a single path from several (see Multipath interference for more details). Diffraction and general attenuation The longer wavelengths have the advantage of diffracting more, and so line of sight is not as necessary to obtain a good signal. Because the frequencies that cell phones use are too high to reflect off the ionosphere as shortwave radio waves do, cell phone waves cannot travel via the ionosphere. (See Diffraction and Attenuation for more details). Different operating frequencies Repeaters are available for all of the GSM frequency bands. Some repeaters will handle different types of networks (such as multi-mode GSM and UMTS). Repeater systems are available for certain Satellite phone systems, allowing these to be used indoors without a clear line of sight to the satellite. Regional Approval Approval in the USA by the FCC It used to be legal to use the low power devices available for home and small scale use in commercial areas (offices, shops, bars, etc.). On February 20, 2013, the FCC released a Report & Order, thus establishing two Safe Harbors and defining the use of "network safe" consumer boosters on licensed spectrum. The Safe Harbors represent a compromise solution between Technology Manufacturers and Wireless Operators. Only a few companies have a product compatible with the new FCC regulations. The FCC has defined two types of repeaters: Wide-band (or broadband) signal boosters are usually repeaters that amplify all frequencies from cell phone carriers. Because interferences can be generated from such boosters, the manufacturers who apply to the FCC must limit their gain (among other things), to 65 dB (for the low LTE 700 MHz bands) to 72 dB (for higher frequencies such as AWS). By limiting the system gain, such boosters are only useful when the outdoor signal is relatively high, and need a complex outdoor installation of specific antennas. Carrier specific (or provider specific) signal boosters. These boosters are only designed to boost those frequencies (and signal) that belong to a particular carrier. Usually, such carrier specific boosters do not produce interferences on other carrier's frequencies, and are allowed to have much larger system gains (sometimes 100 dB). In these conditions, such devices boost signal in a larger coverage area, and can still be efficient when outdoor carrier signals are weak, but are only boosting the signal for the carrier it is designed to operate. These new rules by the FCC were implemented on March 1,