Method to minimize compatibility error in hierarchical modulation using variable phase
The present invention provides a method of hierarchically modulating first and second digital data streams in a broadcast system such as an SDAR system that is compatible with legacy receivers. The second digital data stream, but not the first, is provided with a non-binary pseudo-random encoding. A carrier is first modulated, e.g. QPSK, by the first digital data stream; and a second modulation is performed with the encoded second digital data stream. The encoding includes a multiplication of a matrix formed of 2, 3 or 4 consecutive bits of the secondary data stream by a matrix, e.g. a Hadamard matrix to form a product matrix having non-binary values that are used to modify consecutive symbols of the first modulation. The second modulation appears as Gaussian noise to legacy receivers over time.
1. A method of transmitting digital data in a hierarchical transmission system comprising the steps of:
providing at least a first digital data stream and a second digital data stream;
providing a non-binary, pseudo-random encoding of the second digital data stream but not the first digital data stream, said non-binary, pseudo-random encoding of the second digital data stream comprising consecutive groups of n bits in the second digital data stream, wherein n is one of equal to or greater than two, and creating a n-×-1 matrix and multiplying the same by a predetermined n-×-m matrix of binary numbers, wherein m is at least equal to n and each row of the n-×-m matrix is orthogonal to the other rows thereof, to produce a 1-×-m product matrix of non-binary, pseudo-random numbers;
hierarchically modulating a carrier to produce a signal with a first modulation based on the first digital data stream and a second modulation based on at least the non-binary, pseudo-random encoded second digital data stream; and
transmitting the signal, whereby the transmitted signal when received may be fully demodulated for the second digital data stream or partially demodulated on the first modulation alone for the first digital data stream with the second modulation appearing as pseudo-Gaussian noise.
2. The method of claim 1 further comprising the steps of:
providing at least a third digital data stream;
providing a non-binary, pseudo-random encoding of the third digital data stream; and
further basing the second modulation on the third digital data stream.
3. The method of claim 2 wherein all but the first digital data streams are provided with non-binary, pseudo random encoding and the second modulation is based on the encoded all but the first digital data streams.
4. The method of claim 1 wherein n=2 and the predetermined n-×-m matrix is a 2-×-m matrix comprising 2 orthogonal rows of a Hadamard matrix having at least 2 rows.
5. The method of claim 4 wherein the n-×-m matrix is a 2-×-2 Hadamard matrix.
6. The method of claim 1 wherein n=4 and the predetermined n-×-m matrix is a matrix comprising 4 orthogonal rows of a Hadamard matrix having at least 4 rows.
7. The method of claim 6 wherein the n-×-m matrix is a 4-×-4 Hadamard matrix.
8. The method of claim 1 wherein n=3 and the predetermined n-×-m matrix is a matrix comprising 3 orthogonal rows of a Hadamard matrix having at least 4 rows.
9. The method of claim 8 wherein the Hadamard matrix has 4 rows.
10. The method of claim 1 wherein the step of hierarchically modulating a carrier comprises using each consecutive one of the non-binary numbers of each one of the 1-×-m product matrices to modify a unique, consecutive symbol of a group of m consecutive symbols in the first modulation, whereby each binary bit of a group of n bits in the second digital data stream is divided and spread across the m symbols of the group of symbols in the first modulation that is modulated by the product matrix derived from the group of n bits and the second modulation results in a pseudo-Gaussian modulation of the carrier over time.
11. The method of claim 10 wherein n=2 and the predetermined n-×-m matrix is a 2-×-m matrix comprising 2 orthogonal rows of a Hadamard matrix having at least 2 rows.
12. The method of claim 11 wherein the n-×-m matrix is a 2-×-2 Hadamard matrix.
13. The method of claim 10 wherein n=4 and the predetermined n-×-m matrix is a matrix comprising 4 orthogonal rows of a Hadamard matrix having at least 4 rows.
14. The method of claim 13 wherein the n-×-m matrix is a 4-×-4 Hadamard matrix.
15. The method of claim 10 wherein n=3 and the predetermined n-×-m matrix is a matrix comprising 3 orthogonal rows of a Hadamard matrix having at least 4 rows.
16. The method of claim 15 wherein the Hadamard matrix has 4 rows.
17. The method of claim 1 , wherein n=2, 3, or 4.