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Monday, May 23, 2011

Ubiquitous Radio Access: supporting Relay Technologies

A fundamental challenge in radio interface design is to introduce functionalities that allow for maximum possible coverage while keeping deployment costs down. Technologies to increase coverage, make use of multihop capabilities by means of flexible relay-based deployments, mesh network architectures, and cooperative communications. The concept of flexible relay-based cell deployment distributes the high capacity available at the inner cell area so as to provide a capacity boost in the outer areas. Advanced PHY layer techniques, such as cooperative relaying, that leverage the relay-enhanced deployment can additionally increase the performance of such relay-enhanced cells.

Ubiquitous Radio Access is based on the concept of the WINNER (WIRELESS WORLD INITIATIVE NEW RADIO) System. The WINNER system is a totally new concept in radio access. It is built on the recognition that developing disparate systems for different purposes (cellular, WLAN, short-range access) will no longer be sufficient in the future converged wireless world. Thus, it provides wireless access for a wide range of services and applications across all environments, from short range to wide area, with one single adaptive system concept.

Both RSs with homogeneous radio interfaces and RSs with different radio interface modes are considered in the WINNER concept. The illustration below shows an example of a WINNER deployment scenario, that combines these two types of RSs for coverage in an urban hot-spot area scenario supplemented by wide-area radio coverage.

Several functions of a wireless communication system have to be adapted in order to work well in relay-based deployments. A proper RRM scheme is essential to achieve the full benefits of a relay-based deployment. For that reason an RRM framework for relay-enhanced cells (RECs) was introduced in WINNER. The proposed flexible resource partitioning for RECs allows the use of relay nodes (RNs) for coverage extension, to cover shadowed areas, and to increase the capacity in the cell. Moreover, cooperative relaying was integrated in the RRM framework. The RRM framework was applied to a metropolitan-area and wide-area deployment scenario to verify its flexibility.

One technology developed to support Ubiquitous Radio Access is Cooperative Relaying and intelligent deployment. In cooperative relaying, a receiving node may combine signals from more than one
transmitting node. This Multihop diversity is one example in which a receiving node combines the signals received from previous nodes in the path. Intelligent deployment describes any method for reducing the probability that an Radio Node has a poor link to the BS and has the effect of reducing the mean path length. Cooperative relaying and intelligent deployment reduce the total cost of a multihop network by reducing the number of relays needed for a given performance.

Another key technology that enables the Ubiquitous Radio Access concept is Spatial Processing Spatial processing techniques make use of the additional degrees of freedom provided by multiple antennas at the transmitter and/or the receiver. MIMO techniques may be configured to provide improved link capacity and SINR.

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