Multi-Frame Distributed Protocol for Analog Network Coding in Slow-Fading Channels

The wireless network scenario here is based on N users that communicate one with the others through a central relay node by adopting the Analog Network Coding (ANC) paradigm. In this paper, we propose a communication scheme for ANC able to guaratee the simultaneous transmissions of N ¿ 2 interfering terminals using the concept of multiuser processing (i.e., channel estimation and detection). Under the assumption of slow-varying channels, multi-link channel estimation is achieved through the coherent summation at the physical layer of the invariant training sequences over the different frames, thus enabling multiuser detection. Benefits of the proposed ANC protocol are stressed through comparisons with the traditional TDMA-based routing scheme where the relay is time-shared among the different users. Impacts of the hindrances to our scheme (namely, hardware impairments at the nodes and finite coherence-time of the channels) are also investigated by numerical analysis. The proposed algorithm enables the employment of simple sense-before-talk policies at each user interested in accessing the network, thus avoiding complex forms of centralized coordination by the relay.