Method and apparatus for baseband tracking of a PN code sequence in a spread spectrum receiver

摘要

A method and apparatus for baseband synchronizing of a local PN code sequence with a received PN code sequence incorporated in a received spread spectrum signal is provided. The received spread spectrum signal is translated to baseband to produce an I (in-phase) channel baseband signal and a Q (quadrature-phase) channel baseband signal. Data and error baseband correlators correlate the I channel and Q channel baseband signals with in-phase and quadrature-phase PN signals incorporating the local PN code sequence to produce despread on-time, advanced and delayed I channel and Q channel baseband signals. These despread baseband signals are processed and combined to produce an error signal proportional to a difference between the local PN code sequence and the received PN code sequence. A numerically-controlled oscillator circuit is responsive to the error signal to advance or delay the phase of a reference PN clock signal used to form a local PN clock signal. In operation, the rate of reading the local PN code sequence is accelerated or retarded to synchronize the local and the received PN code sequences.