Cellular system deployment has reached practical limits in many dense urban area while data traffic only continues to increase. This leaves cellular operators with few options to increase the most important metric: area spectral efficiency. Unfortunately, radio link improvements including coding, cognitive transmission, and multiple antennas are reaching their theoretical limits. Consequently, network operators are revisiting conventional cellular system topologies and are considering a new paradigm called heterogeneous networks.
Heterogeneous networks consist of planned macro base station deployments that typically transmit at high power overlaid with several low power nodes such as pico base stations, distributed antennas, femto base stations, and relays. The low power nodes are deployed to eliminate coverage holes in outdoor and indoor environments and also to increase the capacity/area of the network. Remote radio heads or distributed antennas are connected to the macro base station using a high bandwidth low-latency dedicated connection. These radio heads have minimal autonomous intelligence and act as extensions of the base station antenna ports. Fixed relays are infrastructure equipment that connect wirelessly to the network backbone. These relays aid in the signal transmission between the macro base station and the mobile users by receiving and retransmitting the signal. Relays offer flexible option where wireline backhaul is unavailable or not economically feasible. Picocells and femtocells are new small base stations installed in dead spots to increase the coverage and capacity. A major advantage of femtocells as compared to picocells and distributed antenna systems is that they do not need to be planned and maintained by cellular operators: they are connected to the core network through a last-mile Internet backhaul.
My research group is investigating several components of heterogenous networks including relays, distributed antenna systems, and femtocells. One focus has been on analyzing the impact of out-of-cell interference, and developing practical techniques for managing interference. We are also investigating the interaction between different components of heterogenous network, for example the simultaneous deployment of femtocells and relays in the same cell. Check out the links on the left for more details about specific research projects.