Frequency hopping spread spectrum (FHSS) is the best choice for immunity to noise and interference.
The license-free modems within this category use FHSS to deliver your data reliably over very long distances. They also deliver data at a constant throughput: if you have established a link of 5km or 50km, the rate of data transmission is constant. Coupling the aforementioned with maximum allowable transmit power of 1 Watt and excellent receiver sensitivity, you'll be amazed at how far you can communicate.
Please peruse our 900MHz and 2.4GHz ISM-band, license-free, spread spectrum products (OEM versions are listed under their respective enclosed versions at left) and contact us with any questions you may have.