Optical Transceiver Module for DAS Intermodulation Distortion
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Solution Overview
Problem
In DAS systems, existing optical transceiver modules are susceptible to intermodulation distortions due to high dynamic variations and broad bandwidths in uplink signals, particularly when multiple frequency bands are co-existent, leading to interference issues that desensitize receivers and reduce signal quality.
Innovation Solution
The optical transceiver module OTRX 1:4 employs CWDM or DWDM demultiplexers to separate uplink signals from different Remote Units before combining them, using separate optical receivers and a 4:1 combiner with automatic gain control to prevent intermodulation distortions, ensuring each receiver processes only its intended signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple frequency bands are co-existent in the same optical link to reduce fiber counts, then the number of fibers is reduced, but intermodulation distortions occur due to strong signals covering weak signals
Solution Approach 1:
The patent divides the uplink signal processing into separate channels for each frequency band. Each band has its own optical receiver and signal processing path, preventing intermodulation distortions while still using a single optical fiber. The segmentation occurs at the receiver side where signals from different bands are processed independently before being combined.
Solution Approach 2:
The patent introduces an intermediary signal processing stage between the optical fiber and the final combination of signals. This intermediary stage includes separate optical receivers for each frequency band that process signals independently, acting as a mediator that prevents direct interaction between strong and weak signals that would cause intermodulation.
2Device complexity
If a single optical transmitter/receiver is used to drive multiple Remote Units for multiple frequency bands, then device complexity is reduced, but intermodulation issues arise from co-existence of multiple bands
Solution Approach 1:
The patent segments the signal reception function by providing separate optical receivers for each frequency band while maintaining a single optical transmitter. This allows the system to handle multiple bands through one transmitter but with independent reception paths that prevent intermodulation distortions.
Solution Approach 2:
The patent applies local quality by giving each frequency band its own dedicated optical receiver with optimized characteristics for that specific band. This localized processing ensures that each band is handled with appropriate sensitivity and gain control, preventing strong signals from overwhelming weak signals.
3Device complexity
If uplink signals with broad bandwidth and high dynamic variations are processed together, then signal processing is simplified, but intermodulation distortions increase due to strong signals covering weak signals
Solution Approach 1:
The patent segments the uplink signal processing by creating separate processing paths for different frequency bands. Each band is processed independently through its own optical receiver, maintaining signal integrity even with broad bandwidth and high dynamic variations, while still achieving combined output for transmission.
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 configuration effectively eliminates intermodulation distortions by isolating and processing each uplink signal separately, maintaining signal quality and avoiding interference, thus enhancing the reliability of DAS systems.
Implementation Method 1
an optical splitter OS 1:2 of the 1310nm type, connected in input to the laser L
Implementation Method 2
two WDM (Wavelength Division Multiplexing) couplers, indicated in the figures as WDM1 and WDM2
Implementation Method 3
employs CWDM or DWDM demultiplexers to separate uplink signals from different Remote Units
Implementation Method 4
using separate optical receivers and a 4:1 combiner with automatic gain control
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The optical transceiver module (OTRX 1:4) for communications in DAS systems, installable on the Master Unit side of a DAS system connectable to a plurality of Remote Units, comprises an uplink connector (UL RF) and a downlink connector (DL RF) connectable to a radio base station, a first optical connector (COMMON 1) and a second optical connector (COMMON 2) connectable to the Remote Units, a downlink path for the connection between the downlink connector (DL RF) and a first and second optical connector (COMMON 1, COMMON 2), and an uplink path for the connection between the uplink connector (UL RF) and the first and second optical connector (COMMON 1, COMMON, 2), wherein the uplink path comprises a first coupler (WDM 1) of the WDM type and a second coupler (WDM2) of the WDM type connected, respectively, to the first optical connector (COMMON 1) and to the second optical connector (COMMON 2), and wherein the uplink path comprises a first demultiplexer (DWDM1, CWDM1) and a second demultiplexer (DWDM2, CWDM2) connected, respectively, to the outputs of the first coupler (WDM 1) and of the second coupler (WDM2) and adapted to separate the optical signals coming from the Remote Units.