Link Budget

The user enters link parameters such as transmit power, antenna gains, link distance, bit rate etc. This allows the received signal quality to be evaluated. Many link parameters allow different input options. For example the antenna gain may be given in dBi, or the diameter of a dish antenna in meters. This app deals with digital communication links, rather than analog systems. This app includes several on-line examples, for satellite and terrestrial, RF and optical, communication links, plus brief notes on interesting or novel aspects. Examples range from very short links to space communications, with bit rates from bits/second to Gbits/second. A link is provided to a short tutorial on link budget parameters and the formulas used in the app. The latest version provides information on the bandwidth options, given the Eb/N0. For Free Space Optical (FSO) links, we calculate photons per bit as the performance metric. The first screenshot shows the example parameters required for a new link budget. Each of the 8 parameters allows appropriate units to be selected, and provides brief hints. After entering suitable parameters, the user presses the "CALC" button to evaluate the link budget. Numerical values (in dB) that contribute to the final Eb/N0 result (energy per bit over noise spectral density) are shown in the second screenshot which is one of the examples (Ka Band Mars return link). The final bit error rate performance of a digital RF link depends on the Eb/N0 and the modulation/error correction schemes. The examples provide some brief pointers to these issues but modulation and coding are not covered in detail. This app will give accurate values for Eb/N0 for point to point radio links where the path loss is easily calculated. It doesn't attempt to cover the path loss in obstructed links (e.g. cellular communications) or links subject to multipath fading, although some examples mention these issues. The current version also offers a few examples of point to point FSO links. The app doesn't collect any data from users. A user may store one set of link budget parameters, plus their own brief text, about their link budget. These parameters just remain in the app on the installed device. The latest version (0.74) contains small updates to align with the recent Android versions.