Patent ID: 7903629

Claim:
A method for transmitting high priority and low priority digital data in hierarchical modulation from an earth-orbiting satellite, the method comprising the steps: encoding the high priority digital data with a forward error correcting code to provide encoded high priority digital data; performing an Inverse Fast Fourier Transform on the encoded high priority digital data to provide high priority, orthogonal frequency division multiplexed (OFDM) symbols each comprising a first predetermined number of samples in an original high priority sample order, each of the first predetermined number of samples having a sample power; encoding the low priority digital data with a forward error correcting code to provide encoded low priority digital data; performing an Inverse Fast Fourier Transform on the encoded low priority digital data to provide low priority orthogonal frequency division multiplexed (OFDM) symbols each comprising a second predetermined number of samples in an original low priority sample order, wherein the second predetermined number is less than the first predetermined number; selecting one of the high priority OFDM symbols and one of the low priority OFDM symbols; selecting a plurality of samples of the selected high priority OFDM symbol equal in number to the second predetermined number, wherein the selecting is in accordance with a first consistent, deterministic rule using sample power comparisons to eliminate one or more of the highest powered samples of the high priority OFDM symbol from selection; associating each sample of the selected low priority OFDM symbol with a different one of the selected samples of the selected high priority OFDM symbol according to a second consistent, deterministic rule relating the original low priority sample order to the original high priority sample order; deriving a combined OFDM symbol based on the selected high priority OFDM symbol by (1) leaving unchanged each sample of the selected high priority OFDM symbol having no associated sample of the low priority OFDM symbol and (2) superimposing each sample of the selected low priority OFDM symbol onto its associated sample of the selected high priority OFDM symbol to provide a combined sample having a sample power equal to the sum of the sample powers of the associated samples so combined; incorporating the combined OFDM symbol in a radio frequency OFDM signal, whereby the encoded low priority digital data is modulated as secondary data on the encoded high priority digital data, as primary data, in hierarchical modulation; and transmitting the radio frequency OFDM signal on a plurality of orthogonal radio frequency carriers.