HOPING TO increase coverage, telecommunications operators are currently looking at customer-installable end-user terminals, such as femtocells. At Spain's Universidad de Cantabria, a 2x2 multiple-input multiple-output (MIMO) channel underwent experimental characterization in typical indoor-outdoor scenarios in the 3.5-GHz band. This work, which was performed by O. Fernndez, M. Domingo, and R.P. Torres, spawned some useful empirical data and models for the deployment of both future and present broadband fixed-wireless-access systems.

The researchers used a transmitter array to emulate a base station positioned on the terrace of a building. The receiver array, which was situated inside a nearby building, represented the end-user terminal. Given the results for the wideband channel, they discovered that the gain of a 2x2 MIMO channel can compensate for capacity degradation due to penetration losses. In addition, frequency diversity was attainable in those channels.

With a stochastic, 2x2 MIMO, wideband channel method, the researchers simplified the modeling approach. Their approach leads to correct channel fitting in both the time and frequency domains with a low number of parameters. The resulting models were accurate, easy to implement, and computationally efficient. See "Empirical Analysis of Broadband 2x2 MIMO Channels in Outdoor-Indoor Scenarios," IEEE Antennas And Propagation Magazine, Dec. 2010, p. 55.