By Stephen W. Klare and J. M. Rozmus, Scientific-Atlanta
Because of recent interest in cable systems for data transmission as an alternative to use of telephone company leased lines, Scientific-Atlanrn is introducing the 6402 High-Speed Modem which is capable of transmitting and receiving data at standard telephone system rates of 1.544 Mbps (T1) or 6. 312 Mbps (T2). Two features of the 6402 are especially useful for operation on cable systems: high bandwidth efficiency and frequency agility.
The 6402 design is composed of two major parts: the RF section and the baseband processor. The RF section provides modulation, demodulation, frequency translation, and frequency synthesis. The baseband processor recovers both the carrier frequency and the data rate clock from the demodulated baseband signal provided by the RF section using digital processing.
The basic technique used in the 6402 is Quadrature-Amplitude-Shift-Keying (QASK). This method of modulation allows frequency spacing of 750 KHz for T1 channels and 3 MHz for T2 channels with a bit error rate of less than 10^-9.