The mobile radio environment is characterized by fading effects which cause attenuation or even outage of particular links between wireless communication pairs. Fading can be
categorized into (a) large-scale fading, which is caused by distance-dependent path loss
and shadowing and (b) small scale fading, which is caused by multipath propagation.
While the negative effects of large-scale fading can be overcome by planning for reliable communication routes between the wireless nodes, small scale fading effects change within short time that usually does not allow to react with a change of the global communication routes.
The concept of cooperative relaying is a promising means to counteract the effects of
small scale fading. It builds on the concept of cooperative diversity and exploits alternative communication paths by getting assistance from other nodes in the vicinity of sender and receiver of a currently affected communication link. These other nodes act then as relays, i.e., a dedicated or temporarily elected wireless node that assists in forwarding information from a source node to a destination node. The relayed information flow hereby establishes a communication path concurrent to the direct communication flow from source to destination or to communication via other relays. Due to the spatial and time diversity, the alternative path is uncorrelated from the fading effects on the direct link.
The key scientific goals of our research on cooperative relaying include the following:
- Relay selection: what is the decision criteria? by whom, when, and how is relay selection done?
- Cooperative MAC protocols: how do we integrate cooperative relaying into a protocol stack
H. Adam, E. Yanmaz, and C. Bettstetter, “Medium Access with Adaptive Relay Selection in Cooperative Wireless Networks,” IEEE Transactions on Mobile Computing, vol 13., no. 9, pp. 2042-2057, Sept. 2014.
H. Adam, E. Yanmaz, and C. Bettstetter, “Contention-Based Estimation of Neighbor Cardinality,” IEEE Transactions on Mobile Computing, vol. 12, no. 3, pp. 542-555, Mar. 2013.
E. Yanmaz and O. K. Tonguz, “Dynamic Load Balancing and Sharing Performance of Integrated Wireless Networks,” IEEE Journal on Selected Areas in Communications, Special issue on Advanced Mobility Management and QoS Protocols for Next Generation Wireless Internet, vol. 22, no. 5, pp. 862-872, June 2004.