cp4fskmod.m

一个仿真测试4FSK信号的matlab环境GUI程序。可以查看基带IQ波形、眼图、星座图。并可以仿真高斯白噪声、瑞利衰减对信号的影响。

function [I_Symbol,Q_Symbol] = cp4fskmod(BitStream)
% ---------------------------------------------------------------
% Continue Phase Four level FSK modulation Program,used for DMR,ETSI
% This program describe the following routines:
% Bit Stream ---- Symbol ---- modulation symbol ---- RRC filter
% ---- FM modulator -----Output Signal

% Written by zhengliangde, HYT Co.,LTD. 2005.11.4
% Contact: [e-mail]
% ---------------------------------------------------------------
nSamp     = 8;          % number of samples per symbol
Fd        = 4800;       % symbol rate
Fs        = nSamp*Fd;   % sample rate
freq_sep  = 648;        % frequency seperation
prevPhase = 0;          % initial phase
pi_Def    = 3.1416;     % pi define
M         = 4;          % four level FSK

BitStream = randsrc(400,1,[0 1],12321);

% ---------  Check error ----------
if Fs<freq_sep*(M-1)
    error('The max Frequency must be less than or equal to Fs/2.');
end

% Increasing phase calculated formura:
% [1 3 -1 -3]*pi*freq_sep*1/Fs
%PhaseIncr = [0:nSamp-1]'*[0.4241   1.2723  -0.4241  -1.2723];
%PhaseIncr=[...
%         0         0         0         0
%    0.0530    0.1590   -0.0530   -0.1590
%    0.1060    0.3181   -0.1060   -0.3181
%    0.1590    0.4771   -0.1590   -0.4771
%    0.2121    0.6362   -0.2121   -0.6362
%    0.2651    0.7952   -0.2651   -0.7952
%    0.3181    0.9543   -0.3181   -0.9543
%    0.3711    1.1133   -0.3711   -1.1133];
%PhIncrSamp = [0.0530    0.1590   -0.0530   -0.1590];

PhaseIncr = [0:nSamp-1]'*[-3 -1 1 3]*pi_Def*freq_sep*1/Fs;
PhIncrSamp = [-3 -1 1 3]*pi_Def*freq_sep*1/Fs;

% -------------  Serial to Parallel  -------------
I_BitStream = BitStream(1:2:length(BitStream));
Q_BitStream = BitStream(2:2:length(BitStream));

% ----------- Generate four level Symbol -----------
Symbol = I_BitStream*2 + Q_BitStream;

% -----------  Calculate the phase -----------
Phase = zeros(size(Symbol));      % preallocate phase
for iSym=1:length(Symbol)
    Phase(nSamp*(iSym-1)+1:nSamp*iSym) = ...
        prevPhase*ones(nSamp,1) + PhaseIncr(:,Symbol(iSym)+1);
    prevPhase = Phase(nSamp*iSym) + PhIncrSamp(Symbol(iSym)+1);
end

% -------- convert Phase between [0:2*pi] --------
for indx=1:length(Phase)
    while (abs(Phase(indx))>=2*pi_Def)
        if Phase(indx)>0
            Phase(indx) = Phase(indx) - 2*pi_Def;
        elseif Phase(indx)<0
            Phase(indx) = Phase(indx) + 2*pi_Def;
        end
    end
end

% --------  Generate I/Q signal ---------
I_Symbol = cos(Phase);
Q_Symbol = sin(Phase);

% ----------- End of modulation file -----------