ASYNCHRONOUS OFDM PHYSICAL-LAYER NETWORK CODING SYSTEM

Abstract

Recently, Physical-Layer Network Coding (PNC) has been proposed to use traditional network coding (NC) schemes in the physical layer of wireless devices [1]. This is motivated mainly by the broadcast nature of the wireless communications in addition to the ability of the physical layer to perform advanced coding schemes both on the bit and symbol levels. The synchronization issues play an important role in PNC. In fact, the received symbols correspond to the superposition of multiple signals radiated by other terminals. Because of propagation delays, these signals cannot be fully synchronized. In this thesis, we focus on asynchronous PNC system using orthogonal frequency division multiplexing (OFDM) that was proposed in [2]. This approach ensures synchronization between the received symbols by using OFDM with an adequate cyclic prefix (CP). The CP length should take into account the propagation delay of the farthest interesting node. A short CP will allow recombining signals from nearby nodes only. The signals of the other terminals will be considered as noise. On another hand, long CP will allow us to distinguish a large number of signals that could exceed the number of degrees of freedom available at the receiver side. The content of this thesis focuses on understanding the model of asynchronous OFDM-PNC system and then simulation to test the performance of the system. The thesis first describes PNC and the asynchronous PNC based on OFDM. Then, the particular aspect of time misalignment in asynchrony PNC is simulated to confirm the good detection of signals in such situation.