In traditional deployment of Radio Access Networks (RANs) the Base Band Unit (BBU) is co-located with the Remote Radio Unit (RRU). Due to the short distance between the RRU and BBU, latency is generally not an issue.
In 5G ORAN architecture the BBU is split into a Distribution Unit (DU) handling real time L1 and L2 communication with the Radio Unit (RU) and a Central Unit (CU) handling the higher layer communication with the backhaul network. For cost and flexibility reasons one CU can serve several DUs and one DU may serve several RUs. This also means that the RUs, DUs and CUs can be located tens of kilometers apart and therefore, latency can become a challenge.
As a supplier of unified ORAN systems Parallel Wireless naturally wanted to test the latency performance of different configurations of hardware, software, and fiber lengths between the units. “Transport infrastructure and long fibers are essential part of our centralized deployment strategy, so it required big investment and research from Parallel Wireless to identify what will be a proper representation of live deployment.” says Sergey Antoniuk, team leader of the Nano Cell systems engineering team at Parallel Wireless. “Finally, we decided to purchase a 20 km long optical fiber cable, and used it in our lab,” he adds.
“The long fiber worked well to validate the performance at 20 km length but, it did not allow us to challenge the system and we realized we were missing a lot of data,” Sergey explains.
“For instance,” he adds, “we wanted to know how far we can go between the RRU and BBU for any standard configuration.
Another topic was to investigate how much the distance can be increased by tweaking the configurations.”
A seemingly obvious way to obtain performance data at more fiber lengths would be to purchase multiple fiber cables with different lengths. However, this solution is too expensive and time consuming since a lot of cables are needed and they must be connected and disconnected manually for each test case. The link is broken each time the cable is disconnected which does not simulate real life situations and, since the cable is fragile, there is a risk of damaging it each time it is handled. Finally, with a fiber cable there is no option to affect only part of the traffic which means that the entire traffic on a specific fiber cable is impacted by the fiber length.