In order to estimate the signal parameters accurately for mobile systems, it is necessary to estimate a system's propagation characteristics through a medium. Propagation analysis provides a good initial estimate of the signal characteristics. The ability to accurately predict radio-propagation behavior for wireless personal communication systems, such as cellular mobile radio, is becoming crucial to system design. Since site measurements are costly, propagation models have been developed as a suitable, low-cost, and convenient alternative. Channel modeling is required to predict path, loss and to characterize the impulse response of the propagating channel. The path loss is associated with the design of base stations, as this tells us how much a transmitter needs to radiate to service a given region. Channel characterization, on the other hand, deals with the fidelity of the received signals, and has to do with the nature of the waveform received at a receiver. The objective here is to design a suitable receiver that will receive the transmitted signal, distorted due to the multipath and dispersion effects of the channel, and that will decode the transmitted signal. An understanding of the various propagation models can actually address both problems. This paper begins with a review of the information available on the various propagation models for both indoor and outdoor environments. The existing models can be classified into two major classes: statistical models and site-specific models. The main characteristics of the radio channel - such as path loss, fading, and time-delay spread - are discussed. Currently, a third alternative, which includes many new numerical methods, is being introduced to propagation prediction. The advantages and disadvantages of some of these methods are summarized. In addition, an impulse-response characterization for the propagation path is also presented, including models for small-scale fading, Finally, it is shown that when two-way communication ports can be defined for a mobile system, it is possible to use reciprocity to focus the energy along the direction of an intended user without any explicit knowledge of the electromagnetic environment in which the system is operating, or knowledge of the spatial locations of the transmitter and the receiver.

A survey of various propagation models for mobile communication

A polarization reconfigurable E-shaped patch antenna with wideband performance is proposed in this communication. The antenna is capable of switching its polarization from right hand circular polarization (RHCP) to left hand circular polarization (LHCP) and vice versa. Its structure is simple and consists of a single-layer single-feed E-shaped patch and two RF switches placed at appropriate locations in the slots. The design targets the WLAN IEEE 802.11 b/g frequency band (2.4-2.5 GHz) being used in various wireless communication systems. Full wave simulation is used for the antenna analysis, and a prototype of the antenna with an integrated DC biasing circuit has been fabricated and tested. Good agreement is obtained between simulated and measured results. The antenna exhibits a 7% effective bandwidth from 2.4 GHz to 2.57 GHz with a 8.7 dBic maximum gain. The antenna radiation symmetry is maintained upon switching between the two circular polarization modes.

Circular Polarization Reconfigurable Wideband E-Shaped Patch Antenna for Wireless Applications

Electrical and mechanical equipment can be a major source of interference to indoor wireless systems. A receiver system was developed to measure the time-varying nature of such "impulsive noise" in the 450 MHz band, and extensive measurements were made in hospitals and clinics across the United States. Empirical distributions were extracted for the amplitude, inter-arrival time, and duration of the observed noise pulses. The software propagation simulation tool SIRCIM Plus was developed to include the simulation of impulsive noise in indoor environments, based on the measurements reported here.

Measurements and simulation of radio frequency impulsive noise in hospitals and clinics

This paper presents an experimental study of impulsive noise in urban hospitals and clinics. A receiver was designed to resolve impulsive noise bursts as short as 2 /spl mu/s in duration in the 450-MHz band. Extensive measurements were taken at three hospitals and three clinics in three major urban areas across the United States and empirical models are provided for the amplitude, interarrival time, and duration distributions of observed impulsive noise events. This work may be used in modeling the noise found in indoor wireless communication channels.

Characteristics of impulsive noise in the 450-MHz band in hospitals and clinics

In today's world, the ubiquitous nature of wireless personal systems has lead to an increasing concern regarding the safety and reliability of the electromagnetic environment (EME) in hospitals and clinics. Additionally, modern hospitals are becoming populated with wireless medical applications. Research conducted on the EME so far has only considered frequency ranges below 2 GHz. However, many short-range wireless devices such as Bluetooth and wireless LANs operate in the 2.4 GHz ISM band and are already seeing significant use for medical applications such as transferring patient records. These devices are also expected to be integrated in consumer electronics, to the point where patients or visitors may unknowingly bring wireless transmitters into the hospital environment. Electromagnetic interference (EMI) measurements in the 2.4 GHz ISM band were performed in two hospitals. These measurements are considered to be very first effort to characterize the entire 2.4 GHz ISM band in hospitals. Emphasis was given to critical locations such as emergency rooms (ER), intensive care units (ICU), surgery blocks, and radiology.

Characterization of the 2.4 GHz ISM band electromagnetic interference in a hospital environment

The need for electromagnetic compatibility (EMC) is crucial in health care environments, since electromagnetic interference (EMI) effects on critical care medical equipment may be life-threatening. Field strength measurements, made inside and outside five Montreal hospitals at frequencies between 30-1000 MHz, were compared to fields predicted using line-of-sight, and hybrid methods. Although measured fields generally remained below 3 V/m, EMI still caused medical equipment malfunctions at the five hospitals. The line-of-sight prediction method provided a worst-case estimate of the electromagnetic environmental hazard, predicting outside fields to within 20 dB of those measured. The hybrid method predicted fields to within 10 dB.

The measured and predicted electromagnetic environment at urban hospitals

In order to characterize the electromagnetic environment, due to portable sources, inside a typical Montreal area hospital room, fields were measured in the 148-174 MHz, 425-480 MHz and 825-850 MHz ranges over a period of 24 hours. Call durations in each frequency range remained below 8 seconds 50% of the time, while field levels were 63 dB/spl mu/V/m (1.4 V/m) or lower, 50% of the time. Similar field monitoring in high traffic areas, such as emergency, for longer periods of time, should enable the characterization of call profiles, thereby leading to improved susceptibility testing of medical equipment.

http://ieeexplore.ieee.org/iel3/4363/12495/00575311.pdf

The electromagnetic environment due to portable sources in a typical hospital room

Cross-floor signal propagation characteristics at 434, 862, and 1705 MHz were assessed from measured data in a building similar to a hospital as a first step toward maximizing electromagnetic compatibility (EMC) between wireless radiators within a hospital and medical equipment. Certain transmitter-receiver configurations resulted in 1/r/sup d/ signal attenuation (d=2, and 3<4<4), while other configurations exhibited quasi-constant signal levels over increasing transmitter-receiver separations.

Cross-floor signal propagation inside a contemporary ferro-concrete building at 434, 862, and 1705 MHz

The electromagnetic environment of the emergency room of an urban hospital was estimated, characterizing electric fields over a 4.4-day period. Measured fields did not exceed 1 V/m over the 0.1-1 GHz range, but exhibited substantial day-night variation. Such temporal variation was characterized with respect to intensity and frequency of emissions. The observed field level variation implied a substantial temporal variation of electromagnetic-interference-malfunction risk to medical equipment. This risk tended to be highest during the daytime, early evening and weekends.

Hospital emergency room electromagnetic environment

The diurnal behavior of electromagnetic fields within a typical urban-hospital emergency room was measured during a 4.4-day period. The merged 24-hour field plot showed strong day-night variation of field. Such variation indicated that there were times of higher risk of electromagnetic interference (EMI) during the 24-hour cycle, peaking between 12 noon and 10 pm. Using cumulative energy to produce an equivalent effective field, the effect of multiple simultaneous transmissions was found to slightly increase EMI risk.

https://ieeexplore.ieee.org/iel4/5654/15191/00701599.pdf

P. Vlach

Papers

The measured and predicted electromagnetic environment at urban hospitals

The electromagnetic environment due to portable sources in a typical hospital room

Cross-floor signal propagation inside a contemporary ferro-concrete building at 434, 862, and 1705 MHz

Hospital emergency room electromagnetic environment

Variation of emergency-room electromagnetic-interference potential