Linearize non-linear system of quadrotor using Matlab/ Simulink.

Hi, I am undergraduated students from University Malaysia Pahang. Now, I am working on quadrotor simulation for my final year project. I am using this journal as my reference model "Design and Control of an Indoor Micro Quadrotor" . I had decided to use LQR as the controller. However, I need the linearization part since the model I used is the nonlinear system. I have no idea on how to obtain the equation of the linearization and from where should I derive it. I do really need your helps. Thank you 