End-to-end communication test on variable length packet structures ...

N95- 17186

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END-TO-END LENGTH

COMMUNICATION

PACKET

TEST

STRUCTURES

ON VARIABLE

UTILIZING

AOS

TESTBED

/iii+i:L

W. H. Miller*,

V. Sank +, W. Fong*,

Folk**,

B. Conaway

+, K. Michael*,

* Goddard i_?::

J. Miko*,

Space

M. Powers*,

J.

P.-S. Yeh*

Flight Center

.

+ Fredrick ** Advanced

II!:_IIL •

Technology

and Research

recommended

This paper

tecture (AOS)

lessly tem.

describes

a communication

demonstrated

the

compressed images These compressed

formatted mittee

into variable for Space

Data

test, which

transfer

of loss-

in an end-to-end images were

length

Consultative

Systems

(CCSDS)

sysfirst

ferred

from

the

Simulations fiber

link,

tem (TDRSS). back and This

Sands to the

Compackets

Complex

decompressed

back

describes

data

acquired

the data

a

Sysat the

the advent space

data more

instruments

data rates national in order

complicated

and formats.

components in order

achievable

speed

which

components, link charac-

variable

to provide

the international

CCSDS

57

between

commercial

plat-

data

for the

AOST

AOS.

The

is implemented

in

insight

limitations diagram

regarding

for actual in Figure

including

net-

of this (GSFC)

flight

1 shows

an instrument

sim-

channel

transfer

is capable

frame

of implementing

the packet

specified

in the .standards

in Figure

2. A salient

book

feature

of

is the ability to transport varipacket, as opposed to the con-

fixed-length allows

generator.

packet

packet data

to be multiplexed

structures.

from

in a much

This

different

instru-

more

flexible

way in the data system. For :data originating from one single instrument, the variable-length packet is also length

a natural bit string

structure resulting

for holding from

ing fixed-length instrument scan line of image data. a

archi-

ulator followed by a packet generator, a high-speed multiplexer, additional instrument simulators, and a

ments

inter-

to issue

block

the data architecture able-length CCSDS

are

to handle

data

to provide and

and re-illustrated

satel-

generate

The desire

The

architecture

in order

data system

a testbed

these key components

testbed

systems

and

of the

hardware

data

scientific

space

stations

developing

The

cross-support across different platforms to better utilize the science data globally

has prompted

been

key

structure

communication

advanced

has

ventional

of sophisticated

becoming

ground

images.

H L_

With

on space

to transport

algorithm,

INTRODUCTION

lites,

forms,

virtual

captured

original

the compression

flexibility

hardware.

transferred

was

the AOST configuration, key flight data formats, and the communication teristics and test results. 1.0

Satellite

was

to the

via

then transmitted

Relay

(WSC)

where

Frequency

(RFSOC),

was

received

AOST

paper

data and Data

The

Radio

Center

where

the Tracking

White

to the

Operations

optic

through

AOST

standard

specified in the Advanced Orbiting System Blue Book [1]. This architecture provides

works. To demonstrate the capability architecture, Goddard Space Flight Center

in the Advanced Orbiting System Testbed (AOST). The CCSDS :data Structures were trans-

: ili__ •

and Associates

Abstract

successfully

!,? ii_ ,

Herold

the variable-

losslessly data,

such

compressas from

a

In parallel with AOST effort, GSFC is also engagedin the developmentof datacompression technology.Data compressionprovides a viable meansto alleviate the demandson onboardstorage,communicationsbandwidth, station contact time andground archive requirements.There are two types of data compression: a losslesstechnique,which guaranteesfull reconstructionof the data;anda lossytechnique,which generallygives higherdata compactionratio but incurs distortion in the reconstructeddata. Losslesscompression generally results in variable length compressed datadue to statistical nature of the original data. To satisfy the many sciencedisciplines, lossless data compression has become the priority for development.After extensive research,the Rice algorithm [2,3] was chosen and developedinto hardware.In 1991,a hardwareengineeringmodel wasbuilt in an application specificintegratedcircuit (ASIC) for proof of concept.This particular chip setwasnamedthe UniversalSourceEncoder/ UniversalSourceDecoder(USE/USD)(Venbrux, 92)[4]. Later, it wasredesignedwith severaladditional capabilitiesandimplementedin Very Large ScaleIntegration(VLSI) circuits using gatearrays suitable for spacemissions.The flight circuit is referredto asUniversalSourceEncoderfor Space (USES).The fabricated USES chip is capableof processingdata up to 20 Msamples/secondand will take dataof quantizationfrom 4-bit to 15-bit [5]. In the following sections, we will provide a brief

description

rithm, AOST

of the

the overall and physical

2.0

THE

data

compression

communication link characteristics.

LOSSLESS

fixed

imagery

Fig. 3. It consists

of a preprocessor

data samples and subsequently symbols suitable for the entropy This

entity

parallel yielding selected.

is a collection

over

a large

the least This

number

selection

of coding

is performed

the

tested

3.0

SYSTEM

3.1

End to End System

The

on various

system

is linked

which

is depicted

via an optical

transmits

the packetized

and

to the

later

transmitted

communication

4.

to the RF data

to the

a TDRS on a at the WSC

AOST

via

NASA

(NASCOM).

Source

3.2.1 Data

in Figure fiber

(WSC) via was recorded

The

instru-

Description

White Sands Complex Ku band carrier. Data

3.2

on typical

DESCRIPTION

end-to-end

The AOST SOC,

codes

of as

[7].

Equipment

Source

source

data

can be either

simulated

instru-

ment data or a video frame of data acquired from a CCD camera. In both cases, the data is first loaded into a frame buffer before each scan line is passed

to the compression

porates

the USE

is then passed cessing.

chip.

hardware

Each

which

compressed

to the packetizer

Packetizer

packetizer

encapsulates

and

is shown

in

operating The

incor-

scan line

for further

pro-

Multiplexer

System

data

over

a fiber optic at a burst

from

the

packets

transmittertransfer

instrument, [8], and sends

receiver

inter-

rate of 80 Mbps.

A

separate packet is formed for each video scan line with the segmentation flag in the packet header used to treat an entire video frame as a large block. The segment flag is set to "beginning

in

segment"

option

for the first scan line of a video

is set to "continuation

bits will be over

takes

it into CCSDS

face (FOXI)

map them into coding module.

range.

input

to signal

Description

to decorrelate

of options

entropy

by the

is used

of Huffman

[6] and has been

ment data

The

algorithm

determined levels,

that of a collection

3.2.2

the

ALGORITHM

of the Rice

of bits,

quantization

selected option for the block. The performance this algorithm has been shown to be the same

them The architecture

number

sample

adaptability field of a

algo-

system,

DATA

COMPRESSION

of J, typically 16, samples to achieve to scene statistics. An identification

a block

58

segment"

scan lines;

and it is set to "end

final video

scan line of a video

data of

frame;

it

for intermediate of segment" frame.

Frame

for the syn-

_;_,_i _!! ¸!il i! i _!_!II_!'

i_!!i_ii_

chronization is derived the FOXI interface. The

multiplexer

service CCSDS i:_i _

?ii

!i!ili_ ii_ i_,i ?i!i¸

:i •

WTFF.

where through

Access

without (VCA)

and

in

1) path

the multiplexer to the Wideband

to the output

on availability

processing and service mode

channel

a round

proto the

is granted

robin

ing

function.

In general,

rate for a channel, and grants

access

hardware 3.2.3

the more

are given

to be data

rate

are provided

driven.

of

Details

of the

in [9].

The

ence

ii

system

is designed

to serve

1, for up to seven

transition,

the pseudo-noise

is utilized.

user virtual

before

being

as necessary

and

are output

Grade-2

channels

service (RS)

to maintain

on a single

3.3

Data

channel

error

from VCDUs

Virtual and

Channel:

formats

or MPDUs,

it into

virtual

channel

at rates

composed

of five interleaved

bytes

255 bytes (10,200

ing check

up to 100 Mbps. each.

bits)

symbols.

long,

circuits to (CVCDUs

with a frame access

synchronization data

unit (CADU)

was

data

of the pattern to the I

synchronization and is neither

received

transferred

patRS

at the WSC

to a workstation

on the I and pro-

with software tools. The Q sent to a communications bit

test set for real

a hardware

time monitoring.

virtual

RS decoder;

a software

channel

and packet

data

decompressor;

display

package

words

RS

detection

soft-

and a soft-

for the workstation.

original

Detector data

as organized

bits in each byte

byte

boundary

is lost.

searches

the received

basis to find the frame ensure that it is the

are

sequence

con-

(32 bits),

59

and knowledge

The

frame

of

detection

file on a bit by bit

synchronization frame marker

bits that happened

marker,

by the

the file position

marker. To and not a

to be the same pointer

was

moved one frame length from the initial marker and data was examined for a second marker. In all a

which

of data

as the frame

into frames

forming a data frame from the WTFF, the

are serialized

(i.e.,

are appended

is created,

Frame

software

the RS encod-

pattern

PN

Equipment

data

is thus 1275

CVCDUs

byte

a stored

the multiplexer

WTFF is a series of bytes structure. Once transmitted the

user

frames

CVCDU

including

When

The

correcting

? • •

channel

Capture

a software

3.3.1

line.

The frames

RS code

Each

gener-

a preset

Fig. 2).

A VC unit receives

CVCDUs) taining

sent through

rate (BER)

ware;

by including

error

it is, each

with

by the PN generator.

encoder;

from

serial

is provided (255,223)

transition

bit

The capture and analysis equipment is composed of a 32 Mbyte solid state memory connected to a Sun workstation via an ethernet; frame detection

(VC)

with frames

code in each of the eight virtual channel form coded virtual channel data units formed

When

or changed

ware image

rate

(PN)

coded

are padded

data

To ensure

The frame separately

frames.

frames

set by hardware.

or Q data outputs. tern is generated

software;

These

controller

re-configura-

Generator:

is XORed

Data messages arriving from VCs are buffered and then standard format data transfer

a Reed-Solomon

_i! !

Transition

plus an idle channel. any one of the user inserted into CCSDS

CCSDS

_iili ¸¸• •_

as a

providing transfer frame generation using of the AOS services, as defined in Refer-

the idle channel !_ii _ _iiiiili_

[10]

system

system

ID (VCID)

PN Code

cessed predominantly channel signal was

WTFF

by the

or during

Data can be received as a fixed length data unit (MPDU in VCA service) or as CCSDS packets (Path Service).

All packetized

(WTFF)

gateway a subset

initialization

data streams.

caus-

Transfer Frame Formatter

Wideband

VC is configured

upon

CVCDU

the

the number

to that channel,

over I or Q output

Each

ator

polling

the higher

can be transmitted

tion and has a unique

passes Transfer

sequence. This polling occurs once every 400 ns, which is rapid enough that it results in a statistical

requests

7i I

signals

where the multiplexer produces multiplexing tocol data units (MPDU) and transmits them

packet

_

control

in two modes:

Frame Formatter (WTFF) 2) virtual channel access

multiplexing

ii_i_ _ _

operates

mode packets

based _i!!_•

through

of the data collected,

a bit slip (or bit addition)

was

neverobserved,makingthe needfor amoreelaborateframe synchronizationstrategyunnecessary. 3.3.2

Reed

After

byte

decoding

alignment

and

frame

Each

detection,

frame

RS

output

from

the RS decoder has a 16-byte status block appended to it. During the data flow with the compressed

variable

length

image

packets,

the error

rates were never severe enough to cause uncorrectable frames. During the portion of the test where the purpose was to evaluate the Ku band physical link using the CCSDS structure, frames that were found

to be uncorrectable

were examined the correctable frames data ated

the data portion

by computer

using

structure, and the parity by re-encoding the data.

were

also retained

raw data determine 3.3.3

not deleted.

of the frame knowledge

portion CCSDS

and RS decoded.

and

Packet

was

of the

was generidle frames The received

was compared with RS corrected burst error statistics.

Channel

and

data

to

pressed

channel

output

identification

found.

Compressed

(VCID) video

particular

application

particular

virtual

file

for each number

packets

were

identification

channel.

The

PACKET

was run on the VCID file of interest separate output files for each APID

was

assigned

(APID)

block

to convert

algoat the

the data back

format. The resulting image file was then accessed

display

software

TEST PARAMETERS ANALYSIS

4.1

Test

Testing

chip,

package.

AND

LINK

variable

length

Parameters

of the AOST

using

packet

structures was performed by using losslessly pressed images. The first image transmitted

comwas a

prestored Landsat image. After the Landsat image was received, real time images from the video camera and packetized data from the simulators routed

through

on the

the link ured

BER.

equipment

and

I channel at 80 Mbps was not used. PN data

the

source

while trans-

RF Q channel The

WTFF

to run at a continuous

was

used

I channel output

to monitor was

config-

rate of 80 Mbps

a Virtual nel #

on a

program

variable

Chan-

Virtual Channel Mode

Data Source

Data Rate

"1'

Path Service

Simulator

16.0 Mbps

2

VCA Service

CCD

-28 Mbps

3 63

Path Service Idle channel

Simulator WTFF

Link

camera

16.0 Mbps as needed

ANALYSIS

Decompressor

The packet data

(USD)

512 sample line as well at the start of each com-

4.0

4.2 3.3.4

16 sample

by a commercial

and produced found in that

VC. The APID file of interest contained length packets of compressed video data.

performed

(including idle channel fill frames) by using an 80 MHz crystal on its high speed output board. The WTFF configuration was as follows:

virtual that

decompression

Decoder

compressed information

output on the WTFF the WTFF Q channel

Detection

the

the operation

Source

to its uncompressed 512x512x8 bit binary

mitted

a separate

Universal

start of each as the header

were

The file created after RS decoding was then processed by a software program called CHANNEL which examined the CCSDS frame header and produced

performed

simulated

realizing the lossless data decompression rithm. The routine used the reference sample

They

for burst error statistics along with frames. When uncorrectable

occurred,

corrected

were

routine

algorithm by the

Solomon Decoding

was performed.

decoding

was

containing

file associated

further

broken

one compressed

512 variable-length one fixed-length

lines image

with down

the image

flame

into a separate image

frame.

file

These

were decoded to generate frame. In software, this

In addition to evaluating compressed variable length packets, this test allowed an examination of il;

the channel characteristics of the K-band Single Access (KSA) return link through TDRSS. The primary objective was to evaluate a BCH code

i!

proposed

::4:

for a LANDSAT-7

300 Mbps

return

link.

fi!

i::i

60 .::::

It was important

••:!•i ¸i•¸_• ii!i!iiiii,!_ili/;'_i

to understand because

the error

character-

istics

of the channel

the proposed

binary

BCH errors

code (1023,993,3) can only correct in a block of 1023 bits. This section

3 bit will

identical to the digital was found to be true. 5.1

Image

concentrate on the performance of the link used in this experiment in terms of BER vs. Eb/No. Link

Since

analysis

independently

was performed

pattern

of NRZ-M

by transmitting

data

at 300 Mbps,

a PN data QPSK

modu-

lated (150 Mbps on I, 150 Mbps on Q) through the KSA return channel. The data was recorded in one minute samples, and six pairs of C/No and BER measurements were taken at WSC with 223-1 and 27-1 PN coded data. The measurements are summarized

in Table

1. Using

noise density, the required ated power (EIRP) values TABLE

1.

C/No,

Measured C/No (dB)

i_• iiii!ii_iii! _• •

the measured

carder

to

effective isotropic radiwere also calculated.

BER and RF SOC EIRP Measured Bit Error Rate

Data Points

EIRP Required for Measured C/No

No streaks

error Loss

the

of the original.

or drop

outs

occurred

compression

in the images.

technique

to each

scan

line,

was

several image observed.

lines,

5.2

Performance

Channel

but

no

One

of the concerns

was

errors

on the TDRS

Ku band

applied

a decompression

would be expected to corrupt of a user data CCSDS frame

examine

This

Quality

an entire line. would impact

corruptions

were

to evaluate

all the parameters

link.

the burst

A test cannot

that vary

over

a satel-

lite's lifetime, but it can at least provide a snapshot of some of those parameters. In order to simulate an end-to-end

system,

95.1

0.8e-3

51.2

95.3

3.5e-4

51.4

96.5

9.0e-5

52.6

WSC and retransmitted fmally decoded.

98.9

2.0e-5

55.0

During

99.3

3.0e-6

55.4

ing (NRZ-M)

99.9

2.0e-7

56.0

the data

the link portion was

The disadvantage

was recorded

to GSFC

at the

before

being

of the test, differential

used

to avoid

of NRZ-M

data

cod-

inversion.

is that it causes

each

A plot of the six data points are shown in Figure 5 along with the ideal BER vs. Eb/No curve. The

error to appear as two errors which may or may not be consecutive. In the data observed, no errors

separation

greater

from

measurement, of the

the ideal

about

data

points.

implementation the required eters were

curve

an average This

value

varied

with

each

consecutive)

was

Landsat

loss. It is important

taken

as the

to note that for

EIRP calculation, several loss paramassumed based on estimates and the was cloudy

settings, lengths

RESULTS

Since

the WTFF

used

the CCSDS

recommended

(255,223) RS code, it was expected that as long as the BER was about 1"10 -4 or better, the RS decoding would expected error

free

correct

all of the errors.

that the decompression and

the

reproduced

It was therefore process image

would would

be be

?i __i::

61

2 bits in length were

7 power where were

(errors

observed level

when

was

the BER seen

used.

was

(Table

were the

greater,

2). For

power

longer

than 11 consecutive correct starts and ends with an error.

bits.

A burst

burst

of incorno more always

BER vs. Error Burst Characteristics

BER

Max Length Burst

2.2e-5

2

2

1.3e-4

14

4

8.5e-4

22

6

The CCSDS

proposed

this analysis,

as a group there were

2.

always

At lower

burst was arbitrarily defined rect and correct bits where

TABLE

5.0

than

of 3.6 dB fo_ five

weather conditions of that day (which with light rain) at the transmit site.

:?il _

version

frame

sequence

of

count

Max Errors Per Burst

was continuous

with no gaps. Bit slips (or additions) were never observed in this or. other AOST tests with the TDRSS.

a

?!ii(:::ii! i:i:i_

H

i:,

:

6.0 ii

CONCLUSION

The

ii_} _

i !ililI _

CCSDS

recommendations

architecture

have

been

compressed

data

being

separate

for

multiplexed channels.

images

AOS

put to a physical

instrument

compressed :_:i_iii!_ {!,

4. Venbrux,

were

data

test with

Losslessly

5. MRC,

decom-

cause

long

of the decompression

streaks

in the recovered

images

operation.

by the variable

length

ing from lossless compression. TDRSS link contained errors purely

thermal

transmitted

(random)

6. Yeh,

from

the

as

packets

This

result-

for data analysis

is

based on statistics gathered during a short period, therefore no statement can be made about the • : ::i ¸

burst

i__/i_ i

i:?

I

environment

that would

the TDRSS antenna of the Earth.

toward

technical 8. Packet January

when

other areas

Flight

nical tion,"

Data

Links:

sultative CCSDS

ii!

?

Architectural

Committee 701.0-B-1

Available

from

nications

and

TS),

National

istration, 2. Rice,

Systems:

CCSDS Data

systems

Commu-

Division

(Code-

and Space

Admin-

DC 20546,

"Some

Con-

Data Systems, October 1989.

Secretariat,

Aeronautics

E,

and

Specification,

for Space Blue Book,

Washington,

Robert

Networks

practical

USA. universal

noiseless coding techniques," JPL Publication 79-22, 1979. Available from author, JPL, 4800 Oak Grove Drive, Pasadena, CA. 91109, USA. 3. Rice,

Robert

Miller,

E, Pen-Shu

"Algorithms

Noiseless Computing Diego, CA,

Yeh and Warner

for High-Speed

Coding,"Proceedings

H.

Universal of the AIAA

in Aerospace 9 Conference, Oct. 19-21, 1993.

the

1993.

E Rice

Optimality

Coder,"

paper Telemetry

and

Warner

H.

of a Universal

Proceedings

of the

AIAA San

San

62

No. 3441,

1993.

Blue Book

CCSDS

102.0-B-2

1987. Wai, "AOST Technical hardware description," Center,

10. Betancourt,

Orbiting

-

7. Yeh, Pen-Shu and Miller, Warner, "Application Guide for Universal Source Encoding," NASA

References 1. Advanced

for Space

Computing in Aerospace 9 Conference, Diego, CA, Oct. 19-21, 1993.

9. Fong, SEMP

be observed

is pointed

Vol. 2, No.

Encoder

Mexico,

Robert

"On

Noiseless

The Ku band consistent with a

GSFC.

Technology,

Source

of New

Pen-Shu,

Miller,

Therefore

environment

N. Liu,

Lossless on Circuits

Preliminary Product Specification, 2.0, Microelectronics Research Center,

University

one can say that the data generation and recovery system worked as expected. No problems were introduced

"Universal

USES," Version

of compressed data is very senerrors which, if they occur,

results

Yeh and Muye

for High-Speed IEEE Trans.

data

and

pressed without any distortion. The achieved compression ratio is about 1.8 for the Landsat image. This type sitive to channel

Pen-Shu

and Systems for Video 4, Dec. 1992.

with several

received

Jack,

"A VLSI Chip Set Data Compression,"

Description: Goddard Space

1994. Jose and Folk,

John,

"AOST

Tech-

Description: WTFF hardware descripGoddard Space Flight Center, 1994.

Video

VC Input

CCD

Camera 1 Buffer Frame

Compressor

[--7 Multiplexe

Computer File

_Data

LJ

Packetizer_

I Is_SJu_ent_

Packetize

0_'_ 1

Frame Formatter (WTFF)

]

RF SOC

Packet Simulator

i_

Packet

|

_i_iiiil _ Simulator_,---_

Figure




packetID I segcnI packetlen I

data field (variable)

.._

16

16

packet

16

CCSDS

1st header

p_

I (k+l)th

kth packet

packet

MPDU packet

(k+2)th

]

MPDU

zone

J

I frameheaderI VCDUdata unit zone

_r]

CVCDU 32

8872

sync ] marker I

CVCDU

I sync I I markerl

10200

Figure

2. CCSDS

63

Data Unit Structure

CVCDU

CADU

:,i iJ

iiii? ii:::il i_('_: ¸

/ii i_! _'• i!iiii!ii: •

Figure _i_ ii_!

3. Rice Compression

Algorithm

i

TDRSS

°u ceI Capture

"_--'---NASCOM

J

¢

f

Figure

4. End to End Test Block

100 .

i

,

•

,

i

,

,

0 _

10-2

Diagram

,

i

,

,

,

i

,

•

,

meosured /dee/ PSK, no cod[n,

w 10-4

m

0 10-6

o 0

10-8 i

8

i

i

10

i

,

i

12

Eb/No Figure

5. End-to-End

64

Test BER

vs. Eb/No

i

i

I

14

i

i

r

16