列車防撞輔助預警系統，作用于ATP（Automatic Train Protection Unit）切除條件下行駛的軌道列車。系統運行時，將判斷列車運行方向，實時監測前后兩車間距，當兩車距離小于或者處于安全距離臨界值時，系統產生制動信息，實現實時輔助防撞。此系統無需安裝地面設備，自動檢測ATP切除信號，追蹤范圍大、精度高、抗地形天氣等干擾能力強，可以在隧道環境下運行。     

         本系統采用2.4G無線定位測距方案，其中底層調制技術采用片上CSS核心技術。傳統的無線定位技術采用RSSI信號強度檢測方法，在環境障礙、遮擋等典型情況下，測距誤差極大，無法滿足城軌列車多隧道和彎道情況下的定位需求。而CSS技術具有極強的抗干擾、抗頻率偏移特性以及抗多路徑效應能力，使得測距精度大幅提高，這是傳統的無線定位技術所望塵莫及的。            本系統還采用先進的TDOA定位技術，對稱雙邊雙程測距方式，利用信號在兩個非同步的收發機之間往返的傳輸時間來測量距離，抵消了測距過程中因時間非同步帶來的抖動，大幅提高了測距精度。

   URCAS is a train collision avoidance warning system, which is used under the condition of ATP (Train Protection Unit Automatic) cut off. When the system is running, direction of the train is judged, and distance between the two trains is monitored in real time. When distance between the two trains is less than the critical value of the safe distance, braking information is generated, which can realize real-time auxiliary collision avoidance. System good points : no need to install the ground equipment, automatic detection of ATP cut off signal, wide tracking range, high accuracy, anti terrain weather and other interference ability, can run in the tunnel environment.

     The system uses 2.4G wireless positioning scheme, in which the underlying modulation technology using CSS technology. Traditional wireless positioning technology using received signal strength indicator (RSSI) detection method, in obstacle、occlusion and other typical cases, deviation too large to meet the positioning requirements of urban rail train with multi tunnels and curves condition. The CSS technology has very strong anti-jamming and anti frequency offset characteristics and ability against multipath effects, the ranging accuracy is greatly improved. This greatly exceeds the traditional wireless positioning technology.

     The system adopts advanced technology of TDOA location, Symmetric bilateral two-way ranging method, using the signal round-trip transmission time between two non-synchronization transmitter and receiver to measure the distance and offset the jitter in ranging process due to the non synchronization, which increase the ranging accuracy.