Method to demodulate amplitude offsets in a differential modulation system
View Patent ↗Where the additional data throughput is added using an amplitude offset or a combination of phase and amplitude offset, the legacy differential demodulator does not recover the amplitude information. The present invention provides a method for demodulating amplitude offsets in a differential modulation system in order to recover the amplitude information. The demodulated amplitude information may be used to recover the additional Level 2 data transmitted as an amplitude offset or combination phase and amplitude offset in a differential multiple phase shift keying (D-MPSK) transmission, such as across adjacent OFDM symbols and/or adjacent frequency subcarriers.
1. A method for demodulating amplitude offsets in a digital transmission system, comprising the steps of:
a. receiving differential multiple phase shift keying (D-MPSK) modulated symbols comprising Level 1 data, and Level 2 data as amplitude offset information in a hierarchical modulation digital transmission system;
b. differentially demodulating D-MPSK modulated symbols to decode the Level 1 data, wherein demodulated data is aligned with reference subcarriers;
c. differentially remodulating the differentially demodulated D-MPSK modulated symbols to recover original soft, or multi-leveled, symbol data; and
d. demodulating the Level 2 data modulated as the amplitude offsets from the differentially remodulated D-MPSK symbols.
2. The method of claim 1 further comprising the step of:
a. determining amplitude offsets from original soft symbol data.
3. The method of claim 1 further comprising the step of:
a. demodulating Level 2 data modulated as phase and amplitude offsets from the differentially remodulated D-MPSK modulated data.
4. The method of claim 1 wherein the step (a) receives a signal transmitted in an orthogonal frequency-division multiplexing (OFDM) transmission system.
5. The method of claim 1 , wherein the differentially remodulated D-MPSK modulated symbols of step (c) is substantially the same as the received D-MPSK modulated symbols of step (a).
6. The method of claim 1 , wherein the Level 2 data is different than the Level 1 data, such that the Level 2 data is not used for error correction.
7. The method of claim 1 , wherein the Level 2 data appears as noise to a legacy receiver, and the Level 2 data is demodulated by a second generation receiver.
8. An apparatus for demodulating amplitude offsets in a digital transmission system, said apparatus comprising:
a. a digital transmission receiver of a hierarchical modulation digital transmission system adapted to detect differential multiple phase shift keying (D-MPSK) modulated symbols comprising Level 1 data, and Level 2 data modulated as amplitude offsets;
b. a differential demodulator adapted to demodulate D-MPSK modulated symbols to decode the Level 1 data, wherein demodulated data is aligned with reference subcarriers;
c. a differential modulator adapted to remodulate the demodulated D-MPSK modulated symbols to recover original soft, or multi-leveled, symbol data; and
d. an amplitude offset demodulator, wherein the offset demodulator demodulates the Level 2 data modulated as the amplitude offsets from the differentially remodulated D-MPSK symbols.
9. The apparatus of claim 8 further comprising:
a. circuitry coupled to the differential modulator, the circuitry adapted to recover original soft symbol data, determine correct phase and amplitude offsets from original soft symbol data; and demodulate Level 2 data modulated as phase and amplitude offsets from D-MPSK remodulated data.
10. The apparatus of claim 8 , wherein the differentially remodulated D-MPSK modulated symbols of step (c) is substantially the same as the received D-MPSK modulated symbols of step (a).
11. The apparatus of claim 8 , wherein the Level 2 data is different than the Level 1 data, such that the Level 2 data is not used for error correction.
12. The apparatus of claim 8 , wherein the Level 2 data appears as noise to a legacy receiver, and the Level 2 data is demodulated by a second generation receiver.
13. An apparatus for modulating amplitude offsets in a digital transmission system, said apparatus comprising:
a. a digital transmitter of a hierarchical modulation digital transmission system adapted to transmit differential multiple phase shift keying (D-MPSK) modulated symbols comprising Level 1data; and
b. an amplitude offset modulator adapted to provide D-MPSK modulated symbols to the transmitter, wherein the amplitude offset modulator is coupled to circuitry that is adapted to modulate Level 2 data as amplitude offsets imposed on the D-MPSK modulated symbols, such that the D-MPSK modulated symbols are demodulated in order to decode the level 1 data, wherein demodulated data is aligned with reference subcarriers, and remodulated to recover original soft, or multi-leveled, symbol data.
14. The apparatus of claim 13 further comprising:
a. circuitry coupled to said amplitude offset modulator, the circuitry adapted to modulate Level 2 data as phase and amplitude offsets imposed on the D-MPSK modulated symbols.
15. The apparatus of claim 13 , wherein the D-MPSK modulated symbols comprising Level 1 and Level 2 data is received by a digital transmission receiver of the digital transmission system, the digital transmission receiver comprising:
a. a differential demodulator adapted to demodulate D-MPSK modulated symbols to decode the Level 1 data; and
b. a differential modulator adapted to remodulate the demodulated D-MPSK modulated symbols.
16. The apparatus of claim 13 , wherein the Level 2 is different than the Level 1 data, such that the Level 2 data is not used for error correction.