Measurement and modeling of 3D spatial wireless backhaul channels in NLOS scenarios

With the rising popularity of small-cell deployments, the wireless backhaul solution which is more cost-efficient than the wired infrastructure has become an attractive alternative to forward massive backhaul traffic into core networks. The MIMO technology can facilitate high-performance wireless backhaul by directional transmission/reception using antenna arrays. In this case, accurate measurement and modeling of the three-dimensional (3D) multipath propagation in the backhaul channels are crucial for the design and performance prediction of the MIMO wireless backhaul links. In this paper, a field measurement campaign was performed to characterize the 3D non-line-of-sight (NLOS) backhaul channels between a relay eNodeB (eNB) and its donor eNB in a urban environment. The donor eNB was located on the rooftop of a 5-storey building and the relay eNB was placed at two altitudes at 11 positions. Using a wideband channel sounder with two uniformed planar antenna arrays (UPAs), the angular power spectra (APS) and angular spreads (AS) in both the azimuth and elevation domains at the donor eNB were measured. Then based on the measurement data, the normal distribution models for the APS in the two dimensions are proposed. The correlation between the model parameters and the relay eNB's distance and altitude has also been analyzed. The obtained channel models can help with the deployment of wireless backhaul in cities and also to extend the current 3D MIMO channel models.