LAUSR

We propose a method that establishes a direct wireless link from a transmission source to an out-of-range destination with the assistance of the surrounding communication nodes. In this method, a weak (subthreshold) signal is amplified by utilizing the interference signals transmitted from the surrounding communication nodes. To evaluate the amplification gain, we study the mutual information in a multipath fading channel. As a result, we reveal that the mutual information is enhanced owing to the interference signals, and the proposed method enlarges the radio coverage area of the source node. To understand the enhancement mechanism, we introduce a toy model of the propagation channel and discuss the role of the interference signals. We find that the interference signals allow the subthreshold signals into the detectable region in the signal space. Moreover, the mutual information is maximized at the optimal power of the interference signals. In addition, a detailed discussion of the channel capacity shows that there exists an optimal a priori probability of symbol transmission.