Channel Link Research Articles

On Physical Layer Security of Double Rayleigh Fading Channels for Vehicular Communications

In this letter, we study the physical layer secrecy performance of the classic Wyner’s wiretap model over double Rayleigh fading channels for vehicular communications links. We derive novel and closed-form expressions for the average secrecy capacity (ASC) taking into account the effects of fading, path loss, and eavesdropper location uncertainty. The asymptotic analysis for ASC is also conducted. The derived expressions can be used for secrecy capacity analysis of a number of scenarios including vehicular-to-vehicular (V2V) communications. The obtained results reveal the importance of taking the eavesdropper location uncertainty into consideration while designing V2V communication systems.

Optimizing City-Wide White-Fi Networks in TV White Spaces

White-Fi refers to WiFi deployed in the TV white spaces. Unlike its ISM band counterparts, White-Fi must obey requirements that protect TV reception. As a result, optimization of citywide White-Fi networks faces the challenges of heterogeneous channel availability and link quality, over location. The former is because, at any location, channels in use by TV networks are not available for use by White-Fi. The latter is because the link quality achievable at a White-Fi receiver is determined by not only its link gain to its transmitter but also by its link gains to TV transmitters and its transmitter’s link gains to TV receivers. In this paper, we model the medium access control throughput of a White-Fi network. We propose heuristic algorithms to optimize the throughput, given the described heterogeneity. The algorithms assign power, access probability, and channels to nodes in the network, under the constraint that reception at TV receivers is not compromised. We evaluate the efficacy of our approach over example city-wide White-Fi networks deployed over Denver and Columbus (respectively, low and high channel availability) in the USA, and compare with assignments cognizant of heterogeneity to a lesser degree, for example, akin to FCC regulations.

Precoding Design for Correlated MIMO-AF Relay Networks With Statistical Channel State Information

An iterative precoding design of a two-hop amplify-and-forward (AF) multiple-input multiple-output relay network with one source, multiple relays, and one destination is presented. To provide a solution for general scenarios, the source-to-destination direct link and double correlated Kronecker Rician fading channels are considered. Statistical channel state information is used for the average capacity formulation for the sake of its robustness and infrequent update. The source and relay precoders are optimized to maximize a closed-form upper bound of the average capacity giving a suboptimal design. The non-convex design problem is divided into three sub-problems: source precoder, relay beamforming, and relay power allocation (PA). For optimizing the source precoder subject to multiple power constraints, rather than using computationally expensive penalty type algorithms, an efficient design procedure as a type of water-filling with multiple water levels is developed. Its negative PA is handled by a simple method of determining the eigen-modes of positive power. Using the Riemannian steepest descent method and a newly proposed power adaptation to optimize the relay beamforming and relay PA, respectively, the constrained optimization problems become unconstrained. Simulations show that the developed design procedure with trivial initialization provides nearly global optimum performance with fast convergence and efficient computation. The developed methods for the source precoder and relay PA outperform upon the augmented Lagrangian method with respect to convergence and computing time. Furthermore, the generality of the proposed scheme makes the design procedure applicable to AF relay networks with different simplified Kronecker channel models and with/without the direct link.

Improving Multipath TCP Performance over WiFi and Cellular Networks: An Analytical Approach

A complete understanding of the dynamics of Multipath TCP (MPTCP) over Cellular and WiFi networks is still lacking. This is a highly challenging issue, as a consequence of the complex interdependencies between the losses, packet reordering due to heterogeneous wireless channel features, errors, and link layer retransmissions, as well as their (joint) influence on MPTCP's control mechanism. In this paper, we develop a comprehensive approach that is capable of assessing the performance of long-lived MPTCP flows with joint WiFi and Cellular network access, taking into account the diverse characteristics of both types of networks. Relying on a parallel queueing model, we develop a framework that features the controllable network parameters, such as the retransmission limit and the buffer sizes, so as to capture their impact on the TCP-level performance. We include a variety of numerical and simulation results highlighting various non-trivial findings and insights for adaptive MPTCP design. In particular, we design a novel MPTCP algorithm to exploit the route heterogeneity, and demonstrate that the proposed algorithm is capable of learning the network's characteristics. It also identifies the improved MPTCP window increment parameters for any given set of channel errors, retransmission limits, and buffer sizes.

Multi-Objective Optimization of a Wireless Body Area Network for Varying Body Positions.

The purpose of this research was to improve the performance of a wireless body area sensor network, operating on a person in the seated and standing positions. Optimization-focused on both the on-body transmission channel and off-body link performance. The system consists of three nodes. One node (on the user’s head) is fixed, while the positions of the other two (one on the user’s trunk and the other on one leg) with respect to the body (local coordinates) are design variables. The objective function used in the design process is characterized by two components: the first controls the wireless channel for on-body data transmission between the three sensor nodes, while the second controls the off-body transmission between the nodes and a remote transceiver. The optimal design procedure exploits a low-cost Estra, which is an evolutionary strategy optimization algorithm linked with Remcom XFdtd, a full-wave Finite-Difference Time-Domain (FDTD) electromagnetic field analysis package. The Pareto-like approach applied in this study searches for a non-dominated solution that gives the best compromise between on-body and off-body performance.

Quantifying Climatic Controls on River Network Branching Structure Across Scales

AbstractThe branching structure of river networks is an important topologic and geomorphic feature that depends on several factors (e.g., climate and tectonics). However, mechanisms that result in such branching patterns in river networks are poorly understood. Observations from natural catchments have revealed controls of climate on drainage density (Dd). In this study, we investigate the effects of climatic forcing on river network topology and geometry beyond Dd. For this, we selected 26 basins across the United States with equal Dd, however, different climate aridity index (defined here as the ratio of mean annual potential evaporation to precipitation). The river networks of these basins were extracted, using a curvature‐based method, from high‐resolution (1‐m) digital elevation models, and several metrics such as width functions, branching angles, and side branching ratio were computed. We used a multiscale entropy approach to quantify the geometric and topologic irregularity and structural richness of these river networks. Our results revealed the systematic impacts of climate forcing on the structure of river networks. We showed that the width functions of dry basins have higher entropy as compared to those of humid basins across spatial scales. Higher entropy suggests more heterogeneity in drainage network of dry basins. This heterogeneity is manifested in channels and their junctions resulting, on an average, in larger junction angle and longer channel links in dry basins compared to humid basins.

Relay-Assisted Proactive Eavesdropping With Cooperative Jamming and Spoofing

In this paper, we consider a legitimate proactive eavesdropping scenario where a distant central monitor covertly wiretaps the communication between a pair of suspicious users via several multi-antenna full-duplex spoofing relays and a multi-antenna cooperative jammer. Assuming an adaptive transmission policy at the suspicious users, the spoofing relays not only intercept but also forward the manipulated information to control the data rate of the suspicious users in collaboration with the jammer. We provide a technique which jointly optimizes the receive combining vector at the central monitor, the precoders at the relays, and the transmit covariance matrix at the jammer for maximizing the eavesdropping rate. To reveal some fundamental properties of the optimal operation, we first study a single-relay system. It is shown that when the central monitor experiences a poor eavesdropping channel link, the spoofing relay and the jammer should transmit destructive signals and jamming signals, respectively. In this case, the suspicious users are forced to decrease their data rate, while the intercepted information can be successfully decoded by the central monitor. On the other hand, when the eavesdropping channel condition is favorable, the spoofing relay forwards constructive signals to further increase the data rate at the suspicious users in a way that more information can be intercepted from the suspicious users. We then formulate a general eavesdropping rate maximization problem for multiple relays and present a semi-definite relaxation approach. A low-complexity design is also proposed based on our analysis for the single-relay system. Simulation results verify the efficiency of the proposed solutions compared to other baseline schemes in various practical setups.

On indoor visible light communication systems with spatially random receiver

This paper studies the performance of an indoor optical wireless communication system with visible light communication (VLC) technology in a cuboid room with a spatially random receiver. Considering that the receiver is uniformly distributed on the floor of a 4a m x 4b m x H m (where a > 0, b > 0 and H > 0) cuboid room, 4 light emitting diode (LED) lamps are all located at the center of 2a m x 2b m rectangle, which is a quarter of the ceiling area. The receiver chooses the best channel link to receive the information from the LED lamps, which depends on the distance between the receiver and each lamp. By using stochastic geometry theory, we derive the exact/approximated analytical expressions for the outage probability and the ergodic capacity, respectively. Finally, our derived analytical results are verified by Monte Carlo simulations.

Study on Optimization Strategy of Kiwifruit Distribution in Dujiangyan

Kiwi fruit industry in Dujiangyan has a certain size and influence after decades of development. But due to the lack of distribution management, the backward logistics technology, and the complex distribution channel links, the fruit loss rate is high, the efficiency is low, the household income is affected, and the quality and flavor can’t be guaranteed, so there has a great significance to develop the logistics distribution of the Kiwi fruit of Dujiangyan. This thesis, starting from the basic concept of logistics and distribution of agricultural products, analyzes the current situation of distribution, points out the complex distribution channel links, lack of cold-chain technology, low degree of distribution information, and lack of high-end logistics talents, which affect the distribution efficiency. Combining with the actual situation of Dujiangyan, from optimizing logistics distribution channels, developing cold-chain logistics technology, strengthening the construction of logistics information, cultivating high-end logistics talents, this thesis proposes some countermeasures to accelerate the development of kiwi fruit logistics distribution of Dujiangyan.

Time-Varying Communication Channel High Altitude Platform Station Link Budget and Channel Modeling

Because of the high BER (Bit Error Rate), low time delay and low channel transmission efficiency of HAPS (High Altitude Platform Station) in the near space. The link budget of HAPS and channel model are proposed in this paper. According to the channel characteristic, the channel model is set up, combined with different CNR (Carrier Noise Ratio), elevation angle, coding situations of wireless communication link by using Hamming code, PSK (Pulse Shift Keying) and Golay code respectively, then the situations of link quality and BER are analyzed. The simulation results show that the established model of the link budget and channel are suitable for the theoretical analysis results. The elevation of the HAPS communication link is smaller while the BER is increasing. The case of channel in the coding is better than in the un-coded situation. When every bit power and thermal noise power spectral density is larger, the BER of the HAPS communication link is becoming smaller.

TeraSim: An ns-3 extension to simulate Terahertz-band communication networks

In the quest of higher wireless data-rates, Terahertz (THz)-band (0.1-10 THz) communication is envisioned as a key wireless technology of the next decade. In parallel to the development of THz transceivers and antennas, simulation tools are needed to expedite the development of communication and networking protocols tailored to this novel networking paradigm, at a fraction of the cost. The few simulation platforms developed to date for THz communication networks do not capture the peculiarities of the THz channel or the capabilities of THz devices. In this paper, TeraSim, i.e., an open source network simulation platform for THz communication networks is presented. TeraSim is built as an extension for ns-3, which is one of the most widely used teaching and education network simulation software. The simulator has been developed considering two major types of application scenarios, namely, nanoscale communication networks (average transmission range usually below one meter) and macroscale communication networks (distances larger than one meter). The simulator consists of a common channel module, separate physical and link layers for each scenario, and two assisting modules, namely, THz antenna module and energy harvesting module, originally designed for the macroscale and nanoscale scenario, respectively. The structure, relations and content of each module are presented in detail. Extensive simulation and test results are provided to validate the functionalities of the implemented modules. TeraSim is expected to enable the networking community to test THz networking protocols without having to delve into the channel and physical layers.

A Compact Low-Power LoRa IoT Sensor Node with Extended Dynamic Range for Channel Measurements.

As sub-GHz wireless Internet of Things (IoT) sensor networks set the stage for long-range, low-data-rate communication, wireless technologies such as LoRa and SigFox receive a lot of attention. They aim to offer a reliable means of communication for an extensive amount of monitoring and management applications. Recently, several studies have been conducted on their performance, but none of these feature a high dynamic range in terms of channel measurement. In this contribution an autonomous, low-power, LoRa-compatible wireless sensor node is presented. The main uses for this node are situated in LoRa channel characterization and link performance analysis. By applying stepped attenuators controlled by a dynamic attenuation adjustment algorithm, this node provides a dynamic range that is significantly larger than what is provided by commercially available LoRa modules. The node was calibrated in order to obtain accurate measurements of the received signal power in dBm. In this paper, both the hardware design as well as some verification measurements are discussed, unveiling various LoRa-related research applications and opportunities.

Power Optimized Single Relay Selection with an Improved Link-Adaptive-Regenerative Protocol

To improve the reliability and efficiency in cooperative communications, a power optimized single relay selection scheme is proposed by increasing the diversity effort with an improved link-adaptive-regenerative (ILAR) protocol. The protocol determines the forwarding power of a relay node by comparing the signal-to-noise ratio (SNR) at both sides of the node; thus it improves the power efficiency. Moreover, it also proposes a single relay selection strategy to maximize the instantaneous SNR product, which ensures the approximate best channel link quality for good relay forwarding. And the system adjusts the forwarding power in real time and also selects the best relay node participated in the cooperative forwarding. In addition, the cooperation in the protocol is analyzed and the approximate expression of the bit-error-rate (BER) and the outage probability at high SNRs are also derived. Simulation results indicate that the BER and outage probability of the relay selection scheme by the ILAR protocol outperform other contrast schemes of current existing protocols. At BER of 10−2, the proposed scheme with ILAR protocol outperforms those of the decoded-and-forward (DF), the selected DF (SDF), and the amplify-and-forward (AF) protocols by 3.5, 3.5 and 7 dB, respectively. Moreover, the outage probability of the relay system decreases with the growth of the relay number. Therefore, the proposed relay selection scheme with ILAR strategies can be properly used in cooperative communications for good reliability and high power efficiency.

An Integrated Tri-Band/UWB Polarization Diversity Antenna for Vehicular Networks

The design, fabrication, and testing of an integrated polarization diversity antenna array for maximizing the wireless channel link in vehicular networks are presented in this paper. The diversity antenna is constructed using unit cell radiators that provide two operating modes. The mode transition is achieved using a pair of PIN diodes. In one state, the antenna provides multiband operation centered at 2.4, 3.5, and 5.8 GHz. In the other state, the antenna covers the entire ultra-wideband (UWB) spectrum. The unit cell radiators are distributed in the horizontal and vertical plane to achieve polarization diversity. Apart from offering a polarization diversity antenna, the orientation of antennas offers a reliable link with the communication devices. The prototype antenna array is fabricated and tested for diversity performance. The performance metrics such as envelope correlation coefficient, diversity gain, and mean effective gain under isotropic, indoor, and outdoor conditions are evaluated and presented.

3D ray launching simulation of urban vehicle to infrastructure radio propagation links

Vehicular ad hoc networks (VANETs) enable vehicles to communicate with each other as well as with roadside units (RSUs), and Smart Cities must be able to take advantage of its applications and benefits on transportation operations. In urban environments some propagation impairments as reflection from, diffraction around and transmission loss through objects gives rise temporal and spatial variation of path loss and multipath effects. This work evaluates some parameters of a Vehicle-to-Infrastructure (V2I) wireless channel link such as large-scale path loss and multipath metrics in an urban scenario, using a deterministic 3D Ray-Launching (3D-RL) algorithm. Spatial analysis using Wireless Sensor Networks (WSNs) at 868 MHz, 2.4 Ghz and 5.9 GHz is presented. Results show the impact of factors as: geometry, dielectric properties and relative position of the obstacles, placement of the RSU and frequency link, in the V2I communication. The 3D-RL simulation shows better representation of the propagation phenomena when compared with an analytical path loss model, mainly at special types of intersections as roundabouts and give insight of the importance of the spatial distance and scenario segmentation to get consistent results.

A Closed-Form Approximation of Correlated Multiuser MIMO Ergodic Capacity With Antenna Selection and Imperfect Channel Estimation

Antenna selection (AS) is a promising technology to substantially reduce the complexity of massive multiple-input multiple-output (MIMO) systems. However, spatial correlation and imperfect estimation of channel state information (CSI) are well known to have a direct impact on the capacity of feasible MIMO schemes. In this paper, a tight closed-form approximation of the ergodic capacity for correlated Rayleigh fading multiuser MIMO channels with receive AS and imperfect CSI is presented. The derived expression takes into account the spatial correlation at both link sides and channel estimation error at the receiver. It can be used for arbitrary numbers of users, antennas, and receive RF chains. Furthermore, a concise analytical capacity formula is derived in the high signal-to-noise ratio (SNR) region. Numerical results validate the accuracy of our closed-form expressions over different channel conditions and SNRs. The new capacity approximation extends the state-of-the-art and enables efficient performance evaluation of varied multiantenna applications including massive MIMO for 5G systems.

Secure Multi-hop Data Transmission in Cognitive Radio Networks Under Attack in the Physical Layer

Cognitive radio networks (CRNs) have a shortcoming in that attackers can increase their ability to disturb secondary users (SUs). This paper focuses on jamming attacks in the physical layer, in which several attackers try to interrupt SUs by injecting the interference into their communications. Once a jammer transmits interfering signals on the channel during the defined time, all ongoing transmissions on this channel will be corrupted. It is quite difficult for SUs to protect a single-hop data transmission from jammers. So, obtaining a solution for secure multi-hop data transmission in the presence of jammers becomes a more challenging task in CRNs. This paper investigates a strategy to find the optimal route and channels for transmission between cognitive transmitters and receivers in the presence of jammers in CRNs. In this scenario, the jammers are located randomly and their jamming behavior is assumed to follow a Gaussian distribution. We provide an optimal link–channel pair allocation scheme in which the secondary transmitter (the source) selects the best relay and a suitable channel for each hop in the source-to-destination route to protect the information intended to the secondary receiver (the destination) from the jammers. Simulation results prove the efficiency of the proposed scheme in a CR network.

On the performance of 2[formula omitted]2 DF relay mixed RF/FSO airborne system over Exponentiated Weibull fading channel

This paper discuses the performance of a mixed free space optical (FSO)/radio frequency (RF) airborne communication system which consists of a dual-input dual-output (DIDO) relay based on decode-and-forward (DF), single-antenna RF transmitter, and single-aperture optical receiver. The Nakagami-m fading channel and exponentiated Weibull fading channel are adopted for the RF channel and FSO link, respectively. The analytical expressions of probability density function (PDF) and cumulative distribution function (CDF) about the equivalent signal-to-noise ratio (SNR) are obtained. We also analyze the average bit-error-rate and outage probability of the mixed FSO/RF system and derive closed form expressions by the Meijer’s G function. To further verify the performance of the system, we simulate to compare the performance of the DIDO and single-input single-output (SISO) relay-based communication systems. The DIDO relay-based system outperforms the SISO relay system.

A statistical channel model for a decode-and-forward based dual hop mixed RF/FSO relay network

In this paper, we have considered a dual branch with dual hop wireless cooperative communication system which comprises direct radio frequency path as well as indirect path with RF links and a free space optics (FSO) link through a Relay node (R) in between source (S) to destination (D). The faded channel for RF link is modelled with Nakagami-m distribution and the FSO link is modelled using double generalized Gamma fading. This proposed communication system uses the intensity modulation and direct detection technique for optical signal transmission and reception purpose, respectively in the FSO link. Further, we have employed selection combining diversity technique at the receiver during the use of both branches. Moreover, we have also derived probability density function and cummulative distribution function of the proposed communication system which is used to compute the performance metrics such as the outage probability and average bit error rate.

An investigation of S-DF cooperative communication protocol over keyhole fading channel

This paper investigates the keyhole or pinhole effect on the pairwise error probability (PEP) performance of the multiple-input multiple-output (MIMO) space–time block-code (STBC) based selective decode and forward (S-DF) protocol. The closed form PEP expressions are derived for several configurations in terms of number of hops, phases, and relays over Nakagami-m fading channel, with perfect and imperfect channel state information (CSI), and with and without the keyhole condition. Further, a framework is developed for deriving the diversity order (DO) for each configuration. It demonstrates that full DO for cooperation protocol can be achieved when there is a knowledge of perfect CSI. A convex optimization framework is formulated for obtaining the optimal source–relay power allocation factors which significantly improve the end-to-end reliability of the system under power constraint scenarios. Monte Carlo simulations are performed for both equal and optimal power allocation factors and results show the substantial improvement in PEP performance with an increase in the value of the shape parameter and relay to destination (RD) link channel variance. Results show an improved PEP performance by increasing the RD link channel variance in comparison to increasing the source to relay (SR) link channel variance. Also PEP performance degrades for keyhole Nakagami-m fading channel as compared to Nakagami-m fading channel. Simulation results are in close agreement with the analytical results at high signal to noise ratio (SNR) regimes.