Reliability evaluation: a field experience from Motorola's cellular base transceiver systems

The initial predicted MTBF with four hours MTTR, for a base transceiver system (BTS) is 4.0/5.65 years (MIL217/Bellcore standards). With the first 12 months of commercial operation, with actual field data, the MTBF is calculated to be 8.26 years (Bellcore), which is almost double the initial predicted reliability level. The improved manufacturing techniques with (six sigma quality), advanced system test methods, removal of all defective units in early stages of deployment resulted in tremendous reliability growth which exceeded the initial expected reliability. The downtime per year has decreased from 42 min/yr. to 29 min/yr. and the BTS availability has increased from 99.993% to 99.995%, or 5.39 sigma. Further refinement in the reliability is possible by introducing the following steps: (1) establish a minimum qualifying MTBF level for each component of each board; (2) validate the MTBF calculation methodology of vendor of each component; (3) improve MTBF of all weak FRUs by introducing redundancy schemes within each board; (4) introduce individual execution paths for each sector within a BTS; (5) continuous quality improvement techniques to eliminate escaping defects; (6) and establish BTS (HW and SW) stability level with an established release criteria.