Technical questions: You can choose a field from software, controls and signal processing. I chose signal processing. The interview consisted of questions from Math, Signal Processing, C, C++, and MATLAB.
MATLAB: Basic questions like workspaces, memory, functions, scripts, some basic commands. A working knowledge of Matlab is enough to conquer this part of the interview!
C/C++: The usual C++ OOP questions like classes and objects, constructors and destructors, virtual functions. The usual C questions like stack and heap, structs and unions, typedef, etc. Asked to write a few functions like recursive Fibonacci sequence. A few questions on drawing a shown pattern of asterisks in a certain order using C or C++.
Math: Basic questions on Linear Algebra like calculate Eigen Values for a small 2x2 matrix, find derivative of a function, partial differential equations, etc. Nothing advanced, just basic calculus. Refresh some concepts like Eigen values and Eigen vectors, rank of a matrix, null space of a matrix, etc.
Signal Processing: Basic questions about linear and circular convolution, causal systems, they gave input-output equations and asked questions about it like whether the system is linear, causal, etc. Questions about FIR and IIR systems, poles and zeros.