I created custom RF signal generator from I_PWL_File and Q_PWL_File using Verilog-A $table_model() like following.
Code:

analog begin
   @(initial_step) begin
     omega = `M_TWO_PI * frf;
     theta0 = `M_PI * init_phase / 180.0;
   end //initial_step

   Isig = $table_model($abstime, I_PWL_File);
   Qsig = $table_model($abstime, Q_PWL_File);

   theta = omega * $abstime + theta0;
   V(plus, minus) <+ scale * ( Isig*cos(theta) - Qsig*sin(theta) );
end //analog 

However this signal generator is very slow when it is used in Cadence Spectre compared to using two "analoglib/vpwlf".

Is it limitation of $table_model() ?