ration time. However, if the probability of false alarm is small, then the probability of false lock (falsely entering the lock mode) will likewise be small and hence the mean acquisition time will not be significantly increased. In conclusion, it appears that a salient feature of an SLS should be that the detector para- meters are changed upon entering the lock mode from the search mode and vice versa. Furthermore, within each mode, a suitable algorithm should be applied to the "hits" and "misses" (detector threshold crossings or their lack thereof) SO as to circumvent the unique relation (see (1.81)) that exists among false alarm probability, detection probability, and dwell time for a sin- gle threshold decision, and thus allow the conflicting requirements on T dis- cussed above to be satisfied. In order to understand in more detail how the above considerations affect acquisition performance, it is convenient to consider a specific SLS and choose a suitable analytical approach for evaluating its behavior. A typical SLS [9] is illustrated in state/transition form in Figure 1.59. This strategy is implicitly assumed to operate in conjunction with the single dwell time PN acquisition system of Figure 1.4. In particular, for the first time a cell is tested (state 1), a miss (failure of the decision variable Z to exceed the detection threshold) results in immediate rejection of the cell and a phase step to the next cell (see Figure 1.4). On the other hand, a hit (Z exceeds the thresh- old) on the first test of a cell advances the SLS to state 2, whereupon the identical cell is retested. If a second hit occurs, the SLS enters the lock mode. A miss in state 2 causes a return to state 1. Additional hits and misses pro- duce similar transitions between states of the SLS. It is to be emphasized that for the SLS of Figure 1.59, the dwell time Td1 is identical for search states 1 and 2. Just as a single hit does not put the SLS in the lock mode, three succes- sive misses are required to reinitiate the search mode. Any othe