RRH-UE Co-Located Timing Feedback for Fronthaul Latency Compensation
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Solution Overview
Problem
The spatial distribution of RAN elements in wireless communication networks, such as LTE and 5G, introduces unknown and potentially time-varying latencies, leading to phase errors that affect operational requirements like air interface orthogonality and coordinated multipoint (CoMP) requirements, which existing synchronization techniques like GPS and IEEE 1588 may not adequately address, especially in indoor environments where GPS signals are unavailable.
Innovation Solution
Incorporating a limited-functionality or full-functionality UE component, referred to as RRH-UE, into the RRH, which is co-located and operatively coupled to provide control and management signals, including latency information, to adjust timing and synchronize RRHs with BBUs and other RRHs, using wireless communication protocols to correct for fronthaul latency and maintain phase alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If spatial distribution of RAN elements is implemented to separate BBU and RRH, then flexibility and coverage are improved, but phase synchronization accuracy deteriorates due to unknown and time-varying fronthaul latencies
Solution Approach 1:
The patent implements a feedback mechanism where timing information is continuously measured and reported back to the BBU. The BBU uses this feedback to dynamically adjust transmission timing, compensating for variable fronthaul latencies. This closed-loop feedback system maintains phase synchronization accuracy despite the spatial distribution of network elements.
Solution Approach 2:
The patent introduces an intermediary timing measurement and reporting mechanism between the BBU and RRH. This intermediary system measures the actual fronthaul latency and provides correction information, acting as a mediator that reconciles the timing differences introduced by spatial distribution while maintaining synchronization accuracy.
2Reliability
If GPS signals are used to synchronize RRH internal clocks, then synchronization is improved, but reliability deteriorates in indoor environments where GPS signals are unavailable
Solution Approach 1:
The patent implements a self-service synchronization mechanism where each RRH measures its own timing characteristics and reports them to the BBU. The system uses internally generated timing references and measurements rather than relying on external GPS signals, enabling reliable synchronization in any environment including indoor locations where GPS is unavailable.
Solution Approach 2:
The patent merges the timing measurement and synchronization functions into the existing fronthaul communication infrastructure. By combining timing measurements with data transmission over the same fronthaul link, the system eliminates the need for separate GPS receivers and external synchronization infrastructure, achieving environment-independent reliability.
3Ease of operation
If fronthaul network is used to connect BBU and RRH, then deployment flexibility is improved, but timing accuracy deteriorates due to unknown and potentially time-varying latencies
Solution Approach 1:
The patent implements dynamic timing adjustment where the BBU continuously adapts its transmission timing based on measured fronthaul latency variations. Rather than using fixed timing assumptions, the system dynamically compensates for changing conditions in the fronthaul network, maintaining timing accuracy despite the flexibility provided by the packet-switched fronthaul infrastructure.
Solution Approach 2:
The patent performs preliminary timing measurements and establishes timing relationships before actual data transmission begins. By pre-characterizing the fronthaul latency and establishing timing offsets in advance, the system prepares compensation mechanisms that can be applied during normal operation, maintaining timing accuracy while benefiting from fronthaul flexibility.
Data Source
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AI summary
A remote radio head (RRH) of a distributed radio access network (RAN) is equipped with a co-located user equipment (UE). The UE can be a chipset integrated into the RRH, which is connected to other parts of the RAN via a fronthaul network. The UE can be used to relay information, such as management information to and/or from the RRH. Timing information obtained by the UE can be provided to the RRH and used as an indication of fronthaul latency. The RRH can then adjust its operation in response to the indication of fronthaul latency.