You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: FWGN_model.m
    path of file: ./repos/MIMO_OFDM/第2章 SISO信道模型/FWGN信道模型
    
    the code of the file until where you have to start completion: function [h,Nfft,Nifft,doppler_coeff]=FWGN_model(fm,fs,N)
% FWGN(Clarke/Gan) Model 
% Input
%   fm= Maximum Doppler frquency

    
function [h,Nfft,Nifft,doppler_coeff]=FWGN_model(fm,fs,N)
% FWGN(Clarke/Gan) Model 
% Input
%   fm= Maximum Doppler frquency
%   fs= Sampling frequency
%   N = Number of samples
% Output
%   h = Complex fading channel
 
%MIMO-OFDM Wireless Communications with MATLAB¢ç   Yong Soo Cho, Jaekwon Kim, Won Young Yang and Chung G. Kang
%2010 John Wiley & Sons (Asia) Pte Ltd
 
% Make them simple by taking a FFT with some 2^n points.
% tone spacing df=2fm/Nfft
Nfft = 2^max(3,nextpow2(2*fm/fs*N));  % Nfft=2^n
Nifft = ceil(Nfft*fs/(2*fm));
% Generate the inepend