Polar Code Design For Two-way Wiretap Channels And Interference Channels

Polar codes are the first family of channel codes that can provably achieve the capacity of any discrete memoryless channels with low encoding and decoding complexity.They have excellent error performance and have already been adopted by the 5G cellular communication standards.Polar codes are originally designed for point-to-point channels,but recent researches have shown that they can also achieve the capacity regions(or the best achievable rate regions so far)of several multi-user channels,such as multiple access channels(MAC)and broadcast channels.Physical layer security(PLS)has also attracted increasing attention recently,as it does not rely on computational complexity and can guarantee genuine secrecy.As the computational power nowadays grows explosively,tradition upper-layer encryption methods may face great challenges.As a crucial part of a communication system,channel coding techniques can also play an important role in PLS.In this thesis,we study the design of polar codes in multi-user channels and PLS.The main contributions of this thesis include the following three aspects.· We design a low complexity polar coded cooperative jamming scheme for the two-way wiretap channel that achieves the whole secrecy rate region under the strong secrecy criterion.Coded cooperative jamming is an efficient PLS method which allows both users to send useful information simultaneously,while the interference between their codewords can prevent the eavesdropper from obtaining the confidential information.We use rigorous proof to demonstrate the reliability and secrecy of our scheme,and present an example to show the performance of our scheme.Before this work,there was only one paper that presented an explicit code for the two-way wiretap channel,which cannot achieve the whole achievable rate region and can only provide weak secrecy.· We propose a new polar coding scheme for the two-user interference channel(IC)that achieves the whole Han-Kobayashi region,based on a new decoding strategy,which we refer to as partial-joint decoding in this thesis.Existing polar coding schemes for the twouser IC follow the original idea of Han and Kobayashi,in which two auxiliary random variables(ARV)are defined for each sender,and the deterministic mappings from the ARVs to the actual channel inputs are assumed to be known.However,the deterministic mappings might be difficult to obtain in practice.Our proposed scheme is simpler than the existing one as it requires only two ARVs in total and no deterministic mappings are needed.Besides,our scheme has simpler code construction,and can achieve a larger rate region for the same joint distribution of random variables.Further,we extend the partial-joint decoding scheme to discrete memoryless interference networks(DM-IN)and show that it works for DM-INs as well.· We propose a low-complexity,secrecy capacity region achieving polar coding scheme for the cognitive interference channel with confidential messages(CICC)under the strong secrecy criterion.The cognitive interference channel is a basic channel model for the study of cognitive radio.It is similar to the 2-user IC,but one sender(the cognitive sender)knows the other sender’s(the main sender)messages non-causally.Existing polar coding schemes for interference channels rely on the use of polar codes for the MAC,the code construction problem of which can be complicated.Our scheme shows that the whole secrecy capacity region of the CICC can be achieved by simple pointto-point polar codes.This result shows that the cognitivity of an IC not only enlarges the achievable rate region,but also can help simply the code design.Before this work,researches on the CICC mainly focused on the analysis of achievable rate regions.To the best of our knowledge,no explicit coding scheme has been proposed.This thesis shows that polar codes not only are a powerful channel code for traditional pointto-point communications,but also have great potential in multi-user communications and PLS.The research results enriched existing polar coding theories,and can provide guidance in some potential practical scenarios in the future,such as full-duplex communication,non-orthogonal multiple access,and cognitive radio.