Kin Lien Chee

Reverberation and Absorption in an Aircraft Cabin With the Impact of Passengers

Using a similar approach to that applied in acoustics and in microwave reverberation chambers, a theory of wideband propagation in a closed environment is discussed. Here, a room environment is viewed as a lossy cavity, characterized by diffuse scattering from walls and internal obstacles. For experimental results, measurements from 3 to 8 GHz were performed in a 24 passenger section of an aircraft cabin. This UWB system has the transmitter at ceiling height and the receivers at armrest and headrest positions. The measurements were performed for the cabin being unoccupied and fully occupied. In the theoretical model, the closed room environment is characterized by the reverberation time and volume, and these parameters allow derivation of the the remaining parameters such as path loss and average passenger absorption. The RMS delay spread and mean excess delay are also studied. For the mean power the agreement between the theory and measurements is good to within 1-2 dB, indicating the excellent accuracy of the method, which extends to estimating body absorption in real world environments. The total absorption from the seated passengers is dominated by the few who are near the transmitter. In general, this absorbed power is relatively small, so the effect of passengers is marginal for this configuration of a cabin communication system.

Foliage Attenuation Over Mixed Terrains in Rural Areas for Broadband Wireless Access at 3.5 GHz

This paper reports the modeling of foliage attenuation for a broadband wireless access system deployed over mixed terrains in rural areas at 3.5 GHz. The foliage is composed of leaves and leafstalks, and are the dominant scatterers along the transmission paths. The foliage attenuation is determined using the Torrico-Lang model combined with digital topography information. In this model, leaves are modeled as thin lossy circular dielectric discs whereas leafstalks (petioles) are modeled as thin lossy dielectric cylinders. Three measurement campaigns were performed using the mobile WiMAX system (IEEE 802.16 e) deployed in Hetzwege/Abbendorf during winter, spring and mid-summer. Using the winter data as a baseline, the foliage loss due to different degrees of foliation in spring and in winter is studied. The derived foliage loss is then verified and compared with an empirical exponential decay model.

Radiowave Propagation Prediction in Vegetated Residential Environments

This paper proposes a propagation prediction model in vegetated residential areas. The goal is to model the attenuation caused by the tree canopies in vegetated residential areas in a simplified manner. The model is based on the Torrico-Bertoni-Lang model. It describes a vegetated residential area where rows of houses and trees are lying between an elevated transmitting antenna and the receiving antenna that is located at street level. In this scenario, the receiving antenna does not have a direct line of sight (LoS) from the transmitting antenna. Since the transmitting antenna has comparable height to the houses, propagation takes place over the top of the houses. From this viewpoint, the propagation loss is computed by using multiscreen diffraction, where the houses are modeled as absorbing screens, and the trees are modeled as phase screens. Using this approach, the total propagation loss is broken into three components, namely, free-space loss, multiscreen diffraction loss, and rooftop-to-street diffraction loss. In this paper, two main contributions are provided. The first is that a simplified analytical model is proposed to compute the multiscreen diffraction loss in a vegetated residential environment. The second contribution is to include in a simplified manner the effects of vegetation on the rooftop-to-street diffraction loss via the scattering theory of Foldy-Lax. To verify the proposed model, cross-season measurement campaigns at 800 and 3500 MHz were conducted in vegetated residential areas in the north of Germany. The model serves as an important extension of the Walfisch-Bertoni urban model and the COST-231 Walfisch-Ikegami model for applications in vegetated residential areas. The model is valid at the UHF frequency band between 0.5 and 3.5 GHz.

Effects of Carrier Frequency, Antenna Height and Season on Broadband Wireless Access in Rural Areas

The effects of carrier frequency, antenna height and season on a broadband wireless access (BWA) system deployed in a rural area at 825 MHz and 3535 MHz are studied in this paper. With the aid of digital terrain information, both large scale and small scale fading effects present in the rural channel are discussed. Our investigation found that the frequency dependence of a wireless channel varies strongly with the environment. Also, the effects of the antenna height in rural areas of irregular terrains vary with the available clearance above the clutters in the regions. This paper uses extensive measurement campaigns to quantify these effects in winter and spring using a BWA system (IEEE 802.16e) deployed in Hetzwege/Abbendorf, Germany. In the study of small scale fading, the variations of the fading distributions of the wireless channel due to season changes are derived and the corresponding multipath propagations are discussed in this paper.

A Systematic Approach for UWB Channel Modeling in Aircraft Cabins

The Saleh-Valenzuela multipath channel model (SV- model) is often used for the modeling of communication channels in confined environments (1). The model assumes multipath components (MPC) arriving at the receiver in clusters. Instead of identifying clusters from the power delay profile (PDP) via visual inspection as proposed in (2), this paper proposes a syste- matic algorithm for cluster identification in a large wide-bodied aircraft cabin. The performance of the SV model implemented with the proposed best fit algorithm is compared in empty and occupied aircraft cabin scenarios. n analogous to the investigation regarding the influence of passengers in a large wide-bodied aircraft (3), this paper takes a further step to model the UWB propagation chan- nel in the aircraft cabin using the SV-model. Though channel model within single-aisle mid-size aircraft have been reported before (4),(5), parameters extraction, especially the identifica- tion of clusters from a measured impulse response is often done through visual inspection (2). With the aim to derive the channel model in a large wide-bodied aircraft cabin, we take the chance to improve the implementation of SV-model by proposing an algorithm for cluster identification. Channel modeling is investigated in an empty as well as in an occupied cabin. This paper is organized as follows. Section II describes the measurement campaign that were carried out in the occupied and empty cabin. Details of various transmission scenarios will be discussed here. Section III describes the conventional SV- model and its implementation for indoor communication channels. The implementation of the SV-model in the large wide-bodied aircraft cabin is detailed in Section IV. The ex- traction of parameters from the proposed channel model is given in Section V. In Section VI, the performance of the model is verified by comparing the regenerated PDP with the measured PDP in empty cabin and occupied cabin scenarios. Section VI concludes our work in this paper and proposes the outline of future investigations.

Throughput coverage simulations based on signal level measurements at 825 MHz and 3535 MHz

This contribution compares the predicted downlink throughput coverage of a WiMAX-like system - located in a rural environment - for different operating frequencies and transmit power levels. The throughput, which is simulated using the parameters of the IEEE 802.16e-2005 standard, is based on extensive received signal power level measurements carried out with a mobile radio scanner at the frequencies 825 MHz and 3.5 GHz. The resulting path losses are combined with a virtual transmitter-receiver system to compare the throughput coverage at different frequencies and transmit power levels for each location. The outcome of the throughput prediction clearly shows that in built-up areas the use of lower frequencies is beneficial in terms of both needed transmit power and achievable coverage to provide high data rates over the air.

Multihop relaying for broadband wireless access systems at 800 and 3500 MHz in rural areas

This paper addresses the coverage enhancement for broadband wireless access (BWA) at 800 and 3500 MHz in a rural scenario in north Germany using multi-hop relay concepts. The investigation is divided into two phases: In phase I, the coverage of a single BWA system in a rural area is predicted and verified with measurement data. In phase II, the coverage from the BWA system is analyzed and enhanced through the deployment of relay stations. The number of relay stations required for each carrier frequency is determined, and the positions of the relay stations are identified via three different relay placement algorithms, namely path-loss-based, distance-based, and hybrid algorithms. At 800 MHz, the path-loss-based algorithm requires seven relay stations to achieve an overall coverage of 95%. The hybrid and distance-based algorithms require 11 and 14 relay stations, respectively, to achieve the same coverage. At 3500 MHz, path-loss based and hybrid algorithms require 19 and 16 relay stations, respectively, to achieve the same coverage. The distance-based requires 20 relay stations to achieve an overall coverage of 82%. Further increase of relay stations has led to higher interference. Lastly, the transmit power of the relay station is optimized via an intelligent power allocation scheme. The results show that 20% of the total transmit powers from 14 relay stations can be saved at 800 MHz whereas 18% of the total transmit powers from the 20 relay stations can be saved at 3500 MHz.