Microwave links transmit data between two pre-defined locations. The maximum distance between the locations is depends on the antenna size (gain), frequency band, and link capacity, and can vary from a few meters to several kilometers.
Microwave links are used to build private networks where leased lines are either:
a) too expensive
b) take too long to implement or,
c) are not of the required quality.
For these reasons the most used method of connecting GSM and UMTS mobile networks is microwave. This is especially true in Europe because of the high speed of the rollout of competitive networks and in the third world because of the lack of availability of leased line solutions. The USA has a lower percentage at the moment but there is a new driver which is also affecting the USA, this is the capacity/bandwidth that is required to be transported for new mobile non-voice services. These services mean that the OPEX costs that the operators pay in leased line rentals is increasing enormously and the CAPEX costs of a microwave solution achieves a payback in 1-3 years.
When someone decides to use microwave he needs a planning tool to check if he has Line of Sight (LOS) between potential sites and to design the links to a specified availability as at the higher frequencies microwaves are affected by rainfall. One tool that can help automate this is Comsearch IQLink. They offer a free version for small installations over at https://www.comsearch.com/iqlink-solo-for-free/ . Other options include:
New for April 2019: Here's a new tool from Harrison, but we'll let him describe it in his own words:
I maintain
a python-based link budget system (pylink) available under the BSD license from Github. It lets you source-control link budgets, produce compliance reports, solve for variables, run simulations, etc. I just closed down my company and am doing some consulting for the next 6 months or so, which gives me time to field feature-requests. I hope it can be of some use, and please do ping me if you have questions/requests.
While we're on the subject of free link calculators, here's another effort which was pointed out by Patrick:
http://radioworks.en.softonic.com/