CPRI Path Delay Asymmetry Correction in Optical Transport Networks
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Solution Overview
Problem
In radio access networks using the Common Public Radio Interface (CPRI), asymmetric transmission media introduce unequal downlink and uplink delays, making it difficult to accurately estimate one-way delays, which is crucial for synchronization and calibration.
Innovation Solution
The method involves extracting and transmitting path delay data within CPRI data frames to correct for path delay asymmetry, using control words to convey the difference in transit times between nodes, allowing for accurate synchronization even in asymmetric networks like Optical Transport Networks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a point-to-point optical fibre connection is used, then the connection is symmetric with equal uplink and downlink delays, but this assumption cannot be made when using asymmetric connections
Solution Approach 1:
The patent introduces an intermediary mechanism (path delay data exchange through control words) that mediates between the asymmetric transport network and the CPRI interface. This intermediary allows each node to obtain and communicate path delay information, enabling accurate one-way delay calculation even when the underlying transport medium is asymmetric.
Solution Approach 2:
The patent implements a feedback mechanism where nodes exchange path delay data through control words in the CPRI interface. Each node measures its outgoing path delay, transmits this information to the other node, and uses the received feedback data to calculate accurate one-way delays, creating a closed-loop system that compensates for asymmetry.
2Measurement precision
If round-trip delay measurement is used, then the total delay can be measured accurately, but the one way delay cannot be estimated with required accuracy in asymmetric connections
Solution Approach 1:
The patent applies preliminary action by having nodes pre-measure and store their outgoing path delay values before communication occurs. This pre-measured data is then exchanged and used to calculate one-way delays without requiring additional measurement time during actual communication, thus avoiding synchronization delays.
Solution Approach 2:
The patent segments the round-trip delay measurement into two separate one-way measurements by having each node independently measure its own outgoing path delay. Instead of measuring the total round-trip delay and dividing by two (which is invalid in asymmetric networks), each node's measurement is treated as a separate, accurate one-way delay value.
3Reliability
If path delay data is exchanged between nodes, then accurate synchronization can be achieved in asymmetric networks, but additional data transmission requirements are introduced
Solution Approach 1:
The patent makes the existing control words in the CPRI interface multi-functional by using them to carry both their original control information and additional path delay data. This universal use of existing structures avoids adding separate dedicated data transmission channels, thereby reducing overall system complexity while achieving reliable synchronization.
Data Source
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AI summary
Communication between a Radio Equipment Control (REC) and a Radio Equipment (RE) in a wireless network uses a Common Public Radio Interface connection. When the Radio Equipment Control and the Radio Equipment are located remote from each other, and are connected by an asymmetric transport network, such as an Optical Transport Network, path delay data is transmitted in the Common Public Radio Interface data frames. This allows the CPRI end nodes to correct for path delay asymmetry using the path delay data.