Abstract: This paper presents a novel and practical study on the position-based radio propagation channel for High-Speed Railway by performing extensive measurements at 2.35 GHz in China. The specification on the path loss model is developed. In particular, small scale fading properties such as K-factor, Doppler frequency feature and time delay spread are parameterized, which show dynamic variances depending on the train location and the transceiver separation. Finally, the statistical position-based channel models are firstly established to characterize the High-Speed Railway channel, which significantly promotes the evaluation and verification of wireless communications in relative scenarios.

Abstract: Millimeter wave (mmWave) systems must overcome the heavy attenuation at high frequency to support high-throughput wireless communication. The small wavelength in mmWave systems enables beamforming using large antenna arrays to combat path loss with large array gain. Beamforming in traditional microwave systems is often done at baseband for maximum flexibility. Such baseband processing requires a dedicated transceiver chain per antenna element. The high cost of radio frequency (RF) chains in mmWave systems, however, makes supporting each antenna with a dedicated RF chain expensive. This mismatch between the number of antennas and transceiver chains makes baseband processing infeasible; thus mmWave systems typically rely on a traditional approach known as beam steering which can be done at RF using inexpensive phase shifters. Unlike baseband precoding, however, traditional beam steering is not explicitly designed to achieve the capacity of the mmWave channel. In this paper, we consider both beamforming and multi-stream precoding in single user systems with large mmWave antenna arrays at both transmitter and receiver. Using a realistic channel model, we show that the unconstrained capacity-achieving precoding solutions converge to simple beam steering solutions. Therefore, in large mmWave systems, no rate loss is incurred by adopting the traditional lower-complexity solution.

Abstract: Millimeter wave (mmWave) systems must overcome heavy signal attenuation to support high-throughput wireless communication links. The small wavelength in mmWave systems enables beamforming using large antenna arrays to combat path loss with directional transmission. Beamforming with multiple data streams, known as precoding, can be used to achieve even higher performance. Both beamforming and precoding are done at baseband in traditional microwave systems. In mmWave systems, however, the high cost of mixed-signal and radio frequency chains (RF) makes operating in the passband and analog domains attractive. This hardware limitation places additional constraints on precoder design. In this paper, we consider single user beamforming and precoding in mmWave systems with large arrays. We exploit the structure of mmWave channels to formulate the precoder design problem as a sparsity constrained least squares problem. Using the principle of basis pursuit, we develop a precoding algorithm that approximates the optimal unconstrained precoder using a low dimensional basis representation that can be efficiently implemented in RF hardware. We present numerical results on the performance of the proposed algorithm and show that it allows mmWave systems to approach waterfilling capacity.

Abstract: Although acoustic waves are the most versatile and widely used physical layer technology for underwater wireless communication networks (UWCNs), they are adversely affected by ambient noise, multipath propagation, and fading. The large propagation delays, low bandwidth, and high bit error rates of the underwater acoustic channel hinder communication as well. These operational limits call for complementary technologies or communication alternatives when the acoustic channel is severely degraded. Magnetic induction (MI) is a promising technique for UWCNs that is not affected by large propagation delays, multipath propagation, and fading. In this paper, the MI communication channel has been modeled. Its propagation characteristics have been compared to the electromagnetic and acoustic communication systems through theoretical analysis and numerical evaluations. The results prove the feasibility of MI communication in underwater environments. The MI waveguide technique is developed to reduce path loss. The communication range between source and destination is considerably extended to hundreds of meters in fresh water due to its superior bit error rate performance.

Abstract: We discuss the applicability of simplified Two-Ray Ground path loss models to simulation-based performance evaluation studies of Inter-Vehicle Communication (IVC) protocols. We contrast this with the applicability of a more exact Two-Ray Interference model. A key result is that, in most cases, the commonly used simplified Two-Ray Ground models add no additional value compared to the most simple Free-space model — in particular in highway and suburban environments. We further argue that replacing a simplified with a fully featured Two-Ray Interference model can not only substantially improve the accuracy of simulation results but also allow capturing one notable artifact that becomes immediately visible in field tests, namely strong signal attenuation at short and medium ranges. We implemented the Two-ray Interference model within the Veins simulation framework and validated it using analytical predictions and field measurements. We show the impact of the more accurate Two-Ray Interference model, which only comes with negligible additional computational cost for simulation experiments.

Abstract: Underwater physical medium is a challenging environment for communication using radio frequency (RF) or acoustic waves due to strong attenuation, delay, multi-path fading, power and cost limitations. Discovered a century ago, magneto-inductive (MI) communication technique stands as a strong alternative paradigm due to its independence of environmental impairments including multi-path fading, dynamic channels and high propagation delays experienced by acoustic waves. Furthermore, MI technique yields networking solutions exploiting low-cost, easily-deployable and flexible antenna structures, and the possibility of forming networks of magnetic waveguides defeating path loss. In this work, highly power efficient and fully connected underwater communication networks (UWCNs) composed of transceiver and relay induction coils are presented. Three dimensional (3D) UWCNs are analysed in terms of basic communication metrics, i.e, signal-to-noise ratio, bit-error rate, connectivity and communication bandwidth. The performance studies of realistic 3D networks covering hundreds of meters sea depths and a few km2 areas show that fully connected multi-coil networks with communication bandwidths extending from a few to tens of KHz are possible. Furthermore, the performance dependence on coil properties and network size is theoretically modelled. Results show that MI wireless communication is a promising alternative for UWCNs and future research challenges are pointed out.

Abstract: Accurate characterization of the radio channel in tunnels is of great importance for new signaling and train control communications systems. To model this environment, measurements have been taken at 2.4 GHz in a real environment in Madrid subway. The measurements were carried out with four base station transmitters installed in a 2-km tunnel and using a mobile receiver installed on a standard train. First, with an optimum antenna configuration, all the propagation characteristics of a complex subway environment, including near shadowing, path loss, shadow fading, fast fading, level crossing rate (LCR), and average fade duration (AFD), have been measured and computed. Thereafter, comparisons of propagation characteristics in a double-track tunnel (9.8-m width) and a single-track tunnel (4.8-m width) have been made. Finally, all the measurement results have been shown in a complete table for accurate statistical modeling.

Abstract: In this paper, we consider the problem of robotic router formation, where two nodes need to maintain their connectivity over a large area by using a number of mobile routers. We are interested in the robust operation of such networks in realistic communication environments that naturally experience path loss, shadowing, and multipath fading. We propose a probabilistic router formation and motion-planning approach by integrating our previously proposed stochastic channel learning framework with robotic router optimization. We furthermore consider power constraints of the network, including both communication and motion costs, and characterize the underlying tradeoffs. Instead of taking the common approach of formation optimization through maximization of the Fiedler eigenvalue, we take a different approach and use the end-to-end bit error rate (BER) as our performance metric. We show that the proposed framework results in a different robotic configuration, with a considerably better performance, as compared with only considering disk models for communication and/or maximizing the Fielder eigenvalue. Finally, we show the performance with a simple preliminary experiment, with an emphasis on the impact of localization errors. Along this line, we show interesting interplays between the localization quality and the channel correlation/learning quality.

Abstract: A wireless body area network (WBAN) consists of a wireless network with devices placed close to, attached on, or implanted into the human body. Wireless communication within human body experiences loss in the form of attenuation and absorption. A path loss (PL) model is thus necessary to identify these losses in homogeneous medium which is proposed in this paper. The model is based on 3-D electromagnetic simulations and is validated with measurements. Simulations are further extended for different relative permittivity er and conductivity σ combinations spanning a range of human tissues at 2.45 GHz, and the influence of the dielectric properties on PL is investigated and modeled. This model is valid for insulated dipole antennas separated by a distance up to 8 cm. Furthermore, PL in homogeneous medium is also compared with the path loss in heterogeneous tissues. The path loss model for homogeneous medium is the first in-body model as a function of er, σ, and separation between antennas and can be used to design an in-body communication system.

Abstract: Wireless underground networks are an emerging technology which have application in a number of scenarios. For exam-ple, in a mining disaster, flooding or a collapse can isolate portions of underground tunnels, severing wired communication links and preventing radio communication. In this pa-per, we explore the use of low frequency magnetic fields for communication, and present a new hardware platform that features triaxial transmitter/receiverantenna loops. We point out that the fundamental problem of the magnetic channel is the limited bitrate at long ranges, due to the extreme path loss of 60 dB/decade. To this end, we present two complementary techniques to address this limitation. Firstly, we demonstrate magnetic vector modulation, a technique which modulates the three dimensional orientation of the magnetic vector. This increases the gross bitrate by a factor of over 2.5, without an increase in transmission power or bandwidth. Secondly, we show how in a multi-hop network latencies can be dramatically reduced by receiving multiple parallel streams of frequency multiplexed data in a many-to-one configuration. These techniques are demonstrated on a working hardware platform, which for flexible operation, features a software defined magnetic transceiver. Typical communication range is approximately 30 m through rock.

Abstract: The objective of this paper is to illustrate that electromagnetic macro modeling can properly predict the path-loss exponent in mobile cellular wireless communication. This represents the variation of the path loss with distance from the base-station antenna. Specifically, we illustrate that the path-loss exponent in cellular wireless communication is three, preceded by a slow-fading region, and followed by the fringe region, where the path-loss exponent is four. The sizes of these regions are determined by the heights of the base-station transmitting antennas and the receiving antennas. Theoretically, this is illustrated through the analysis of radiation from a vertical electric dipole situated over a horizontal imperfect ground plane, as first considered by Sommerfeld in 1909. To start with, the exact analysis of radiation from the dipole is made using the Sommerfeld formulation. The semi-infinite integrals encountered in this formulation are evaluated using a modified saddle-point method for field points moderate to far distances away from the source point, to predict the appropriate path-loss exponents. The reflection-coefficient method is also derived by applying a saddle-point method to the semi-infinite integrals, and this is shown to not provide the correct path-loss exponent that matches measurements. The various approximations used to evaluate the Sommerfeld integrals are described for different regions. It is also important to note that Sommerfeld's original 1909 paper had no error in sign. However, Sommerfeld overlooked the properties associated with the so-called “surface-wave pole.” Both accurate numerical analyses, along with experimental data, are provided to illustrate the above statements. In addition, Okumura's experimental data, and extensive data taken from seven different base stations in urban environments at two different frequencies, validate the theory. Experimental data revealed that a macro modeling of the environment, using an appropriate electromagnetic analysis, can accurately predict the path-loss exponent for the propagation of radio waves in a cellular wireless communication scenario.

Abstract: A Bayesian method for dynamical off-line estimation of the position and path loss model parameters of a WLAN access point is presented. Two versions of three different on-line positioning methods are tested using real data. The tests show that the methods that use the estimated path loss parameter distributions with finite precisions outperform the methods that only use point estimates for the path loss parameters. They also outperform the coverage area based positioning method and are comparable in accuracy with the fingerprinting method. Taking the uncertainties into account is computationally demanding, but the Gauss-Newton optimization method is shown to provide a good approximation with computational load that is reasonable for many real-time solutions.

Abstract: This paper investigates the aggregate interference on a primary user caused by a random number of cognitive radio transmitters distributed in a finite ring. A composite model involving path loss, Rayleigh fading, and shadowing is considered. The exact closed-form moment generating function and an accurate approximation are derived. The aggregate interference is shown to be accurately approximated by a Gamma distribution. The exact outage and an asymptotic approximation are derived.

Abstract: An experimental characterization of the ultrawideband (UWB) propagation channel in an underground mine environment over the frequency range from 3 GHz to 10 GHz is reported in this paper. Two kinds of antennas, directional and omnidirectional, were used to investigate the effect of the antenna directivity on the path loss propagation and on the time dispersion parameters in both line-of-sight (LOS) and no-line-of-sight (NLOS) underground galleries. The measurement and simulation results show that the path loss exponents in an underground environment are larger than their counterparts in an indoor environment. In NLOS, the directional-directional (Direct-Direct) antenna combination showed better radiation efficiency for reducing the time dispersion parameters while the omnidirectional-omni directional (Omni-Omni) case resulted better performance in term of path loss. After extracting the channel parameters, a statistical modeling of the UWB underground channel based on data measurements was conducted.

Abstract: In this paper, a novel single-scatter path loss model is presented for non-line-of-sight (NLOS) ultraviolet (UV) channels. This model is developed based on the spherical coordinate system and extends the previous restricted models to handle the general noncoplanar case of arbitrarily pointing transmitter and receiver. Numerical examples on path loss are illustrated for various system geometries. These results are verified with a Monte Carlo (MC) model, demonstrating the validity of this model.

Abstract: There are provided a base station, a terminal, a communication system, and a communication method in a communication system in which a base station 101 and a terminal 102 communicate with each other, in which the base station 101 can efficiently notify the terminal 102 of control information. The terminal includes a receiving unit 605 configured to receive a radio resource control signal including information concerning a path loss reference resource and information concerning an uplink power control related parameter configuration, and a transmit power control unit 6015 configured to set a path loss and an uplink transmit power on the basis of the information concerning the path loss reference resource and the information concerning the uplink power control related parameter configuration.

Abstract: A multihop transmission scheme is proposed and studied, where all the relay nodes (RNs) of a multihop link are assumed to have buffers for temporarily storing their received packets. Hence, the RNs are operated under the so-called store-and-forward relaying scheme. As a benefit of storing packets at the RNs, during each time slot, the best hop typically has the highest signal-to-noise ratio (SNR), which can be selected from the set of hops that have packets awaiting transmission in the buffer. A packet is then transmitted over the best hop. This hop selection procedure is reminiscent of selection diversity, which is referred to here as multihop diversity (MHD). In this paper, we investigate both the bit error and outage probability and the delay performance of the MHD scheme when assuming that each hop experiences both propagation path loss and independent and identically distributed (i.i.d.) flat Rayleigh fading. The medium access control (MAC) layer implementation and several closed-form formulas are derived. Both numerical and simulation results are provided to characterize the achievable performance of the MHD scheme. Our performance results show that relying on multiple hops has the potential to provide a significant diversity gain, which may be exploited for enhancing the reliability of wireless multihop communications.

Abstract: In a communication system including multiple mobile station apparatuses and at least one base station apparatus, the base station apparatus efficiently controls transmission of an uplink signal to the mobile station apparatuses. A path loss calculator calculates path loss on the basis of a reference signal received by a reception processing unit. A transmit power setter sets desired transmit power of an uplink signal using the path loss calculated by the path loss calculator. Additionally, a power head room controller generates power head room that is information concerning a margin of the transmit power using the desired transmit power set in the transmit power setter to control transmission of the power head room. The power head room controller determines to transmit the power head room upon switching of a kind of the reference signal used in the calculation in the path loss calculator.

Abstract: We seek to provide practical lower bounds on the prediction accuracy of path loss models. We describe and implement 30 propagation models of varying popularity that have been proposed over the last 70 years. Our analysis is performed using a large corpus of measurements collected on production networks operating in the 2.4 GHz ISM, 5.8 GHz UNII, and 900 MHz ISM bands in a diverse set of rural and urban environments. We find that the landscape of path loss models is precarious: typical best-case performance accuracy of these models is on the order of 12–15 dB root mean square error (RMSE) and in practice it can be much worse. Models that can be tuned with measurements and explicit data fitting approaches enable a reduction in RMSE to 8-9 dB. These bounds on modeling error appear to be relatively constant, even in differing environments and at differing frequencies. Based on our findings, we recommend the use of a few well-accepted and well-performing standard models in scenarios where a priori predictions are needed and argue for the use of well-validated, measurement-driven methods whenever possible.

Abstract: This paper considers the analytical performance of primary users (PUs) subject to interference due to secondary users (SU) in an underlay cognitive radio system over Rayleigh fading. In particular, we focus on a more general spatial configuration where the interfered PU, not only located at the center of the cell, is having a protective region which is free of SUs and the SUs are distributed over a finite area in contrast to the commonly used infinite area assumption. We first characterize the statistical properties of the aggregate interference at the PU due to SUs, by deriving new exact closed form expressions for the moment generating function, cumulants, first, second and third moments and first order expansions of the cumulative distribution functions corresponding to propagation scenarios with path loss factors, two and four. We then investigate the PU performance by presenting new analytical expressions for the outage probability, amount of fading as well as the diversity order and coding gain. Our results indicate that the PU can achieve the full diversity gain given a non-zero protective region around the PU.

Abstract: In this paper we address two basic questions in wireless communication: First, how long does it take to schedule an arbitrary set of communication requests? Second, given a set of communication requests, how many of them can be scheduled concurrently? Our results are derived in an interference model with geometric path loss and consist of efficient algorithms that find a constant approximation for the second problem and a logarithmic approximation for the first problem. In addition, we analyze some important properties of the interference model and show that it is robust to various factors that can influence the signal attenuation. More specifically, we prove that as long as such influences on the signal attenuation are constant, they affect the capacity only by a constant factor.

Abstract: The present invention proposes a method and device for controlling uplink power. A central processing unit firstly determines a path loss generation mode for a user equipment according to a predetermined rule and then transmits an instruction to the user equipment, the instruction including the determined path loss generation mode so that the user equipment determines uplink power of fee user equipment according to the path loss generation mode. A user equipment acquires an instruction from a central processing unit to indicate a path loss generation mode of the user equipment., then determines a path loss of the user equipment according to the path loss generation mode indicated by the central processing unit., and then acquires uplink transmission power of the user equipment according to the determined path loss of the user equipment. With the inventive solution, a central processing unit may configure a path loss generation mode flexibly for a user equipment to accommodate different uplink CoMP scenarios and thereby achieve better CoMP performance.

Abstract: Near-ground channel characterization is an important issue in most military applications of wireless sensor networks. However, the channel at the ground level lacks characterization. In this paper, we present a path loss model for three near-ground scenarios. The path loss values for each scenario were captured through extensive measurements, and then a least-square linear regression was performed. This indicates that the log-distance-based model is still suitable for path loss modeling in near-ground scenarios, and the prediction accuracy of the two-slope model is superior to that of the one-slope model. The validity of the proposed model was further verified by comparisons between the predicted and measured far-field path losses. Finally, compared to the generic models, the proposed model is more effective for the path loss prediction in near-ground scenarios.

Abstract: Antenna misalignment can lead to a severe performance deterioration of wireless THz communication links. In this paper, we propose to model the misalignment as a random process. Based on the misalignment model, Monte Carlo simulations are conducted in order to assess the impact of misalignment on THz communication channels in an office scenario. Ray tracing accounts for correct propagation conditions. Results are demonstrated in terms of the effective antenna gains and the effective resulting path losses. Different antenna directivities are considered for the transmitter and receiver. The optimum antenna configuration is determined. Furthermore, a misalignment-dependent path loss model is derived.

Abstract: In this paper, the challenges with and motivations for developing millimeter wave and terahertz communications are described. A high-level candidate architecture is presented, and use cases highlighting the potential applicability of high-frequency links are discussed. Mobility challenges at these higher frequencies are also discussed. Difficulties that arise as a result of high carrier frequencies and higher path loss can be overcome by practical, higher-gain antennas that have the added benefit of reducing intercell interference. Simulation methodology and results are given. The results show that millimeter wave coverage is possible in large, outdoor spaces, and only a reasonable number of base stations are needed. Network throughput can exceed 25 Gbit/s, and cell-edge user throughput can reach approximately 100 Mbit/s.

Abstract: Future enhanced oil recovery technology requires wireless sensor networks to effectively operate in underground oil reservoirs. In this case, the millimeter scale sensor nodes with the antennas at the same scale have to be deployed in the confined underground oil reservoir fractures. This necessitates the sensor nodes to be operating in the THz frequency range. In this paper, the propagation based on electromagnetic (EM) waves in the Terahertz band (0.1–120.0 THz) through a crude oil/water mixture and soil medium is analyzed in order to explore its applicability in underground oil reservoir assessments. The developed model evaluates the total path loss and the absorption loss that an EM wave experiences when propagating through the crude oil/water mixture and soil medium. Our results show that sensors can communicate successfully for distances up to 1 centimeter and we have determined the existence of two transmission bands, in which the path loss is below 100 dB. Among those, the frequency window, which provides best performance, determined as 70 to 85 THz. Different path and absorption loss schemes considered, which suggests that the 70 to 85 THz band is suitable for sensor communications in a medium of crude oil/water mixture and soil.

Abstract: Indoor off-body wireless MIMO links between a mobile user equipped with wearable textile patch antennas and a fixed base station exhibit specific channel behavior due to the near presence and movements of the human body. Therefore, they require a dedicated channel model that captures the effects of correlated small-scale Rayleigh fading and correlated lognormal shadowing. A methodology is presented to construct such a model, allowing to predict the bit error characteristics and channel capacity curves based on the shadowing and fading correlation matrices that are extracted from channel measurements. It is shown that by separating shadowing, including effects caused by movement and reorientation of the human body, from small-scale fading, the main mechanisms of the off-body communication link are accurately captured by the model. A clear dependence of the shadowing correlation values on the physical layout of the antenna system is found. In our measurements, shadowing is not significantly decorrelated by polarization diversity or front-to-back diversity whereas the small-scale fading is clearly decorrelated. From the model, MIMO channel realizations with identical bit error rate and channel capacity characteristics as the measured channel can be quickly generated for link emulation purposes.

Abstract: Intra-vehicular wireless sensor networks is a promising new research area that can provide part cost, assembly, maintenance savings and fuel efficiency through the elimination of the wires, and enable new sensor technologies to be integrated into vehicles, which would otherwise be impossible using wired means, such as Intelligent Tire. The most suitable technology that can meet high reliability, strict energy efficiency and robustness requirements of these sensors in such a harsh environment at short distance is Ultra-Wideband (UWB). However, there are currently no detailed models describing the UWB radio channel for intra-vehicular wireless sensor networks making it difficult to design a suitable communication system. We analyze the small-scale and large-scale statistics of the UWB channel based on a measurement campaign for a variety of sensor locations beneath the chassis of a vehicle. The analysis for large-scale statistics show that the characteristics of the channel around the tires is very different from the other parts under the chassis. The path loss exponents around the tires and under chassis are 4 and 2.2 respectively. The clustering phenomenon observed in the averaged power delay profile can be well-modeled by Saleh-Valenzuela model. The clusters decay exponentially with arrival time but with a smaller decay constant after 30ms. The decay rate of ray amplitudes is increasing with delay and can be modeled using a dual slope linear model in logarithmic scale. The best fit for inter-cluster arrival time is Weibull distribution. The analysis for small-scale statistics on the other hand show that the best fit for the received energies in each bin at 81 locations of the measurement grid is lognormal distribution with decreasing μ and almost constant σ parameters. Moreover, different bins of the delay can be assumed to fade independently. This is the first work to model small-scale channel characteristics for intra-vehicular wireless sensor networks.

Abstract: We present an ultra-wideband transceiver designed for ultra-low-power communication at sub-10 cm range. The transceiver operates at a 5.6 GHz carrier frequency, chosen to minimize path loss when using a 1 cm2 antenna, and can switch its architecture between self-synchronous rectification and low-IF to adapt its power consumption to the channel characteristic in real time. A low-power digital circuit exploits redundancy in the modulation scheme to provide a real-time BER estimate used to close the mode-switching loop. Implemented in 65 nm CMOS, the transceiver consumes 25 μW when transmitting and 245 μW when receiving in low-power mode, plus 45 μW in the clock generator, and only requires an external antenna. Dual-mode operation allows range extension and mitigates interference.