Key Engineering Materials
ISSN: 1662-9795, Vols. 277-279, pp 845-850
doi:10.4028/www.scientific.net/KEM.277-279.845
Journal Citation (to be inserted by the publisher)
©
2005 Trans
Tech Publications,
Switzerland
Copyright
by Trans
Tech Publications
Online: 2005-01-15
Development of RF System Performance Evaluation
Test Set for KOMPSAT-2
Tae Youn Kim, Seong Bin Lim, Yong Sik Chun and Seok Weon Choi
Korea Aerospace Research Institute, P.O. Box 113, Yusung, Daejeon, Korea
Keywords: RF system, communication link, command/telemetry, RF test set, RF test software
KOMPSAT-2, up/down link, satellite automatic system.
Abstract. The satellite RF system is an essential part of the control and management of a satellite
from the ground station and provides a communication link during the entire satellite mission life.
The RF system should be fully evaluated for reliability and stability on the ground, as defined by
the requirements of the satellite mission. The evaluation of an RF system can be verified by
measuring the RF link parameter and then comparing and analyzing the result with the RF system
requirements. Since the system test for satellites requires advanced technology and has a high cost
with limited time, however, it is difficult to access technically for many parts. This paper describes
the design and verification of the RFTS (Radio Frequency Test Set) and the RTS (RFTS Test
Software), which AITC developed in KARI to evaluate a satellite RF system. The developed test
system was used to perform an RF functional test on an ETB (Engineering Test Bed), and the
RFTS’s full functions were debugged to provide a reliable function for the KOMPSAT-2 Satellite
Test. The RFTS showed a high degree of reliability, conformity and repeatability for each test case
at any time. It is now being applied to the RF system evaluation test of KOMPSAT-2 FM during
KOMPSAT-2’s integration and environment test phases. Hereinafter, this system can be applied to
the next generation of satellites as well as to the RF payload system as a unique KOMPSAT series
RF test system.
Introduction
The KOMPSAT-2(KOrea Multi Purpose SATellite-2) satellite, which consists of a MSC(MultiSpectral Camera) payload and a spacecraft bus, is on a sun-synchronous low-earth orbit. The
satellite interfaces with the ground via both S-band (uplink and downlink) and X-band (downlink
only) communications capabilities. The S-band link provides for satellite commanding and
transmits satellite SOH(State-of-Health) data to the ground station. It also has a ranging capability.
The X-band link transmits high-rate image data and may parallel a path for the playback of the
stored SOH and OBC (On-board Computer) mass memory data [1]. This satellite communications
system, which provides the communications link to carry out the satellite mission on orbit, should
be fully evaluated using the RF performance test, which is performed by measuring the RF link
parameters in the various operation modes of KOMPSAT-2 from the development steps. To
perform this RF performance test, a test system is required. AITC thus developed a measurement
system (RFTS) and an operating software (RTS) in KARI. During the RF functional test, the RFTS
provided the KOMPSAT-2 RF environment, and the RF link parameters were measured using the
RTS [2]. The results of the test were used to evaluate the system, the performance of which was
found to be suitable for the KOMPSAT-2 requirements. This paper describes how the RFTS and the
RTS were designed and verified. Moreover, it describes how the RF system was evaluated using the
performance test. The function of the developed system was verified using several steps, and
reliable and repeatable results were shown through the RF functional test on the ETB of
KOMPSAT-2. The verified RFTS and RTS were used to evaluate the RF performance of the
KOMPSAT-2 FM system during the integration and test phases.
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans
Tech Publications, www.ttp.net. (ID: 130.203.136.75, Pennsylvania State University, University Park, USA-16/05/16,20:18:55)
846
On the Convergence of Bio-, Information-, Enrivonmental-, Energy-, Spaceand
Title of Publication
(toNano-Technolgies
be inserted by the publisher)
Design of the Radio Frequency Test Set (RFTS)
System Architecture. Fig. 1 shows a block diagram of the RFTS. The RFTS is designed to
provide the command and telemetry link functions via the RF links and to measure the RF system
parameters during the integration of KOMPSAT-2. It consists of the following instruments:
An RTS for the operation of the RFTS and measurement of the RF parameters;
A frequency synthesizer for the provision of an uplink signal to the satellite receiver;
A test system receiver for the provision of telemetry data to the TCTS (Telemetry
Command Test Set);
A spectrum analyzer for analyzing the downlink signal spectrum;
A frequency counter for the measurement of the ranging time delay;
A power meter for the measurement of the downlink signal power; and
Switching modules for the conditioning and monitoring of the RF/base-band link signals.
The base-band signal from the TCTS or the simulated ranging tone from the RFTS itself is
delivered to the frequency synthesizer and modulated onto the uplink carrier signal. The modulated
uplink carrier signal is sent to the spacecraft through the RF switch and the RIU (Remote Interface
Unit). The RF switch matrix provides up/down link paths and makes the path up to the RF signal
analyzers. The up and down link signal characteristics were measured using a spectrum analyzer, a
power meter and a universal counter. The downlink signal was demodulated using a test set
receiver, and the demodulated base-band signal was sent to the TCTS through the base-band signal
conditioner.
Fig. 1. RFTS Block Diagram
Functions. The RFTS is designed to execute the modulation/demodulation of S-band
up/downlink signals through the RIU, which provides an RF signal to KOMPSAT-2. The link
carrier power level should be limited for the safety of the flight hardware through the coupled
attenuation of the RIU. The major function of the RFTS is decided according to the KOMPSAT-2
system specifications. It is designed to perform the following functions:
Receives the base-band command (BPSK modulated 2 Kbps NRZ-M (Non Return to ZeroMark) command stream on a 16-kHz subcarrier) from the TCTS and modulates onto an
uplink carrier signal;
Receives the telemetry data (BPSK modulated 2 Kbps NRZ-L (Non-Return to Zero-Level)
real time telemetry on a 1024-MHz subcarrier or direct PCM (Pulse Code Modulation) 1.5
Mbps NRZ-L playback telemetry on the main carrier}, demodulates the carrier signal and
passes the resulting base-band signal to the TCTS (There are two modes of operation for K-
Key Engineering Materials Vols. 277-279
Title of Publication (to be inserted by the publisher)
847
2: the low- and the high-rate modes. The low-rate mode is a 2.0-kbps sub-modulated data
and the high-rate mode is a 1.5-Mbps direct modulated signal. Normally, K-2 operates in
the high-rate mode and keeps in the low-rate mode for contingencies);
Generates a simulated ranging signal and modulates it onto the command link, and then
measures the time delay from the demodulated base-band signal and compares the received
ranging signal to the transmitted ranging signal; and
Performs the leveling set function of the command signals, the measurement of both the
command and the telemetry link parameters, the routing of the link signals, and the display
of the current test system status to include the configuration, the telemetry lock status and
the attenuator settings.
Development of the RF Test Software (RTS)
Design. The RTS should be designed to obtain the KOMPSAT-2 RF link parameters as well as to
manage the interface of the RF system. It is designed for automatic test system configuration and
measurement of the RF parameters. It was developed using the Visual C++ program. It receives a
command message from the SATS (Satellite Automatic Test System), parses a command message,
executes a command function, analyzes an uplink and downlink signal characteristic, modulates the
base-band signal, demodulates the downlink signal, and supports the network functions [3]. The
RTS consists of the following program modules that perform the defined functions:
The main measurement functional program and subroutines;
Instruments: S/W drivers and control program;
The networking program (SATS communication links);
The telemetry data formatting program;
The message and global file-handling program;
Acceptability through an automatic test sequence under the direction of the SATS;
Uplink and downlink calibration with compensation of path loss; and
Database control.
Functions. The RTS’s functions are mainly analysis of the satellite RF system’s characteristics
that are included in the command acquisition, the command lock, the command threshold, the
telemetry modulation index and the RF system time delay. It also performs uplink/downlink
calibration and uplink power set-up. More importantly, the RFTS command processor receives a
command message from the SATS and decodes a command message, and then executes the
functions. The executed command function calls the subroutine and the library function and handles
the global files, the test log file and the instrument drivers. The main functions of the RTS are
shown in Table 1.
Table 1. The RTS’s Main Function
RTS Function
RFTS Command Processor
Command Acquisition
Command Lock
Command Threshold
Power Set
Ranging Frequency
Telemetry Mod. Index 1
Telemetry Mod. Index 2
Time Delay
Down Calibration
Up Calibration
Description
Test system operating command processor
Measurement of the command acquisition
Satellite receiver locking
Measurement of the command threshold
Setup of the uplink signal power at a nominal level
Measurement of the ranging tone power flatness
Measurement of the low rate telemetry mod. index
Measurement of the high rate telemetry mod. index
Measurement of the RF system time delay
Downlink calibration with path loss
Uplink calibration with path loss
848
On the Convergence of Bio-, Information-, Enrivonmental-, Energy-, Spaceand
Title of Publication
(toNano-Technolgies
be inserted by the publisher)
Message Communication. An example of the test system configuration command format is
described in Table 2. The format has a message type, a source/destination node, a message number,
a command counter and a format flag, commonly a header byte. Data is assigned to the appended
tail byte according to the message type. The data format is as follows:
Configure command and status (SATS ⇔ RTS)
Test data set (RTS to SATS)
Spacecraft command request and status (RTS ⇔ SATS)
Spacecraft telemetry request and response (RTS ⇔ SATS)
Error message (RTS ⇔ SATS)
Shutdown request and accept (SATS ⇔ RTS)
Table 2. The RTS to SATS Interface Format Example
Items
Message Type
Source Node
Destination
Message Number
Not Used
Command Count
Format Flag
Command Mne
Not Used
Argument 1… 8
…
Total
Length [bytes]
2
8
8
2
2
2
2
8
2
4*8
Type
Char
Char
Char
Short
Char
Short
Char
Char
Char
Ch/Fl
Contents
“CO”
“SATS” + Space (0x20)
“RFTS” + Space (0x20)
Number of the command in a packet
“MN”
Mnemonic string
Argument 1 ~ 8 (4 bytes an argument)
Repeat Format Flag ~ Argument 8
464
Verification of the RFTS with the Test Software
The RFTS and the RTS should be designed with a high degree of reliability for both the hardware
and the software. Their functions are evaluated in three stages, such as the development test, the
limited functional test and the full functional test. The development test verifies the basic functions
of the RFTS and the RTS. In this phase, the function of the instrument, the interface of the test
system, and the measurement of path loss/time delay in the loop back mode are verified. The
limited functional test is performed with the completely integrated RFTS and RTS using the
simulated signal. It validates the function of the calibration for the up/downlink path and the
measurement, which is composed of the downlink carrier power, the ranging time delay and the
modulation. The full functional test is performed on an ETB platform. This test evaluates the
debugged RFTS itself as well as the parameters of the KOMPSAT-2 RF system. It also measures
the transponder output signal modulation index, the command acquisition, the receiver threshold,
the command lock and other functions, using the SATS (Satellite Automatic Test System) via an
Ethernet link. Through these stages, the RFTS with the test software verifies that the functional test
result is repeatable and acceptable in the satellite RF test.
Evaluation of the RF System
The KOMPSAT-2 RF system was evaluated by performing the RF functional test through the
developed RFTS and its operational software, RTS. RF functional tests are included in the
measurement of the RF path loss through the RF assembly and the RF link parameters, which are
composed of the command acquisition, the command lock, the command threshold, the telemetry
modulation index and the ranging time delay. Fig. 2 shows the RF functional test configuration for the
evaluation of the KOMPSAT-2 RF system on an ETB. Table 3 shows the RF functional test matrix.
Key Engineering Materials Vols. 277-279
Title of Publication (to be inserted by the publisher)
849
Fig. 2. KOMPSAT-2 RF Performance Test Configuration
Table 3. KOMPSAT-2 RF Functional Test Matrix
No.
1
2
3
4
5
6
7
Test Item
S-band Communication Link
Downlink Signal
Modes of Downlink Signal
Communication Mode Selection
Downlink Phase Modulated Carrier
Compatibility with S-band SGICD
RF Uplink Signal
Modes of Uplink Signal
Uplink Data Rate
Ranging Delay
Ranging Capability
Linear Modulation for Ranging Mode
Turn-around Signal Mod. Index
The downlink signal, the modes of the downlink signal, the communications mode selection, and
the downlink phase modulated carrier were tested by measuring the modulation index in the realtime and playback modes using the RTS. Compatibility with S-band SGICD, the RF uplink signal,
and modes of the uplink signal were obtained by measuring the command acquisition. The uplink
data rate measured the command threshold and the command lock status, and the ranging delay
measured the ranging turnaround time delay by the RTS. The KOMPSAT-2 RF system functions
can be measured with the RFTS software functions. In the RTS functions, the modulation index is
calculated using the carrier signal level, modulation loss, and the Bessel functions. The low-rate
(real-time mode) mod. index was obtained from the ratio of the carrier power and the first side lobe
power, and the high-rate (playback mode) mod. Index and ranging were obtained from the ratio of
the unmodulated carrier power and the modulated carrier power. The command threshold verifies
the receiver tracking threshold for a command, and is proved using the uplink power level when the
command lock is lost. The command acquisition measures the probability of the receiver command,
and is verified by counting the number of acquired commands and comparing this with the number
of continuous commands. The time delay for measuring the ranging was calculated using the phase
difference between the loop back time delay of the RFTS and the time delay of the RF system.
Table 4 shows the RF performance of KOMPSAT-2 ETB. The test results were satisfactory
850
On the Convergence of Bio-, Information-, Enrivonmental-, Energy-, Spaceand
Title of Publication
(toNano-Technolgies
be inserted by the publisher)
compared with the requirements of KOMPSAT-2. During the test, all the test commands were
manually handled to verify the RTS function, and the RF subsystem was configured for an A-side
nadir/zenith antenna and a transmitter/receiver A.
Table 4. Measurement of the RF Link Parameter
Test Functions
TLM D/L Mod. Power
TLM Mod. Index
Ranging Mod. Index
Test Results
36.06 [dBm]
1.01 [rad] (required: 1.0 rad±12%)
0.389999 [rad] (required: 0.4 rad±3%)
Ranging Freq. Response
1.419662 [dB]
Ranging Time Delay
Total: 1757 [nsec] / Loop: 375.5 [nsec] / Del. Time: 1381.5
[nsec] (required: less than 3000 ns )
TLM D/L Mod. Power
36.06 [dBm]
RCVR. Command
Threshold
Carrier Threshold: -133 dBm
Command Threshold: -129 dBm (required: minimum -123
dBm)
RCVR. Acquisition
Probability
100% (required: greater than 99%)
Conclusions
This paper describes how the RFTS and the RTS were designed and how the RF system was
evaluated using a functional test. The RFTS was developed to perform command and telemetry link
functions via the RF links and to execute the modulation/demodulation of the S-band up/downlinks,
and the RTS was designed to analyze the characteristics of satellite RF systems and to measure the
RF link parameters. Its functions are verified using the RF functional test on an ETB. The test
results show that the RF system of the KOMPSAT-2 can be easily verified and reviewed, and test
time can be reduced, using the automatic test set. This test set is now being applied to the evaluation
test of the RF system on KOMPSAT-2 FM during its integration and environment test phases.
References
[1] KARI: KOMPSAT-2 Telemetry, Command and Ranging Subsystem Specifications (Korea
Aerospace Research Institute, Daejoen, Korea, 2002), K2-SP-480-001.
[2] S. Lim, S. Lee and T. Byoung: Introduction to the Concept Design of the RFTS for
KOMPSAT-2, Proceedings of the KSAS Fall Annual Meeting (2000), pp. 187.
[3] J. Park, J. Choi and Y. Chun: The Development and Operation of a Spacecraft Automated Test
System, Proceedings of the KSAS Spring Annual Meeting (2000), pp. 145.
[4] KARI: KOMPSAT-2 Telemetry, Command and Ranging Subsystem Analysis Report (Korea
Aerospace Research Institute, Daejoen, Korea, 2002), K2-D0-480-001.
[5] E.A. Lee and D.G. Messerschmitt: Digital Communication (Kluwer Academic Publications,
1997).
[6] M. Richharia: Satellite Communication System Design Principles (McGrawhill, 1995), pp.
188~214.
On the Convergence of Bio-, Information-, Enrivonmental-, Energy-, Space- and Nano-Technolgies
10.4028/www.scientific.net/KEM.277-279
Development of RF System Performance Evaluation Test Set for KOMPSAT-2
10.4028/www.scientific.net/KEM.277-279.845