Measurement-Based Evaluation of Spectral Efficiencies in Outdoor-Indoor Multiuser MISO Systems in Femto-Cells

Based on measurements for a street-canyon-type femto-cell, we compare the downlink spectral efficiencies of various intra-cell interference mitigation systems. This includes zero-forcing (ZF), regularized ZF (RZF), and dirty-paper coding (DPC). As a reference for comparison, we consider subsectorization and time-division multiple access (TDMA). Outof-cell interference, treated as additive Gaussian noise, is included in two modes: 1) all cells transmit simultaneously and 2) neighboring cells transmit in alternated time slots. We find that ZF, RZF, and DPC can offer increases in spectral efficiency over subsectorization and TDMA by factors of ~4 under interference-limited conditions. This contrasts with the estimated gains of only ~2 when using a standard 3GPP mode instead of our measured data. This difference is due to the greater inter-cell isolation that characterizes our street-canyon-type test environment. We find that RZF achieves over 80% of the DPC's spectral efficiency under virtually all operating conditions.