- PRBS-Ranging measures the receiving time of a regular Pseudo Random Binary Sequence (PRBS) transmitted in the beacon message. Multiple RX stations deliver their measurements into a central database. From the RX location and measured distance to the satellite TLE’s can be calculated.
- The PRBS consists of 32 bytes (256 bits) of pseudo-random data that can be used, with multiple receiving stations, to measure the distance to and location of the satellite. From that TLE can be calculated. The selected PRBS is the same as specified for the pseudo-randomizer of an ECSS downlink (see [Space engineering – Space data links – Telemetry synchronization and channel coding, ECSS-E-ST-50-01C]). The pseudo‐random sequence is generated using the following polynomial:
- The sequence generated with this polynomial is periodic and repeats after 255 bits. The 256th bit of the PRBS is therefore a repetition of the 1st and is present to round the length of the PRBS to a integral number of bytes.The generated sequence of 32 bytes is the following (hexadecimal bytes):FF 48 0E C0 9A 0D 70 BC 8E 2C 93 AD A7 B7 46 CE
5A 97 7D CC 32 A2 BF 3E 0A 10 F1 88 94 CD EA B1It is transmitted in this exact bit order, i.e. most significant bits first. This means the bytes will appear bit-reversed when read from FX.25 frame content.Reference to some classic “PRBS-Ranging and TLE reconstruction” documents: