%==============================
% S-V channel model generation
%==============================

function imp_response=channel_model(ts,CM)

% ts : sampling time (nsec)
 if nargin==0
    ts = 0.167;   % 根據(jù)提案的頻帶范圍確定
    CM = 1;
end

%S-V模型的參數(shù)
if CM == 1
    
    Lam=0.0233;
    lambda=3.75;
    Gam=7.1;
    gamma=4.37;
    std_ln=4.8;

elseif CM == 2
    
    Lam=0.4;
    lambda=1;
    Gam=5.2;
    gamma=6.5067;
    std_ln=4.8;
    
elseif CM == 3
    
    Lam=0.0667;
    lambda=3;
    Gam=14.93;
    gamma=7.03;
    std_ln=4.8;
    
else CM == 4
    
    Lam=0.0667;
    lambda=3;
    Gam=17;
    gamma=12;
    std_ln=4.8;
    
end
       
% Lam=0.0233;                % 修改1：Cluster arrival rate，(1/nsec)    Lam
%                            % CM1為0.0233，CM2為0.4，CM3為0.0667，CM4為0.0667
% lambda=3.75;               % 修改2：Ray arrival rate ，(1/nsec)       lambda
%                            % CM1為3.75，CM2為1，CM3為3，CM4為3
% Gam=7.1;                   % 修改3：Cluster decay factor，Gam
%                            % CM1為7.1，CM2為5.2，CM3為14.93，CM4為17
% gamma=4.37;                % 修改4：Ray decay factor，gamma
%                            % CM1為4.37，CM2為6.5067，CM3為7.03，CM4為12
% std_ln=4.8;                % 修改5：total std of log-normal shadowing for each multipath arrival
%                            % CM1為4.8，CM2為4.8，CM3為4.8，CM4為4.8

std_ln_1=4.8/sqrt(2);             % Standard deviation of log-normal variable associated with Clusters
std_ln_2=4.8/sqrt(2);             % Standard deviation of log-normal variable Rays within a cluster

std_L=sqrt(1/(2*Lam));
std_lam=sqrt(1/(2*lambda));


index_imp_resp=floor((10*Gam+10*gamma)/ts)+1;
imp_response=zeros(index_imp_resp,1);

% Determine Cluster arrivals
Tc=0;                   % 修改6：First cluster arrival occurs at time 0
%根據(jù)需要選擇第一簇到達(dá)時(shí)間的設(shè)定
% Tc=(std_L*randn)^2+(std_L*randn)^2;  % allow for random first arrival
while (Tc<10*Gam)
    tmp_imp_response=zeros(floor((10*Gam+10*gamma)/ts)+1,1);
    tmp_imp_response_index=floor(Tc/ts)+1;
    
    mu=(-10*Tc/Gam)/log(10)-(std_ln)^2*log(10)/20;
    ln_rv_temp=std_ln_1*randn;                          % Cluster shadowing
    ln_rv=mu+std_ln_1*randn+ln_rv_temp;                 % first cluster arrival fading
    % ln_rv=mu+std_ln*randn;
    pk=2*round(rand)-1;
    tmp_imp_response(tmp_imp_response_index)=10^(ln_rv/20)*pk;
    
    % Determine Ray arrivals for each cluster
    Tr=(std_lam*randn)^2+(std_lam*randn)^2;
    while (Tr<10*gamma)
        tmp_imp_response_index=floor((Tc+Tr)/ts)+1;
        
        mu=(-10*Tc/Gam)/log(10)+(-10*Tr/gamma)/log(10)-(std_ln)^2*log(10)/20;  % this assumes log(Omega)=0
        ln_rv=mu+std_ln_2*randn+ln_rv_temp;             % Ray fading
        % ln_rv=mu+std_ln*randn;
        pk=2*round(rand)-1;
        tmp_imp_response(tmp_imp_response_index)=10^(ln_rv/20)*pk;
        Tr=Tr+(std_lam*randn)^2+(std_lam*randn)^2;
    end;
    
    imp_response=imp_response+tmp_imp_response;   % this sums cluster and ray arrivals
    Tc=Tc+(std_L*randn)^2+(std_L*randn)^2;
end;

% 歸一化能量
imp_response=imp_response/sqrt(imp_response'*imp_response);
imp_response=imp_response';