search mode dwell time versus the search mode false alarm probability with the lock mode false alarm probability as a parameter. Also the lock mode dwell time is assumed to be five times the search mode dwell time as in the example considered in [9], which has practical application to the Space Shuttle program. Finally, the mean acquisition time is obtained by substituting (1.293) and (1.299) in (1.288). As a numerical illustration of the result of these substitu- tions, we continue with the example considered in [9] where the following Search / Lock Strategies PFA2 0.5 Figure 1.62. Mean dwell time versus search mode false alarm probability (reprinted from [9]). additional parameter specifications were given: = Search Mode Dwell Time = .91 ms Lock Mode Dwell Time = 5Td1 = 4.55 ms = Number of Search Cells = 4094 (PN code of length 2047 chips searched in 1/2 chips increments) = Predetection bandwidth = 500 kHz (P/No)o = Nominal signal-to-noise spectral density = 54.7 dB-Hz. (1.301) Furthermore, a worst case correlation loss L = .5 was assumed during the search mode, while during the lock mode L was set equal to .81 to simulate a delay error of .1 chip. Using the above, we first compute the effective signal-to-noise ratio y' in the pre-detection filter bandwidth as defined by (1.62) (with A2 = P) Pseudonoise Code Acquisition in Direct-Sequence Receivers multiplied by L, i.e., (search mode) (1.302) 10- 6 (lock mode) Then, using y' of (1.302) for A2/NB in (1.81), this equation can be applied to find PD1 when PEA1 = .01 and BTd = 455, and PD2 when P FA2 = 0.5 and BT d2 = 2275. The results of these computations are illustrated in Figure 1.63. Combining the results of Figure 1.63 for PD1 versus P/N and those of Figure 1.61 for PL versus PD1 enables one to determine PL as a function of P/N. For a lock mode false alarm probability P EA2 = 0.5 and search mode false 0.9999 (LOCK MODE) PFA2 = 0.5 (SEARCH MODE) PFA1 = 0.01 0.005 0.0001 Figure 1.63. Detection performance (reprinted from [9]). Search / Lock Strategies alarm prob