On the Benefits of Moving Relay Nodes in Wireless Networks

Licentiate thesis, 2012

In order to meet the needs of high speed wireless connections, a new generation of cellular network, i.e., Long Term Evolution (LTE) has been standardized and deployed by the 3rd Generation Partnership Project (3GPP). By employing ad- vanced smart antenna techniques, fast channel dependent scheduling, adaptive coding and modulation, etc., LTE offers a very high peak data rate in ideal conditions. However, the capacity of the LTE network is not evenly distributed, i.e., the cell edge users have much worse throughput than cell center users. The successor of LTE, the LTE-Advanced, aims at both further improve the sys- tem capacity and improve the cell edge user experiences. In order to extend the coverage for heavily shadowed or remote areas, and guarantee good user experiences at certain capacity demanding hotspot areas, a heterogeneous and small cell networks (HetSNets) design paradigm has been introduced in LTE- Advanced systems. In this thesis, we study the impacts of the deployment of a new type of relay node (RN), i.e., moving RN (MRN) on current cellular systems. There are several benefits as well as challenges of using MRNs to serve users inside public transportation vehicles. In a noise limited single cell system, the deploy- ment of MRN can significantly lower the end-to-end outage probability (OP) at the user equipment (UE) on board compared to serving the UE by direct or fixed RN (FRN) assisted transmission. The studies have been extended to more practical setups when considering the impact of co-channel interference. In such scenarios, MRN assisted transmission still greatly outperforms direct transmission and FRN assisted transmission in terms of end-to-end OP, when the vehicular penetration loss (VPL) is moderate to high. Moreover, due to the low transmit power nature of an MRN, it generates much less interference to the UEs outside the vehicle, which is very appreciated in a densely deployed urban scenario, since link availabilities are usually dependent on interference rather than on coverage. Hence using MRNs seems very promising for improving the quality-of-service for vehicular users in future mobile communication systems.