TDD Control Signal Multiplexing on Coax Cables
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Solution Overview
Problem
Existing time division duplex (TDD) wireless communication systems face challenges in reliably transmitting and receiving control signals over coax cables due to interference and high error rates, especially when using wireless methods, and difficulties in separating DC power changes from RF signals when injecting control signals directly into RF cables.
Innovation Solution
A multiplexing system that modulates the transmit/receive control signal onto a separate control frequency and multiplexes it with DC power and RF signals over coax cables, using a 10.7 MHz oscillator and LC elements to ensure reliable transmission and minimize electromagnetic interference, allowing for independent RF paths to maintain system operation even if one path fails.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dedicated cable is used to transmit the transmit/receive control signal from the transceiver to the amplifier, then the control signal transmission is reliable, but the system becomes expensive to implement and maintain
Solution Approach 1:
The patent combines the transmit/receive control signal transmission with the existing RF cable that carries DC power and RF signals. By modulating the control signal onto a separate timing control operating at a separate control frequency and multiplexing it onto the RF cable, the system eliminates the need for a dedicated control cable, thereby reducing implementation and maintenance costs while maintaining reliable control signal transmission.
Solution Approach 2:
The RF cable is made multi-functional by enabling it to carry multiple signals simultaneously: DC power, RF signals, and the modulated transmit/receive control signal. This universal utilization of the existing cable infrastructure eliminates the need for additional dedicated cables, reducing system complexity and cost while preserving control signal reliability.
2Device complexity
If the transmit/receive control signal is passed wirelessly from the transceiver to the amplifier, then the system cost is reduced, but aerial interference causes high error rates
Solution Approach 1:
The patent uses the RF cable as an intermediary medium to transmit the control signal, avoiding wireless transmission and its associated aerial interference problems. By modulating the control signal onto a separate frequency and transmitting it through the shielded RF cable infrastructure, the system achieves reliable control signal transmission without the high error rates associated with wireless methods, while still avoiding the cost of a dedicated control cable.
3Device complexity
If the DC level of the transmit/receive control signal is injected directly into the RF cable using a bias tee, then the control signal can be transmitted over the existing cable, but the DC level change is difficult to separate from DC power changes
Solution Approach 1:
The patent changes the parameter domain of the control signal from DC level to a modulated AC signal at a separate control frequency. By modulating the transmit/receive control signal onto a separate timing control operating at a separate control frequency, the control signal can be easily distinguished from DC power changes through frequency separation, eliminating the measurement precision problems associated with direct DC level injection.
Solution Approach 2:
The patent uses signal modulation at a separate control frequency to create a distinguishable signal pattern that can be easily separated from DC power variations. The modulated signal oscillates at a specific frequency, allowing the receiving end to use frequency-selective filtering and demodulation to extract the control signal accurately, independent of DC power level changes.
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 solution provides a reliable and cost-effective method for transmitting TDD control signals, reducing error rates and maintenance costs by using coax cables to pass DC power and control signals, while ensuring independent RF paths to prevent system failure from single-point issues.
Implementation Method 1
a separate timing control signal, different from the RF signal, is generated and modulated by the transmit/receive control signal
Implementation Method 2
LC elements to ensure reliable transmission and minimize electromagnetic interference
Implementation Method 3
the transmit/ receive control signal modulates a separate timing control operating on a separate control frequency
Data Source
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AI summary
A method and system is disclosed for passing a transmit/receive control signal and a power signal through a coax cable from a base transceiver station to a tower top device in a time division duplex communication system. After generating the transmit/receive control signal and a radio frequency signal for communications, the transmit/receive control signal modulates a separate timing control operating on a separate control frequency. It is then multiplexed on at least one coax cable along with the radio frequency signal and DC power. At the tower top device, the modulated transmit/receive control signal is converted back to a DC level for providing a time division duplex control reference.