This dialog allows you to set up how reliability (or availability) will be calculated. Reliability in this sense is the percent of time that an RF link will be usable over a period, typically one year.

You can set up different methods and choose from among them for use with the receiver that makes up the final end of the RF link. At the top of this dialog you’ll see a drop-down list for which method is currently being edited, as well as buttons to add or delete methods. The method used for a given receiver/study will depend on which of these methods has been assigned to it. The methods are  assigned as part of Area Study details, Point-to-point Link receiver details, and Multipoint Study details.

RF link reliability is affected by three things: median signal level, multipath fading and additional path attenuation. First, the median signal level at the receiver has to be sufficiently higher than the receiver threshold (typically 5dB or better) to provide adequate thermal fade margin. The median signal level is found from all the gains and losses in the system including the path loss.

With a given received median signal level, the signal level at the receiver can still sometimes fall below the threshold level due to 1) multipath fading, and 2) additional path attenuation due to rain along the path. This dialog box gives you options for selecting how multipath fade outage probability and rain outage probability are calculated.

Edit/Add/Delete Reliability Method Name

Allows you to create different reliability configurations and save them, so when you choose a method from a study setup dialog box, you can pick the name of the set up from the drop-down list menu.

Multipath Analysis

For multipath fade outage analysis, you can select from four methods using the Fade outage analysis method drop-down list:

• Vigants-Barnett

• ITU-R 530-8 (the method in ITU-R Rec. 530-8)

• ITU-R 530-10 (the method in ITU-R Rec. 530-10)

• User Fade Outage Table (A user-defined fade outage table - see Appendix H)

• None

Depending on your selection, you must input some additional parameters in the other dialog box sections. See Appendix H for information on making these selections. Selecting None means there will be no fade outage calculation (no reduction in reliability due to fading).

Other Exterior

You may also enter a value for the adjacent channel and external (co-channel) interference. The Other Exterior value will be used in the calculation of the flat-fade margin as described in Appendix H. An entry of -150.00 disables this option.

Dispersive Fade Margin

In this input field, you can enter a value for the dispersive-fade margin. This is applicable to digital systems only, and is incorporated in the overall fade margin as described in Appendix H. The Dispersive-fade margin is typically a specification found in manufacturer's literature for digital microwave radios. An entry of 80.0 disables this option.

Fade Occurrence Factor

This fade occurrence factor is derived from empirical data about the rate of fading. It is set using the maps found in Appendix H. A typical value for this input field is 5.0.

Rain Fade Analysis

Rain outage analysis can be done by one of the following methods:

• Crane (the Crane method)

• ITU-R Rec 530-8/9/10 (the method found in ITU-R Rec. 530-8/9/10)

• ITU-R specified rain rate (ITU-R Rec. 530 with a specified rain rate)

• User Rain Outage Table (A user-defined rain outage table - see Appendix H).

• None

Rain Rate Table Data

With EDX software you have the flexibility to use any of four rain rate tables with any of the first three rain outage calculation methods listed above. Normally you will want to use Crane data with the Crane method and ITU-R data with the ITU-R method, but you are not limited to those combinations here.

Rain Region

The rain regions available for selection in this drop-down list will depend on the rain rate table data you have selected. The appropriate rain region for your area can be found in the tables in Appendix H.

Use Correlated Rain Fade Analysis

EDX software has the unique ability to take into account interfering signals which experience rain fades that are similar to the desired signal. When this option is selected, the assumption is made that the signal from the interfering transmitter is arriving along a path that is similar to that of the desired signal. In this circumstance, the rain fade along the two paths is most likely the same (correlated) because both signals experience the same rain conditions. Therefore, the C/I ratio to this interferer will not change during a fade. Recognizing this condition can be important to correctly calculating interference in high-density Point-to-Multipoint (PMP) and Consecutive Point Network (CPN) systems. The details of the correlated rain fade analysis, and the associated data files that define co-polarized and cross-polarized fading correlation (as a function of angle off bore sight and rain fade depth) are found in Appendix H.

Alternate Lognormal Fading Distribution

Finally, at the bottom of the dialog box you can choose an alternate distribution method of calculating fade on the assumption that the fading is log normally-distributed (a normal or Gaussian distribution in dB). Given this assumption, there is only one other parameter to set to describe the fading distribution: the standard deviation. You can set the standard deviation of the distribution one of three ways:

• Based on the land use (clutter) type at the receiver. The actual standard deviation values for each clutter type are set on the Database>Land Use (Clutter) dialog box in the attenuation file. Click on the Edit Attenuation File button.

• Using standard deviations specified in a file as a function of path length. Appendix H describes the format of this file.

• As a fixed value in dB to be used regardless of path length or land use (clutter) type. A typical value here might be 6 to 8 dB.

Regardless of the way in which the standard deviation is chosen, the program will use that value to establish a lognormal distribution to describe the fading. From that distribution, a determination can be made as to the percent of time the signal falls below the service threshold and from that, calculate link availability.