Title page for ETD etd-07022008-174027

Type of Document Master's Thesis
Author Akkawi, Bandali K.
Author's Email Address bakkawi@hotmail.com
URN etd-07022008-174027
Title Physical Layer Secrecy Channel Coding
Degree Master of Science in Electrical Engineering (M.S.E.E.)
Department Electrical & Computer Engineering
Advisory Committee
Advisor Name Title
Wei, Shuangqing Committee Chair
Liang, Xue-Bin Committee Member
Naraghi-Pour , Morteza Committee Member
  • security
  • catastrophic codes
  • parallel paths
  • error and LLR correlation
  • SCCC
Date of Defense 2008-06-26
Availability unrestricted
Wireless communications is expanding and becoming an indispensable part of our daily

life. However, due to its channel open nature, it is more vulnerable to attacks, such as

eavesdropping and jamming which jeopardize the confidentiality of wireless data, compared

to its counter-part, wireline communications. Security in wireless communication is

thus a very important factor that should be perfected to accommodate the rapid growth

of wireless communication today.

Motivated by information theoretic secrecy definitions, we adopt a simple way to define

the secrecy of a system by looking at its Bit-Error-Rate (BER) curves, the correlation

of error vectors and Log Likelihood Ratios (LLRs) of the decoded information bits. The

information bit errors and LLRs of a physical layer secure system should be uncorrelated

and the BER curve should have an acceptable sharp transition from high to low BERs

at prescribed signal to noise ratio (SNR) thresholds.

We study catastrophic codes and Serial Concatenated Convolutional Codes (SCCC)

as two candidates. For the former, we provide both detailed analytical and simulation

results, to demonstrate how we can change the encoding parameters to make the resulting

BER curves have the intended properties. For SCCC, we study two options. One is

having a catastrophic code as an inner code. The other is to use regular SCCC. Several

approaches are proposed to change the shape of the resulting BER curves.

In addition, the correlation present in their information bit errors and LLRs are investigated

to see how it can be used to detect or even correct errors. We find that regular

SCCC codes have strong correlation in their error vectors which is captured by the associated

LLRs. In low SNR regions, eavesdropper can easily make reliable decisions on

which packets to drop based on LLRs, which thus undermines the security of the main

channel data. On the other hand, by selecting proper outer codes, SCCC with catastrophic

encoder does not have such a weakness.

We conclude that Catastrophic convolutional codes, as well as serial concatenated

catastrophic codes have desired properties. Therefore, they can be considered promising

approaches to achieving practical secrecy in wireless systems.

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