ltiple dwell technique can also be used with coher- ent detectors. In fact, the results in this section are independent of the type of detector used. However, when it becomes necessary to relate the performance to the acquisition system para- meters, we shall pursue only the non-coherent case. DECISION DEVICE RECEIVED SIGNAL DETECTOR PLUS NOISE 'dl' 9 PDI, PFAI ALL DETECTORS INDICATE SYNC, DETECTOR STOP SEARCH. LOCAL PN CODE de PD2,PFA2 AS SOON AS GENERATOR ONE DETECTOR DOES NOT INDICATE SYNC, STOP EXAMINATION, RETARD 44 BY Tc/2 DETECTOR AND CONTINUE TON' PDN,PFAN SEARCH. CODE PHASE UPDATE Figure 1.15. The N-dwell serial synchronization system with half chip search. Pseudonoise Code Acquisition in Direct-Sequence Receivers the decision to continue or stop the search at the present cell is made by sequentially examining the N detector outputs (starting with the first) and applying the following algorithm: (1) If all of the N detectors (tested in succession) indicate that the pre- sent cell is correct, i.e., each produces a threshold crossing, then the decision is made to stop the search. (2) If any one detector fails to indicate that the present cell is correct, i.e., it fails to produce a threshold crossing, then the decision is made to continue the search and the time delay T of the local PN generator is retarded by the chosen phase update increment, whereupon the next cell is examined. Thus, as soon as one detector indicates that the codes are misaligned, the search may move on without waiting for the decisions of the remaining detectors. Note from the foregoing that the maximum time to search a given cell is TdN, whereas the maximum time is Td1. Herein lies the power of the N-dwell system, namely, that most of the cells can be dismissed after a dwell time Tdk; << N, whereas the single dwell system requires that each and every cell be examined for a time equivalent to TdN. A block diagram of an N-dwell time PN acquisition system using non- coherent detection is illustrated in Figure 1.16. In the form in which t