How To Interpret RSSI parameters in 2G, 3G and LTE routers.

Modified on Fri, 24 Apr, 2020 at 2:39 PM

Scope

This article applies for all 2G, 3G and LTE devices.

Althoug RSSI is not relevant in LTE it can be calculated from other parameters.

Intended Audience

Public

In This Task

- Summary of issue

- Solution

- Related Articles

- Troubleshooting

Prerequisites

dB, dBm, dBi and dBd:

https://help.venntelecom.com/a/solutions/articles/44001930982?lang=en

Summary

All devices (smartfones, 4G routers, ...) display some parameters to help optimizing 2G/3G/4G connexions.

This article explains how to interpret and optimize one of them : RSSI.

The Signal Strength is a very important and essential measure for any technology (GSM, CDMA, UMTS, LTE, etc.). However, it is not the only one. This article talks about another magnitude, equally important: the RSSI (dbm), which impacts strength of signal.

Although this ratio is of fundamental importance to any cellular system, it is not well understood by many professionals. On the opposite side, professionals with a good understanding of this ratio are able for example, to correctly assess the RF links, and also to perform more extensive optimizations, obtaining the best possible performance of the system.

There are many different factors that influence signal strength and quality, including but not limited to:

Tower load
Proximity to the cellular tower
Signal going through a cellular repeater
Competing signals
Physical barriers (mountains, buildings, trains, etc.)
Weather

Important note: measurements like Signal strength RSSI do not incorporate all of the relevant factors to describe the quality of the connection.

The other values to take in account are described in other related articles:

EC/IO - Downlink carrier-to-interference ratio (signal quality) (dB) (2G, 3G & LTE)
SINR - Signal-to-Interference-plus-Noise Ratio (signal quality) (dB) (LTE only)
RSCP - Received Signal Code Power (signal power) (dBm) (3G only)
RSRP - Reference Signal Received Power (signal power) (dBm) (LTE only)
RSRQ - Reference Signal Received Quality (signal quality) (dB) (LTE only)

Disclaimers

Both Signal Strength and Signal Quality must be considered for successful cellular data connection
Measured or reported values vary by modem, carrier, and network environment
There is no black/white answer to what constitutes a successful connection
Although signal strength may appear to be adequate, throughput speeds may vary due to dependencies on cellular tower loads

Note that Power parametrs are expressed in dBm, Quality parameters in dB

Solution

RSSI

RSSI - Received Signal Strength Indication (RSSI) is the exact signal strength, measured in dBm

RSSI represents the entire received power including the wanted power from the serving cell as well as all cochannel power and other sources of noise.

The RSSI of the modem is indicated by a negative dBm value.

This value relates to the signal strength of the cellular signal from the tower to the modem. The higher the number, the better the signal. The exact numbers vary between cellular carriers. However, -70 dBm and higher values usually equate to the modem being in an excellent coverage area. The closer to 0 dBm, the stronger the signal. There is a point at which trying to obtain more signal delivers diminishing returns, because the quality of the connection is defined by more values than just RSSI (you will find more information on the other measurements in other related articles).

The dBm scale is roughly between -50 and -120dBm, with -50 being perfect signal and -120 being when you fall off the network. RSSI measures both the usable signal and the noise in a single figure.

RSSI in 2G:

2G (GSM) Signal strength is defined by only one value: RSSI - Received Signal Strength Indicator;

RSSI is a negative value, and the closer to 0, the stronger the signal.

RSSI in 3G:

The RSSI standard values for 3G are basically the same as for 2G.

Some articles use following values:

RSSI in LTE:

RSSI for LTE is a calculated from several other signal related measurements.

RSSI = wideband power = noise + serving cell power + interference power.

RSSI and other measurements

As mentionned in summary, measurements like Signal Strength (RSSI) do not incorporate all of the relevant factors to describe the quality of the connection.

All values to take in account are described in related articles:

EC/IO - downlink carrier-to-interference ratio (signal quality) (dB) (2G, 3G & LTE)
SINR - Signal-to-Interference-plus-Noise Ratio (signal quality) (dB) (LTE only)
RSCP - Received Signal Code Power (signal power) (dBm) (3G only)
RSRP - Reference Signal Received Power (signal power) (dBm) (LTE only)
RSRQ - Reference Signal Received Quality (signal quality) (dB) (LTE only)

For example, a 4G LTE modem might report an RSSI of -68 dBm, but:

RSRP = -102 dBm

RSRQ = -16 dB

SINR = -1.8 dB

In this case, the signal quality is actually very poor. This could be due to the device being some distance away from the LTE transmitter. It’s also possible that something is interfering with the signal, such as a building or other obstructions between the device and the tower.

For formula lovers, relationships between RSSI and other measurements:

For 3G: