Software defined radios get the green light

Under new US FCC rules, software modifications in a ‘software defined radio’ can be made through a ‘permissive change,’ which has a streamlined filing process.

The US Federal Communications Commission (FCC) has adopted rule changes to accommodate the authorisation and deployment of a new generation of radio equipment known as software defined radios (SDRs).

Software defined radios can be quickly reprogrammed to transmit and receive on multiple frequencies in different transmission formats. This reprogramming capability could change the way users traditionally communicate across wireless services and promote more efficient use of radio spectrum.

In a software defined radio, functions that were formerly carried out solely in hardware, such as the generation of the transmitted radio signal and the tuning of the received radio signal, are performed by software.

Because these functions are carried out in software, the radio is programmable, allowing it to transmit and receive over a wide range of frequencies and to emulate virtually any desired transmission format.

In December 2000, the FCC released a Notice of Proposed Rule Making seeking comments on proposed changes to streamline the equipment authorisation rules for software defined radios. Under the previous rules, if a manufacturer wanted to make changes to the frequency, power or type of modulation for an approved transmitter, a new approval was required, and the equipment had to be re-labelled with a new identification number. Because software defined radios have the capability of being reprogrammed in the field, these requirements could be overly burdensome and hinder the deployment of software defined radios to consumers.

Under the new rules, software modifications in a software defined radio can be made through a ‘permissive change,’ which has a streamlined filing process. The FCC identification number will not have to be changed, so equipment in the field will not have to be re-labelled. These permissive changes can be obtained only by the original grantee of the equipment authorisation.

To allow for changes to equipment by other parties such as software developers, the Commission will permit an optional ‘electronic label’ for software defined radios, in which the FCC identification number could be displayed on an LCD or similar screen. It will allow another party to obtain an equipment approval in its name and become the party responsible for compliance instead of the original grantee.

The Commission also adopted a proposal to require that a grantee must take adequate steps to prevent unauthorised software modifications to radios, but it declined to set specific security requirements at this time.

This will allow manufacturers flexibility to develop innovative equipment while at the same time provide for oversight of the adequacy of such steps through the equipment authorisation process.