Overlay modulation technique for COFDM signals based on amplitude offsets
View Patent ↗Systems and methods are presented for transmitting additional data over preexisting differential COFDM signals by changing the amplitude of the legacy data symbols. In exemplary embodiments of the present invention, additional data capacity can be achieved for a COFDM signal which is completely backwards compatible with existing legacy satellite broadcast communications systems. In exemplary embodiments of the present invention, additional information can be overlaid on a legacy COFDM signal by applying an amplitude offset to the legacy symbols. In exemplary embodiments of the present invention, special receiver processing can be implemented to extract this additional information, which can include performing channel equalization across frequency bins to isolate the amplitude modulated overlay signal. For example, at each FFT symbol time, average power across neighboring active data bins can be used to determine the localized power at the corresponding FFT bins, and a channel inversion can then, for example, be performed on the data bins to restore, as best as possible, the original transmitted symbol amplitude.
1. A method of transmitting additional data over a preexisting signal, comprising:
providing a first modulated signal; and
overlaying additional information on the first signal by changing the amplitude of data symbols of said first modulated signal to create an output signal,
wherein the first signal is a differential COFDM signal, and
wherein said overlay information is applied by changing the amplitude of said first modulated symbols for each bit of said additional information from 1 to one of (1−C) and (1+D) for an overlay information bit “ 1 ” and from 1 to the other of said (1−C) and (1+D) for an overlay information bit “ 0 ”, for real numbers C and D,
and wherein said C and D satisfy the equation [(1−C) 2 +(1+D) 2 ]/(2*2)=1.
2. The method of claim 1 , wherein the first modulated signal is generated using a differential phase encoding process.
3. The method of claim 1 , wherein said overlaying additional information is done in such a manner that said overlaying has minimal effect on maximum ratio combining at a receiver.
4. The method of claim 1 , wherein the overlay data can be decoded by computing the vector distance of each point and comparing against a center decision ring.
5. The method of claim 1 , wherein said changing the amplitude of data symbols of the signal comprises applying an amplitude offset.
6. The method of claim 5 , wherein said amplitude offset is applied after a differential modulation process.
7. The method of claim 1 , wherein any 3 dB loss in detection probability is avoided due to the multiplicative effect of differential demodulation.
8. The method of claim 1 , wherein to recover the overlay data at a receiver, channel amplitude equalization is used to extract said data.
9. A program storage device readable by a processing unit, tangibly embodying a program of instructions executable by the processing unit to implement a method of transmitting additional data over a preexisting signal, said method comprising:
providing a first modulated signal; and
overlaying additional information on the first signal by changing the amplitude of data symbols of said first modulated signal to create an output signal,
wherein the first signal is a differential COFDM signal, and
wherein said overlay information is applied by changing the amplitude of said first modulated symbols for each bit of said additional information from 1 to one of (1−C) and (1+D) for an overlay information bit “ 1 ” and from 1 to the other of said (1−C) and (1+D) for an overlay information bit “ 0 ”, for real numbers C and D,
and wherein said C and D satisfy the equation [(1−C) 2 +(1+D) 2 ]/(2*2)=1.
10. The program storage device of claim 9 , wherein the first modulated signal is generated using a differential phase encoding process.
11. The program storage device of claim 9 , wherein said overlaying additional information is done in such a manner that said overlaying has minimal effect on maximum ratio combining at a receiver.
12. The program storage device of claim 9 , wherein the overlay data can be decoded by computing the vector distance of each point and comparing against a center decision ring.
13. The program storage device of claim 9 , wherein said changing the amplitude of data symbols of the first modulated signal comprises applying an amplitude offset.
14. The program storage device of claim 9 , wherein said amplitude offset is applied after a differential modulation process.
15. The program storage device of claim 9 , wherein in said method 3 dB loss in detection probability is avoided due to the multiplicative effect in differential demodulation.
16. The program storage device of claim 9 , wherein in said method to recover the overlay data at a receiver, channel amplitude equalization is used to extract said data.
17. The method of claim 1 , wherein the output signal is transmitted with an average unity power across each frequency bin.
18. The program storage device of claim 9 , wherein the output signal is transmitted with an average unity power across each frequency bin.
19. The method of claim 1 , wherein C is not equal to D.
20. The method of claim 1 , wherein C=0.2928 and D =0.8708.