Relay Enhanced Cellular Networks

Relay Nodes (RNs) have been proposed as coverage extensions in cellular systems since several years ago. Apart from this main goal of coverage extension, introducing relay concepts can also help in:

- Provision of high-bit-rate coverage in high shadowing environment;

- Reducing average radio-transmission power at the User Equipment (UE), thereby leading to long battery life

- Enhancing cell capacity and effective throughput, e.g., increasing cell-edge capacity and balancing cell load;

- Enhancing overall performance and deployment cost of RAN.

After being carefully considered in pre-standardization activities like WWI / WINNER, relay systems are achieving the level of maturity that is needed in ongoing standardization activities. The best evidence of this maturity is the 802.16j standardization where relays are added on top of 802.16e standard. This recent development has increased the pressure to consider relays also in LTE standardization.

In order to keep LTE competitive it is more than probable that relay extensions to LTE are to be studied within future releases of LTE. Discussions have already started regarding LTE Advanced standardization, and relaying has been proposed as one of the key candidate features

There are many kinds of relay systems proposed starting from the simplest one i.e. amplify/forward (applied in single frequency DVB-H networks, for example) ending up to the most complex one, which utilizes a network coding to improve the overall performance. The most common relay type that is proposed for cellular relaying is a detect/forward type of relay, where an input signal is detected and retransmitted using the same procedure as in the original transmission. Such an approach is assumed in this invention report.

Relaying can be realized at the different layers of the protocol stack. A simple amplify and forward relaying can be realized at the L1 of the protocol stack where the relay is required to have only (some part of) the PHY layer. L2 RNs, which include the protocol stack up to the MAC/RLC layers, enable the possibility of doing decentralized radio resource management. L3 or higher layer RNs could almost be considered as wireless base stations and support all the protocol layers of normal base stations. L3 or higher layer relaying is the main focus of this project, but L1 and L2 relays are also considered when/if necessary.

The main goal of this project is to put a conceptual framework of relaying in cellular networks, with special emphasis on LTE and LTE-Advanced networks. The main focus is on the design of an architectural framework, protocol structure and Radio Resource Management (RRM) mechanisms that are as backward compatible as possible with LTE release 8 systems. Backward compatibility is especially important from the UE side, as it will allow users to benefit from relaying with their LTE Release 8 terminals.