Radiofrequency exposure in the French general population: Band, time, location and activity variability

Information on the exposure of individual persons to radiofrequency (RF) fields is scarce, although such data are crucial in order to develop a suitable exposure assessment method, and frame the hypothesis and design of future epidemiological studies. The main goal of this survey is to assess individual RF exposure on a population basis, while clarifying the relative contribution of different sources to the total exposure. A total of 377 randomly selected people were analyzed. Each participant was supplied with a personal exposure meter for 24-hour measurements (weekday), and kept a time–location–activity diary. Electric field strengths were recorded in 12 different RF bands every 13 s. Summary statistics were calculated with the robust regression on order statistics method. Most of the time, recorded field strengths were not detectable with the exposure meter. Total field, cordless phones, WiFi-microwave, and FM transmitters stood apart with a proportion above the detection threshold of 46.6%, 17.2%, 14.1%, and 11.0%, respectively. The total field mean value was 0.201 V/m, higher in urban areas, during daytime, among adults, and when moving. When focusing on specific channels, the highest mean exposure resulted from FM sources (0.044 V/m), followed by WiFi-microwaves (0.038 V/m), cordless phones (0.037 V/m), and mobile phones (UMTS: 0.036 V/m, UMTS: 0.037 V/m). Various factors, however, contributed to a high variability in RF exposure assessment. These population-based estimates should therefore be confirmed by further surveys to better characterize the exposure situation in different microenvironments.     

基于WiFi的煤矿井下应急救援无线通信系统的研究

随着现代化煤矿的要求及无线通信技术的发展,地面无线通信技术开始应用于煤矿井下通信。本文从煤矿井下灾害环境的特殊性及救援工作的安全性、紧迫性出发,通过分析W iF i短距离无线通信技术,提出了基于W iF i技术建立一种新的煤矿井下应急救援无线通信系统,重点介绍了其原理、硬件设计和软件仿真。该系统在灾后煤矿井下电力供应完全切断的情况下,仍能迅速建立应急救援无线通信链路。该系统基于S3C2410X ARM9硬件平台,硬件设计主要包括采集终端设备和链路路由设备两部分,可实现井下事故现场的环境参数监测、数据实时传输、语音通信等功能。通过NS2离线事件仿真器对系统仿真结果可以看,出该系统的时延小、抖动率低,传输速率随着时间的增加呈现稳定增长趋势,理论上基本满足井下应急救援通信需要,且性能比较稳定。     

基于WiFi的无线远程视频监控系统

WiFi是当前流行的一种无线局域网技术,具有组网方便、易于扩展等特点。通过对WiFi技术的研究,提出一种基于WiFi的无线远程视频监控系统。系统采用Infrastructure模式组网,物理层采用OFDM技术,数据链路层采用PCF模式,并利用IEEE802.1x认证技术保证系统安全。