freq_offset.m

这个程序主要是实现空时编码的matlab编解码仿真。

function [freq_diff, delta_theta, alpha]=freq_offset(inphase, quad, fs, fc)

%   [freq_diff, delta_theta, alpha]=freq_offset(inphase, quad, fs, fc)
%
%	Output:
%	freq_diff       - The resulting difference in carrier-frequency between transmitter and receiver.
%   delta_theta     - Returns the phase-shift per sample.
%   alpha           - Is the factor, where alpha fs2 = alpha * fs1
%
%	inphase         - Inphase part after downconversion and LP-filtering
%   quad            - Quad part after downconversion and LP-filtering
%   fs              - Used sampling frequency
%   fc              - Carrier frequency used in transmitter
%
%   Short Theoretical Background for the Function:
%   
%   Compensating for rotation on sinus-signal.
%   Assuming rotation is less than one halfcircle!!!!!!
%   This function needs the sinussignal to be present from
%   first sampel to the last. 
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%     
%%% Function part of simulation for Space-Time
%%% coding project, group Grey-2001.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%   Author: Stefan Uppg錼d
%   Date: 29-03-2001
%   Version: 1.0
%   Revision (Name & Date & Comment):
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

complex_signal_in = complex(inphase, quad);
fi = angle(complex_signal_in);                          % Phase for downconverted signal

A = [[1:length(fi)]' ones(length(fi),1)];               % Solving least-square for straight-line equation
y = fi';
x = A\y;                                                % x = A\y, d鋜 x = [k m]'

first_angle = x(2);
end_angle   = x(1)*length(fi)+x(2);

freq_diff = (fs/(2*pi)) * (end_angle - first_angle) * (1/length(fi));
figure(9), plot(fi), hold on, plot([1 length(fi)], [x(2) x(2)+x(1)*length(fi)], 'red'), hold off;
delta_theta = (end_angle - first_angle) / length(fi);
alpha = 1/(1-(freq_diff/fc));