTRACT FROM AUTHOR]

Small cell base stations (SBSs) in 5G and beyond networks will play multiple roles in addition to radio access, and will be deployed in a very high density. They can facilitate mobile edge computing (MEC), such that SBSs can store, process, and control network data signals, becoming important elements in ultra-dense networks (UDNs). However, intercell interference may jeopardize the gains from network densification, and thus coordinated multi-point (CoMP) transmission is important in UDNs. MEC and CoMP are different technologies, but they can work jointly to benefit UDNs. In this article, we aim to bridge the gap between MEC and CoMP based on three MEC functions. We will show that CoMP transmission reduces UDN complexity and transmission delay with collaboration among MEC servers in UNDs. In return, MEC-enabled UDNs can alleviate the backhaul pressure on CoMP transmission and make it possible to implement scalable CoMP. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including wireless local area networks, critical aspects of cognitive orthogonal frequency division mutiplexing (OFDM) systems, and ways to improve Attribute-Based Encryption's (ABE) efficiency.

Increased intelligence and automation in smart grid results in many heterogeneous applications benefiting from the Internet of Things, such as demand response, energy delivery efficiency/reliability, and fault recovery. However, vulnerabilities in smart grid arise due to public communication infrastructure and Internet-based protocols. To deal with security threats, energy big data should be thoughtfully stored and processed to extract critical information, and security and blackout warnings should be given in an early stage. This work gives a comprehensive tutorial and survey to highlight research challenges on the aforementioned issues in the Internet-of-Things-based smart grid. We demonstrate that a stealthy and blind energy big data attack can be launched using a replay scheme. Also, we elucidate an intuitive geometric viewpoint for this type of attack. The proposed attack can bypass bad data detection successfully using either DC or AC state estimation. [ABSTRACT FROM AUTHOR]

Ultra-dense networks (UDNs) are one of the key enabling techniques for implementation of 5G wireless communication systems, and inter-cell interference is a major issue in UDNs. Coordinated Multipoint Joint Transmission (CoMP-JT) helps reduce inter-cell interferences. However, due to randomly and densely distributed access entities in UDNs, many challenging issues need to be dealt with to implement CoMP-JT in UDNs. In this article, we aim to address the issues on how to achieve maximal per area spectral efficiency in UDNs based on CoMP-JT technology. The performance of UDNs with different joint transmission schemes are evaluated with the help of computer simulations to show the effective deployment schemes of small cells. [ABSTRACT FROM AUTHOR]

Providing diverse and strict quality-of-service (QoS) guarantees is one of the most important requirements in machine-to-machine (M2M) communications, which is particularly need for appropriate resource allocation for a large number of M2M devices. To efficiently allocate resource blocks (RBs) for M2M devices while satisfying QoS requirements, we propose group-based M2M communications, in which M2M devices are clustered based on their wireless transmission protocols, their QoS characteristics, and their requirements. To perform joint RB and power allocation in SC-FDMA-based LTE-A networks, we formulate a sum-throughput maximization problem, while respecting all the constraints associated with SC-FDMA scheme, as well as QoS requirements in M2M devices. The constraints in uplink SC-FDMA air interface in LTE-A networks complicate the resource allocation problem. We solve the resource allocation problem by first transforming it into a binary integer programming problem and then formulate a dual problem using the Lagrange duality theory. Numerical results show that the proposed algorithm outperforms traditional Greedy algorithm in terms of throughput maximization while satisfying QoS requirements, and its performance is close to the optimal design. [ABSTRACT FROM PUBLISHER]

With an increasing demand to improve spectrum efficiency and energy efficiency in cellular networks, device-to-device (D2D) communications have drawn a lot of attention from both academia and industry. Cooperative D2D networking, which allows for cooperation among mobile users (MUs) via D2D links while communicating with other MUs or base stations (BSs), is one of the most promising techniques in D2D communications. In cooperative D2D communications, two major issues need to be investigated: network performance evaluation and peer selection. In order to enhance evaluation accuracy while maintaining data privacy, it is essential to employ social interactions among MUs in cooperative D2D communications. In this article, we investigate social aware cooperative D2D networks. We first introduce social relationship formation, and then social learning based cooperative network evaluation and social relationship based peer selection are investigated, respectively. Numerical results show the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

The article discusses several authentication issues related to smart grid applications and proposes a machine-to-machine (M2M) authentication process. It mentions that the authetication process involves two-way communications between smart meters and the utility. It adds that the authentication process envisions an interconnected power distribution network that streamlines energy production, power transmission and monitoring.

Mobile cloud computing (MCC) can significantly improve the processing/storage capacity and standby time of mobile terminals by migrating data processing and storage to the remote cloud. However, due to the wireless resource limitations of access points/base stations, data streaming of MCC suffers poor quality-of-service (QoS) in multiuser multiservice scenarios, such as long buffering time and intermittent disruptions. In this paper, we propose a backoff-based wireless resource scheduling (BWRS) scheme, in which real-time services have higher priority than non-real-time services. BWRS can improve the QoS of real-time streams and the overall performance of MCC networks. We formulate an M/M/1 queueing model and propose a queueing-delay-optimal control algorithm to minimize the average queueing delay of non-real-time services. Furthermore, a delay-constrained control algorithm is developed not only to minimize the queueing delay of non-real-time services of multiservice users but to support users' non-real-time services under delay constraints as well. The simulation results show that the proposed scheme can minimize the average queueing delay while still meeting the delay requirement and can significantly improve blocking probability and channel utilization. [ABSTRACT FROM PUBLISHER]

Due to its flexible deployment and high mobility of unmanned aerial vehicles (UAVs), the UAV-assisted cognitive radio (CR) network has attracted a lot of attention as one of the most promising techniques to address spectrum congestion issues in futuristic networks. However, its performance can be severely affected by the blocked line-of-sight (LoS) channel in its air-to-ground (A2G) links. In this paper, we propose a UAV CR system enabled by a reconfigurable intelligent surface (RIS), which helps to reconstruct reliable links in UAV-assisted cognitive radio (CR) networks. Our goal is to maximize the achievable rate of a secondary receiver (SR) through the proper selection of the UAV trajectory, transmit power, and RIS phase shifts based on a given interference temperature threshold and other practical constraints. In addition, we solve the corresponding non-convex optimization problem using block coordinate descent (BCD) and successive convex approximation (SCA) algorithms. The simulation results will demonstrate the effectiveness of the proposed algorithms. [ABSTRACT FROM AUTHOR]

Owing to ideal correlation properties of complementary codes (CCs), a complementary coded code-division multiple-access (CC-CDMA) system outperforms traditional CDMA systems in terms of its interference–resistance capabilities. However, it may lose its interference–resistance feature and suffer performance degradation over asynchronous frequency-selective fading channels due to the fact that it is incapable of reconstructing ideal complementary cross-correlation functions at a receiver. Based on the analysis on combining and detection algorithms designed for CC-CDMA systems, this paper proposes a joint pre-equalization and adaptive combining scheme. Pre-equalization is used at a transmitter to either enhance diversity gain or compensate channel selectivity leveraged by a controlling parameter $\zeta$, whereas a recursive least square (RLS) adaptive combining algorithm is employed at a receiver to determine the optimal combining coefficients, aiming at minimizing detection errors under different channel conditions. Simulation results show the superiority of the proposed scheme in terms of bit error rate (BER) and its adaptability to varying channel states. [ABSTRACT FROM AUTHOR]

Due to random arrivals of primary-user signals, the timing misalignment issue should be considered for spectrum sensing in cognitive radio (CR) systems, such as CR-based femtocell networks. To deal with this issue, two approaches were recommended in the literature, including Bayesian and generalized likelihood ratio test (GLRT) detectors. However, the Bayesian test requires perfect knowledge of the distribution of unknown parameters. Therefore, it is impractical due to its implementation complexity. To design a low-complexity energy detector (ED), this work proposes an ED scheme based on the GLRT algorithm. As a result, maximum-likelihood estimation for the timing misalignment is devised, and the performance of the proposed scheme is analyzed. The results show that the proposed GLRT detector features a low-complexity and satisfactory performance. [ABSTRACT FROM PUBLISHER]

Physical-layer network coding (PNC) is an attractive technique because it can significantly enhance the throughput of a wireless network with a relatively simple implementation, as compared with conventional network coding (NC) schemes. In this paper, we first investigate PNC with frequency shift keying (FSK) through the derivation of its bit-error rate (BER) and capacity, as well as the impact of imperfect synchronization to the overall performance. Based on the discussions on PNC with 2FSK, we then further expand the analysis to PNC with $M$-ary FSK (MFSK). Theoretical results indicate that the BER performance of PNC with 2FSK is a bit worse than that of PNC with 2PSK. As the constellation dimension $M$ increases, the BER performance of PNC with $M$-ary FSK improves at the expense of bandwidth efficiency degradation. [ABSTRACT FROM PUBLISHER]

Although 5G networks have enabled mobile users to get a better experience, task scheduling remains challenging for massive Internet of Things (IoT) devices in remote areas. This paper investigates the task scheduling problem for delay-aware IoT applications in civil aircraft-augmented space-air-ground integrated networks (CAA-SAGIN), where the normalized sky access platforms (SAPs) can collect and forward the terrestrial tasks. Specifically, we first propose an access control scheme for a non-preemptive priority queuing system and a transmission control scheme with cross-layer optimization. Secondly, considering the uncertain distribution of the transmission numbers and generated data, we formulate a robust two-stage stochastic optimization problem of delay minimization. With the proposed robust task scheduling with risk aversion (RTS-RA) algorithm, the original problem can be decomposed into two subproblems, which can be further transformed into tractable semi-definite program (SDP) problems respectively. Simulation results show that the cross-layer optimization scheme can achieve a good tradeoff between delay and throughput. Also, the RTS-RA algorithm outperforms the exiting offloading schemes in terms of end-to-end delay, transmitted data, and energy consumption with lower computational complexity. [ABSTRACT FROM AUTHOR]

Normally, authentication in vehicular ad hoc networks (VANETs) uses public key infrastructure to verify the integrity of messages and the identity of message senders. The issues considered in the authentication schemes include the level of security and computational efficiency in the verification processes. Most existing schemes mainly focus on assuring the security and privacy of VANET information. However, these schemes may not work well in VANET scenarios. For instance, it is difficult for a roadside unit (RSU) to verify each vehicle's signature sequentially when a large number of vehicles emerge in the coverage areas of an RSU. To reduce the computational overhead of RSUs, we propose a proxy-based authentication scheme (PBAS) using distributed computing. In the PBAS, proxy vehicles are used to authenticate multiple messages with a verification function at the same time. In addition, the RSU is able to independently verify the outputs from the verification function of the proxy vehicles. We also design an expedite key negotiation scheme for transmitting sensitive messages. It is shown from the analysis and simulations that an RSU can verify 26 500 signatures per second simultaneously with the help of the proxy vehicles. The time needed to verify 3000 signatures in the PBAS can be reduced by 88% compared with existing batch-based authentication schemes. [ABSTRACT FROM PUBLISHER]

This article reviews an emerging wireless information and power transfer (WIPT) technique with an emphasis on its performance enhancement employing multi-antenna techniques. Compared to traditional wireless information transmission, WIPT faces numerous challenges. First, it is more susceptible to channel fading and path loss, resulting in a much shorter power transfer distance. Second, it gives rise to the issue of how to balance spectral efficiency for information transmission and energy efficiency for power transfer in order to obtain an optimal tradeoff. Third, there exists a security issue for information transmission in order to improve power transfer efficiency. In this context, multi-antenna techniques, e.g. energy beamforming, are introduced to solve these problems by exploiting spatial degree of freedom. This article provides a tutorial on various aspects of multi-antenna based WIPT techniques, with a focus on tackling the challenges by parameter optimization and protocol design. In particular, we investigate the WIPT tradeoffs based on two typical multi-antenna techniques: the limited feedback multi-antenna technique for short-distance transfer; and the large-scale multiple-input multiple-output (LS-MIMO, also known as massive MIMO) technique for long-distance transfer. Finally, simulation results validate the effectiveness of the proposed schemes. [ABSTRACT FROM PUBLISHER]

Despite many attractive features of an orthogonal frequency-division multiplexing (OFDM) system, the signal detection in an OFDM system over multipath fading channels remains a challenging issue, particularly in a relatively low signal-to-noise ratio (SNR) scenario. This paper presents an iterative synchronization-assisted OFDM signal detection scheme for cognitive radio (CR) applications over multipath channels in low-SNR regions. To detect an OFDM signal, a log-likelihood ratio (LLR) test is employed without additional pilot symbols using a cyclic prefix (CP). Analytical results indicate that the LLR of received samples at a low SNR can be approximated by their log-likelihood (LL) functions, thus allowing us to estimate synchronization parameters for signal detection. The LL function is complex and depends on various parameters, including correlation coefficient, carrier frequency offset (CFO), symbol timing offset, and channel length. Decomposing a synchronization problem into several relatively simple parameter estimation subproblems eliminates a multidimensional grid search. An iterative scheme is also devised to implement a synchronization process. Simulation results confirm the effectiveness of the proposed detector. [ABSTRACT FROM PUBLISHER]

SUMMARY Resource reservation or the other prioritization strategies adopted by Call Admission Control (CAC) schemes in wireless networks lead to unfair resource allocation to users belonging to different service classes (SCs) due to high divergence among the respective call blocking probabilities (CBPs). In this paper, we propose dynamic optimization of probabilistic CAC (P-CAC) schemes to assure CAC fairness among users of different SCs in wireless networks. The approach is based on users utility combined with fairness optimization, aiming at dynamically determining the probability value in the P-CAC scheme. This optimal probability is adjusted to network ongoing traffic, CBPs of each SC, prioritization levels characterizing the SCs supported, and the users risk aversion, which reflects their behavior toward the perceived QoS. The existence and uniqueness of the optimal probability that leads to absolute fairness among the users of a wireless network are proven. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The performance analysis of a distributed access wireless network, in which nodes are randomly distributed [namely, a random wireless network (RWN)] over a large area, is challenging. An effective mathematical modeling of these networks can help network designers to predict whether a given set of quality-of-service (QoS) requirements can be satisfied prior to the real network deployment. Previous models for the performance analysis of multihop RWNs fail to give accurate results due to the assumption of a single-hop, limited, and a priori known number of stations; negligence of the hidden terminals; and the use of a Boolean logic collision model. In this paper, we develop an alternative probabilistic modeling approach to analyze the performance of these networks in medium-access-control (MAC) and network layers. Using the proposed modeling approach and obtained metrics, we can identify a set of optimal parameters to maximize the performance of the networks. [ABSTRACT FROM PUBLISHER]

Smart grid is an intelligent power network featured by its two-way flows of electricity and information. With an integrated communication infrastructure, smart grid manages the operation of all connected components to provide reliable and sustainable electricity supplies. Many advanced communication technologies have been identified for their applications in different domains of smart grid networks. This paper focuses on wireless communication networking technologies for smart grid neighborhood area networks (NANs). In particular, we aim to offer a comprehensive survey to address various important issues on implementation of smart grid NANs, including network topology, gateway deployment, routing algorithms, and security. We will identify four major challenges for the implementation of NANs, including timeliness management, security assurance, compatibility design, and cognitive spectrum access, based on which the future research directions are suggested. [ABSTRACT FROM PUBLISHER]

Scrambling code planning (SCP) for time-division synchronous code-division multiple-access (TD-SCDMA) systems is a challenging issue due to the poor cross correlations between the spreading codes generated by cell-specific scrambling codes. In this paper, a novel SCP algorithm is proposed. Intercell interference is modeled as a function not only of the cross correlations between spreading codes but of the radio propagation conditions and traffic distributions as well. The cross correlation of spreading codes is analyzed, and the concept of the scrambling code family is proposed to simplify the code planning process. The proposed algorithm facilitates the assignment and selection of scrambling codes. Numerical results shows that the proposed algorithm can achieve a much lower intercell interference than the existing SCP algorithms. [ABSTRACT FROM PUBLISHER]

In this paper, we consider a secrecy relaying communication scenario where all nodes are equipped with multiple antennas. An eavesdropper has the access to the global channel state information (CSI), and all the other nodes only know the CSI not associated with the eavesdropper. A new secrecy transmission protocol is proposed, where the concept of interference alignment is combined with cooperative jamming to ensure that artificial noise from transmitters can be aligned at the destination, but not at the eavesdropper due to the randomness of wireless channels. Analytical results, such as ergodic secrecy rate and outage probability, are developed, from which more insightful understanding of the proposed protocol, such as multiplexing and diversity gains, can be obtained. A few special cases, where outage probability cannot be decreased to zero regardless of SNR, are also discussed. Simulation results are provided to demonstrate the performance of the proposed secrecy transmission protocol. [ABSTRACT FROM AUTHOR]

SUMMARY Link adaptation (LA) plays an important role in adapting an IEEE 802.11 network to wireless link conditions and maximizing its capacity. However, there is a lack of theoretic analysis of IEEE 802.11 LA algorithms. In this article, we propose a Markov chain model for an 802.11 LA algorithm (ONOE algorithm), aiming to identify the problems and finding the space of improvement for LA algorithms. We systematically model the impacts of frame corruption and collision on IEEE 802.11 network performance. The proposed analytic model was verified by computer simulations. With the analytic model, it can be observed that ONOE algorithm performance is highly dependent on the initial bit rate and parameter configurations. The algorithm may perform badly even under light channel congestion, and thus, ONOE algorithm parameters should be configured carefully to ensure a satisfactory system performance. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The successful application of pervasive services running in mobile wireless networks and devices relies on its ability to provide efficient and cost-effective QoS (Quality of Service) support. This paper proposes a comprehensive QoS model specifically for pervasive services. It considers not only user-perceived factors but also mobile wireless network characteristics. The corresponding formula to calculate each QoS criterion is also devised. In particular, this paper formulates the QoS-aware service selection problem for pervasive service composition and proposes some solutions to the problem, i.e., global-search-based LOSSA (local optimal service selection algorithm) and limited broadcast based LOSSA- k. The evaluation results of the algorithms have shown the effectiveness of the QoS model and the efficiency of the proposed LOSSAs. [ABSTRACT FROM AUTHOR]

Orthogonal user pairing (OUP) was proposed for virtual multiple-input multiple-output (V-MIMO) in uplink 3G LTE system. However, its complexity is too high for practical implementation, especially when user population is large. To improve on this, semi-orthogonal user pairing (SUP) was suggested as an alternative. In this paper, two novel SUP algorithms, namely correlative angle-based SUP (CA-SUP) and Frobenius norm-based SUP (FN-SUP) algorithms are proposed. In view of the fact that ideal power control is difficult to implement, fixed power allocation (FPA) and adaptive power allocation (APA) constraints for the user pairing algorithms are introduced. Ergodic capacities for CA-SUP and FN-SUP algorithms with APA and FPA constraints, in terms of the numbers of users and antennas at Node-B, are evaluated and their capacity upper bounds are derived. Analysis and simulation results show that FN-SUP and CA-SUP algorithms requiring only limited channel state information (CSI) perform well and suit in particular for virtual V-MIMO systems. [ABSTRACT FROM AUTHOR]