LTE relay backhaul design for sparsely-populated environments

In the latest release of the Long Term Evolution (LTE) standards, which will be completed in September 2011, it was decided to standardize relay nodes (RN) for the purpose of improving coverage. This makes RNs very suitable tools for increasing the coverage of low population density areas. The RN is a new type of node that was not previously standardized in 3GPP before and, as such, created new challenges. In particular, for RN, the backhaul link (connecting the enhanced Node B (eNB) and the RN) needs to be defined, and both uplink and downlink grants need to be conveyed to the RNs, either using existing channels (e.g., the Packet Dedicated Control Channel (PDCCH)), or a new channel (commonly referred to as the Relay-PDCCH (R-PDCCH)). In this paper, we discuss both channels for the Frequency Division Duplex (FDD) mode and show that using a R-PDCCH is a more efficient channel. In addition, several features are provided to ensure good performance for the R-PDCCH, such as robust use of frequency diversity by transmitting the R-PDCCH using Distributed Virtual Resource Blocks (DVRBs), or use of rate-matching to ensure optimal usage of the allocated resources for R-PDCCH transmission. This robustness is considered necessary to ensuring good reliability for sparsely populated areas.