| 摘要 |
PROBLEM TO BE SOLVED: To stabilize the synchronization of a direct spread system spread spectrum receiver by instantaneously acquiring synchronization of a PN (spread code) series, on the basis of a sliding correlation method. SOLUTION: A 1st inverse spread circuit 14 multiplies a received spread spectrum signal with a reference spread code to demodulate a 1st inverse spread signal. A frequency divider circuit 31 frequency-divides a frequency fB(=f1-Δf).n1) of a 2nd oscillation circuit 19 at a frequency division ratio of n1 via a changeover circuit 25, in order to acquire synchronization, and a frequency-divided signal is given to a spread code generating circuit 35, which provides a lead spread code to a 2nd inverse spread circuit 46, a shift register 38 of a phase shifter 37 generates the reference spread code and a delayed spread code and gives them to 1st and 3rd inverse spread circuits 14, 47. A 1st oscillation circuit 18 gives a frequency fA signal to the frequency divider circuit 31, when a level L1 is maximum on the basis of output levels L1, L2, L3 of the circuits 14, 46, 47 to change the frequency fB into the frequency fA so as to control the phase shift, thereby maintaining the synchronization. A crystal oscillator is employed for the oscillation circuits 18, 19. The frequency (f1-Δf) is a frequency resulting from deviating a predetermined frequency deviation Δf from a half of a main lobe bandwidth 2.f1 of the received spread spectrum signal. |
