ANALYSIS AND STUDY ON ERROR CONTROL TECHNOLOGY OF MICRO
SATELLITE FOR REMOTE SENSING
LI Shi-zhong *, HU Xin, Lv Yuan, HU Guo-jun
Xi'an Research Institute of Surveying and Mapping, 710054 Xi'an, China
-xalsz(@0163.net,HuXin327(@sina.com,lvyuang2000@sina.com,hgj 2000@163.com
Commission THS, WG THS/3
KEY WORDS: Data Transmission, Micro Satellite for the Remote Sensing, Error Control, Coding and Decoding, Communication
Control Unit
ABSTRACT:
With the development and the maturity of modern small satellite technology, it is promising and significant to use the new
technology for the Remote Sensing. The paper presents a set of adaptive forward error correction coding theme and finishes analysis
and design for the satellite-earth communication control unit in the light of error control coding and decoding principle and
corresponding high level data link control. We do an experiment using the CCD photographic image of 1632x1032 array at noisy
channel. The statistics of the experiment result indicate: Applications of error control technique enhance the reliability of the down-
link of telemetry parameters such as satellite down-link state, orbit, satellite-borne computer and of photographic image data of CCD
camera.
1. PREFACE
The modern small satellite, which was developed in the middle
of 1980s, is growing promptly in the world and applied widely
in commerce and civilian by reason of its many remarkable
characteristics such as multiple use, small size, light weight,
low cost, short development period, flexible orbit setting and
convenient launching etc. Additionally, the Surrey University in
British, a representative of small satellite development, and
some universities and research institutes, bring forward and
manufacture many kinds of small satellites and micro satellites
successively, that shows abroad application foreground of small
satellite technology. With the development of economy and
technology, especially the advance of the concept "Digital
Earth", the requirement for different sorts of earth observation
information is increasing rapidly. Therefore, using small
satellite technology to strengthen national economic
construction associating with the economic foundation is
imperative under the situation. The paper presents a set of
adaptive forward error correction coding theme and finishes
analysis and design for the satellite-earth communication
control unit in the light of error control coding and decoding
principle and corresponding high level data link control.
2. FUNDAMENTAL PRINCIPLE
Error control coding is also called channel coding in the
transmission of spatial data. The channel coder is to change
input digital sequences of the coder into input coding sequences
of the channel. On the contrary, the decoder is to change output
coding sequences of the channel into output digital sequences of
the decoder. Thus, we can lessen the effects of channel noise to
minimum. That is to say, we can lessen the contrast between
output digital sequences of the decoder and input digital:
sequences of the coder to minimum. The means is to bring in
redundancy via channel coder and resume digital information as
precisely as possible by using the redundancy in decoder. If
selecting a kind of efficient coding and a good project for
decoding, only the lower values of load-to-noise ratio and
signal-to-noise ratio than those of no coding transmission are
needed so far as the fixed error rate and the data transmitting
rate are concerned! ?*
2.1 Coding Type
Commonly there are 2 types of usual codes in the spatial-link
model. One is called Block Codes. The coder cuts continuous
data stream into blocks of k bits and codes each block solely.
That is to take k bits of informational codes into n bits of
channel codes(n>k).The group of channel coding is a codeword
and n is the length of codeword. Another is Trellis Codes.
While carrying out coding operation for informational data
stream, it needn't cut the stream into blocks but processes
continuously. Trellis coder turns a long informational data
stream (which is semi-boundless hardly) to a sequence which
includes redundant code bits. Convolutional Codes are an
important subclass of Trellis Codes. They have the widest
application among Trellis Codes because their coding methods
are simpler than other Trellis Codes.
2.2 Cyclic Redundancy Checking Codes
The (n, k) Cyclic Redundancy Check Codes (CRCC for short)
are a kind of Linear Block Codes. Its code length is n and its
number of informational bits is k. They have the following
attribute: Each cycle shift of any codeword will get another
codeword of the group. That is to say if (Cii, Cy», Cs5,..., Co)
is one codeword of the (nk) group, then (C45, C,5...., Co,
C,.; )is also one codeword of the (n,k) group. Its principle is
shown in Figurel. There are digital sequences p(x), P(x), G(x)
* LIShi-zhong. Xi'an Research Institute of Surveying and Mapping, 710054 Xi'an, China.
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