IS-GPS-800A - US Coast Guard Navigation Center

3.2.2 PRN Code CharacteristicsThe characteristics of the L1C P -, L1C D -, and the L1C O -codes are defined below in terms of their structure and thebasic method used for generating them. Figures 3.2-1 and 3.2-2 depict simplified block diagrams of the scheme forgenerating the L1C PRN codes.3.2.2.1 L1C CodesThe PRN ranging codes L1C Pi (t) and L1C Di (t) for PRN signal number i are independent, time synchronized, and 10milliseconds in length at a chipping rate of 1.023 Mbps, for total length of 10230 chips. In addition, there is anoverlay modulation code L1C Oi (t) for PRN signal number i which also is independent, time synchronized, and 18seconds in length at a rate of 100 bps, for total length of 1800 bits. The overlay code, L1C Oi (t), is modulo-2 addedto L1C Pi (t). (See Figure 3.3-2 for timing relationship.)Assignment of these code segments by PRN signal number is given in Table 3.2-2 and Table 3.2-3. The tablesprovide code segments for 63 PRN numbers that are designated for GPS use.3.2.2.1.1 Ranging Code StructureBoth L1C Pi (t) and L1C Di (t) are constructed using the same method. Each ranging code is derived from a uniquelength-10223 sequence with a common 7-bit expansion sequence inserted at a PRN signal number-dependent point.The unique length-10223 sequence for each ranging code is derived from a single fixed length-10223 sequencecalled a Legendre sequence L(t), for t = 0, …, 10222. L(t) is defined as,L(0) = 0 ;L(t) = 1, if there exists an integer x such that t is congruent to x 2 modulo 10223;L(t) = 0, if there exists no integer x such that t is congruent to x 2 modulo 10223.Table 6.2-1 in Section 6.2.3 provides the generated sequence of the above defined L(t).7 IS-GPS-800A8 June 2010