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FEC over Wireless Channels using Cryptographic Check Values as Coding Redundancy

FEC over Wireless Channels using Cryptographic Check Values as Coding Redundancy. Belgrade, April 2, 2009 Nataša Živić. Wireless Communication Systems. Wireless communication systems have found heavy deployments over recent years

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FEC over Wireless Channels using Cryptographic Check Values as Coding Redundancy

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  1. FEC over Wireless Channels using Cryptographic Check Values as Coding Redundancy Belgrade, April 2, 2009 Nataša Živić

  2. Wireless Communication Systems • Wireless communication systems have found heavy deployments over recent years • Many popular applications have emerged for wireless networks including, voice calls, SMS, MMS, web browsing and video conferencing, to name a few. • These services not only needs to be provided but rather provided in a secure and reliable manner • Our work focus on reliablity of data transfer, from source to destination, using security mechanisms as a tool ITG-Fachgruppensitzung

  3. Channel Coding & Cryptography • We consider the following two basic limitations of a wireless channel, • Wireless channel is inherently prone to transmission errors • Forward Error Correction (FEC) is used as a solution in those scenarios where the feedback link is missing and thus Automatic Repeat Request (ARQ) can not be used • Wireless channel is prone to the problem of data security too • Cryptography and digital signatures are used as a solution to these problems • Cryptography solves the problems of eves-dropping & digital signatures is a solution to repudiation by the sender ITG-Fachgruppensitzung

  4. Joint Channel Coding & Cryptography • So far, data security and the correction of errors induced by the transmission channel have been dealt separately • In this work we present a novel technique which combines these two different areas together to give a joint solution to both the problems discussed before • We use cryptography (in the form of cryptographic check functions) to improve the BER over the channel • Moreover we use the channel coding to improve the results of cryptography as well • We call this technique as Joint Channel Coding & Cryptography ITG-Fachgruppensitzung

  5. Data Communication (Building Blocks) Data (Text, Audio, video) SOURCE SOURCE ENCODER CHANNEL ENCODER MODULATOR NOISY CHANNEL L-values SINK CHANNEL DECODER DEMODULATOR SOURCE DECODER Received Data (probably with errors)

  6. SOURCE SOURCE ENCODER ENCRYPTOR CHANNEL ENCODER MODULATOR Objective Data (Text, Audio, video) NOISY CHANNEL Received Data (probably with errors) L-values SINK SOURCE DECODER DECRYPTOR CHANNEL DECODER DEMODULATOR L-values

  7. CHANNEL DECODER (SISO) L (1.bit) L (2.bit) L (3.bit)… SOFT INPUT DECRYPTOR Soft Input Soft Input Decryption L = L-Values (Obtained from probability distribution) SID block

  8. Channel SISO Channel Decoder Ordering of bits into an increasing array of their |L|-values Soft Input Decryption Process L Values of bits Decryptor (Verification) Bit flipping No Number of trials exceeded the max? Verification successful? No Unsuccessfully verified data (contains errors) Successfully verified data No Yes Source Decoder Soft Input Decryption Algorithm

  9. CHANNEL DECODER (SISO) Feedback information about correct decoded bits L (1.bit) L (2.bit) L (3.bit)… SOFT INPUT DECRYPTOR Soft Input Soft Input Decryption with Feedback SID block

  10. ma mb … … V: CCF CCF key key nb na block b mb || nb block a ma || na a a a a b b b … … … b b b … … u Assembling message u for Transmission CCF – Cryptographic Check Function

  11. Channel Demodulation SISO Channel Decoding BERcd1 Step 1 Step 1 Segmentation of u‘ (into blocks a‘ & b‘) Block a‘ Block b‘ SID of Block a‘ SID of Block b‘ BER1,SID BER1,SID SISO Channel Decoding SISO Channel Decoding BERfeedback BERfeedback Step 2 SID of Block a‘ SID of Block b‘ BER2,SID BER2,SID Step 3 Parallel Soft Input Decryption Algorithm

  12. Simulation Parameters • 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

  13. Simulation Results

  14. Summary • 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

  15. Thank you very much for your attention!

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