Network operators are struggling on how to release broadband mobile services in highly dense and hot-spot scenarios. The 5th generation of mobile networks is targeting per user downlink and uplink rates of 300 Mb/s and 50 Mb/s respectively. In ultra-dense environments such as stadiums, airports, shopping malls and tourist hot-spots, the aggregated bit rate becomes enormous. To make it more concrete, Belgium’s national football stadium (King Baudouin) is taken as example. The stadium can accommodate 50.000 spectators. Even if an average bit-rate of only 50 Mb/s needs to be provided, an aggregated bit-rate of 2.5 Tb/s is required. Given the small area of a stadium (18 000 m2 seating area), this results in an astonishing capacity per area of 140 Tb/s/km2 or 140 Mb/s/m2. This is a 10-fold increase compared to area traffic capacity targeted in 5G and a 100-fold increase compared to the current 4G technologie.
Especially for hotspot environments, Distributed MaMIMO (Massive MIMO) is a very interesting approach. To go beyond the capacity per area envisioned in 5G and support very high bit rates in ultra-dense environments, the MaMIMO technology should be exploited at mm-wave frequencies (typ. 28 and 60 GHz range). However, this comes with an additional difficulty: MaMIMO demands a very rich scattering environment to support a very high number of orthogonal streams. However, the absorption at mm-wave frequencies limits scattering. To overcome this, a distributed antenna system (DAS) was developed. Instead of relying on passive scattering, different antennas can be distributed to mimic reflections actively. However, very tight synchronization of the transmitted signals is required, which requires full centralized processing.
In BI-SDMoF, we further developed bit-interleaved sigma-delta modulation over fiber to connect the antennas with the central unit. This approach combines the different advantages of both analog RoF and classical digital CPRI-based solutions.
The project has realized a BI-SDMoF-enabled distributed antenna system (DAS). In the system, sigma-delta-modulated signals are interleaved and transmitted via optical links between the central site, called distributed unit (DU) to align with the 5G next-generation RAN (NG-RAN) terminology, and the remote radio units/heads (RRUs/RRHs). This setup was realized using a RRU consisting of an in-house developed 4-channel transceiver and an FPGA, and had as primary goal to demonstrate frequency and timing synchronization over the fronthaul.
The major impact is expected in the 6G area (and all its application possibilities, e.g. augmented and virtual reality), and more specifically to implement cell-free Massive MIMO solutions.
