LSIS V1.0 Draft August 31, 2023 1

LunaNet Signal-In-Space Recommended 

Standard - Augmented Forward Signal

(LSIS)

Draft Version 1

Noted as Applicable Document 1 [AD1] in LNIS V5
LSIS V1.0 Draft August 31, 2023 2

TABLE OF CONTENTS

1. Introduction ............................................................................................................................................. 3

1.1. Scope ........................................................................................................................................... 4

1.2. Acronyms and Definitions ........................................................................................................... 4

1.2.1. Acronyms...........................................................................................................................................4

1.2.2. Definitions.........................................................................................................................................5

2. Augmented Forward Signal Specifications............................................................................................... 6

2.1. Interface Definition...................................................................................................................... 6

2.1.1. AFS signal and data structure ...........................................................................................................6

2.2. AFS signal specifications.............................................................................................................. 7

2.2.1. Composite signal...............................................................................................................................7

2.2.2. Modulation........................................................................................................................................9

2.2.3. Logic levels......................................................................................................................................10

2.2.4. Transmitted Signals Coherency .......................................................................................................10

2.2.5. Spreading codes characteristics......................................................................................................11

2.3. AFS Navigation message format specification .......................................................................... 14

2.3.1. General navigation message structure ...........................................................................................14

2.3.2. Subframe1 message specification...................................................................................................16

2.3.3. Frame structure...............................................................................................................................16

2.4. AFS Messages and data content................................................................................................ 22

2.4.1. Checksum ........................................................................................................................................22

2.4.2. LunaNet Network Access Information (MSG-G1)............................................................................22

2.4.3. Health and Safety (MSG-G2)...........................................................................................................22

2.4.4. Clock and Ephemeris data (CED, MSG-G4)......................................................................................23

2.4.5. MOrbit Almanac (MSG-G5).............................................................................................................23

2.4.6. Time of transmission (MSG-G8) ......................................................................................................23

2.4.7. Maneuver (MSG-G10) .....................................................................................................................25

2.4.8. SAttitude State/ Ephemeris (MSG-G11) ..........................................................................................25

2.4.9. Conjunction (MSG-G14) ..................................................................................................................25

2.4.10. Maplet (MSG-G15)..........................................................................................................................25

2.4.11. Ancillary info (MSG-G17).................................................................................................................25

2.4.12. LunaSAR (MSG-S19 and MSG-S20)..................................................................................................25

2.4.13. Acknowledge of non-SAR MSG (MSG-G22).....................................................................................25

2.4.14. GNSS Augmentation (MSG-G23).....................................................................................................25

2.4.15. Detection Alert (MSG-G24) .............................................................................................................25

2.4.16. Science (MSG-G25)..........................................................................................................................25

2.4.17. UIS Response (MSG-G27) ................................................................................................................26

2.4.18. User Schedule Notice (MSG-G28)....................................................................................................26

2.4.19. FF Commands (MSG-G29)...............................................................................................................26
LSIS V1.0 Draft August 31, 2023 3

1. INTRODUCTION

This document forms part of the LunaNet Interoperability Specification (LNIS) and describes the 

characteristics of the signals and messages to support, at the minimum, the PNT services defined in the 

LNIS. The current version is provided as draft and covers the specifications to ensure interoperability 

among LunaNet Service Providers (LNSP) supporting the Lunar Augmented Navigation System (LANS). 

As defined in LNIS, LANS is a service from multiple provider nodes to multiple users at the same time, 

using a concept similar to Global Navigation Satellite Systems (GNSS). This service is to be provided in 

2483.5-2500MHz band via the Augmented Forward Signal (AFS).

Figure 1 outlines the Position, Navigation, and Timing (PNT) services. LANS is shown on the right, and 

PNT from Point-to-Point (P2P) communication signals is shown on the left. Future versions of 

recommended standards will include specifications for the other signals and messages required to 

implement the P2P PNT services.

Figure 1 – PNT Services Provided by Multiple LNSP

This document is intended as a recommended standard, using a definition like Consultative Committee 

for Space Data Systems (CCSDS) standards. The adoption of the standard by a service provider is 

voluntary, however, as mentioned in LNIS, a service provider that claims to be LunaNet compliant 

(becoming an LNSP) must conform to this recommended standard in all of its parts.

LunaNet may encompass systems of different nature, including different orbits, different Earth segments, 

etc. Thus, some aspects of specific LunaNet services might be implemented differently by different 

LNSP, without impacting the service interoperability. Therefore, it is important to define specifications to 

the right level, leaving flexibility to each LNSP to implement their specific concepts, without impacting 

interoperability. For this reason, this document implements two categories of specifications, broadly 

defined as follows:

1) precise specifications are provided to avoid ambiguity, with no flexibility at the LNSP level.

2) general specifications are provided in order to guarantee interoperability and provide flexibility to

the LNSP to define a specific implementation. 
LSIS V1.0 Draft August 31, 2023 4

Per number 2 above, general specifications left for definition by the LNSP are referred to as LNSP 

implementation flexibility. Examples of LNSP implementation flexibility include but are not limited to the 

data content dissemination cadence, the update rate of the data, etc.

In order to achieve interoperability, the detailed definition covered by the LNSP implementation 

flexibility will need to be known to develop LunaNet compatible user terminals. Therefore, it is expected 

that an LNSP-specific signal in space interface control document (SISICD) will need to be generated and 

made available by the LNSP to a TBD distribution1

.

Future versions of this document will clarify the content associated with LNSP implementation 

flexibility. 

In summary, each LNSP that intends to be interoperable as defined in LNIS shall:

1. comply with this document, and

2. define a SISICD2 that provides definition to the items identified as having LNSP implementation 

flexibility in this document, and make it available to a TBD distribution, and

3. define user algorithms and models required to process the data specified in the provider specific

SISICD and develop an example software implementation of the user processing, including test 

vectors, and make those available to the TBD distribution.

This document was written and reviewed by European Space Agency (ESA) and National Aeronautics 

and Space Administration (NASA). 

1.1. SCOPE 

This document defines, at the minimum, the specifications for interoperability among LNSP providing 

PNT services. It aims to maximize compatibility across multiple LNSP at the user level, while, at the 

same time, leaving sufficient flexibility to enable tailoring of the services and potential future evolutions.

1.2. ACRONYMS AND DEFINITIONS 

1.2.1. ACRONYMS 

Acronym Definition

AD Applicable Document

AFS Augmented Forward Signal

BI Block Interval

BPSK Binary Phase Shift Key

CRC Cyclic Redundancy Check

EIRP Equivalent Isotropic Radiated Power

FID Frame Identifier

GNSS Global Navigation Satellite Systems

1 The actual distribution list and/or the rules for the dissemination of the LNSP-specific SISICD will be clarified in 

the future. 2 SISICD in this context means definition of signal characteristics and messages.
LSIS V1.0 Draft August 31, 2023 5

Acronym Definition

ITOW Interval Time of Week

LANS Lunar Augmented Navigation Service

LNIS LunaNet Interoperability Specification

LNSP LunaNet Service Provider

LRT LunaNet Reference Time

LSB Least Significant Bit

MSB Most Significant Bit

P2P Peer-to-Peer

PNT Position, Navigation, and Timing

RD Reference Document

RHCP Right-Hand Circularly Polarized

SB1 Subframe 1

SB2 Subframe 2

SB3 Subframe 3

SB4 Subframe 4

SECWEEK Seconds in a week

SISE Signal In Space Error

SISEvel Signal In Space Error for velocity

SP Synchronization Pattern

sps Symbol per second

SV Space Vehicle

WN Week Number

1.2.2. DEFINITIONS 

The following definitions are used throughout this document:

TBC: To Be Confirmed. It is used when a value is proposed, but it might change in future 

versions of this document.

TBD: To Be Determined. It is used when something is defined at a conceptual level, but no 

details are provided (e.g.: when a parameter is identified, but its numerical value is not yet 

defined).

TBW: To Be Written. It is used when a paragraph/section is planned to be written in future 

versions of this document.

The following conventions apply for the normative specifications in this Recommended Standard:

a. the words ‘shall’ and ‘must’ imply a binding and verifiable specification; 

b. the word ‘should’ implies an optional, but desirable, specification; 

c. the word ‘may’ implies an optional specification; 

d. the words ‘is’, ‘are’, and ‘will’ imply statements of fact.
LSIS V1.0 Draft August 31, 2023 6

2. AUGMENTED FORWARD SIGNAL SPECIFICATIONS

2.1. INTERFACE DEFINITION 

This section provides the specifications for the interfaces between the LNSP and the user of the AFS. The 

AFS is used within the LANS GNSS-like concept as detailed in LNIS. This section aims to provide 

enough information to ensure that the AFS broadcast by different LNSP can be used without major 

modifications by a receiver in cislunar space. 

The interoperability among different LNSP is ensured by the compliance with the specifications in this 

document, compliance with the Signal in Space Error (SISE) requirements in LNIS, the Lunar Reference 

System and Lunar Time System Standard described in LNIS AD5, and, when relevant, compliance with 

LNIS AD3. The compliance to the SISE will ensure that the errors under control of the LNSP (e.g.: orbit 

prediction error, time synchronization error, satellite payload biases, etc.) are within a limit, guaranteeing 

the users that the errors remain within a predefined envelope.

The following approach is adopted for the messages:

• When a message is defined and/or specified in the same way (e.g.: at bit level) in multiple 

LunaNet PNT services (e.g. LANS and P2P), its definition is provided in LNIS AD3, so the 

related paragraph in section 2.4 includes the encapsulation of the message in AFS and refers to

LNIS AD3 for the message detailed definition. 

• When a message is implemented differently in AFS with respect to other LunaNet PNT services, 

its detailed specification and/or definition are provided in section 2.4.

2.1.1. AFS SIGNAL AND DATA STRUCTURE 

The AFS signal defined in this document is a fixed frequency signal consisting of two main components:

one denoted as AFS-I that is spread by a ranging code and modulated by a data message, and AFS-Q that 

is spread by a ranging code without any data message (pilot component).

AFS-I and AFS-Q use binary shift phase key (BSPK) modulation and are linearly multiplexed to generate 

the AFS signal as described in 2.2.2.

The AFS-I and AFS-Q components are transmitted using ranging codes defined in section 2.2.5.

The message structure and data encoding techniques for the data message on AFS-I are defined in section 

2.3 and the content of the message transmitted by the AFS is provided in section 2.4.
LSIS V1.0 Draft August 31, 2023 7

2.2. AFS SIGNAL SPECIFICATIONS 

2.2.1. COMPOSITE SIGNAL 

2.2.1.1. FREQUENCY PLAN

LSIS-010: Frequency Band

The navigation signal shall be transmitted in S-band between 2483.5 MHz and 2500 MHz.

Note: This is in line with SFCG recommendation 32-2, that identifies the band between 2483.5 MHz 

and 2500 MHz for “In-situ Lunar based RNSS/RDSS to Lunar Orbit and Lunar Surface.”

LSIS-020: Carrier Frequency

The navigation signal carrier frequency shall be 2492.028 MHz.

LSIS-030: Carrier Frequency maximum offset

The maximum deviation of the transmitted signal carrier frequency from the required signal carrier 

frequency shall be less than 10Hz TBC.

Note: The knowledge of the carrier frequency at the user level is bounded by the SISEvel requirement.

2.2.1.2. SIGNAL POLARIZATION

LSIS-040: Signal Polarization

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

LSIS-050: Signal Axial Ratio

The transmitted AFS shall preserve an RHCP signal axial ratio of less than 3 dB (TBC) over the 

antenna beamwidth that covers the service volume defined in LNIS.

2.2.1.3. CARRIER PHASE NOISE

LSIS-060: Navigation Signal Phase Noise

The phase noise spectral density of the un-modulated carrier shall allow a second-order phase locked 

loop with damping of 1 and with 10 Hz one-sided noise bandwidth to track the carrier to an accuracy 

of 0.02 (TBD) radians RMS.

2.2.1.4. SPURIOUS TRANSMISSIONS

LSIS-070: Maximum In-Band Spurious Transmissions

The aggregate EIRP of all unwanted emissions (including discrete emissions and parasitic emissions) 

integrated over the transmit bandwidth of each signal shall not exceed -35 dB (TBC) relative to the 

total power emitted in the bandwidth specified in 2.2.1.5.

LSIS-080: Maximum Out-Of-Band Emissions

TBW

2.2.1.5. CORRELATION LOSSES

Correlation loss is defined as the difference between the space vehicle (SV) power received per 

component in the bandwidth defined below and the signal power recovered in an ideal correlation 

receiver of the same bandwidth using an exact replica of the waveform within an ideal sharp-cutoff 

filter bandwidth centered at the carrier frequency specified in 2.2.1.1.
LSIS V1.0 Draft August 31, 2023 8 

LSIS-090: Receiver reference bandwidth

The receiver reference bandwidth centered on the carrier frequency to be considered for the correlation 

losses shall be 15.944MHz (TBC). 

LSIS-100: Correlation losses due to payload distortions 

For each signal component, the correlation loss due to payload distortions shall be below 0.6 dB 

(TBC).

2.2.1.6. RECEIVED POWER LEVELS IN THE SERVICE VOLUME

LSIS-105: LNSP-Defined service volume

The LNSP shall identify in its SISICD any LNSP-specific service volume on or above the lunar geoid 

where its contribution to LANS is provided. 

Note: The objective for LANS is to achieve full-service volume per LNIS. However, individual LNSP 

may focus on different volumes. LSIS-110 and LSIS-120 requirements apply to the LNSP-defined 

service volume. 

LSIS-110: Minimum and maximum received power levels within LNSP-defined service volume

The minimum and maximum received power level at the lunar geoid (as defined in LNIS AD5) within 

the LNSP-defined service volume, with the following assumptions: 

• an ideally matched 0dBi RHCP receiver antenna 

• receiver antenna boresight direction pointing zenith (aligned to the vector starting at the center

of the Moon towards the user receiver antenna)

• user antenna masking angle on the local horizon of 5 degrees 

shall be according to Table 1. 

Table 1: Received Minimum and Maximum Power

AFS Component Received minimum power 

[dBW]

Received maximum power 

[dBW]

I -166 (TBC) -153 (TBC)

Q -166 (TBC) -153 (TBC)

Note: The power values in Table 1 are subject to revision and might change in future versions. 

2.2.1.7. RECEIVED POWER LEVEL OUTSIDE THE LNSP-DEFINED SERVICE VOLUME

LSIS-120: Maximum received power levels outside the LNSP-defined service volume

The maximum received power level at the lunar geoid (as defined in LNIS AD5) outside the LNSPdefined service volume, with the following assumptions: 

• an ideally matched 0dBi RHCP receiver antenna

• receiver antenna boresight direction pointing zenith (aligned to the vector starting at the center

of the Moon towards the user receiver antenna)

• user antenna masking angle on the local horizon of 5 degrees 

shall be according to Table 2. 
LSIS V1.0 Draft August 31, 2023 9 

Table 2: Received Maximum Power

AFS Component Received maximum power 

[dBW]

I -143 (TBC)

Q -143 (TBC)

The signal may be transmitted outside the LNSP-defined service volume to enable opportunistic use. 

However, its power shall be within the maximum defined in Table 2 in order to minimize the noise on 

the user receiver. 

Note: The power values in Table 2 are subject to revision and might change in future versions. 

2.2.2. MODULATION 

The navigation signal is composed of two components, one in-phase and one quadrature, called 

respectively data and pilot. Both components use Binary Phase Shift Keying (BPSK), with chip rate of n 

× 1.023 (Mchip/s); the data component consists of a BPSK (1) modulation, while the quadrature 

component is a BPSK (5). Figure 2 provides a generic view of the AFS generation.

LSIS-125: Signal multiplexing

The AFS components shall be linearly multiplexed according to Figure 2. 

Figure 2: Modulation Scheme for AFS Signal

LSIS-130: Signal component generation

The AFS components shall be generated according to the following: 

• eeAAAAAA−II (data component) from the navigation data stream DDAAAAAA−II modulated with the ranging code CCAAAAAA−II

• eeAAAAAA−QQ (pilot component) from the ranging code CCAAAAAA−QQ

The mathematical description is: 

ssAAAAAA(tt) = 

1

√2

�eeAAAAAA−II(tt) + jjeeAAAAAA−QQ(tt)�

Where: 

eeAAAAAA−II(tt) = � �ccAAAAAA−II,|ii|LLAAAAAA−IIddAAAAAA−II,|ii|DDDDAAAAAA−IIrr TTcc,AAAAAA−II (tt − iiTTcc,AAAAAA−II)�

+∞

ii=−∞
LSIS V1.0 Draft August 31, 2023 10 

eeAAAAAA−QQ(tt) = � �ccAAAAAA−QQ,|ii|LLAAAAAA−QQrr TTcc,AAAAAA−QQ(tt − iiTTcc,AAAAAA−QQ)�

+∞

ii=−∞

Table 3 provides the description of the parameters used in the equations. 

Table 3: Signal Description Parameters

Parameter Explanation Unit

LLAAAAAA−II, LLAAAAAA−QQ Ranging code repetition period (data and 

pilot)

Chip

ccAAAAAA−II, ccAAAAAA−QQ Binary (NRZ modulated) ranging code (data 

and pilot)

N/A

ddAAAAAA−II, kk kktthsymbol of the navigation message N/A

TTcc,AAAAAA−II, TTcc,AAAAAA−QQ Ranging code chip length (data and pilot) s

DD AAAAAA−II Number of chips per symbol N/A

|ii|LLAAAAAA−II

, |ii|LLAAAAAA−QQ ii modulo LLAAAAAA−II or LLAAAAAA−QQ N/A

rr TT (tt) Function “rectangle” which is equal to 1 for 

0≤t<T and equal to 0 elsewhere

N/A

LSIS-140: signal ranging code chip-rate and symbol-rate

The satellites shall transmit the AFS signal components with the ranging codes chip rates and symbol 

rates stated in Table 4. 

Table 4: AFS Chip Rates and Symbol Rates

Component Ranging code chip-rate [Mchip/s] Symbol-rate [symbols/s]

I 1.023 500 

Q 5.115 No data (pilot component)

2.2.3. LOGIC LEVELS 

LSIS-150: Logic levels for the code bits 

The correspondence between the logic level code bits used to modulate the signal and the 

signal level shall be according to the values stated in Table 6. 

Table 5: Logical to Signal Level Assignment

Logic level Signal level

1 -1.0

0 1.0

2.2.4. TRANSMITTED SIGNALS COHERENCY 

LSIS-160: Primary code / data coherency 

The code-data coherency between the primary code and data symbol shall be less than 0.5ns (TBC). Start 

of periodic spreading codes shall coincide with the start of a data symbol.

Note: The synchronization pattern is considered as data for the purpose of this requirement. 

LSIS-170: Secondary Code / Primary Code Coherency

The code-code coherency between the primary and secondary codes shall be less than 0.5ns (TBC). 

The start of primary code shall coincide with the start of a secondary code chip.

Note: Secondary codes are defined in 2.2.5.2

Note: Code-Code Coherency is the time difference measured between code delays of any two signal 

components within the same signal. 
LSIS V1.0 Draft August 31, 2023 11 

LSIS-180: Code-Code (Data/Pilot) Coherency

The code-code coherency between the data and pilot component shall be less than 0.5ns (TBC). The 

edges of code chips shall be synchronous for the data and pilot components. 

Note: Code-Code Coherency is the time difference measured between code delays of any two signal 

components within the same signal. 

LSIS-190: Code/Carrier Phase Coherency

The maximum of the difference between code phase and carrier phase on any single signal component in 

any 8-hour period at the phase center of the satellite transmit antenna shall be less than 0.13 ns (1-sigma) 

(TBC).

2.2.5. SPREADING CODES CHARACTERISTICS 

2.2.5.1. CODE LENGTHS

The ranging codes are built from so-called primary and secondary codes by using tiered codes 

construction described in paragraph 2.2.5.2. 

LSIS-200: Codes Length and Duration

The code length to be used for each signal component shall be according to Table 6. 

Table 6: Code Lengths

AFS

Component

Primary code 

period [ms]

Secondary code 

period [ms]

Code length [chips]

Primary Secondary

I 1 (TBC) N/A 1023 N/A

Q 1 (TBC) 20 (TBC) 5115 20 (TBC)

LSIS-210: Code-Code (Data/Pilot) Synchronicity

The data and pilot primary and secondary code and the data symbols shall be transmitted according to 

Figure 3. 
LSIS V1.0 Draft August 31, 2023 12

Figure3: Data and Pilot Channel Code and Data Synchronization

LSIS-220: Secondary Code Synchronization

The edge of the first chip of the secondary code shall be synchronized with the edge of the first chip of 

synchronization pattern (see 2.3.1.2).

Note: This requirement ensures that the secondary code is aligned with the synchronization pattern, 

and accordingly to the edge of the second as defined in 2.4.6

2.2.5.2. TIERED CODES GENERATION

Long spreading codes are generated by a tiered code construction, whereby a secondary code sequence 

is used to modify successive repetitions of a primary code, as shown in Figure 4 for a primary code of 

length N and chip rate fc, and a secondary code of length NS and chip rate fcs (for actual values refer to 

paragraph 2.2.2 and 2.2.5.1). The duration of N chips is also called a primary code epoch in Figure 4. 

In logical representation, the secondary code chips are sequentially added (mod-2) with the primary 

code, always one chip of the secondary code per period of the primary code.
LSIS V1.0 Draft August 31, 2023 13

Figure4: Tiered Codes Generation with Secondary Code

The current structure of the pilot signal does not preclude the use of additional information provided in 

the pilot channel by means of overlay symbols on top of the pilot secondary code (e.g.: one symbol 

every one secondary code period), as shown in Figure 5. Examples of capabilities provided by the 

overlay codes are: faster synchronization with the 12 second data frame duration, faster provision of 

health status, faster time dissemination, etc.

Figure5: Tiered Codes Generation with Overlay Code

2.2.5.3. PRIMARY CODES GENERATION AND DEFINITION

LSIS-230: Primary Code Assignment Per LNSP Satellite

Each LNSP satellite shall have unique data and pilot primary codes assigned.

TBW

2.2.5.4. SECONDARY CODE GENERATION AND DEFINITION

LSIS-240: Secondary Code Assignment Per LNSP Satellite 

Each LNSP satellite shall have a unique secondary code assigned. (TBC)

TBW
LSIS V1.0 Draft August 31, 2023 14

2.2.5.5. CODE ASSIGNMENT TO SATELLITES/LNSP

TBW

2.3. AFS NAVIGATION MESSAGE FORMAT SPECIFICATION 

2.3.1. GENERAL NAVIGATION MESSAGE STRUCTURE 

LSIS-300: Spare Bits Definition

When not specified otherwise, the spare bits in the message structure shall be defined as a sequence of 

zeros and ones starting with zero on the MSB.

LSIS-310: Message Frame Structure

Each frame shall be composed of:

1) the uncoded synchronization pattern

2) one subframe (called SubFrame1, SB1) that contains at least the Time-Of-Interval (TOI) and 

the FrameID (FID)

3) and subsequent subframes that depend on the specific FID value. 

See Figure 6.

Figure 6: Navigation Message Generic Structure
LSIS V1.0 Draft August 31, 2023 15 

2.3.1.1. BIT AND BYTE ORDERING CRITERIA 

LSIS-320: Bit and Byte Ordering Criteria 

All data values shall be encoded using the following bit and byte ordering criteria: 

• For numbering, the most significant bit/byte is numbered as bit/byte 0 

• For bit/byte ordering, the most significant bit/byte is transmitted first 

2.3.1.2. SYNCHRONIZATION PATTERN 

LSIS-330: Synchronization Pattern (SP)

The synchronization pattern (SP) shall be according to Table 7. 

Note: The synchronization pattern allows the receiver to achieve synchronization to the frame 

boundary. 

Table 7: Synchronization Pattern

Number of 

symbols

Binary pattern

TBD TBD

LSIS-340: Uncoded Synchronization Pattern

The SP shall not be encoded. 

2.3.1.3. INTERLEAVING

The 5896 (TBC) symbols representing the SB2, SB3, and SB4 are interleaved, after encoding, using a 

block interleaver. The block interleaver is conceptually described using a two-dimensional array of 67 

(TBC) rows and 88 (TBC) columns. Symbols are written first (MSB first) into the interleaver from left 

to right starting at Row 1. After Row 1 is filled, Row 2 is filled from left to right and this process 

continues until the 5896th symbol (LSB of LDPC encoded symbol of the last subframe) is written into 

the rightmost cell of the last (67th) row. Once all 5896 symbols are written into the array, the symbols 

are sequentially read out of the array, for broadcast to user, from top to bottom starting at Column 1. 

After reading out the last symbol of the 67th row in Column 1, Column 2 symbols are read out from top 

to bottom and this process continues until the last symbol in the 67th row of the last column (88th) is 

read out.

LSIS-350: Symbol interleaving parameters 

All the symbols of the frame, except for the SP and SB1 symbols, shall be interleaved according to the 

parameters in Table 8. 

Table 8: Interleaving Parameters

Parameters Values

Block interleaver size (symbols) 5896 (TBC)

Block interleaver dimensions (n columns x k rows) 88 x 67 (TBC)
LSIS V1.0 Draft August 31, 2023 16 

2.3.2. SUBFRAME1 MESSAGE SPECIFICATION 

2.3.2.1. SUBFRAME1 ENCODING

TBW

2.3.2.2. SUBFRAME1 (SB1) DATA SPECIFICATION

LSIS-400: Subframe 1 Data Bit Allocation 

The TBC data bits of the SB1 shall be allocated in line with Table 9. 

Table 9: Subframe1 Data Bits Allocation

SB1 data

TOI

FID

9 (TBC) TBD

LSIS-410: Subframe 1 Data Definition 

The fields of the SB1 data shall follow the description in Table 10. 

Table 10: SubFrame1 Fields Specification

Parameter Definition Bits Scale factor Unit Values

TOI Time of interval 9 N/A dimensionless 0...399

FID Frame ID TBD N/A dimensionless 0...TBD

Note: The FID is used to identify the structure of the frame as described in 2.3.3. The TOI is used to 

reconstruct the time at the user level as described in 2.4.6. 

2.3.3. FRAME STRUCTURE 

The FrameID (FID) field is used to define different types of frames and allows for implementation of 

different schemes, including:

• different type of encoding of the “Other Subframes” other than SB1, 

• different type and number of subframes. 

LSIS-420: Frame Structure Identification 

The frame structure shall be identified using the FrameID (FID) field in SB1 in line with the values in 

Table 11. 

Table 11: Frame Structure Identification

FID Definition Reference

0 Frame structure including 

SB2, SB3 and SB4

Paragraph 

2.3.3.1

1 to TBD Reserved for future use TBD

2.3.3.1. FRAMEID 0 MESSAGE STRUCTURE

In addition to the SP and SB1 that maintain the structure defined in 2.3.2, another 3 subframe types are 

specified within this frame type.
LSIS V1.0 Draft August 31, 2023 17

Subframe 2 (SB2) is always broadcast in every frame and its structure is not changing, as described in 

2.3.3.1.4.

Subframe 3 (SB3) is a variable data frame that might contain different information. The specific 

information broadcasted is identified by the subframe identifier as described in 2.3.3.1.5.

Subframe 4 (SB4) is a variable frame that will contain variable data potentially supporting services 

other than the navigation service. Message specification is provided in 2.3.3.1.6.

Note for the current version of this document: The structure of the frame is meant to ensure 

dissemination of the mandatory and optional messages as defined in LNIS. At the same time, the 

proposed concept leaves flexibility to the LNSP to implement their specific concepts, so some aspects 

(e.g.: dissemination structure, dissemination frequency, etc.) are not specified in this version of the 

document. A clear example is the possibility to disseminate some messages in SB3 and/or SB4 and the 

possibility to use multiple frames to disseminate the complete message (e.g.: the almanac may be 

disseminated using multiple SB3 and/or SB4 over multiple frames). The next version of this document 

is expected to contain additional requirements to guide LNSP towards a common concept and ensure

interoperability. 

LSIS-430: FrameID 0 Structure Identification

The frame structure identified with FID equal to zero shall be in accordance with Figure 7.

Figure7: Frame Structure of FrameID Equal to Zero (values are TBC)
LSIS V1.0 Draft August 31, 2023 18 

2.3.3.1.1. SUBFRAME ENCODING (NON-SUBFRAME 1)

LSIS-440: Subframe 2 Encoding 

The 1200 (TBC) bits of SB2 data shall be encoded using 1

2� (TBC) LDPC codes. 

LSIS-450: Subframe 3 Encoding 

The 874 (TBC) bits of SB3 data shall be encoded using 1

2� (TBC) LDPC codes. 

LSIS-460: Subframe 4 Encoding 

The 874 (TBC) bits of SB4 data shall be encoded using 1

2� (TBC) LDPC codes. 

2.3.3.1.2. LDPC ENCODING

TBW, details of the LDPC encoder structure will be provided in future versions of this document. 

2.3.3.1.3. SUMMARY OF FRAMEID 0 ENCODING

This section provides a summary of the encoding parameters for the different subframes. The values 

in the table are TBC.

Table 12: FrameID=0 Bits and Symbols Allocation to Subframes 

bits coding

coding 

rate symbols

SubFrame2 1200 LDPC 1/2 2400 

SubFrame3 874 LDPC 1/2 1748 

SubFrame4 874 LDPC 1/2 1748 

2.3.3.1.4. SUBFRAME 2 MESSAGE SPECIFICATIONS

LSIS-500: Subframe2 Dissemination

The SB2 shall be broadcast in every frame.

LSIS-510: Subframe2 Structure

The SB2 structure shall be identical in every frame. 

LSIS-520: Subframe2 Dissemination

SB2 shall contain at least the following data:

• Clock and ephemeris data (CED) (MSG-G4, see also 2.4.4) 

• Week Number (WN) (MSG-G8, precise definition provided in 2.4.2) 

• Interval Time of Week (ITOW) (MSG-G8, precise definition provided in 2.4.2) 

• Health status (MSG-G2, see also 2.4.3) 

• Cyclic Redundancy Check (CRC) (see 2.4.1) 
LSIS V1.0 Draft August 31, 2023 19 

LSIS-530: Subframe2 Layout 

The SB2 layout shall be according to Table 13. 

Table 13: SubFrame2 Bits Allocation

Data CRC

1176 (TBC) 24

LSIS-540: Subframe2 LNSP Specific Data

Additional data specified by the LNSP may be broadcasted in SB2 in addition to the mandatory data.

LSIS-550: Subframe2 Mandatory Spare Bits 

TBC bits shall be kept as spare for future use. 

Note: Spare bits shall be positioned before the CRC. Depending on the definition of the data field in 

SB2 the number of spare bits might vary and potentially might be removed entirely.

2.3.3.1.5. SUBFRAME 3 MESSAGE SPECIFICATIONS

The SB3 is a dynamic subframe that will have different structures depending on the SB3 type. This 

message may be used for multiple purposes, including specific custom messages from the LNSP that 

are not specified in this document (e.g.: proprietary messages).

LSIS-560: Subframe3 Layout 

The SB3 layout shall be according to Table 14. 

Table 14: SubFrame3 Bits Allocation

SB3 type Data CRC

4 or 6 (TBC) 844 or 846 (TBC) 24

LSIS-570: Subframe3 Dynamic Data Content 

The SB3 data content shall be identified by the SB3 type field. 

LSIS-580: Subframe3 Mandatory Type of Data Content

The following data shall be disseminated using SB3: 

• Almanac data (note that the almanac data for the full constellation is expected to be 

disseminated using multiple SB3) (MSG-G5, see also 2.4.5).

• LunaSAR return link message (covering both MSG-S19 and MSG-S20, (precise 

definition provided in 2.4.8) 

• Alerts messages (MSG-G24, precise definition in 2.4.15).

Note: The data listed in this requirement does not need to be disseminated every frame, the 

frequency of the dissemination of the data is not defined in this document. The data of a specific 

message might be disseminated over multiple frames.

LSIS-590: Subframe3 Optional Type of Data Content

The following data should be disseminated using SB3: 

• MAntennaProperties (MSG-G3)
LSIS V1.0 Draft August 31, 2023 20

• GNSS Augmentation (MSG-G23)

• Maneuver (MSG-G10)

• SAttitude State/ Ephemeris (MSG-G11)

• Conjunction (MSG-G14)

• Detection Alert (MSG-G24)

• Custom messages defined by the LNSP.

2.3.3.1.6. SUBFRAME 4 MESSAGE SPECIFICATIONS

The SB4 is a dynamic subframe that will have different structures depending on the SB4 type. This 

message may be used for multiple purposes, including specific custom messages from the LNSP that 

are not specified in this ICD (e.g.: proprietary messages).

LSIS-600: Subframe4 Layout

The SB4 layout shall be according to Table 15.

Table 15: SubFrame4 Bits Allocation

SB4 type Data CRC

4 or 6 (TBC) 844 or 846 (TBC) 24

LSIS-610: Subframe4 Dynamic Data Content

The SB4 data shall be identified by the SB4 type field.

LSIS-620: Subframe3 Mandatory Type of Data Content

The following data shall be disseminated using SB4:

• LunaNet Network Access Information (MSG-G1).

Note: The data listed in this requirement does not need to be disseminated in every frame, the 

frequency of the dissemination of the data is not defined in this document. The data of a specific 

message might be disseminated over multiple frames.

LSIS-630: Subframe4 Optional Type of Data Content

The following data should be disseminated using SB4:

• MAntennaProperties (MSG-G3)

• Almanac data (note that the almanac data for the full constellation is expected to be 

disseminated using multiple SB4) (MSG-G5, see also 2.4.5)

• Maneuver (MSG-G10)

• SAttitude State/ Ephemeris (MSG-G11)

• GNSS Augmentation (MSG-G23)

• Scheduling information for communication service (MSG-G27, MSG-G28)

• Updates of lunar maps or lunar DEM (MSG-G15)

• Ancillary info (MSG-G17)

• Conjunction (MSG-G14)

• Science data (MSG-G25)

• Acknowledge- of non-SAR MSG (MSG-G22)

• UIS Response (MSG-G27)

• FF Commands (MSG-G29)

• Custom messages defined by the LNSP.
LSIS V1.0 Draft August 31, 2023 21 

Note: The data listed in this requirement does not need to be disseminated in every frame, the 

frequency of the dissemination of the data is not defined in this document. The data of a specific 

message might be disseminated over multiple frames.

2.3.3.1.7. ALLOCATION OF LUNANET MESSAGES TO SUBFRAMES

This section contains the mapping between LunaNet messages (see annex D of LNIS) with the 

subframes specified in this document. In line with LNIS, a label is used to identify which category 

applies to that message/service combination within the available AFS bandwidth: F = Fundamental, 

meaning it shall be broadcasted by the LNSP; O = Optional, meaning it might be broadcasted by the 

LNSP; and C = Comm, meaning it may be transmitted on AFS to facilitate LunaNet services.

Table 16: LNIS Message Allocation to Subframes

LunaNet Interoperability Specifications [AD.1] LSIS (this document)

MSG ID MSG Title Category SubFrame Notes

MSG-G1 LunaNet Network Access 

Information F SB4 periodic

MSG-G2 Health and Safety F SB2 periodic

MSG-G3 MAntennaProperties O SB3 and/or SB4 TBD

MSG-G4 Sorbit Ephemeris & clock 

correction F SB2 periodic

MSG-G5 MOrbit Almanac F SB3 and/or SB4 periodic

MSG-G8 Time of transmission F SB2 and SB3 periodic

MSG-G10 Maneuver O SB3 and/or SB4 Ad-hoc

MSG-G11 SAttitude State/ Ephemeris O SB3 and/or SB4 Ad-hoc

MSG-G14 Conjunction O SB3 and/or SB4 Ad-hoc

MSG-G15 Maplet O SB4 Ad-hoc

MSG-G17 Ancillary info O SB4 Ad-hoc

MSG-S19 Acknowledge- of SAR - LvL1 F SB3 Ad-hoc

MSG-S20 Acknowledge- of SAR - LvL2 F SB3 Ad-hoc

MSG-G22 Acknowledge- of non-SAR MSG O SB4 Ad-hoc

MSG-G23 GNSS Augmentation O SB3 and/or SB4 Ad-hoc

MSG-G24 Detection Alert O SB3 Ad-hoc

MSG-G25 Science C SB4 Ad-hoc

MSG-G27 UIS Response C SB4 Ad-hoc

MSG-G28 User Schedule Notice C SB4 Ad-hoc

MSG-G29 FF Commands C SB4 Ad-hoc
LSIS V1.0 Draft August 31, 2023 22

2.4. AFS MESSAGES AND DATA CONTENT 

This chapter describes the messages and data content applicable to AFS. When a message is defined in 

the same way (e.g.: at bit level) in multiple LunaNet PNT services (e.g., LANS and P2P), the related 

paragraph includes the message encapsulation in AFS, while the message detailed definition is identified 

in LNIS AD3. Otherwise, each paragraph specifies the specific implementation applicable to AFS. In this 

case, the same type of message may be implemented differently in different LunaNet PNT services.

Note for the current version of this document: the content of many of the messages is currently undefined 

and it is expected to be specified in the next version of this document. It is important to note that different 

messages might follow different approaches. In general, we identify two ways to specify the content of a 

message:

1) precise message specification is provided to avoid ambiguity, with no flexibility at the LNSP 

level (e.g.: CRC and MSG-G8)

2) General message specification is provided at higher level than the bit representation, the 

specification ensures that all the required information is defined, however the specific 

implementation is left free to the LNSP, and it is meant to be detailed in the LNSP-specific 

SISICD.

This approach is currently under assessment and will be further detailed in the next version of this 

document, including which approach is planned to be adopted for each of the messages.

2.4.1. CHECKSUM 

The checksum, which employs a CRC technique, is used to detect the reception of corrupted data.

LSIS-700: Checksum Field Generator Polynomial

For the SB2, SB3 and SB4 a CRC of 24 bits shall be generated from the following generator polynomial:

GG(XX) = (1 + XX) ∗ PP(XX)

where P(X) is the primitive and irreducible polynomial with the following definition:

PP(XX) = XX23 + XX17 + XX13 + XX12 + XX11 + XX9 + XX8 + XX7 + XX5 + XX3 + XX1

LSIS-710: Checksum Field Computation

The CRC shall be composed of a sequence of 24 parity bits ppii with the following values.

For any ii from 1 to 24, ppii is the coefficient of XX24−ii in RR(XX),

Where:

• RR(XX) is the remainder of the binary polynomial algebra division of the polynomial m(XX) ∙ XX24 by GG(XX)

mm(XX) = mm1XXkk−1 + ⋯ + mmkk−2XX2 + mmkk−1XX + mmkk with mm1, mm2, ... mmkk the sequence of k-bits 

information to be protected by the CRC, and mm1 as the MSB.

2.4.2. LUNANET NETWORK ACCESS INFORMATION (MSG-G1) 

TBW

2.4.3. HEALTH AND SAFETY (MSG-G2) 

TBW
LSIS V1.0 Draft August 31, 2023 23 

2.4.4. CLOCK AND EPHEMERIS DATA (CED, MSG-G4) 

TBW, additional information will be provided in future versions of this document, but some preliminary 

information is provided to allow understanding of the type of information expected to be broadcast to the 

user. MSG-G4 is expected to contain or specify:

− The data to allow a user to compute the position and velocity of the phase center of the 

navigation antenna of the LNSP satellite transmitting the AFS, in the reference frame defined 

in LNIS AD5

− the data to allow a user to correct any clock synchronization error impacting the AFS 

transmitted by LNSP satellite, in the time scale defined in LNIS AD5

− the validity period of the data contained in MSG-G4

− the reference epoch to which the data refers 

− the expected quality estimated by the LNSP of the data contained in MSG-G4 (e.g.: similar to 

GPS URA or Galileo SISA) 

2.4.5. MORBIT ALMANAC (MSG-G5) 

TBW

2.4.6. TIME OF TRANSMISSION (MSG-G8) 

The time of transmission (ToT) may be retrieved by a receiver combining multiple fields provided in the 

navigation message and exploiting tracking of the spreading codes. 

A user receiver may resolve the time (multiple of the frame duration) since the starting LunaNet Reference 

Time (LRT) epoch with the following formula: 

TT = WWWW ∗ SSSS SSSSSS + II II ∗ BB dd + TT ∗ FFdd

Where

• TT is the time in seconds since the starting LRT epoch, with increments that are a multiple 

of the duration of a frame. 

The synchronization within the frame duration may be achieved counting the number of primary/secondary 

codes and the phase within the primary code since the leading edge of the first chip of the first code sequence 

of the frame (e.g.: the edge of the first chip of the synchronization pattern). 

LSIS-720: ToT Fields Definition

The fields needed to retrieve time of transmission shall be in accordance with the following definitions (see

Figure 8): 

• SSSS SSSSSS is the number of seconds in a week (604800). 

• BB dd is the block interval duration in seconds. This is computed multiplying the frame duration 

with the maximum TOI value (400) (BB dd = 12 ∗ 400 (TT ) = 4800 (TBC) seconds = 

1h20min). 

• FFdd is the frame duration, which length is 12 seconds. 
LSIS V1.0 Draft August 31, 2023 24 

• The Time of Interval (TOI) is represented with 9 (TBC) bits and represents the number of frames 

from the beginning of the block interval (BI). A BI lasts 4800 (TBC) seconds (1 hour and 20 

minutes), a frame lasts for 12 seconds, so TOI needs to represent 400 (TBC) values. The TOI is

referred to the leading edge of the first chip of the first code sequence of the frame (leading edge 

of the first chip of the SP). 

TT = ffffffff �

mm (tt, BB dd)

FFdd

�

Where tt is the time in seconds since the LRT start epoch.

• The Interval Time of week (ITOW) count is defined as being equal to the number of block 

intervals (BI) that have occurred since the transition from the previous week. The ITOW is 

represented with 7 (TBC) bits, covering the 126 (TBC) BI in a week.

II II = ffffffff �

mm (tt, SSSS SSSSSS)

BB dd

�

Where tt is the time in seconds since the LRT start epoch.

• The Week Number (WN) is an integer counter that gives the sequential week number from the 

LRT start epoch. This parameter is represented with 13 (TBC) bits, which covers 8192 weeks 

(about 157 years). Then the counter is reset to zero to cover an additional period modulo 8192.

WWWW = ffffffff � tt

SSSS SSSSSS�

Where tt is the time in seconds since the LRT start epoch.

• The LunaNet Reference Time (LRT) start epoch is TBD (LRT is defined in LNIS AD5).

Figure 8: Time of Transmission Concept
LSIS V1.0 Draft August 31, 2023 25 

LSIS-730: ToT Fields Binary Representation

The fields required to retrieve ToT shall be according to Table 17. 

Table 17: Time of Transmission Fields Binary Representation

Parameter Definition Bits Scale factor Unit Values

TOI Time of interval 9

(TBC)

N/A dimensionless 0...399

ITOW Interval time of week 7

(TBC)

N/A dimensionless 0...125

WN Week Number 13

(TBC)

1 week 0...8191

2.4.7. MANEUVER (MSG-G10) 

TBW

2.4.8. SATTITUDE STATE/ EPHEMERIS (MSG-G11) 

TBW

2.4.9. CONJUNCTION (MSG-G14) 

TBW

2.4.10. MAPLET (MSG-G15) 

TBW

2.4.11. ANCILLARY INFO (MSG-G17) 

TBW

2.4.12. LUNASAR (MSG-S19 AND MSG-S20) 

TBW

2.4.13. ACKNOWLEDGE OF NON-SAR MSG (MSG-G22) 

TBW

2.4.14. GNSS AUGMENTATION (MSG-G23) 

TBW

2.4.15. DETECTION ALERT (MSG-G24) 

TBW

2.4.16. SCIENCE (MSG-G25) 

TBW
LSIS V1.0 Draft August 31, 2023 26

2.4.17. UIS RESPONSE (MSG-G27) 

TBW

2.4.18. USER SCHEDULE NOTICE (MSG-G28) 

TBW

2.4.19. FF COMMANDS (MSG-G29) 

TBW