Asynchronous Spread-Spectrum Satellite Return Link Interference Cancellation

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Solution Overview

Problem

Existing satellite communication systems face challenges in efficiently implementing a low-cost, high-performance return link for non-real-time messaging services with low duty-cycle mobile terminals, particularly in S-band communications, due to issues with timing synchronization, power control, access control, and high signaling overhead in current random access protocols like Slotted Aloha and Spread Aloha.

Innovation Solution

A method using Successive Interference Cancellation (SIC) in a Spread-Aloha scheme with a sliding processing window and smart open-loop packet transmission control, optimized for burst mode operations, to enhance throughput and reduce signaling overhead, while allowing gateway scalability and low-cost implementation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If Slotted Aloha or CRDSA protocols are used for random access, then the system can handle low duty-cycle mobile terminals, but the signaling overhead becomes unacceptable and MAC throughput is poor

Engineering Contradiction:

Improvecapability to handle low duty-cycle terminalsVSAvoidsignaling overhead

Core Design Contradiction:

Adaptability or versatilityVSLoss of information

Solution Approach 1:

The patent changes the fundamental access mechanism from time-slotted random access to continuous code-domain random access. Terminals transmit packets continuously with unique spreading codes instead of waiting for slots, eliminating slot synchronization signaling and reducing overhead while maintaining compatibility with low duty-cycle operation

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the time-domain slot-based access mechanism with a code-domain spreading mechanism. Instead of using time division multiple access with slots, the system uses code division multiple access where each terminal is assigned a unique spreading code, substituting temporal coordination with code-based differentiation to eliminate signaling overhead

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Productivity

If Spread Aloha scheme is used, then throughput capability is higher than SA or CRDSA, but the system becomes highly sensitive to multiple access carrier power unbalance

Engineering Contradiction:

Improvethroughput capabilityVSAvoidsensitivity to power unbalance

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent introduces an intermediary processing stage at the gateway that performs power normalization and interference cancellation on received signals before decoding. This intermediary processing equalizes the effect of power unbalance, allowing the system to maintain high throughput while becoming robust to carrier power variations

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent converts the harmful effect of power unbalance into a beneficial feature by using it as a signature characteristic. The gateway measures received power levels to identify and separate different terminal signals, transforming what was previously a source of interference into a useful discrimination mechanism that enhances throughput while managing power variations

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Productivity

If closed loops for timing synchronization, power control, and access control are implemented, then system performance can be optimized, but the complexity and cost increase significantly

Engineering Contradiction:

Improvesystem performanceVSAvoidcontrol mechanism complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent implements self-service mechanisms where terminals autonomously select their own spreading codes and transmit without centralized coordination. The gateway autonomously processes incoming signals using the measured power levels and code sequences, eliminating the need for complex closed-loop control mechanisms while maintaining system performance

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent performs preliminary actions by pre-assigning unique spreading codes to terminals before transmission and pre-configuring the gateway with the corresponding code sequences. This preliminary setup enables the gateway to directly process incoming signals without requiring real-time synchronization or power control loops, reducing complexity while maintaining performance

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentEP2159926B1Methods, apparatuses and system for asynchronous spread-spectrum communication

Publication Date: 2019.10.23 EUROPEAN SPACE AGENCY

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AI summary

A method of receiving data packets asynchronously transmitted by a plurality of user terminals using a spread-spectrum medium access protocol, comprising a step of cancelling interferences between colliding packets according to an innovative "sliding window" processing algorithm. A gateway receiver adapted for carrying out interference cancellation according to said algorithm. A method for controlling asynchronous packet transmission from a user terminal, comprising estimating a parameter indicative of the quality of information transmission through a communication channel; and inhibiting or allowing data transmission depending on a comparison between said estimated parameter and an adaptively varying threshold. A user terminal comprising transmission control means adapted for carrying out such a method. A communication system comprising a plurality of mobile user terminal communicating with a gateway through a satellite channel using an asynchronous spread-spectrum medium access protocol without closed-loop power control, wherein said user terminals and said gateway are of the kind described above.