channel_estimator_.m

这个程序主要是实现空时编码的matlab编解码仿真。

function [alpha,theta]=channel_estimator_(quad_train_seq, inphase_train_seq, orig_train, model, channel)

%   [alpha,theta]=channel_estimator_(quad_train_seq, inphase_train_seq, orig_train, model, channel)
%
%   Output:
%   alpha		        - Alpha in channelmodel alpha = exp(j*theta)
%   theta               - Theta in dito
%
%   Input:
%   quad_train_seq	    - Quadrature part of training-sequence as seen in receiver.
%   inphase_train_seq   - Inphase dito	 
%   orig_train  	    - Original training-sequence. (Binary!) (on Antenna 1!)
%							   (not using training info from antenna 2.)
%	 model			    - If 0: No Alamouti coding (only sending on antenna 1)
%								if 1: Alamouti coding is used for transmitting antennas.
%	 channel	        - 1 if referring to channel 0 (or 2) in Alamouti's paper.
%								2 if referring to channel 1 (or 3)
%   
%   Short Theoretical Background for the Function:
%
%   Only one channel is estimated!!! 
%	 
%	Estimates the one-tap channel. 
%   (Referring to Appendix A in George J鰊grens master of sciense
%   thesis for mathematical theories)
%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%     
%%% Function part of simulation for Space-Time
%%% coding project, group Grey-2001.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%   Author: Stefan Uppg錼d
%   Date: 2001-03-22
%   Version: 1.1
%   Revision (Name & Date):
%		SU	2001-03-24 Adding variable: model and modifying code for that
%						  Also: changed inputargument "sent_training_seq" be binary.
%						  (not BPSK:ed)
%       SU  2001-03-27 Added if for calculating theta.
%       SU  2001-04-08 Put the mean-expressions on 1/abs(w) and angle(w) instead of on r*conj(r).
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


%%% This is the straigt-forward channel-estimator according to the described theories.

sent_train_seq = bpsk(orig_train,model);

h_real = mean(sent_train_seq .* inphase_train_seq);
h_imag = mean(sent_train_seq .* quad_train_seq);

alpha = sqrt(h_real^2 + h_imag^2);        

if h_real < 0
    theta = atan(h_imag/h_real) + pi;
elseif h_real > 0
    theta = atan(h_imag/h_real);
else
    theta = pi/2;
end