tial (see Figure I.I) LIMITED NON-LIMITED RETURNING ABSORBING DISCRETE CONTINUED STATE STATE SWEEP UNIFORM RANDOM FIXED NON-UNIFORM PENALTY PENALTY Z-TYPE EXPANDING WINDOW TYPE BROKEN CONTINUOUS International BROKEN CONTINOUS Figure 1.2. Classification of acquisition schemes (reprinted from [38]). SAMPLE AT 1=18 d RECEIVED STORE Zi; SIGNAL SQUARE-LAW CHOOSE LOCAL 1/4/19 / dt CORRECT CODE ENVELOPE PN CODE PHASE DETECTOR CORRESPONDING TO PHASE DECISION NOISE max Zi LOCAL UPDATE CODE PHASE BY Tc's Tc AT t=itd; i= 1,2, PN CODE GENERATOR a = TOTAL NUMBER OF CODE PHASE POSITIONS EXAMINED TC = DURATION (IN SECONDS) OF A PN CODE CHIP Figure 1.3. A serial realization of the maximum-likelihood search technique. DETECTOR PN CODE ESTIMATE PN GENERATOR PN CODE FEEDBACK LOGIC AND MODULO 2 ADDER TRACK RECEIVED SIGNAL PN CODE PLUS NOISE DETECTOR CLOCK EXAMINATION LOAD/TRACK PERIOD LOGIC GENERATOR TO CODE TRACK TRACKING LOOP Figure 1.4. A rapid acquisition by sequential estimation (RASE) technique. Historical Survey property that the next combination of register states depends only on the present combination of states, if indeed this present combination is correct (i.e., all n input chips are correctly estimated), all the following states can be predicted based on the knowledge of only this initial condition. Such is the manner in which the RASE maintains synchronization once it has been determined that the n detected chips provide the correct starting position, i.e., from that point on it no longer needs estimates of the input code chips. Until such time, however, the local PN shift registers must be periodically, at a rate determined by an examination period generator, loaded with new estimates where the decision when to stop the reload procedure is based upon a threshold crossing of an in-lock detector. The test statistic upon which this in-lock detector makes its decision is the cross-correlation of the input code with that produced by the local PN generator whose shift reg- ister contents correspond to the present estimate o