Blind Spot Detection for Lane Changes in intelligent cars by using ultrasonic sensing

I need you to write about Blind Spot Detection for Lane Changes in intelligent cars by using ultrasonic sensing 

- how the car defined the blind spot. (include some figure). 

- talk about  the safety approach. 

- when can be use and why.   

the min word 1000. 

(( please please  no need for introduction or conclusion))  

using this two references, 

1- Pérez, J., Gonzalez, D., & Milanés, V. (2015). Vehicle control in adas applications: State of the art. Intelligent Transport Systems: Technologies and Applications, 206.

2- Liu, J., Han, J., Lv, H., & Li, B. (2015). An ultrasonic sensor system based on a two-dimensional state method for highway vehicle violation detection applications. Sensors, 15(4), 9000-9021.