Cell Selection Using Round Trip Delay Measurements
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Solution Overview
Problem
In air-to-ground communications, user equipment (UE) devices face challenges in connecting to network cells due to large distances, leading to unsuccessful attachment procedures and suboptimal performance, as existing technologies lack protection against out-of-range cells and incorrect timing advance value evaluations, resulting in prolonged connection times.
Innovation Solution
A method that determines round trip delay (RTD) measurements from multiple base stations, ranks cells based on RTD, RSRP, and signal quality, and initiates attachment to the highest-ranked cell, while using a fail counter to prevent prolonged attempts on unresponsive cells and storing timing offset values to minimize reconnection delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the UE initiates attachment to the eNodeB with the highest RSRP according to 3GPP LTE standard, then the connection is established quickly, but the UE may attach to an out-of-range cell or a cell with excessively large RTD, resulting in attachment failure or suboptimal performance
Solution Approach 1:
The UE performs preliminary RTD measurements and range checks on detected cells before initiating the attachment procedure. By evaluating whether the cell is within PRACH preamble range and whether RTD is below the threshold in advance, the UE prevents attachment attempts to unsuitable cells, thereby avoiding attachment failures while maintaining efficient connection establishment.
Solution Approach 2:
The system incorporates feedback mechanisms where the UE measures RTD and RSRP of detected cells, evaluates their suitability based on pre-defined thresholds, and uses this information to select the optimal cell for attachment. This feedback-driven cell selection process ensures that the UE attaches to a cell that is both strong in signal quality and within operational range, resolving the contradiction between speed and reliability.
2Area of stationary object
If the UE transmits a sequence of PRACH preambles with different timing advance offsets to cover large distances, then the coverage range is extended, but the attachment procedure time increases significantly when the cell is out of range
Solution Approach 1:
The UE performs preliminary RTD measurements and range evaluations before initiating the attachment procedure. By determining whether the detected cell is within the PRACH preamble range (i.e., RTD is below the threshold), the UE avoids unnecessary transmission of multiple PRACH preambles with different timing advance offsets to out-of-range cells, thereby significantly reducing attachment procedure time while maintaining extended coverage capability.
Solution Approach 2:
Instead of transmitting the full sequence of PRACH preambles with all possible timing advance offsets to every detected cell, the UE performs a preliminary check to determine if the cell is within range. Only if the cell passes the range check does the UE proceed with the PRACH preamble transmission sequence. This partial action approach avoids excessive transmissions to out-of-range cells, reducing time loss while preserving the ability to cover large distances when necessary.
3Adaptability or versatility
If the eNodeB incorrectly evaluates the timing advance value in the PRACH preamble, then the RAR message contains incorrect timing information, but the UE continues to re-attempt attachment using the same timing advance value, causing prolonged connection delays
Solution Approach 1:
The UE implements a feedback mechanism that monitors the outcome of attachment attempts. When an attachment fails or when the T300 timer expires, the UE evaluates whether the failure may be due to incorrect timing advance evaluation by the eNodeB. Based on this feedback, the UE adjusts its behavior by trying the next timing advance offset in the sequence or selecting an alternative cell, rather than indefinitely retrying with the same incorrect parameters. This feedback-driven approach maintains attachment retry capability while preventing prolonged connection delays.
Solution Approach 2:
The UE dynamically adjusts its attachment strategy based on real-time conditions. When an attachment attempt fails, the UE does not statically persist with the same timing advance value but instead dynamically changes its approach by trying the next timing advance offset or selecting a different cell. This dynamic behavior allows the system to adapt to incorrect timing advance evaluations by the eNodeB, maintaining versatility in attachment methods while reducing connection establishment time through timely strategy changes.
Data Source
AI summary
Embodiments described herein relate to a method of selecting a cell for communication over a network, the method comprising: determining a round trip delay (RTD) measurement from a device to each of a plurality of base stations, each of the plurality of base stations being in a respective one of a plurality of cells; ranking the plurality of cells based at least in part on the RTD measurements; selecting the highest-ranked cell; and initiating attachment to the selected cell.