Base station search method and mobile terminal apparatus

A method for a CDMA communication system mobile radio terminal apparatus to search for a base station with which to communicate, comprising:

• a first step of receiving synchronization acquisition signals sent from a plurality of base stations at different timings, applying despreading processing to the received synchronization acquisition signals, measuring reception power levels of the synchronization acquisition signals, comparing the reception power levels and detecting the highest reception power level;
• a second step of comparing said detected highest reception power level with a threshold indicating the minimum allowable reception power level, controlling said despreading processing timing when said reception power level has reached said threshold so as to be synchronized with said reference signal with the maximum reception power and executing processing necessary to get ready to communicate with the base station that has sent said reference signal with the maximum reception power;
• and
• a third step of, when the result of a comparison of said detected maximum reception power level with said threshold shows that said reception power level is lower than said threshold, adding a reception power value of another synchronization acquisition signal sent from another base station which is different from the base station that has sent said synchronization acquisition signal indicating a maximum reception power level to said maximum reception power value, and considering, when this addition result shows that the reception power level is equal to or greater than said threshold, that the reception power level of said synchronization acquisition signal with the maximum reception power is equal to or greater than said threshold, controlling said despreading processing timing so as to be synchronized with said synchronization acquisition signal with the maximum reception power and executing processing necessary to get ready to communicate with the base station that has sent said synchronization acquisition signal with the maximum reception power.

A CDMA-based mobile terminal apparatus that receives signals useful for synchronization acquisition sent from a plurality of base stations, selects one of said received signals and performs processing for getting ready to communicate with the base station that has sent the selected signal, comprising:

• a delay profile creation circuit that creates a delay profile for each base station based on the signals useful for said synchronization acquisition received from said plurality of base stations;
• a reception power level detection circuit that calculates a reception power level of each base station using the created delay profile;
• a combination circuit that adds reception power values of other base stations to a reception power value of one base station;
• a selection circuit that compares said reception power levels of the respective base stations and selects the maximum reception power level;
• a reception power level decision circuit that detects whether either the reception power level selected by the selection circuit or the reception power level combined by said combination circuit has reached a threshold indicating a minimum allowable limit;
• and
• a control circuit that carries out processing for getting ready to communicate with anyone of said plurality of base stations when said reception power level decision circuit decides that said selected reception power level is lower than said threshold, while said combined reception power level is equal to or greater than said threshold.

A mobile terminal apparatus carrying out a CDMA-based communication, comprising:

• a search correlation circuit that receives signals useful for synchronization acquisition sent from a plurality of base stations, detects said signals, compares reception levels of the detected signals and selects only one signal with the highest reception level;
• a reception power calculation section that calculates reception power of said selected signal;
• a decision circuit that decides whether the reception power level of said calculated signal is equal to or greater than the minimum reception limit level;
• a phase shift measuring circuit that measures relative phase shifts of said plurality of signals detected by said search correlation circuit;
• a phase shift circuit that shifts the phase of said symbol which is not selected by said search correlation circuit so as to eliminate the phase shift measured by said phase shift measuring circuit;
• a combination circuit that adds, when the result of decision by said decision circuit shows that the reception power level of said signal selected by said search correlation circuit is lower than said minimum reception level, signals output from said phase shift circuit to said selected signal until said minimum reception level is satisfied;
• and
• a synchronization acquisition control section that decides, when said decision circuit decides that the reception power level of said signal combined by said combination circuit is equal to or higher than said minimum reception limit level, the range of a search to acquire initial synchronization with the base station that has sent said signal selected by said search correlation circuit and executes synchronization acquisition processing.