Hierarchical Modulation Offset Sequences for SDAR Capacity
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Solution Overview
Problem
The limited allocation of the electromagnetic spectrum for satellite digital broadcasting hinders the amount of data that can be transmitted from communication satellites to receivers in SDAR systems, particularly in urban areas with limited line-of-sight coverage.
Innovation Solution
The implementation of hierarchical modulation schemes in SDAR systems, where two levels of data are transmitted by generating a first modulated signal and superimposing additional modulations on it, allowing for increased data transmission capacity while maintaining backward compatibility with legacy receivers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If hierarchical modulation is implemented to increase data transmission capacity, then the amount of data transmitted is improved, but the device complexity increases
Solution Approach 1:
The patent segments the data transmission into two hierarchical levels: a first level for legacy receiver compatibility and a second level for enhanced data capacity. This segmentation allows the system to maintain backward compatibility while adding advanced functionality, resolving the contradiction between increased capacity and system complexity.
Solution Approach 2:
The patent embeds the second level of modulation within the first level modulation structure. The hierarchical modulation scheme nests additional data streams within the existing signal framework, enabling increased capacity without proportionally increasing overall system complexity.
2Productivity
If additional modulations are superimposed on the first modulated signal, then the data transmission capacity is improved, but the compatibility with legacy receivers deteriorates
Solution Approach 1:
The patent divides the modulation into distinct levels where the first level maintains legacy compatibility and the second level provides enhanced capacity. Legacy receivers process only the first level while advanced receivers extract both levels, resolving the compatibility-capacity contradiction.
Solution Approach 2:
The patent applies partial modulation by superimposing additional modulations only on the first modulated signal rather than replacing it entirely. This partial action enables enhanced capacity for advanced receivers while preserving the original signal integrity for legacy receivers.
Data Source
AI summary
The present invention provides a method, receiver and transmitter for use in a SDAR system. The method involves generating a first modulated signal based on first input data. Additional modulation is superimposed on the first modulated signal based on additional input data, being spread across a plurality of symbols in the first modulated signal in a predetermined pattern to generate a modified signal which is then transmitted. The modified signal is decoded by performing a first demodulation of the first modulated signal then additional demodulation is performed to obtain additional input data. The superimposing step uses a plurality of offset sequence values to add the additional modulation to the first modulated signal. The offset sequence may appear as a pseudo-random distribution of offset sequence values, and may include at least one zero offset value. Alternatively, the additional modulated signal may be a formed as a direct sequence spread spectrum modulation and the offset sequence appearing as a pseudo-noise distribution. A Hadamard matrix sequence may be used as the direct sequence code.