RESEARCH Open Access

Two-way amplify-and-forward relaying with carrier offsets in the absence of CSI: differential modulation-based schemes Wu Zhuo*†, Li Guangxiang* † and Wang Tao*† In this paper, differential modulation (DM) schemes, including single differential and double differential, are proposed for amplify-and-forward two-way relaying (TWR) networks with unknown channel state information (CSI) and carrier frequency offsets caused by wireless terminals in high-speed vehicles and trains. Most existing work in TWR assumes perfect channel knowledge at all nodes and no carrier offsets. However, accurate CSI can be difficult to obtain for fast varying channels, while increases computational complexity in channel estimation and commonly existing carrier offsets can greatly degrade the system performance. Therefore, we propose the two schemes to remove the effect of unknown frequency offsets for TWR networks, when neither the sources nor the relay has any knowledge of CSI. Simulation results show that the proposed differential modulation schemes are both effective in overcoming the impact of carrier offsets with linear computational complexity in the presence of high mobility