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The aim of channel models is the effective prediction of wireless channels in applicationspecific environments in order to successfully design wireless communication systems. For THz communications, deterministic ray-optical channel predictions are very common. This paper shows inherent limitations of ray-tracing based models due to the accuracy of three-dimensional models of the environment in the context of THz communications and presents a new hybrid channel model approach that combines ray-optical channel predictions with an analytic path gain model extracted from measurements. The model is applied for switchable, point-to-point, wireless inter-rack links at THz frequencies in a data center that make the data center network reconfigurable at runtime. The channel parameters derived by the novel hybrid approach show promising results compared with channel parameters extracted from conducted reference measurements with an overall path gain error below 5 dB for residual multipath components.

This article presents comprehensive double-directional channel measurements with time-domain channel sounding at 300 GHz that characterize the channel of wireless links in a data center. The channels are classified into three scenario-dependent use cases and are individually analyzed providing channel parameters as a function of the required signal-to-noise ratio of the prospective communication system. The spatial and temporal analysis of the channel reveals relevant propagation effects such as the influence of scattering and derives relations between the channel parameters of the propagation and the radio channel. The analysis shows that multipath propagation becomes relevant for systems with high signal-to-noise ratio requirements despite high-gain directional antennas. A first order approximation of relevant propagation effects complements the analysis. The measurement data of the whole measurement campaign with 18250 calibrated impulse responses including all meta data is published so that the research community has a collective benefit.

One of the fundamental challenges in 5G and beyond technologies is to support short packet transmissions while ensuring ultra-reliable communication. Due to the distributed nature of the networks, such as machine-to-machine (M2M) communications, interference is unavoidable. The impact of interference on the system’s performance must be better understood when users are constrained to transmit short packets. In addition, users’ traffic is bursty. Thus, they may not always have data to send. This work considers a two-user Z-interference channel (Z-IC) under Rayleigh fading. The work characterizes the stability region corresponding to prominent interference mitigation schemes such as treating interference as noise, successive interference cancellation, and joint decoding schemes using the finite block-length information theory framework. The developed results consider the packet length, rate, and underlying channel model. Evaluating stability region involves determining the probability of successful decoding for the various interference mitigation techniques. The different probabilities of successful decoding are characterized for various interference mitigation techniques. These results are not explored in the existing literature in the context of Z-IC. The developed results also help to explore the impact of interference on average delay and the average age of information for various interference mitigation techniques.

Millimeter-wave (mmWave) communications promise Gigabit/s data rates thanks to the availability of large swaths of bandwidth between 10–100 GHz. Although cellular operators prefer the lower portions of the spectrum due to popular belief that propagation there is more favorable, the measurement campaigns to confirm this – conducted by ten organizations thus far – report conflicting results. Yet it is not clear whether the conflict can be attributed to the channel itself – measured in different environments and at different center frequencies – or to the differences in the organizations’ channel sounders and sounding techniques. In this paper, we propose a methodology to measure mmWave frequency dependence, using the 26.5–40 GHz band as an example. The methodology emphasizes calibration of the equipment so that the measurement results represent the channel alone (and not the channel coupled with the channel sounder). Our results confirm that free-space propagation is indeed frequency invariant – a well understood phenomena but to our knowledge reported nowhere else at mmWave to date. More interestingly, we found that specular paths – the strongest after the line-of-sight path and so pivotal to maintaining connectivity during blockage – are the least invariant compared to weaker diffracted and diffuse paths.

Wireless systems have become an increasingly pivotal part of our lives. Various critical applications and use cases such as healthcare, financial transactions, e-commerce, transportation, industrial automation, etc. rely on secure and reliable communication for their proper operation. Despite their widespread adoption, conventional cryptographic security mechanisms are unable to scale with the increasingly decentralized and heterogeneous networks. Physical layer security (PLS), on the other hand, provides a promising complementary solution to ensure authenticity, confidentiality, integrity, and availability of legitimate transmissions by exploiting the dynamic characteristics of the wireless environment. Despite the plethora of literary works regarding different facets of PLS being present, a unified framework is still absent. In this paper, we provide a PLS framework that not only encompasses the existing works but also enables the development of next-generation PLS methods. In line with this, the importance of PLS for emerging technologies such as joint sensing and communication, vehicular communication, non-terrestrial networks, millimeter-wave, terahertz communication, etc. is highlighted. Furthermore, the key challenges and directions for future PLS mechanisms are identified.

The low terahertz band (0.1–1 THz) offers very high data rates for novel mobile applications and constitutes a promising candidate to meet the requirements in aviation, enabling future wireless in-flight entertainment (IFE) systems. An extensive knowledge of the propagation effects in the radio channel in complex scenarios is a prerequisite to successfully design a communication system. This article presents a measurement campaign in a real aircraft investigating the radio channel at 300 GHz for different deployments of a wireless IFE system. The propagation effects as well as temporal and spatial channel characteristics are analyzed for likely communication links between an access point and a user equipment (UE). In the same way, interference links between two UEs are studied, reporting transmission and reflection losses for various components of the aircraft. A deterministic and geometry-based channel model is derived and extended to cover the effect of human blockage that suggests an integration of the access point into the passenger service unit. The measurement and realistic path loss models can be used in further link and system level simulations and contribute to the design of future IFE systems. [ABSTRACT FROM AUTHOR]

Go provides a new concurrency mechanism based on message-passing, which brings a series of new concurrency bugs. The existing tools are highly dependent on model-checking methods in which they take the source program as the input of model-checking tools to detect the potential concurrent bugs. However, these methods can only qualitatively obtain the concurrency of the program but not obtain the exact number of concurrency bugs in the program. Meanwhile, these approaches are not sensitive to dead codes, which are prone to false negatives. Furthermore, few works have been done on detecting WaitGroup-related bugs in Go concurrent programming, which may cause deadlock. To this end, this paper proposes a novel approach GoDetector to detect concurrent bugs. GoDetector uses a detecting algorithm and a pushdown automaton to verify the channel-related concurrent bugs and WaitGroup-related concurrent bugs separately. To support the evaluation of the tool, 30 benchmarks are collected from the existing tools. GoDetector reports 2 channel safety errors, 29 deadlocks, and 11 WaitGroup-related errors. Compared with the existing tool Godel, GoDetector has the capacity to report more concurrency bugs and fewer false positives. GoDetector also offers additional support for the detection of WaitGroup variables. The experimental results indicate that GoDetector is more efficient at detecting the concurrency in regards to accuracy and diversity.

This paper presents a novel technique for estimating the path loss parameters of radio channels using monostatic radar. To this end, a two-way path loss model for a scenario using monostatic radar for a sub-terahertz (sub-THz) band channel measurement is expressed as a function of a parameter of a one-way path loss model, and then the path loss parameters are estimated using the maximum-likelihood estimation algorithm based on linear regression models, which is based on single reference distance and dual reference distances. To verify the effectiveness of the proposed method, a path loss measurement experiment is conducted in an indoor environment using a frequency modulated continuous wave (FMCW) radar system with the base frequency of 119.5 GHz and the bandwidth of 5 GHz, and then the estimation results based on the proposed method are analyzed.

Underwater collaborative work between small mobile platforms (SMP) such as divers, litter submarine or AUV, requires a high data rate communication system which is compact, reliable, affordable and eye-safe. The high bandwidth of LED-based underwater wireless optical communication (UWOC) is an advantage. Artificial, emulated as well as simulated, turbid underwater channel has been studied recently, but no practical nature water. To fully meet the requirements of challenging turbid underwater channel scenarios for SMP, we demonstrated a green LED-based UWOC system up to a bandwidth of 3.4 MHz in a highly-turbid nature lake water. Through a contrast wireless optical communication (WOC) experiment in air, turbid water channel is observed to compensates the receiving signal amplitude attenuates after propagating a longer attenuation length due to multiple-scattered light caused diffusion, and thus to be more like a single-input multi-output (SIMO) system. From our experimental observation, the SIMO channel model could be employed not only in turbulent UWOC, but also in highly turbid UWOC. Moreover, turbid water channel is observed a “frequency selection” effect, thus LED with lower threshold voltage at higher frequency would optimize bandwidth and link range, and a robust pre-code for interference cancellation would be a well-direct choice to constructing different UWOC system in highly turbid water for SMP. Our finding will provide a new reference complementing the current LED-based UWOC systems in realistic water environment.

Online word of mouth is shifting from personal computer (PC)-based channels to mobile-based channels in this mobile marketing age, which leads to the question of whether mobile word of mouth is shorter and louder than the PC word of mouth? By investigating the 162 452 pieces of online word of mouth created by 19 496 users on a top-three online shopping website in China during a two-year period, this paper successfully discovered that mobile reviews are shorter than PC reviews and that mobile ratings are more extreme than the PC ratings. These findings lead to the managerial implications that on one hand, managers may direct reviewers to PC channels to generate longer and consequently higher-quality reviews. On the other hand, managers of higher/lower quality products may prefer mobile/PC channels such that there products' merits can be underlined whereas their products' shortcomings may be obscured.

A 28 GHz millimeter-wave (mm-wave) propagation measurement campaign was performed to predict the multiple-input multiple-output (MIMO) channel performance in a tunnel environment. Two kinds of polarization configurations were studied in this paper. In order to overcome the serious path loss (PL) of mm-wave propagation, a high gain directional horn antenna was used in the measurements of tunnel environment. The measurement results and simulation results at same specific locations are compared. The result of comparison indicates that the simulation model matches the measurement well. Then the MIMO capacity at other locations of the tunnel can be predicted by the simulation model. Further-more, it is inferred that the antenna array elements of horizontally polarized configuration have higher capacity than the vertically polarized under the constant signal-to-noise ratio (SNR).

We employ ZnSe films and graphene to act as light-absorbing layer and channel, respectively. Low-flexibility yet high-absorbance ZnSe light-absorbing layer makes contribution to the absorbance and have no negative impact on the device flexibility, while high-flexibility graphene films determine the flexibility. As a result, the image sensors based on 4-inch flexible ZnSe/graphene hybrids with a high responsivity of $1.5\times 10^{{6}}$ A/W could work stably under the large strain up to 0.2%. This is one order of magnitude larger than that of pure ZnSe films-based devices. More importantly, they make a stable performance under the strain of 0.2% after 10,000 bending cycles or a bending duration of 1000 h. [ABSTRACT FROM AUTHOR]

In this paper, we propose an agent-based architecture for remote collaboration support systems that enables the exchange of synchronous and asynchronous multimedia streams at remote sites using an Internet of Multimedia Things (IoMT) approach. First, we design and implement Internet of Things (IoT) applications that contain simple sensors and actuators. These applications are modularized into agent-based subsystems that can be incorporated into an IoT application with agent operations. Our aim is to develop remote collaboration support applications composed of video, data, and document channels. Because the applications will exchange enormous multimedia streams between remote sites, we propose a novel IoMT system architecture composed of several channel types that consist of various resource and network components. Users can dynamically incorporate these channels into applications to update the IoMT system’s effects. Finally, we demonstrate and discuss the experimental results of our application to validate its ability to rapidly supply multimedia resources via multi-agent collaboration. Adding to its novelty, the developed system is in practical use for collaboration between France and Japan.

Bluetooth low energy (BLE) technology coupled with fingerprinting provides a simple way to position users with high accuracy in indoor environments. In this paper, we study the effect of BLE protocols and channels on indoor positioning using different distance and similarity measures in a controlled environment. With the aim of reproducing a real positioning system situation, we also study the effect of the user's orientation in the positioning phase and, consequently, provide accuracy and precision results for each orientation. In a 168-m2 testbed, 12 beacons configured to broadcast with the Eddystone and iBeacon protocols were deployed and 40 distance/similarity measures were considered. According to our results, in a specific orientation there is a group of distance metrics coupled with a protocol-channel combination that produces similar accuracy results. Therefore, choosing the right distance metric in that specific orientation is not as critical as choosing the right protocol and, especially, the right channel. There is a trend whereby the protocol-channel combination that provides the best accuracy is almost unique for each orientation. Depending on the orientation, the accuracies obtained for the above mentioned group of distances are within the range of 1.1-1.5 m and the precisions are 90% within the range of 1.5-2.5 m.

We address the estimation of the Ricean $K$ factor when the available complex channel samples are noisy and subject to Nakagami- $m$ shadowing, i.e., the line-of-sight component is modeled as a Nakagami- $m$ random variable. We propose two estimators: one based on the expectation-maximization (EM) procedure, and a second one based on the method of moment (MoM). The MoM estimator can be used to initialize the EM procedure. We show by simulations that the two proposed estimators outperform the existing ones. [ABSTRACT FROM AUTHOR]

In this brief, a novel algorithm is proposed for timing and frequency synchronization and doubly selective channel (DSC) estimation in the uplink of orthogonal frequency division multiple access systems. By using a basis expansion model (BEM) to represent a DSC, a maximum likelihood approach is proposed to jointly estimate the timing and carrier frequency offsets of different users as well as the BEM coefficients of the time-varying channels. A space-alternating generalized expectation-maximization algorithm is then employed to transform the maximization problem for all users into several simpler maximization problems for a single user. Implementation issues are investigated and, the computational complexity and mean square error of the proposed scheme are evaluated. Performance assessment of the new scheme shows a significant improvement as compared with previous methods. [ABSTRACT FROM AUTHOR]

We investigate the dynamics of a chirped Airy pulse in a fiber under the action of third-order dispersion. We found an interesting phenomenon in which the pulse is focused and where the pulse profile changes slowly within a distance of several dispersion lengths, which is named a channel. The amplitude and the length of the channel depends on the chirp parameter. The underlying physical mechanism for this phenomenon is also discussed.

Recently, field-programmable gate array (FPGA) vendors (such as Altera) have started to address the programmability issues of FPGAs via OpenCL SDKs. In this paper, we analyze the performance of relational database applications on FPGAs using OpenCL. In particular, we study how to improve the performance of data partitioning, which is a very important building block in relational database. Since the data partitioning causes random memory accesses, it is time-consuming, and then, it has been the major bottleneck for database operators, such as partitioned hash join. In particular, we import the state-of-the-art OpenCL implementation of data partitioning from OmniDB, which was originally designed and optimized for CPUs/GPUs, and we find that this implementation suffers from both lock overhead and memory bandwidth overhead. Accordingly, we present a multikernel approach to address the lock overhead by leveraging two emerging features (task kernel and channel) from Altera OpenCL software development kit. In order to reduce the memory bandwidth overhead, on-chip buckets are used to reduce the number of random global memory transactions. We further develop an FPGA-specific cost model to guide the parameter configuration. We evaluate the proposed design on a recent OpenCL-based FPGA. We have applied our optimized partitioning method to a number of data processing tasks, including hash join, histogram, and hash search. Our experimental results demonstrate that our cost model can accurately guide the user to determine the optimal parameter combination for data partitioning and the optimal parameter combination can achieve $16.6\times$ speedup over the default multithreaded implementation. [ABSTRACT FROM PUBLISHER]

The biological function of a macromolecule often requires that a small molecule or ion is transported through its structure. The transport pathway often leads through void spaces in the structure. The properties of transport pathways change significantly in time; therefore, the analysis of a trajectory from molecular dynamics rather than of a single static structure is needed for understanding the function of pathways. The identification and analysis of transport pathways are challenging because of the high complexity and diversity of macromolecular shapes, the thermal motion of their atoms, and the large amount of conformations needed to properly describe conformational space of protein structure. In this paper, we describe the principles of the CAVER 3.0 algorithms for the identification and analysis of properties of transport pathways both in static and dynamic structures. Moreover, we introduce the improved clustering solution for finding tunnels in macromolecules, which is included in the latest CAVER 3.02 version. Voronoi diagrams are used to identify potential pathways in each snapshot of a molecular dynamics trajectory and clustering is then used to find the correspondence between tunnels from different snapshots. Furthermore, the geometrical properties of pathways and their evolution in time are computed and visualized. [ABSTRACT FROM PUBLISHER]

This paper presents for the first time the design, fabrication, and demonstration of a micromachined silicon dielectric waveguide based sub-THz interconnect channel for a high-efficiency, low-cost sub-THz interconnect, aiming to solve the long-standing intrachip/interchip interconnect problem. Careful studies of the loss mechanisms in the proposed sub-THz interconnect channel are carried out to optimize the design. Both theoretical and experimental results are provided with good agreement. To guide the channel design, a new figure of merit is also defined. The insertion loss of this first prototype with a 6-mm-long interconnect channel is about 8.4 dB at 209.7 GHz, with a 3-dB bandwidth of 12.6 GHz. [ABSTRACT FROM AUTHOR]

We present an original batch process to connect a bulk microfluidic channel to a surface nanofluidic channel for a wide variety of microfluidic and lab-on-chip applications. The approach relies on a two-step lithography process using a thermally decomposable polynorbornene resist unity to form the sacrificial channel layer. A high aspect ratio silicon via is deep reactive ion etched to the subsurface microchannel. Lithography of a high viscosity unity plug is followed by lithography of a low viscosity unity sacrificial layer to form the nanofluidic channel. A plasma-enhanced chemical vapor deposition nitride layer is deposited to encapsulate the nanochannel and the sacrificial polymer is decomposed by baking. This technique enables fabrication of complete off-chip to nanochannel fluidic systems. We emphasize the benefit of sacrificial polymers to form long 3-D nanofluidic channels. [2014-0288] [ABSTRACT FROM AUTHOR]

Modern radio front ends are required to operate over diverse channel conditions requiring the incorporation of significant performance overheads into their design. This results in significantly higher power consumption over most of the operational period since the worst case channels are not statistically prevalent. Adaptive systems solve this problem by adapting the performance and power consumption depending on channel conditions. In this paper, it is demonstrated that depending upon the throughput requirements of the system multiple low-power adaptation modes can be designed. These modes ensure either highest throughput operation or lowest energy-per-bit operation. The operation of these modes is demonstrated in simulation using multiple-input-multiple-output (MIMO) receiver and transmitter front ends. Subsequently, the concepts are demonstrated in hardware for both MIMO and single-input-single-output front ends. [ABSTRACT FROM PUBLISHER]

Anytime transmission was previously shown to be necessary and sufficient for tracking and controlling an unstable plant over a noisy channel. In this paper, we propose an efficient channel coding scheme for anytime transmission. We design this coding scheme based on spatially coupled codes and investigate its performance over binary erasure channels (BEC) and binary input additive white Gaussian noise (BIAWGN) channels. Through density evolution analysis, we asymptotically show the desired anytime properties of the proposed code. For the BEC, we derive the corresponding delay-exponent and numerically predict the finite-length performance of the proposed anytime code. We also propose adaptive window decoding techniques to ensure low complexity anytime receivers. [ABSTRACT FROM PUBLISHER]

The problem of optimum signal detection for the channel-aided free-space optics (FSO) communications is addressed. It is assumed that the avalanced-photo-detection (APD) is utilized for the direct-detection (DD) of on-off-keying (OOK) signals impaired by optical turbulence. The average primary photon count due to the background radiation is assumed to be large enough to allow for a Gaussian operation for the APD receiver. In the presence of large signal fluctuations, it is shown that the optimum structure, motivated by the maximum a-posteriori (MAP) rule, is a dual-threshold architecture where the thresholds are functions of the channel state. To remedy the channel effects, the channel state is estimated and the estimates are used to set the receiver thresholds, thereby resulting in a channel-aided scenario. Performance of the proposed optimum receiver is assessed in terms of the overall bit error rate. To assess performance, it is assumed that the turbulent channel obeys a Gamma-Gamma (GG) distribution and that the channel estimator yields an unbiased and efficient estimate of the channel state. This study shows that channel-aided reception reduces the error floor. Further, channel-aided receivers have error-floor-free signal ranges that are larger than those of the standard receivers'. [ABSTRACT FROM AUTHOR]