RSRP/RSSI/RSRQ

RSRP

RSRP and RSSI measurements are power measurements where RSRP is the Reference Signal Received Power, which is also called the SS-RSRP (Synchronization Signal RSRP). For SS-RSRP, the UE measures a single resource element belonging to the SSS.

Considering this, in contrast to RSSI, the RSRP measurement is normally lower than the RSSI measurement.

RSSI

RSSI is measured across the entire channel bandwidth, which includes all resource elements, noise, and interference.

Generally, the larger the channel size, the more resource elements that are measure by the UE, meaning the UE will likely measure larger bandwidths at a higher RSSI value than smaller bandwidths.

A fun analogy for this is…

Imagine you have two tables, one small and one large. There is a loaf of bread on each table, that is nearly the length of the table, sliced into equal size bread pieces. With slicing the bread, creates crumbs on the table. Someone comes by to clean up each table, the larger table with the larger loaf of break created more crumbs that needed to be cleaned up than the smaller table.

• Table: Bandwidth
• Bread Slices: Subcarriers/Resource Elements
• Crumbs: Power per Hz
• Cleaner: UE
• Crumbs Collected: RSSI

RSRQ

RSRQ takes into consideration the RSRP, RSSI, and the channel bandwidth when determining the channel quality.

Lets look at an example where the RSRP is -80 and RSSI is -70

• Convert the RSRP and RSSI dBM values to mW (linear)
• Divide the RSRP mW value by the RSSI mW value
• Multiply this value by N (number of resource blocks in the channel) which is 52 in this example
• Convert this value to dB by using the logarithm of the given ratio (5.2)

Relationship

The charts below show the relationship between RSRP, RSSI, and RSRQ across multiple bandwidths (10, 15, and 20 MHz).

The RSRP is shown in steps where it is constant given the changing RSSI value from -120 to -40 dBm.

As the RSSI increases for a given RSRP, the RSRQ value decreases. In the spec, RSRQ is given the range of -43 to 20 dB, so some of the results outside of this bounds have been removed. Generally, RSRQ from 10 to -10 is considered good, -10 to -15 is average, and below -15 is poor. Channel conditions would have to be ideal to see RSRQ values above 10 dB, though it is possible.

In the charts below

• Good RSRQ values are indicated in pink

• Average RSRQ values are indicated in orange.

Examples

Below are examples of an LTE cell being measured by a UE. This shows the true nature of how the three measurement values behave in real world environments. The UE measures RSRP and RSSI at constantly varying levels while influence the RSRQ calculation.

• N = 100 Resource Blocks
• RSRP = -90.88
• RSSI = -51.75
• RSRQ = -18

Compared to the previous example, the example below has much better RSRQ at the time of the screen capture. Though, as you can see from the graph, the RSRQ values are constantly varying between -18 and -8