lms6: nrz-ambiguity

lms6/lms6.txt

@@ -5,7 +5,7 @@ Lockheed Martin Sippican LMS6
 
 FSK 4800 baud
 convolutional code R=1/2, K=7 (CCSDS)
-(inv(c0),c1)
+(c0,inv(c1))
 polyA = x^6+x^3+x^2+x+1    (0x4f)
 polyB = x^6+x^5+x^3+x^2+1  (0x6d)
 
@@ -85,13 +85,13 @@ qA = x^6+x^5+x^4+x+1
 qB = x^4+x^3+x^2+x
 
 receive:
-...,a(n-1),b(n-1),a(n),b(n),a(n+1),b(n+1),...
+...,a(n-1),b(n-1),a(n),b(n),a(n+1),b(n+1),...  (or inverted)
 if NRZ-S demod:
-alpha(n)=[a(n)==b(n-1)]=a(n)+b(n-1)+1
-beta(n)=[a(n)==b(n)]=b(n)+a(n)+1
+alpha(n) = [a(n)==b(n-1)] = a(n)+b(n-1)+1 = [a'(n)==b'(n-1)] , a' = inv(a) = a + 1/(1+x)
+beta(n) = [a(n)==b(n)] = b(n)+a(n)+1 = [a'(n)==b'(n)] , b' = inv(b) = b + 1/(1+x)
 
-alpha = a + x*b + 1/(1+x)
-beta = a + b + 1/(1+x)
+alpha = a + x*b + 1/(1+x) = a' + x*b' + x/(1+x)
+beta = a + b + 1/(1+x) = a' + b' + 1/(1+x)
 
 m*pA = alpha
 m*pB = beta
@@ -108,9 +108,13 @@ polyA + x*polyB = (x+1)qA = pA
 beta = m*pB = m*polyA + m*polyB = cA + cB
 alpha = m*pA = m*polyA + x*m*polyB = cA + x*cB
 
-alpha + beta = (1+x)cB = (1+x)b
-alpha + x*beta = (1+x)cA = (1+x)a + 1
+alpha + beta = (1+x)cB = (1+x)b = (1+x)b' + 1
+alpha + x*beta = (1+x)cA = (1+x)a + 1 = (1+x)a'
+
+cA = a + 1/(1+x) = a'
+cB = b = b' + 1/(1+x)
+
+here:
+cA = a' , cB = inv(b')
 
-cB = b
-cA = a + 1/(1+x)
 

lms6/lms6ccsds.c

@@ -1007,7 +1007,7 @@ int main(int argc, char **argv) {
         for (i = 0; i < len; i++) {
 
             inc_bufpos();
-            bit = rbit ^ (bc%2);  // (inv(c0),c1)
+            bit = rbit ^ (bc%2);  // (c0,inv(c1))
             bc++;
             buf[bufpos] = 0x30 + bit;
 
@@ -1035,7 +1035,7 @@ int main(int argc, char **argv) {
 
             while ( pos < RAWBITBLOCK_LEN ) {
                 if (read_rawbit(fp, &rbit) == EOF) break;
-                bit = rbit ^ (bc%2);  // (inv(c0),c1)
+                bit = rbit ^ (bc%2);  // (c0,inv(c1))
                 bc++;
                 blk_rawbits[pos] = 0x30 + bit;
                 pos++;