Communication over Asynchronous Networks: Signaling and Rate-Reliability Analysis

Asynchronism inherently exists in many communication systems specially in multi-terminal networks mainly due to the effect of multi-path and propagation delay. While in theoretical analysis of communication systems perfect synchronization of the terminals is often presumed, in some cases in which the nodes are randomly distributed over a geometrical area, it might be impossible to synchronize the nodes even if an ideal infrastructure service provider is used. In this work, two major categories of multi-user communication systems, i.e., relay networks and interference channels, are considered and the effect of the asynchronism among the terminals on characteristic properties of these channels are investigated. In Chapter 2, the construction of distributed space-time codes for a general two-hop asynchronous cooperative relay network is considered. A novel algebraic structure is proposed and shown to achieve full diversity for arbitrary number of relays, arbitrary input alphabets, and arbitrary delay profiles among the relays. Unlike previously proposed delay tolerant schemes, the new design has minimum length which translates into smaller decoding complexity at the same transmission rate. Full-rate and full-diversity are achieved by the new designs with or without the use of guard intervals between successive transmissions. Simulation results confirm the mathematical analysis of the proposed codes. In Chapter 3, the underlying asynchronous network is examined for various relaying protocols such as non-orthogonal selection decode-and-forward, orthogonal selection decode-and-forward, non-orthogonal amplify-and-forward (NAF), and orthogonal amplify-and-forward (OAF). The transmitter nodes send pulse amplitude modulation (PAM) signals, in which information symbols are linearly modulated by a shaping waveform to be sent to the destination, asynchronously. We consider two different cases with respect to the type of the shaping waveforms used in the structure of the PAM signals. In the theoretical case where band-limited shaping waveforms are used, it is shown that the asynchronism does not affect the DMT performance of the system and the same DMT as that of the corresponding synchronous network is obtained for all the aforementioned protocols. In the practical case where time-limited shaping waveforms are used, it is shown that