Simplified scrambling scheme for satellite broadcasting systems
A simplified scrambling scheme that unifies all signals of a satellite broadcasting system, including frame header ( 404 ), frame body ( 402 ) and pilot symbols ( 408 ) with a common reference phase. This results in the simplification and increased flexibility of the receiver front-end design without affecting the overall system performance. In many current communications systems with frame headers and pilot symbols, the phases of frame headers and pilot syrnbols are not designed to be aligned with any constellation points of the modulated data from the frame body. This scrambling scheme takes into account possible impact due to irregular phase changes between frame headers/pilot symbols and modulated data.
1. A method of generating a scrambled signal having real symbols I S,k and imaginary signals Q S,k from a signal having real symbols I k and imaginary symbols Q k , comprising the steps of:
generating a real part of a k th element of a complex scrambling sequence (d I,k );
generating an imaginary part of the k th element of the complex scrambling sequence (d Q,k );
generating a scrambling phase multiplier n k according to:
n k =2 d I,k +d Q,k ; and
generating the scrambled signal:
I
S
,
k
+
j
Q
S
,
k
=
(
I
k
+
j
Q
k
)
ⅇ
j
(
2
π
n
k
4
)
.
2. A method of scrambling symbols in a data transmission system, comprising:
scrambling all elements of a frame prior to transmission of the frame by the system so that all of the elements have a common reference phase;
wherein the scrambling step comprises performing a complex scrambling operation according to:
I
S
,
k
+
j
Q
S
,
k
=
(
I
k
+
j
Q
k
)
·
exp
{
j
2
π
n
k
4
}
wherein:
I k , Q k represents original symbols,
I S,k , Q S,k represents scrambled symbols,
n k represents a scrambling phase multiplier, such that n k =2d I,k +d Q,k , and
d I,k and d Q,k are real (I) and imaginary (Q) components of a k th element of the complex scrambling sequence.
3. The method of claim 2 , wherein the elements of the frame comprise a frame header or frame body.
4. The method of claim 2 , wherein the elements of the frame further comprise one or more pilot symbols.
5. The method of claim 2 , wherein the complex scrambling operation comprises simple component swapping and sign changing according to:
d I,k
d Q,k
n k
Rotation
I S,k + jQ S,k
0
0
0
0°
I k + jQ k
0
1
1
90°
−Q k + jI k
1
0
2
180°
−I k − jQ k
1
1
3
270°
Q k − jI k .
6. An apparatus for scrambling symbols in a data transmission system, comprising:
means for scrambling all elements of a frame prior to transmission of the frame by the system so that all of the elements have a common reference phase, the means for scrambling comprising means for performing a complex scrambling operation according to:
I
S
,
k
+
j
Q
S
,
k
=
(
I
k
+
j
Q
k
)
·
exp
{
j
2
π
n
k
4
}
wherein:
I k , Q k represents original symbols,
I S,k , Q S,k represents scrambled symbols,
n k represents a scrambling phase multiplier, such that n k =2d I,k +d Q,k , and
d I,k and d Q,k are real (I) and imaginary (Q) components of a k th element of the complex scrambling sequence.
7. The apparatus of claim 6 , wherein the elements of the frame comprise a frame header or frame body.
8. The apparatus of claim 6 , wherein the elements of the frame further comprise one or more pilot symbols.
9. The apparatus of claim 6 , wherein the complex scrambling operation comprises simple additions and subtractions according to:
d I,k
d Q,k
n k
Rotation
I S,k + jQ S,k
0
0
0
0°
I k + jQ k
0
1
1
90°
−Q k + jI k
1
0
2
180°
−I k − jQ k
1
1
3
270°
Q k − jI k .
10. An apparatus for generating a scrambled signal having real symbols I S,k and imaginary signals Q S,k from a signal having real symbols I k and imaginary symbols Q k , comprising:
means for generating a real part of a k th element of a complex scrambling sequence (d I,k );
generating an imaginary part of the k th element of the complex scrambling sequence (d Q,k );
means for generating a scrambling phase multiplier n k according to:
n k =2 d I,k +d Q,k ; and
means for generating the scrambled signal:
I
S
,
k
+
jQ
S
,
k
=
(
I
k
+
jQ
k
)
ⅇ
j
(
2
π
n
k
4
)
.