| 摘要 |
<p>In the transferring of a digital data signal from a transmitter to a receiver using the spread spectrum technique, the data signal is modulo-2 added with a PN code sequence, the bit rate of which is very much higher than the bit rate of the data signal. A carrier is then modulated and transmitted with the-thereby resulting spread data signal. In the receiver, the modulated carrier is demodulated and the demodulated signal, to obtain the digital data signal, is multiplied with a PN code sequence produced in the receiver, coinciding and synchronised with the PN code sequence of the transmitter. In the transmitter, the carrier is modulated by FSK- or BPSK-modulation with the spread data signal. In addition, modulation is carried out by means of the respectively other of these two modulation types with a synchronising signal representing the synchronising information of the the PN code sequence. In the receiver the modulated carrier is demodulated by means of a quadrature demodulator, from the output signal of which then both the spread data signal and also the synchronising signal can be derived by filtering. <IMAGE></p> |
