ISO 17810:2014

INTERNATIONAL ISO
STANDARD 17810
First edition
2014-07-01
Space data and information transfer
systems — Data transmission and
pseudo-random noise (PN) ranging for
2 GHz code division multiple access
(CDMA) link via data relay satellite
Systèmes de transfert des données et informations spatiales —
Transmission de données et mesure du pseudo bruit pour la liaison
AMRC à 2 GHz par satellite relais de données

Reference number
©
ISO 2014
©  ISO 2014
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any
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ii © ISO 2014 – All rights reserved

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described in the
ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of ISO
documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights.
ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified
during the development of the document will be in the Introduction and/or on the ISO list of patent declarations
received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not constitute an
endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as
well as information about ISO's adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the
following URL: Foreword - Supplementary information
ISO 17810 was prepared by the Consultative Committee for Space Data Systems (CCSDS) (as CCSDS 415.1-B-1,
September 2011) and was adopted (without modifications except those stated in Clause 2 of this International
Standard) by Technical Committee ISO/TC 20, Aircraft and space vehicles, Subcommittee SC 13, Space data and
information transfer systems.
iii
INTERNATIONAL STANDARD ISO 17810:2014(E)

Space data and information transfer systems — Data
transmission and pseudo-random noise (PN) ranging for 2 GHz
code division multiple access (CDMA) link via data relay
satellite
1 Scope
This International Standard defines CDMA spread spectrum modulation schemes in terms of:
a) the services provided to the users of this specification;
b) spreading code formats; and
c) the procedures performed to generate and process the code formats.
It does not specify:
a) individual implementations or products;
b) the methods or technologies required to perform the procedures; or
c) the management activities required to configure and control the system.
This International Standard provides only those parameter requirements relating to signal compatibility with
the existing SNIP PN spread modulation systems (see C.1). There are many other types of requirements, not
specifically related to PN spread modulation signal formats, which must be met to ensure system compatibility
with existing SNIP hardware. Examples would include forward error correction coding format, data signal
formats, etc.
This International Standard applies to the creation of agency standards and to the future data communications
over space links between CCSDS agencies in cross-support situations. This International Standard includes
comprehensive specification of the data formats and procedures for inter-agency cross support. It is neither a
specification of, nor a design for, real systems that may be implemented for existing or future missions.
This International Standard is to be invoked through the normal standards programs of each CCSDS agency,
and is applicable to those missions for which cross support based on capabilities described in this International
Standard is anticipated. Where mandatory capabilities are clearly indicated in sections of this International
Standard, they must be implemented when this document is used as a basis for cross support. Where options
are allowed or implied, implementation of these options is subject to specific bilateral cross-support agreements
between the agencies involved.
2 Requirements
Requirements are the technical recommendations made in the following publication (reproduced on the
following pages), which is adopted as an International Standard:
CCSDS 415.1-B-1, September 2011, Data transmission and PN ranging for 2 GHz CDMA link via data relay
satellite
For the purposes of international standardization, the modifications outlined below shall apply to the specific
clauses and paragraphs of publication CCSDS 415.1-B-1.
Pages i to vi
This part is information which is relevant to the CCSDS publication only.
Page C-1
Add the following information to the reference indicated:
[C2] Document CCSDS 414.1-B-1, March 2009, is equivalent to ISO 18423:2013.
[C4] Document CCSDS 503-0-B-1, November 2007, is equivalent to ISO 13526:2010.
3 Revision of publication CCSDS 415.1-B-1
It has been agreed with the Consultative Committee for Space Data Systems that Subcommittee
ISO/TC 20/SC 13 will be consulted in the event of any revision or amendment of publication CCSDS 415.1-B-
1. To this end, NASA will act as a liaison body between CCSDS and ISO.
2 © ISO 2014 – All rights reserved

Recommendation for Space Data System Standards
DATA TRANSMISSION AND
PN RANGING FOR 2 GHZ
CDMA LINK VIA DATA
RELAY SATELLITE
RECOMMENDED STANDARD
CCSDS 415.1-B-1
BLUE BOOK
September 2011
CCSDS RECOMMENDED STANDARD FOR DATA TRANSMISSION AND
PN RANGING FOR 2 GHz CDMA LINK VIA DATA RELAY SATELLITE
AUTHORITY
Issue: Recommended Standard, Issue 1
Date: September 2011
Location: Washington, DC, USA
This document has been approved for publication by the Management Council of the
Consultative Committee for Space Data Systems (CCSDS) and represents the consensus
technical agreement of the participating CCSDS Member Agencies. The procedure for
review and authorization of CCSDS documents is detailed in the Procedures Manual for the
Consultative Committee for Space Data Systems, and the record of Agency participation in
the authorization of this document can be obtained from the CCSDS Secretariat at the
address below.
This document is published and maintained by:

CCSDS Secretariat
Space Communications and Navigation Office, 7L70
Space Operations Mission Directorate
NASA Headquarters
Washington, DC 20546-0001, USA
CCSDS 415.1-B-1 Page i September 2011

CCSDS RECOMMENDED STANDARD FOR DATA TRANSMISSION AND
PN RANGING FOR 2 GHz CDMA LINK VIA DATA RELAY SATELLITE
STATEMENT OF INTENT
The Consultative Committee for Space Data Systems (CCSDS) is an organization officially
established by the management of its members. The Committee meets periodically to address
data systems problems that are common to all participants, and to formulate sound technical
solutions to these problems. Inasmuch as participation in the CCSDS is completely
voluntary, the results of Committee actions are termed Recommended Standards and are
not considered binding on any Agency.
This Recommended Standard is issued by, and represents the consensus of, the CCSDS
members. Endorsement of this Recommendation is entirely voluntary. Endorsement,
however, indicates the following understandings:
o Whenever a member establishes a CCSDS-related standard, this standard will be in
accord with the relevant Recommended Standard. Establishing such a standard
does not preclude other provisions which a member may develop.
o Whenever a member establishes a CCSDS-related standard, that member will
provide other CCSDS members with the following information:
-- The standard itself.
-- The anticipated date of initial operational capability.
-- The anticipated duration of operational service.
o Specific service arrangements shall be made via memoranda of agreement. Neither
this Recommended Standard nor any ensuing standard is a substitute for a
memorandum of agreement.
No later than five years from its date of issuance, this Recommended Standard will be
reviewed by the CCSDS to determine whether it should: (1) remain in effect without change;
(2) be changed to reflect the impact of new technologies, new requirements, or new
directions; or (3) be retired or canceled.
In those instances when a new version of a Recommended Standard is issued, existing
CCSDS-related member standards and implementations are not negated or deemed to be
non-CCSDS compatible. It is the responsibility of each member to determine when such
standards or implementations are to be modified. Each member is, however, strongly
encouraged to direct planning for its new standards and implementations towards the later
version of the Recommended Standard.
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CCSDS RECOMMENDED STANDARD FOR DATA TRANSMISSION AND
PN RANGING FOR 2 GHz CDMA LINK VIA DATA RELAY SATELLITE
FOREWORD
This document is a technical Recommended Standard for use in developing spread spectrum
modulation systems and has been prepared by the Consultative Committee for Space Data
Systems (CCSDS). The spread spectrum modulation concept described herein is intended
for missions that are cross-supported between Agencies of the CCSDS.
The spread spectrum modulation systems currently used by the Space Network
Interoperability Panel (SNIP) agencies involve Direct Sequence Spread Spectrum (DSSS) in
the form of pseudo-random noise (PN) Gold codes and Maximal Length codes. The PN code
libraries used by NASA Users are also shared by Users of the European Space Agency
(ESA) and Japan Aerospace Exploration Agency (JAXA). Included in this Recommended
Standard are proposed techniques for expanding the code libraries for additional CCSDS
Users. The expanded code library fits into the existing SNIP architecture.
Attention is drawn to the possibility that some of the elements of this document may be the
subject of patent rights. CCSDS shall not be held responsible for identifying any or all such
patent rights.
Through the process of normal evolution, it is expected that expansion, deletion, or
modification of this document may occur. This Recommended Standard is therefore subject
to CCSDS document management and change control procedures, which are defined in the
Procedures Manual for the Consultative Committee for Space Data Systems. Current
versions of CCSDS documents are maintained at the CCSDS Web site:
http://www.ccsds.org/
Questions relating to the contents or status of this document should be addressed to the
CCSDS Secretariat at the address indicated on page i.
CCSDS 415.1-B-1 Page iii September 2011

CCSDS RECOMMENDED STANDARD FOR DATA TRANSMISSION AND
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At time of publication, the active Member and Observer Agencies of the CCSDS were:
Member Agencies
– Agenzia Spaziale Italiana (ASI)/Italy.
– Canadian Space Agency (CSA)/Canada.
– Centre National d’Etudes Spatiales (CNES)/France.
– China National Space Administration (CNSA)/People’s Republic of China.
– Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR)/Germany.
– European Space Agency (ESA)/Europe.
– Federal Space Agency (FSA)/Russian Federation.
– Instituto Nacional de Pesquisas Espaciais (INPE)/Brazil.
– Japan Aerospace Exploration Agency (JAXA)/Japan.
– National Aeronautics and Space Administration (NASA)/USA.
– UK Space Agency/United Kingdom.
Observer Agencies
– Austrian Space Agency (ASA)/Austria.
– Belgian Federal Science Policy Office (BFSPO)/Belgium.
– Central Research Institute of Machine Building (TsNIIMash)/Russian Federation.
– China Satellite Launch and Tracking Control General, Beijing Institute of Tracking
and Telecommunications Technology (CLTC/BITTT)/China.
– Chinese Academy of Sciences (CAS)/China.
– Chinese Academy of Space Technology (CAST)/China.
– Commonwealth Scientific and Industrial Research Organization (CSIRO)/Australia.
– CSIR Satellite Applications Centre (CSIR)/Republic of South Africa.
– Danish National Space Center (DNSC)/Denmark.
– Departamento de Ciência e Tecnologia Aeroespacial (DCTA)/Brazil.
– European Organization for the Exploitation of Meteorological Satellites
(EUMETSAT)/Europe.
– European Telecommunications Satellite Organization (EUTELSAT)/Europe.
– Geo-Informatics and Space Technology Development Agency (GISTDA)/Thailand.
– Hellenic National Space Committee (HNSC)/Greece.
– Indian Space Research Organization (ISRO)/India.
– Institute of Space Research (IKI)/Russian Federation.
– KFKI Research Institute for Particle & Nuclear Physics (KFKI)/Hungary.
– Korea Aerospace Research Institute (KARI)/Korea.
– Ministry of Communications (MOC)/Israel.
– National Institute of Information and Communications Technology (NICT)/Japan.
– National Oceanic and Atmospheric Administration (NOAA)/USA.
– National Space Agency of the Republic of Kazakhstan (NSARK)/Kazakhstan.
– National Space Organization (NSPO)/Chinese Taipei.
– Naval Center for Space Technology (NCST)/USA.
– Scientific and Technological Research Council of Turkey (TUBITAK)/Turkey.
– Space and Upper Atmosphere Research Commission (SUPARCO)/Pakistan.
– Swedish Space Corporation (SSC)/Sweden.
– United States Geological Survey (USGS)/USA.
CCSDS 415.1-B-1 Page iv September 2011

CCSDS RECOMMENDED STANDARD FOR DATA TRANSMISSION AND
PN RANGING FOR 2 GHz CDMA LINK VIA DATA RELAY SATELLITE
DOCUMENT CONTROL
Document Title Date Status
CCSDS Data Transmission and PN Ranging September Current issue
415.1-B-1 for 2 GHz CDMA Link via Data 2011
Relay Satellite, Recommended
Standard, Issue 1
CCSDS 415.1-B-1 Page v September 2011

CCSDS RECOMMENDED STANDARD FOR DATA TRANSMISSION AND
PN RANGING FOR 2 GHz CDMA LINK VIA DATA RELAY SATELLITE
CONTENTS
Section Page
1  INTRODUCTION . 1-1

1.1  PURPOSE . 1-1
1.2  SCOPE . 1-1
1.3  APPLICABILITY . 1-2
1.4  RATIONALE . 1-2
1.5  DOCUMENT STRUCTURE . 1-3
1.6  NOMENCLATURE AND CONVENTIONS . 1-3
1.7  REFERENCES . 1-4

2  OVERVIEW . 2-1

2.1  ARCHITECTURE . 2-1
2.2  SUMMARY OF FUNCTIONS . 2-3
2.3  PN CODE TYPES . 2-6

3  SERVICE AVAILABILITY OF PN SPREAD LINKS FOR
A COMMUNICATION SYSTEM . 3-1

3.1  CCSDS PN CODE ASSIGNMENT . 3-1
3.2  FORWARD AND RETURN DATA SERVICES . 3-1
3.3  COHERENT RETURN . 3-1
3.4  VEHICLE TRACKING . 3-1
3.5  INTEROPERABILITY . 3-1
3.6  FORWARD . 3-1
3.7  RETURN . 3-1
3.8  TIME TRANSFER . 3-2

4  FORWARD SERVICE MODE PN SPREAD SIGNAL FORMAT . 4-1

4.1  GENERAL . 4-1
4.2  COMMAND CHANNEL (I) . 4-1
4.3  COMMAND LINK SIGNAL PARAMETERS. 4-1
4.4  COMMAND LINK PN CODE PROPERTIES . 4-3
4.5  RANGE CHANNEL (Q) . 4-3
4.6  RANGE LINK SIGNAL PARAMETERS . 4-4
4.7  RANGE LINK PN CODE PROPERTIES . 4-4

CCSDS 415.1-B-1 Page vi September 2011

CCSDS RECOMMENDED STANDARD FOR DATA TRANSMISSION AND
PN RANGING FOR 2 GHz CDMA LINK VIA DATA RELAY SATELLITE
CONTENTS (continued)
Section Page
5  RETURN SERVICE MODE PN SPREAD SIGNAL FORMAT . 5-1

5.1  GENERAL . 5-1
5.2  COHERENT MODES . 5-1
5.3  NON-COHERENT MODE . 5-4

6  NETWORK ELEMENT REQUIREMENTS . 6-1

6.1  OVERVIEW . 6-1
6.2  TRANSMIT REQUIREMENTS . 6-1
6.3  RECEIVE REQUIREMENTS . 6-1
6.4  PN RANGING CALIBRATION . 6-1
6.5  PN TIME TRANSFER . 6-2

7  USER ELEMENT REQUIREMENTS FOR PN SPREADING . 7-1

7.1  OVERVIEW . 7-1
7.2  GENERAL . 7-1
7.3  RECEIVE REQUIREMENTS . 7-1
7.4  PERFORMANCE REQUIREMENTS . 7-2
7.5  TRANSMIT REQUIREMENTS . 7-2
7.6  RANGING PERFORMANCE . 7-3
7.7  TIME TRANSFER REQUIREMENTS . 7-4
7.8  PN CODE PERFORMANCE . 7-5

ANNEX A SECURITY (INFORMATIVE) . A-1
ANNEX B GLOSSARY (INFORMATIVE) .B-1
ANNEX C INFORMATIVE REFERENCES (INFORMATIVE) . C-1
Figure
1-1  Shift Register with Corresponding Characteristic Polynomial . 1-4
2-1  DSSS System Network Element Architecture . 2-1
2-2  DSSS System User Element Architecture . 2-2
4-1  CCSDS Command Link Gold Code Generator . 4-3
4-2  CCSDS Range Channel Code Generator . 4-4
5-1  Coherent Return Modes PN Code Generator . 5-3
5-2  Non-coherent Return Mode CCSDS PN Gold Code Generator . 5-6
7-1  Time Transfer Interface Timing Diagram . 7-4

CCSDS 415.1-B-1 Page vii September 2011

CCSDS RECOMMENDED STANDARD FOR DATA TRANSMISSION AND
PN RANGING FOR 2 GHz CDMA LINK VIA DATA RELAY SATELLITE
CONTENTS (continued)
Table Page
4-1  Forward I Channel Service Signal Parameters . 4-2
4-2  Salient Characteristics of PN Codes for Forward Services . 4-2
4-3  Forward Q Channel PSK Service Signal Parameters . 4-4
5-1  Coherent Return Service Signal Parameters . 5-2
5-2  Non-coherent Return Service Signal Parameters . 5-5

CCSDS 415.1-B-1 Page viii September 2011

CCSDS RECOMMENDED STANDARD FOR DATA TRANSMISSION AND
PN RANGING FOR 2 GHz CDMA LINK VIA DATA RELAY SATELLITE
1 INTRODUCTION
1.1 PURPOSE
The purpose of this Recommended Standard is to specify a set of Code Division Multiple
Access (CDMA) Direct Sequence (DS) spread spectrum modulation schemes for CCSDS
Users. The schemes described in this Recommended Standard are currently used by NASA,
ESA, and JAXA Users but are considered applicable to a wider CCSDS community. These
schemes are to be used over space-to-space communications links by space missions.
Use of a common set (family) of spreading codes allows for minimum interference among
Users and keeps signals from exceeding power spectral density limitations. The schemes
described here are from the point of view of a LEO satellite or other satellite below GEO
altitude transmitting to a relay satellite at GEO altitude in the 2 GHz frequency band.
The signals can also radiate upon the Earth and be received by an Earth station. Although it
is not the intent of this document, an agency may choose to use the direct-to-Earth link. In
order to avoid interference between such an operation and the Users of the relay link, the
CCSDS recommends that, if any CCSDS member agency chooses such a link, it uses these
codes so as to avoid mutual interference.
CDMA spread spectrum modulation has the inherent characteristic that the codes may be
used for ranging.
The codes in this book are pseudo random and have been specifically chosen to limit the
signal Power Spectral Density (PSD) at the Earth’s surface and minimize Multiple Access
Interference (MAI).
CCSDS recommends that member agencies that require PN ranging via Data Relay Satellite,
use the codes described in this book.
1.2 SCOPE
This Recommended Standard defines CDMA spread spectrum modulation schemes in terms of:
a) the services provided to the Users of this specification;
b) spreading code formats; and
c) the procedures performed to generate and process the code formats.
It does not specify:
a) individual implementations or products;
b) the methods or technologies required to perform the procedures; or
c) the management activities required to configure and control the system.
CCSDS 415.1-B-1 Page 1-1 September 2011

CCSDS RECOMMENDED STANDARD FOR DATA TRANSMISSION AND
PN RANGING FOR 2 GHz CDMA LINK VIA DATA RELAY SATELLITE
This Recommended Standard provides only those parameter requirements relating to signal
compatibility with the existing SNIP PN spread modulation systems (reference [C1]). There
are many other types of requirements, not specifically related to PN spread modulation signal
formats, which must be met to ensure system compatibility with existing SNIP hardware.
Examples would include forward error correction coding format, data signal formats, etc.
1.3 APPLICABILITY
This Recommended Standard applies to the creation of agency standards and to the future
data communications over space links between CCSDS agencies in cross-support situations.
This Recommended Standard includes comprehensive specification of the data formats and
procedures for inter-agency cross support. It is neither a specification of, nor a design for,
real systems that may be implemented for existing or future missions.
The Recommended Standard specified in this document is to be invoked through the normal
standards programs of each CCSDS agency, and is applicable to those missions for which cross
support based on capabilities described in this Recommended Standard is anticipated. Where
mandatory capabilities are clearly indicated in sections of this Recommended Standard, they
must be implemented when this document is used as a basis for cross support. Where options
are allowed or implied, implementation of these options is subject to specific bilateral cross-
support agreements between the agencies involved.
1.4 RATIONALE
There is a Space Network Interoperability Panel (SNIP) agreement between three of the
CCSDS agencies, NASA, ESA, and JAXA, that use a family of CDMA codes referred to as
the SNIP code family. Recently, other CCSDS space agencies have shown interest in using
similar CDMA techniques. If these agencies used PN spreading codes that were not
compatible with the existing codes, interference and degraded service would be more likely
to occur with both Users of the existing codes and Users of the new codes. The SNIP code
family is limited in number and not sufficient for all of the CCSDS agencies that would like
to participate. In order to promote interoperability and broaden the available set of codes
agencies are permitted to use, CCSDS has developed a new family of codes presented here,
referred to as the CCSDS PN code family, that have the same properties as the codes used by
the SNIP agencies.
The CCSDS believes it is important to document the rationale underlying the
recommendations chosen, so that future evaluations of proposed changes or improvements
will not lose sight of previous decisions.
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1.5 DOCUMENT STRUCTURE
This document is divided into seven numbered sections and three annexes:
a) section 1 presents the purpose, scope, applicability, rationale and structure of this
Recommended Standard and lists the conventions used throughout the document;
b) section 2 provides an overview of PN code usage for CDMA spread spectrum links;
c) section 3 provides requirements that are applicable on a system level for managing
CCSDS Spread Spectrum modulation;
d) section 4 specifies forward service mode PN spread signal formats (network-to-User);
e) section 5 specifies return service mode PN spread signal formats (User-to-network);
f) section 6 specifies PN code requirements relating to network elements;
g) section 7 specifies functional and performance requirements for User element
equipment in a system employing CCSDS PN Spread modulation formats relating to
compatible CCSDS transponder/transceiver;
h) annex A contains link security information;
i) annex B is a glossary of abbreviations and terms used in the document;
j) annex C provides informative references.
1.6 NOMENCLATURE AND CONVENTIONS
1.6.1 NOMENCLATURE
1.6.1.1 Terms Used in Normative Statements
The following conventions apply throughout 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.
1.6.1.2 Terminology Used for Code Groupings
Type Maximal vs. Gold
Family distinguish SNIP and CCSDS PN code sets
Set User group of PN codes (forward, return, coherent, non-coherent)
Library list of all codes used to make code sets for Users
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1.6.2 CONVENTIONS
PN codes are generated by simple linear shift register circuits, called Linear Feedback Shift
Register (LFSR). The values in the tapped stages are combined using modulo-2 addition and
the results are fed back to the first stage of the register on the next shift. The feedback tap
configuration of an N-stage shift register is defined by a characteristic polynomial of order N.
An example of a characteristic polynomial and its corresponding shift register is shown
below in figure 1-1. The maximum length pattern that can be generated with an N-stage shift
N
register is L = 2 – 1.
+
Stage numbers:
12 3 45
2 3 4 5
f(x)=1+x +x +x +x
Figure 1-1: Shift Register with Corresponding Characteristic Polynomial
The notation used in this Recommended Standard follows the above diagram. The feedback
tap locations correspond to the exponents of x with non-zero polynomial coefficients.  In the
2 3 4 5
example polynomial above, f(x) = 1 + x + x + x + x , the feedback taps are on the second,
third, fourth, and fifth stage of the five stage shift register. The first stage has no feedback
tap and corresponds to the zero valued coefficient of x .  The leading ‘1’ in the polynomial
represents x , which is the feedback input to the first stage of the shift register. The output of
the register is from the fifth stage.
Some key points to note about LFSRs and the characteristic polynomial used to describe
them are:
– The length of the shift register (i.e., the number of stages) equals the order of the
polynomial.
– The highest order term of the polynomial is the last stage of the shift register and is
always used in the shift register feedback path.
– The feedback tap represents the ‘1’ (x ) term in the polynomial.
1.7 REFERENCES
This Recommended Standard contains no normative references. Informative references are
contained in annex C.
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2 OVERVIEW
2.1 ARCHITECTURE
Figures 2-1 and 2-2 contain block diagrams of the Network and User elements in a Direct
Sequence Spread Spectrum (DSSS) RF communications system.
DSSS Network
Transmitter
Modulo
Modulator
2 added
I Channel
FWD Link
IData
FWD Link I Chan
PN Code Gen
Carrier
PN Code Clock ∑
Generator
UQPSK
FWD Link Q Chan
PN Code Gen
I:Q = 10:1
90 deg
PN epoch
I/Q chips aligned
to Range
Extractor
Q Channel
Modulator
DSSS Network
Receiver
Modulo
DeModulator
2 added
I Channel Symbol Time
I Data
Recovery
Rtn Link
(Symbol Synch)
I Data
PN epoch
Rtn Link I Chan
to Range
PN Code Gen
Extractor
Carrier
PN Acquisition PN
Acquisition
and Tracking
Code
Received
and tracking
Clock
RF signal
Rtn Link Q Chan
SQPN
PN Code Gen
90 deg
Rtn Link
Not used for
Symbol Time
Mode 3
Q Data Q Data
Recovery
(Symbol Synch)
Q Channel
Modulo DeModulator
2 added
Figure 2-1: DSSS System Network Element Architecture
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CCSDS RECOMMENDED STANDARD FOR DATA TRANSMISSION AND
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DSSS User
Receiver
Modulo
DeModulator
2 added
Symbol Time
I Channel
I Data
Recovery
Fwd Link
(Symbol Synch)
I Data
Fwd Link I Chan
PN Code Gen
Carrier
PN Acquisition PN
Acquisition
and Tracking
Code
Received
and tracking
Clock
RF signal
Fwd Link Q Chan
UQPSK
90 deg
PN Code Gen
Fwd Link Not used for
Mode 2
PN code
Q Channel
Modulo DeModulator
Epoch Carrier
2 added
Synchronization Synchronization
to Rtn PN Generator for Coherent
(also used for spacecraft Rtn RF
clock correlation)
Epoch Carrier
DSSS User
Synchronization Synchronization
Transmitter
For Coherent For Coherent
RTN PN RTN RF
Modulo
2 added
Modulator
I Channel
RTN Link
IData
RTN Link I Chan
PN Code Gen
Carrier
∑
PN Code Clock
Generator
SQPN
RTN Link Q Chan
I:Q = 1:4
PN Code Gen
90 deg
or 1:1
RTN Link Not used for
½ chip delay
Mode 3
QData
Q Channel
Modulo Modulator
2 added
Figure 2-2: DSSS System User Element Architecture
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The network element transmits forward service data to the User element and the User
element transmits return service data back to the network. In these figures, a QPSK type
modulation format is used to transmit the PN spread signals. The forward modulation format
is referred to as Quadrature PN (QPN) modulation, and on the return link it is referred to as
Staggered Quadrature PN (SQPN) modulation since the QPSK chips are staggered (see
7.8.2). However, in order to improve the command signal, a BPSK modulation format could
also be used to transmit the forward PN spread data when RF and PN coherency is not
required. When a spread spectrum BPSK modulation is used, the Q channel sections in
figures 2-1 and 2-2 do not exist.
In both the network and the User transmitters, data bits (or coded data symbols) are placed
into I and Q channels which are spread separately by modulo-2, asynchronously, adding the
symbols to PN sequences. In these figures, distinct pattern PN sequences are used on the
return signals for the non-coherent case and pattern-shifted PN sequences (same pattern,
different phase) are used on the I and Q return channels for the coherent case. The particular
choice of how the Q channel pattern is shifted relative to the I channel pattern is not a
requirement for DSSS, but it does represent this recommendation.
Spread symbol sequences are input to BPSK modulators on each channel, and the outputs of
these are combined to produce the QPN or SQPN signal. At the receiver side, carrier
acquisition, PN acquisition, de-spreading, and symbol timing recovery are depicted as
separate operations, although they may be performed in parallel. Since acquisition requires
both PN correlation and carrier correlation, sweeping the forward link would not guarantee
that both will be achieved simultaneously. Therefore the network element performs Doppler
pre-compensation for the PN code chip rate and carrier.
PN acquisition is accomplished by adjusting a correlator until the timing offset between the
reference PN sequence generated internally and the PN sequence in the received signal are
aligned. When this occurs, the received signal is de-spread.
The transmit User element in figure 2-2 is configured to synchronize the epoch of the return
signal spreading sequences with the received forward signal epoch. This facilitates the
ranging measurement depicted in figure 2-1.
2.2 SUMMARY OF FUNCTIONS
2.2.1 OVERVIEW
The Network Transmitter accepts spacecraft command symbols from the MOC; PN spreads
them and modulates them on the I, command channel. A second, Q channel (range channel),
contains the Ranging PN code but no data symbols, and the two are combined into a QPSK
channel with unequal power, UQPSK. The ranging PN code is also available for the User
Spacecraft Clock Calibration System (USCCS) time transfer service.
The User Receiver de-spreads and demodulates the command symbols and, if used,
correlates its internal PN generator to the received ranging PN code. When the ranging
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service is used, the ranging code phase information is passed to the User transmitter, and,
when the time transfer service is also used, a pulse is output to the User spacecraft.
The chip rates considered in this standard are designed to be coherent with the carrier. The
rates are approximately 3 Mchips/s. The User Transmitter spreads both the I and Q channel
for channel symbol rates at and under 300 ks/s and modulates them in an SQPN format.
When the ranging service is used, the return I channel PN code is in phase with the received
Q channel PN code.
The Network Receiver de-spreads and demodulates the I and Q channel symbols and outputs
PN range code phase information which, when combined with the Network Transmitter
range code phase, results in spacecraft range data. The network receiver also generates
messages required for the time transfer function.
2.2.2 GENERAL
DSSS provides the following functions over a space link:
a) multiple simultaneous Users;
b) reduced power spectral density (PSD);
c) reduction in interference susceptibility (including jamming and multipath); and
d) capability of supporting PN ranging and time transfer operations.
2.2.3 MULTIPLE SIMULTANEOUS USERS
One of the key applications for CDMA systems is to allow multiple Users to utilize the same
frequency band simultaneously to transmit PN spread signals. The composite RF signal in
this band then is the sum of the multiple RF DSSS signals plus any noise or external
interference. Each of the Users is assigned a unique set of PN spreading sequences.
The properties of CDMA are such that when a signal is spread using one sequence,
de-spreading with another sequence leaves the unwanted signal in a spread state. This allows
receivers operating on the composite signal to pull out the signal corresponding to their
assigned PN sequence.
After de-spreading, the composite PSD consists of the desired signal narrowband high power
component plus the wideband, low power contributions from the other Users’ signals (MAI)
and noise. Since the wideband low power PSD contributions from other Users are mostly flat
over the narrow desired signal frequency band, they are often described as ‘noise-like’
interference, and the effect of adding more Users is characterized as ‘increasing the noise
floor’.
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2.2.4 REDUCED PSD
The PSD of a spread signal is greatly reduced compared to that of an unspread signal, by a
factor of the PN rate to the symbol rate. Because of emission spectra restrictions on the
Earth’s surface, this is advantageous when a relay satellite is used and the forward signal is
being transmitted in the direction of the Earth instead of away from the Earth. Since the
return link to a GEO relay satellite, in terms of power emission, significantly exceeds the
direct-to-Earth link, the reduced PSD of PN spreading is again advantageous.
2.2.5 REDUCTION IN INTERFERENCE SUSCEPTIBILITY
DSSS is used to reduce susceptibility to RF interference, whether that interference is
accidental or the result of deliberate jamming efforts. In the receiver, the entire composite
signal (noise, intended signal, and interferer) is modulo-2 added to the high rate PN
sequence. This has three effects. First, it re-constitutes the original high power spectral
density narrowband desired signal. Second, it causes other spread signals to remain spread
and appear noise like.  Third, it spreads the power in narrowband interfering signal over the
wider PN sequence bandwidth just as is done in the DSSS transmitter.
2.2.6 SUPPORT OF PN RANGING OPERATIONS
In a system where RF links between two elements employ PN spread modulation formats,
the spreading code can be used for range measurements. The mechanism by which this is
accomplished is similar to that described in the CCSDS PN Ranging Book (reference [C2])
and described in the series of steps below (the codes in reference [C2] are not appropriate for
CDMA and hence are not appropriate for a near-Earth relay satellite):
a) The element functioning as the network generates a PN sequence, uses this sequence
to spread forward link symbols, and transmits the signal to the User element.
b) The User element (generally a transponder or transceiver) generates the same PN
sequence and uses it to de-spread the forward link symbols. In order to do this, it aligns
in time (correlates) its internally generated sequence with that of the received signal.
c) The User element then generates a second PN sequence (to spread the return link
symbols) aligns the epoch of this sequence with that of the received signal, spreads
the return link symbols, and transmits the resulting spread signal to the first element
(network).  This is called regenerative PN. Transparent PN, where the PN code is
retransmitted without being regenerated, is not considered in this Recommended
Standard.
d) The network element receives the return link signal, generates a matching PN code,
aligns it to the received signal, and de-spreads the return link symbols.
e) The time offset between the transmitted forward link PN sequence and the received
return link PN sequence is a measure of the unambiguous portion of the total round-
trip delay time. By removing the processing time delays, adding the number of
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known PN periods, and multiplying by the speed of light, a measure of the (round-
trip) range is obtained.
2.3 PN CODE TYPES
There are two types o
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