Coded orthogonal frequency multiplex (COFDM) is used in new audio transmission systems so that numerous low-power broadcast transmitters spaced over a wide area can broadcast the identical signal on the same identical frequency. As an automobile travels around the region, CD quality reception is obtained continuously with no interference or receiver retuning required.

Radio broadcast data systems have digital subcarriers superimposed or added to the existing channel spectrum. These subcarriers transmit such information to the receivers as station call letters, road conditions, program or music names, and other data believed to be useful in a moving automobile.

One of digital technology s main advantages is the applicability of computer processing power and features so that the challenges of scrambling and signal security can be approached with new techniques. Unfortunately, with cable television systems, this advanced digital technology also provides new means of attack for the would-be cable television pirate. To counter this problem, it must be possible to respond to a security attack by replacing the breached security element. If the cable operator owns the set-top boxes, they can be replaced. If the set-top boxes were sold to the subscriber, a plug-in card or module, called the point of deployment module, is used. It remains the property of the cable operator and can be disabled electronically. The subscriber would then be given a new POD device based on a system not yet breached. R.J.