This article is about Network-wide Synchronization Deviation Detection.
Background.
TDD networks require precise clock synchronization, as any out-of-synchronization base station can cause interference with others. This interference can lead to poor service, network access issues for UEs, and increased likelihood of service drops or handover failures. A single unsynchronized base station may affect up to 100 other base stations, highlighting the broad impact of synchronization problems.
In LTE/NR TDD, Timing Advance (TA) adjusts uplink timings to ensure signals from UEs at different distances reach the base station simultaneously. TAoffset, a fixed value (20.3 μs for LTE, 13 μs for low-frequency NR, and 7 μs for high-frequency NR), helps base stations switch from uplink to downlink transmission. If the TA value equals the propagation delay, base stations must immediately transmit downlink subframes after receiving uplink subframes. If synchronization exceeds the allowed deviation, clock interference may occur, disrupting network operations.
To switch from uplink to downlink transmission, base stations need a specific time (GAP). Therefore, in addition to TA (equal to the propagation delay), UEs advance uplink transmission by TAoffset, and base stations receive uplink subframes early by TAoffset. This allows the base station time to switch from uplink to downlink. If the synchronization deviation between the reference and interfering base stations exceeds GAP or TAoffset, clock interference occurs.
In NR TDD high-frequency scenarios, the TAoffset value is very small, requiring extremely precise synchronization between base stations. When multiple base stations have synchronization issues simultaneously, it becomes difficult to identify the ones with problems. In such cases, most base stations in a small area may exhibit synchronization deviations, and only a few may be synchronized, making it challenging to pinpoint which base stations are experiencing synchronization issues.
Principles.
To accurately detect synchronization deviations, the network-wide synchronization deviation detection function is introduced. It uses a majority of properly synchronized base stations as references to identify those with deviations. The OSS analyzes synchronization deviation data across the network and calculates the deviation through sequence detection. By measuring bidirectional air interface delays, the inter-base-station synchronization deviation can be quantified. This ensures accurate identification of base stations with synchronization issues, especially when many in a small area are out of sync.
The delay between the sequence sent by base station A and received by base station B is measured as ΔT1 and ΔT2.
The delay represents the air interface propagation time, calculated as the average of ΔT1 and ΔT2. delay = (ΔT1 + ΔT2)/2.
The offset represents the synchronization difference between the base stations, calculated as half the difference between ΔT1 and ΔT2. This method enables the identification of synchronization issues by measuring delays and offsets between base stations. offset = ΔT1 – delay = (ΔT1 – ΔT2)/2.
Network-wide synchronization deviation detection includes the following components:
- Centralized control by OSS: Ensures sequence detection consistency across the network, specifying frequencies, subframe configurations, and detection periods for base stations.
- Periodic execution: Base stations periodically perform sequence detection as instructed by OSS, and report results back to the OSS for analysis and deviation identification.
This method ensures that synchronization deviations are detected and managed across the network, ensuring accurate timing across all base stations.
The OSS centralizes the analysis of synchronization deviation detection data, performing cluster analysis on sequence detection results. It identifies base stations with excessive synchronization deviation (beyond the threshold) and those suspected of being out of sync. Suspected base stations are those that could not receive characteristic sequences during the current period, or those affected by out-of-sync interference from neighboring stations. The results are displayed on the OSS GUI, listing affected base stations.
Prerequisites for this article are: