function [g_T]= rrc_filter(alpha, filterOrder, N, T)
%alpha為滾降系數
%filterOrder為濾波器階數
%N為每符號采樣點數
%T
% alpha = 0.24;
% filterOrder = 63; %
% T = 1;
% N = 4;  %sample point number per symbol
n = -(filterOrder - 1)/2:1:(filterOrder - 1)/2;
for i  = 1:length(n)
    g_T(i) = 0;    
    for m = -(filterOrder - 1)/2:1:(filterOrder - 1)/2
%         g_T(i) = g_T(i) + sqrt(Xrc(4 * m/(filterOrder * T), alpha, T)) * exp(j * 2 * pi * m * (n(i)) / filterOrder); 
        g_T(i) = g_T(i) + sqrt(xrc(N*m/(filterOrder* T), alpha, T)) * cos(2 * pi * m * (n(i)) / filterOrder); 
    end
    
end
g_T = g_T /max(g_T)/2;
% sum(g_T)
% [G_T, W] = freqz(g_T, 1);
% magG_Tin_dB = 20 * log10(abs(G_T)/max(abs(G_T)));
% n2 = 0:(filterOrder - 1);
% g_R = g_T;
% resp = conv(g_T, g_R);
% [RESP, W2] = freqz(resp, 1);
% magRESPin_dB = 20 * log10(abs(RESP)/max(abs(RESP)));
% n3 = 0:(length(resp) - 1);
% figure(1);
% stem(n2, g_T);grid on;
% figure(2);
% plot(W/max(W), magG_Tin_dB);
% grid on;
% figure(3);
% stem(n3, resp);grid on;
% figure(4);
% plot(W2/max(W2), magRESPin_dB);
% grid on;