Spatial Compression for Fronthaul-Constrained Uplink Receiver in 5G Systems

Cloud-radio access network (C-RAN) based architecture is widely considered as a fundamental part of 5G networks, where the disaggregation of RAN functionality between a Central Unit (CU) and multiple Distributed Unites (DU) is under hot discussion. With massive multiple-input-multiple-output (MIMO) implemented in the DU part to guarantee the high throughput performance, the limited capacity of the fronthaul between CU and DU becomes the bottleneck for the system performance improvement in the network deployment. Therefore, the spatial compression technique is essential in the uplink receiver structure. In this work, the fronthaul-constrained uplink CU-DU structure is fully discussed and the performance of two alternatives, closed-loop and open-loop spatial compression, are evaluated and compared with 2D cross-polarized antenna arrays. A 2D Kronecker product codebook to dynamically adapt with the antenna array dimension is proposed to achieve better compression performance and it is investigated in the context of the 3rd Generation Partnership Project (3GPP) 5G New Radio (NR) Release 15 standard. The link level simulation results show that the performance with the spatial compression is sensitive with the oversampling size of codebook and reference signal transmission period and the proposed adaptive codebook outperforms the traditional ones.