Method of Improving Performance in a Hierarchical Modulation System

A method of demodulating a hierarchically modulated transmission frame including an overlay layer modulated onto a base layer, the base layer providing basic service and the overlay layer providing additional services, the method comprising:

• receiving a transmission frame including first data symbols modulated using a first modulation technique combined with second data symbols modulated using a second modulation technique;
• demodulating a first data symbol of the received transmission frame using a first demodulation technique corresponding to the first modulation technique;
• synchronizing the received frame according to the demodulated first data symbol;
• and
• demodulating a received second data symbol of the received transmission frame using a second hierarchical demodulation technique corresponding to the second modulation technique.

A method of hierarchically modulating a transmission frame including an overlay layer modulated onto a base layer, the base layer providing basic service and the overlay layer providing additional services, the method comprising:

• synchronously aligning an overlay layer frame to a base layer frame,
• inserting additional data bits at the beginning of the aligned frame, wherein the additional data bits are related to a synchronization bit or pattern;
• splitting the aligned base layer frame and the additional bits among a first multi-carrier modulation symbol and a plurality of second multi-carrier modulation symbols, wherein the first multi-carrier modulation symbol comprises the additional data bits;
• designating a plurality of subcarriers in each of the second multi-carrier modulation symbols as pilot carriers;
• modulating the first multi-carrier modulation symbol and the plurality of pilot carriers using a first modulation technique;
• and
• hierarchically modulating the remaining subcarriers for each of the second multi-carrier modulation symbols using a second modulation technique overlaid on the first modulation technique to modulate the overlay layer onto the base layer.

A method of demodulating a hierarchically modulated transmission frame including an overlay layer modulated onto a base layer, the base layer providing basic service and the overlay layer providing additional services, the method comprising:

• receiving a transmission frame including a first multi-carrier modulation symbol and a plurality of second multi-carrier modulation symbols, wherein the first multi-carrier modulation symbol and the plurality of second multi-carrier modulation symbols comprise a plurality of subcarriers;
• demodulating the first multi-carrier modulation symbol using a first demodulation technique, wherein the first multi-carrier modulation symbol enables synchronization of the transmission frame;
• determining which of the subcarriers for each of the plurality of second multi-carrier modulation symbols are designated as pilot carriers;
• demodulating the pilot carriers for each of the second multi-carrier modulation symbols using the first demodulation technique;
• and
• demodulating the remaining subcarriers for each of the second multi-carrier modulation symbols using a second demodulation technique to extract the overlay layer from the base layer.

An apparatus configured to demodulate a transmission frame including an overlay layer modulated onto a base layer, the base layer providing basic service and the overlay layer providing additional services, the apparatus comprising:

• a receiver configured to receive a transmission frame including first data symbols modulated using a first modulation technique combined with second data symbols modulated using a second modulation technique, wherein the first data symbols are interspersed through the received transmission frame and comprise synchronization bits for the received transmission frame, and the second data symbols comprise payload data symbols for the base layer services and the overlay services, wherein the first data symbols are modulated using only the first modulation technique;
• and
• a processor configured to:
• demodulate a first data symbol of the received transmission frame using a first demodulation technique corresponding to the first modulation technique;
• synchronize the received frame according to the demodulated first data symbol;
• and
• demodulate a received second data symbol of the received transmission frame using a second hierarchical demodulation technique corresponding to the second modulation technique.

A computer readable medium having instructions stored thereon for modulating a transmission frame including an overlay layer modulated onto a base layer, the base layer providing basic service and the overlay layer providing additional services, the instructions performing the steps of:

• synchronously aligning an overlay layer frame to a base layer frame,
• inserting additional data bits at the beginning of the aligned frame and at a selected interval throughout the aligned frame, wherein the additional data bits are related to a synchronization bit or pattern;
• modulating the additional bits using a first modulation technique;
• and
• hierarchically modulating each other bit of the aligned frame using a second modulation technique based on the first modulation technique.