DAS Node Delay Normalization for E911 Location Accuracy
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Solution Overview
Problem
In wireless communication systems, particularly in CDMA networks with distributed antenna systems (DAS), there is an inherent accuracy problem in locating mobile devices for E911 services due to fiber delays and differential delays between simulcast nodes, which affect the synchronization and accuracy of location-based services.
Innovation Solution
A method and system that uses a lookup table to determine the serving node for an E911 call by calculating round trip delay (RTD) ranges for each node, normalizing the delays by adding calculated RF delays to known fiber delays, and employing triangulation to determine the exact location of the wireless unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If fiber fed distributed antenna system (DAS) is introduced to CDMA network, then network coverage and capacity are improved, but synchronization accuracy and location service precision deteriorate due to fiber delays
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing round trip delay (RTD) ranges for each DAS node in a lookup table before location determination is needed. This allows the system to quickly retrieve and apply the appropriate RTD values during location calculations, compensating for fiber delays without adding real-time computational complexity. The RTD ranges are calculated based on known fiber delays and air delays, enabling accurate location determination despite the distributed antenna architecture.
Solution Approach 2:
The patent introduces an intermediary mechanism by using a lookup table that stores pre-calculated RTD ranges as an intermediate data structure. This lookup table acts as a mediator between the complex fiber delay calculations and the final location determination process. The system queries the lookup table with measured RTD values to identify the serving node, thereby simplifying the location calculation process while maintaining accuracy.
2Reliability
If simulcast nodes are used in DAS network, then signal coverage reliability is improved, but location calculation accuracy deteriorates due to differential fiber delays between nodes
Solution Approach 1:
The patent applies local quality by associating specific RTD range values with each individual DAS node in the lookup table. Each node has its own locally optimized RTD parameters based on its specific fiber delay characteristics and geographic location. This allows the system to accurately determine which node is serving a particular mobile device by matching the measured RTD to the appropriate local node parameters, thereby maintaining location accuracy despite the distributed nature of simulcast nodes.
3Device complexity
If traditional triangulation method is used for location determination, then implementation simplicity is maintained, but location accuracy deteriorates due to unaccounted fiber delays
Solution Approach 1:
The patent maintains implementation simplicity while improving accuracy by pre-calculating RTD ranges for each node and storing them in a lookup table. This preliminary action eliminates the need for complex real-time fiber delay calculations during location determination. The system simply queries the lookup table with measured RTD values to identify the serving node and performs standard triangulation, thereby maintaining low computational complexity while achieving accurate location determination.
Solution Approach 2:
The lookup table serving RTD ranges acts as an intermediary that bridges the gap between traditional triangulation methods and the requirements of fiber-fed DAS networks. It translates the complex fiber delay characteristics into simple queryable ranges, allowing the system to use traditional triangulation algorithms while accounting for fiber delays through the intermediary lookup table mechanism.
Data Source
AI summary
A method and system for normalizing various simulcasting nodes within a distributed antenna system (DAS) simulcast sector uses the simulcast sector's known fiber delays, the distance between the nodes, and its corresponding RF delays. The methodology includes adding calculated delays to the known fiber delays to normalize each node's delay. Each normalized node delay value is equal to the value of the fiber delay of the furthest node plus the respective RF delay distance from that node.