Link Planning Software

While calculating a link budget by hand is straightforward, there are a number of tools available that will help automate the process. In addition to calculating free space loss, these tools will take many other relevant factors into account as well (such as tree absorption, terrain effects, climate, and even estimating path loss in urban areas). In this section, we will discuss two free tools that are useful for planning wireless links: Green Bay Professional Packet Radio's online interactive network design utilities, and Radio Mobile.

Interactive design CGIs

The Green Bay Professional Packet Radio group (GBPRR) has made a variety of very useful link planning tools available for free online. You can browse these tools online at www.qsl.net/n9zia/wireless . Since the tools are available online, they will work with any device that has a web browser and Internet access.

We will look at the first tool, Wireless Network Link Analysis, in detail. You can find it online at my.athenet.net .

To begin, enter the channel to be used on the link. This can be specified in MHz or GHz. If you don't know the frequency, consult the table in Appendix

B. Note that the table lists the channel's center frequency, while the tool asks for the highest transmitted frequency. The difference in the ultimate result is minimal, so feel free to use the center frequency instead. To find the highest transmitted frequency for a channel, just add 11MHz to the center frequency.

Next, enter the details for the transmitter side of the link, including the transmission line type, antenna gain, and other details. Try to fill in as much data as you know or can estimate. You can also enter the antenna height and elevation for this site. This data will be used for calculating the antenna tilt angle. For calculating Fresnel zone clearance, you will need to use GBPRR's Fresnel Zone Calculator.

The next section is very similar, but includes information about the other end of the link. Enter all available data in the appropriate fields.

Finally, the last section describes the climate, terrain, and distance of the link. Enter as much data as you know or can estimate. Link distance can be calculated by specifying the latitude and longitude of both sites, or entered by hand.

Now, click the Submit button for a detailed report about the proposed link. This includes all of the data entered, as well as the projected path loss, error rates, and uptime. These numbers are all completely theoretical, but will give you a rough idea of the feasibility of the link. By adjusting values on the form, you can play “what-if?” to see how changing various parameters will affect the connection.

In addition to the basic link analysis tool, GBPRR provides a “super edition” that will produce a PDF report, as well as a number of other very useful tools (including the Fresnel Zone Calculator, Distance & Bearing Calculator, and Decibel Conversion Calculator to name just a few). Source code to most of the tools is provided as well.

Radio Mobile

Radio Mobile is a tool for the design and simulation of wireless systems. It predicts the performance of a radio link by using information about the equipment and a digital map of the area. It is public domain software that runs on Windows, or using Linux and the Wine emulator.

Radio Mobile uses a digital terrain elevation model for the calculation of coverage, indicating received signal strength at various points along the path. It automatically builds a profile between two points in the digital map showing the coverage area and first Fresnel zone. During the simulation, it checks for line of sight and calculates the Path Loss, including losses due to obstacles. It is possible to create networks of different topologies, including net master/ slave, point-to-point, and point-to-multipoint.

Figure 3.9: Link feasibility, including Fresnel zone and line of sight estimate, using Radio Mobile.

The software calculates the coverage area from the base station in a point-to-multipoint system. It works for systems having frequencies from 20 kHz to 200 GHz. Digital elevation maps (DEM) are available for free from several sources, and are available for most of the world. DEMs do not show coastlines or other readily identifiable landmarks, but they can easily be combined with other kinds of data (such as aerial photos or topographical charts) in several layers to obtain a more useful and readily recognizable representation. You can digitize your own maps and combine them with DEMs. The digital elevation maps can be merged with scanned maps, satellite photos and Internet map services (such as Mapquest) to produce accurate prediction plots.

Download Radio Mobile here: www.cplus.org

The main Radio Mobile webpage, with examples and tutorials, is available at: www.cplus.org

Radio Mobile under Linux

Radio Mobile will also work using Wine under Ubuntu Linux. While the application runs, some button labels may run beyond the frame of the button and can be hard to read.

We were able to make Radio Mobile work with Linux using the following environment:

• IBM Thinkpad x31
• Ubuntu Breezy (v5.10)
• Wine version 20050725, from the Ubuntu Universe repository

There are detailed instructions for installing Radio Mobile on Windows at www.cplus.org. You should follow all of the steps except for step 1 (since it is difficult to extract a DLL from the VBRUN60SP6.EXE file under Linux). You will either need to copy the MSVBVM60.DLL file from a Windows machine that already has the Visual Basic 6 run-time environment installed, or simply Google for MSVBVM60.DLL, and download the file.

Now continue with step 2 at from the above URL, making sure to unzip the downloaded files in the same directory into which you have placed the downloaded DLL file. Note that you don't have to worry about the stuff after step 4; these are extra steps only needed for Windows users.

Finally, you can start Wine from a terminal with the command:

#'wine'RMWDLX.exe

You should see Radio Mobile running happily in your XWindows session.