BeiDou Signal Plan

Fundamentals
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.

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:

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

Where:
• Superscript j: satellite number.
• A_B1I : amplitude of B1I.
• C_B1I : ranging code of B1I.
• D_B1I : data modulated on ranging code of B1I.
• f₁ : carrier initial phase of B1I.
• Ѱ_B1I : carrier initial phase of B1I.

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

Beidou B1I signal characteristics

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 37.736 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.

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 S_{B1C_data}(t) is the data component, which is generated from the navigation message data DS_{B1C_data}(t) and the ranging code CS_{B1C_data}(t) modulated with the sine-phase BOC(1,1) subcarrier scS_{B1C_data}(t). S_{B1C_pilot}(t) is generated from the ranging code C_{B1C_pilot}(t), modulated with the QMBOC(6,1,4/33) subcarrier sc_{B1C_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	37.736 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 20,64 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.

As also done for the rest of GNSS bands, we show in the next figure all the systems together.

Figure 4: Spectra of Galileo and BeiDou signals in the E5 - B2 bands.

To conclude, some technical characteristics on the BeiDou B2 signals are presented more in detail in the next table:

Table 2: BeiDou B2 signal technical characteristics [Compass ITU Filing] .

BeiDou B3 Band

Finally, the spectral characteristics of the BeiDou B3 signals are also shown here. Similar to the B1 and B2 bands, not all the technical aspects of the BeiDou signals are defined yet. Next figure shows the Power Spectral densities of the proposed BeiDou signals in B3:

Figure 5: Spectra of BeiDou Signals in the E6 - B3 band.

In order to have a better insight on how the Galileo E6 – BeiDou B3 band looks like, the following figure presents all the planned signals together.

Figure 6: Spectra of Galileo and BeiDou Signals in the E6 - B3 band.

To conclude, some technical characteristics on the BeiDou B3 signals are provided next [Compass ITU Filing] .

Table 3: BeiDou B3 signal technical characteristics [Compass ITU Filing] .

Credits

The information presented in this NAVIPEDIA’s article is an extract of the PhD work performed by Dr. Jose Ángel Ávila Rodríguez in the FAF University of Munich as part of his Doctoral Thesis “On Generalized Signal Waveforms for Satellite Navigation” presented in June 2008, Munich (Germany)