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 receiver, comprising:
a receiving stage to receive layer 1 I,Q symbols that have been further modulated with a layer 2 overlay amplitude change;
a trellis decoder to decode the layer 1 I,Q symbols;
a channel equalization stage to recover the originally transmitted signal amplitude; and
an overlay demodulation stage to detect a direction of the overlay amplitude change.
2. The receiver of claim 1 , wherein the channel equalization stage performs channel equalization across frequency bins to isolate the amplitude modulated overlay signal.
3. The receiver of claim 1 , wherein the channel equalization stage determines the localized power at corresponding FFT bins of the signal and then performs channel inversion on the data bins to restore, as best as possible, the original transmitted symbol amplitude.
4. The receiver of claim 3 , wherein said channel inversion is performed using one of zero forced or minimum mean square error.
5. The receiver of claim 1 , wherein at each FFT symbol time, a calculation of average power across neighboring active data bins is used to determine the localized power at the corresponding FFT bins.
6. The receiver of claim 5 , wherein said average power is calculated using a finite impulse response filter.
7. The receiver of claim 1 , wherein the overlay data is decoded by slicing between the data rings.
8. The receiver of claim 7 , wherein said slicing includes computing the vector distance of each constellation symbol after channel equalization and comparing against a center decision ring.
9. The receiver of claim 8 , wherein said center decision ring is calculated by at least one of slicing equally between two received symbol rings and with reference to non-amplitude modulated reference symbols.
10. The receiver of claim 9 , wherein said non-amplitude modulated reference symbols are obtained from an adjacent FFT bin.