Process for automatic correction of the spectral inversion in a demodulator and device to implement the process
A process of correction of the spectral inversion for a receiver in a digital communication system: the process allows the reception in the receiver of a training sequence presumably known according to a modulation of type π/2 BPSK or MDP2. The process includes the following steps: Demodulating of the training sequence; Calculating of the differential correlation on a set of N received samples (R n ) and presumably sent (S n ) to generate a result; Using the result to detect the beginning of the frame and to order a spectral inversion in the chain of reception of the aforementioned receiver before launching the detection of the beginning of the frame. A receiver to process automatically the spectral inversion is also described.
1. A process for correction of spectral inversion in a digital communication system, the process comprising:
demodulating, in a receiver, a training sequence being received;
calculating, in the receiver, a differential correlation on a set of N received samples and N presumably sent samples to generate a result; and
detecting, in the receiver, a frame and a sign of the result, and using a value of the sign of the result to control a spectral inversion in a reception sequence by using the differential correlation.
2. The process according to claim 1 , wherein the training sequence is at least one of:
μ/2BPSK (binary phase shift keying) modulations type; and
MDP2 (modulation par déplacement de phase à 2 états) modulations type.
3. The process according to claim 1 , further comprising:
calculating an absolute value of a real part of the result of the differential correlation in order to determine a start of the frame; and
testing the sign of the real part of the result in order to control the spectral inversion in the reception sequence.
4. The process according to claim 2 , wherein the modulation type is applied to a portion of the reception sequence and another type of modulation for a subsequent sequence.
5. The process according to claim 3 , wherein a first modulation type is applied to a portion of the reception sequence and second type of modulation for a subsequent sequence.
6. The process according to claim 5 , wherein the modulation type is applied to a portion of the reception sequence compatible with a DVBS2 (Digital Video Broadcasting Satellite) standard in which several blocks and symbols having different types of modulations, including a portion using the μ/2 BPSK modulation type.
7. The process according to claim 6 , wherein a heading comprises a set of 90 symbols of which at least 26 are transmitted via the modulation of type μ/2 BPSK.
8. The process according to claim 1 , wherein calculating a differential correlation on the set of N received samples for a differential symbol of emission D k and a differential symbol of reception X k is given by variable C as follows:
C
=
∑
k
=
0
N
-
1
X
k
·
D
k
*
.
9. A receiver comprising:
a demodulator for demodulating a training sequence being received;
means for calculating a differential correlation on a set of N received samples and N presumably sent samples to generate a result;
means for detecting a frame and a sign of the result in order to control a spectral inversion in a reception sequence by using the differential correlation;
means for calculating an absolute value of a real part of the result of the differential correlation in order to determine a start of the frame; and
means for testing the sign of the real part of the result in order to control the spectral inversion in the reception sequence.
10. The receiver according to claim 9 , wherein the training sequence is at least one of:
μ/2 BPSK (binary phase shift keying) modulations type; and
MDP2 (modulation par déplacement de phase à 2 états) modulations type.
11. The receiver according to claim 9 , wherein the modulation type is applied to a portion of the reception sequence and another type of modulation for a subsequent sequence.
12. The receiver according to claim 9 , wherein a modulation type is applied to a portion of the reception sequence and another type of modulation for a subsequent sequence.
13. The receiver according to claim 12 , wherein the modulation type is applied to a portion of the reception sequence compatible with a DVBS2 (Digital Video Broadcasting Satellite) standard in which several blocks and symbols having different types of modulations, including a portion using the μ/2 BPSK modulation type.
14. The receiver according to claim 13 , wherein a heading comprises a set of 90 symbols of which at least 26 are transmitted via the modulation of type μ/2 BPSK.
15. The receiver according to claim 9 , wherein calculating a differential correlation on the set of N received samples for a differential symbol of emission D k and a differential symbol of reception X k is given by variable C as follows:
C
=
∑
k
=
0
N
-
1
X
k
·
D
k
*
.
16. A digital communication system comprising a receiver equipped with a spectral inversion device, comprising:
means for demodulating a training sequence being received with a MDP2 (modulation par déplacement de phase à 2 états) modulations type;
means for calculating a differential correlation on a set of N received samples and N presumably sent samples to generate a result; and
means for detecting a frame, and using a value of the sign of the result to control a spectral inversion in a reception sequence by using the differential correlation.