Spread-Spectrum Pilot Signal Interference Cancellation in HAPS Multi-Feeder Links
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Solution Overview
Problem
Dynamic interference in multi-feeder links of aerial-floating type communication relay apparatuses is challenging due to the movement of the upper-air relay apparatus, which complicates effective frequency utilization and requires a simple configuration for interference suppression.
Innovation Solution
The system employs a relay communication station with a feeder-link communication section that transmits and receives relay signals on the same frequency from multiple gateway stations, using spectrally spread pilot signals and inverse-spreading to estimate propagation path responses, calculate weights, and subtract interference signals, thereby suppressing interference between feeder links.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple gateway stations transmit feeder link signals on the same frequency to improve frequency utilization efficiency, then frequency utilization efficiency is improved, but dynamic interference occurs between feeder links
Solution Approach 1:
The patent changes the parameter of pilot signal bandwidth from narrowband to spread-spectrum (wideband), and changes the signal processing method from direct reception to inverse-spreading followed by correlation processing. This enables the system to resolve dynamic interference while maintaining frequency reuse, as the spread-spectrum pilot signals provide robust channel estimation despite interference.
Solution Approach 2:
The patent replaces the conventional narrowband pilot signal mechanism with a spread-spectrum pilot signal mechanism. Instead of using traditional narrowband frequency references, the system uses wideband spread-spectrum signals that are processed through inverse-spreading and correlation operations, substituting the mechanical/frequency-based approach with a signal-processing-based approach that is more resilient to dynamic interference.
2Measurement precision
If narrowband pilot signals are used for propagation path response measurement, then measurement precision is improved, but stable oscillation circuits and narrowband reception filters are required, increasing device complexity
Solution Approach 1:
The patent substitutes the mechanical hardware requirements (stable oscillation circuits and narrowband reception filters) with a signal processing approach. By using spread-spectrum pilot signals and processing them through inverse-spreading and correlation operations, the system achieves propagation path response measurement without requiring highly stable local oscillators or complex narrowband filtering hardware.
Solution Approach 2:
The patent changes the fundamental parameter of the pilot signal from narrowband to spread-spectrum wideband. This parameter change transforms the measurement approach from one that requires precise frequency stability to one that uses processing gain and correlation to achieve measurement precision, thereby eliminating the need for stable oscillation circuits and simplifying the receiver configuration.
Data Source
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AI summary
A downlink interference is dynamically suppressed in a multi-feeder link of a same frequency between an aerial-floating type communication relay apparatus and plural gateway (GW) stations with a simple configuration. A plurality of pilot signals, which are spectrally spread using a plurality of spread codes orthogonal to each other, are transmitted and received between the relay communication station of the aerial-staying type communication relay apparatus and plural GW stations, a propagation path response between plural GW stations and an antenna for feeder link of the communication relay apparatus in a transmission signal band of the feeder link is estimated based on reception results in which the plural pilot signals are spectrally inverse-spread, plural weights respectively corresponding to the plural of GW stations are calculated based on the plural propagation path responses, and with respect to each of the plural GW stations, a signal to be transmitted and received via a directional beam corresponding to another GW station is multiplied by the weight corresponding to the other GW station and subtracted from a signal to be transmitted and received via the directional beam corresponding to the GW station.