digital inter relay communication (access area) (DIRC)

Digital Inter Relay Communication (DIRC) is a radio network. The difference to other radio networks is that the terminals, the cell phones, are both terminal and base station( relay station). Each of them thus represents a kind of node computer.

The decentralized network of relay stations in DIRC networks regulates itself and does not require a central switching unit. As relays, the terminal units also have a routing function. They pass the connection on to the next relay station. In practice, this can involve up to 1,000 hops over distances of up to 5 km each. In accordance with the CCITT recommendations, the connection switching takes place within 150 ms so that no excessive delay times occur during voice transmissions. The DIRC network is therefore a self-organized network( SON) in which each station transmits its position at irregular intervals. If the central registry does not receive a signal from a station for a certain period of time, it removes it from the network scheme. On the other hand, it is dynamically assigned when it is switched on again.

The DIRC stations transmit in the frequency range between 2.3 GHz and 2.4 GHz. The transmission rate of a channel is 32 kbit/s, and transmission rates of up to 40 Mbit/s are to be achieved with dynamic channel bundling. Control information is transmitted via a control channel with a frequency width of 10 kHz using the TCP/ IP protocol. With a transmitting power of 2.1 W, distances of up to 5 km can be bridged with DIRC. In urban areas, the distances are correspondingly shorter. The signals are encrypted using the RSA method and transmitted digitally using Orthogonal Frequency Division Multiplex( OFDM).

The DIRC concept is an interesting approach to the last mile problem. For example, solutions for high-speed Internet access at 512 kbit/s are being implemented in this area, and later also at 2 Mbit/s.