Reference Signal Pollution with example- LTE RF Optimization
Reference Signal Pollution with example
The concept of Reference Signal (RS) pollution is new in the industry; some engineers still refer to RS pollution as pilot pollution (a term inherited from 3G systems). In general, it is known that RS pollution is bad but it is important to keep in mind the reasons why it is bad.
For this workshop, assume the definition of DL RS pollution is a situation in which there are two or more additional cells with DL RS of comparable values to the serving cell.
The difference in dB of these signals determine how bad the pollution is. Please note that this definition may vary for each service provider.
In this example, if the serving cell’s RSRP is measured at -72 dBm, we are in a polluted coverage if we measure two or more neighbor cells within 3 dB range (say, -73 dBm, and -74.5 dBm).
The important thing to note here is this condition of strong interferers (due to lack of soft handover in LTE) result in lower signal quality (RSRQ and RS-SINR) and thus results in possible dropped connection (lower retainability KPI), lower data rates (lower integrity KPI), and/ or increased handovers (lower retainability and lower integrity KPIs).
This example illustrates a UE detecting the reference signal of six Node Bs.
- Cell 1 is the dominant cell and is seen with an RSRP of -72 dBm.
- Cell 2 is seen with an RSRP of -73.5 dBm (1.5 dB down from best).
- Cell 3 is seen with an RSRP of -78 dBm (6 dB down from best).
- Cell 4 is seen with an RSRP of -75.5 dBm (3.5 dB down from best).
- Cell 5 is seen with an RSRP of -74.5 dBm (2.5 dB down from best).
- Cell 6 is seen with an RSRP of -78.7 dBm (6.7 dB down from best).
In this example, there are three additional RS coming from different cells (Cells 2, 4, and 5) within 3 dB of the strongest, and thus it is considered a RS polluted area.
You may also like to go throughWhat is RF Optimization?,4G-LTE KPIs,3GPP Accessibility KPI,Retainability KPI in LTE, Throughput KPI & Latency KPI, Mobility KPI, Cell Availability KPI in LTE, Coverage of an LTE Cell, Cell-specific DL Reference Signal, UE Measurement- Reference Signal Received Power (RSRP), RSRQ and SINR, Coverage Analysis in LTE, What is the “right” coverage, What limits the coverage and Typical Reference Signal scenarios.