Indoor Multipath Channel Research Articles

Impact of Human Blockage on Dynamic Indoor Multipath Channels at 27 GHz

Human blockage and its dynamics are potential challenges for millimeter-wave (mm-wave) mobile communication. This article presents the results of wideband measurements at 27 GHz with one human blocker close by a dynamic mobile terminal (MT) as well as one or multiple dynamic human blockers further away from an MT. The measured human blockage loss is largest when the direct path (DP) in a line-of-sight (LOS) is blocked, but this loss is limited by other multipath components (MPCs). For nonline-of-sight (NLOS) channels, it is shown that human blockage loss is typically negligible. The presented measurement results show that human blockage loss in multipath channels is much smaller than that reported in diffraction- and measurement-based models, which neglect or minimize the contribution of all MPCs other than the DP. This suggests that the multipath nature of the indoor wireless channel highly limits the impact of human blockage.

A novel singular value decomposition-based ultra wide band time-of-arrival estimation for multiple targets

It is widely <span>admitted that the estimation of ultra wide band (UWB) time-of-arrival (TOA) for multiple targets in indoor multipath channels is a very challenging task. The existing algorithms deal with a limited number of targets and require a complex exchange of several messages. In this paper, a novel TOA estimation algorithm for multiple targets is developed. The proposed algorithm estimates the first path (FP) TOA of a number of targets without exchanging messages or using collision avoidance techniques. As a first step, the singular value decomposition (SVD) is employed to extract the first path (FP) of each target and then a matched filter, followed by an iterative threshold crossing algorithm, is used to determine the number of targets and the corresponding FP TOAs. The simulation results with four targets, using the CM1 IEEE 802.15.4a channel model, showed that the proposed novel algorithm can effectively detect the FP of each target and estimate its corresponding TOA.</span>

A Modified Interference Approximation Scheme for Improving Preamble Based Channel Estimation Performance in FBMC System

Filter bank multi carrier (FBMC) is considered a competitive waveform candidate for 5G that can replace orthogonal frequency division multiplexing (OFDM). However, channel estimation (CE) is a big challenge in FBMC because it suffers from intrinsic interference which is due to the orthogonality of the subcarrier functions in the real field only. In this paper, we investigate a proposed modified interference approximation scheme (M-IAM) by approximating the intrinsic interference from the neighboring pilots to accommodate the complex channel frequency and thus improving CE performance besides simplifying its processing. The M-IAM scheme has larger pseudo pilot magnitude than other conventional preamble schemes, namely the interference approximation method (IAM) with its versions (IAM-C) and (E-IAM-C); in addition to the novel preamble design (NPS). In addition, the proposed (M-IAM) scheme is characterized by the lower transmitted power needed. The CE performance of the M-IAM is investigated through 512 and 2048 subcarriers via different types of outdoor and indoor multipath fading channels that are time-invariant such as IEEE 802.22, IEEE 802.11, Rician, and additive white Gaussian noise (AWGN), as well as time varying channels such as Rayleigh and Vehicular A (Veh-A). Simulation results demonstrate that the proposed M-IAM scheme achieves a lower bit error rate (BER), lower normalized mean square error (NMSE) and lower peak-to-average power ratio (PAPR) over the conventional preamble schemes under the aforementioned channel models. The proposed scheme has the advantage of saving the transmitted power, a requirement that could match 5G low power requirements.

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.

Spectral-Efficient Hybrid Dimming Scheme for Indoor Visible Light Communication: A Subcarrier Index Modulation Based Approach

Communication and illumination are two basic functions of the indoor visible light communication (VLC). In this paper, a novel spectral-efficient hybrid dimming scheme is proposed for the indoor VLC system, where the frequency-domain subcarrier selection is utilized to maximize the channel capacity and the intensity-domain dimming strategy is used to further adjust the illumination level. Simulations are carried out in both the indoor line-of-sight channel and the indoor multipath channel. Simulation results substantiate the superior performance of the proposed hybrid dimming scheme over the state-of-the-art schemes.

Towards 5G wireless systems: A modified Rake receiver for UWB indoor multipath channels

This paper presents a modified receiver based on the conventional Rake receiver for Ultra-Wide Band (UWB) indoor channels of femtocell systems and aims to propose a new solution to mitigate the multipath phenomenon. Furthermore, this work proposes an upgrade for the conventional Rake receiver to fulfill the needs of 5G wireless systems through a new concept named “hybrid femtocell” that joins UWB with millimeter wave (mmWave) signals. The modified receiver is considered to be a part of the UWB/mmWave hybrid femtocell system, where it is developed for confronting the indoor multipath channels and to ensure a flexible transmission based on an Intelligent Controlling System (ICS). Hence, we seek to exploit the circumstances when the channel is less complex to switch the transmission to a higher data rate through higher M-ary Pulse Position Modulation (PPM). Furthermore, an ICS algorithm is proposed and an analytical model is developed followed by performance studies through simulation results. The results show that using the UWB technology through the modified receiver in femtocells could aid in mitigating the multipath effects and ensuring high throughputs. Thus, the UWB based system promotes Internet of Things (IoT) devices in indoor multipath channels of future 5G.

Spectral efficient pulse shape design for UWB communication with reduced ringing effect and performance evaluation for IEEE 802.15.4a channel

Ultra-Wideband (UWB) faces some regulations due to the interference issues with the co-existing narrowband communication systems, due to which the effective utilization of bandwidth is not possible that causes lower data rate of transmission. We propose a pulse shaping method which can curtail the interference with the co-existing band of communication and have an ability to depress the ringing oscillation. The modified pulse shape has an ability to control over the transmitted power spectral density and offers improved antenna power resolution. To obtain the specific results, the seventh derivative of Gaussian pulse is used as a basic pulse. This pulse is spectrally modified by windowing with Gaussian window to achieve the desired performance. The analysis is not only limited to spectral management but also inculcate the performance estimation of the resultant pulse in multi-user scenario for indoor multipath channel IEEE 802.15.4a. We have also analysed the modified pulse to prove its ability in the location accuracy improvement for high-end application of UWB communication.

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.

Performance of Optical Spatial Modulation in Indoor Multipath Channel

In this paper, the performance of optical spatial modulation (OSM) in the indoor multipath optical wireless channel is investigated. Multipath propagation of the transmitted signal results in the temporal dispersion which causes intersymbol interference (ISI) especially in high-speed communications. The OSM schemes have been investigated in line-of-sight (LOS) channels. However, given the recent trend in Gigabits/s communication, there is a need to investigate the impact of the neglected higher-order reflections. Two variants of OSM are explored as case studies: optical space shift keying and spatial pulse position modulation. The multipath-induced ISI is modeled to account for the spreading of the transmitted signal, and the analytical upper bound on the symbol error rate of both OSM schemes in the multipath channel is derived. The derived analytical bounds are validated by closely matching simulation results. Furthermore, using the spatial distributions of the multipath-induced power penalty, the LOS channel response and the delay spread across the room, we demonstrate how the interaction between these parameters impacts error performance. Multipath-induced ISI has a significant adverse impact on the performance of OSM schemes, particularly on the detection of the activated transmitter as the incurred ISI can alter the channel gain of the received symbol.

A Unified Geolocation Channel Model--Part I (Path Loss)

Indoor geolocation systems have emerged and have attracted a wide audience recently. There are three important components that constitute an indoor geolocation system: (1) transmitter, (2) receiver, and (3) indoor channel model. To some extent the primary transmitter design requirements are transmit power and a frequency or a set of frequencies of operation. The receiver is designed to operate at a certain distance from the transmitter and at the same frequency or set of frequencies of operation. Hence, any indoor channel model must take into account these two important design requirements. The indoor channel is perhaps very intriguing because multipath is ubiquitous due to high signal scattering, reflection, and refraction. It is been widely accepted in the literature that the two primary channel effects are (1) path loss and (2) multipath distribution. First, the path loss model is currently accepted to be a function of the transmitter and receiver geometry and frequency of operation. Second, the most widely used and accepted indoor channel multipath distribution models are Raleigh, Rician, and lognormal. As indicated in the second paper (or part II) the Rayleigh distribution is wider than Rician and Rician is wider than lognormal. This implies that the Rayleigh fading channel is the most severe and Rician fading is more severe than lognormal and lognormal is the least severe channel. Unfortunately, the dependency of the path factor on the frequency of operation in the context of a unified channel model is overlooked in the literature. Furthermore, there is no agreement on an indoor multipath distribution channel model. Although a unified channel model has not yet been found, in this paper we make a first attempt to present a unified channel model which consists of a unified path loss model and a unified multipath distribution model. The unified path loss model consists of an approach for linking together the path loss models of the three geolocation systems (macro-outdoor, micro-outdoor, and indoor) with the distance between the transmitter and receiver, R, and the frequency of operation, f. Although there are several parameters that affect the power loss factor, we consider R and f as the most important parameters for two reasons. Most of the geolocation systems presented in the literature are based on a direct measure of the time of travel; i.e., distance between the transmitter and receiver. The frequency of these systems varies; hence, the path loss factor varies as well. While unifying the path loss model was to some extent initiated in the literature, unifying the multipath distribution model is currently a silent quest in the literature. It appears that the tendency is to come up with newer and more sophisticated models that would explain the characteristics of the old models. The approach that we present in part II (on in a separate paper in the future) to unify the multipath distribution models is rather simple. The theoretical performance results are validated from the measurements currently reported in the literature.

Performance Evaluation of High Data Rate M-OAM UWB Physical Layer for Intelligent Transportation Systems

In this paper, a high data rate modulation scheme for impulse radio ultra-wideband (IR-UWB) communication system using orthogonal waveforms is presented. The proposed M-state Orthogonal Amplitude Modulation (M-OAM) is evaluated under additive White Gaussian noise and indoor multipath channels IEEE.802.15. The simulation results show that the proposed system performance, in term of bit error rate (BER), is of the same order as that of the traditional UWB modulation. In addition, the M-OAM modulations provide a high data rate for short range wireless applications. Nevertheless, the multipath effect reduces the quality of transmission. Thus, the performances of three receiver architectures, that employ different pulse combining schemes, are investigated. Namely, a conventional matched filter receiver, a RAKE receiver and a minimum mean square error equalizer are considered. This study shows that the proposed M-OAM communication system offers good performances in term of quality of services, channel capacity and BER.

Performance analysis of precoding-based asymmetrically clipped optical orthogonal frequency division multiplexing wireless system in additive white Gaussian noise and indoor multipath channel

We have compared the bit error rate (BER) performance of precoding-based asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) and pulse amplitude modulated discrete multitone (PAM-DMT) optical wireless (OW) systems in additive white Gaussian noise (AWGN) and indoor multipath frequency selective channel. Simulation and analytical results show that precoding schemes such as discrete Fourier transform, discrete cosine transform, and Zadoff-Chu sequences do not affect the performance of the OW systems in the AWGN channel while they do reduce the peak-to-average power ratio (PAPR) of the OFDM output signal. However, in a multipath indoor channel, using zero forcing frequency domain equalization precoding-based systems give better BER performance than their conventional counterparts. With additional clipping to further reduce the PAPR, precoding-based systems also show better BER performance compared to nonprecoded systems when clipped relative to the peak of nonprecoded systems. Therefore, precoding-based ACO-OFDM and PAM-DMT systems offer better BER performance, zero signaling overhead, and low PAPR compared to conventional systems.

Cramer-Rao Bound for Clock Drift in UWB Ranging Systems

This correspondence computes the Cramer-Rao lower bound on the variance of frequency drift estimates in oscillators for UWB ranging applications. An indoor multipath channel is assumed but, unlike previous investigations, the received pulses are not taken as separate from each other. Overlaps are possible and are accounted for. A simple formula is derived for the bound, which neatly shows its dependence on the channel parameters and the pulse shape. Comparisons are made with the case of separable pulses.

Measurement-Based Analysis of Spatial Degrees of Freedom in Multipath Propagation Channels

A method of estimating spatial degrees of freedom (DoF) from measured multipath propagation channels in the multiple-input single-output regime is presented. The DoF of the multipath channels on the transmit (Tx) side is derived by means of the spherical-wave expansion of electromagnetic fields radiated from a Tx antenna array having a certain aperture size. The DoF estimates are independent of particular realization of antenna elements on the Tx aperture. For a given aperture size, the DoF provides the number of the Tx antenna elements for efficient improvement of the system performance by utilizing the spatial diversity. Having confirmed the soundness of our DoF estimation method by channel measurements in an anechoic chamber, the DoF of indoor multipath channels is analyzed. The DoF on the Tx side of the considered multipath channels reveals larger values when the antenna aperture size is increased at a fixed frequency, and when the frequency increases for a fixed antenna aperture size. For a fixed frequency, increasing the antenna aperture size is more effective in observing extra DoF in the obstructed and non-line-of-sight channels than in the line-of-sight channels. Furthermore, for a fixed antenna aperture size, the use of the higher frequency brings larger DoFs in many propagation scenarios. The results also show that electrically smaller antennas are more efficient in observing the DoF. Finally, the solid angle of multipath is derived as a Tx antenna-independent metric of the multipath richness. It is defined as an angular range of dominant multipath clusters subtended on a unit sphere. Our analysis method is extendable to the multiple-input multiple-output regime in a straightforward manner.

The blind demodulation scheme based on MP algorithm in chirp-BOK UWB system

In this paper, a blind demodulation scheme for chirp-binary orthogonal keying (BOK)-ultra wide band (UWB) system was proposed based on matching pursuit (MP) algorithm. The scheme was validated in additive white Gaussion noise (AWGN) and indoor multi-path channels that suggested by the IEEE P802.15 criterion. From the simulation results, it shows that the performance of the proposed MP method is consistent well with that of the traditional coherent method in communication circumstance with high quality requirement, and the performance difference of MP method and coherent method is less than 0.8 dB when the bit error rate (BER) is set as 0.001. As the requested BER getting small, the MP method has a comparable performance with the coherent method. It also presented an efficient way for spectrum sharing with other communication systems.

An improved exclusive region scheduling algorithm‐based timeslot allocation scheme for mmWave WPANs

ABSTRACTThis article focuses on improving the system capacity of 60‐GHz wireless personal area networks (WPANs) and presents an effective time slot allocation scheme for spatial reuse, which combines the existing exclusive region (ER)‐based scheduling algorithm with simple power control. In the study, the concept of ER for concurrent transmissions is introduced first. Considering the large path loss in the millimeter‐wave band and the characteristics of typical indoor multipath channels, we generalize the signal propagation model as well as ER radius for 60‐GHz WPANs. Then, we propose an improved ER‐based scheduling algorithm, which employs power control instead of constant transmitting power. In this algorithm, devices are assumed to receive data at the receiver sensitivity, which refers to the minimum receiving power to ensure the reliability for communications. Implementation feasibility is provided within the current standards framework. Some more practical analysis based on the beamforming codebook specified by of the IEEE 802.15.3c standard is also developed. In addition, the impact of the antenna radiation efficiency and receiver sensitivity is discussed. Computer simulations validate the excellent performance of the proposed scheme, which can significantly improve the channel capacity under different antenna configurations. Copyright © 2012 John Wiley & Sons, Ltd.

Error Probability Analysis of Time-Hopping Biorthogonal Pulse Position Modulation UWB Systems with a RAKE Receiver over Indoor Multi-Path Fading Channels

This paper presents the error probability analysis of Time-Hopping Biorthogonal Pulse Position Modulation (TH-BPPM) ultra-wideband (UWB) systems with a RAKE receiver over indoor multi-path fading channels. UWB signals suffer from severe multi-path interference when employed in an indoor fading environment. A RAKE receiver can be used to improve the performance of UWB systems. TH-BPPM has attracted much attention in recent years due to its many advantages, such as low probability of error and low complexity. In this paper, the IEEE 802.15.3a indoor channel model is employed to analyze the performance of TH-BPPM UWB systems with different RAKE receivers. The bit error rate (BER) of ARake, PRake, and SRake TH-BPPM UWB systems is derived. The results indicate that ARake has the best performance, SRake is better than PRake when the number of fingers is same.

Classical and Bayesian Linear Data Estimators for Unique Word OFDM

Unique word - orthogonal frequency division multiplexing (UW-OFDM) is a novel OFDM signaling concept, where the guard interval is built of a deterministic sequence - the so-called unique word - instead of the conventional random cyclic prefix. In contrast to previous attempts with deterministic sequences in the guard interval the addressed UW-OFDM signaling approach introduces correlations between the subcarrier symbols, which can be exploited by the receiver in order to improve the bit error ratio performance. In this paper we develop several linear data estimators specifically designed for UW-OFDM, some based on classical and some based on Bayesian estimation theory. Furthermore, we derive complexity optimized versions of these estimators, and we study their individual complex multiplication count in detail. Finally, we evaluate the estimators' performance for the additive white Gaussian noise channel as well as for selected indoor multipath channel scenarios.

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.

Performance analysis of asynchronous multicarrier code division multiple access against direct sequence code division multiple access and long polyphase sequences for uplink powerline communication systems with impulsive noise

In this study, the performance of two asynchronous multi-access direct sequence code division multiple access (DS-CDMA) and multicarrier code division multiple access (MC-CDMA) systems with binary and polyphase long sequences is compared. An indoor multipath powerline channel model generated from random impedance networks is used. The powerline background, narrowband and impulsive noise are modelled statistically, based on models and measurements done in previous works. A complete analytical performance study is done for asynchronous MC-CDMA employing an interval guard in the form of a cyclic prefix (CP) and periodic long sequences, which provides a better channel coding than short sequences. The analytical results are completed with Monte Carlo simulations for both, DS-CDMA and MC-CDMA systems. Under impulsive noise an upper bound in the bit error rate (BER) performance for DS-CDMA and MC-CDMA systems is obtained analytically, which is confirmed by the Monte Carlo simulations.