Ultra low cost base station timing module

Abstract

An adaptive frequency stabilization approach is presented which enables a low cost single oven oscillator, having an absolute frequency stability variation over temperature of 4 ppb/75C and ageing rate of 1 ppb/day to meet the time synchronization requirements of WiMAX and CDMA base stations during 24 hour holdover operation. It is demonstrated that for typical temperature variations experienced within the base station the local base station clock can be maintained within 1 micro-second of universal time coordinates for holdover time frames in excess of 24 hours. The stabilization approach enables the oscillator frequency stability to be decreased by 10 times with respect to temperature and 20 times with respect to ageing relative to incumbent solutions. Such a result is world class and has immediate cost and size benefit to the timing module. It is demonstrated that the power consumption of the base station oscillator can be reduced from that required by a DOCXO of 9.6 W to that of the OCXO at 3.5 W under worst case warm up conditions. In addition the supply voltage can be dropped from 12 V to 5 V removing the requirement for specialized power regulation systems. Reduction in the power supply requirements results in a reduction in the overall timing module footprint enabling migration of time base circuit from a stand alone module to its integration onto the radio modem card. System simulation, control loop algorithm implementation and hardware performance results are detailed demonstrating the working validity of the approach for next generation wireless base station timing modules.