Modacom operates in the frequency range from 417 MHz to 427 MHz with a duplex spacing between upstream and downstream of 10 MHz; the channel spacing is 12.5 kHz. The radio cell radius is 3 km to 8 km with a base stationtransmit power of 5 W to 25 W. In rural areas, the radio cell can cover up to 25 km. The mobile stations have 3 W to 6 W transmitting power.
At Modacom, the signal is modulated with four- level frequency shift ke ying, and DSMA is used as the channel access method, which is characterized by high data throughput. The gross transmission rate is 9.6 kbit/s, while the net rate is reduced to about half due to the protocol overhead. Modacom uses the error-protected RD-LAPnkArticleID= "5744" ArticleURL=" LAP- link-access- procedure-LAP-protocol" ArticleTitle="LAP-protocol">LAP protocol with cyclic block checking(CRC) and trellis codingas the transmission protocol. The bit error rate is typically `10^-8` for an end-to-end connection, `10^-6` is guaranteed. In addition to throughput, response time is an important criterion for data communications applications. This is typically between 1 s and 3 s.
The switching protocol is packet-switched with a user data length between 12 bytes and 512 bytes.