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Universität SiegenUniversität SiegenInstitut für Digitale KommunikationssystemeInstitut für Digitale KommunikationssystemeUniv.-Prof. Dr. Christoph RulandUniv.-Prof. Dr. Christoph RulandHölderlinstraße 3Hölderlinstraße 3D-57076 SiegenD-57076 Siegenhttp://www.dcs.uni-siegen.dehttp://www.dcs.uni-siegen.de
FEC over Wireless Channels using FEC over Wireless Channels using Cryptographic Check Values as Coding Cryptographic Check Values as Coding
RedundancyRedundancy
Belgrade, April 2, 2009Belgrade, April 2, 2009Nataša ŽivićNataša Živić
Wireless Communication SystemsWireless Communication Systems
Wireless communication systems have found heavy Wireless communication systems have found heavy deployments over recent yearsdeployments over recent years
Many popular applications have emerged for wireless Many popular applications have emerged for wireless networks including, voice calls, SMS, MMS, web browsing networks including, voice calls, SMS, MMS, web browsing and video conferencing, to name a few.and video conferencing, to name a few.
These services not only needs to be provided but rather These services not only needs to be provided but rather provided in a secure and reliable mannerprovided in a secure and reliable manner
Our work focus on reliablity of data transfer, from source to Our work focus on reliablity of data transfer, from source to destination, using security mechanisms as a tooldestination, using security mechanisms as a tool
18.04.2008 ITG-Fachgruppensitzung 2
Channel Coding & CryptographyChannel Coding & Cryptography
We consider the following two basic limitations of a wireless We consider the following two basic limitations of a wireless channel,channel,
1.1. Wireless channel is inherently prone to transmission errorsWireless channel is inherently prone to transmission errors Forward Error Correction (FEC) is used as a solution in those Forward Error Correction (FEC) is used as a solution in those
scenarios where the feedback link is missing and thus Automatic scenarios where the feedback link is missing and thus Automatic Repeat Request (ARQ) can not be usedRepeat Request (ARQ) can not be used
2.2. Wireless channel is prone to the problem of data security Wireless channel is prone to the problem of data security tootoo Cryptography and digital signatures are used as a solution to these Cryptography and digital signatures are used as a solution to these
problemsproblems Cryptography solves the problems of eves-dropping & digital Cryptography solves the problems of eves-dropping & digital
signatures is a solution to repudiation by the sendersignatures is a solution to repudiation by the sender
18.04.2008 ITG-Fachgruppensitzung 3
Joint Channel Coding & CryptographyJoint Channel Coding & Cryptography
So far, data security and the correction of errors induced by So far, data security and the correction of errors induced by the transmission channel have been dealt separatelythe transmission channel have been dealt separately
In this work we present a novel technique which combines In this work we present a novel technique which combines these two different areas together to give a joint solution to these two different areas together to give a joint solution to both the problems discussed beforeboth the problems discussed before
We use cryptography (in the form of cryptographic check We use cryptography (in the form of cryptographic check functions) to improve the BER over the channelfunctions) to improve the BER over the channel
Moreover we use the channel coding to improve the results Moreover we use the channel coding to improve the results of cryptography as wellof cryptography as well
We call this technique as Joint Channel Coding & We call this technique as Joint Channel Coding & CryptographyCryptography
18.04.2008 ITG-Fachgruppensitzung 4
SOURCESOURCE
ENCODERCHANNELENCODER
MODULATOR
DEMODULATORCHANNELDECODER
SINK
Data Communication (Building Blocks)
SOURCEDECODER
L-values
NOISY CHANNEL
Data (Text, Audio, video)
Received Data (probably with errors)
Objective
MODULATORCHANNELENCODER
SOURCEENCODER
SOURCE ENCRYPTOR
DECRYPTOR DEMODULATORCHANNEL DECODER
SOURCEDECODER
SINK
L-values
L-values
Data (Text, Audio, video)
Received Data (probably with errors)
NOISY CHANNEL
CHANNEL DECODER(SISO)
SOFT INPUT DECRYPTOR
SID block L (1.bit) L (2.bit) L (3.bit)…
Soft Input
L = L-Values(Obtained from probability distribution)
Soft Input DecryptionSoft Input Decryption
Soft Input Decryption AlgorithmSoft Input Decryption Algorithm
Channel
SISO Channel Decoder
Number of trials exceeded
the max?
No
Source Decoder
No
Bit flipping
No Successfully verified data
Verification successful?
Unsuccessfully verified data
(contains errors) Yes
L Values of bits
Ordering of bits into an increasing array of their |L|-
values
Decryptor (Verification)
Soft Input Decryption Process
Feedback information about correct decoded bits
CHANNEL DECODER(SISO)
SOFT INPUT DECRYPTOR
SID block L (1.bit) L (2.bit) L (3.bit)…
Soft Input
Soft Input Decryption with FeedbackSoft Input Decryption with Feedback
ma || na
block a
mb || nb
block b
a b … b a b … b a … … a b … b
u
…V: …
ma mb
na nb
CCF CCFkey key
CCF – Cryptographic Check Function
Assembling message u for TransmissionAssembling message u for Transmission
Parallel Soft Input Decryption AlgorithmParallel Soft Input Decryption Algorithm
Demodulation
Channel
SID of Block a‘ SID of Block b‘
SISO Channel Decoding
Block a‘ Block b‘
BER1,SID BER1,SID
SISO Channel Decoding
BERfeedback
SID of Block a‘ SID of Block b‘
BER2,SID
Step
1
Step 1
Step 2
Step 3BER2,SID
BERcd1
SISO Channel Decoding
Segmentation of u‘
(into blocks a‘ & b‘)
BERfeedback
Encoder: - Convolutional encoder (1/2) BPSK modulation AWGN channel Decoder: - Convolutional MAP decoder (1/2 and 1/3) Length of SID Blocks: 192 bits (128 bit message and 64 bit cryptographic
check value) 8 (16) bits with the minimal absolute L-values are tested Eb/N0 increased in steps of 0,5 dB For each result (point of curves) 50 000 tests are done
Simulation ParametersSimulation Parameters
Simulation ResultsSimulation Results
Joint Soft Input Decryption and Source Channel Coding
Improvement of arithmetic efficiency of Soft Input Decryption method
Development of new strategies for Soft Input Decryption
Extension of Soft Input Decryption with Feedback to Turbo principle
Analysis of the impact of the channel encoder to Soft Input Decryption
SISO decryption
SummarySummary
Thank you very much
for your attention!