京都大学 大学院情報学研究科｜通信情報システムコース

A goal of this talk is to provide audience with the knowledge about the relationship between lossy-forwarding relay systems and the Distributed Coding techniques for correlated sources.

This talk will be started by briefly reviewing the historical background and progress of Information Theory and Signal Processing for Wireless Communications. Especially, how and why iterative (turbo) decoding can achieve asymptotically the close-limit performance will be addressed. Then, the focus of this talk is shifted to cooperative communications. It is shown that performance of the conventional decode-and-forward system can significantly be improved by performing another interleaving at the relay, with which the resulting network structure is equivalent to distributed turbo code. Furthermore, since the knowledge about the bit error probability of the source-relay node can be used as the correlation between the two frames, one from the source, and the other from the relay, we can well exploit the Slepian-Wolf theorem; With the utilization of the theorem, the relay can forward the frame even though it detects errors in the information part, and the destination can recover the data losslessly.

Then, this talk further introduces the idea, from lossless-likn-design-based to lossy-based. In this part, we assume that none of the relays at the final stage has no errors in the information parts of the frames. This category of the problems belongs to Distributed Lossy Coding, represented by the Chief Executive Officer (CEO) problem, in Network Information Theory. This talk briefly explains major results of analysis we have achieved up until now, but because of the time limitation, we do not go into very deep level of mathematical derivations of the formulas.

Finally, this talk briefly introduces “Links-on-the-fly Technology for Robust, Efficient and Smart Communication in Unpredictable Environments (RESCUE) a EU FP7 ICT-2013 project, of which concept was motivated by the technological bases described above. The objective of the project is to create energy- and spectrally-efficient communication systems which are robust against unpredictable network topology changes. The origin of the project proposal is that massive earthquakes including series of aftershock hit the Tohoku and Kanto areas in Japan on March 11, 2011, followed by unprecedentedly huge Tsunami waves of up to 40 m height. After the huge devastative/disastrous event clearly indicated several limitations in operability of the conventional wireless communication systems based on the accurate link budget allocation concept and communication chain design (coding, signaling chain, as well as also higher layer protocols), and the continuation of the communication is supported by a proper handover algorithm. The systems, which are expected to keep its operability in unpredicted network damages, have to be robust against the network topology change.

The results are expected to be applicable to machine-to-machine and vehicle-to-vehicle communications as well as communication for internet-of-things since they should also require the robustness against the network topology change, and have to be highly energy-efficient. This talk provides the participants with the knowledge of technological bases towards achieving this goal, performance limit/outage derivations, and some practical coding/decoding algorithms. The issues described above are explained mainly from the viewpoint of lossless/lossy distributed correlated source coding theorems in network information theory.