Timing Half-Duplex Satellite Transmissions
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Solution Overview
Problem
Wireless communication systems, particularly those using OFDMA, face challenges with Doppler shift and time synchronization issues due to motion and varying distances between devices and receivers, which are exacerbated in satellite communications and when dealing with half-duplex devices that cannot send and receive simultaneously.
Innovation Solution
Implementing a system that accurately times uplink and downlink transmissions to prevent overlapping and partitions half-duplex devices into groups to transmit and receive at different times, using timing information to align transmissions and reduce synchronization complexity, thereby enhancing bandwidth efficiency and reducing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If OFDMA is used to enable simultaneous transmissions from multiple devices, then spectral efficiency is improved, but time and frequency synchronization problems worsen due to Doppler shift and varying propagation delays
Solution Approach 1:
The patent segments the communication system into multiple groups of half-duplex devices, where each group is assigned specific time slots for transmission and reception. This segmentation allows the system to maintain high spectral efficiency through OFDMA while managing synchronization by treating each group independently with dedicated timing configurations that account for their specific propagation delays and Doppler effects.
2Device complexity
If half-duplex devices are used to reduce device complexity and cost, then device complexity is reduced, but overlapping transmission and reception problems worsen due to inability to send and receive simultaneously
Solution Approach 1:
The patent implements dynamic time slot allocation where the transmission and reception time slots for half-duplex devices are dynamically adjusted based on their specific propagation delays and the current communication conditions. This dynamic approach allows the system to adapt to varying channel conditions while preventing overlapping transmissions, maintaining simplicity of half-duplex operation without the harmful effects of interference.
3Area of stationary object
If satellite-based communications are used to extend coverage area, then coverage area is expanded, but time synchronization problems worsen due to vast distances and high satellite velocities
Solution Approach 1:
The patent applies preliminary timing adjustments and synchronization configurations before actual communication begins with satellite-connected devices. By pre-calculating and pre-configuring the timing parameters based on known satellite ephemeris data and expected propagation delays, the system establishes accurate synchronization references in advance, which then guide the actual communication process and maintain time synchronization despite the vast distances and high satellite velocities.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively prevents overlapping transmissions, reduces synchronization complexity, and improves bandwidth efficiency and latency for half-duplex devices in wireless communication systems, especially in satellite-based communications.
Implementation Method 1
OFDMA schemes are sensitive to Doppler shift and time synchronization problems. For example, OFDMA schemes can be prone to frequency synchronization problems caused by motion (e.g., Doppler effects)
Data Source
AI summary
Systems, methods, and non-transitory media are provided for timing transmissions in a wireless communication system. An example method can include determining, at a satellite, a maximum round-trip propagation delay associated with one or more user terminals of a plurality of user terminals, determining, based on the maximum round-trip propagation delay, a respective downlink to uplink (DL/UL) offset for each user terminal, wherein the DL/UL offset comprises a time difference between a first downlink frame at the satellite and a first corresponding uplink frame at the satellite, transmitting a first downlink frame, receiving a first uplink frame from a first user terminal associated with the maximum round-trip propagation delay during the first corresponding uplink frame at the satellite, and receiving a second uplink frame from a second user terminal associated with a round-trip propagation delay less than the maximum round-trip propagation delay during the first corresponding uplink frame at the satellite.