Wireless Communications and Networking

Low Power Wide Area (LPWA) networks are attracting a lot of attention primarily because of their ability to offer affordable connectivity to the low-power devices distributed over very large geographical areas. In realizing the vision of the Internet of Things (IoT), LPWA technologies complement and sometimes supersede the conventional cellular and short range wireless technologies in performance for various emerging smart city and machine-to-machine (M2M) applications. This review paper presents the design goals and the techniques, which different LPWA technologies exploit to offer wide-area coverage to low-power devices at the expense of low data rates. We survey several emerging LPWA technologies and the standardization activities carried out by different standards development organizations (e.g., IEEE, IETF, 3GPP, ETSI) as well as the industrial consortia built around individual LPWA technologies (e.g., LORa Alliance,WEIGHTLESS-SIG, and DASH7 Alliance). We further note that LPWA technologies adopt similar approaches, thus sharing similar limitations and challenges. This paper expands on these research challenges and identifies potential directions to address them. While the proprietary LPWA technologies are already hitting the market with large nationwide roll-outs, this paper encourages an active engagement of the research community in solving problems that will shape the connectivity of tens of billions of devices in the next decade.

Wireless charging is a technology of transmitting
power through an air gap to electrical devices for the purpose
of energy replenishment. The recent progress in wireless
charging techniques and development of commercial products
have provided a promising alternative way to address the energy
bottleneck of conventionally portable battery-powered devices.
However, the incorporation of wireless charging into the existing
wireless communication systems also brings along a series of
challenging issues with regard to implementation, scheduling, and
power management. In this article, we present a comprehensive
overview of wireless charging techniques, the developments
in technical standards, and their recent advances in network
applications. In particular, with regard to network applications,
we review the static charger scheduling strategies, mobile charger
dispatch strategies and wireless charger deployment strategies.
Additionally, we discuss open issues and challenges in implementing
wireless charging technologies. Finally, we envision some
practical future network applications of wireless charging.

Spectrum efficiency and energy efficiency are two critical issues in designing wireless networks. Through dynamic spectrum access, cognitive radios can improve the spectrum efficiency and capacity of wireless networks. On the other hand radio frequency (RF) energy harvesting has emerged as a promising technique to supply energy to wireless networks and thereby increase their energy efficiency. Therefore, to achieve both
spectrum and energy efficiency, the secondary users in a cognitive radio network (CRN) can be equipped with the RF energy harvesting capability, and such a network can be referred to as an RF-powered cognitive radio network. In this article we provide an overview of the RF-powered CRNs and discuss the challenges that arise for dynamic spectrum access in these networks. Focusing on the trade-off among spectrum sensing, data transmission, and RF energy harvesting,
we then discuss the dynamic channel selection problem in a multi-channel RF-powered CRN. In the RF-powered CRN a secondary user can adaptively select a channel to transmit
data when the channel is not occupied by any primary user. Alternatively, the secondary user can harvest RF energy for data transmission if the channel is occupied. The optimal channel selection policy of the secondary user can be obtained
by formulating a Markov decision process (MDP) problem. We present some numerical results obtained by solving this MDP problem.

Low Power Wide Area (LPWA) networks are making spectacular progress from design, standardisation, to commercialisation. At this time of fast-paced adoption, it is of utmost importance to analyse how well these technologies will scale as the number of devices connected to the Internet of Things (IoT) inevitably grows. In this letter, we provide a stochastic geometry framework for modelling the performance of a single gateway LoRa network, a leading LPWA technology. Our analysis formulates unique peculiarities of LoRa, including its chirp spread-spectrum modulation technique, regulatory limitations on radio duty cycle, and use of ALOHA protocol on top, all of which are not as common in today's commercial cellular networks. We show that the coverage probability drops exponentially as the number of end-devices grows due to interfering signals using the same spreading sequence. We conclude that this fundamental limiting factor is perhaps more significant towards LoRa scalability than for instance spectrum restrictions. Our derivations for co-spreading factor interference found in LoRa networks enables rigorous scalability analysis of such networks.

The millimeter wave (mmWave) frequency band is seen as a key enabler of multi-gigabit wireless access in future cellular networks. In order to overcome the propagation challenges, mmWave systems use a large number of antenna elements both at the base station and at the user equipment, which lead to high directivity gains, fully-directional communications, and possible noise-limited operations. The fundamental differences between mmWave networks and traditional ones challenge the classical design constraints, objectives, and available degrees of freedom. This paper addresses the implications that highly directional communication has on the design of an efficient medium access control (MAC) layer. The paper discusses key MAC layer issues, such as synchronization, random access, handover, channelization, interference management, scheduling, and association. The paper provides an integrated view on MAC layer issues for cellular networks, identifies new challenges and tradeoffs, and provides novel insights and solution approaches.

Cellular networks have evolved to support high peak bitrates with low loss rates as observed by the higher layers. However, applications and services running over cellular networks are now facing other difficult congestion-related challenges, most notably a highly variable link capacity and bufferbloat. To overcome these issues and improve performance of network traffic in 4G/5G cellular networks, a number of in-network and end-to-end solutions have been proposed. Fairness between interacting congestion control algorithms (CCAs) has played an important role in the type of CCAs considered for research and deployment. The placement of content closer to the user and the allocation of per-user queues in cellular networks has increased the likelihood of a cellular access bottleneck and reduced the extent of flow interaction between multiple users. This has resulted in renewed interest in end-to-end CCAs for cellular networks by opening up room for research and exploration. In this work, we present end-to-end CCAs that target a high throughput and a low latency over highly variable network links, and classify them according to the way they address the congestion control. The work also discusses the deployability of the algorithms. In addition, we provide insights into possible future research directions, such as coping with a higher degree of variability, interaction of CCAs in a shared bottleneck, and avenues for synergized research, such as CCAs assisted by software defined networking and network function virtualization. We hope that this work will serve as a starting point for systematically navigating through the expanding number of cellular CCAs.

The need for low power, long range and low cost connectivity to meet the requirements of IoT applications has led to the emergence of Low Power Wide Area (LPWA) networking technologies. The promise of these technologies to wirelessly
connect massive numbers of geographically dispersed devices at a low cost continues to attract a great deal of attention in the academic and commercial communities. Several rollouts are already underway even though the performance of these technologies is yet to be fully understood. In light of these developments, tools to carry out ‘what-if analyses’ and predeployment studies are needed to understand the implications of choices that are made at design time. While there are several
promising technologies in the LPWA space, this paper specifically focuses on the LoRa/LoRaWAN technology. In particular, we present LoRaWANSim, a simulator which extends the LoRaSim tool to add support for the LoRaWAN MAC protocol, which
employs bidirectional communication. This is a salient feature not available in any other LoRa simulator. Subsequently, we provide vital insights into the performance of LoRaWAN based networks through extensive simulations. In particular, we show
that the achievable network capacity reported in earlier studies is quite optimistic. The introduction of downlink traffic can have a significant impact on the uplink throughput. The number of transmit attempts recommended in the LoRaWAN specification
may not always be the best choice. We also highlight the energy consumption versus reliability trade-offs associated with the choice of number of retransmission attempts.

Wireless communications are becoming an important part of our everyday lifestyle. One major area that will have an enormous impact on the performance of wireless ad hoc networks is the medium access control (MAC) layer. Current random access MAC protocols for ad hoc networks support reliable unicast but not reliable broadcast. In this paper, we proposed a random access MAC protocol, Broadcast Support Multiple Access (BSMA), which improves broadcast reliability in ad hoc networks.

Radio frequency (RF) energy harvesting and transfer techniques have recently become alternative methods to power the next generation of wireless networks. As this emerging technology enables proactive replenishment of wireless devices, it is advantageous in supporting applications with quality-of-service (QoS) requirement. This article focuses on the resource allocation issues in wireless networks with RF energy harvesting capability, referred to as RF energy harvesting networks (RF-EHNs). First, we present an overview of the RF-EHNs, followed by a review of a variety of issues regarding resource allocation. Then, we present a case study of designing in the receiver operation policy, which is of paramount importance in the RF-EHNs. We focus on QoS support and service differentiation, which have not been addressed by previous literature. Furthermore, we outline some open research directions.

A simple mechanical beam steering antenna concept is proposed for ground mobile terminals of Ka-band satellite and high altitude platform (HAP) providing broadband access services. The wide-angle elevation beam steering is achieved by in-plane translation of a thin offset flat lens in front of a stationary primary feed while full azimuth coverage is obtained by simple 360º rotation of the lens. A new strategy is also proposed to reduce the effective F/D of the focusing system and consequently the total antenna height without increasing beam distortion: a second small flat lens is added on top of the primary feed to create a virtual focus located well below the feed phase center. The challenge is to conciliate high gain both with wide beam scanning and reduced antenna height. Design rules are presented for this antenna concept along with a 27.3-dBi gain fabricated example for the up-link Ka-band (29.5–30 GHz), with circular polarization, 0◦ to 50◦ 20 elevation scan, better than 2.8-dB scan loss and an effective F/D of only 0.55. Both lenses are 3.35-mm thick, formed by a suitable assembly of phase shifting unit cells with less than 0.4 dB of transmission loss in simulation. The main lens dimensions are 195 mm × 145 mm and its weight is 215 g. Total antenna height, including the feed is 26 84 mm.

Opportunistic Spectrum Access (OSA) brings new research challenges in MAC protocol design. It allows unlicensed users to share licensed spectrum in space and time with no or little interference to Primary Users (PUs). When designing an OSA MAC protocol, one of the most difficult but important problem is how the unlicensed users decide when and which channel they should sense and access without conflicting the communications among PUs. To solve this problem, the unlicensed users should have the ability of adaptively and dynamically seeking and exploiting opportunities in both licensed and unlicensed spectrum and along both the time and the frequency dimensions. Secondary Users (SUs) as unlicensed users are required to sense radio frequency band, and when PU are detected, they must vacate the channel immediately within certain amount of time. Due to hardware and energy constraints, full spectrum availability cannot be sensed as well as they do not monitor when there is no data to be transmitted. In this paper, we study MAC protocol design for OSA in Cognitive Radio (CR) ad hoc network under Partially Observable Markov Decision Process (POMDP) algorithm that maximizes achievable throughput for SUs with sufficient protection to PUs. Furthermore, we study tractable greedy algorithm to reduce the complexity of POMDP calculation. The derivation of greedy approach proves that sensing problem can be solved either optimally or approximate the optimal solution. Computer simulation is used to evaluate the performances both of optimal and sub optimal strategy.

Millimeter wave (mmWave) communication systems use large number of antenna elements that can potentially overcome severe channel attenuation by narrow beamforming. Narrow-beam operations in mmWave networks also reduce multiuser interference, introducing the concept of noise-limited wireless networks as opposed to interference-limited ones. The noise-limited or interference-limited regime heavily reflects on the medium access control (MAC) layer throughput and on proper resource allocation and interference management strategies. Yet, these regimes are ignored in current approaches to mmWave MAC layer design, with the potential disastrous consequences on the communication performance. In this paper, these regimes are investigated in terms of collision probability and throughput. Tractable closed-form expressions for collision probability and MAC layer throughput of mmWave ad hoc networks, operating under slotted ALOHA, are derived. The new analysis reveals that mmWave networks may exhibit a non-negligible transitional behavior from a noise-limited regime to an interference-limited one, depending on the density of the transmitters, density and size of obstacles, transmission probability, operating beamwidth, and transmission power. Such transitional behavior necessitates a new framework of adaptive hybrid resource allocation procedure, containing both contention-based and contention-free phases with on-demand realization of the contention-free phase. Moreover, the conventional collision avoidance procedure in the contention-based phase should be revisited, due to the transitional behavior of interference, to maximize throughput/delay performance of mmWave networks. It is concluded that, unless proper hybrid schemes are investigated, the severity of the transitional behavior may significantly reduce throughput/delay performance of mmWave networks.

In this letter, an optimal placement and distribution of cooperative unmanned aerial vehicles (UAVs) in the next generation heterogeneous networks is presented in order to optimize the overall network delays. The positioning issue is formulated as a minimax facility problem which is then resolved using the entropy nets by formation of an optimal placement algorithm. The effectiveness of the proposed approach is demonstrated in terms of significant gains including increased UAV positioning accuracy and reduced delays in UAV allocation.

In this paper, we propose a novel energy saving scheme, termed the Gossip-based Sleep Protocol (GSP). With GSP, each node randomly goes to sleep for some time with gossip sleep probability p. When the value of p is small enough, the network stays connected. GSP does not require a wireless node to maintain the states of other nodes. It requires few operations and scales to large networks. We propose two versions of GSP, one for synchronous networks and one for asynchronous networks, and show the advantages of the GSP approach through both simulations and analysis.

Cooperative diversity transmission exploits spatial diversity created by antenna sharing in a wireless network. The objective of this paper is to investigate cooperative diversity technique performing in a multi-hop DS-CDMA system, where limiting factor on the system is multi-access interference (MAI). We focus on the use of minimum meansquare error (MMSE) multiuser detection (MUD) in the uplink of cooperative CDMA networks. MMSE detectors are designed to suitably combine signals from direct path and relaying path and minimize the signal to interference-and -noise ratio at the receiver output. We evaluate the bit error rate (BER) performance of cooperative transmission in narrow-band block fading channel. Also, MMSE detection is applied in a random CDMA network and the average performance is presented through Monte-Carlo simulations. It is illustrated that, through using MMSE detection in a non-orthogonal CDMA system, cooperation is beneficial in terms of introducing additional diversity gain and thus ensuring a low bit error rate.

With the increasing demands of copyright protection, watermarking technology has being paid more and more attention. In the design of a watermarking algorithm, a good watermark detection scheme can improve the detection rate, which pushes an increasing number of researchers to work with optimum detectors. In this paper, we propose a locally optimum using a locally most powerful test with respect to Barni's multiplicative water marking which is based on the human visual system (HVS). In the proposed detection scheme, the probability density function of DWT coefficients is modeled using the generalized Gaussian distribution, and the decision threshold is obtained by the Neyman-Pearson (NP) criterion. Additionally, we prove that the existing correlation detection is a special case of the proposed locally optimum detection, and we provide an improved correlation threshold under the condition of locally optimum detection.

Next generation cellular radio systems will exceed the limitations of UMTS. The convergence of data and voice traffic will be supported by a flexible OFDM-based PHY layer and an OFDMA-capable MAC layer. The long term evolution (LTE) successor of the 3G systems incorporates this. But problems concerning coverage and capacity at the cell border still remain for the classical cellular layout. Relaying or Multihop operation is an option to massively improve the coverage as well as the capacity issue at low cost, without the need of a cable or fibre access. For the performance analysis of such cellular systems models for ISO-OSI layers 1+2 (PHY+MAC) are needed. In this paper an analytic modelling framework and results are presented for the cellular LTE performance in two multihop scenarios.

This paper provides analytical expressions to evaluate the performance of a random access wireless network in terms of user throughput and network throughput, subject to the constraint of proportional fairness amongst users. The proportional fair scheduling (PFS) algorithm is considered an attractive bandwidth allocation criterion in wireless networks for supporting high resource utilization while maintaining good fairness among network flows. The most challenge of a PFS problem is the lack of analytic expression. Though the PFS algorithm has been a research focus for some time, the results are mainly obtained from computer simulations. It is known that a PFS problem is NP-hard and, until recently, there are very few papers which give analytic insights into the PFS algorithm. Typically, existing works use simplified form of the PF preference metric and assume simple linear model, or the given analytic expression is valid only for very limited cases. In this research, we give analytical results of the PFS algorithm by providing closed-form expressions for the throughput in Rayleigh fading networks. We use Gaussian approximation method to model the feasible data rate in Rayleigh fading environments. Results obtained from the simulation and numerical analysis verifies the high accuracy of the closed-form expressions given in the paper. In particular, the analytic expressions given here will provide great help for the system design of a PFS-enable network, not only in that it is obtained from more realistic rate model, but also it applies to various kinds of network scenarios.

WiMAX is a wireless technology which offers high data rate transmission in broadband. In this paper, the architecture of a WiMAX physical layer simulator is presented. The main blocks are implemented with the aid of the Matlab programming language and the bit error rate (BER) curves in Rayleigh fading channel, are presented and commented.

Wireless sensor networks (WSN) are emerging in various fields like disaster management, battle field
surveillance and border security surveillance. A large number of sensors in these applications are
unattended and work autonomously. Clustering is a key technique to improve the network lifetime, reduce
the energy consumption and increase the scalability of the sensor network. In this paper, we study the
impact of heterogeneity of the nodes to the performance of WSN. This paper surveys the different clustering
algorithm for heterogeneous WSN.

If nowadays, positioning becomes more and more accurate, and covers better and better a territory (indoor and outdoor), it remains territories where traditional (and basic) positioning system (GPS, gsm or WiFi) and hybrid ones (GPSgsm, GPS-WiFi, GPS-WiFi-gsm, ...) are insufficient and requires research investment treating combined positioning. In this paper we propose a GPS-WiFi combined positioning algorithm, based on trilateration technique. Real experiments and other simulation are conduced and demonstrate accuracy gains, even where various criteria dilution of precision (GPS dop's criteria, or ours WiFi geometrical and signal attenuation's dop proposal, or hybrid dop one's) indicate all the disruption of positioning service. A testbed scenario issued from a real urban campus environment validates not only our GPS-WiFi combined positioning algorithm but also an implementation of pertinent positioning techniques and dop's criteria. This work constitutes a further step to better position everywhere and to ensure continuity of a positioning service.

Internet enabled wireless devices continue to proliferate and are expected to surpass traditional Internet clients in the near future. This has opened up exciting new opportunities in the mobile e-commerce market. However, data security and privacy remain major concerns in the current generation of "wireless Web" offerings. All such offerings today use a security architecture that lacks end-to-end security. This unfortunate choice is driven by perceived inadequacies of standard Internet security protocols like SSL (secure sockets layer) on less capable CPUs and low-bandwidth wireless links. This paper presents our experiences in implementing and using standard security mechanisms and protocols on small wireless devices. Our results show that SSL is a practical solution for ensuring end-to-end security of wireless Internet transactions even within todays technological constraints.

In this paper we study the system level performance of cognitive radio (CR) networks under average received interference power constraints. Under the assumption of uniform node placements and a simple power control scheme, we derive the closed-form expression for the cumulative distribution function (CDF) of the maximum allowable transmit power of the target CR transmitter. We further study two CR network scenarios: a CR based central access network and a CR assisted virtual multiple-input multiple-output (MIMO) network. The average uplink capacities of both networks are derived and analyzed, with an emphasis on understanding the effect of the numbers of primary users and CR users on the capacity. Numerical and simulation results demonstrate that the CR based central access network is more suitable for less-populated rural areas where a lower density of primary receivers is expected, while the CR assisted virtual MIMO network performs better in urban environments with a dense population of mobile CR users.

This paper presents a novel Tone-based 802.11b protocol for use in wireless networks where nodes are equipped with adaptive array antennas. The protocol relies on the ability of the antenna and Angle of Arrival (AoA) algorithms to identify the direction of transmitters and then beamform appropriately to maximize SINR (Signal to Interference and Noise Ratio) at the receiver. The performance of the protocol is evaluated using detailed simulation in OPNET and Matlab where we demonstrate the benefits of using adaptive antenna arrays. The impact of using different number of antenna elements is also studied for this environment.

A wide variety of applications aiming to improve traffic efficiency or to provide information/entertainment to passengers in vehicles are intended to be delivered in Vehicular Ad hoc Networks in the near future. Most of these applications require vehicles to access a remote network. However, due to the high costs for deploying and maintaining an ubiquitous roadside infrastructure, just a few stationary Road-side Units (RSUs) are expected to be installed, which provide discontinuous and shortlived network connections.

Routing in delay tolerant networks (DTN) can benefit from the fact that most real life DTN, especially in the context of people-centric networks (e.g. Pocket Switching Networks (PSN)), exhibit some sort of periodicity in their mobility patterns. For example, public transportation networks follow periodic schedules. Even most individuals have fairly repetitive movement patterns, for example, driving to and from work at approximately the same time everyday. This paper proposes a Bayesian classifier based DTN routing framework that adopts a methodical approach for computing the routing metrics by utilizing the network parameters (e.g. spatial and temporal information at the time of packet forwarding) that capture the periodic behavior of DTN nodes. After the calculation of routing metrics, different routing instantiations are possible based on this framework. We simulate a real-world vehicular DTN network using mobility traces from a metropolitan public transportation bus network and demonstrate that even a simplistic single-copy forwarding scheme based on our framework outperforms existing gradient-based single copy schemes by 25% in terms of delivery ratio. To the best of our knowledge this work is one of the first studies that adopts Bayesian inference in the context of DTN routing.

We present a description of a technique to embed secret data to an image, called information hiding or stegnography. We utilize some simple observed relationships between the binary representation of a pixel, the gray code representation, and the utilization of a simple Exclusive-OR operation based upon N images available to the sender and the receiver, called the cover images. We present the algorithms for embedding the secret data in the altered, last image, N+l, called the stego image; as well as extracting this data on the receiving side. We present some experimental images utilizing two cover images, and one stego image and show that the procedure we propose has a high PSNR value, and an almost identical histogram when compared to the before stego image.

One of the most debated issues surrounding wireless connectivity is performance especially under different topographic and climatic scenarios. Performance has a direct relationship with throughput measured in terms of how well a given wireless connectivity provides consistent services over a given period compared to the wired alternative. Research has shown that wireless connectivity is constrained by significant physical components such as topography, weather conditions, propagation frequency, and distance. It is commonplace to see notable vendors of wireless network products make claims as to how their technologies are designed to remedy any signal degradation that may arise from the aforementioned physical elements. This paper is aimed at evaluating the performance of a point to multipoint connectivity using Ubiquiti's 5.8 GHz Point to Multipoint Base Stations deployed within a landscape marked by series of undulating highlands and lowlands. In this experiment, a base station node is established with connectivity to two other nodes of same specifications with one node as the destination radio whereas the other acts as the control which is located on a table land. The nodes were separated by triangular distances of 3 km and network connectivity was maintained over thirty days during periods of rainfall. Packets sent and received across each node was carefully recorded. The results from the analysis showed that packet losses to and from the control node was significantly lower than that of the other node under same weather conditions.

Non-cooperative behaviors in communication networks can significantly adversely affect the entire network. Recently, researchers have begun to study such non-cooperative communication systems within a game theory framework and strive to engineer the system to prevent performance degradation under non-cooperative behaviors. The WWAN/WLAN two-hoprelay system described in [1] integrates two types of wireless technologies to improve wireless access throughput and coverage. The relay nodes in the two-hop-relay system can be wireless relay routers deployed by wireless service providers, or dual-mode users who voluntarily relay traffic for other users. However, it is reasonable to assume that all dual-mode terminals are selfish and are not willing to relay for other users without an incentive. In this paper, we propose a proper scheduling algorithm as an incentive mechanism for the hybrid wireless relay network. We will use the basic concepts of game theory, especially the concept of the Nash Equilibrium, to design our scheduling algorithms. Several scheduling algorithms, including the maximum rate C/I scheduler, the proportional fair scheduler, and the round robin scheduler, are examined to understand performance while operating under the assumption that all users are selfish. Under the C/I scheduler or the proportional fair scheduler, Nash Equilibriums exist at the operating points where no user will relay for other users ---an undesirable situation. Under the round robin scheduler, selfish users are indifferent on relaying voluntarily or not relaying. Therefore, we are inspired to design a novel incentive scheduling algorithm to encourage relay. By applying the proposed incentive scheduler at the base station, all selfish users relay cooperatively at the Nash Equilibrium.

Straightforward, transparent mobility management has now been available for some time with IPv6 through the Mobile IPv6 protocol. There are numerous MIPv6 implementations available and some have been successfully deployed and tested in real world scenarios. Yet, certain aspects of that mobility support, such as security, seamless handovers, and heterogeneous network technologies support are still being discussed and improved by working groups on the IETF and in various research communities. One such example is the continuing work on the "Fast Handovers For Mobile IPv6" protocol that aims to reduce the packet loss and latency inherent to the handover process. In this document we present a set of experiments with an implementation of that protocol and the resulting performance evaluation. All tests take place over IEEE Wireless LANs, and are performed using the fmipv6.org protocol implementation for the Linux operating system, that we have developed and contributed to the open source community. The paper, exposes an analysis of the provided results and brings out some issues, not currently addressed by the protocol, like for example connection and packet loss occurring during the IEEE 802.11 scanning procedure, and lack of more appropriate alternative mechanisms for discovery and selection of candidate access points. The purpose of the document is to provide evaluation material based on a link layer protocol that is (to our understanding) among the primary link layer protocols that FMIPv6 was built to work on. We find such an evaluation quite necessary for the pending optimisations of the protocol.

This paper proposes an energy-efficient clock syn-chronization scheme for Wireless Sensor Networks (WSNs) based on a novel time synchronization ap-proach. Within the proposed synchronization approach, a subset of sensor nodes are synchronized by over-hearing the timing message exchanges of a pair of sensor nodes. Therefore, a group of sensor nodes can be synchronized without sending any extra messages. This paper brings two main contributions: 1. Devel-opment of a novel synchronization approach which can be partially or fully applied for implementation of new synchronization protocols and for improving the performance of existing time synchronization protocols. 2. Design of a time synchronization scheme which significantly reduces the overall network-wide energy consumption without incurring any loss of synchroniza-tion accuracy compared to other well-known schemes.

This letter proposes a new method to estimate the number of competing stations in IEEE 802.11 networks. Due to the nonlinear/non-Gaussian nature of measurement model, a nonlinear filtering algorithm, called the Gaussian mixture sigma point particle filter (GMSPPF), is proposed herein to estimate the number of competing stations. Since GMSPPF represents a better alternative to the conventional extended Kalman filter (EKF), unscented Kalman filter (UKF), particle filter (PF), and unscented particle filter (UPF) for nonlinear/non-Gaussian (or Gaussian) tracking problems, we apply this filter for IEEE 802.11 WLANs. GMSPPF provides a more viable means for tracking in any con-ditions the number of competing stations in IEEE 802.11 WLANs relative to EKF, UKF, PF, and UPF. Further, GMSPPF presents both high accuracy as well as prompt reactivity to changes in the network occupancy status. For the more accurate method (GMSPPF), the combined access mode is shown to maximize the system throughput by switching between the basic access mode and the RTS/CTS access mode.

The data traffic originating on mobile computing devices has been growing exponentially over the last several years. Lossless data compression and decompression can be essential in increasing communication throughput, reducing communication latency, achieving energy-efficient communication, and making effective use of available storage. This paper experimentally evaluates several compression utilities and configurations on a modern smartphone. We characterize each utility in terms of its compression ratio, compression and decompression throughput, and energy efficiency for representative use cases. We find a wide variety of energy costs associated with data compression and decompression and provide practical guidelines for selecting the most energy efficient configurations for each use case. For data transfers over WLAN, the best configurations provide a 2.1-fold and 2.7-fold improvement in energy efficiency for compressed uploads and downloads, respectively, when compared to uncompressed data transfers. For data transfers over a mobile broadband network, the best configurations provide a 2.7-fold and 3-fold improvement in energy efficiency for compressed uploads and downloads, respectively.

The paper addresses wireless the 2-Way Relay Channel (2-WRC) system with a Hierarchical Decode and Forward strategy. This strategy uses a Hierarchical eXclusive Code (HXC) that allows full decoding of the hierarchical symbols at the relay. The HXC represents two data sources only through the exclusive law and requires side information on the complementary data at the destination (which naturally holds for the 2-WRC). The HDF strategy has the advantage over classical MAC stage relaying with joint decoding that its rate region extends beyond the classical MAC region. We evaluate the hierarchical MAC capacity regions for various alphabets, constellation point indexing and various channel parametrization and compare that to the alphabet limited and unconstrained cut-set bounds.

The broadcast nature of communication channels in infrastructureless wireless networks poses challenges to security. In this paper, we propose a novel technique namely Secure Multi-channel Group Key Generation (MuGKeG) algorithm. We utilize the available channels switching behaviour between multiple nodes to hide our key from eavesdropper. We provide descriptions for an illustrative base case of three users and one eavesdropper and expand it for the case of N users with C channels and M eavesdroppers. Repeated application of the MuGKeG algorithm on the order of O(log N) allows scaling the size of the group in the order of millions. We provide an analytical closed-form solution for the entropy of the secret group key generated when eavesdroppers follow an optimal attack strategy, and verify it by ns-3 simulations. Comparison with previous state-of-the-art schemes suggests that MuGKeG can provide upto 20 kbps increase in secrecy rate with a scalable key size.

The number of mobile users is rapidly increasing. Therefore, the bandwidth demand of mobile users significantly growing. To answer users’ demand, Carrier Aggregation is proposed in LTE systems. In Carrier Aggregation, communication between users and base stations are achieved by multi bands which have different coverage areas and mobile users can simultaneously connect one or multi carrier components in
each band. Because of mobility of users and quality of carriers,
the best available Carrier Components of each band should
be assigned to each user in order to provide desired service
to users. Several works have been proposed in the literature
to address Carrier Components assignment methods in LTE
systems by using Channel Quality Indicator, quality of service
and service types. Although the previous works on carrier
assignment methods significantly increase the performance of
LTE system, continuously increasing bandwidth demand of users forces the operators to manage resource allocation more intelligently. Therefore, we have proposed a novel Carrier Component assignment method which considers user profiles and channel quality indicator to increase quality of services and experiences getting by mobile users. Results show that the proposed method uses system resources efficiently and can improve performance of LTE systems. Our method will help service providers build efficient carrier components assignment methods through considering user profile and performance metrics, such as band usage, throughput and delay.

This paper presents the energy performance of a new radio access technology (RAT) component in 5G, here denoted as 5G-NX. The 5G-NX RAT encompasses massive beamforming and an ultra-lean design as two of its key technology components. The user throughput, resource utilization of the cells and daily average area power consumption are evaluated by means of system level simulations in an Asian city scenario, and the results are compared with a traditional LTE deployment using the same network layout. The simulation results indicate that the  new 5G-NX system provides much better energy performance compared to LTE and this is primarily due to the ultra-lean design and the high beamforming gain that provides both longer and more efficient component sleep in the network. At expected traffic levels beyond 2020, 5G-NX is shown to decrease the network energy consumption by more than 50% while providing around 10 times more capacity.

By exploiting a general cyclostationary (CS) sta-tistics-based framework, this letter develops a rigorous and unified asymptotic (large sample) performance analysis setup for a class of blind feedforward timing epoch estimators for linear modulations transmitted through time nonselective flat-fading channels. Within the proposed CS framework, it is shown that several estimators proposed in the literature can be asymptotically interpreted as maximum likelihood (ML) estimators applied on a (sub)set of the second- (and/or higher) order statistics of the received signal. The asymptotic variance of these ML estimators is established in closed-form expression and compared with the modified Cramér–Rao bound. It is shown that the timing esti-mator proposed by Oerder and Meyr achieves asymptotically the best performance in the class of estimators which exploit all the second-order statistics of the received signal, and its performance is insensitive to oversampling rates as long as 3. Further, an asymptotically best consistent estimator, which achieves the lowest asymptotic variance among all the possible estimators that can be derived by exploiting jointly the second- and fourth-order statistics of the received signal, is also proposed.

Opportunistic beamforming with proportional fair scheduling is a very promising technique that exploits multiuser diversity to achieve high data rates on the downlink while ensuring a certain level of fairness. However, it greatly improves system performance only for sufficiently large mobile user population. This paper proposes a technique enhancing opportunistic beamforming at the transmitter with antenna selection at each mobile receiver to overcome this limitation. Significant performance improvement is achieved especially for small number of users. The simplicity and inexpensive deployment of this technique make it a highly desirable enhancement to opportunistic beamforming.

In IEEE 802.15.4 beacon-enabled wireless personal area networks (WPANs), the PAN coordinator will periodically broadcast beacon frames to let its associated end devices keep synchronized. One of the benefits in a beacon-enabled WPAN is that end devices can thus turn off their transceiver during the inactive periods to preserve their energy. Another benefit is that the PAN coordinator can allocate contention-free GTSs (guaranteed time slots) for admitted devices. This paper, first pointed out slot size-induced bandwidth waste problem, which is due to the innate defect of the super frame structure. Then the authors propose the novel multi-beacon super frame (MBS) structure to overcome this problem. To demonstrate the power of MBS, we also propose a greedy GTS allocation algorithm. Simulation results reveal that a WPAN using MBS can attain relatively higher bandwidth utilization at the expense of only a small increase of the device's active period.

Mobile adhoc network (MANET) is a network of a number of mobile routers and associated hosts, organized in a random fashion via wireless links. During recent years MANET has gained enormous amount of attention and has been widely used for not only military purposes but for search-and-rescue operations, intelligent transportation system, data collection, virtual classrooms and ubiquitous computing. Service discovery is one of the most important issues in MANET. It is defined as the process of facilitating service providers to advertise their services in a dynamic way and to allow consumers to discover and access those services in an efficient and scalable manner. In this paper, we are proposing a flexible and efficient approach to service discovery for MANET by extending the work of Dante Arias Torres and J. Antonio Garcia-Macias (2004). Most of the service discovery protocols proposed in literature don't provide an appropriate route from consumer to service provider. Hence after services are discovered, a route request needs to be initiated in order to access the service. In this paper, we are proposing a robust and flexible approach to service discovery for MANET that not only discovers a service provider in the vicinity of a node, but at the same time, it also provides a route to access the service. We have extended the approach proposed in Dante Arias Torres and J. Antonio Garcia-Macias for efficiency by adding the push capabilities to service discovery.

Uplink and downlink cloud radio access networks are modeled as two-hop K-user L-relay networks, whereby small base-stations act as relays and are connected to a central processor via orthogonal fronthaul links of finite capacities. Based on noisy network coding and distributed decode-forward inner bounds on the capacity regions for uplink and downlink, respectively, the total fronthaul link capacity required to approach the centralized MIMO sum-rate is characterized. The capacity scaling law when the network size increases is examined under certain uplink and downlink network models, both theoretically and via simulations.

This letter proposes a class of blind feedforward carrier-phase estimators for higher order quadrature ampli-tude-modulated transmissions. As an extension of the Viterbi and Viterbi (V&V) estimator, a constellation-dependent optimal matched nonlinear estimator is derived such that its asymptotic variance is minimized. The asymptotic variances of the optimal matched and V&V estimators are established in closed-form expressions and compared. Computer simulations are presented to corroborate the theoretical performance analysis.

In an indoor bidirectional visible light communications (VLC), a line-of-sight (LOS) transmission plays a major role in obtaining adequate performance of a VLC system. Signals are often obstructed in the LOS transmission path, causing an effect called optical shadowing. In the absence of LOS, the performance of the VLC system degrades significantly and, in particular, at uplink transmission this degradation becomes severe due to design constraints and limited power at uplink devices. In this paper, a novel concept and design of an optical bidirectional beacon (OBB) is presented as an efficient model to counter the performance degradation in a non-line-of-sight (NLOS) VLC system. OBB is an independent operating bidirectional transceiver unit installed on walls, composed of red, green, and blue (RGB) light emitting diodes (LEDs), photodetectors (PDs) and color filters. OBB improves the coverage area in the form of providing additional or alternate paths for transmission and enhances the performance of the VLC system in terms of bit error rate (BER). To verify the effectiveness of the proposed system, simulations were carried out under optical shadowing conditions at various locations in an indoor environment. The simulation results and analysis show that the implementation of OBB improves the performance of the VLC system significantly, especially when the LOS bidirectional transmission paths are completely or partially obstructed.

NGN is an increasingly becoming the market reality of the Information and communication sector and hence has put forward many challenges to the National Regulatory Authorities of the whole world. In this period of migration from the legacy networks to the NGN, every regulator has adopted an approach different from other depending upon the regulatory environment in which they operate and the future plans of the market player. Fundamentally, the NGNs decouple the functionality between network and the services to be offered on these networks. This decoupling brings different types of business models with respect to the degree of integration of transport, control and service provision. In the presence of these business models the continuity of perfect competition and economic growth is a challenging task for the NRAs. In this paper we will elaborate the regulatory challenges posed by network evolution, some current regulatory options, role of the geographic markets in the regulatory framework and then will conclude that "All-in-one" regulatory approach is not suitable for the regulation of NGN, particularly during this transition period.

According to recently presented QoS architecture by 3GPP [1], a traffic conditioner may be deployed to provide conformance of the negotiated QoS in UMTS. The traffic conditioning is performed by traffic shaping or/and policing. A framework of traffic conditioning with QoS provisioning in 3G radio access network is proposed in this paper. The main idea of our traffic conditioning approach is to employ traffic shaping at each UE and traffic policing at the RNC. The traffic generated at each UE is regulated by a traffic shaper in the form of a token bucket, and the conformance of the traffic is policed at the RNC according to traffic policing policies. A system model based on the proposed framework is implemented. The simulation results regarding the impact of traffic shaping on packet discarding probability, the tradeoff between probability of non-compliance and shaping delay are also presented in this paper.

Water is indispensable for sustaining life on earth. Millions of people lack access to clean water owing to geographical and anthropogenic factors. Ground water contamination has always been a reason of concern and it is very expensive and difficult to clean
up. In a country like India where the population density and land use is high, ground water is highly prone to contamination. The consequences of contamination manifests as poisoning and diseases such as hepatitis and cancer. Hence an assessment and subsequent
action is needed.The present work is a survey of ground water samples in rural and urban location of Thiruvannamalai district
in the state of Tamil Nadu, India. The physico-chemical parameters of water samples like pH, EC, Total Hardness, Ca, Mg, Na, K,
sulphate,nitrate,Chloride are analyzed. A comparison of each parameter is performed with that of the standard permissible limit as recommended by World Health Organization (WHO). Our main objective is to determine the quality of ground water with the help of Geographical Information System (GIS) which gives the exact location of ground water contamination.

In recent decades, staggering number of mobile applications have been developed in the wireless technology arena. The Wireless Fidelity (WiFi) and the Long Term Evolution (LTE) have become the most common wireless technologies used for those applications. Mobile applications are classified into Real-Time (RT) and Non Real-Time (NRT). The growth in the number of users burdens the network with more congestion which requires techniques to carry different types of traffic simultaneously in order to alleviate the problem. Different types of traffic (RT or NRT) are managed by Quality of Service (QoS) provisioning techniques. The main issue with the dominant services (RT applications) is the fact that they are delay sensitive, and this is the motivation for building a scheme that enables both LTE and WiFi systems to achieve reasonable values for delay, jitter, and packet loss. In this paper, we propose a QoS provisioning method that could be adopted by both LTE and WiFi, separating the traffic into RT and NRT applications. In the first stage, Class-Based Weighted Fair Queuing (CBWFQ) and Round Robin (RR) disciplines are used for RT and NRT applications respectively. In the second step, Deficit Weighted Round Robin Queuing (DWRRQ) is used for all applications. In this paper, we have analyzed the results of implementation of the proposed scheme in LTE and WiFi networks, and have made a comparison between their results (jitter, end-to-end delay, and traffic received). Simulation results demonstrate improvement in delay for RT in both networks.

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.