Indoor Multipath Propagation Research Articles

Enabling Robust Radar-Based Localization and Vital Signs Monitoring in Multipath Propagation Environments.

Over the last two decades, radar-based contactless monitoring of vital signs (heartbeat and respiration rate) has raised increasing interest as an emerging and added value to health care. However, until now, the flaws caused by indoor multipath propagation formed a fundamental hurdle for the adoption of such technology in practical healthcare applications where reliability and robustness are crucial. Multipath reflections, originated from one person, combine with the direct signals and multipaths of other people and stationary objects, thus jeopardizing individual vital signs extraction and localization. This work focuses on tackling indoor multipath propagation. We describe a methodology, based on accurate models of the indoor multipaths and of the radar signals, that enables separating the undesired multipaths from desired signals of multiple individuals, removing a key obstacle to real-world contactless vital signs monitoring and localization. We also demonstrated it by accurately measure individual heart rates, respiration rates, and absolute distances (range information) of paired volunteers in a challenging real-world office setting. The approach, validated using a frequency-modulated continuous wave (FMCW) radar, was shown to function in an indoor environment where radar signals are severely affected by multipath reflections. Practical applications arise for health care, assisted living, geriatric and quarantine medicine, rescue and security purposes.

Over-the-Air Performance Evaluation in Indoor and Outdoor Multipath Propagation Channels of Antenna Diversity Systems inside Anechoic Chamber

With the ever-growing requirement for higher data rates, terminals supporting multiple-input multiple-output (MIMO) technologies are being developed for next-generation. As for wireless device manufacturers, a radio performance evaluation of multi-antenna terminals in desired environments is mandatory before product release. This paper discusses the Over the Air (OTA) performance evaluation of antenna diversity systems in Indoor and Outdoor multi-path propagation channel models inside anechoic chamber, in terms of correlation coefficients and diversity gain (DG). These channel models have been emulated in terms of angles of arrivals (AoA) and cross-polarization ratio (XPR) with Rayleigh fading. For this purpose, SATIMO SG24 measurement system has been used. However, the actual configuration of this system is not able to emulate desired realistic environments. Therefore, an innovative methodology based on the SG24 probes control has been developed. The obtained results in simulations and measurements have shown a good agreement.

A Study of Diffuse Scattering in Massive MIMO Channels at Terahertz Frequencies

The use of massive multiple-input multiple-output (MIMO) systems is becoming progressively feasible, as well as progressively important, as the carrier frequency increases. Terahertz (THz) frequencies lead to smaller-sized RF components including antennas, so that even antenna arrays with a large number of antennas have a reasonable form factor while providing large beamforming gain and multi-user MIMO (MU-MIMO) capability. However, the THz propagation mechanisms differ in various ways from previously explored channels. In fact, reflections by a rough surface and diffuse scattering mechanisms are the most critical features contributing to spatial and temporal dispersion at THz frequencies. For this article, first, we develop a hybrid modeling approach of 3-D ray-tracing simulations in a realistic office room at 300 and 350 GHz to obtain estimates of the impact of surface roughness on the channel capacity which depends on generic channel characteristics. Then, the indoor multipath propagation and its impact on massive MIMO channels considering smooth and rough surfaces are investigated by employing the Beckmann-Kirchhoff (B-K) model. Finally, channel capacities of indoor THz massive MIMO channels with different surface roughnesses for both line-of-sight (LoS) and non-LoS (NLoS) scenarios are calculated. Though based on modeling results, the scattering properties of materials can favorably be exploited to maximize spatial multiplexing gains, especially in LoS scenarios.

Local Average Signal Strength Estimation for Indoor Multipath Propagation

A comprehensive study of approaches for the estimation of the local average of the received signal strength (RSS) for indoor multipath propagation is presented. The effects of the required number of the RSS data samples and the Euclidean distances between the neighboring samples are investigated over 1D, 2D, and 3D configurations. It was found that the effect of fast fading was reduced to an acceptable level using a 2D horizontal arrangement with a relatively large spacing configuration. Furthermore, averaging was enhanced with a larger spacing compared to smaller spacing when considering the same number of samples.

Experimental Evaluation of Multipath Mitigation in TDOA-Based Indoor Passive Localization System Using A Beam Steering Broadband Circular Polarization Antenna

An experimental evaluation of multipath mitigation using a beam steering broadband circular polarization antenna (BSBCPA) in indoor passive localization system based on time differences of arrival (TDOA) is presented in this paper. The BSBCPA consists of a beam switch network, four identical hexagon patch elements and their respective feeding networks. By controlling the states of a radio frequency (RF) switch in the beam switch network, four steering circular polarization beams can be excited separately for azimuth omnidirectional coverage. Combining the spatial selectivity of steering beams and circular polarization in the BSBCPA, the positioning inaccuracy from indoor multipath propagation can be mitigated. In two different indoor environments with line of sight (LOS), complex multipath, when transmitting a 20 MHz bandwidth signal in WLAN, the 2D positioning mean error obtained is 0.7 m and 0.82 m, respectively. Compared with conventional omnidirectional linear polarization antenna (OLPA), the BSBCPA can at least improve positioning accuracy by 51%. The experimental results show that the proposed BSBCPA can significantly mitigate multipath propagation for TDOA-based indoor passive localization.

Study on frequency and impulse response of novel triple band notched UWB antenna in indoor environments

In this paper, a novel fork shaped structure backed plane is added to a simple UWB (ultra wideband) slot antenna to enhance the impedance bandwidth as well as create triple band notched characteristics for Impulse Radio (IR) UWB applications. This fork-shaped structure is connected to a rectangular radiating patch at four different points through the cylindrical pins. The proposed antenna with this fork-shaped structure shows a very wide impedance bandwidth which spans from 2.5 up to more than 20 GHz and offers triple band-notched properties in WiMAX, WLAN and X-band downlink satellite communication spectrums. Moreover, the proposed antenna shows good radiation features such as gain, radiation efficiency and radiation patterns. A comprehensive investigation on the antenna time domain performance is also performed throughout the paper, and the effect of the proposed antenna on the two popular excitation pulses including modulated Gaussian (MG) and square root raised cosine (SRRC) pulses is fully investigated. A frequency-domain measurement setup is applied to measure time domain characteristics of the proposed antenna. Also, the realistic indoor multipath propagation channel characteristics when the proposed antennas are applied as the transmitter and receiver antennas are studied. Sub-band divided ray tracing method is used to simulate channel characteristics.

Modeling Infrared Signal Reflections to Characterize Indoor Multipath Propagation.

In this paper, we propose a model to characterize Infrared (IR) signal reflections on any kind of surface material, together with a simplified procedure to compute the model parameters. The model works within the framework of Local Positioning Systems (LPS) based on IR signals (IR-LPS) to evaluate the behavior of transmitted signal Multipaths (MP), which are the main cause of error in IR-LPS, and makes several contributions to mitigation methods. Current methods are based on physics, optics, geometry and empirical methods, but these do not meet our requirements because of the need to apply several different restrictions and employ complex tools. We propose a simplified model based on only two reflection components, together with a method for determining the model parameters based on 12 empirical measurements that are easily performed in the real environment where the IR-LPS is being applied. Our experimental results show that the model provides a comprehensive solution to the real behavior of IR MP, yielding small errors when comparing real and modeled data (the mean error ranges from 1% to 4% depending on the environment surface materials). Other state-of-the-art methods yielded mean errors ranging from 15% to 40% in test measurements.

Effect of Quasi-Isotropic Antenna Orientation on Indoor Multipath Propagation Characteristics in RSN Applications

In the RFID sensor networks (RSN), the orientations of the antennas used in the network nodes have a significant influence on the propagation characteristics. In this article, we investigated the effects of the two antennas’ orientation of different radiation and polarization on the multipath propagation characteristics. This study is evaluated in a typical indoor environment by computer simulations based on the three-dimensional (3D) ray-tracing method. This method is based on geometric optics and uniform diffraction theory and also it offers significant advantages in terms of accurate and comprehensive prediction of propagation characterization. The simulations have been performed at frequency 915 MHz and the propagation characteristics are compared in terms of received power level (Pr) and Root-Mean-Square (RMS) delay spread for a quasi-isotropic 3D cubic antenna with circular polarization and for an omnidirectional dipole with linear polarization in the LOS, NLOS, and OLOS scenarios.

Frequency Hopping for Indoor Fading Channels With Varying Level of Environmental Mobility

The operation range and reliability of single-carrier wireless transmission systems are limited due to effects of the indoor multipath propagation environment. Multichannel systems can exploit frequency diversity and increase the reliability. Common frequency-hopping protocols change the channel continuously without consideration of the actual channel quality and require regular frame exchange for synchronization. However, in residential application scenarios, control data traffic occurs only very sporadic. In this letter, we describe an asynchronous wireless multichannel system, which utilizes good channels and avoids unnecessary overhead, but at the same time is able to change the frequency in case of a deep fade. The optimal protocol for the initial connection setup is extended for efficient long-term operation. The hopping sequences are modified based on successful transmissions in the past. The method is evaluated and simulated.

A Deterministic Satellite-to-Indoor Entry Loss Model

Advances in satellite and receiver technology make former denied areas like indoors accessible for satellite based radio services. As a consequence, suitable penetration loss models are of significant importance for service availability planning. Standard penetration loss models ignore the building layout in relation to the transmitter-receiver geometry. Within this paper, we introduce the term entry loss as a measure for the additional loss of a wideband impulse received at the geometrical line-of-sight path delay caused by the building materials. Knowing the received power caused by indoor multipath propagation, the penetration loss and the entry loss are deterministically related. As a contribution, we propose an entry loss model which is able to include the geometrical relation of walls, receiver and transmitter positions. Within the model, we treat walls, windows and doors as apertures and, therefore, as sources for signal penetration and diffraction. A verification of the model using wideband channel sounder measurement data is performed. By simulations, we show the comparability between existing models and the proposed one. Moreover, a short description on the usage of the proposed entry loss model for wideband channel simulations is provided.

Performance Bound on Ergodic Capacity of MIMO Beam-Forming in Indoor Multi-Path Channels

This paper aims to characterize the ergodic capacity of multiple input multiple output (MIMO) antenna beam-forming in indoor multi-path propagation environments. Using Double-Directional Cluster-Ray (DDCR) channel models, the second order statistics of the strongest eigen-mode of the channel is analyzed. An upper bound on the ergodic capacity of the MIMO beam-forming is derived and the impact of channel propagation parameters, such as cluster/ray arrival rates and power decay profiles, on this upper bound is investigated. The theoretical results are subsequently applied to estimate the capacity of the next generation very high throughput WLAN at the 60 GHz frequency band.

Indoor Characterisation using High-Resolution Signal Processing Based on Five-Port Techniques for Signal Input Multiple Output Systems

Problem statement: The development of wideband mobile communication systems requires a deep knowledge of the characteristics of the indoor mobile radio channel. The characterization of the indoor multi-path propagation structure is important in developing antifading techniques for high-speed digital radio access. The high-resolution of the estimation of the Time of Arrival (ToA) and the Direction of Arrival (DoA) of multi-path signals in wireless communication involves locating a source of Radio Frequency (RF) waves and then directing the beam of antenna in the estimated direction. The time dispersion is relatively small and the frequency dispersion is rather low compared to those expected in outdoor environments. Those characteristics require a high resolution system. This improved the performance of communication system. Approach: The DoA was estimated by measuring the phase difference of signals detected by an antenna array while the estimation of ToA was based on the phase difference measured over two successive frequencies. Low cost and high-resolution were obtained by using five-port receivers and the MUSIC algorithm. The simulation of five ports junction was developed using Advanced Design System (ADS). It was used to optimize the parameters of the structure and the antennas. Results: We obtained the adapted ring with the desired functions, splitting the received power equally over the output branches with a dephasing of 120°. The corresponding output signals appear with an amplitude variation depending on the dephasing between the RF and OL signals. Conclusion: Simulation results, performed around the 2.4 GHz frequency, showed an excellent estimation of the ToA and DoA with a high resolution and a reduced errors in both the time and the direction of multi-path signals.

Estimation of the information transmission rate in local area ultrawideband communication systems in the multipath propagation environment

The problem of indoor multipath propagation of ultrawideband signals is considered for direct chaotic communications systems. The values of the guard interval between the information symbols, which provides the quality of reception at a level of Perr ∼ 10−3 to 10−5, are estimated theoretically. The estimation procedure is based on the models of the multipath channels of wireless area networks that have been proposed by the IEEE workgroup.

Analysis of the interference immunity during reception of ultrawideband chaotic signals in an indoor multipath propagation environment

The models of indoor multipath propagation of wideband and ultrawideband (UWB) signals are considered. Application of these models is recommended by an IEEE working group. In the framework of one of the models corresponding to the line-of-sight conditions, the algorithms for reception of UWB chaotic signals in the presence of reflection from multiple surfaces (echo signals) are proposed and analyzed. The efficiency of reception techniques is estimated from the viewpoint of the error probabilities. Limitations caused by the specific properties of echo signals are revealed, and the methods for improvement of reception quality are discussed.

Schemes for Indoor Network Synchronization in UWB Positioning

Location Positioning is a major technology for ubiquitous computing. A research on Location Positioning using UWB is ongoing. In order to construct an indoor location network, synchronization of base stations is very important. NTP is popularly used as a clock synchronization protocol ranging from LAN to WAN. The Master-Slave scheme, however, is the simplest method for synchronizing an indoor network that uses UWB. In this paper, we compare and analyze the NTP and Master-Slave schemes according to the statistical channel model for an indoor multi-path propagation environment. Error ranges are calculated at various circumstances such as when the indoor network expands from one primary base station to several base stations. In particular, we compare the correctness of the NTP and Master-Slave synchronization methods. We have found that NTP is a more reasonable synchronization protocol in UWB positioning.

Spatial and Temporal CM Equalization for Broadband Wireless Indoor Networks at Millimeter Waves

Based on a new multipath channel model, a spatial-temporal combined CM equalization approach is derived at millimeter waves. Computer simulations are presented to testify the theoretical analysis. It is shown that this method can compensate the signal degradation caused by indoor multipath propagation. The convergence behavior of the spatial-temporal CMA is also analyzed.

Effects of antenna directivity and polarization on indoor multipath propagation characteristics at 60 GHz

In millimeter-wave indoor communications systems, the radiation patterns and polarizations of the antennas at base stations and remote terminals have a significant influence on channel characteristics. The work reported in this paper investigated the effects of the radiation patterns of the antennas at remote terminals on multipath propagation characteristics. These effects were investigated by indoor propagation measurements at 60 GHz conducted in a modern office room and by ray-tracing simulations based on geometrical optics. Multipath channel characteristics are compared in terms of impulse responses and their root-mean-square (rms) delay spreads for an omnidirectional antenna and for three directive antennas with different beam widths. From the results of measurements and ray-tracing simulations, the use of a directive antenna at the remote terminal is demonstrated to be an effective method of reducing the effects of multipath propagation. Further reduction in the multipath effects is found to be achieved by the use of circular polarization instead of linear polarization with the directive antennas.

Millimeter‐wave indoor high‐capacity transmission characteristics

AbstractTo realize a high‐capacity wireless access, the millimeter‐wave frequencies have been investigated. Research on indoor multipath propagation has been pursued intensively.This paper proposes an evaluation method for the millimeter‐wave indoor high‐capacity digital transmission characteristics. First, the broadband propagation characteristics under indoor multipath environment were measured so that the multiple‐wave configurations are clarified.Next, to quantify the digital transmission characteristics under the multiple wave environment, the level ratio (D/U) of the desired wave to the interference wave was evaluated for a bit error rate of 10−4 by means of a 4 PSK‐100 Mb/s and a multipath fading simulator. It was found that the bit error rate is determined by the level ratio (D/UT) of the desired wave to the total interference waves and not by the delay time of the interference wave if the delay time of the interference wave exceeds the symbol duration and that the desired D/UT approaches the signal‐to‐noise (S/N) ratio (N: Gaussian noise) giving such a bit error rate. From the foregoing results, this paper proposes a channel design method using the D/U in indoor high‐capacity wireless communication.

Performance of Quadrature Amplitude Modulation for Indoor Radio Communications

The performance of M -QAM for indoor radio communications is evaluated via a realistic model for indoor multipath propagation [1]. It is found that the outage (BER < 10-4) is about 0.3 percent at 1 Mbit/s and 20 percent at 4 Mbits/s. Two-antenna predetection diversity reduces the outage from 1.2 to 0.04 percent at 2 Mbits/s. Increasing the signaling pulse rolloff factor from 0.5 to 1.0 reduces the outage by not more than 35 percent.

A Statistical Model for Indoor Multipath Propagation

The results of indoor multipath propagation measurements using 10 ns, 1.5 GHz, radarlike pulses are presented for a medium-size office building. The observed channel was very slowly time varying, with the delay spread extending over a range up to about 200 ns and rms values of up to about 50 ns. The attenuation varied over a 60 dB dynamic range. A simple statistical multipath model of the indoor radio channel is also presented, which fits our measurements well, and more importantly, appears to be extendable to other buildings. With this model, the received signal rays arrive in clusters. The rays have independent uniform phases, and independent Rayleigh amplitudes with variances that decay exponentially with cluster and ray delays. The clusters, and the rays within the cluster, form Poisson arrival processes with different, but fixed, rates. The clusters are formed by the building superstructure, while the individual rays are formed by objects in the vicinities of the transmitter and the receiver.