Heterogeneity and multi-cell cooperation in wireless cellular networks

The performance of most urban cellular networks is limited by inter-cell interference. This is particularly true of a cellular network with heterogeneous infrastructure, wherein the same spectrum is shared by different types of base-stations such as macro-cells, pico-cells, femto-cells and relays. Performance of such dense/heterogeneous deployments may be greatly enhanced through the use of smart association techniques, coupled with adaptive interference management. Unlike traditional cellular systems where association is predominantly based on maximizing signal quality between the base-station and the user, a smart association scheme in a heterogeneous network should be based on several additional criteria such as aggressive load-balancing, path-loss minimization, or minimization of interference to other links. Aggressive load-balancing (in particular) requires advanced interference management, which can may be realized through (soft) resource partitioning, beam-coordination or joint signal processing at the base-stations. Multi-cell signal processing (or distributed MIMO) can be used in homogeneous networks as well, in order to mitigate inter-cell interference without compromising degrees of freedom associated with the transmit signals. In this tutorial, we demonstrate how these techniques may be incorporated into the design of a cellular system, and the performance gains resulting from such a system design.