Questiny Group

Having completed most of the accounting system conversion, I had some time to return to the development of the Land-mobile Satellite Network Simulator (LMSNS). Specifically, I have manged to create a set of object classes that implement models for monofilar helical antennas operating in the first mode of the axial condition. Such antennas look much like that shown below.  The objective of this activity was to work out the object/class designs for the antenna portion of the software design, but helical antennas are common among satellite systems. The software can now create an antenna object whose subclass is a helix antenna. Based upon a design frequency and number of turns in the helix an object will be created along with all of the helix parameters. I have included methods to calculate the gain pattern for the helix and a sample result is plotted below. The plot shows the hemispherical gain pattern for a 17-turn and 4-turn helix each designed for 150 MHz operation. Gain patterns at 170 MHz are also shown. Measured patterns would likely show a drop in gain at 170 MHz, but this is a consequence of the models accuracy. The models were taken from “Antennas for All Applications”, by John Kraus and Ronald Marhefka. This develops the software basis for which other antenna classes may be developed for the LMSNS. One activity will be to implement the coordinate transformations that covert a direction to a earth terminal location to azimuth and elevation angles relative to the antenna main axis.

We are making progress on the development of Questiny’s Land-mobile Satellite Network Simulator (LMSNS). We have just completed its ability to download two-line elements from NORAD, propagate those elements to a common time, and predict the satellite locations. Below is a plot of the satellite orbits for 200 minutes. The four satellite planes are clearly visible.

In addition, our tool can now estimate the visibility of the satellite relative to a location on the earth. We have taken a location of 0.0 degrees N, 0.0 degrees E, and determined the elevation angle to each of the satellites. This location was chosen as the equator provides the most pronounced gaps for LEO constellations. The satellites are spaced the farthest apart along the equator, so we felt that it might be a most interesting case. The orbit locations were calculated every 2 mintues throughout the 200 minute simulation duration. Calculating these elevation angles that were above 5 degrees and summing the number of such satellite at each time period results in the number of visible satellites. We have plotted this in the graph below.

The interesting thing about this plot is that most of the time an earth terminal will have good visibility to the constellation, but it is not without gaps. We see that there is about a 2 minute gap around 82 minutes into the simulation, and a one minute gap around 19 minutes into the simulation. That means using Orbcomm for continuous back-haul communications is difficult in the current constellation. The reasons for this gap may be due to an incomplete constellation. If so, these gaps would disappear when the constellation is fully populated. In addition to the technical algorithms and software, wer are making progress on the GUI as well. We currently have a mock-up of the GUI, and are developing a working prototype within Matlab. We hope to have furhter progress on it this week.

Next week I will meet with EDX Wireless regarding the use of their products to assist us in the development of our UHF SATCOM Campaign Planner. The provide an engineering tool for the capacity estimation and planning of wireless networks. We will be reviewing their products looking for synergies. More of information can be seen in myBrain under the UHF SATCOM Campaign Planner/Other USCP Technology.