A study of the ground illumination footprint of meteor scatter communication
An examination is made of the ground illumination footprint of meteor trails and its effect on the simultaneous reception of meteor scatter transmissions by multiple receivers. A technique for calculating the ground illumination footprint of individual trails which provides added insight into the physical mechanisms is presented. The probability of adjacent station reception as a function of location on the ground is calculated by computing the ground illumination footprint of individual trails at different locations and orientations within the common volume and weighting each footprint by the number of trails at that location and orientation. Two different models for the spatial arrival pattern of meteor trails are considered: the first model assumes that trails arrive uniformly over the common volume, and the second calculates the number of arrivals from the spatial distribution of meteor orbits, antenna patterns, time of day, and season. The effect of antenna patterns on the ground illumination footprint of meteor scatter communication is examined. >
Direct sequence CDMA for large meteor burst networks
The authors examine the application of direct-sequence random code-division multiple-access to large meteor-burst network. Narrowband meteor burst networks have succesfully supported networks of up to a few hundred nodes on a single channel by relying on the natural spatial multiplexing of the meteor channel to support communications. For large high-density meteor-burst networks, however, this spatial multiplexing can fail to provide adequate diversity to avoid collisions. A spread spectrum system can accommodate many thousands of nodes, and through a combination of channel propagation delay and the introduction of random time offsets operate with a single common spreading code. Throughput and waiting time predictions for such a system are illustrated as a function of the number of simultaneous users, network size, bandwidth, and signal level differences between users. It is shown that a spread spectrum system can accommodate very large networks and provide several orders of magnitude improvement over a conventional single channel system.<<ETX>>
Electron dose-rate conversion factors for external exposure of the skin from uniformly deposited activity on the body surface.
Dose-rate conversion factors have been calculated for external exposure of the skin from electrons emitted by sources that are deposited uniformly on the body surface. The dose-rate factors are obtained from electron scaled point kernels developed by Berger (Be71; Be73; Be74). The dose-rate factors are calculated at depths of 4, 8, and 40 mg cm-2 below the body surface as recommended by Whitton (Wh73), and at a depth of 7 mg cm-2 as recommended in ICRP Publication 26 (ICRP77). The dependence of the dose-rate factors at selected depths on the energy of the emitted electrons is displayed. The dose-rate factors for selected radionuclides of potential importance in radiological assessments are tabulated.