说明：  The following two MATLAB functions show how you can easily implement the LTE modulation and demodulation algorithms, with all their specifications, using System objects of the Communications System Toolbox The Modulator function has two input arguments: the input bit stream (u) and a parameter representing the modulation mode (Mode). As its output, the function computes the modulated symbols. The function implements the three different types of modulator used in the LTE standard. For example, in the case of QPSK, we use a comm.PSKModulator System object and set its modulation order to 4. Similarly, in the case of 16QAM and 64QAM we use the comm.RectangulatQAMModulator System objects and set their modulation orders to 16 and 64, respectively. Depending on the value of the modulation mode, we process the input bits to generate the modulated symbols as the output.