Two-way amplify-and-forward relaying with carrier offsets in the absence of CSI: differential modulation-based schemes

Wu Zhuo,Li Guangxiang,Wang Tao

doi:10.1186/1687-1499-2014-111

Wu Zhuo, Li Guangxiang + Show 1 more

Open Access

https://doi.org/10.1186/1687-1499-2014-111

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Abstract

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.

Highlights

Two-way relaying (TWR) has attracted much interest recently [1,2,3,4,5,6,7], where two source terminals communicate with each other through an intermediate relay
A multiple symbol double-differential detection based on least squares criteria was proposed in [16], where the system performance was proved to be insensitive to different carrier offsets
Double-differential modulation bidirectional relay networks under carrier offsets we investigate the double-differential modulation for TWR

Summary

Introduction

Two-way relaying (TWR) has attracted much interest recently [1,2,3,4,5,6,7], where two source terminals communicate with each other through an intermediate relay. If the carrier frequency is 2 GHz, the induced Doppler shift may be up to 880 Hz. One technique to mitigate frequency offset is to estimate it at the receiver using a frequency acquisition and tracing circuit and compensate it with single-differential modulation, resulting in increased computational complexity in the relay and reduced data rate [12,13].

Results

Conclusion