LiFi Transmit Branch Combining Against Multi-Path Fading
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Solution Overview
Problem
Optical wireless communication systems face challenges with multi-path induced fading due to differences in travel time and cable length, leading to signal cancellations and reduced bit rates, especially in high-speed communication scenarios.
Innovation Solution
A MIMO system with a combiner that generates multiple output signals by combining transmit branch signals using linear combinations, ensuring these signals are received in overlapping reception areas of spatially separated transmitters, thereby reducing the likelihood of signal cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple optical transmitters are used to provide overlapping coverage areas, then system reliability is improved, but multi-path induced fading occurs due to differences in travel time and cable length
Solution Approach 1:
The patent changes the parameters of the transmitted signals by applying different linear combinations to the input signals at each transmitter. This modifies the signal characteristics (amplitude, phase relationships) so that when signals arrive at the receiver through different paths, they do not cancel each other out. The linear combination parameters are specifically chosen to ensure that signals from different transmitters with different path delays do not create destructive interference patterns.
2Reliability
If linear combinations are applied to transmit branch signals, then robustness against multi-path fading is improved, but device complexity increases
Solution Approach 1:
The patent segments the signal processing function by applying linear combinations at each individual transmitter rather than requiring complex centralized processing. Each transmitter independently processes its assigned linear combination of input signals, which simplifies the overall system architecture while achieving the desired robustness against multi-path fading. This segmentation distributes the computational complexity across multiple simple transmitter units.
Data Source
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AI summary
A LiFi system having multiple transceivers (11) and a single multiple-input- multiple-output (MIMO) modem (41) with at least M outputs, wherein the M transmit outputs of the MIMO modem (41) are fed to a linear combiner (42). The linear combiner creates M distinct linear combinations based on the N MIMO transmit branch signals of the MIMO modem and the linear combinations are chosen such that they allow decoding of each of the5 N MIMO transmit branch signals when N of the M distinct output signals are received.