Multiband Operations

PLZ File Format

Pathloss 6 is utilizes an extensible file format for storing all information necessary for link design. This file has the extension plz and is currently used for multiband and passive repeater links. This format is extensible to account for future requirements.

Multiband operation allows you to add an additional set of equipment to an existing link. Each band will contain a complete set of equipment parameters, antenna heights, a channel table, design frequency and polarization. The site information, path profile and all calculation options are common to all bands in the link.

Creating a Multiband Link

There are a few different methods to create multiband links.

Using Existing Link Files (Single Link)

Open a link file in the Transmission Analysis window. Then click Operations – Multiband – Add Band – Import Link File. This will allow you to select a file to use as the template for the new band in the link.

Once the band is added, you can switch between bands using the menu Operations – Multiband – Switch Band or by pressing Ctrl+B. The Title bar of the Link Window displays the current band.

Any changes to the equipment, antenna heights, frequency, channel table, or polarization will apply only to the current band. Any changes to the profile, or calculation options will apply to the link as a whole. This is true whether the changes are made manually or by using the auto designer or other methods.

The multiband link will be saved as a .plz file and the original link files are not modified. The network will be updated with the new filename as required.

Using Design Rules Files (Single Link)

From the Transmission Analysis window, you can use the Design Link menu item to design the current band using a link design rules file. You can also add a new band and design it in one step by clicking Operations – Multiband – Add Band – Use Design File.

Using Existing Link Files (Network)

Multiband files can also be created by importing the link file for each band into the network.  When overlapping links are detected, the user is prompted to resolve the conflict. Multiband links can be created at this point.

The .plz file will be created and associated with the link in the network. The original link files are not modified.

Using Design Rules (Network)

Similar to the above procedure, Multiband links can be created by repeated use of the automatic link design operations (Create PTP Links, Design Links) using different design rules files for each band.

When finalizing the designed links, if overlapping files would be created, the user will be prompted to resolve the conflict. Multiband links can be created at this time with the selection.

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Carrier Aggregation

The Carrier Aggregation report works with multiband links to determine the sum capacity of the link over the range of availabilities. This is a purely mathematical operation and by its nature assumes that the multipath fade probabilities in each band are independent from one another i.e., best case.

Carrier aggregation depends on the radio file having capacities defined for each modulation state. These should be in the file as a number in Mbps.

Multipath Aggregation Algorithm

Each band contributes a certain capacity for some percentage time of the year – Availability or “Time in Mode”. The algorithm determines all possible combinations of these states between bands. For each combination, the sum of the capacity and the probability of this combination occurring is computed.

As an example, we can look at a dual band configuration where each band is a fixed modulation. Therefore, each band is either available or unavailable. There are 4 possible combinations: both available, one or the other available, or neither available.

If we look at the same dual band configuration except now each band has 3 modulation states. Each band can then contribute 4 possible capacities after accounting for no capacity when the band is unavailable. Therefore, there are 4x4 = 16 possible state combinations.

The total capacity of a combination is the sum of the state capacities. Combination State Time is defined as the percentage of the year this combination is expected to occur and is calculated as the product of the “time in mode” values for each state. The availability of a state combination is defined as the availability of that capacity or greater.

Carrier Aggregation Report

Click Operations – Multipath – Carrier Aggregation Report to perform the calculation and view the results.  The dialog box has three areas: the control panel on top, a plot display of capacity across the domain of availabilities, and an information panel below that.

The plot display shows the aggregate capacities between a minimum and maximum availability. You can use the mouse wheel with the cursor over the plot display to adjust the minimum availability. Hold Ctrl and use the mouse wheel to adjust the maximum availability. Hold Shift plus mouse wheel to “scroll” the display by adjusting both availability bounds. Left click to select a state for detailed display. You can also set the minimum and maximum availability by typing the value in to the controls on the left.

The information panel can show a summary of the multiband calculation, detailed information about a particular combination, or the effect of rain. You can use the radio buttons at the bottom of the controls to select what is displayed. You can also click on one of the bars in the plot display to show the details for that combination.

Settings

You can change the calculation options in the top part of the control panel. These settings affect how the results are presented:

  • Group Low occurrence combinations. This option will group relatively uncommon combinations with the next lower combination. Each combination that occurs for less that 5% of the time of the next lower common combination will be grouped. You can view the detailed display for a state to see all combinations that are contributing ordered by expected amount of time.
  • List all combinations in report. If this option is unchecked, only the most commonly occurring combination will be shown in the report. Otherwise, all the grouped combinations will be listed and ordered by occurrence time.
  • Output CSV will print the capacity vs. availability data at the end of the report as a simple csv.

Click Save and Close to accept the settings. These will be stored with the plz file when it is next saved. Or click Save and Show Report to save and close the dialog and generate the report in the RTF report window. Cancel closes the dialog without saving.