SINR Definition.
The SINR (Signal to Interference plus Noise Ratio) measures the quality of the signal relative to the interference and noise it experiences. In LTE networks, SINR is crucial because it directly impacts the quality of communication, including data rates and call stability.
PDCCH SINR Calculation:
PDCCH SINR = RS power of the best serving cell / interference from the coverage cell.
Different network operators set varying SINR requirements based on their specific deployment and optimization strategies. For example, China Mobile requires that 95% of cells should have an SINR greater than -3 dB. During optimization, efforts are made to ensure that only a small percentage of cells fall below this threshold to maintain network performance.
Root Causes of Low SINR:
- Weak Coverage: When the signal strength from the serving cell is low, the SINR drops, leading to poor communication quality.
- Interference: Signals from neighboring cells or other sources can cause interference, reducing the SINR and affecting the overall network performance.
To address low SINR, network optimization techniques such as adjusting antenna tilts, modifying power settings, and reducing interference sources are used.
How to Find a Cell of Low SINR?
Below are the steps to Find a Cell with Low SINR Using DT Test Data.
Accessing Server Cell RSRP in CNA:
- In the CNA interface, navigate to the sub-node Measurement of MS1 from the navigation tree on the left.
- Find Server Cell RSRP under this sub-node.
- Right-click on Server Cell RSRP and select View In Map from the shortcut menu, or alternatively, drag and drop Server Cell RSRP into the map window on the right
Adding Dynamic Link:
- In the navigation tree on the left, locate Dynamic Link under the MS1 node.
- Right-click Dynamic Link and choose Add from the shortcut menu.
Configuring LTE-SC Link:
Click Apply and wait for the success message to be displayed. In the pop-up dialog box, select LTE-SC Link.
Visualizing GPS and Signal Strength:
From the toolbar, click the appropriate tool
and select LTE-SC Link from the drop-down list. Ensure the GPS dotted line is selected.
Check the connection lines between the server cell and the RSRP legends. This will allow you to observe the signal intensity in the area of interest and identify regions with low SINR.
How to Raise the SINR of a Cell?
To improve the SINR of a cell in an LTE network, you can apply the following methods:
- Avoid Handovers and Overlapped Coverage:
- Minimize unnecessary handovers and overlap between cells with the same network schema. This reduces interference between cells, leading to an increase in SINR.
- Reduce Pilot Frequency Pollution:
- Decrease the likelihood of pilot frequency pollution, where signals from multiple cells interfere with each other. Proper cell planning and power adjustments can help in reducing such interference.
- Eliminate Poor Coverage and Overshooting Areas:
- Address areas with poor coverage and eliminate overshooting, where a cell’s signal extends beyond its intended coverage area. This ensures that users are connected to the optimal cell, improving SINR.
- Resolve RRC Re-establishment Issues:
- Fix issues related to RRC re-establishment caused by delayed handovers, missed handovers, and handover failures. Timely and successful handovers ensure that the UE maintains a strong and interference-free connection, thereby enhancing SINR.
Study Case of Low SINR in Cell PCI150 and Cell PCI144 Caused by Handover Failure.
Problem Description
The test UE fails to complete the handover from cell PCI150 to cell PCI144.
Problem Analysis
After the test UE sends the measurement report for cell PCI150, the eNodeB does not make a handover judgment. Two seconds later, the UE triggers RRC re-establishment, but the request is rejected. The neighboring cell relationship configuration has been verified as correct. This situation suggests that the lack of handover judgment and the rejection of RRC re-establishment are due to low-speed measurement, which prevents timely processing.
Solution
Introduce a 3dB offset when the test UE conducts handover from cell PCI150 to cell PCI144 to improve the likelihood of successful handover and reduce the chances of low SINR caused by the handover failure.
