Impact of path loss and delay spread on base station cooperation

In this paper, we investigate the maximum inter-site distance (ISD) for performing joint signal processing between cooperative base stations. As a metric, we use the maximum excess delay measured at 95% point of the cumative power delay profile from all base stations. For the distance-dependent channel parameters, we consider Greenstein's statistical propagation model, which we extended for broadband transmissions. We extract all model parameters from 2.6 GHz multi-cell measurements in our field trial and parametrize the model at a fixed ISD. We also investigate the impact of antenna downtilt and find that when a larger downtilt is used, the rms delay spread and 95% excess delay are smaller. However, there are critical 3D effects close to the sites not included in the model. Then we consider larger ISDs and indicate how the delay parameters grow. Based on Greensteins model, the short cyclic prefix in LTE is hardly violated for realistic ISD at 2.6 GHz