Mismatched Roll-off Factors for Spectral Efficiency
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Solution Overview
Problem
Current satellite broadcast systems face limitations in spectral efficiency due to fixed bandwidth allocations, making it difficult to transmit additional signals and support increased programming without significant hardware upgrades or performance degradations.
Innovation Solution
Implementing a system with a modulator having a smaller root-raised cosine filter roll-off factor than the receivers, allowing for increased symbol rates and carrier capacity within the allocated bandwidth, while minimizing hardware costs and performance degradations by using Field Programmable Gate Arrays to reprogram modulators and maintaining existing demodulator roll-off factors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the roll-off factor is reduced to increase spectral efficiency, then bandwidth utilization improves, but signal quality and reliability deteriorate
Solution Approach 1:
The patent applies parameter changes by reducing the roll-off factor of the root-raised cosine filter in the modulator from conventional values (0.2-0.35) to a smaller value (0.1-0.15), thereby narrowing the signal bandwidth and increasing spectral efficiency. This parameter modification directly addresses the contradiction by optimizing the bandwidth utilization while managing the associated signal quality trade-offs through system-level compensation mechanisms.
2Productivity
If the symbol rate is increased to transmit more channels, then productivity improves, but bandwidth requirements increase causing interference
Solution Approach 1:
The patent modifies the temporal parameter by increasing the symbol rate to transmit more channels within the allocated bandwidth, directly improving productivity. Simultaneously, it applies spectral parameter changes by reducing the roll-off factor to narrow the signal bandwidth, thereby containing the harmful spectral leakage and interference that would otherwise result from higher symbol rates.
3Device complexity
If existing receivers are used with modified transmitters, then device complexity is reduced, but performance degradation occurs
Solution Approach 1:
The patent implements a one-sided parameter change strategy by modifying only the transmitter's roll-off factor while keeping the receiver's demodulator parameters unchanged. This asymmetric approach reduces device complexity by avoiding receiver hardware upgrades, while the performance degradation is managed through careful selection of the roll-off factor mismatch tolerance and potential software-based compensation in the receiver.
Data Source
AI summary
Systems for delivering a plurality of broadcast programs where the transmitter and receiver roll-off factors are mismatched. A system in accordance with the present invention comprises a transmitter comprising a modulator, and a plurality of receivers, each receiver in the plurality of receivers receiving the plurality of broadcast programs, each receiver in the plurality of receivers further comprising a demodulator; wherein the modulator has a first root-raised cosine filter having a first roll-off factor and each receiver has a second root-raised cosine filter having a second roll-off factor, the first roll-off factor being smaller than the second roll-off factor.