RRH Timing Alignment in Heterogeneous Wireless Networks
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Solution Overview
Problem
In heterogeneous wireless networks, remote radio heads (RRHs) often experience timing misalignment with macro base stations due to propagation delays in fiber optic connections, which can exceed cyclic prefix periods, failing to meet synchronization requirements for services like MBMS and macro/RRH-diversity.
Innovation Solution
A method involving a user equipment (UE) that assists in RRH synchronization by reporting its proximity to the RRH, allowing the macro base station to determine one-way delays, and a base band unit (BBU) that calculates and applies a timing advance to align RRH signals with macro base station signals, using system time synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fiber optic connections are used to connect RRHs to macro base stations, then signal transmission quality is improved, but propagation delays increase causing timing misalignment
Solution Approach 1:
The system performs preliminary timing measurements using reference signals before actual data transmission. The macro base station and RRH exchange reference signals to measure propagation delays in advance, then apply timing advance adjustments to pre-compensate for the fiber optic propagation delays, ensuring synchronized transmission without affecting signal quality
Solution Approach 2:
The system implements a feedback mechanism where the macro base station measures the timing of reference signals received from the RRH, calculates the propagation delay, and sends timing advance commands back to the RRH. This closed-loop feedback continuously adjusts the RRH transmission timing to compensate for fiber optic delays, maintaining synchronization while preserving transmission quality
2Reliability
If timing advance is applied to compensate for propagation delays, then synchronization is improved, but system complexity increases due to additional measurement and calculation requirements
Solution Approach 1:
The system uses self-service by having the network infrastructure itself perform the timing measurements and calculations. The macro base station and RRH autonomously exchange reference signals and compute propagation delays using existing network resources, eliminating the need for external timing synchronization equipment or complex external coordination systems
Solution Approach 2:
The reference signal exchange mechanism serves multiple functions: it enables timing synchronization, provides channel quality information, and supports mobile device handover decisions. By making the reference signals multi-functional, the system avoids adding separate dedicated timing measurement signals, thereby reducing overall system complexity while achieving synchronization
3Measurement precision
If reference signals are used for timing measurements, then timing accuracy is improved, but network overhead increases
Solution Approach 1:
The reference signals are designed to serve multiple purposes simultaneously: timing synchronization, channel estimation, and mobile device measurement for handover decisions. By making these signals multi-functional, the system achieves accurate timing measurements without requiring additional dedicated timing signals, thereby minimizing network overhead while maintaining high timing precision
Data Source
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AI summary
The apparatus includes a base band unit including a processor. The processor is configured to receive a first message, the first message including information identifying a remote radio head and a first time delay, the first time delay indicating a propagation time delay between a user equipment and a base station, receive a second message, the second message indicating the user equipment is associated with the remote radio head, receive a reference signal, the reference signal including a time stamp, determine a second time delay based on the time reference, the second time delay indicating a propagation time delay between the user equipment and the base band unit, determine a time value based on the first time delay and the second time delay, and transmit a data packet to the user equipment via the remote radio head, the transmitting being advanced in time by the time value.