2024-30760. Impact of L-Band MSS ‘Direct-to-Device’ Operations on GPS

Table 1—C/N0 Degradation vs Separation Distance—GNSS Receiver With Isotropic Receive Antenna

Degradation to C/N0 (dB)	Received interference level (dBW/Hz)	Required separation (m)
1	−207.4	79.1
3	−201.5	40.3
6	−196.8	23.3
10	−192.0	13.4

Using a model for the relative antenna gain pattern of a GNSS high precision receiver (HPR) towards a vertically polarized source at 1575.42 MHz ^[3] and assuming a maximum boresight gain of +3 dBic, Figure 1 shows the area around a single D2D device where the receiver could experience a 1, 3, or 10 dB C/N0 degradation. The plot assumes the D2D or IoT device is 2 m above the ground and that free space path loss conditions exist.

Figure 1. Impact on HPR Due to −70 dBW/MHz Emissions in 1559-1605 MHz

The required lateral separations to keep a high precision GNSS receiver C/N0 degradation with the modeled antenna below 1, 3, or 10 dB shown in Figure 1 are slightly less than the results for a receiver with isotropic receive antenna in Table 1. This observation can be explained by the fact that a typical HPR antenna may have a gain towards a vertically polarized source at the horizon that is below 0 dBi. The results for other GPS/GNSS receiver classes are slightly worse ( i.e., requiring additional separation for the same C/N0 degradation) since their noise floors are similar to HPR devices but they ( print page 105545) typically have higher antenna gain at low elevation angles (see Table 2). Sample calculations for the separation distances in Tables 1 and 2 are provided in Appendix C.

Table 2—Separation Distances from D2D Handset or IoT Device Necessary To Limit C/N0 Degradation for Various GPS/GNSS Receiver Classes

GPS/GNSS receiver class	Noise floor, N0 (dBW/Hz) *	Required separation to limit C/N0 degradation to 1, 3, and 10 dB (m) **
High precision (HPR)	−201.5	52.2 (1 dB), 27.5 (3 dB), 10.1 (10 dB)
General Location/Navigation (GLN)	−200.5	59.6 (1 dB), 31.0 (3 dB), 10.9 (10 dB)
Cellular (CEL)	−200.5 to −201.5	99.8 to 112.0 (1 dB), 50.9 to 57.1 (3 dB), 16.9 to 19.0 (10 dB)
Certified Aviation *** or General Aviation (GAV)	−201.5	66.7 (1 dB), 34.6 (3 dB), 12.2 (10 dB)
* Based upon receiver system noise temperature values in ITU-R M.1903.
** Using representative antenna gain patterns for each receiver class from https://rosap.ntl.bts.gov/​view/​dot/​35535, and assuming the transmit antenna is at 2 m height above ground.
*** See Appendix B for an assessment of a scenario in which the D2D equipment is operated by a passenger on a commercial aircraft.