down_converter.m

来自「这个程序主要是实现空时编码的matlab编解码仿真。」· M 代码 · 共 47 行

function [quad,inphase]=down_converter(received,fc,fs,T,cut_off,order)

%   [quad,inphase]=down_converter(received,fc,fs,T,cut_off,order)
%
%	Output:
%	quad		- Quadrature component of the received signal, in baseband
%	inphase		- Inphase component of the received signal, in baseband
%	
%   Input:
%   received    - Received signal, in passband 
%   fc          - Carrier frequency
%   fs          - Sampling frequency
%   T           - Symbol period
%   cut_off     - Cut off frequency for the lowpass filter
%   order       - Order of the lowpass filter
%
%   Short Theoretical Background for the Function:
%   
%   Downconverts the received passband signal to a baseband signal which
%   is lowpass filtered and split into a quadrature and an inphase component 
%   The function low_pass is used for lowpass filtering
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%     
%%% Function part of simulation for Space-Time
%%% coding project, group Grey-2001.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%   Author:  Fredrik Hansson
%   Date:    2001-03-20
%   Version: 1.0
%   Revision (Name & Date):
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

oversamp = fs*T;

t = 0:T/oversamp:(length(received)*T-T)/oversamp; % timescale


ri = received.*(2*cos(-2*pi*fc*t));      % downconversion, still containing
                                         % high frequency components
rq = received.*(2*sin(-2*pi*fc*t));      % downconversion, still containing
                                         % high frequency components

inphase = low_pass(cut_off,order,ri);    % The inphase component only
quad    = low_pass(cut_off,order,rq);    % The quadrature component only