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Table 39.1 shows a comparison between the GPS L1 C/A code signal and the MBS 2 MHz signal. The MBS system is a broadcast system similar to the GPS, the only difference being that the MBS system is terrestrially broadcast. The MBS is a spread‐spectrum system which has pretty much all its key characteristics identical to GPS C/A except that the spreading codes selected may be optimized for multipath. With regard to multiple access, the MBS system uses a combination of CDMA/TDMA/Frequency Offset Multiple Access, whereas the GPS system uses CDMA. The MBS system provides a cross‐correlation rejection of >40 dB as against the worst‐case CDMA code rejection of 23 dB in GPS systems. The MBS system’s beacon transmissions are synchronized to one another, just as for GPS satellite transmissions. The MBS data bit duration and coding in MBS are similar to the Wide Area Augmentation System (WAAS) or European Geostationary Navigation Overlay Service (EGNOS) systems. The MBS data content is, in general, analogous to the GPS data content with the MBS beacon coordinates corresponding to the GPS ephemeris/almanac and the MBS timing correction corresponding to the GPS satellite clock correction. Note also that MBS data may be encrypted using a conditional access scheme to control receiver access to the data stream. Location estimation using the MBS system is similar to the GPS system in that trilateration can be done using pseudorange measurements. The key difference is that the MBS trilateration process may estimate altitude independently using the receiver barometric pressure reading. The MBS receiver can operate in both stand‐alone and assisted modes, just as a GPS receiver. Also, the position may be computed at the receiver or at the server.

Table 39.1 Comparison between GPS L1 C/A code and MBS 2 MHz signal

System Feature	GPS L1 C/A Code	MBS 2MHz Signal
System type	BroadcastSatellite system	BroadcastTerrestrial system
Signal properties	Spread spectrumFull bandwidth 20 MHzFirst null‐to‐null bandwidth 2.046 MHzSinc‐shaped spectrum with slow sinc roll‐off of spectrum sidelobes	Spread spectrumFull bandwidth 2.046 MHzFirst null‐to‐null bandwidth2.046 MHzSinc‐like spectrum shape similar to GPS in‐band and very sharp spectrum roll‐off beyond null‐to‐null bandwidth
Spreading codes (chip rate, code length, duration)	Chip rate: 1.023 McpsCode length: 1023 chipsSpreading: BPSKCode duration: 1 msSpreading code type: Selected Gold codes	Chip Rate:1.023 McpsCode length: 1023 chipsSpreading: BPSKCode duration: 1 msSpreading code: GPS family of Gold codes, optimized for multipath
Multiple access	CDMASatellite transmissions cross‐correlation > 23 dB	CDMA/TDMA/frequency offset (optional)Beacon transmissions cross‐correlation > 40 dB TDMA slots 100 ms over 1 s transmission periodSlots can contain preamble, pilot, and data
Synchronization	Relative and absolute synchronizationSV transmissions at antenna aligned to each other and to common GPS system time	Relative and absolute synchronizationBeacon transmissions at antenna aligned to each other and to common MBS system timeMBS system time aligned to GPS system time
Data (rate, modulation, and coding)	Bit duration: 20 msBPSK modulation dataNo forward error correction	Bit duration: 1 msBPSK modulation dataForward error correction scheme similar to WAAS/EGNOS
Data (content)	Satellite orbit information, clock corrections, and atmospheric corrections through ephemeris and almanacData on the C/A code is not encrypted	Beacon locations, beacon clock corrections, and atmospheric informationData may be optionally encrypted using a conditional access scheme to control receiver access
Receiver trilateration method	Pseudorange‐based 3D trilaterationGPS system timing (pps) available as by‐product	Pseudorange‐based 2D or 3D trilaterationMBS system timing available as by‐product
Receiver operation mode	Stand‐alone and assisted modesAssisted mode provides greater sensitivity and quicker TTFFPosition computed on receiver or on the network	Stand‐alone and assisted modesAssisted mode provides greater sensitivity and quicker TTFFPosition computed on receiver or on the network

The MBS 5 MHz signal is a spread‐spectrum signal similar to the 2 MHz signal. The 5 MHz signal provides better multipath resolvability due to its wider bandwidth. The code duration of the 5 MHz signal is the same as the 2 MHz signal, whereas its code and code length (2046) are chosen similar to GNSS signals such as BeiDou to facilitate GNSS receiver reuse. The 5MHz signal may optionally contain data modulation. The 5 MHz signal is synchronized at the beacon antenna along with the 2 MHz signal potentially allowing trilateration with a mix of 2 MHz and 5 MHz signals. When both 2 MHz and 5 MHz signals are available from the same beacon, it may be preferable to acquire using the 2 MHz signal due to its shorter code length.