[Nspcsg] Possible discrepancy between SARPs and MOPS

[Kazushi Suzuki]

CSG Members,

I have just noticed possible discrepancy related to airborne receiver design space
(correlator spacing and pre-correlation bandwidth).

In the following, I extracted parts describing airborne receiver design space constraints,
from both of the documents.
(The version of the documents I am looking at are ones distributed by Tim
 prior to RTCA/CSG joint teleconference.)
For me, it seems that design space reduction for GBAS airborne equipment described in
8.11.4.1 of SARPs is not reflected in 2.3.6.4.1 of MOPS.

Do we need any action toward RTCA from CSG?
Or if anyone knows any information on this regard, please share it.

●SARPs Attachment D：
8.11.4  For aircraft receivers using early-late correlators and tracking GPS satellites, the precorrelation bandwidth of the installation, the correlator spacing and the differential group delay are within the ranges defined in Table D-11, except as noted below.

8.11.4.1  For GBAS airborne equipment using early-late correlators and tracking GPS satellites, the precorrelation bandwidth of the installation, the correlator spacing and the differential group delay are within the ranges defined in Table D 11, except that the region 1 minimum bandwidth will increase to 4 MHz and the average correlator spacing is reduced to an average of 0.21 chips or instantaneous of 0.235 chips.

8.11.4.2  For GBAS Airborne Equipment Class D (GAEC D) receivers using early-late correlators and tracking GPS satellites, the precorrelation bandwidth of the installation, the correlator spacing and the differential group delay are within the ranges defined in Table D-11, regions 2, 3 or 4 only.  


●MOPS：
2.3.6.4.1 GPS Tracking Constraints
GPS satellites shall [LAAS-303] be tracked using either an early-minus-late or double delta delay lock loop discriminator.
For early-minus-late (E-L) delay lock loop (DLL) discriminator tracking of GPS satellites, the pre-correlation bandwidth of the installation, the correlator spacing (d), and the differential group delay shall [LAAS-091] be within the ranges as defined in Table 2-6 for the applicable GAEC and illustrated in Figure 2-3.

in Table 2-6, the constraints on bandwidth and correlator spacing for Region 1
are shown as 2<BW<=7MHz, and 0.045-1.1 [C/A chips] respectively.