Direct-Y and it's impact on user equipment technology

It has become evident that GPS must undergo evolutionary changes in order to fully satisfy both civil and military requirements in the next century. Currently, the military must improve the antijam performance of the system to ensure its availability for precision delivery of weapons and general navigation functions in the battlefield. A key component to this strategy is reducing the military's reliance on C/A code to acquire the GPS signal via a direct acquisition of the encrypted Y code. Currently fielded UE/sup 2/ have notable deficiencies which must be remedied before robust D-Y acquisition performance in the face of jamming can be achieved. Since the Y-code is essentially infinite in length (vice 1 msec C/A code), the frequency and code phase error must either be reduced considerably or the resultant uncertainties searched quicker. It turns out the most practical solution involves components in both domains (frequency and code phase) and both involve application of improved UE technologies to effect a quick D-Y acquisition in a jammed environment. The terminology proposed by the JPO and generally adopted to describe this process has come to be known as D-Y which stands for "Direct-Y Acquisition". This paper will highlight two key technologies in the areas of VLSI technology and low power timekeeping and formulate some credible simulation models to describe D-Y performance for the next generation of advanced user equipment. Some discussion of improved signal structures will also be included.