Digital radio is one of the biggest improvements in broadcasting since the introduction of FM. Digital radio signal can be broadcasted for more than 35,000 kilometers (22,000 miles) with complete clarity and high quality sound. You will never get static interferences while listening to over 100 radio channels. The idea behind digital radio has appeared in 1992, when the United States Federal Communications Commission granted a spectrum of the S band (the 2.3 GHz frequency) for Digital Audio Radio Service. The license to broadcast in that band was allocated to Sirius digital Radio and XM digital Radio in 1997. Now there are three companies that provide digital radio in the world: Sirius and XM in Northern America and WorldSpace in Asia, Europe and Africa.
Each of these companies offer different broadcasting systems, since the radio signal of each is proprietary. This means that you will have to buy different hardware depending on your subscription to one of these companies. However, there are three components common to all digital radio services: the digitals, the ground repeaters and the radio receivers.