he con- figuration is drawn, all of the N integrate-and-dump circuits initiate their integration at the same instant in time, each one dumping, however, at a later and later time instant in view of (1.100). Thus, because of this overlap in the integration times of the integrate-and-dump circuits, the outputs Z, Z, ZN represent a set of fully dependent random variables. ²0 As such, the prob- ability that Z crosses its threshold depends on the probability that Zk; k = , i - 1 crossed their respective thresholds. This fact will be impor- tant in what follows later on. In accordance with the search update algorithm, the output of the i-th integrate-and-dump is sampled and compared to a threshold only if all of the previous i - 1 integrate-and-dump outputs have previously exceeded their respective thresholds. Otherwise, the first inte- grate-and-dump output to fall below its threshold causes the local code to update its phase and search the next cell thereby resetting all of the inte- grate-and-dump circuits. In reality, Figure 1.16 represents only a conceptual implementation of the N-dwell system. In practice, the N integrate-and-dumps would be realized by a single continuous-time integrator whose output is sequentially sampled (but not dumped) at time instants t = + Tdi depending, as above, on the outcomes of the first i 1 threshold comparisons. This single integrator would again be reset only after a deci- In [8], an N-dwell configuration is considered wherein the N integrate-and-dump outputs Z, , ZN are independent by virtue of the fact that the i-th integrate-and-dump, =2,3, N, initiates its integration at the instant in time at which the (i - 1)-st is dumped. RECEIVED SQUARE-LAW 21571 SIGNAL DETECTOR THRESHOLD ENVELOPE COMPARISON NOISE 21>31 I2S, 72 THRESHOLD 12/1701 COMPARISON 22792 INS IN THRESHOLD COMPARISON LOCAL CODE PHASE PN CODE GENERATOR UPDATE Figure 1.16. Block diagram of an N-dwell time PN acquisition system with non-coherent detection. Pseudonoise Code Acquisition in Direct-Sequence Receivers sion is