M.Sc Thesis

M.Sc StudentBraginskiy Evgeniy
SubjectInformation Theoretical Aspects of Cooperation in Wireless
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROF. Shlomo Shamai )Shitz(


We consider a wireless network in which a source terminal communicates  with a destination, while a relay terminal is occasionally present in close proximity to the source without source's awareness. We suggest oblivious protocols, intended to boost the achievable rates when the relay is available, while keeping the rates no lower than those attained for a direct transmission when relay is absent. As a figure of merit we consider maximizing the average throughput. The source-relay collocation induced channel, is modeled by a fixed gain AWGN channel while the source-destination and the relay- destination channels are subject to a block flat Rayleigh fading. A  perfect CSI at the respective receivers only is assumed. The cooperation strategies examined are based on the Decode-and-Forward (DF) scheme- Sequential DF (SDF) and Block-Markov DF (BMDF).This work focuses on the embedding of multi-layer broadcasting strategies  into the aforementioned protocols. A source transmitting strategy using a two layer coding is studied, where the information is split into two superimposed layers corresponding to a "bad" and a "good" channel states, allowing better adaptation to the actual channel state without any feedback link to the transmitter. Continuous broadcasting, in which the transmission is carried out via infinite number of  differential rate layers, is also treated. Two relay configurations are examined:  simplex relay which either  receives or transmits and full-duplex relay capable of simultaneous receive/transmit action. At the destination we first employ the suboptimal successive decoding and  then proceed to the optimal decoding procedure which includes joint decoding strategy. Achievable rate expressions are derived and various system settings are studied as well as the behavior in the limit of infinite SNR under adjusted power  allocation .

For the BM with regular encoding and backwards decoding, the focus is  first put on the single layer transmission. Under a general setting, the uncertainty region of the optimal correlation coefficient is shown to be reduced for an equal source-relay power from the result previously reported and a conjecture regarding the  optimality of the uncorrelated transmission in terms of maximal average throughput is suggested. Also, it is explicitly shown that the BM strategy achieves the 2x1 MISO bound with any positive (in dB) collocation gain for the oblivious setting. The results are then shown to extend to the two-layer transmission along similar lines. For the uncorrelated transmission, the 2x1 MISO bound is attained.