Multi-Carrier (OFDM) Cooperative Transmission in MANETs with Multiple Carrier Frequency Offsets

Cooperative transmission, realized by aggregating several nodes to a virtual multiple input system, is an auspicious approach to establish a more robust and effective communication in MANETs. In such a setup, impairments, i. e. multiple timing and carrier frequency offsets (TO, CFO) will occur. While multi-carrier schemes, e. g. Orthogonal Frequency Division Multiplexing (OFDM), are well-known to mitigate the impact of multipath propagation and TO, multiple CFO causes inter-carrier-interference (ICI) which typically degrades the performance significantly. Within this paper, we propose an effective code and equalizer structure that allows to overcome this limitation. It mitigates the impact of multiple CFO that can be significantly larger than the subcarrier spacing with a reasonable computational effort. For that, we utilize inherent code properties of Linear-Scalable Dispersion Codes (LSDCs) and propose a communication system composed of an equalizer structure in combination with LSDCs that enables multi-carrier distributed cooperative transmission for practical MANETs with high node mobility. We demonstrate the benefits of cooperative transmission in comparison to classical non-cooperative multi-hop or concurrent transmission by outage simulations, which clearly indicate that our proposal can be of crucial importance for the overall MANET scalability. Lastly, we compare our OFDM system with a recently proposed time-domain equalization single-carrier system and point out use cases, where the OFDM system can be more advantageous.