Code sequence generator in a CDMA modem

A Code Division Multiple Access (CDMA) modem that transmits and receives telecommunication signals over a transmit and a receive channel having respective first and second pilot code signals, the second pilot code signal being synchronous with the first pilot code signal and the telecommunication signals including information signals, the modem comprising

• a modem transmitter having:
• a) code generation means comprising a first pilot code means for providing the first pilot code signal selected from a plurality of distinct pilot code signals and a message means for generating a plurality of distinct transmit message code signals, related to and synchronous with the first pilot code signal;
• b) spreading means coupled to the message means for combining each of the information signals, with a respective one of the plurality of transmit message code signals to generate a plurality of spread-spectrum processed message signals comprising a transmit Code Division Multiplex (CDM) signal for transmission over the transmit channel, and the first pilot signal wherein each of the plurality of transmit message code signals is synchronous with the pilot code signal;
• and
• a modem receiver having:
• a) local code generation means comprising a local second pilot code means for providing a local version of the second pilot code signal related to the first pilot code signal and a local message code means for generating a plurality of local receive message code signals related to the second pilot code signal, the second pilot code means being synchronous with the local message code means;
• b) a pilot code acquisition means for acquiring the second pilot code signal comprising a pilot vector correlator for estimating a channel impulse response associated with the second pilot code signal wherein the channel impulse response estimate is determined by estimating a complex channel response affecting each multipath component of the second pilot code signal, and for correlating a plurality of phase-delayed versions of the second pilot code signal with a received CDM signal from the receive channel using the channel impulse response estimate to produce a despread second pilot signal, the code phase of the second pilot code signal being changed responsive to an acquisition signal;
• and detection means for detecting the presence of the despread associated pilot signal to produce an acquisition signal, the acquisition signal indicating a degree of synchronization between the second pilot code signal, the received second pilot code signal and the first pilot code signal;
• c) a second pilot code tracking means including means for adjusting the local second pilot code signal in phase responsive to the acquisition signal in a sense which tends to increase the level of the despread second pilot signal;
• and
• d) message signal acquisition means for providing a plurality of despread receive message signals, the message signal acquisition means correlating the plurality of local receive message code signals with the received CDM signal using the channel response estimate of the second pilot code signal to produce the plurality of despread receive message signals.