Indoor Wireless Environment Research Articles

Frequency domain detectors for ultra-wideband communications in short-range systems

In this paper, we propose an original detection scheme for high rate short-range impulse radio ultra-wideband systems. The proposed receiver relies on both the introduction of the cyclic prefix at the transmitter and the use of a frequency domain multiuser detector at the receiver. Zero forcing (ZF) and minimum mean square error (MMSE) detection strategies have been investigated and compared with the classical RAKE, considering a scenario where several mobile terminals communicate with a base station in an indoor environment characterized by severe multipath propagation. The results show that the MMSE receiver achieves the best performance, irrespective of the number of active terminals, both in the uplink and in the downlink communications. Hence, the proposed approach is well suited in indoor wireless environments where the multipath propagation tends to increase the effects of both the inter-path and the inter-user interference.

Wideband EM architecture of buildings: six-to-one dual-passband filter for indoor wireless environments

The application of closely packed elements to obtain wideband isolation at mobile phone frequency bands, while allowing transparency at the emergency TETRA and Bluetooth bands, is proposed. The intention is to modify the EM architecture of buildings over a very wide frequency range, permitting access at these two very separated bands. In particular, buildings are considered with restricted mobile phone usage such as public libraries, theatres, policing services and secure offices. Experimentally validating the design required scaling the operating frequencies by a factor of ten.

Field Measurements with a 5.25 GHz Broadband MIMO-OFDM Communication System

Theoretical capacity calculations and corresponding simulations show significant capacity/throughput gains from MIMO systems. Whether these gains are achievable in a real system, deployed in a practical environment, depends on a variety of factors, such as the choice of the communication algorithms, analog impairments and the "quality" of the wireless channel to sustain MEMO communications. In this paper, a 5.25 GHz broadband MIMO-OFDM testbed is described along with field measurements conducted with it. The MIMO-OFDM communication algorithms and also the impact of analog impairments on the performance of the system are described. Detailed system calibration results are described which serve as a baseline for results of field measurements. The results of wireless measurements are compared with the theoretical capacity, computed with the channel estimates obtained during the demodulation process. The average achievable capacity in the indoor wireless environment is shown to be 9.97 bps/Hz (bits per sec per Hz) while the capacity loss due to analog impairments and the choice of algorithms is about 2.33 bps/Hz. Also, field measurements conducted with the system in various environments are presented comparing the average throughput/capacity achieved in each of these environments.

Frequency Domain Detectors in Different Short-Range Ultra-Wideband Communication Scenarios

We study the performance of an innovative communication scheme for ultra-wideband systems which are based on impulse radio in two different short-range communication scenarios: the proposed system relies on both the introduction of the cyclic prefix at the transmitter and the use of a frequency domain detector at the receiver. Two different detection strategies based either on the zero forcing (ZF) or on the minimum mean square error (MMSE) criteria have been investigated and compared with the classical RAKE, considering two scenarios where a base station transmits with a different data rate to several mobile terminals in an indoor environment characterized by severe multipath propagation. The results show that the MMSE receiver achieves a remarkable performance, especially in the case of highly loaded high data-rate systems. Hence, the proposed approach is well suited for high-throughput applications in indoor wireless environments where multipath propagation tends to increase the effects of the interference.

Virtual Subcarrier Assignment (VISA) for Spatial Filtering of OFDM Signals

In this paper, we propose a novel spatial filtering technique for orthogonal frequency division multiplexing (OFDM) signals called Vlrtual Subcarrier Assignment (VISA). Here, virtual subcarrier is a subcarrier which is not used for data transmission. When a wireless terminal is equipped with multiple antennas, VISA can easily achieve a space division multiple access (SDMA) by assigning a different spectral position of virtual subcarrier to a different user. To realize VISA in an already-existing OFDM-based wireless local area network (WLAN), we discuss an antenna weight control method in the preamble of a signal burst format designed for the IEEE802.11a standard and evaluate the bit error rate (BER) performance in typical indoor wireless environments.

A Frequency-Selective Wall for Interference Reduction in Wireless Indoor Environments

Modifying the indoor wireless physical propagation environment to reduce the interference level was investigated and demonstrated in this research. A common office partition wall (that was in the main propagation path) was transformed into a frequency-selective (FS) wall by attaching a custom-designed band-stop frequency-selective surface (FSS) as a cover on the wall surface. In-situ measurements showed that this frequency-selective wall filtered out signals operating at 5.4-6.0 GHz (IEEE 802.11a) by an additional attenuation of 10-15 dB compared to the unmodified wall, for incident angles ranging from 0deg-55deg in the azimuth plane and 0deg-20deg in the elevation plane. An attenuation of 10-15 dB in signal strength in the stop band is considered to be significant and beneficial in interference reduction, whereas in the pass-band region (such as 1.8 GHz for cellular telephones), signals experienced only marginally more attenuation than that through the unmodified wall. Results also suggest that the interactions between the FSS and the wall surface can be minimized with an appropriate FSS design, which leads to a feasible and practical product solution: frequency-selective wallpapers. In addition, installation issues, such as misalignment of FSS sheets on the wall, were also examined

An Efficient Parallel Architecture for Implementing LST Decoding in MIMO Systems

Recovering the symbols in a multiple-input multiple-output (MIMO) receiver is a computationally intensive process. The layered space-time (LST) algorithms provide a reasonable tradeoff between complexity and performance. Commercial digital signal processors (DSPs) have become a key component in many high-volume products such as cellular telephones. As an alternative to power-hungry DSPs, we propose to use a moderately parallel single-instruction stream, multiple-data stream (SIMD) coprocessor architecture, called DSP-RAM, to implement an LST MIMO receiver that offers high performance with relatively low power consumption. For a typical indoor wireless environment, a 100-MHz DSP-RAM can potentially provide more than ten times greater decoding throughput at the receiver of a (4,4) MIMO system compared with a conventional 720-MHz DSP. The DSP-RAM processor has been coded in a hardware description language (HDL) and synthesized for both available field-programmable gate arrays (FPGAs) and for a 0.18-mum CMOS standard cell implementation

Radio propagation in frequency selective buildings

AbstractThis work proposes the deployment of frequency selective surfaces (FSS) in indoor wireless environments and investigates their effect on radio wave propagation. FSS could be used to isolate coverage in indoor areas by increasing the transmission loss through the interfaces. At the same time they can channel the signals into other areas of interest. Simulations have been carried out at two frequencies in order to verify the frequency selectivity of FSS. Copyright © 2006 AEIT

Optically Based Direct Sequence Binary Phase Shift Keying Modulation Scheme for Indoor Ultrawide-Band Wireless Systems

In this study, we focus on the design of an optical-based ultrawide-band (UWB) transmission system with a direct sequence-binary phase shift keying (DS-BPSK) modulation scheme for indoor wireless communication environments. The distinct pseudorandom noise (PN) code sequences are assigned to users that share a channel in the UWB multiple-access system. Filtered second-order Gaussian monocycle pulses can provide large bandwidths for very high-speed communications. Moreover, fiber dispersion and intersymbol interference (ISI) problems can be avoided by properly adjusting pulse width. The simulation and analytical results demonstrate that the presented scheme indeed provides several GHz bandwidths for future indoor UWB wireless applications.

Numerical modeling of an indoor wireless environment for the performance evaluation of WLAN systems

A site-specific numerical model, based on the finite-difference time-domain method, is developed in this paper for the indoor radio channel. The scenario of interest is concerned with wave propagation in a typical office environment, for which several simulations are performed considering different placements of the transmitting antenna. Both the 2- and 5-GHz bands are examined, where contemporary wireless local area networks operate. Important channel characteristics are evaluated via the estimation of received power levels, as well as the examination of small-scale fading and time dispersion

A Rapid and Reliable Signal Acquisition Scheme for Indoor UWB Systems

We propose a rapid and reliable signal acquisition scheme for UWB (Ultra Wide Band) systems in indoor wireless environments. The proposed scheme is a two-step search with different thresholds and search windows, where each step utilizes the single-dwell search with the bit reversal. Simulation results show that the proposed scheme for the UWB signals can achieve significant reduction of the required mean acquisition time as compared to other schemes including general double-dwell search scheme for various threshold levels. Furthermore, it is also observed that the proposed scheme can achieve much faster and reliable signal acquisition as the first threshold is larger in noisy environments.

Improvement on Virtual Subcarrier Assignment (VISA) for Spatial Filtering of OFDM Signals: Multiple Subcarrier Puncturing

We have proposed a novel spatial filtering technique named Virtual Subcarrier Assignment (VISA) for orthogonal frequency division multiplexing (OFDM) signals, which enables the transceiver equipped with an adaptive array antenna (AAA) to selectively receive or reject OFDM signals through coloring them with different virtual subcarrier positions in their frequency spectra. In this paper, we develop the VISA to use multiple virtual subcarrier assignment, which assigns a different combination of multiple virtual subcarrier positions in the frequency spectrum to each OFDM signal. Furthermore, we present two kinds of recursive least square (RLS)-based array weight control methods to support the VISA with multiple subcarrier puncturing in an IEEE802.1 la-based system and evaluate the link-level performance in typical indoor wireless environments by computer simulations.

An Accurate UTD Model for the Analysis of Complex Indoor Radio Environments in Microwave WLAN Systems

An accurate uniform theory of diffraction (UTD) model for the analysis of complex indoor radio environments, in which microwave WLAN systems operate, is presented. The model employs a heuristic UTD coefficient suitable to take into account the effects of building floors, walls, windows, and the presence of metallic and penetrable furniture. A numerical tool based on an enhanced tridimensional beam-tracing algorithm, which includes diffraction phenomena, has been developed to compute the field distribution with a high degree of accuracy. After the validation of the model, obtained by means of some comparisons with measurements available in literature, an accurate electromagnetic characterization of typical indoor environments has been performed. The numerical results show that the electromagnetic field distribution and the channel performances are significantly influenced by the diffraction processes arising from the presence of furniture.

Design Template and Measurements for Antenna Planning in an Indoor Radio Environment at 1800 MHz

Recently, the demand for an accurate design on the distribution of the antennas in shopping malls is growing rapidly. To provide a guaranteed coverage inside the shopping malls, mobile operators may have installed a lot more antennas than that is really needed. This over-engineering design has increased the installation and operation cost. Therefore, the need to have a relatively more accurate indoor design is the most requesting goal in the telecommunication industry. The purpose of this paper is to derive an indoor design template, which can facilitate mobile operators to evaluate efficiently the optimized number of antennas and their locations within a premises. A tunnel propagation model is used to represent the propagation loss in an indoor environment. Measurements are also taken to derive the losses of various media. Field tests are finally performed to verify the accuracy of the distribution of RF signal strength predicted by the design template.

Variable bit allocation for FH-CDMA wireless communication systems

In the wireless indoor environment, the channel may vary slowly as users and the interferers may move at slow speeds. A frequency-hopped code-division multiple-access system can adapt to the different interference levels in hopping patterns and assign the slots different bit rates to increase the system capacity. We show that the maximum throughput bit-rate/channel-assignment problem is NP-hard. Several practical ad hoc bit-allocation algorithms are designed based on the insights derived from exhaustive searches. The algorithms that achieve the most system capacity perform interference avoidance. Users concentrate their throughput in a small fraction of the slots with low interference by transmitting large signal constellations, while avoiding the channels with large interference. Simulations show that the flexibility of users to adjust their bit rates to the interference environment can significantly increase the system capacity.

An analysis of the performance of a handset diversity antenna influenced by head, hand, and shoulder effects at 900 MHz .I. Effective gain characteristics

For pt.I see ibid., vol.50, no.3, p.830-44 (2001). In Part I of this two-part paper, we described the effective gain characteristics of the handset diversity antenna comprising a retractable whip antenna and a built-in planar inverted F antenna (PIFA). In order to achieve a high diversity effect, the correlation between the diversity branches must be small while at the same time maintaining a high effective gain, and this is contained in this paper. Further analysis includes an evaluation of the diversity gain with which the diversity effect shown by the analyses of the effective gain in Part I and the correlation in Part II is described. In addition, the mechanism for obtaining a small correlation coefficient is clarified by investigating the amplitude and phase radiation patterns when the whip length and the body inclination angle are changed. From these we obtain various numerical results that provide sufficient insight for design purposes. The validity of the analytical results is verified by an experiment in an indoor radio wave propagation environment.

An analysis of the performance of a handset diversity antenna influenced by head, hand, and shoulder effects at 900 MHz .II. Correlation characteristics

For pt.I see ibid., vol.50, no.3, p.830-44 (2001). In Part I of this two-part paper, we described the effective gain characteristics of the handset diversity antenna comprising a retractable whip antenna and a built-in planar inverted F antenna (PIFA). In order to achieve a high diversity effect, the correlation between the diversity branches must be small while at the same time maintaining a high effective gain, and this is contained in this paper. Further analysis includes an evaluation of the diversity gain with which the diversity effect shown by the analyses of the effective gain in Part I and the correlation in Part II is described. In addition, the mechanism for obtaining a small correlation coefficient is clarified by investigating the amplitude and phase radiation patterns when the whip length and the body inclination angle are changed. From these we obtain various numerical results that provide sufficient insight for design purposes. The validity of the analytical results is verified by an experiment in an indoor radio wave propagation environment.

Performance of fast start-up equaliser for broadband indoor radio

High-speed TDMA wireless networks require high data rate efficiency and fast turnaround times. In dispersive multipath channels, an equaliser is needed to remove ISI from the signal. The equaliser may be trained more quickly if its taps are preloaded with initial values. The paper describes a fast start-up equaliser which uses a power ratio approximation to estimate the initial tap values. The authors report on the performance of the fast start-up equaliser on data measured in an indoor radio environment.

A new spatio-temporal equalization method based on estimated channel response

This paper proposes a new spatio-temporal equalization method, which simultaneously utilizes an adaptive antenna array and a decision feedback equalizer (DFE). For effective spatio-temporal equalization with less computational cost, how to split equalization functionality into spatial processing, and temporal processing is quite important. One of the answers which we have given is incoming signals with larger time delays should be cancelled at the spatial equalization part. The weights of both adaptive antenna array elements and taps of DFE are calculated only using the estimated channel impulse response, therefore, it requires no information on direction of arrival (DoA). We show the performance of the proposed system in multipath fading channels often encountered in indoor wireless environments and discuss the attainable bit error rate (BER), antenna patterns, and the computational complexity in comparison with other equalization methods such as spatial equalization and temporal equalization.

Power control and capacity analysis for a packetized indoor multimedia DS-CDMA network

This paper proposes a packetized indoor wireless system using direct-sequence code-division multiple-access (DS-CDMA) protocol. The indoor radio environment is characterized by slow Rayleigh fading with or without lognormal shadowing. The system supports multimedia services with various transmission rates and quality of service (QoS) requirements and allows for seamless interfacing to asynchronous transfer mode (ATM) broadband networks. All packets are transmitted with forward error correction (FEC) using convolutional code for voice packets and Bose-Chaudhuri-Hocquenghem (BCH) code for data packets with an automatic retransmission request (ARQ) protocol and for video packets without ARQ. A queueing model is used for servicing data transmission requests. A power control algorithm is proposed for the system, which combines closed-loop power control with channel estimation to give the best performance. The cell capacity of each traffic type and various multimedia traffic configurations in both single-cell and multiple-cell networks are evaluated theoretically under the assumption of perfect power control. The effect of power control imperfection on the capacity using the proposed power control algorithm is investigated by computer simulation.