Antenna Array Designs for OFDM WLAN Indoor Transmission

Wireless local area networks (WLAN??s) based on the 802.11 standards are ubiquitous. However, the popularity of WLAN??s has made interference between WLAN users an issue. Spatial division multiple access (SDMA) is one way to orthogonalize these users and reduce interference. The contribution of this paper is to use real antenna array prototypes to determine the best array design for implementing indoor SDMA. Two SDMA antenna array prototypes are constructed and used to collect propagation measurements in an indoor environment. The propagation data is then incorporated into an SDMA orthogonal frequency division multiplexing (OFDM) analysis. This approach is able to very accurately predict how the two array designs will influence SDMA-OFDM performance in the indoor environment where the measurements are collected. The results indicate that the compact sectorized antenna array prototype performs better than the linear array prototype for in-room communication and that the reverse is true for inter-room communication.     

Prediction of noise and interference cancellation with a moving compact receiver array in an indoor environment

An interference and noise cancellation technique based on a reference signal is studied for a compact receiver antenna array placed in an indoor environment. The exact active element pattern method is used to model the radiation characteristics of the array, including mutual coupling between the antenna elements. A two-dimensional ray-tracing technique describes the signal propagation in the indoor environment for a moving receiving antenna.     

Path-loss and time dispersion parameters for indoor UWB propagation

The propagation of ultra wideband (UWB) signals in indoor environments is an important issue with significant impacts on the future direction and scope of the UWB technology and its applications. The objective of this work is to obtain a better assessment of the potentials of UWB indoor communications by characterizing the UWB indoor communication channels. Channel characterization refers to extracting the channel parameters from measured data. An indoor UWB measurement campaign is undertaken. Time-domain indoor propagation measurements using pulses with less than 100 ps width are carried out. Typical indoor scenarios, including line-of-sight (LOS), non-line-of-sight (NLOS), room-to-room, within-the-room, and hallways, are considered. Results for indoor propagation measurements are presented for local power delay profiles (local PDP) and small-scale averaged power delay profiles (SSA-PDP). Site-specific trends and general observations are discussed. The results for path-loss exponent and time dispersion parameters are presented.     

Propagation modelling for indoor wireless communication

It is important to characterise the indoor radio propagation channel to ensure satisfactory performance of a wireless communication system. Site measurements can be costly; propagation models have been developed as a suitable low-cost alternative. The existing models can be classified into two major classes: statistical models and site-specific propagation models. Statistical models rely on measurement data; site-specific propagation models are based on electromagnetic wave propagation theory. The ray-tracing technique is very useful in site-specific propagation modelling. This paper gives an overview of indoor propagation modelling and concentrates on a discussion of the ray-tracing modelling technique because of its practical appeal and its applicability to any environment     

Focused phased array measurements

Measurements describing the patterns of a linear phased array antenna which has been electronically focused to a point in the Fresnel region, located a few aperture widths distance from the array face are given. The measurements were taken inside a building with no effort made to reduce extraneous reflections. A comparison of the results with patterns taken on a conventional far-field range reveals that the estimated measurement accuracy of the level of the first few sidelobes is on the order ofpm1dB. The technique provides a good performance monitor check, is easily implemented, permits an indoor measurement, and offers the advantage of simplicity over far-field measurements.     

Blind separation of synchronous co-channel digital signals using anantenna array. I. Algorithms

We propose a maximum-likelihood (ML) approach for separating and estimating multiple synchronous digital signals arriving at an antenna array at a cell site. The spatial response of the array is assumed to be known imprecisely or unknown. We exploit the finite alphabet property of digital signals to simultaneously estimate the array response and the symbol sequence for each signal. Uniqueness of the estimates is established for BPSK signals. We introduce a signal detection technique based on the finite alphabet property that is different from a standard linear combiner. Computationally efficient algorithms for both block and recursive estimation of the signals are presented. This new approach is applicable to an unknown array geometry and propagation environment, which is particularly useful In wireless communication systems. Simulation results demonstrate its promising performance     

A nonlinear algorithm for output power maximization of an indooradaptive phased array

An adaptive receiving phased-array antenna is considered as one of the desirable features of the next generation of personal wireless indoor system. Such a feature will render this communication system much less sensitive to the signal fluctuations due to multipath propagation. This paper presents a prototype adaptive phased array based on an original nonlinear method. This adaptive algorithm which uses as performance criterion the maximization of the array output power to adjust a phase angle, is developed and applied to antenna system in order to control automatically its directivity pattern. Numerical results for a linear eight element array are presented. To test the algorithm experimentally, an eight element 20-GHz array, constructed using horn antennas and analog phase shifters, was used. The results obtained so far with such an array are discussed in the context of its eventual, implementation in MHMIC     

Artificial neural network based simulation of correlated short-term fading

This paper presents a novel method for simulation of two correlated short-term fading envelopes in mobile radio channel. Proposed method is enabled by artificial neural network principles. The main idea was to base the simulation approach solely on the measurement results. In order to obtain an adequate measured data set, extensive electric field strength measurements were carried out in an indoor environment, in a nonline-of-sight scenario. For verification of the proposed method, performance comparisons were made against the contemporary coloring matrix based method. According to comprehensive quantitative and qualitative statistical analysis it seems that the proposed method is in better agreement with the short-term fading phenomenon experienced in real propagation environment.     

Alternating projection method applied to indefinite correlation matrices for generation of synthetic MIMO channels

Complex correlation multiple-input multiple-output (MIMO) matrices estimated from measurements under realistic propagation conditions occasionally have positive, zero and negative eigenvalues, converting them to indefinite matrices. In this framework, this paper presents a novel correction procedure (CP) based on the alternating projection (AP) method to find the Hermitian and positive definite matrix closest to an estimated indefinite full spatial correlation (FSC) MIMO matrix. This corrected matrix allows the Cholesky factorisation usually used for generation of synthetic MIMO channel samples. The applicability of the CP has been analysed using real data from non-line-of-sight (NLOS) indoor measurements. The results reported in this paper show that a proper selection of the CP parameters has not a sensitive impact on the cumulative distribution function (CDF) of the eigenvalues of the estimated FSC MIMO matrices. This characteristic makes the CP useful for channel characterisation, allowing to assess the performance of a MIMO system. As an example of the CP application, a study of ergodic and outage MIMO capacities for different array configurations is presented .     

Distributed Antennas for Indoor Radio Communications

The idea of implementing an indoor radio communications system serving an entire building from a single central antenna appears to be an attractive proposition. However, based on various indoor propagation measurements of the signal attenuation and the multipath delay spread, such a centralized approach appears to be limited to small buildings and to narrow-band FDMA-type systems with limited reliability and flexibility. In this paper, we present the results of indoor radio propagation measurements of two signal distribution approaches that improve the picture dramatically. In the first, the building is divided into many small cells, each served from an antenna located in its own center, and with adjacent cells operating in different frequency bands. In the second approach, the building is divided into one or more large cells, each served from a distributed antenna system or a "leaky feeder" that winds its way through the hallways. This approach eliminates the frequency cell handoff problem that is bound to exist in the first approach, while still preserving the dramatic reductions in multipath delay spread and signal attenuation compared to a centralized system. For example, the measurements show that, with either approach, the signal attenuation can be reduced by as much as a few tens of decibels and the rms delay spread becomes limited to 20 to 50 us, even in large buildings. This can make possible the implementation of sophisticated broad-band TDMA-type systems that are flexible, robust, and virtually building-independent.     

Adaptive Empirical Path Loss Prediction Models for Indoor WLAN

This paper presents robust empirical path loss models to characterize indoor propagation for access point (AP) deployed at different heights. The proposed models are developed with wireless local area network infrastructure at 2.4 GHz. The models are backed by extensive received signal strength (RSS) measurements acquired in line of sight and obstructed line of sight regions. The models are developed for two conditions, viz; quasi realistic and realistic RSS measurements. The quasi realistic measurements are taken after suppressing human intervention and electrical interferences to minimum. While the realistic RSS measurements are made in presence of all the human interventions and electrical interferences. The shadow fading component for both quasi realistic and realistic conditions is statistically modeled with the dependency on AP height. The proposed technique can be applied with higher confidence level to the buildings with similar construction features where RSS measurements are made upon. The results reveal that the performance of the proposed propagation models is significantly higher than the existing International Telecommunication Union-path loss model. The results also demonstrate that the realistic path loss model is more robust than the quasi realistic model.     

Smart-antenna operation for indoor wireless local-area networks using OFDM

This paper reports link-level Monte Carlo simulations for a system that is compatible with the physical layer of the 5-GHz IEEE 802.11a wireless-local-area network and utilizes an adaptive antenna array at the access point for single-user smart-antenna operation, as well as for space-division multiple access (SDMA). For the spatial indoor radio propagation channel, complex impulse-response recordings are used. These are obtained in wideband channel-sounder measurements in three different buildings at 5.3 GHz. Thus, no unrealistic assumptions about channel conditions are involved. The paper studies how the packet-error-rate performance for the downlink (DL) is affected by time evolution of the radio channel that takes place after the uplink operation in which channel estimation is performed, and before DL operation in which the estimated channel information is utilized. Based on simulations two-user SDMA is possible with four-antenna elements under indoor propagation conditions and with six antennas three users can simultaneously be served. Delay spreads, coherence bandwidths, and correlation properties (in space, frequency, and polarization) of the radio channels obtained in the measurements are also discussed. The results suggest that indoor time-division-duplex systems with access-point-controlled scheduling are desirable communication systems which can benefit from SDMA.     

Indoor propagation models based on rigorous methods for site-specific multipath environments

This paper presents a full wave simulation technique for modeling indoor propagation channels. A key feature of the technique is the use of a domain decomposition approach that accounts for repeatable components such as bricks, chairs, tables, etc. This leads to significant memory reduction, thus permitting the modeling of an entire classroom. Several simulations with different transmitting locations are presented and used to predict the statistical profiles of the received signal strength. These profiles are subsequently used to evaluate the bit error rate for specific digital modulation schemes.     

A sensitivity study for an indoor channel

The context of this paper is the 3D wave propagation simulation with a software based on a ray tracing technique in typical indoor environments. The presented works are complementary to these of the literature which propose the validation of a propagation model in comparison with measurements. Indeed, the presented study consists of a sensitivity analysis of an already validated propagation model. The considered parameters are electromagnetic, geometric and electric; they directly intervene in the two parts of a simulation: the modelling of the wave propagation and of the environment. The aim of this study is to contribute to the setting up of parameterisation rules of a simulation software according to two criteria: the accuracy and the compromise between accuracy and computation time.     

Super-resolution TOA estimation with diversity for indoor geolocation

This paper presents an in-depth investigation of frequency-domain super-resolution time-of-arrival (TOA) estimation with diversity techniques for indoor geolocation applications. A methodology for performance evaluation of super-resolution techniques based on the measurements of indoor radio propagation channels is presented. The performance of super-resolution techniques is compared with the performance of conventional TOA estimation techniques. The effects of diversity techniques on the performance of super-resolution techniques are evaluated. The measurement and simulation methods presented in this paper can be used to establish empirical performance bounds for real implementation of super-resolution indoor geolocation systems.