Method for frequency acquisition of a mobile communications device
View Patent ↗A method is provided for frequency acquisition, particularly for initial frequency acquisition, pursuant to a known synchronization sequence for synchronizing a mobile communications device having a local oscillator with previously known transmit frequencies of a base station that transmit in a known channel raster with defined frequency points within a band, wherein the method includes the steps of determining the inband power of the known synchronization sequence via a sensor by scanning a frequency band, performing coarse determination of the local power maximum of the inband power and, thus, of the received carrier frequency over the scanned frequency band, producing a presumed channel frequency at which the base station is transmitting on the basis of knowledge of the channel raster of the transmit frequencies of the base station, performing fine determination of the received carrier frequency by comparison with the known synchronization sequence, and correcting the frequency deviation of the local oscillator from the transmitted carrier frequency.
1. A method for frequency acquisition via a known synchronization sequence for synchronizing a mobile communications device having a local oscillator with previously known transmit frequencies of a base station that transmit in a known channel raster with defined frequency points within a band, the method comprising the steps of:
determining an inband power of a received carrier frequency via a power sensor by scanning a frequency band;
performing coarse determination of a local power maximum of the inband power at a coarse carrier frequency, and thus of the received carrier frequency over the scanned frequency band;
producing a presumed channel frequency at which the base station is transmitting based on the coarse carrier frequency and knowledge of the channel raster of the transmit frequencies of the base station, the presumed channel frequency being different than the coarse carrier frequency; and
simultaneously performing fine determination of the received carrier frequency using a synchronization channel, the synchronization channel having a correlation peak at a frequency that is different than the presumed channel frequency and different than the coarse carrier frequency.
2. A method for frequency acquisition as claimed in claim 1 , wherein the method is applied upon at least one of a first startup and each further startup of the mobile communications device.
3. A method for frequency acquisition as claimed in claim 1 , the method further comprising the step of adopting an accurately determined frequency of the local oscillator as reference by storing the frequency in a memory of the mobile communications device.
4. A method for frequency acquisition as claimed in claim 1 , wherein the method is applied in a Universal Mobile Telecommunications System (UMTS) mobile radio network, with the determination of the inband power being performed by a power sensor and the fine determination of the received carrier frequency being performed by an Synchronization Channel (SCH) correlator.
5. A method for frequency acquisition as claimed in claim 1 , wherein the mobile communications device carries out a callup to the base station and a switch is made to a second base station during the call.