BeiDou Navigation Satellite System

Signal In Space
Interface Control Document

Open Service Signal (Version 2.0)

China Satellite Navigation Office

December 2013
 2013 China Satellite Navigation Office

Content

1 Statement ........................................................................................... 1

2 Scope ................................................................................................. 1

3 BeiDou System Overview .................................................................. 1

3.1 Space Constellation .................................................................... 1

3.2 Coordinate System...................................................................... 2

3.3 Time System ............................................................................... 2

4 Signal Specifications .......................................................................... 3

4.1 Signal Structure .......................................................................... 3

4.2 Signal Characteristics ................................................................. 4

4.2.1 Carrier Frequency ............................................................. 4

4.2.2 Modulation Mode ............................................................. 4

4.2.3 Polarization Mode ............................................................ 4

4.2.4 Carrier Phase Noise .......................................................... 5

4.2.5 User-Received Signal Power Level ................................... 5

4.2.6 Signal Multiplexing Mode ................................................ 5

4.2.7 Satellite Signal Bandwidth and Out-band Suppression ..... 5

4.2.8 Spurious ........................................................................... 6

4.2.9 Signal Coherence .............................................................. 6

4.2.10 Equipment Group Delay Differential ............................... 6

4.3 Ranging Code ............................................................................. 6

I BDS-SIS-ICD-2.0
2013-12
 2013 China Satellite Navigation Office

5 NAV Message .................................................................................... 9

5.1 General ....................................................................................... 9

5.1.1 NAV Message Classification ............................................ 9

5.1.2 NAV Message Information Type and Broadcasting ........... 9

5.1.3 Data Error Correction Coding Mode ............................... 11

5.2 D1 NAV Message ..................................................................... 15

5.2.1 Secondary Code Modulated on D1 ................................. 15

5.2.2 D1 NAV Message Frame Structure ................................. 16

5.2.3 D1 NAV Message Detailed Structure .............................. 17

5.2.4 D1 NAV Message Content and Algorithm ...................... 23

5.3 D2 NAV Message ..................................................................... 42

5.3.1 D2 NAV Message Frame Structure ................................. 42

5.3.2 D2 NAV Message Detailed structure .............................. 43

5.3.3 D2 NAV Message Content and Algorithm ...................... 67

6 Acronyms......................................................................................... 77

II BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

1 Statement
BeiDou Navigation Satellite System Signal-In-Space Interface Control
Document (hereafter referred to as ICD) is issued by the China Satellite
Navigation Office, which reserves the right for final explanation.

2 Scope
This ICD defines the specification related to open service signal B1I and
B2I between the space segment and the user segment of the BeiDou Navigation
Satellite System. B2I will be gradually replaced by a better signal with the
construction of global system.

3 BeiDou System Overview

3.1 Space Constellation

BeiDou Navigation Satellite System is called BeiDou System for short,
with the abbreviation as BDS. When fully deployed, the space constellation of
BDS consists of five Geostationary Earth Orbit (GEO) satellites, twenty-seven
Medium Earth Orbit (MEO) satellites and three Inclined Geosynchronous
Satellite Orbit (IGSO) satellites. The GEO satellites are operating in orbit at an
altitude of 35,786 kilometers and positioned at 58.75°E, 80°E, 110.5°E, 140°E
and 160°E respectively. The MEO satellites are operating in orbit at an altitude
of 21,528 kilometers and an inclination of 55°to the equatorial plane. The IGSO
satellites are operating in orbit at an altitude of 35,786 kilometers and an
inclination of 55°to the equatorial plane.
By the end of 2012, there are five GEO, four MEO and five IGSO BeiDou
navigation satellites in orbit.

1 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

3.2 Coordinate System

BDS adopts the China Geodetic Coordinate System 2000 (CGCS2000),
and the definition is listed below:
The origin is located at the mass center of the Earth;
The Z-axis is in the direction of the IERS (International Earth Rotation and
Reference System Service) Reference Pole (IRP);
The X-axis is directed to the intersection of IERS Reference Meridian
(IRM) and the plane passing the origin and normal to the Z-axis;
The Y-axis, together with Z-axis and X-axis, constitutes a right handed
orthogonal coordinate system.
The origin of the CGCS2000 is also the geometric center of the CGCS2000
ellipsoid, and the Z-axis is the rotation axis of the CGCS2000 ellipsoid. The
parameters of the CGCS2000 ellipsoid are as follows:
Semi-major axis: a = 6378137.0 m
Geocentric gravitational constant (mass of the earth atmosphere included):

μ = 3.9860044181014 m3/s2

Flattening: f = 1/298.257222101
Rate of earth rotation:  = 7.292115010-5 rad/s
 e

3.3 Time System

The time reference for the BDS uses the BeiDou navigation satellite
system Time (BDT). BDT adopts international system of units (SI) seconds,
rather than leap seconds, as the basic unit for continuous accumulation. The
start epoch of BDT was 00:00:00 on January 1, 2006 of Coordinated Universal
Time (UTC). BDT is counted with week and seconds of week (SOW). BDT is
related to the UTC through UTC(NTSC). BDT offset with respect to UTC is
controlled within 100 nanoseconds (modulo 1 second). The leap seconds are

2 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

broadcast in navigation (NAV) message.

4 Signal Specifications
4.1 Signal Structure

The signals on B1 and B2 are the sum of channel I and Q which are in
phase quadrature of each other. The ranging code and NAV message are
modulated on carrier. The signal is composed of the carrier frequency, ranging
code and NAV message.
The signals on B1 and B2 are expressed as follows:
SBj 1（t） A B1ICB1I
j j
(t) DB1I (t) cos（2 πf1t  B1I
j
)  A B1Q CB1
j
Q (t) D B1Q (t) sin(2 πf1 t  B1Q )
j j

SBj 2（t） A B2ICB2I

j j
(t) DB2I (t) cos（2 πf2 t  B2I
j
)  A B2Q CB2
j
Q (t) D B2 Q (t) sin(2 πf 2 t  B2 Q )
j j

Where,
Superscript j: satellite number;
AB1I: amplitude of B1I;
AB2I: amplitude of B2I;
AB1Q: amplitude of B1Q;
AB2Q: amplitude of B2Q;
CB1I: ranging code of B1I;
CB2I: ranging code of B2I;
CB1Q: ranging code of B1Q;
CB2Q: ranging code of B2Q;
DB1I: data modulated on ranging code of B1I;
DB2I: data modulated on ranging code of B2I;
DB1Q: data modulated on ranging code of B1Q;
DB2Q: data modulated on ranging code of B2Q;
f1: carrier frequency of B1I;

3 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

f2: carrier frequency of B2I;

υB1I: carrier initial phase of B1I;
υB2I: carrier initial phase of B2I;
υB1Q: carrier initial phase of B1Q;
υB2Q: carrier initial phase of B2Q.

4.2 Signal Characteristics

4.2.1 Carrier Frequency

The carrier frequencies of B1I and B2I shall be coherently derived from a
common reference frequency source on board of the satellite. The nominal

frequency of B1I signal is 1561.098 MHz，and the nominal frequency of B2I

signal is 1207.140 MHz.

4.2.2 Modulation Mode

The transmitted signal is modulated by Quadrature Phase Shift Keying

(QPSK).

4.2.3 Polarization Mode

The transmitted signal shall be Right-Handed Circularly Polarized (RHCP).

The signal polarization ellipticity is specified in Table 4-1.

Table 4-1 Signal polarization ellipticity

Satellite type Signal polarization ellipticity

GEO Ellipticity is no worse than 2.9 dB, angular range: 10 from boresight.
MEO Ellipticity is no worse than 2.9 dB, angular range: 15 from boresight.
IGSO Ellipticity is no worse than 2.9 dB, angular range: 10 from boresight.

4 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

4.2.4 Carrier Phase Noise

The phase noise spectral density of the unmodulated carrier is as follows:

-60 dBc/Hz @ f0±10 Hz
-75 dBc/Hz @ f0±100 Hz
-80 dBc/Hz @ f0±1 kHz
-85 dBc/Hz @ f0±10 kHz
-95 dBc/Hz @ f0±100 kHz
Where, f0 is the carrier frequency of B1I or B2I.

4.2.5 User-Received Signal Power Level

The minimum user-received signal power level is specified to be -163dBW

for channel I, which is measured at the output of a 0 dB RHCP receiving
antenna (located near ground), when the satellite’s elevation angle is higher than
5 degree.

4.2.6 Signal Multiplexing Mode

The signal multiplexing mode is Code Division Multiple Access (CDMA).

4.2.7 Satellite Signal Bandwidth and Out-band Suppression

（1）Bandwidth (1dB): 4.092 MHz (centered at carrier frequency of B1I)；

20.46MHz (centered at carrier frequency of B2I).

Bandwidth (3dB): 16MHz (centered at carrier frequency of B1I);
36MHz (centered at carrier frequency of B2I).

（2）Out-band suppression: no less than 15 dB on f0±30 MHz, where f0 is

the carrier frequency of B1I or B2I signal.

5 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

4.2.8 Spurious

In-band spurious shall be at least 50 dB below the unmodulated carrier

over the satellite signal bandwidth (1 dB).

4.2.9 Signal Coherence

（1）The random jitter of the ranging code phase difference (satellite

transmitter time delay included) among 4 channels of I and Q on B1, B2 is less

than 1ns (1σ).

（2）The random jitter of the initial phase differenal between the ranging

code modulated on the carrier and the carrier is less than 3°(1σ) (relative to the
carrier) for B1I,B2I.

（3）Carrier phase quadrature difference between channels I and Q:＜5°

(1σ).

4.2.10 Equipment Group Delay Differential

Equipment group delay is defined as the delay between the antenna phase
center of a satellite and the output of the satellite onboard frequency source. The
reference equipment group delay is included in the clock correction parameter
a0 in NAV message with uncertainty less than 0.5ns(1σ).The equipment group
delay differential of radiated signals on B1 and B2 with respect to that of
reference is given in TGD1 and TGD2 respectively in NAV message with
uncertainty less than 1ns(1σ).

4.3 Ranging Code

The chip rate of the B1I and B2I ranging code is 2.046 Mcps, and the
6 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

length is 2046 chips.

The B1I and B2I ranging code (hereinafter referred to as CB1I and CB2I) is a
balanced Gold code truncated with the last one chip. The Gold code is generated
by means of Modulo-2 addition of G1 and G2 sequences which are respectively
derived from two 11-bit linear shift registers.
The generator polynomials for G1 and G2 are as follows:
G1(X)=1+X+X7+X8+X9+X10+X11
G2(X)=1+X+X2+X3+X4+X5+X8+X9+X11
The initial phases of G1 and G2 are:
G1: 01010101010
G2: 01010101010
The generator of CB1I and CB2I is shown in Figure 4-1.

G1 sequence
1 2 3 4 5 6 7 8 9 10 11

Reset control clock Phase selection logic

Set to initial phases G2 sequence Ranging code
Shift control clock

1 2 3 4 5 6 7 8 9 10 11

Figure 4-1 The generator of CB1I and CB2I

The different phase shift of G2 sequence is accomplished by respective

tapping in the shift register generating G2 sequence. By means of Modulo-2
addition of G2 with different phase shift and G1, a ranging code is generated for
each satellite. The phase assignment of G2 sequence is shown in Table 4-2.

7 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Table 4-2 Phase assignment of G2 sequence

Ranging code Phase assignment of

No. Satellite type
number G2 sequence
1 GEO satellite 1 1⊕3
2 GEO satellite 2 1⊕4
3 GEO satellite 3 1⊕5
4 GEO satellite 4 1⊕6
5 GEO satellite 5 1⊕8
6 MEO/IGSO satellite 6 1⊕9
7 MEO/IGSO satellite 7 1⊕10
8 MEO/IGSO satellite 8 1⊕11
9 MEO/IGSO satellite 9 2⊕7
10 MEO/IGSO satellite 10 3⊕4
11 MEO/IGSO satellite 11 3⊕5
12 MEO/IGSO satellite 12 3⊕6
13 MEO/IGSO satellite 13 3⊕8
14 MEO/IGSO satellite 14 3⊕9
15 MEO/IGSO satellite 15 3⊕10
16 MEO/IGSO satellite 16 3⊕11
17 MEO/IGSO satellite 17 4⊕5
18 MEO/IGSO satellite 18 4⊕6
19 MEO/IGSO satellite 19 4⊕8
20 MEO/IGSO satellite 20 4⊕9
21 MEO/IGSO satellite 21 4⊕10
22 MEO/IGSO satellite 22 4⊕11
23 MEO/IGSO satellite 23 5⊕6
24 MEO/IGSO satellite 24 5⊕8
25 MEO/IGSO satellite 25 5⊕9
26 MEO/IGSO satellite 26 5⊕10
27 MEO/IGSO satellite 27 5⊕11
28 MEO/IGSO satellite 28 6⊕8
29 MEO/IGSO satellite 29 6⊕9
30 MEO/IGSO satellite 30 6⊕10
31 MEO/IGSO satellite 31 6⊕11
8 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Ranging code Phase assignment of

No. Satellite type
number G2 sequence
Phase assignment of G2
No. Satellite type Ranging code number
sequence
32 MEO/IGSO satellite 32 8⊕9
33 MEO/IGSO satellite 33 8⊕10
34 MEO/IGSO satellite 34 8⊕11
35 MEO/IGSO satellite 35 9⊕10
36 MEO/IGSO satellite 36 9⊕11
37 MEO/IGSO satellite 37 10⊕11

5 NAV Message
5.1 General

5.1.1 NAV Message Classification

NAV messages are formatted in D1 and D2 based on their rate and

structure. The rate of D1 NAV message which is modulated with 1 kbps
secondary code is 50 bps. D1 NAV message contains basic NAV information
(fundamental NAV information of the broadcasting satellites, almanac
information for all satellites as well as the time offsets from other systems);
while D2 NAV message contains basic NAV and augmentation service
information (the BDS integrity, differential and ionospheric grid information)
and its rate is 500 bps.
The NAV message broadcast by MEO/IGSO and GEO satellites is D1 and
D2 respectively.

5.1.2 NAV Message Information Type and Broadcasting

The NAV message information type and broadcasting are shown in Table
5-1. The detailed structure, bits allocations, contents and algorithms will be
described in later chapters.
9 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Table 5-1
NAV message information contents and their broadcasting
No. of
Message information content Broadcasting
Bits
Preamble (Pre) 11
Subframe ID (FraID) 3 Occurring every subframe
Seconds of week (SOW) 20
Week number (WN) 13
Fundamental NAV information of the broadcasting satellite

User range accuracy index

4
(URAI)
Autonomous satellite health
1
flag (SatH1)
Equipment group delay D1: broadcast in subframes 1, 2 and 3,
20
differential (TGD1,TGD2) repeated every 30 seconds.
Age of data, clock (AODC) 5

Basic NAV information, broadcast in every satellite

Clock correction parameters D2: broadcast in the first five words
74 of pages 1~10 of subframe 1, repeated
(toc, a0, a1, a2)
every 30 seconds.
Age of data, ephemeris
5
(AODE)
Ephemeris parameters Updating rate: every 1 hour.
(toe, A , e, ω, Δn, M0, Ω0,  ,
371
i0, IDOT, Cuc, Cus, Crc, Crs, Cic,
Cis)
Ionosphere model parameters
64
(αn, βn, n=0~3)
D1: broadcast in subframe 4 and
Page number (Pnum) 7 subframe 5.
D2: broadcast in subframe 5.
D1: broadcasting in pages 1~24 of
subframe 4 and pages 1~6 of
subframe 5, repeated every 12
Alamanac parameters
minutes.
 , δi,
(toa, A , e, ω, M0, Ω0,  176
D2: broadcast in pages 37~60,
a0, a1)
Almanac

95~100 of subframe 5, repeated every

6 minutes.
Updating period: less than 7 days.
Week number of alamanac D1: broadcast in pages 7~8 of
8 subframe 5, repeated every 12
(WNa)
minutes.
Health information for 30 D2: broadcast in pages 35~36 of
9×30 subframe 5, repeated every 6 minutes.
satellites（Heai, i=1~30）
Updating period: less than 7 days.

10 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

No. of
Message information content Broadcasting
Bits
Time parameters relative to
Time offsets from other

UTC (A0UTC, A1UTC, ΔtLS, 88 D1: broadcast in pages 9~10 of

ΔtLSF,WNLSF, DN) subframe 5, repeating every 12
Time parameters relative to
systems

30 minutes.
GPS time (A0GPS, A1GPS）
D2: broadcast in pages 101~102 of
Time parameters relative to
30 subframe 5, repeated every 6 minutes.
Galileo time (A0Gal, A1Gal)
Time parameters relative to Updating period: less than 7 days.
30
GLONASS time(A0GLO, A1GLO)
Page number for basic NAV D2: broadcast in pages 1~10 of

Integrity and differential correction information and ionospheric grid information are
information (Pnum1) 4 subframe 1.
Page number for integrity and
D2: broadcast in pages 1~6 of
differential correction information 4
subframe 2.
(Pnum2)
Satellite health flag for integrity and D2: broadcast in pages 1~6 of
differential correction information 2 subframe 2.
(SatH2) Updating rate: every 3 seconds.
BDS Satellite identification for D2: broadcast in pages 1~6 of

broadcast by GEO satellites only.

integrity and differential correction 1×30 subframe 2.
information (BDIDi, i=1~30) Updating rate: every 3 seconds.
correction information of BDS

User differential range error D2: broadcast in subframe 2.

4×18
Integrity and differential

index (UDREIi, i=1~18) Updating rate: every 3 seconds.

Regional user range accuracy

4×18
index (RURAIi, i=1~18) D2: broadcast in subframe 2 and
subframe 3.
Equivalent clock correction Updating rate: every 18 seconds.
13×18
(Δti, i=1~18)
Ionospherc grid

Vertical ionospheric delay at

informatioin

9×320
grid point (dτ) D2: broadcast in pages 1~13, 61~73
of subframe 5.
Grid ionospheric vertical delay
4×320 Updating rate: every 6 minutes.
error indiex (GIVEI)

5.1.3 Data Error Correction Coding Mode

The NAV message encoding involves both error control of BCH(15,11,1)

and interleaving. The BCH code is 15 bits long with 11 information bits and
11 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

error correction capability of 1 bit. The generator polynomial is g(X)=X4+X+1.

The NAV message bits are grouped every 11 bits in sequence first. The
serial/parallel conversion is made and the BCH(15,11,1) error correction
encoding is performed in parallel. Parallel/serial conversion is then carried out
for every two parallel blocks of BCH codes by turns of 1 bit to form an
interleaved code of 30 bits length. The implementation is shown in Figure 5-1.

BCH(15,11,1) encoding
Serial/
parallel Parallel/
Input converting serial Output
converting
for each by turns
block of of 1 bit
11 bits BCH(15,11,1) encoding

Fig 5-1 Error correction encoding and interleaving of down-link NAV message

The implementation of BCH (15,11,1) encoder is shown in Figure 5-2.

Initially the four stages of the shift register are all reset to zero, Gate1 is on and
Gate2 is off. The 11 bits of information block X are sent into a dividing circuit
g(X). Meantime the information bits are sent out of the encoder through gate
―or‖ as the output. The dividing operation finishes when all the 11 bits have
been sent in and then the states of the four register stages represent the parity
check bits. Now switch Gate 1 off and Gate 2 on. The four parity check bits are
shifted out of the encoder through gate ―or‖ to form a 15 bits code in
combination with the output 11 bits of information block. Then switch Gate1 on
and Gate2 off and send in the next information block and the procedure above is
repeated again.

12 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Gate1

D0 D1 D2 D3 Gate2 Output
OR

Input information block X

Fig 5-2 BCH(15, 11, 1) encoder

For the received NAV message by receivers near ground a serial/parallel

conversion by turns of 1 bit is required first, followed by an error correction
decoding of BCH(15,11,1) in parallel. Then a parallel/serial conversion is
carried out for each 11 bits block to form a 22 bits information code in sequence.
The processing is shown in Figure 5-3.

BCH(15,11,1) decoding
Serial/ parallel/
Input parallel Serial Output
converting transforming
by turns for each 11
of 1 bit bits
BCH(15,11,1) decoding

Fig 5-3 Processing of received down-link NAV message

The decoding logic of BCH(15,11,1) is shown in Figure 5-4. The initial

states of the four register stages are all zeros. BCH codes are sent in bit by bit
into a division circuit and a fifteen stages buffer simultaneously. When all
fifteen bits of a BCH code are inputted, the ROM list circuit forms a fifteen-bit
table based on the states D3, D2, D1 and D0 of the four register stages. Then the
15 bits in the table and 15 bits in the buffer are Modulo-2 added and an error
corrected information code obtained is output. The ROM table list is shown in
Table 5-2.

13 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

BCH code input

Gate1

D0 D1 D2 D3

ROM list circuit

15 stage buffer

Decoder output

Fig 5-4 BCH(15,11,1) decoding logic

Table 5-2 ROM table list for error correction

D3D2D1D0 15 bits data for error correction
0000 000000000000000
0001 000000000000001
0010 000000000000010
0011 000000000010000
0100 000000000000100
0101 000000100000000
0110 000000000100000
0111 000010000000000
1000 000000000001000
1001 100000000000000
1010 000001000000000
1011 000000010000000
1100 000000001000000
1101 010000000000000
1110 000100000000000
1111 001000000000000

The interleaving pattern of 30 bits code is as follows:

X11 X12 X12 X22 … X11

1 X112 P11 P21 P12 P22 P13 P23 P14 P24

14 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

where Xij is the information bit, subscript i stands for the bit in BCH code
of block i and i=1 or 2; superscript j stands for the information bit j in block i
and j=1 to 11; Pim is the check parity bit, subscript i stands for the bit in BCH
code of block i and i=1 or 2; superscript m stands for the parity bit m in BCH
code of block i and m=1 to 4.

5.2 D1 NAV Message

5.2.1 Secondary Code Modulated on D1

For D1 NAV message in format D1 of rate 50 bps a secondary code of

Neumann-Hoffman (NH) code is modulated on ranging code. The period of NH
code is selected as long as the duration of a NAV message bit. The bit duration
of NH code is the same as one period of the ranging code. Shown as in Figure
5-5, the duration of one NAV message bit is 20 milliseconds and the ranging
code period is 1 millisecond. Thus the NH code (0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 1, 0,
1, 0, 0, 1, 1, 1, 0) with length of 20 bits, rate 1 kbps and bit duration of 1
millisecond is adopted. It is modulated on the ranging code synchronously with
NAV message bit.
NH code NAV message

Ranging
code

NAV 0 1 0 0 1
message
20 ms

Period (1 bit duration of NAV message)

NH 0 0 0 0 0 1 0 0 1 1 0 1 0 1 0 0 1 1 1 0
code 1ms

Ranging
Ranging code period (1 bit duration of NH code）
code
Fig 5-5 Secondary code and its timing
15 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

5.2.2 D1 NAV Message Frame Structure

The NAV message in format D1 is structured in the superframe, frame and

subframe. Every superframe has 36000 bits and lasts 12 minutes. Every
superframe is composed of 24 frames (24 pages). Every frame has 1500 bits and
lasts 30 seconds. Every frame is composed of 5 subframes. Every subframe has
300 bits and lasts 6 seconds. Every subframe is composed of 10 words. Every
word has 30 bits and lasts 0.6 second.
Every word consists of NAV message data and parity bits. In the first word
of every subframe, the first 15 bits is not encoded and the following 11 bits are
encoded in BCH(15,11,1) for error correction. So there is only one group of
BCH code contained and there are altogether 26 information bits in the word.
For all the other 9 words in the subframe both BCH(15,11,1) encoding for error
control and interleaving are involved. Each of the 9 words of 30 bits contains
two blocks of BCH codes and there are altogether 22 information bits in it.
(reference paragraph 5.1.3)
The frame structure in format D1 is shown in Figure 5-6.
Superframe 36000 bits, 12 min

Frame 1 Frame 2 …… Frame n …… Frame 24

Frame 1500 bits, 30 sec

Subframe 1 Subframe 2 Subframe 3 Subframe 4 Subframe 5

Subframe 300 bits, 6 sec

Word 1 Word 2 …… Word 10

Word 1, 30 bits, 0.6 sec Word 2~10, 30 bits, 0.6 sec

26 information bits 4 parity bits 22 information bits 8 parity bits

Fig 5-6 Frame structure of NAV message in format D1

16 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

5.2.3 D1 NAV Message Detailed Structure

The main information contents of NAV message in format D1 are basic

NAV information, including fundamental NAV information of the broadcasting
satellites (seconds of week, week number, user range accuracy index,
autonomous satellite health flag, ionospheric delay model parameters, satellite
ephemeris parameters and their age, satellite clock correction parameters and
their age and equipment group delay differential), almanac and BDT offsets
from other systems (UTC and other navigation satellite systems). It takes 12
minutes to transmit the whole NAV message.
The D1 frame structure and information contents are shown in Figure 5-7.
The fundamental NAV information of the broadcasting satellite is in subframes
1, 2 and 3. The information contents in subframes 4 and 5 are subcommutated
24 times each via 24 pages. Pages 1~24 of subframe 4 and pages 1~10 of
subframe 5 shall be used to broadcast almanac and time offsets from other
systems. Pages 11~24 of subframe 5 are reserved.

Subframe 1 Subframe 2 Subframe 3 … …

… Subframe 4 Subframe 5

Fundamental NAV information

of the broadcasting satellite
Almanac and
time offsets from other systems

Fig 5-7 Frame structure and information contents of NAV message in format D1

The bits allocations of format D1 are shown in Figure 5-8~5-11.

17 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 1 （300 bits） bits allocation
Word 1
Subframe Page
1 12 16 19 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW SatH1 AODC URAI WN toc toc TGD1 TGD2 TGD2 α0 α1 α2 α3 β0 β0 β1 β2 β3 β3 a2 a0 a0 a1 a1 AODE
1 N/A P 12bits 1bit 5bits 4bits P 13bits P P P P P P P P
11bits 4bits 3bits 8bits 9bits 8bits 10bits 4bits 6bits 8bits 8bits 8bits 8bits 6bits 2bits 8bits 8bits 4bits 4bits 11bits 7bits 17bits 5bits 17bits 5bits
8MSBs 12LSBs 9MSBs 8LSBs 4MSBs 6LSBs 6MSBs 2LSBs 4MSBs 4LSBs 7MSBs 17LSBs 5MSBs 17LSBs

Fig 5-8 Bits allocation of subframe 1 in format D1

Direction of data flow MSB first

MSB LSB
Subframe 2 （300 bits） bits allocation
Word 1
Subframe Page
No. No. 1 12 16 19 27 31 61 91 121 151 181 211 241 271
Pre Rev FraID SOW SOW Δn Δn Cuc Cuc M0 M0 e e Cus Crc Crc Crs Crs A A toe
2 N/A 11bits 4bit 3bits 8bits P 12bits 10bits P 6bits 16bits P 2bits 20bits P 12bits 10bits P 22bits P 18bits 4bits P 14bits 8bits P 10bits 12bits P 20bits 2bits P

8MSBs 12LSBs 10MSBs 6LSBs 16MSBs 2LSBs 20MSBs 12LSBs 10MSBs 22LSBs 4MSBs 14LSBs 8MSBs 10LSBs 12MSBs 20LSBs 2MSBs

Fig 5-9 Bits allocation of subframe 2 in format D1

18 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 3 （300 bits） bits allocation
Word 1
Subframe Page
No. No. 1 12 16 19 27 31 61 91 121 151 181 211 241 271
i0 P i0 Cic P Cic    Cis IDOT P IDOT Ω0 P Ω0 ω P ω Rev P
P 
Pre Rev FraID SOW SOW toe toe Cis
3 N/A 11bits 4bits 3bits 8bits P 12bits P P
10bits 5bits 17bits 15bits 7bits 11bits 11bits 13bits 9bit 9bits 13bits 1bit 21bits 11bits 11bits 21bits 1bit
8MSBs 12LSBs * 5LSBs 17MSBs 15LSBs 7MSBs 11LSBs 11MSBs 13LSBs 9MSBs 9LSBs 13MSBs 1LSB 21MSBs 11LSBs 11MSBs 21LSBs

* These are data bits next to MSBs and before LSBs.

Fig 5-10 Bits allocation of subframe 3 in format D1

Direction of data flow MSB first

MSB LSB
Subframe 4、5（300 bits）bits allocation

Word 1
Subframe Page
No. No. 1 27 31 53 61 91 121 151 181 211 241 271

4 1~24 Pre Rev FraID SOW

P
SOW Rev Pnum A P A P a 1 a0 P  0 P  0
e  i P
i toa 
 P

 ω P ω
M0 P M0 Rev P
5 1~6 11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 22bits 11bits 11bits 22bits 2bits 17bits 3bits 13bits 8bits 1bit 16bits 6bits 18bits 4bits 20bits 2bits
8MSBs 12LSBs 2MSBs 22LSBs 22MSBs 2LSBs 3MSBs 13LSBs 1MSB 16LSBs 6MSBs 18LSBs 4MSBs 20LSBs

Fig 5-11-1 Bits allocation of pages 1 through 24 in subframe 4 and pages 1 through 6 in subframe 5 of format D1

19 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 53 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Hea1 Hea1 Hea2 Hea3 Hea3 Hea4 Hea15 Hea16 Hea17 Hea18 Hea18 Hea19 Rev
5 7 P P P … P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 7bits 9bits 6bits 3bits 9bits 1bit 9bits 9bits 3bits 6bits 9bits 7bits
8MSBs 12LSBs 2MSBs 7LSBs 6MSBs 3LSBs 1LSB 3MSBs 6LSBs

Fig 5-11-2 Bits allocation of page 7 in subframe 5 of format D1

Direction of data flow MSB first

MSB LSB
Subframe 5（300 bits）bits allocation
Word 1
Subframe Page
1 27 31 53 61 91 121 151 181 211
No. No.
Pre Rev FraID SOW SOW Rev Pnum Hea20 Hea20 Hea21 Hea27 Hea28 Hea29 Hea30 WNa toa toa Rev P 24bits
5 8 11bits 4bits 3bits 8bits P 12bits 1bit 7bits 2bits P 7bits 9bits … P … P … P P P
Parity of 3 words
4bits 9bits 9bits 9bits 8bits 5bits 3bits 63bits
8MSBs 12LSBs 2MSBs 7LSBs 4LSBs 5MSBs 3LSBs

Fig 5-11-3 Bits allocation of page 8 in subframe 5 of format D1

20 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5（300 bits） bits allocation
Word 1
Subframe Page 1 27 31 61 91 121 151 181 211
No. No.
Pre Rev FraID SOW SOW Rev Pnum Rev Rev Rev A0GPS A1GPS A1GPS A0Gal A0Gal A1Gal A0GLO A1GLO A1GLO Rev P 24bits
5 9 11bits 4bits 3bits 8bits P 12bits 1bit 7bits 2bits P 22bits P 6bits 14bits 2bits P 14bits 8bits P 6bits 16bits P 14bits 8bits P 8bits 58bits Parity of 3 words
8MSBs 12LSBs 2MSBs 14LSBs 8MSBs 6LSBs 8MSBs 8LSBs

Fig 5-11-4 Bits allocation of page 9 in subframe 5 of format D1

Direction of data flow MSB first

MSB LSB
Subframe 5（300bits） bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151
No. No.
Pre Rev FraID SOW SOW Rev Pnum ΔtLS ΔtLS ΔtLSF WNLSF A0UTC P A0UTC A1UTC P A1UTC DN Rev P 40bits
5 10 P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 6bits 8bits 8bits 22bits 10bits 12bits 12bits 8bits 90bits Parity of 5 words
8MSBs 12LSBs 2MSBs 6LSBs 22MSBs 10LSBs 12MSBs 12LSBs

Fig 5-11-5 Bits allocation of page 10 in subframe 5 of format D1

21 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction data of flow MSB first

MSB LSB
Subframe 5（300 bits）bits allocation
Word 1
Subframe Page 1 27 31
No. No.
Pre Rev FraID SOW SOW Rev Pnum Rev P 72bits
5 11~24 11bits 4bits 3bits 8bits P 12bits 1bit 7bits 178 bits Parity of 9 words
8MSBs 12LSBs

Fig 5-11-6 Bits allocation of reserved pages 11~24 in format D1 subframe

22 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

5.2.4 D1 NAV Message Content and Algorithm

5.2.4.1 Preamble (Pre)

The bits 1~11 of every subframe are preamble (Pre) of

―11100010010‖ from modified Barker code of 11 bits. SOW count occurs
at the leading edge of the preamble first bit which is for time scale
synchronization.

5.2.4.2 Subframe identification (FraID)

The bits 16, 17 and 18 of every subframe are for subframe

identification (FraID). The detailed definitions are as follows:

Table 5-3 FraID definitions

Code 001 010 011 100 101 110 111

Identification of
1 2 3 4 5 Rev Rev
subframe

5.2.4.3 Seconds of Week (SOW)

The bits 19~26 and bits 31~42, altogether 20 bits of the each
subframe are for seconds of week (SOW) which is defined as the number
of seconds that have occurred since the last Sunday, 00:00:00 of BDT.
The SOW count occurs at the leading edge of preamble first bit of the
subframe.

5.2.4.4 Week Number (WN)

There are altogether 13 bits for week number (WN) which is the
integral week count of BDT with the range of 0 through 8191. Week
number count started from zero at 00:00:00 on Jan. 1, 2006 of BDT.

23 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

5.2.4.5 User Range Accuracy Index (URAI)

The user range accuracy (URA) is used to describe the

signal-in-space accuracy in meters. There are 4 bits for the user range
accuracy index (URAI). The range of URAI is from 0 to 15. See Table
5-4 for the corresponding relationship between URAI and URA.

Table 5-4 Corresponding relationship between URAI and URA

Code URAI (N) URA range (meters, 1σ)

0000 0 0.00 < URA ≤ 2.40
0001 1 2.40 < URA ≤ 3.40
0010 2 3.40 < URA ≤ 4.85
0011 3 4.85 < URA ≤ 6.85
0100 4 6.85 < URA ≤ 9.65
0101 5 9.65 < URA ≤ 13.65
0110 6 13.65 < URA ≤ 24.00
0111 7 24.00 < URA ≤ 48.00
1000 8 48.00 < URA ≤ 96.00
1001 9 96.00 < URA ≤ 192.00
1010 10 192.00 < URA ≤ 384.00
1011 11 384.00 < URA ≤ 768.00
1100 12 768.00 < URA ≤ 1536.00
1101 13 1536.00 < URA ≤ 3072.00
1110 14 3072.00 < URA ≤ 6144.00
1111 15 URA > 6144.00

When an URAI is received by the user, the corresponding URA (X)

is computed by the following equations:
If 0 ≤ N < 6, X = 2N/2+1;
If 6 ≤ N < 15, X = 2N-2;
If N=15, it means the satellite is in maneuver or there is no accuracy

24 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

prediction;
If N=1, 3 and 5, X should be rounded to 2.8, 5.7, and 11.3 meters,
respectively.

5.2.4.6 Autonomous Satellite Health flag (SatH1)

The autonomous satellite health flag (SatH1) occupies 1 bit. ―0‖

means broadcasting satellite is good and ―1‖ means not.

5.2.4.7 Ionospheric Delay Model Parameters (αn, βn)

There are 8 parameters, altogether 64 bits for ionospheric delay

model. All the 8 parameters are in two’s complement. See Table 5-5 for
details.
Table 5-5 Ionospheric delay model parameters

Parameter No. of bits Scale factor (LSB) Units

α0 8* 2-30 s
α1 8* 2-27 s/π
α2 8* 2-24 s/π2
α3 8* 2-24 s/π3
β0 8* 211 s
β1 8* 214 s/π
β2 8* 216 s/π2
β3 8* 216 s/π3
* Parameters so indicated are two’s complement, with the sign bit (+ or –)
occupying the MSB.

The user computers the vertical ionospheric delay correction I 'z (t)

with the 8 parameters and Klobuchar model as follows:

 9 2 π(t  50400 )
5  10  A 2 cos [ ],|t  50400 |  A 4 / 4
I (t)  
'
z
A4
5  10 9 ,|t  50400 |  A 4 / 4

25 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Where I 'z (t) is the vertical ionospheric delay in seconds for B1I, t
is the local time (range 0~86400 sec) for the place under the intersection
point (M) of ionosphere and the direction from receiver to satellite.
A2 is the amplitude of Klobuchar cosine curve in the day time
computed from the αn.
3
 α n  M , A2  0
n

A 2  n 0
0 A2  0
 ,

A4 is the period of cosine curve in seconds. It is computed from the

βn..
172800 , A 4  172800
 3
A 4   n M ,

n
172800  A 4  72000
 n 0
72000 , A 4  72000


Where, M is the geographic latitude of earth projection of the

ionosphere intersection point in semi-circles (π). The geographic latitude
M and longitude λ M of the intersection point M are computed as:
 M  arcsin sin  u  cosψ  cos u  sinψ  cosA 

 sinψ  sinA 
λ M  λ u  arcsin 
 cos M 
Where,  u is the user’s geographic latitude in radians. A is the
satellte azimuth from the user location in radians. ψ is the earth’s central
angle in radians between the user location and ionospheric intersection
point. It is computed as:
π  R 
ψ  E  arcsin  cos E 
2  R  h 
Where,R is the mean radius of the earth (6378 km). E is the satellite
elevation from the user’s location in radians. h is the height of ionosphere
(375 km).
I 'z (t ) can be converted to the ionospheric delay along the B1I

26 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

propagation path IB1I(t) through the equation as follows and the unit is
seconds.
1
I B1I (t)   Iz (t)
2
 R 
1-  cos E 
Rh 

For B2I, users need to multiply a factor k(f) to calculate the

ionospheric delay along the B2I propagation path, and its value is as
follows:
2
f12  1561.098 
k(f)   
f 22  1207.140 

Where, f1 refers to the nominal carrier frequency of B1I, f2 refers to

the nominal carrier frequency of B2I, and the unit is MHz.

The dual-frequency (B1I and B2I) user shall correct for the group

delay due to ionospheric effects by applying the expression:

PR B2I -k(f)  PR B1I C  (TGD2 -k(f)  TGD1 )

PR  
1-k(f) 1  k(f)

where，

PR: pseudorange corrected for ionospheric effects；

PRB1I: pseudorange measured on B1I(corrected by the satellite clock

correction parameters and TGD1)；

PRB2I: pseudorange measured on B2I(corrected by the satellite clock

correction parameters and TGD2)；

TGD1: equipment group delay differential on B1I；

TGD2: equipment group delay differential on B2I；

C: the light speed, and its value is 2.99792458×108 m/s.

27 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Note: When user adopts the ionospheric delay model in the south
hemisphere, the ionospheric correction accuracy is slightly worse than
that in the north.

5.2.4.8 Equipment Group Delay Differential (TGD1 ,TGD2)

The equipment group delay differential (TGD1,TGD2) in the satellite is

10 bits long respectively. It is in two’s complement with sign bit (+ or –)
occupying MSB. Sign bit ―0‖ means positive and ―1‖ means negative.
The scale factor is 0.1 and the unit is nanoseconds，and the detailed
algorithm is defined in paragraph 5.2.4.10.

5.2.4.9 Age of Data, Clock (AODC)

Age of data, clock (AODC) is updated at the start of each hour in

BDT, and it is 5 bits long with definitions as follows:
Table 5-6 AODC definitions

AODC Definition
< 25 Age of the satellite clock correction parameters in hours
25 Age of the satellite clock correction parameters is two days
26 Age of the satellite clock correction parameters is three days
27 Age of the satellite clock correction parameters is four days
28 Age of the satellite clock correction parameters is five days
29 Age of the satellite clock correction parameters is six days
30 Age of the satellite clock correction parameters is seven days
31 Age of the satellite clock correction parameters is over seven days

5.2.4.10 Clock Correction Parameters (toc, a0, a1, a2)

Clock correction parameters are toc, a0, a1 and a2 in 74 bits altogether.

toc is the reference time of clock parameters in seconds with the effective

range of 0~604792. Other 3 parameters are two’s complement.

28 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

The definitions of clock correction parameters are listed in Table

5-7.
Table 5-7 Clock correction parameters

Parameter No. of bits Scale factor (LSB) Effective range Units

toc 17 23 604792 s
a0 24* 2-33 — s
a1 22* 2-50 — s/s
a2 11* 2-66 — s/s2
* Parameters so indicated are two’s complement, with the sign bit (+ or –)
occupying the MSB.

The system time computation is as follows:

The user is able to compute BDT at time of signal transmission as:
t = tsv – Δtsv
where, t is BDT in seconds at time of signal transmission;

tsv is the effective satellite ranging code phase time in seconds at

time of signal transmission;

Δtsv is the offset of satellite ranging code phase time in seconds and
is given by the equation:
Δtsv = a0 + a1(t – toc) + a2(t – toc)2 + Δtr
Where, t can be replaced by tsv regardless of its sensitivity.
Δtr is the correction term to relativistic effect with value of
t r  F  e  A  sin E k

e is the orbit eccentricity, which is given in ephemeris of the

broadcasting satellite;
A is the square root of semi-major axis of satellite orbit, which is

given in ephemeris of the broadcasting satellite;

Ek is eccentric anomaly of satellite orbit, which is given in
ephemeris of the broadcasting satellite;

29 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

F = -2μ1/2/C2;
μ = 3.986004418×1014 m3/s2, is the value of earth’s universal
gravitational constant;
C = 2.99792458×108 m/s, is the light speed.
The B1I user should make a further correction as follows:
(Δtsv)B1I = Δtsv－TGD1
The B2I user should make a further correction as follows:
(Δtsv)B2I = Δtsv－TGD2

5.2.4.11 Age of Data, Ephemeris (AODE)

Age of data, ephemeris (AODE) is updated at the start of each hour

in BDT, and it is 5 bits long with definitions as follows:

Table 5-8 AODE definitions
AODE Definition

< 25 Age of the satellite ephemeris parameters in hours

25 Age of the satellite ephemeris parameters is two days
26 Age of the satellite ephemeris parameters is three days
27 Age of the satellite ephemeris parameters is four days
28 Age of the satellite ephemeris parameters is five days
29 Age of the satellite ephemeris parameters is six days
30 Age of the satellite ephemeris parameters is seven days
31 Age of the satellite ephemeris parameters is over seven days

5.2.4.12 Ephemeris Parameters (toe,  , i0,

A , e, ω, Δn, M0, Ω0, 

IDOT, Cuc, Cus, Crc, Crs, Cic, Cis)

The ephemeris parameters describe the satellite orbit during the

curve fit interval, including 15 orbit parameters and an ephemeris

30 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

reference time. The update rate of ephemeris parameters is one hour.

The definitions of ephemeris parameters are listed in Table 5-9.
Table 5-9 Ephemeris Parameters definitions

Parameter Definition

toe Ephemeris reference time

A Square root of semi-major axis

e Eccentricity

ω Argument of perigee

Δn Mean motion difference from computed value

M0 Mean anomaly at reference time

Longitude of ascending node of orbital of plane computed according to

Ω0
reference time


 Rate of right ascension

i0 Inclination angle at reference time

IDOT Rate of inclination angle

Cuc Amplitude of cosine harmonic correction term to the argument of latitude

Cus Amplitude of sine harmonic correction term to the argument of latitude

Crc Amplitude of cosine harmonic correction term to the orbit radius

Crs Amplitude of sine harmonic correction term to the orbit radius

Cic Amplitude of cosine harmonic correction term to the angle of inclination

Cis Amplitude of sine harmonic correction term to the angle of inclination

Characteristics of ephemeris parameters are shown in Table 5-10.

31 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Table 5-10 Ephemeris parameters characteristics

Parameter No. of Bits Scale factor (LSB) Effective Range Units

toe 17 23 604792 s

A 32 2-19 8192 m1/2

e 32 2-33 0.5 —

ω 32* 2-31 1 π

Δn 16* 2-43 3.7310-9 π/s

M0 32* 2-31 1 π

Ω0 32* 2-31 1 π

 24* 2-43 9.5410-7 π/s

i0 32* 2-31 1 π

IDOT 14* 2-43 9.3110-10 π/s

Cuc 18* 2-31 6.1010-5 rad

Cus 18* 2-31 6.1010-5 rad

Crc 18* 2-6 2048 m

Crs 18* 2-6 2048 m

Cic 18* 2-31 6.1010-5 rad

Cis 18* 2-31 6.1010-5 rad

* Parameters so indicated are two’s complement, with the sign bit (+ or –)
occupying the MSB.

The user receiver shall compute the satellite antenna phase center
position in coordinate system CGCS2000 according to the received
ephemeris parameters. The algorithms are listed in Table 5-11.

32 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Table 5-11 Ephemeris algorithm for user

Computation Description
Value of the earth’s universal gravitational
μ = 3.986004418×1014 m3/s2
constant of CGCS2000
  7.2921150 10 5 rad/s Value of the earth’s rotation rate of
 e
CGCS2000
Ratio of a circle’s circumference to its
π = 3.1415926535898
diameter

A  A 2
Computed semi-major axis


n0  Computed mean motion (radians/sec)
A3
Computed time from ephemeris reference
t k  t  t oe *
epoch
n  n 0  n Corrected mean motion

M k  M 0  nt k Computed mean anomaly

Kepler’s Equation for Eccentric anomaly

M k  E k  e sin E k
solved by iteration (radians)
 1  e 2 sin E k
sin v k 
 1  e cos E k
 Computed true anomaly
cos v  cos E k  e
 k
1  e cos E k

k  v k   Computed argument of latitude

u k  C us sin 2 k   C uc cos2 k  Argument of latitude correction


rk  C rs sin 2 k   C rc cos2 k  Radius correction
i  C sin 2   C cos2 
 k is k ic k Inclination correction

u k   k  u k Corrected Argument of latitude parameters

rk  A1  e cos E k   rk Corrected radius

i k  i 0  IDOT  t k   i k Corrected inclination

x k  rk cos u k
 Computed satellite positions in orbital plane
 y k  rk sin u k

33 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Computation Description

 k  0   
 
 t 
e k
 t 
e oe
Corrected longitude of ascending node in
CGCS2000;
X k  x k cos  k  y k cos i k sin  k MEO/IGSO satellite coordinates in

Yk  x k sin  k  y k cos i k cos  k CGCS2000
Z  y sin i
 k k k

 t 
 k  0    t Corrected longitude of ascending node in
k e oe
inertial coordinate system;
X GK  x k cos  k  y k cos i k sin  k
 GEO satellite coordinates in user-defined
YGK  x k sin  k  y k cos i k cos  k
Z  y sin i inertial system;
 GK k k

X k  X GK 
 Y   R ( t )R (5  )  Y  GEO satellite coordinates in CGCS2000
 k Z e k X  GK 
 Z k   Z GK 

Where,
1 0 0 
 
R X ()   0  cos   sin  
 0  sin   cos  
 

  cos   sin  0 
 
R Z ()    sin   cos  0 
 1 
 0 0
* In the equations, ―t‖ is the time of signal transmission in BDT. ―tk‖ is the total
time difference between t and ephemeris reference time t oe after taking account of
beginning or end of a week crossovers. That is, subtract 604800 seconds from t k if tk
is greater than 302400, add 604800 seconds to tk if tk is less than -302400 seconds.

5.2.4.13 Page number (Pnum)

The bits 44 through 50, 7 bits altogether of subframe 4 and subframe
5 are for page numbers (Pnum). subframe 4 and subframe 5 are
subcommutated 24 times via pages 1 through 24. Pnum identifies the
page number of the subframe.
The almanac information of SV ID 1 through 24 is arranged in pages
1 through 24 of subframe 4. The almanac information of SV ID 25
through 30 is arranged in pages 1 through 6 of subframe 5. The page
number corresponds to the SV ID one by one.
34 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

5.2.4.14 Almanac Parameters （toa, A , e, ω, M0, Ω0,  , δi, a0, a1）

Almanac parameters are updated within every 7 days.
Definitions, characteristics and user algorithms of almanac
parameters are listed in Tables 5-12, 5-13 and 5-14 respectively.
Table 5-12 Almanac parameters definitions
Parameter Definition
toa Almanac reference time
A Square root of semi-major axis
e Eccentricity
ω Argument of Perigee
M0 Mean anomaly at reference time
Longitude of ascending node of orbital plane computed according
Ω0
to reference time

 Rate of right ascension
δi Correction of orbit reference inclination at reference time
a0 Satellite clock bias
a1 Satellite clock rate

Table 5-13 Almanac parameters characteristics

Parameter No. of Bits Scale factor (LSB) Effective range Units
toa 8 212 602112 s
A 24 2-11 8192 m1/2
e 17 2-21 0.0625 —
ω 24* 2-23 1 π
M0 24* 2-23 1 π
Ω0 24* 2-23 1 π

 17* 2-38 — π/s
δi 16* 2-19 — π
a0 11* 2-20 — s
a1 11* 2-38 — s/s
* Parameters so indicated are two’s complement, with the sign bit (+ or –)
occupying the MSB.

35 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Table 5-14 Almanac algorithms for users

Computation Description
Earth’s universal gravitational constant of
μ = 3.986004418×1014 m3/s2
CGCS2000
  7.2921150 10 5 rad/s
 Value of the earth’s rotation rate of CGCS2000
e

A  ( A)2 Computed semi-major axis


n0  Computed mean motion (rad/sec)
A3

t k  t  t oa * Computed time from Almanac reference epoch

Mk  M0  n0t k Computed mean anomaly

Kepler’s equation for eccentric anomaly by

M k  E k  e sin E k
iteration (radians)
 1  e 2 sin E k
sin v k 
 1  e cos E k
 Computed true anomaly
cos v  cos E k  e
 k
1  e cos E k


k  v k   Computed argument of latitude

rk  A(1  e cos E k ) Corrected radius

x k  rk cos  k
 Computed satellite positions in orbital plane
 y k  rk sin  k

 
 )t  
 t Corrected longitude of ascending node in
k  0  ( e k e oa
CGCS2000
i  i 0   i ** Orbit inclination at reference time

X k  x k cos  k  y k cos i sin  k

 Computed GEO/MEO/IGSO satellite
Yk  x k sin  k  y k cos i cos  k
Z  y sin i coordinates in CGCS2000
 k k

* In the equations, ―t‖ is the time of signal transmission in BDT. ―t k‖ is the total
time offset between time t and Almanac reference time t oa taking account of beginning
or end of a week crossover. That is, subtract 604800 seconds from t k if tk is greater
than 302400, add 604800 seconds to tk if tk is less than -302400.
** For MEO/IGSO satellites, i0=0.30 semi-circles; for GEO satellites, i0=0.00.

36 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Almanac time computation is as follows:

t = tsv – Δtsv
where
t is BDT in seconds at time of signal transmission;
tsv is the effective satellite ranging code phase time in seconds at
time of signal transmission;
Δtsv is the offset of satellite ranging code phase time in seconds and
is given by the equation:
Δtsv= a0 + a1(t– toa)
Where t can be replaced by tsv regardless of its sensitivity. The
almanac reference time toa is counted from the starting time of almanac
week number (WNa).

5.2.4.15 Almanac Week Number (WNa)

Almanac week number (WNa) of 8 bits is the BDT integer week

count (Modulo 256) with effective range of 0 to 255.

5.2.4.16 Satellite Health Information (Heai, i=1~30)

The satellite health information (Heai) occupies 9 bits. The 9th bit
indicates the satellite clock health flag, while the 8th bit indicates the B1I
signal health status. The 7th bit indicates the B2I signal health status,and
the 2th bit indicates the information health status. The definitions are in
Table 5-15.

37 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Table 5-15 Satellite health information definitions

Bit allocation Information code Health information definition

Bit 9 0 Satellite clock OK

(MSB) 1 *
0 B1I Signal OK
Bit 8
1 B1I Signal Weak**
0 B2I Signal OK
Bit 7
1 B2I Signal Weak**
0 Reserved
Bit 6~3
1 Reserved
0 NAV Message OK
Bit 2
1 NAV Message Bad (IOD over limit)

Bit 1 0 Reserved
(LSB) 1 Reserved
* the satellite clock is unavailable if the other 8 bits are all ―0‖; the satellite is in
failure or permanently shut off if the last 8bits are all ―1‖; the definition is reserved
if the other 8 bits are in other values.
** The signal power is 10 dB lower than nominal value.

5.2.4.17 Time Parameters relative to UTC （ A0UTC, A1UTC, ΔtLS,

WNLSF, DN, ΔtLSF）

These parameters indicate the relationship between BDT and UTC.

Definition of the parameters are listed in Table 5-16.
Table 5-16 Parameters relative to UTC
Parameter No. of bits Scale factor(LSB) Effective range Units
A0UTC 32* 2-30 — s
A1UTC 24* 2-50 — s/s
ΔtLS 8* 1 — s
WNLSF 8 1 — week
DN 8 1 6 day
ΔtLSF 8* 1 — s
* Parameters so indicated are two’s complement, with the sign bit (+ or –)
occupying the MSB.
38 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

A0UTC: BDT clock bias relative to UTC;

A1UTC: BDT clock rate relative to UTC;
ΔtLS: Delta time due to leap seconds before the new leap second
effective;
WNLSF: Week number of the new leap second;
DN: Day number of week of the new leap second;
ΔtLSF: Delta time due to leap seconds after the new leap second
effective;
Conversion from BDT into UTC:
The broadcast UTC parameters, the WNLSF and DN values make
users compute UTC with error not greater than 1 microsecond.
Depending upon the relationship of the effectivity time of leap
second event and user’s current BDT, the following three different cases
of UTC/BDT conversion exist.
1) Whenever the effectivity time indicated by the WN LSF and the DN
values is not in the past (relative to the user’s present time), and
the user’s current time tE is prior to DN+2/3, the UTC/BDT
relationship is given by:
tUTC = (tE – ΔtUTC)[modulo 86400], seconds
ΔtUTC = ΔtLS + A0UTC + A1UTC × tE, seconds
Where, tE is the SOW in BDT computed by user.
2) Whenever the user’s current time tE falls within the time span of
DN+2/3 to DN+5/4, proper accommodation of leap second event
with possible week number transition is provided by the following
equation for UTC:
tUTC =W[modulo(86400 + ΔtLSF – ΔtLS)], seconds
where,
W=( tE – ΔtUTC – 43200)[modulo 86400] + 43200, seconds
ΔtUTC = ΔtLS + A0OUT + A1UTC × tE, seconds
39 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

3) Whenever the effectivity time of leap second event, as indicated

by the WNLSF and DN values, is in the past (relative to the user’s
current time), and the user’s current time tE is after DN+5/4, the
UTC/BDT relationship is given by:
tUTC = (tE – ΔtUTC)[modulo86400], seconds
where,
ΔtUTC = ΔtLSF + A0UTC + A1UTC × tE, seconds
The parameter definitions are the same with those in case 1).

5.2.4.18 Time Parameters relative to GPS time （A0GPS, A1GPS）

These parameters indicate the relationship between BDT and GPS

time as in Table 5-17. (Not broadcast temporarily)
Table 5-17 Time parameters relative to GPS time
Parameter No. of Bits Scale factor (LSB) Units
A0GPS 14* 0.1 ns
A1GPS 16* 0.1 ns/s
* Parameters so indicated are two’s complement, with the sign bit (+ or –)
occupying the MSB.

A0GPS: BDT clock bias relative to GPS time;

A1GPS: BDT clock rate relative to GPS time.
The relationship between BDT and GPS time is as follows:
tGPS = tE – ΔtGPS
where, ΔtGPS = A0GPS + A1GPS×tE;
tE is the SOW in BDT computed by user.

5.2.4.19 Time Parameters relative to Galileo time(A0Gal, A1Gal)

These parameters indicate the relationship between BDT and Galileo

time as in Table 5-18. (Not broadcast temporarily)

40 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Table 5-18 Time parameters relative to Galileo time

Parameter No. of Bits Scale factor (LSB) Units
A0Gal 14* 0.1 ns
A1Gal 16* 0.1 ns/s
* Parameters so indicated are two’s complement, with the sign bit (+ or –)
occupying the MSB.

A0Gal: BDT clock bias relative to Galileo system time;

A1Gal: BDT clock rate relative to Galileo system time.
Relationship between BDT and Galileo system time is as follows:
tGal = tE – ΔtGal
where ΔtGal = A0Gal + A1Gal×tE;
tE is the SOW in BDT computed by user.

5.2.4.20 Time Parameters relative to GLONASS time (A0GLO, A1GLO)

These parameters indicate the relationship between BDT and

GLONASS time as in Table 5-19. (Not broadcast temporarily)
Table 5-19 Time parameters relative to GLONASS time
Parameter No. of Bits Scale factor (LSB) Units
A0GLO 14* 0.1 ns
A1GLO 16* 0.1 ns/s
* Parameters so indicated are two’s complement, with the sign bit (+ or –)
occupying the MSB.

A0GLO: BDT clock bias relative to GLONASS time;

A1GLO: BDT clock rate relative to GLONASS time.
Relationship between BDT and GLONASS time is as follows:

tGLO = tE – ΔtGLO
where ΔtGLO = A0GLO + A1GLO×tE;
tE is the SOW in BDT computed by user.

41 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

5.3 D2 NAV Message

5.3.1 D2 NAV Message Frame Structure

The NAV message in format D2 is structured with superframe, frame

and subframe. Every superframe is 180000 bits long, lasting 6 minutes.
Every superframe is composed of 120 frames each with 1500 bits and
lasting 3 seconds. Every frame is composed of 5 subframes, each with
300 bits and lasting 0.6 second. Every subframe is composed of 10 words,
each with 30 bits and lasting 0.06 second.
Every word is composed of NAV message data and parity bits. The
first 15 bits in word 1 of every subframe is not encoded, and the last 11
bits is encoded in BCH(15,11,1) for error correction. For the other 9
words of the subframe both BCH(15,11,1) encoding and interleaving are
involved. Thus there are 22 information bits and 8 parity bits in each
word. See Figure 5-12 for the detailed structure.

Superframe of 180000 bits, 6 min

Frame 1 Frame 2 … Frame n … Frame120

Frame of 1500 bits, 3 sec

Subframe1 Subframe2 Subframe3 Subframe4 Subframe5

Subframe of 300bits, 0.6 sec

Word 1 Word 2 … Word 10

Word 1, 30 bits, 0.06 sec Word 2~10, 30 bits, 0.06 sec

NAV message data, 26 bits 4 Parity bits NAV message data, 22 bits 8 Parity bits

Fig 5-12 Structure of NAV message in format D2

42 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

5.3.2 D2 NAV Message Detailed structure

Information in format D2 includes: the basic NAV information of the

broadcasting satellite, almanac, time offset from other systems, integrity
and differential correction information of BDS and ionospheric grid
information as shown in Figure 5-13. The subframe 1 shall be
subcommutated 10 times via 10 pages. The subframe 2, subframe 3 and
subframe 4 shall be subcommutated 6 times each via 6 pages. The
subframe 5 shall be subcommutated 120 times via 120 pages.

…
Subframe 2 Subframe 3 Subframe 4
Subframe 1

…
Subframe 5

Basic NAV information of Integrity and differential correction Almanac, ionospheric grid points and
the broadcating satellite information of BDS time offsets from other systems

Fig 5-13 Frame structure and information contents of NAV message in format D2

The bit allocation of each subframe in format D2 is shown in Figures

5-14 through 5-18. The 150 LSBs of pages 1 through 10 in subframe 1,
pages 1 through 6 of subframe 4, pages 14 through 34, pages 74 through
94 pages and 103 through 120 of subframe 5 in format D2 are to be
reserved.

43 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
150 MSBs of Subframe 1 (300bits)
Word1
Subframe Page
1 12 16 19 27 31 61 91 121
No. No.
Pre Rev FraID SOW SOW Pnum1 SatH1 AODC URAI WN toc toc TGD1 TGD2 Rev
1 1 P P P P P
11bits 4bits 3bits 8bits 12bits 4bits 1bit 5bits 4bits 13bits 5bits 12bits 10bits 10bits 12bits
8MSBs 12LSBs 5LSBs 12LSBs

Fig 5-14-1 Bits allocation of 150 MSBs of page 1 in subframe 1 of format D2

Direction of data flow MSB first

MSB LSB
150 MSBs of Subframe 1 (300bits)
Word 1
Subframe Page
1 12 16 19 27 31 61 91 121
No. No.
Pre Rev FraID SOW SOW Pnum1 α0 α0 α1 α2 α3 α3 β0 β1 β2 β2 β3 Rev
1 2 P P P P P
11bits 4bits 3bits 8bits 12bits 4bits 6bits 2bits 8bits 8bits 4bits 4bits 8bits 8bits 2bits 6bits 8bits 8bits
8MSBs 12LSBs 6MSBs 2LSBs 4MSBs 4LSBs 2MSBs 6LSBs

Fig 5-14-2 Bits allocation of 150 MSBs of page 2 in subframe 1 of format D2

44 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
150 bits MSBs of Subframe 1 (300bits)
Word 1
Subframe Page
1 12 16 19 27 31 61 91 121
No. No.
Pre Rev FraID SOW SOW Pnum1 Rev Rev Rev a0 a0 a1 Rev
1 3 P P P P P
11bits 4bits 3bits 8bits 12bits 4bits 6bits 22bits 10bits 12bits 12bits 4bits 6bits
8MSBs 12LSBs 12MSBs 12LSBs 4MSBs

Fig 5-14-3 Bits allocation of 150 MSBs of page 3 in subframe 1 of format D2

Direction of data flow MSB first

MSB LSB
150 bits MSBs of Subframe 1 (300bits)
Word 1
Subframe Page
1 12 16 19 27 31 61 91 121
No. No.
Pre Rev FraID SOW SOW Pnum1 a1 a1 a2 a2 AODE Δn Cuc Rev
1 4 P P P P P
11bits 4bits 3bits 8bits 12bits 4bits 6bits 12bits 10bits 1bit 5bits 16bits 14bits 8bits
8MSBs 12LSBs * 12LSBs 10MSBs 1LSB 14MSBs

* These are data bits next to MSBs and before LSBs.

Fig 5-14-4 Bits allocation of 150 MSBs of page 4 in subframe 1 of format D2

45 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
150 bits MSBs of Subframe 1 (300bits)
Word 1
Subframe Page
1 12 16 19 27 31 61 91 121
No. No.
Pre Rev FraID SOW SOW Pnum1 Cuc M0 M0 M0 Cus Cus e Rev
1 5 P P P P P
11bits 4bits 3bits 8bits 12bits 4bits 4bits 2bits 22bits 8bits 14bits 4bits 10bits 8bits
8MSBs 12LSBs 4LSBs 2MSBs * 8LSBs 14MSBs 4LSBs 10MSBs

* These are data bits next to MSBs and before LSBs.

Fig 5-14-5 Bits allocation of 150 MSBs of page 5 in subframe 1 of format D2

Direction of data flow MSB first

MSB LSB
150 bits MSBs of Subframe 1 (300bits)
Word 1
Subframe Page 1 12 16 19 27 31 61 91 121
No. No.
Pre Rev FraID SOW SOW Pnum1 e e A A A Cic Rev
1 6 P P P P P
11bits 4bits 3bits 8bits 12bits 4bits 6bits 16bits 6bits 22bits 4bits 10bits 8bits
8MSBs 12LSBs * 16LSBs 6MSBs * 4LSBs 10MSBs

* These are data bits next to MSBs and before LSBs.

Fig 5-14-6 Bits allocation of 150 MSBs of page 6 in subframe 1 of format D2

46 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
150 bits MSBs of Subframe 1 (300bits)
Word 1
Subframe Page
1 12 16 19 27 31 61 91 121
No. No.
Pre Rev FraID SOW SOW Pnum1 Cic Cic Cis toe toe i0 i0 Rev
1 7 P P P P P
11bits 4bits 3bits 8bits 12bits 4bits 6bits 2bits 18bits 2bits 15bits 7bits 14bits 8bits
8MSBs 12LSBs * 2LSBs 2MSBs 15LSBs 7MSBs *

* These are data bits next to MSBs and before LSBs.

Fig 5-14-7 Bits allocation of 150 MSBs of page 7 in subframe 1 of format D2

Direction of data flow MSB first

MSB LSB
150 bits MSBs of Subframe 1 (300bits)
Word 1
Subframe Page
1 12 16 19 27 31 61 91 121
No. No.
Pre Rev FraID SOW SOW Pnum1 i0 i0 Crc Crc Crs 
 
 Rev
1 8 P P P P P
11bits 4bits 3bits 8bits 12bits 4bits 6bits 5bits 17bits 1bit 18bits 3bits 16bits 6bits
8MSBs 12LSBs * 5LSBs 17MSBs 1LSB 3MSBs *

* These are data bits next to MSBs and before LSBs.

Fig 5-14-8 Bits allocation of 150 MSBs of page 8 in subframe 1 of format D2

47 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
150 bits MSBs of Subframe 1 (300bits)
Word 1
Subframe Page
1 12 16 19 27 31 61 91 121
No. No.
Pre Rev FraID SOW SOW Pnum1 
 Ω0 Ω0 Ω0 ω ω Rev
1 9 P P P P P
11bits 4bits 3bits 8bits 12bits 4bits 5bits 1bit 22bits 9bits 13bits 14bits 8bits
8MSBs 12LSBs 5LSBs 1MSB * 9LSBs 13MSBs *

* These are data bits next to MSBs and before LSBs.

Fig 5-14-9 Bits allocation of 150 MSBs of page 9 in subframe 1 of format D2

Direction of data flow MSB first

MSB LSB
150 bits MSBs of Subframe 1 (300bits)
Word 1
Subframe Page
1 12 16 19 27 31 61 91 121
No. No.
Pre Rev FraID SOW SOW Pnum1 ω IDOT IDOT Rev Rev Rev
1 10 P P P P P
11bits 4bits 3bits 8bits 12bits 4bits 5bits 1bit 13bits 9bits 22bits 22bits
8MSBs 12LSBs 5LSBs 1MSB 13LSBs

Fig 5-14-10 Bits allocation of 150 MSBs of page 10 in subframe 1 of format D2

48 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 2 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 96 121 151 172 181 211 241 271 276
No. No.
i Pre Rev FraID SOW SOW Rev Pnum2 SatH2 BDID1 BDID30 Rev Rev Rev UDREI1 UDREI18 RURAIi1 Δti1
2 P … P … P … P P P … P … P … P … P
(i=1~6) 11bits 4bits 3bits 8bits 12bits 1bit 4bits 2bits 1bit 1bit 17bits 22bits 21bits 1bit 4bits 4bits 13bits
8MSBs 12LSBs 1MSB
Satellite Identification for
RURAI and Δt of BDS
Integrity and differential UDREI of BDS (18 Parameters altogether)
where i1=3(i-1)+1
correction information of BDS

Fig 5-15 Bits allocation of subframe 2 of format D2

Direction of data flow MSB first

MSB LSB
Subframe 3 (300 bits) bits allocation
Word 1
Subframe Page
No. No. 1 12 16 19 27 31 61 91 121 151 181 211 241 271
i Pre Rev FraID SOW SOW Rev RURAI i2 Δt i2 Δt i2 RURAI i3 Δti3 Δt i3 Rev Rev Rev Rev Rev Rev Rev
3 P P P P P P P P P P
(i=1~6) 11bits 4bits 3bits 8bits 12bits 1bit 4bits 5bits 8bits 4bits 10bits 3bits 19bits 22bits 22bits 22bits 22bits 22bits 22bits
8MSBs 12LSBs 5MSBs 8LSBs 10MSBs 3LSBs
RURAI and Δt of BDS
where i2=3(i-1)+2；i3=3(i-1)+3

Fig 5-16 Bits allocation of subframe 3 of format D2

49 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 4 (300 bits) bits allocation
Word 1
Subframe Page
No. No. 1 27 31
i Pre Rev FraID SOW SOW Rev Rev
4 P 72bits Parity for 9 words
(i=1~6) 11bits 4bits 3bits 8bits 12bits 1bit 185bits
8MSBs 12LSBs

Fig 5-17 Bits allocation of subframe 4 of format D2

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion1 Ion1 Ion2 Ion2 Ion3 Ion4 Ion4 Ion11 Ion12 Ion13 Rev
5 1 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

dτ 3 GIVE 3
9bits 4bits

Fig 5-18-1 Bits allocation of page 1 of subframe 5 in format D2

50 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion161 Ion161 Ion162 Ion162 Ion163 Ion164 Ion164 Ion171 Ion172 Ion173 Rev
5 61 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

dτ 163 GIVE 163

9bits 4bits

Fig 5-18-2 Bits allocation of page 61 of subframe 5 in format D2

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion14 Ion14 Ion15 Ion15 Ion16 Ion17 Ion17 Ion24 Ion25 Ion26 Rev
5 2 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-3 Bits allocation of page 2 of subframe 5 in format D2

51 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion174 Ion174 Ion175 Ion175 Ion176 Ion177 Ion177 Ion184 Ion185 Ion186 Rev
5 62 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-4 Bits allocation of page 62 of subframe 5 in format D2

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion27 Ion27 Ion28 Ion28 Ion29 Ion30 Ion30 Ion37 Ion38 Ion39 Rev
5 3 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-5 Bits allocation of page 3 of subframe 5 in format D2

52 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion187 Ion187 Ion188 Ion188 Ion189 Ion190 Ion190 Ion197 Ion198 Ion199 Rev
5 63 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-6 Bits allocation of page 63 of subframe 5 in format D2

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion40 Ion40 Ion41 Ion41 Ion42 Ion43 Ion43 Ion50 Ion51 Ion52 Rev
5 4 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-7 Bits allocation of page 4 of subframe 5 in format D2

53 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion200 Ion200 Ion201 Ion201 Ion202 Ion203 Ion203 Ion210 Ion211 Ion212 Rev
5 64 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-8 Bits allocation of page 64 of subframe 5 in format D2

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion53 Ion53 Ion54 Ion54 Ion55 Ion56 Ion56 Ion63 Ion64 Ion65 Rev
5 5 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-9 Bits allocation of page 5 of subframe 5 in format D2

54 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion213 Ion213 Ion214 Ion214 Ion215 Ion216 Ion216 Ion223 Ion224 Ion225 Rev
5 65 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-10 Bits allocation of page 65 of subframe 5 in format D2

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion66 Ion66 Ion67 Ion67 Ion68 Ion69 Ion69 Ion76 Ion77 Ion78 Rev
5 6 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-11 Bits allocation of page 6 of subframe 5 in format D2

55 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion226 Ion226 Ion227 Ion227 Ion228 Ion229 Ion229 Ion236 Ion237 Ion238 Rev
5 66 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-12 Bits allocation of page 66 of subframe 5 in format D2

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion79 Ion79 Ion80 Ion80 Ion81 Ion82 Ion82 Ion89 Ion90 Ion91 Rev
5 7 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-13 Bits allocation of page 7 of subframe 5 in format D2

56 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion239 Ion239 Ion240 Ion240 Ion241 Ion242 Ion242 Ion249 Ion250 Ion251 Rev
5 67 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-14 Bits allocation of page 67 of subframe 5 in format D2

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion92 Ion92 Ion93 Ion93 Ion94 Ion95 Ion95 Ion102 Ion103 Ion104 Rev
5 8 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-15 Bits allocation of page 8 of subframe 5 in format D2

57 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion252 Ion252 Ion253 Ion253 Ion254 Ion255 Ion255 Ion262 Ion263 Ion264 Rev
5 68 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-16 Bits allocation of page 68 of subframe 5 in format D2

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW EncF5 Pnum Ion105 Ion105 Ion106 Ion106 Ion107 Ion108 Ion108 Ion115 Ion116 Ion117 Rev
5 9 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-17 Bits allocation of page 9 of subframe 5 in format D2

58 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion265 Ion265 Ion266 Ion266 Ion267 Ion268 Ion268 Ion275 Ion276 Ion277 Rev
5 69 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-18 Bits allocation of page 69 of subframe 5 in format D2

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion118 Ion118 Ion119 Ion119 Ion120 Ion121 Ion121 Ion128 Ion129 Ion130 Rev
5 10 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-19 Bits allocation of page 10 of subframe 5 in format D2

59 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion278 Ion278 Ion279 Ion279 Ion280 Ion281 Ion281 Ion288 Ion289 Ion290 Rev
5 70 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-20 Bits allocation of page 70 of subframe 5 in format D2

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion131 Ion131 Ion132 Ion132 Ion133 Ion134 Ion134 Ion141 Ion142 Ion143 Rev
5 11 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-21 Bits allocation of page 11 of subframe 5 in format D2

60 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion291 Ion291 Ion292 Ion292 Ion293 Ion294 Ion294 Ion201 Ion202 Ion203 Rev
5 71 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-22 Bits allocation of page 71 of subframe 5 in format D2

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion144 Ion144 Ion145 Ion145 Ion146 Ion147 Ion147 Ion154 Ion155 Ion156 Rev
5 12 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-23 Bits allocation of page 12 of subframe 5 in format D2

61 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion304 Ion304 Ion305 Ion305 Ion306 Ion307 Ion307 Ion314 Ion315 Ion316 Rev
5 72 P P P P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 9bits 13bits 13bits 9bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs 9LSBs

Fig 5-18-24 Bits allocation of page 72 of subframe 5 in format D2

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion157 Ion157 Ion158 Ion158 Ion159 Ion160 Ion160 Rev Rev Rev Rev Rev Rev
5 13 P P P P P P P P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 16bits 22bits 22bits 22bits 22bits 22bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs

Fig 5-18-25 Bits allocation of page 13 of subframe 5 in format D2

62 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
1 27 31 61 91 121 151 181 211 241 271
No. No.
Pre Rev FraID SOW SOW Rev Pnum Ion317 Ion317 Ion318 Ion318 Ion319 Ion320 Ion320 Rev Rev Rev Rev Rev Rev
5 73 P P P P P P P P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 11bits 11bits 2bits 13bits 7bits 6bits 16bits 22bits 22bits 22bits 22bits 22bits
8MSBs 12LSBs 2MSBs 11LSBs 11MSBs 2LSBs 7MSBs 6LSBs

Fig 5-18-26 Bits allocation of page 73 of subframe 5 in format D2

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
SubFrame Page
No. No. 1 27 31 53 61 91 121 151 181 211 241 271
Pre Rev FraID SOW SOW Rev Pnum Hea1 Hea1 Hea2 Hea3 Hea3 Hea4 Hea15 Hea16 Hea17 Hea18 Hea18 Hea19 Rev
5 35 P P P … P … P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 7bits 9bits 6bits 3bits 9bits 1bit 9bits 9bits 3bits 6bits 9bits 7bits
8MSBs 12LSBs 2MSBs 7LSBs 6MSBs 3LSBs 1LSB 3MSBs 6LSBs

Fig 5-18-27 Bits allocation of page 35 of subframe 5 in format D2

63 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
No. No. 1 27 31 53 61 91 121 151 181 211
Pre Rev FraID SOW SOW Rev Pnum Hea20 Hea20 Hea21 Hea27 Hea28 Hea29 Hea30 WNa toa toa Rev 24bits Parity for 3
5 36 P P … P … P … P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 7bits 9bits 4bits 9bits 9bits 9bits 8bits 5bits 3bits 63bits words
8MSBs 12LSBs 2MSBs 7LSBs 4LSBs 5MSBs 3LSBs

Fig 5-18-28 Bits allocation of page 36 of subframe 5 in format D2

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
No. No. 1 27 31 53 61 91 121 151 181 211 241 271
37~60 Pre Rev FraID SOW
P
SOW Rev Pnum A P A P a1 a0 P
Ω 0 P Ω 0 e  i P
i toa 
 P

 ω P
ωM0
P
M0 Rev
P
5
95~100 11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 22bits 11bits 11bits 22bits 2bits 17bits 3bits 13bits 8bits 1bit 16bits 6bits 18bits 4bits 20bits 2bits
8MSBs 12LSBs 2MSBs 22LSBs 22MSBs 2LSBs 3MSBs 13LSBs 1MSB 16LSBs 6MSBs 18LSBs 4MSBs 20LSBs

Fig 5-18-29 Bits allocation of pages 37 through 60 and pages 95 through 100 of subframe 5 in format D2

64 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
No. No. 1 27 31 61 91 121 151 181 211
Pre Rev FraID SOW SOW Rev Pnum Rev Rev Rev A0GPS A1GPS A1GPS A0Gal A0Gal A1Gal A0GLO A1GLO A1GLO Rev 24bits Parity for 3
5 101 11bits 4bits 3bits 8bits P 12bits 1bit 7bits 2bits P 22bits P 6bits 14bits 2bits P 14bits 8bits P 6bits 16bits P 14bits 8bits P 8bits 58bits words
8MSBs 12LSBs 2MSBs 14LSBs 8MSBs 6LSBs 8MSBs 8LSBs

Fig 5-18-30 Bits allocation of page 101 of subframe 5 in format D2

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
No. No. 1 27 31 61 91 121 151
Pre Rev FraID SOW SOW Rev Pnum ΔtLS ΔtLS ΔtLSF WNLSF A0UTC A0UTC A1UTC A1UTC DN Rev 40bits Parity for 5
5 102 P P P P P
11bits 4bits 3bits 8bits 12bits 1bit 7bits 2bits 6bits 8bits 8bits 22bits 10bits 12bits 12bits 8bits 90bits words
8MSBs 12LSBs 2MSBs 6LSBs 22MSBs 10LSBs 12MSBs 12LSBs

Fig 5-18-31 Bits allocation of page 102 of subframe 5 in format D2

65 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Direction of data flow MSB first

MSB LSB
Subframe 5 (300 bits) bits allocation
Word 1
Subframe Page
No. No. 1 27 31
14~34
Pre Rev FraID SOW SOW Rev Pnum Rev
5 74~94 P 72bits Parity for 9 words
11bits 4bits 3bits 8bits 12bits 1bit 7bits 178bits
103~120
8MSBs 12LSBs

Fig 5-18-32 Bits allocation of reserved pages 14 through 34, pages 74 through 94 and pages103 through 120 of subframe 5 in format D2

66 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

5.3.3 D2 NAV Message Content and Algorithm

D2 NAV message contains basic NAV information and augmentation

service information.

5.3.3.1 Basic NAV Information

D2 NAV message contains all the basic NAV information as follows:

Fundamental NAV information of the broadcasting satellite:
 Preamble (Pre)
 Subframe identification (FraID)
 Seconds of week (SOW)
 Week number (WN)
 User range accuracy index (URAI)
 Autonomous satellite health flag (SatHl)
 Ionospheric delay model parameters (αn, βn, n=0~3)
 Equipment group delay differential (TGD1,TGD2)
 Age of data, clock (AODC)
 Clock correction parameters (t oc, a0, a1, a2)
 Age of data, ephemeris (AODE)
 Ephemeris parameters (toe, A,  , i0, IDOT, Cuc，
e, ω, Δn, M0, Ω0, 
Cus, Crc, Crs, Cic, Cis)

Page number (Pnum)

Almanac information:
 Almanac parameters (toa, A,  , δi, a0, a1)
e, ω, M0, Ω0, 
 Almanac week number (WNa)
 Satellite health information (Heai, i=1~30)
Time offsets from other systems:
 Time parameters relative to UTC (A0UTC, A1UTC, ΔtLS, WNLSF, DN,
67 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

ΔtLSF)
 Time parameters relative to GPS time (A0GPS, A1GPS)
 Time parameters relative to Galileo time (A0Gal, A1Gal)
 Time parameters relative to GLONASS time (A0GLO, A1GLO)
The definition of basic NAV information is the same as that in format D1,
except the page number (Pnum), seconds of week (SOW), which are different
from those in format D1. Thus only the meanings of Pnum and SOW are given
as follows.
(1) Page number (Pnum)
In format D2, the information of subframe 5 is broadcast via 120 pages and
the page number is identified by Pnum.
(2) Seconds of week (SOW)
In format D2, the bits 19 through 26 and the bits 31 through 42, altogether
20 bits of every subframe are for the seconds of week (SOW). SOW count starts
from zero at 00:00:00 of BDT on every Sunday.
In format D2, SOW refers to the leading edge of preamble first bit in
subframe 1 of each frame.

5.3.3.2 Page Number for Basic NAV Information (Pnum1)

The bits 43 through 46, altogether 4 bits of subframe 1 are for page number
of the basic NAV information (Pnum1). Pnum1 is broadcast in pages 1 through
10 of subframe 1.

5.3.3.3 Page Number for Integrity and Differential Correction

Information (Pnum2)

The bits 44 through 47, altogether 4 bits of the subframe 2 are for the page
number of the integrity and differential correction information (Pnum2). Pnum2
are broadcast in pages 1 through 6 of subframe 2.

68 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

5.3.3.4 Satellite Health Flag for Integrity and Differential Correction

Information (SatH2)

The satellite health flag for integrity and differential correction information
SatH2 is in 2 bits. The MSB indicates the check result of the satellite for the
received up-link regional user range accuracy (RURA), user differential range
error (UDRE) and equivalent clock correction (Δt). The LSB indicates the check
result of the satellite for received up-link ionospheric grid information.
See Table 5-20 for detailed definitions.
Table 5-20 SatH2 definitions
Bit allocation Code Definition of SatH2
0 RURA, UDRE and Δt are good by check
MSB
1 RURA, UDRE and Δt are bad by check
0 Ionospheric grid information is good by check
LBS
1 Ionospheric grid information is bad by check

5.3.3.5 BDS Satellite Identification for Integrity and differential

correction information (BDIDi)

The BDS satellite identification for integrity and differential correction

information (BDIDi, i=1~30) is in 30 bits to identify BDS satellites for which
the integrity and differential information are broadcast. Every bit identifies one
satellite. ―1‖ means the integrity and differential correction information for the
satellite are broadcast and ―0‖ means not.
For BDS the integrity and differential correction information of 18
satellites at most can be broadcast once continuously. Integrity and differential
correction information are allocated in ascending order of the SV ID.

5.3.3.6 BDS Regional User Range Accuracy Index (RURAI)

Regional User Range Accuracy (RURA), the BDS satellite signal integrity
information, is used to describe the satellite signal pseudo-range error in meters.
The satellite signal integrity information is indicated with the Regional User
69 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

Range Accuracy Index (RURAI). It occupies 4 bits for each satellite so the
effective range of RURAI is 0 to 15. The update rate is 18 seconds. See Table
5-21 for the corresponding relationship between RURAI and RURA.
Table 5-21 RURAI definitions
RURAI RURA（meters, 99.9%）
0 0.75
1 1.0
2 1.25
3 1.75
4 2.25
5 3.0
6 3.75
7 4.5
8 5.25
9 6.0
10 7.5
11 15.0
12 50.0
13 150.0
14 300.0
15 > 300.0

5.3.3.7 BDS Differential Correction and Differential Correction Integrity

Information (Δt, UDREI)

5.3.3.7.1 Equivalent Clock Correction (Δt)

The BDS differential correction information is expressed in equivalent

clock correction (Δt). It occupies 13 bits for each satellite with the unit and scale
factor of meter and 0.1 respectively and is expressed with two’s complement.
The MSB is for the sign bit (+ or –). The update rate of Δt is every 18 seconds.
The user adds the value of Δt to the observed pseudorange to correct the
residual error of the satellite clock offset and ephemeris.

70 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

The equivalent clock correction Δt broadcasted on B1I and B2I is

respectively related to its own carrier frequency. It is not necessary that Δt
broadcasted on B1I and B2I is the same. It means the Δt is not available if the
value is -4096.

5.3.3.7.2 User Differential Range Error Index (UDREI)

User differential range error (UDRE), the BDS differential correction

integrity, is used to describe the error of equivalent clock correction in meters. It
is indicated by user differential range error index (UDREI). It occupies 4 bits
for each satellite within the range of 1~15 and the update rate is 3 seconds. The
corresponding relationship between UDRE and UDREI is shown in Table 5-22.
The user shall lookup UDRE in the table to determine the accuracy of the
differential correction for the satellite.

Table 5-22 UDREI definitions

UDREI UDRE（meters, 99.9％）

0 1.0
1 1.5
2 2.0
3 3.0
4 4.0
5 5.0
6 6.0
7 8.0
8 10.0
9 15.0
10 20.0
11 50.0
12 100.0

71 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

UDREI UDRE（meters, 99.9％）

13 150.0
14 Not monitored
15 Not available

5.3.3.8 Ionospheric Grid Information (Ion)

The information about each ionospheric grid point (Ion) consists of the
vertical delay at grid point (dτ) and its error index (GIVEI), occupying 13 bits
altogether. The data arrangement and definitions are as follows.

Table 5-23 Ion definitions

Parameter dτ GIVEI
No. of bits 9 4

The ionospheric grid covers 70 to 145 degrees east longitude and 7.5 to 55
degrees north latitude. This area is divided into 320 grids of 5×2.5 degrees. The
definition of ionospheric grid point (IGP) numbers less than or equal to 160 is
listed in Table 5-24-1. Pages 1 through 13 broadcast ionospheric grid correction
information according to this table.

Table 5-24-1 IGP numbers

E-Log.
70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145
N-Lat.
55 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160
50 9 19 29 39 49 59 69 79 89 99 109 119 129 139 149 159
45 8 18 28 38 48 58 68 78 88 98 108 118 128 138 148 158
40 7 17 27 37 47 57 67 77 87 97 107 117 127 137 147 157
35 6 16 26 36 46 56 66 76 86 96 106 116 126 136 146 156
30 5 15 25 35 45 55 65 75 85 95 105 115 125 135 145 155
25 4 14 24 34 44 54 64 74 84 94 104 114 124 134 144 154
20 3 13 23 33 43 53 63 73 83 93 103 113 123 133 143 153
15 2 12 22 32 42 52 62 72 82 92 102 112 122 132 142 152
10 1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151
72 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

When IGP≤160, the corresponding longitudes and latitudes are:

L  70  INT((IGP  1) / 10)  5

B  5  (IGP  INT((IGP  1) / 10) 10)  5

Where INT(*) refers to round down.

The definition of ionospheric grid point (IGP) numbers more than 160 is
shown in Table 5-24-2. Pages 60 through 73 broadcast grid ionospheric
correction information according to this table.

Table 5-24-2 IGP numbers

E-Log.
70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145
N-Lat.
52.5 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320
47.5 169 179 189 199 209 219 229 239 249 259 269 279 289 299 309 319
42.5 168 178 188 198 208 218 228 238 248 258 268 278 288 298 308 318
37.5 167 177 187 197 207 217 227 237 247 257 267 277 287 297 307 317
32.5 166 176 186 196 206 216 226 236 246 256 266 276 286 296 306 316
27.5 165 175 185 195 205 215 225 235 245 255 265 275 285 295 305 315
22.5 164 174 184 194 204 214 224 234 244 254 264 274 284 294 304 314
17.5 163 173 183 193 203 213 223 233 243 253 263 273 283 293 303 313
12.5 162 172 182 192 202 212 222 232 242 252 262 272 282 292 302 312
7.5 161 171 181 191 201 211 221 231 241 251 261 271 281 291 301 311

When IGP > 160, the corresponding longitudes and latitudes are:
L  70  INT((IGP  161) / 10)  5

B  2.5  (IGP  160  INT((IGP  161) / 10) 10)  5

Where INT(*) refers to round down.

5.3.3.8.1 Vertical Delay at Ionospheric Grid Points (dτ)

dτi is the vertical ionosphere delay on B1I signal at the ith grid point,
expressed in scale factor of 0.125 and with unit of meters. The effective range of
dτi is between 0 to 63.625 meters. IGP is not monitored when the dτi is
111111110 (=63.750meters) and vertical ionosphere delay is not available when

73 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

the dτi is 111111111 (=63.875meters).

Making use of the ionospheric correction at grid points, the users compute
the ionospheric correction for the intersection point of ionosphere and direction
from user to observed satellite by interpolation and add it to the observed
pseudo-range. The reference altitude of ionosphere is 375 km.

5.3.3.8.2 Grid Ionospheric Vertical Error Index (GIVEI)

The grid ionosphere vertical error (GIVE) describes the delay correction
accuracy at ionosphere grid points and is indicated with GIVEI. See Table 5-25
for the relationship between GIVEI and GIVE.

Table 5-25 GIVEI definitions

GIVEI GIVE (meters, 99.9%)

0 0.3
1 0.6
2 0.9
3 1.2
4 1.5
5 1.8
6 2.1
7 2.4
8 2.7
9 3.0
10 3.6
11 4.5
12 6.0
13 9.0
14 15.0
15 45.0

74 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

5.3.3.8.3 Suggestions on User Grid Ionospheric Correction Algorithm

The user can select effective data of the grid points adjacent to or nearby
the observed intersection point with dτi and GIVEI to design the model and
compute the delay correction for ionospherc pierce point (IPP) by interpolation.
The guiding fitting algorithm for user grid ionospheric correction is given as
follows:
4 3

IPP

1 2
Fig 5-19 User IPP and Grid Points

Fig 5-19 illustrates the user IPP and its surrounding grid points. IPP,
represented with geographic latitudes and longitudes as ( p ,  p ), is the
geographic location where the line-of-sight between the user and the satellite
intersects with the ionospheric layer. The positions of the four surrounding grid
points are represented with (  i ,  i , i=1~4) and the vertical ionospheric delays on
the grid points are represented with VTECi(i=1~4) respectively. And ωi(i=1~4)
shows the distance weight between IPP and the four grid points.

As long as there are at least three grid points surrounding the user IPP are
available and effective, the IPP ionospheric delay can be calculated from the
vertical ionospheric delay of these effective grid points through the bilinear
interpolation algorithm.
4

 i  VTEC i
Ionodelay p  i 1
4


i 1
i

 p  1  p  1
Where x p  ， yp  ，
 2  1  4  1

1  (1  x p )  (1  y p ) ， 2  x p  (1  y p ) ， 3  x p  y p ， 4  (1  x p )  y p
75 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

If any grid point of this observation epoch is marked as ineffective, its

weight is zero.
For B2I, users need to multiply a factor k(f) to calculate the grid
ionospheric correction, and its value is as follows:
2
f 2  1561.098 
k(f)  12   
f 2  1207.140 

Where, f1 refers to the nominal carrier frequency of B1I, f2 refers to the

nominal carrier frequency of B2I, and the unit is MHz.

76 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

6 Acronyms

BDS BeiDou Navigation Satellite System

BDT BeiDou Navigation Satellite System Time
bps bits per second
CDMA Code Division Multiple Access
CGCS2000 China Geodetic Coordinate System 2000
dBW Decibel with respect to 1 watt
GEO Geostationary Earth Orbit
GIVE Grid point Ionospheric Vertical delay Error
GIVEI Grid point Ionospheric Vertical delay Error Index
GLONASS GLObal Navigation Satellite System
GPS Global Positioning System
ICD Interface Control Document
ID Identification
IERS International Earth Rotation and Reference Systems Service
IGP Ionospheric Grid Point
IGSO Inclined Geosynchronous Satellite Orbit
AODC Age of Data, Clock
AODE Age of Data, Ephemeris
IPP Ionospheric Pierce Point
IRM IERS Reference Meridian
IRP IERS Reference Pole
Mcps Mega chips per second
MEO Medium Earth Orbit
MHz Megahertz
N/A Not Applicable
NAV Navigation
MSB Most Significant Bit
NTSC National Time Service Center
QPSK Quadrature Phase Shift Keying
77 BDS-SIS-ICD-2.0
2013-12
  2013 China Satellite Navigation Office

RHCP Right-Handed Circularly Polarized

RURA Regional User Range Accuracy
RURAI Regional User Range Accuracy Index
SOW Seconds of Week
SV Space Vehicle
UDRE User Differential Range Error
UDREI User Differential Range Error Index
URA User Range Accuracy
UTC Coordinated Universal Time
WN Week Number

78 BDS-SIS-ICD-2.0
2013-12