Abstract: We propose a simplified and accurate path loss equation for calculating the free space path loss for 802.11 WLAN line-of-sight links with antennas between 1 and 2.5 meters in height. We validated the accuracy of our WLAN propagation model with empirical measurements using several wireless LAN systems. We compared our model with other models including Lee's (1986), free space's, Hata's (1980) and Cost231 models and found that our model is superior for predicting the propagation performance of radios with very low antenna heights. This result is very useful for modeling and simulation of wireless LANs and mobile ad-hoc radio networks.

Abstract: The indoor propagation channel appears differently to ultra-wideband (UWB) wireless systems than it does to narrowband (NB) sine wave systems. UWB impulses are short and generally do not overlap as multipath sine waves do. This paper presents the results of measurements made on the UWB indoor propagation channel. The channel impulse response (CIR) of the indoor office channel is extracted from the measurements using a variant of the CLEAN algorithm. The UWB propagation channel statistics are calculated from the CIRs. The analysis produces the following results. i) The pathloss versus distance obeys a power law (1/d/sup N/) curve fit, with the peak received power falling off with N=2.9 and the total received power falling off with N=2.1. This suggests that receiver architectures that can take advantage of the total received power can overcome much of the indoor channel pathloss. ii) A 4 element RAKE receiver shows a benefit as the peak power plus RAKE gain falls off with N=2.5, somewhat offsetting the excess pathloss of the channel. iii) The log-normally distributed standard deviation of the mean pathloss versus distance was found to be 4.75 dB, 4.04 dB, and 3.55 dB for the peak, peak plus RAKE, and total power pathloss, respectively. This suggests that a relatively small fading margin is required for UWB systems (compared to NB systems). iv) The RMS delay spread of the indoor channel increases with increasing T-R separation and also with increasing path loss. These results can aid in the design of UWB systems to overcome the challenges posed by the indoor channel.

Abstract: A method and apparatus for determining the transmission power level between a plurality of stations located within the coverage area of a basic service set (BSS) in a wireless local area network (WLAN). The receiving station measures a received signal power from the transmitting station, then the path loss estimation is computed based on the difference between the received signal power and the transmit power level extracted from the incoming signal. The computed path loss is updated according predetermined criteria. Based on the updated path loss information, the transmit power level and/or the transmission rate of a receiving station is adjusted.

Abstract: In this paper, we demonstrate the energy-efficient point coordination function (PCF) operation of IEEE 802.11a wireless LAN (WLAN) via both transmit power control (TPC) and physical layer (PHY) rate adaptation. First, we derive the energy-consumption performance analytically for uplink data transmissions under the PCF. From the evaluation results, we observe that significant energy savings can be achieved by combining TPC with adaptive PHY rate selection. A key requirement for a transmitter to select the most energy-efficient combination of transmit power level and PHY rate is the knowledge of the path loss between the receiver and itself. We present a novel scheme for accurate path loss estimation in 802.11 WLAN. Results and conclusions presented in this paper can serve as a valuable guidance or reference for the design of future 5 GHz 802.11 WLAN systems.

Abstract: In this paper path loss and delay spread predictions of a 3D ray tracing software are compared to wideband radio channel measurements made in Helsinki city center. Measurements were carried out in the 2 GHz band by using a wideband radio channel sounder, which gives out complex channel impulse responses. Reference delay spreads were obtained from power delay profiles, and path losses were available after appropriate cable calibration measurements. Comparisons between measurement and propagation predictions were made in cases where a realistic directional BS antenna was placed (a) slightly below the rooftop level and (b) slightly above the rooftop level. For propagation modeling a fully 3D ray optical model was used.

Abstract: This paper contains measured data for 2.5 and 60 GHz in-building partition loss. Path loss measurements were recorded using a broadband sliding correlator channel sounder which recorded over 39000 power delay profiles (PDP) in 22 separate locations in a modern office building. Transmitters and receivers were separated by distances ranging from 3.5 to 27.4 meters, and were separated by a variety of obstructions, in order to emulate future single-cell-per-room wireless networks. These measurements may aid in the development of future in-building wireless networks in the unlicensed 2.4 GHz and 60 GHz bands.

Abstract: A measurement-based prediction method for radiation path loss over a predetermined area comprises the steps of : determining a received signal strength (2) at least one first station resulting from a transmission of known properties (4, 6) from at least one second station, the first and second stations having known locations ; determining radiation path loss data on the basis of the received signal strengths (2) and topographical information (6) of the predetermined area ; analysing the determined radiation path loss data to determine coefficients for a radiation propagation model ; applying the radiation propagation model (10) to generate first predicted radiation path loss data at each of the locations of the first stations and over the predetermined area ; determining shadowing values on the basis of differences between the received signal strength (2) and the first predicted radiation path loss data at each of the locations of the first stations ; analysing the shadowing values to yield shadowing parameters representative of the predetermined area ; and generating shadowing predictions over the predetermined area on the basis of the shadowing parameters and combining such shadowing predictions with the first predicted radiation path loss data to generate second predicted radiation path loss data over the predetermined area (22).

Abstract: A system and method for selecting an appropriate transmit power and data rate at which a communication signal is transmitted over a link between nodes in a wireless ad-hoc communication network based on factors such as variations in path loss in the link, fading conditions, noise level estimation and overall link quality. The system and method perform the operations of computing path loss in the link based on information provided to the source node from the destination node pertaining to characteristics of a message that was transmitted by the source node and received by the destination node, determining a noise factor at the destination node, and calculating the power level and rate at which the data is transmitted over the link from the source node to the destination node based on the path loss and the noise factor. More specifically, the method calculates the power level based on the path loss, the noise factor and signal fading, and determines the rate based on the calculated power level. Furthermore, the path loss is computed dynamically as conditions of said link change over time. Accordingly, the system and method are capable of determining the proper level of transmit power and data rate for assuring that the destination node will receive the data transmitted by the source node at a reliability of at least 90%.

Abstract: This paper present a statistical indoor path loss model derived from 18 GHz experimental data collected in laboratory building There are two models which are considered: (1) a distance-dependent path loss model and (2) a floor attenuation-factor (FAF) path loss model These models have been developed based on the number of floors, concrete and mirror walls between the transmitter and the receiver, and provide simple prediction rules which relate signal strength to the log of distance The standard deviation between measured and predicted path loss is 87 dB for the entire data set Average floor attenuation factors (FAF), which describe the second path loss (in decibels) caused by the floors between transmitter and receiver are found for as many as three floors in a typical building

Abstract: We present the results of propagation measurements at 2.485 GHz for fixed wireless loops. Path loss measurements were performed and characterized at 43 subscriber locations around a base station antenna located on top of Crawford Hill in Holmdel, NJ. This suburban location is characterized by rolling hills, foliage, and terrain blockages. Temporal and horizontal motion path loss fluctuations were found to be uncorrelated, each characterized by a different Ricean distribution. Lower r.m.s. delay spreads were obtained with directive subscriber antennas than with omni-directional antennas. No substantial gain loss (less than 2 dB) of subscribers' directive antennas was observed. The effects of trees, with foliage, surrounding the base station upon the path loss and the ratio of scattered power to specular power are also examined. The distance exponent of path loss versus distance (about 1.5) was observed to be less than free-space. Diffraction loss from hilltop trees, shadowing the base station, are suspected to be the cause. This loss decreases as the remote moves further away and comes out of the shadow. Scattered power from directions other than line-of-sight was observed to be as high as one half of the specular contribution when tree scattering near the base station was significant.

Abstract: Scaled models of simple two-dimensional (2-D) urban environments are considered in order to investigate propagation along a vertical plane. Specifically, path loss measurements are taken for different positions of the transmitting and receiving antennas at 25 GHz. Then measurement results are compared with theoretical predictions computed by a ray-tracing polygonal line simulator. The measurements indicate a very good agreement between the ray-tracing model and the experiments.

Abstract: This work deals with path-loss modeling of the indoor 60-GHz multipath channel. Measurement campaigns show that radio waves are confined inside rooms and allow fadings to be investigated. To identify the distributions describing both small- and large-scale fadings, goodness-of-fit tests are used and show they can be modeled by a log-normal distribution. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 158–162, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10402

Abstract: When designing wireless communication systems, it is very important to know the optimum locations for the base station antennas. In this paper, a model has been developed to set up an optimization problem, the solution of which provides the information for the optimum location of the base station antennas particularly for an indoor environment. Several methods for the optimization of the cost function are presented and the final results are compared with each other. This methodology can be applied for the design and planning of the location of base station antennas for indoor wireless communication systems. Two numerical examples have been presented to illustrate the application of this methodology.

Abstract: Using a directional receive (RX) antenna array the channel capacity of an 8 /spl times/ 8 multiple-input multiple-output (MIMO) system in an office scenario at 5.2 GHz for different RX directions and positions is measured. The average MIMO capacity can be related to dominant wave propagation. However, when path-loss is normalised out, MIMO capacity is nearly independent of RX direction and position.

Abstract: This paper summarizes the propagation characteristics of a 20 MHz channel at a carrier frequency of 3.676 GHz transmitted from a two-antenna base to a two-antenna mobile receiver. The experiments were conducted in a moderate density suburban setting outside Chicago, Illinois. The transmit and receive systems are described, as are the data collection procedures and data analysis. The results include path loss measurements and various metrics of the MIMO channel, such as channel impulse responses, rms delay spread, and other spatial characteristics.

Abstract: The results obtained with a two-dimensional (2-D) propagation model for wireless communications in an urban environment are compared against the results of other propagation models, such as COST-231 Walfisch-Ikegami (1988, 1984), Hata's (1980), and Zhang's (1997).

Abstract: Implementation digital fixed wireless systems, such as digital FM, high definition TV (HDTV) and wireless local loop (WILL), require a high level of accuracy of propagation prediction in the VHF and UHF bands. This paper presents a theoretical model that predicts the average path loss from an elevated base station to subscriber antennas at rooftop level in residential areas for frequencies in the approximate band from 30 MHz up to 3 GHz. In addition, the model gives the standard deviation of the path loss at the average rooftop level and the height gain for subscriber antennas above or below the average rooftop level. The approach used here generalizes that of Walfisch and Bertoni (1988), who developed a theoretical model of UHF propagation in urban environments. The rows of buildings in residential areas are modeled as a series of dielectric screens having random heights and uniform spacing. Propagation takes place over and through the dielectric screens, and ground reflections are included. The fields at the plane of each screen are obtained in terms of repeated numerical evaluation of the physical optics (PO) integral. Results obtained for the variation of the range dependence on frequency and row spacing are consistent with those previously found for high frequencies by assuming the screens to be totally absorbing. Using the results at different heights of receiving antenna allows computation of the height gain. The predictions are in agreement with the International Telecommunication Union Radio Communication (ITRU-R) recommendations in the VHF and UHF bands.

Abstract: This paper presents the results of the generalized radial basis function neural networks applications for the prediction of propagation path loss in urban and suburban environment. We have studied two types of neural network based models; the first one is used for path loss prediction while the second one is a hybrid prediction model based on error control. The performances of the neural models are compared to the path loss values measured in the city of Kavala and in Oia village on Santorini Island, Greece, based on the absolute mean error, standard deviation and root mean square error between predicted and measured values.

Abstract: A method of scheduling data communication over an uplink. The method enables two or more users seeking to transmit data over the uplink to be scheduled in response to their path loss. The user having the most attractive determined path loss among the two or more users seeking to transmit data over the uplink us scheduled first. Thereafter, the next user having the next most attractive path loss among the remaining users may be subsequently scheduled if the total noise rise leftover is greater than zero. This process repeats so long as or until the total noise rise leftover is about zero.

Abstract: The millimeter-wave frequency band is emerging as an interesting choice for high data-rate indoor wireless communications. The features of large bandwidth, small antenna size and high indoor path loss to isolate separate channels offer many advantages. This paper reports on the experimental setup, the experimental results, and statistical characteristics of line-of-sight (LOS) indoor wireless propagation channels using a low-profile directional antenna for both transmit and receive functions at 30 GHz. The path loss and small-scale fading characteristics are explored. The measured results are used to determine the coefficients used in Rician and Nakagami distribution models at 30 GHz.

Abstract: A radiated emission measurement process for CDMA (IS-95) and GSM (ETSI GSM 11.22) wireless handsets was developed. Spurious radiated emissions were efficiently characterized from devices tested in either a semi-anechoic or reverberation chamber, in terms of effective isotropic radiated power. Eight representative handsets (4 GSM, 4 CDMA) were commanded to operate while varying their radio transmitter parameters (power, modulation, etc.). The measurement process and resulting data may subsequently be used by others as a basis of consistent evaluation for cellular/PCS phones, Bluetooth, IEEE802.11b, IEEE802.11a, FRS/GMRS radios, and other portable transmitters. Aircraft interference path loss (IPL) and navigation radio interference threshold data from numerous reference documents, standards, and NASA partnerships were compiled. Using this data, a preliminary risk assessment is provided for CDMA and GSM wireless phone interference to aircraft localizer, Glideslope, VOR, and GPS radio receivers on typical transport airplanes. Existing data for device emissions, IPL, and navigation radio interference thresholds needs to be extended for an accurate risk assessment for wireless transmitters in aircraft.

Abstract: Outer loop/weighted open loop power control apparatus controls transmission power levels in a spread spectrum time division duplex communication base station. The base station receives a communication including a transmitted power level and measures its received power level. Based in part on the measured power level and the transmitted power level, a path loss estimate is determined. A quality of the path loss estimate is also determined. The transmission power level for a communication from the base station is based in part on weighting the path loss estimate in response to the estimate's quality.

Abstract: This paper presents results of continuous wave and swept frequency response measurements over the frequency range of U-NII lower and middle bands from 5.15GHz to 5.35GHz in indoor environments. From the continuous wave measurements at 5.2GHz, the excess path loss, and the statistical characteristics of the temporal and spatial fading were found. By sweeping the frequency over the band, envelope correlation as a function of frequency was found and the coherence bandwidth (CBW) was determined from the envelope correlation. Using a channel model, the CBW was used to evaluate RMS delay spread. The dependence of CBW on the antenna polarization was simulated and compared with the measurement results. The influence of room size and separation of transmitter and receiver for LOS paths on RMS delay spread was discussed.

Abstract: We investigate different allocation problems in mobile ad hoc networks. The objective is to minimize the power consumption and end-to-end distortion when transmitting images. Therefore, we use progressive image coding in combination with unequal erasure protection. We investigate two different scenarios, independent packet loss events and path loss events. For both cases, the expected distortion for progressive image transmission without error protection as well as for unequal erasure protection has been derived. Also, the expected power consumption for a certain path allocation pattern is obtained. The construction of operational distortion-power curves is presented by optimizing the unequal error protection and extracting the convex hull of all possible path allocation patterns. The profit of applying UEP to the progressively coded image bitstream in a multipath environment is shown. The presented error protection and rate allocation can be used as a framework for studying the allocation problem concerning the tradeoff between power and distortion for progressive image transmission in different multipath environments.

Abstract: This report describes a prediction technique for the calculation of the field strength of radio waves over irregular terrain paths. The concept of an "equivalent rounded obstacle" is used to account for radio propagation losses over various possible irregular terrain shapes, including shapes which cannot easily be described geometrically. The technique replaces an arbitrary terrain profile with an equivalent rounded obstacle for which a value of path loss can be calculated using appropriate formulas.

Abstract: An apparatus and method for estimating a cell coverage includes: a terrain data processor for dividing an area for calculation of the coverage into pixels of a size; a traffic calculator for estimating a traffic volume by the pixels; a forward coverage estimator for calculating path loss information according to the pixel-based traffic volume and a traffic carrying capacity of the base station and determining a forward link capacity and a forward coverage; and a backward coverage estimator for calculating a same-cell interference and an adjacent-cell interference using the path loss information between the base stations and determining a backward link capacity and a backward coverage, thus determining a cell coverage approximating the actual coverage by including a same-cell interference and an adjacent-cell interference.

Abstract: Wideband direct-sequence (DS)-code-division multiple-access (CDMA) is a strong candidate for both terrestrial and satellite components of UMTS. The forward-link capacity of a satellite DS-CDMA system with a conventional matched filter (MF) receiver is limited by interference from adjacent beams and possibly overlapping beams from multiple satellites. In this paper, we study the performance of the linear minimum mean squared error (MMSE) receiver for the satellite forward link. System constraints are long propagation delay, which prevents accurate closed-loop power control, and low on-board power consumption, which implies a low received bit energy to noise density ratio at the mobile receiver. We consider a "one-step" power adjustment algorithm which attempts to compensate for random shadowing and path loss, and compare the associated performance of the MMSE and MF receivers. Dual-satellite diversity is also considered. The effect of code rate on performance is studied through the use of punctured convolutional codes and the evaluation of random coding bounds. Our results indicate that linear MMSE interference suppression can improve the quality of service and increase system capacity significantly.

Abstract: An adaptive handover algorithm for wireless communications systems is proposed in this paper. The algorithm makes use, among others, of the least squares estimate of path loss parameters and is presented as a generalized version (G-ELS) of the ELS (extended least squares) algorithm. The relevant novelty of the proposed algorithm consists of detecting sudden variations of path loss parameters (a knee in line-of-sight and the street corner effect) in microcellular environments by re-initializing the estimate. A simple hysteresis adaptation rule is also included. It is seen that the G-ELS algorithm yields good performance in the microcellular environment, without determining performance losses with respect to the ELS in macrocellular environments. Furthermore, it may still yield better performance than the classical AVG (averaging) algorithm.