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BeiDou Signal Plan

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FundamentalsFundamentals
Title BeiDou Signal Plan
Author(s) J.A Ávila Rodríguez, University FAF Munich, Germany.
Level Advanced
Year of Publication 2011

Presently, the in-orbit operational BDS satellites providing open services include 5 GEO satellites, 7 IGSO satellites and 21 MEO satellites, which can be further divided as 15 BDS-2 satellites ( 5 BDS-2G, 7 BDS-2I, 3 BDS-2M) and 18 BDS-3 satellites (BDS-3M). In addition to B1I and B2I signals, the B1C and B2a ones have started broadcasting by the BDS-3M satellites[1].


BeiDou B1I Band

The B1I signal is composed of the carrier frequency, ranging code and navigation message. The ranging code and navigation message are modulated on carrier. The B1I signal is expressed as follows[2]:

 SjB1I (t) = AB1ICjB1I(t)DjB1I(t)cos(2πf1t + ѰjB1I)

Where:
• Superscript j: satellite number.
• AB1I : amplitude of B1I.
• CB1I : ranging code of B1I.
• DB1I : data modulated on ranging code of B1I.
• f1 : carrier initial phase of B1I.
• ѰB1I : carrier initial phase of B1I.

To conclude some technical characteristics of the BeiDou B1 signals are given next:

Beidou B1I signal characteristics [3]
Technical KPI High Level Description
Carrier Frequency 1561.098 MHz
Modulation Mode Binary Phase Shift Keying (BPSK)
Polarization Mode Right-Hand Circularly Polarized (RHCP)
Carrier Phase Noise Third-order phase locked loop with 10 Hz one-sided noise bandwidth
Received Power Levels on Ground -163 dBW (measured at the output of a 0 dBi RHCP user receiving antenna when the satellites are above a 5-degree elevation angle)
Signal Multiplexing Mode Code Division Multiple Access (CDMA)
Signal Bandwidth 4092 MHz (centered at the carrier frequency)
Spurious Shall not exceed -50dBc
Signal Coherence The random jitters of the ranging code phase differentials between B1I, B2I and B3I shall be less than 1ns (1σ).
The random jitter of the initial phase differential between the ranging code and the corresponding carrier shall be less than 3° (1σ).
Equipment Group Delay Differential TGD1 (less than 1ns)

BeiDou B1C Band

This section defines the characteristics of the open service signal B1C transmitted by the Medium Earth Orbit (MEO) satellites and the Inclined GeoSynchronous Orbit (IGSO) satellites of BDS-3 for providing open service, and shall not be transmitted by the Geostationary Earth Orbit (GEO) satellites. The signal characteristics described in this chapter pertain to the B1C signal contained within the 32.736 MHz bandwidth with a center frequency of 1575.42MHz. The carrier frequencies, modulations and symbol rates of the B1C signal are shown in the following table.[4]

Beidou B1C components: frequencies and modulations
Signal Signal component Carrier frequency (MHz) Modulation Symbol rate (sps)
B1C Data component B1C_data 1575.42 BOC(1,1) 100
Pilot component B1C_pilot QMBOC(6, 1, 4/33) 0

The complex envelope of the B1C signal is expressed as:

 SB1C(t) = SB1C_data(t)+jS SB1C_pilot (t)

Where the SB1C_data(t) is the data component, which is generated from the navigation message data DSB1C_data(t) and the ranging code CSB1C_data(t) modulated with the sine-phase BOC(1,1) subcarrier scSB1C_data(t). SB1C_pilot(t) is generated from the ranging code CB1C_pilot(t), modulated with the QMBOC(6,1,4/33) subcarrier scB1C_pilot(t). The power ratio of the data component to the pilot component is 1:3.
In the next table appear phase relationship, as well as the power ratio of each component.

Beidou B1C phase relationship and power ratio per component
Component Modulation Phase relationship Power ratio
SB1C_data(t) Sine BOC(1,1) 0 1/4
SB1C_pilot_a (t) QMBOC (6,1,4/33) Sine BOC(1,1) 90 29/44
SB1C_pilot_b (t) Sine BOC(6,1) 0 1/11

To conclude some technical characteristics of the BeiDou B1C signals are given bellow:

Beidou B1C signal characteristics
Technical KPI High Level Description
Carrier Frequency 1575.42 MHz
Modulation Mode BOC/QMBOC
Polarization Mode Right-Hand Circularly Polarized (RHCP)
Carrier Phase Noise Third-order phase locked loop with 10 Hz one-sided noise bandwidth
Received Power Levels on Ground -159 dBW for MEO and -161 dBW for IGSO satellites
Signal Multiplexing Mode Code Division Multiple Access (CDMA)
Signal Bandwidth 32.736 MHz (centered at the carrier frequency)
Spurious Shall not exceed -50dBc
Signal Coherence The time difference between the ranging code phases of all signal components <= 10 ns.
Correlation Loss The correlation loss due to payload distortions <= 0.3 dB
Data/Code Coherence The edge of each data symbol is aligned with the edge of the corresponding ranging code chip. The start of the first chip of the periodic ranging codes is aligned with the start of a data symbol.
The edge of each secondary chip is aligned with the edge of a primary code chip. The start of the first chip of the primary codes is aligned with the start of a secondary code chip.

BeiDou B2a Band

The signal characteristics described in this point correspond to the B2a signal contained within the 20,46 MHz bandwidth with a center frequency of 1176,45 MHz. The following table shows the carrier frequencies, modulations and symbol rates of the B2a signal [5].

Beidou B2a components: frequencies and modulations
Signal Signal component Carrier frequency (MHz) Modulation Symbol rate (sps)
B2a Data component B2a_data 1176.45 BPSK(10) 200
Pilot component B2a_pilot 0

Taking into account both aforementioned signal components, the complex envelope of the B2a signal is:

 SB2a (t) = SB2a_data(t)+jS SB2a_pilot (t)

Where, the data component is generated from the navigation message data (DB2a_data(t)) modulated with the ranging code CB2a_data(t), while the pilot component contains the ranging code CB2a_Pilot(t) only. They both adopt BPSK(10) modulation. The power ratio of the data component to the pilot component is 1:1.
In the next table appear phase relationship, as well as the power ratio of each component.

Beidou B2a phase relationship and power ratio per component
Component Modulation Phase relationship Power ratio
SB2a_data(t) BPSK(10) 0 1/2
SB2a_pilot (t) 90

To conclude, some technical characteristics on the BeiDou B2a signals are presented more in detail in the next table:

Beidou B2a signal characteristics
Technical KPI High Level Description
Carrier Frequency 1176.45 MHz
Modulation Mode Binary Phase Shift Keying (BPSK)
Polarization Mode Right-Hand Circularly Polarized (RHCP)
Carrier Phase Noise Third-order phase locked loop with 10 Hz one-sided noise bandwidth
Received Power Levels on Ground -163 dBW (measured at the output of a 0 dBi RHCP user receiving antenna when the satellites are above a 5-degree elevation angle)
Signal Multiplexing Mode Code Division Multiple Access (CDMA)
Signal Bandwidth 20.46 MHz (centered at the carrier frequency)
Spurious Shall not exceed -50dBc
Signal Coherence The time difference between the ranging code phases of all signal components <= 10 ns.
Data/Code Coherence The edge of each data symbol is aligned with the edge of the corresponding ranging code chip. The start of the first chip of the periodic ranging codes is aligned with the start of a data symbol.
The edge of each secondary chip is aligned with the edge of a primary code chip. The start of the first chip of the primary codes is aligned with the start of a secondary code chip.

BeiDou B3 Band

Finally, this section of the document defines the characteristics of the open service signal B3I, transmitted by the BDS-2 and BDS-3 satellites including MEO, IGSO and GEO satellites for providing open service.

The B3I signal is composed of the carrier frequency, ranging code and navigation message. The ranging code and navigation message are modulated on carrier. The B3I signal is expressed as follows [6]:

 SjB3I (t) = AB3ICjB3I(t)DjB3I(t)cos(2πf3t + ѰjB3I)

Where:
• Superscript j: satellite number
• AB3I : amplitude of B3I
• CB3I : ranging code of B3I
• DB3I : data modulated on ranging code of B3I
• f3 : carrier initial frequency of B3I
• ѰB3I : carrier initial phase of B3I

To conclude, some technical characteristics on the BeiDou B3 signals are provided next.

Beidou B3I signal characteristics
Technical KPI High Level Description
Carrier Frequency 1268.520 MHz
Modulation Mode Binary Phase Shift Keying (BPSK)
Polarization Mode Right-Hand Circularly Polarized (RHCP)
Carrier Phase Noise Third-order phase locked loop with 10 Hz one-sided noise bandwidth
Received Power Levels on Ground -163 dBW (measured at the output of a 0 dBi RHCP user receiving antenna when the satellites are above a 5-degree elevation angle)
Signal Multiplexing Mode Code Division Multiple Access (CDMA)
Signal Bandwidth 20.46 MHz (centered at the carrier frequency)
Spurious Shall not exceed -50dBc
Signal Coherence The random jitters of the ranging code phase differentials between B1I, B2I and B3I shall be less than 1ns (1σ).
The random jitter of the initial phase differential between the ranging code and the corresponding carrier shall be less than 3° (1σ).
Equipment Group Delay Differential Tref (less than 0.5ns)

References

  1. ^ [1] BeiDou Navigation Satellite System Open Service Performance Standard(Version 2.0)
  2. ^ [2]BeiDou Navigation Satellite System Signal In Space Interface Control Document Open Service Signal B1I (Version 3.0)
  3. ^ [3] Beidou B1I signal characteristics
  4. ^ [4] BeiDou Navigation Satellite System Signal In Space Interface Control Document Open Service Signal B1C (Version 1.0)
  5. ^ [5] BeiDou Navigation Satellite System Signal In Space Interface Control Document Open Service Signal B2a (Version 1.0).
  6. ^ [6] BeiDou Navigation Satellite System Signal In Space Interface Control Document Open Service Signal B3I (Version 1.0)


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