%function?vHat?=?decodeProbDomain（rx?H?N0?iteration）
%?Probability-domain?sum?product?algorithm?LDPC?decoder
%
%??rx????????:?Received?signal?vector?（column?vector）
%??H?????????:?LDPC?matrix
%??N0????????:?Noise?variance
%??iteration?:?Number?of?iteration
%
%??vHat??????:?Decoded?vector?（0/1）?
%
%
%?Copyright?Bagawan?S.?Nugroho?2007?
%?http://bsnugroho.googlepages.com
H=[1?1?1?0?0?0?0?0;0?0?0?1?1?1?0?0;1?0?0?1?0?0?1?0;0?1?0?0?1?0?0?1];
[M?N]=size（H）;rate=M/N;N0=1;
en=10^（N0/10）;?
sigma=1/sqrt（2*rate*en）;

c=[1?0?1?0?1?1?1?1];
rx=c+sigma*randn（1N）;


%?Prior?probabilities
P1?=?ones（size（rx））./（1?+?exp（-2*rx./（N0/2）））;
P0?=?1?-?P1;

%?Initialization
K0?=?zeros（M?N）;
K1?=?zeros（M?N）;
rji0?=?zeros（M?N）;
rji1?=?zeros（M?N）;
qij0?=?H.*repmat（P0?M?1）;
qij1?=?H.*repmat（P1?M?1）;

iteration=100;
for?n?=?1:iteration
???fprintf（‘\n‘）;
???fprintf（‘\n‘）;
???fprintf（‘Iteration?:?%d\n‘?n）;
???
???%?-----?Horizontal?step?-----
???for?i?=?1:M
??????
??????%?Find?non-zeros?in?the?column
??????c1?=?find（H（i?:））;
??????
??????for?k?=?1:length（c1）
?????????
?????????%?Get?column?products?of?drji\c1（l）
?????????drji?=?1;
?????????for?l?=?1:length（c1）
????????????if?l~=?k
???????????????drji?=?drji*（qij0（i?c1（l））?-?qij1（i?c1（l）））;
????????????end
?????????end?%?for?l
?????????
?????????rji0（i?c1（k））?=?（1?+?drji）/2;
?????????rji1（i?c1（k））?=?（1?-?drji）/2;
?????????
??????end?%?for?k
??????
???end?%?for?i
???
???%?------?Vertical?step?------
???for?j?=?1:N
??????
??????%?Find?non-zeros?in?the?row
??????r1?=?find（H（:?j））;
??????
??????for?k?=?1:length（r1）
????????
?????????%?Get?row?products?of?prodOfrij\ri（l）
?????????prodOfrij0?=?1;
?????????prodOfrij1?=?1;???
?????????for?l?=?1:length（r1）
????????????if?l~=?k
???????????????prodOfrij0?=?prodOfrij0*rji0（r1（l）?j）;
???????????????prodOfrij1?=?prodOfrij1*rji1（r1（l）?j）;
????????????end
?????????end?%?for?l
?????????
?????????%?Update?constants
?????????K0（r1（k）?j）?=?P0（j）*prodOfrij0;
?????????K1（r1（k）?j）?=?P1（j）*prodOfrij1;
?????????
?????????%?Update?qij0?and?qij1
?????????qij0（r1（k）?j）?=?K0（r1（k）?j）./（K0（r1（k）?j）?+?K1（r1（k）?j））;
?????????qij1（r1（k）?j）?=?K1（r1（k）?j）./（K0（r1（k）?j）?+?K1（r1（k）?j））;
???????????????
??????end?%?for?k
??????
??????%?Update?constants
??????Ki0?=?P0（j）*prod（rji0（r1?j））;
??????Ki1?=?P1（j）*prod（rji1（r1?j））;
??????
??????%?Get?Qj
??????Qi0?=?Ki0/（Ki0?+?Ki1）;
??????Qi1?=?Ki1/（Ki0?+?Ki1）;
??????if（j==1）?
??????????fprintf（‘Q1=%f???‘Qi1）;
??????else
??????????fprintf（‘%f???‘Qi1）;
??????end
??????%?Decode?Qj????????
??????if?Qi1?>?Qi0
?????????vHat（j）?=?1;
??????else
?????????vHat（j）?=?0;
??????end
?????????
???end?%?for?j
??fprintf（‘\nc=‘）;
??
???????fprintf（‘%d???????????‘vHat）;
???????
???????
???if?mod（vHat*H‘2）==0
???????break;end
???
end?%?for?n

?屬性????????????大小?????日期????時間???名稱
-----------?---------??----------?-----??----
?????文件???????84992??2010-01-04?16:08??Ldpc?碼.doc
?????文件????????2901??2010-01-04?16:08??decodeProbDomain.m