Overview of Vehicle-Ground Fast Link Handover

Definition

Huawei's vehicle-ground fast link solution uses WLAN Mesh technology to implement the seamless handover of Mesh links, ensuring high-quality data communications between a moving train and the ground network.

Purpose

The vehicle-ground communication subsystem is an integral part of the Passenger Information System (PIS). It provides data channels for transmitting information services between fast moving trains and the ground network. Vehicle-ground communications mainly rely on wireless communication technologies, and WLAN technology is the most widely used due to its easy deployment and cost effectiveness.

A WLAN-based vehicle-ground communication subsystem creates more economic benefits for rail transit enterprises. Due to limited coverage of APs, a fast-moving train needs to continuously switch from one AP to another, causing terminals to roam. WLAN roaming usually takes 100 ms or longer, and data loss or delay that occurs in this period may result in video freeze or garbled image. This would fail to meet the requirements of the vehicle-ground communication subsystem.

Vehicle-ground fast link handover enables seamless Mesh link switching and provides reliable, stable data links for high-speed terminals, allowing passengers to enjoy smooth vehicle-mounted information services.

Benefits

Vehicle-ground fast link handover offers the following advantages:

Low communication costs: Unlike other wireless communication technologies such as 3G and LTE, WLAN Mesh technology applied in vehicle-ground fast link handover works on the Industrial, Scientific, Medical (ISM) spectrum. This can be used without the need to apply for a license. In addition, vehicle-ground fast link handover incurs no additional communication costs and can better integrate into the existing rail transit network, which facilitates rail transit service expansion.
High reliability: Vehicle-ground fast link handover inherits link redundancy features from WLAN Mesh technology. In the forward direction of a train, a vehicle-mounted AP sets up Mesh links with multiple trackside APs. When the quality of the active link deteriorates, the vehicle-mounted AP chooses a better link as the active link to ensure quality of vehicle-ground communications.
High-quality data transmission: Seamless Mesh link switching ensures smooth multimedia services. With larger bandwidth, WLAN technology provides faster data services than other wireless technologies.