Performance Analysis of Resource Allocation and Interference Mitigation Methods for Inband Decode and Forward Relaying

Abstract

Relay Enhanced Cellular (REC) concept provides a promising extension for the 4G and 5G mobile communication systems. In this regard, Decode-and-Forward (DF) relaying nodes with local coverage and low transmission power enable improved network performance and play an important role in the future mobile systems. This thesis focuses on the performance analysis of dual-hop DF relaying under the overlaying macro-cellular network. As a practical framework, we consider the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) Release 10 and beyond Type 1 inband half-duplex DF relaying.

First, we consider Resource Allocation (RA) between the Relay Link (RL) and the Access Link (AL) that comprise together the end-to-end (e2e) connection between the User Equipment (UE) and the base station (also called as eNB in LTE). We carry out a comparative study of different RA schemes, with main focus in resource optimal RA. For the performance evaluation, we deduce closed-form expressions for the e2e outage and mean rates, and verify results through simulations.

Second, we study the interference mitigation in RL. Due to scarce radio resources interference in RL easily becomes a limiting factor for the e2e data rate. Therefore, we introduce and analyze a simple beamforming technique with limited side information that can be used to mitigate the interference in the RL. Performance results, based on analytic formulas, show that especially in Rician channel the interference mitigation can be effectively executed with only few bit side information from relay to the interfering base station. The mitigation of RL interference improve clearly the e2e data rate in many scenarios.

Third, a case study on the use of outdoor nomadic relay for the in-building coverage improvement is carried out. In case of e.g. emergency the poor in-building coverage and capacity may harness the operations of emergency responders. This problem can be relaxed by employing nomadic relay that is brought close to the site of an emergency. We consider the performance of such REC concept in case of three different building types. It is found that nomadic relay can provide a notable performance improvement for the in-building users.

Results from the mentioned studies show that relaying provides an effective concept to enhance mobile systems coverage and capacity. Yet, from e2e performance point of view it is of crucial importance that special care is spent on the RA between RL and AL, and on the RL interference mitigation. It was also found that a nomadic relay admit good potential when temporary coverage and capacity boost is needed in a local area.