This paper proposes a path loss model for crowded outdoor environments that can consider the density of people. Measurement results in an anechoic chamber with three blocking persons showed that multiple human body shadowing can be calculated by using finite width screens. As a result, path loss in crowded environments can be calculated by using the path losses of the multipath and the multiple human body shadowing on those paths. The path losses of the multipath are derived from a ray tracing simulation, and the simulation results are then used to predict the path loss in crowded environments. The predicted path loss of the proposed model was examined through measurements in the crowded outdoor station square in front of Shibuya Station in Tokyo, and results showed that it can accurately predict the path loss in crowded environments at the frequencies of 4.7GHz and 26.4GHz under two different conditions of antenna height and density of people. The RMS error of the proposed model was less than 4dB.

The radio wave shadowing by a two-dimensional human body is examined numerically as the scattering problem by using the Method of Moments (MoM) in order to verify the equivalent human body diameter. Three human body models are examined: (1) a circular cylinder, (2) an elliptical cylinder, and (3) an elliptical cylinder with two circular cylinders are examined. The scattered fields yields by the circular cylinder are compared with measured data. Since the angle of the model to an incident wave affects scattered fields in models other than a circular cylinder, the models of an elliptical cylinder and an elliptical cylinder with two circular cylinders are converted into a circular cylinder of equivalent diameter. The frequency characteristics for the models are calculated by using the equivalent diameter.

In recent years, multiple-input multiple-output (MIMO) channel models for crowded areas, such as indoor offices, shops, and outdoor hotspot environments, have become a topic of significant interest. In such crowded environments, propagation paths are frequently shadowed by moving objects, such as pedestrians or vehicles. These shadowing effects can cause time variations in the delay and angle-of-arrival (AoA) characteristics of a channel. In this paper, we propose a method for modeling the shadowing effects of pedestrians in a cluster-based channel model. The proposed method uses cluster power variations to model the time-varying channel properties. We also propose a novel method for estimating the cluster power variation properties from measured data. In order to validate our proposed method, channel sounding in the 3GHz band is conducted in a cafeteria during lunchtime. The results for the K parameter, delay spreads, and AoA azimuth spreads are compared for the measured data and the channel data generated using the proposed method. The results indicate that the time-varying delay-AoA characteristics can be effectively modeled using our proposed method.

This paper proposes the use of two transmit and two receive antennas spaced at roughly the width of a human body to improve communication quality in the presence of shadowing by a human body in the 60GHz band. In the proposed method, the transmit power is divided between the two transmit antennas, and the receive antenna that provides the maximum receive level is then chosen. Although the receive level is reduced by 3dB, the maximum attenuation caused by human body shadowing is totally suppressed. The relationship between the antenna element spacing and the theoretical spacing based on the 1st. Fresnel zone theory is clarified. Experiments confirm that antenna spacing several centimeters wider than that given by the 1st. Fresnel zone theory is enough to attain a significant performance improvement.

In this paper, we present a weighted-polarization wearable multiple-input multiple-output (MIMO) antenna that is based on radio-frequency (RF) signal processing to realize ultra-high-speed and high-capacity mobile communications. The proposed antenna is comprised of three orthogonal dipoles, two of which can be selected according to a weight function in different usage scenarios. The weight function is determined by considering the variation in the cross-polarization power ratio (XPR) and the antenna inclination angle which depend on the radio-propagation environment and human motion. To confirm the suitability of the proposed antenna, we perform preliminary experiments to evaluate the channel capacity of a weighted-polarization wearable MIMO antenna with an arm-swinging dynamic phantom. The measured and analytical results are in good agreement, which verifies the effectiveness of the proposed antenna. We demonstrate that the proposed antenna is suitable for realizing gigabit mobile communications in future wearable MIMO applications.

In this paper, we propose a simple model for estimating the effects of human body shadowing (HBS) in high frequency bands. The model includes two factors: the shadowing width (SW), which is the width of the area with shadowing loss values greater than 0dB, and the median shadowing loss value (MSLV), which is obtained by taking the median of the shadowing loss values within the SW. These factors are determined by formulas using parameters, i.e. frequency, distance between the base station (BS) and human body, distance between the terminal and human body, BS antenna height, and direction of the human body. To obtain the formulas, a method for calculating the effects of HBS based on the uniform theory of diffraction (UTD) and a human body model comprising lossy dielectric flat plates is proposed and verified. Then, the general forms of the formulas are predicted using the theory of knife-edge diffraction (KE). A series of computer simulations using the proposed calculation method with random changes in parameters is conducted to verify the general formulas and derive coefficients for these formulas through regression formulas.

In order to verify the channel sum-rate improvement by multi-user multiple-input multiple-output (MU-MIMO) transmission in distributed antenna systems (DASs), we investigate and compare the characteristics of channel sum-rates in both centralized antenna systems (CASs) and DASs under the effects of path loss, spatially correlated shadowing, correlated multi-path fading, and inter-cell interference. In this paper, we introduce two different types of functions to model the shadowing, auto-correlation and cross-correlation, and a typical exponential decay function to model the multi-path fading correlation. Thus, we obtain the distribution of the channel sum-rate and investigate its characteristics. Computer simulation results indicate that DAS can improve the performance of the channel sum-rate compared to CAS, even in the case under consideration. However, this improvement decreases as interference power increases. Moreover, the decrease in the channel sum-rate due to the increase in the interference power becomes slow under the effect of shadowing correlation. In addition, some other analyses on the shadowing correlation that occurs on both the transmit and receiver sides are provided. These analysis results show that the average channel sum-rate in a DAS without inter-cell interference considerably decreases because of the shadowing correlation. In contrast, there appears to be no change in the CAS. Furthermore, there are two different types of sum-rate changes in a DAS because of the difference in shadowing auto-correlation and cross-correlation.

The performance of multiuser multiple-input single-output (MU-MISO) systems is not only affected by small-scale multipath fading but also by large-scale fading (i.e., shadowing) and path loss. In this paper, we concentrate on the sum rate distribution of MU-MISO systems employing linear zero-forcing beamforming, accounting for both multipath fading and shadowing effects, as well as spatial correlation at the transmit and receiver sides. In particular, we consider the classical spatially correlated lognormal model and propose closed-form bounds on the distribution of the achievable sum rates in MU-MISO systems. With the help of these bounds, we derive a relationship between the interuser distance and sum rate corresponding to 10% of the cumulative distribution function under different environmental conditions. A practical conclusion from our results based on the considered system is that the effect of spatially correlated shadowing can be considered to be independent when the interuser distance is approximately five times the shadowing correlation distance. Furthermore, a detailed analysis of the effects of composite channel attenuation consisting of multipath fading and shadowing is also provided.

The exact power distribution of the inter-cell interference is obtained explicitly for cell edge users who are surrounded by circular guard zones. Compared with recent works, the underlying channel model is generalized from Rayleigh fading to a combination of Nakagami fading and Gamma shadowing. In addtion, asymptotic analysis shows that the mean power of intercell interference changes from infinite to finite with a guard zone. Based on this interference distribution, the average capacity at the cell edge is further obtained. Special case approximation indicates that the capacity scales proportionally to the exponential of the guard zone size. Analytical capacities are validated by Monte Carlo simulations.

This paper presents an experimental study of on-body ultra-wideband (UWB) radio propagation channels within an enclosed space. To facilitate high-speed wireless body area networks, UWB is a promising technology because of its low power consumption and anti-multipath capabilities. The motivation of this study is to examine the effects of nearby humans on the UWB channels by varying the population within an elevator cabin from one (subject alone) to 20 (full capacity of the elevator). The first domain (0 < delay, t ≤ 4ns) in the measured delay profiles was either a direct (for line-of-sight) or diffracted (for non-line-of-sight) wave, which was found almost unrelated to the population; whereas the second domain (t > 4ns) highly depended on it. Total received power and delay spreads decreased with increasing the population. In addition, by varying human population, average power delay profiles were modeled based on measurements.

This paper describes a robust three-dimensional (3D) surface reconstruction method that can automatically eliminate shadowing errors. For modeling shadowing effect, a new shadowing compensation model based on the angle distribution of backscattered electrons is introduced. Further, it is modified with respect to some practical factors. Moreover, the proposed iterative shadowing compensation method, which performs commutatively between the compensation of image intensities and the modification of the corresponding 3D surface, can effectively provide both an accurate 3D surface and compensated shadowless images after convergence.

This paper presents the shadowing analysis of a body area network (BAN) diversity antenna based on the statistical measurements of the human walking motion. First, the dynamic characteristics of the arm-swing motion were measured using human subjects, and a statistical analysis was then carried out using the measured data to extract useful information for the analysis of a BAN diversity antenna. Second, the analytical results of the shadowing effects of the BAN antenna were shown based on the statistical data of the swing motion. The difference between the typical and the realistic arm-swinging models significantly affected the bit error rate (BER) characteristic of the BAN antenna. To eliminate the shadowing caused by the movement of the arms, a BAN diversity antenna was used. Particular emphasis was placed on the evaluation of the spatial separation of the diversity antennas to attain reduction of the signal-to-noise ratio (SNR) required to achieve a specific BER performance, considering the combined outcome of shadowing and multipath fading unique to BAN antenna systems. We determined that an antenna angle separation of greater than 80° is required to reduce the shadowing effects when the diversity antenna is mounted at the left waist in a symmetrical configuration. Further, an antenna angle separation of 120° is required when the diversity antenna is mounted in an asymmetric configuration.

In this letter, we provide an asymptotic error rate performance evaluation of space-time block codes from coordinate interleaved orthogonal designs (STBCs-CIODs), especially in shadowed Rayleigh fading channels. By evaluating a simplified probability density function (PDF) of Rayleigh and Rayleigh-lognormal channels affecting the STBC-CIOD system, we derive an accurate closed-form approximation for the tight upper and lower bounds on the symbol error rate (SER). We show that shadowing asymptotically affects coding gain only, and conclude that an increase in diversity order under shadowing causes slower convergence to asymptotic bound due to the relatively larger loss of coding gain. By comparing the derived formulas and Monte-Carlo simulations, we validate the accuracy of the theoretical results.

Reliable detection of other radio systems is crucial for systems that share the same frequency band. In wireless communication channels, there is uncertainty in the received signal level due to multipath fading and shadowing. Cooperative sensing techniques in which radio stations share their sensing information can improve the detection probability of other systems. In this paper, a new cooperative sensing scheme that reduces the false detection probability while maintaining the outage probability of other systems is investigated. In the proposed system, sensing information is collected using multi-hop transmission from all sensing stations that detect other systems, and transmission decisions are based on the received sensing information. The proposed system also controls the transmit power based on the received CINRs from the sensing stations. Simulation results reveal that the proposed system can reduce the outage probability of other systems, or improve its link success probability.

Independent shadowing losses are often assumed for evaluating the link capacity of direct sequence code division multiple access (DS-CDMA) cellular system. However, shadowing losses may be partially correlated since the obstacles surrounding a mobile station block similarly the desired signal and the interfering signals. In this letter, we discuss how the shadowing correlation impacts the reverse link capacity of a power-controlled DS-CDMA cellular system, by numerical analysis.

We describe a layer 3 diversity reception scheme that enhances the transmission characteristics of Ku-band mobile satellite communication systems. This scheme can realize high-speed communication for vehicles that experience shadowing caused by terrestrial obstacles such as tunnels, buildings and bridges, especially for trains that frequently experience shadowing from the trolley wire structures. Layer 3 diversity was chosen for long distance diversity to prevent signal shadowing caused by terrestrial obstacles while minimizing the alterations of existing receivers. The technology enables high-speed communication under shadowing conditions in a running train environment.

This paper proposes cell selection (CS) based on shadowing variation for the forward-link Orthogonal Frequency and Code Division Multiplexing (OFCDM) packet wireless access. We clarify its effects using a broadband propagation channel model in a comparison with fast cell selection (FCS), which tracks the instantaneous fading variation, and with the conventional slow CS, which tracks only the distance-dependent path loss, based on radio link level simulations that take into account time-varying instantaneous fading and shadowing variations. The simulation results show that the achievable throughput with FCS improves slightly in a broadband channel with an increasing number of paths when the average path-loss difference between two cells is greater than 2 dB. Nevertheless, we show that the optimum CS interval becomes approximately 100 msec, because the interval can track the time-varying shadowing variation considering low-to-high mobility up to the maximum Doppler frequency of 200 Hz. Consequently, we show that the throughput by employing the CS based on shadowing variation with the selection interval of 100 msec is increased by approximately 5 and 15% compared to that using the conventional slow CS with the selection interval of 1 sec, for the maximum Doppler frequency of 20 and 200 Hz, respectively.

In the road-to-vehicle communication (RVC) on intelligent transport systems (ITS), the frequent occurrence of shadowing caused by other vehicles deteriorates wireless transmission quality because of a small sized zone. However, a diffraction wave generated at the edge of vehicle can be utilized in applying adaptive modulation method with decreased modulation level. Therefore, it can be expected to keep communication only with a diffraction wave under shadowing. Hence this paper proposes an application of adaptive modulation for RVC system. This paper first reveals its improved effect in shadowing duration by computer simulation considering practical traffic flow, radio reflection and diffraction, and then shows that applying adaptive modulation can increase throughput performance largely.

Independent shadowing losses are often assumed for computing the frequency reuse distance of cellular mobile communication systems. However, shadowing losses may be partially correlated since the obstacles surrounding a mobile station block similarly the desired signal and interfering signals. We investigate, by computer simulation, how the shadowing correlation impacts the frequency reuse distance of a power controlled cellular system. It is pointed out that the shadowing correlation impacts the frequency reuse distance differently for the uplink and downlink.

In this letter, a concise formula for the SNR degradation of OFDM caused by carrier frequency offset is derived by approximations over a shadowed two-path channel, which explicitly shows the sensitivity of SNR degradation to various parameters including the frequency offset. It is shown that, for small frequency offset, the SNR degradation is proportional to the square of the frequency offset and the square of the number of subcarriers. It is also shown that, if Es/N0 is reasonably large, the SNR degradation becomes insensitive to Es/N0, which is contrary to the case of the AWGN channel.