RF Recommendations

Support for RF capabilities is optional. If RF is included, the implementation must meet the PC 98 general device requirements. More specific recommendations are expected as RF standards emerge, especially for home PCs.

Manufacturers who are implementing designs that include RF devices are encouraged to join the USB Implementers Forum and other relevant RF industry associations to work with other manufacturers on standardization of RF protocols and media within the computer industry.

The following recommendations are offered to help designers make appropriate choices if RF solutions are being considered in a particular system design:

• Select a low-power RF alternative. For relatively short-range wireless devices that cannot use IR, it is possible to use low-power RF. Use an RF solution appropriate to the application. For example, cordless keyboard and track-ball devices that need RF instead of Control IR require a maximum range of only 15 to 20 feet.
  
  
• Provide a method to defeat noise and conflict with other RF devices in the environment. RF devices should be able to defeat noise such as electromagnetic interference (EMI). Also, programmable channel selection, carrier sensing, or the relatively expensive spread-spectrum or frequency-hopping techniques can be used to share the RF medium with other RF devices that might be in the environment.

  Many of the issues discussed in this recommendation are addressed by the governing regulatory agencies.

• Obtain separate local certification for the system and for the RF device. Rules for certifying low-power, short-range, unlicensed RF devices vary greatly from country to country. By configuring the RF device as a system add-on, local certification of the system will not be blocked while waiting for certification of the RF device, which might take longer. Configuring the RF device as a system add-on also enables adding RF support to legacy hardware.