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A New Radio Propagation Model at 2.4 GHz for Wireless Medical Body Sensors in Outdoor Environment

CSEF · 2013 Electronics & Electromagnetics

Daniel S. Yang · Woodbridge High School, Irvine, Orange County

Overview

Objectives/Goals This project investigates the effect of antenna height, receive antenna on human body, and path distance on the loss of wireless signal power in order to systematically develop a radio propagation model for wireless body sensors. While many studies looked at only distance, this project is novel as it also examines the effect of antenna height and on-body antenna. Studying the effect of on-body antenna is central to wireless telemedicine sensors, which have notable healthcare benefits. Methods/Materials Received power in dBm was measured as a function of 4 independent variables: transmit (Tx) antenna heights of 1, 2, and 3m, receive (Rx) antenna heights of 1m (waist height) and 1.65m (head height), Rx antenna placed on-body and off-body, and 11 distances from 1 to 45m--resulting in 132 data points. For Tx unit, a home wireless router hung on a vertical plank was used. For Rx unit, a wireless USB device hung on a vertical stick, a laptop and spectrum analyzer software were used to measure received power. Results Multiple regression and t-test are used to analyze data. Significance of a variable is tested by comparing its p-value with alpha (5%); model fit is assessed using adjusted R^2 and standard deviation (sigma) of residuals. Experimental results support the 3 hypotheses that placing Rx antenna on-body and increasing distance would decrease received signal power; increasing antenna height would increase power--but only for Tx antenna. Rx antenna height has a surprising/opposite effect in on-body case, in which mean received power for waist-height antenna is significantly higher than that for head-height antenna, a phenomenon possibly due to a focusing effect in antenna pattern when Rx antenna is near the abdomen. Conclusions/Discussion Successive models improved as adjusted R^2 increased. Regression coefficients are incorporated in an extension of classical log-distance model to generate new on-body and off-body empirical propagation models. More accurate models allow lower Tx power margins, making devices more energy-efficient and saving battery--important in small wireless sensors. The final, off-body and on-body multiple regression models have respective sigma of residuals of 3.0 and 4.2dB (measures of model accuracy), as compared favorably to those of past studies (e.g., sigma=6 to 10dB reported). The new empirical model can be utilized to design more reliable wireless links for medical body sensors.

Summary statement

This project collected field data on received power as a function of distance, transmit antenna height, receive antenna height, and antenna on/off the body to develop a new multivariate radio propagation model for wireless medical sensors.

Help received

My teacher supervised the project and my parents helped me on the background research and field measurement setup.

Competition history

  • CSEF 2013 Electronics & Electromagnetics · Entry S0922

Resources

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