Remote Radio Unit Noise Generator for Analog RoF Linearity
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Solution Overview
Problem
Conventional analog RoF systems face challenges in increasing system linearity for long-distance transmission, particularly due to chromatic dispersion effects in optical fibers, which reduces the adjacent channel power ratio and increases hardware complexity in the remote radio unit.
Innovation Solution
The implementation of a noise generator in the remote radio unit to produce a stimulus signal with known statistical properties, allowing for blind identification and equalization of the uplink ROF channel, and the introduction of a power control unit to ensure system robustness and adaptability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional digital pre-distortion is used for downlink nonlinearity compensation, then system linearity is improved, but hardware complexity in the remote radio unit increases
Solution Approach 1:
The patent extracts the nonlinearity compensation function from the remote radio unit and places it in the central unit. The central unit performs digital pre-distortion on downlink signals and digital post-distortion on uplink signals, while the remote radio unit only performs simple analog amplification. This extraction resolves the contradiction by maintaining system linearity through centralized processing while reducing remote radio unit hardware complexity.
Solution Approach 2:
The patent introduces an intermediary processing architecture where the central unit acts as the intermediary for all digital signal processing and nonlinearity compensation. The remote radio unit serves as a simple analog intermediary for signal amplification. This intermediary architecture allows complex nonlinearity compensation to be performed centrally while keeping the remote unit simple, resolving the hardware complexity issue while maintaining system linearity.
2Duration of action of stationary object
If ADC and DAC are provided in the remote radio unit for digital RoF system, then transmission distance is improved, but device complexity and size of the remote radio unit increases
Solution Approach 1:
The patent extracts the ADC and DAC converters from the remote radio unit and places them in the central unit. The central unit performs analog-to-digital conversion for uplink signals and digital-to-analog conversion for downlink signals. This extraction enables long-distance transmission with digital signal processing capabilities while significantly reducing the device complexity and size of the remote radio unit.
Solution Approach 2:
The patent inverts the conventional architecture by placing the complex digital processing components (ADC, DAC, DSP) in the central unit rather than the remote radio unit. This inversion allows the remote radio unit to remain simple and compact while still enabling long-distance transmission through the centralized digital processing that compensates for fiber transmission effects.
3Use of energy by stationary object
If analog RoF system is used for long distance transmission, then power consumption is reduced, but system linearity deteriorates due to chromatic dispersion
Solution Approach 1:
The patent introduces digital signal processing as an intermediary layer in the central unit that compensates for chromatic dispersion effects. The central unit performs digital pre-distortion on downlink signals and post-distortion on uplink signals, acting as an intermediary that counteracts the nonlinearities introduced by long fiber transmission. This allows analog RoF system to maintain low power consumption while improving system linearity through centralized digital compensation.
Solution Approach 2:
The patent implements feedback mechanisms where the central unit receives uplink signals, performs digital post-distortion to compensate for nonlinearities, and sends corrected downlink signals back through pre-distortion. This feedback loop continuously compensates for chromatic dispersion effects, enabling long-distance transmission with maintained linearity while preserving the low power consumption advantage of analog RoF systems.
Data Source
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AI summary
The invention relates to a remote radio unit, RRU, (510) for a base transceiver station (500). The remote radio unit (510) comprises: a noise generator (511) configured to provide a RF noise signal having predefined statistical properties, in particular second-order statistics and/or higher-order statistics; a communication interface (513) configured to transmit the RF noise signal as a stimulus signal over a radio-over-fiber, ROF, uplink channel (520b) between the remote radio unit (510) and a central unit (530) of the base transceiver station (500) for determining a pre-distortion of a target signal to be transmitted by the remote radio unit (510), wherein the communication interface (513) is further configured to receive the pre-distorted target signal over a ROF downlink channel (520a) between the remote radio unit (510) and the central unit (530) of the base transceiver station (500); and an antenna (515) for transmitting the pre-distorted target signal received by the communication interface (513). Moreover, the invention relates to a corresponding central unit (530) for the base transceiver station (500) as well as corresponding methods of operating these units.