Interference Channels With Half Duplex Source Cooperation
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Interference Channels with Half-duplex Source Cooperation
The performance gain of allowing half-duplex source cooperation is studied for Gaussian interference channels. The source cooperation is in-band, meaning that each source can listen to the other source's transmission, but there is no independent channel between the sources; half-duplex assumes that, at each time instant, the sources can either transmit or listen but cannot do both. This assumption differs from some previous works on source cooperation. When the cooperation is bidirectional and the channel gains are symmetric, the sum capacity is characterized within a constant. When the cooperation is unidirectional, from the primary to the secondary, it is essentially a cognitive channel. By requiring the primary to achieve a rate at most a constant from its link capacity, the best possible rate for the secondary is characterized within a constant. A general coding scheme is proposed for this type of channel. In the first step, only one source transmits and the other source listens. The active source can send data to its destination, share information with the other nodes, or relay data from the other source to the other destination. In the second step, both sources transmit. The shared information from the previous step and the interference channel together can be viewed as a virtual channel. On this virtual channel, the sources can do beamforming for the shared messages, and the destinations can partially cancel the interference, achieving better rates compared with the original interference channel.
Information Theory, Combinatorics, and Search Theory
This volume is dedicated to the memory of Rudolf Ahlswede, who passed away in December 2010. The Festschrift contains 36 thoroughly refereed research papers from a memorial symposium, which took place in July 2011. The four macro-topics of this workshop: theory of games and strategic planning; combinatorial group testing and database mining; computational biology and string matching; information coding and spreading and patrolling on networks; provide a comprehensive picture of the vision Rudolf Ahlswede put forward of a broad and systematic theory of search.
Coherent Cooperative Relaying in Low Mobility Wireless Multiuser Networks
In this thesis, several important aspects of cooperative wireless multiuser networks are investigated. The focus lies on coherent two-hop relaying networks where several amplify-and-forward (AF) relays assist the communication between multiple source-destination pairs. First, the impact of local oscillator (LO) imperfections and I/Q imbalance at the relays on two-hop relaying is investigated. A special focus lies on the comparison between frequency division duplexing (FDD) and time division duplexing (TDD) relays. Based on the observation that the direction in which a channel between two wireless nodes is measured has an impact on the estimate, phase synchronization requirements for coherent relaying networks are then found. Several channel estimation protocols that differ in the direction in which the single-hop channels are measured are furthermore identi'ed and their performance is compared. Next, a very simple phase synchronization scheme is presented that provides a set of relays with a common LO phase. Two coherent beamforming schemes, namely multiuser zero-forcing (MUZF) and multiuser minimum mean squared error (MMSE) relaying, are then investigated. Finally, a real-world demonstrator for distributed wireless communication networks (called RACooN Lab) is presented. It was used to implement coherent cooperative communication schemes on a practical two-hop relaying network.