LTE Amplify and Forward Relaying for Indoor Coverage Extension

In many countries more than 70 % of the traffic on cellular networks originates or terminates inside buildings. Driven by an increasing demand for mobile data services, the iPhone effect, this number is expected to rise even higher within the next years. When rolling out new systems addressing high speed data needs, e.g. LTE or HSPA+, a cost effective solution is explored by extending the outdoor macro coverage to in-side. In order to reduce the building penetration path loss, a relay can be used in an amplify and forward (AF) or decode and forward (DF) operation for improving the signal quality. The benefits of a DF relay on the achievable LTE downlink indoor coverage extension has been demonstrated in a previous paper. Implementing the DF relay, however, adds complexity to the system and decreases overall air-interface capacity due to the in-band backhauling. The question then arises as to what level of performance can be expected from a straight forward AF system. This paper reports on first measurement results from deploying a standard optical distributed antenna system (DAS) for the LTE downlink at 2.6 GHz in a LTE real-time testbed. Field trials are performed in a single cell single user setup within an indoor office scenario with various MIMO antenna installations. Results show that the full data throughput of 150 Mbps can be transferred from the macro cell to the inside of the building.