A Cooperative Network Coding Strategy for the Interference Relay Channel.

In this paper, we study an interference relay network with a satellite as relay. We propose a cooperative strategy based on physical layer network coding and superposition modulation decoding for uni-directional communications among users. The performance of our solution in terms of throughput is evaluated through capacity analysis and simulations that include practical constraints such as the lack of synchronization in time and frequency.We obtain a significant throughput gain compared to the classical time sharing case

Novel transmission schemes for application in two-way cooperative relay wireless communication networks

Recently, cooperative relay networks have emerged as an attractive communications technique that can generate a new form of spatial diversity which is known as cooperative diversity, that can enhance system reliability without sacrificing the scarce bandwidth resource or consuming more transmit power. To achieve cooperative diversity single-antenna terminals in a wireless relay network typically share their antennas to form a virtual antenna array on the basis of their distributed locations. As such, the same diversity gains as in multi-input multi-output systems can be achieved without requiring multiple-antenna terminals. However, there remain technical challenges to maximize the benefit of cooperative communications, e.g. data rate, asynchronous transmission, interference and outage. Therefore, the focus of this thesis is to exploit cooperative relay networks within two-way transmission schemes. Such schemes have the potential to double the data rate as compared to one-way transmission schemes. Firstly, a new approach to two-way cooperative communications via extended distributed orthogonal space-time block coding (E-DOSTBC) based on phase rotation feedback is proposed with four relay nodes. This scheme can achieve full cooperative diversity and full transmission rate in addition to array gain. Then, distributed orthogonal space-time block coding (DOSTBC) is applied within an asynchronous two-way cooperative wireless relay network using two relay nodes. A parallel interference cancelation (PIC) detection scheme with low structural and computational complexity is applied at the terminal nodes in order to overcome the effect of imperfect synchronization among the cooperative relay nodes. Next, a DOSTBC scheme based on cooperative orthogonal frequency division multiplexing (OFDM) type transmission is proposed for flat fading channels which can overcome imperfect synchronization in the network. As such, this technique can effectively cope with the effects of fading and timing errors. Moreover, to increase the end-to-end data rate, a closed-loop EDOSTBC approach using through a three-time slot framework is proposed. A full interference cancelation scheme with OFDM and cyclic prefix type transmission is used in a two-hop cooperative four relay network with asynchronism in the both hops to achieve full data rate and completely cancel the timing error. The topic of outage probability analysis in the context of multi-relay selection for one-way cooperative amplify and forward networks is then considered. Local measurements of the instantaneous channel conditions are used to select the best single and best two relays from a number of available relays. Asymptotical conventional polices are provided to select the best single and two relays from a number of available relays. Finally, the outage probability of a two-way amplify and forward relay network with best and Mth relay selection is analyzed. The relay selection is performed either on the basis of a max-min strategy or one based on maximizing exact end-to-end signal-to-noise ratio. MATLAB and Maple software based simulations are employed throughout the thesis to support the analytical results and assess the performance of new algorithms and methods

Cooperative Compute-and-Forward

We examine the benefits of user cooperation under compute-and-forward. Much like in network coding, receivers in a compute-and-forward network recover finite-field linear combinations of transmitters' messages. Recovery is enabled by linear codes: transmitters map messages to a linear codebook, and receivers attempt to decode the incoming superposition of signals to an integer combination of codewords. However, the achievable computation rates are low if channel gains do not correspond to a suitable linear combination. In response to this challenge, we propose a cooperative approach to compute-and-forward. We devise a lattice-coding approach to block Markov encoding with which we construct a decode-and-forward style computation strategy. Transmitters broadcast lattice codewords, decode each other's messages, and then cooperatively transmit resolution information to aid receivers in decoding the integer combinations. Using our strategy, we show that cooperation offers a significant improvement both in the achievable computation rate and in the diversity-multiplexing tradeoff.Comment: submitted to IEEE Transactions on Information Theor

When Network Coding and Dirty Paper Coding meet in a Cooperative Ad Hoc Network

We develop and analyze new cooperative strategies for ad hoc networks that are more spectrally efficient than classical DF cooperative protocols. Using analog network coding, our strategies preserve the practical half-duplex assumption but relax the orthogonality constraint. The introduction of interference due to non-orthogonality is mitigated thanks to precoding, in particular Dirty Paper coding. Combined with smart power allocation, our cooperation strategies allow to save time and lead to more efficient use of bandwidth and to improved network throughput with respect to classical RDF/PDF.Comment: 7 pages, 7 figure

Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey

This paper provides a comprehensive review of the domain of physical layer security in multiuser wireless networks. The essential premise of physical-layer security is to enable the exchange of confidential messages over a wireless medium in the presence of unauthorized eavesdroppers without relying on higher-layer encryption. This can be achieved primarily in two ways: without the need for a secret key by intelligently designing transmit coding strategies, or by exploiting the wireless communication medium to develop secret keys over public channels. The survey begins with an overview of the foundations dating back to the pioneering work of Shannon and Wyner on information-theoretic security. We then describe the evolution of secure transmission strategies from point-to-point channels to multiple-antenna systems, followed by generalizations to multiuser broadcast, multiple-access, interference, and relay networks. Secret-key generation and establishment protocols based on physical layer mechanisms are subsequently covered. Approaches for secrecy based on channel coding design are then examined, along with a description of inter-disciplinary approaches based on game theory and stochastic geometry. The associated problem of physical-layer message authentication is also introduced briefly. The survey concludes with observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials, 201

Compute-and-Forward: Harnessing Interference through Structured Codes

Interference is usually viewed as an obstacle to communication in wireless networks. This paper proposes a new strategy, compute-and-forward, that exploits interference to obtain significantly higher rates between users in a network. The key idea is that relays should decode linear functions of transmitted messages according to their observed channel coefficients rather than ignoring the interference as noise. After decoding these linear equations, the relays simply send them towards the destinations, which given enough equations, can recover their desired messages. The underlying codes are based on nested lattices whose algebraic structure ensures that integer combinations of codewords can be decoded reliably. Encoders map messages from a finite field to a lattice and decoders recover equations of lattice points which are then mapped back to equations over the finite field. This scheme is applicable even if the transmitters lack channel state information.Comment: IEEE Trans. Info Theory, to appear. 23 pages, 13 figure