CBB’s advanced roaming technology achieves a very low PER (Packet Error Rate).
In some environments using directional antennas, roaming decisions can become complex when faced with radio profiles with erratic levels.
These include the presence of backlobs behind directional antennas, which can distort roaming decisions. In this case, performance is degraded, with a high rate of transfer errors due to poor signal quality.
This type of antenna is widely used in the railway sector for on-board ground communication, as they have a long range and are installed linearly along the track.
When using such a linear topology, the radio system becomes more predictive and roaming cases are better defined.
On this basis, ACKSYS decided to develop a software overlay adapted to roaming in the context of these rail links: PLH (Predictive Linear Handover). As the radio profile in the railway system is easily predictive (directional ground antennas and signal levels that only increase as you approach the antenna, or decrease as you move away from it), this enables us to further optimize roaming phases and to rule out roaming cases that do not correspond to this profile, e.g. connection to antenna backlobs.
Improving roaming performance for on-board ground WiFi communication in metro systems.
This system has been deployed on several Paris metro lines. Significant improvements in performance and quality of service have been observed on the metro.
On the trackside, directional antennas are connected to the RailBox to carry the signal very far.
These antennas are not omnidirectional, but directive. As a result, the signal is mainly located in the front lob of the radiation pattern, while the rear lob is very weak. This is a very specific radio profile.
In train-to-ground communication, when the on-board WiFi client (on board the metro) approaches a trackside AP, the signal gets stronger and stronger, and when it passes the AP the signal degrades very rapidly (drops), leading to an increase in lost packets.
In this case, the most effective solution is the exclusive ACKSYS PLH technology: the connection is immediately made to the front lob of the next AP, ensuring optimum continuity of service.
