How To Interpret SINR parameters in 2G, 3G and LTE routers. : Venn Telecom

Scope

This article applies to wifi and LTE devices.

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 : SINR.

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 SINR (db), which impacts quality 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 Quality SINR 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)
RSSI - Received Signal Strength Indication (signal power) (dBm) (2G, 3G and LTE)
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

Noise

Let's say you are having a conversation with someone in a kitchen that happens to have a loud refregirator.

Let's say the refregirator makes a noise of 50 dB.

If that someone whispers at 30 dB (signal) you will understand nothing. If that someone speaks at 60 dB you will still not understand everything. But if that someone speaks at 90 dB it may seem mre like a shouting match but at least every word will be clearly heard.

That's the idea behind as signal-to-noise ratio.

SINR Definition

SINR : Signal-to-Interference-plus-Noise Ratio

SINR is defined as the power of a certain signal of interest divided by the sum of the interference power (from all the other interfering signals) and the power of some background noise.

It is a quantity used to give theoretical upper bounds on channel capacity (or the rate of information transfer) in wireless communication systems..

Analogous to the SNR used often in wired communications systems, the SINR is defined as the power of a certain signal of interest divided by the sum of the interference power (from all the other interfering signals) and the power of some background noise.

If the power of noise term is zero, then the SINR reduces to the signal-to-interference ratio (SIR). Conversely, zero interference reduces the SINR to the signal-to-noise ratio (SNR), which is used less often when developing mathematical models of wireless networks such as cellular networks.

SINR is commonly used in wireless communication as a way to measure the quality of wireless connections.

Typically, the energy of a signal fades with distance, which is referred to as a path loss in wireless networks.

Conversely, in wired networks the existence of a wired path between the sender or transmitter and the receiver determines the correct reception of data. In a wireless network one has to take other factors into account (e.g. the background noise, interfering strength of other simultaneous transmission). The concept of SINR attempts to create a representation of this aspect.

SINR is not actually a ratio but the difference in decibels between the received signal and the background noise level (noise floor).

For example, if a radio (client device) receives a signal of -75 dBm and the noise floor is measured at -90 dBm, the SNR is 15 dB. Data corruption and therefore re-transmissions will occur if the received signal is too close to the noise floor.

In 802.11 networks, re-transmissions adversely affect throughput and latency.

SINR is a better way to judge the quality of signal because it also takes the noise floor or ambient noise of the RF environment into account. For instance, a received signal of -65 dBm can be considered good at location that has a noise floor of -90 dBm (SNR 25 dB) but not so much at a location with a noise floor of -80 dBm (SNR 15 dB).

Generally, a signal with a SINR value of 20 dB or more is recommended for data networks where as an SINR value of 25 dB or more is recommended for networks that use voice applications.

If SINR is available it is the easiest to use for alignment of antennas for example.

SINR impacts performance

The SINR of an access point signal, measured at the user device, decreases as range to the user increases because the applicable free space loss between the user and the access point reduces signal level. The same goes for the signals propagating from the user device to the access point. An increase in RF interference from microwave ovens and cordless phones, which increases the noise level, also decreases SINR.

SINR directly impacts the performance of a wireless connection. A higher SINR value means that the signal strength is stronger in relation to the noise levels, which allows higher data rates and fewer retransmissions – all of which offers better throughput. Of course the opposite is also true. A lower SINR requires wireless LAN devices to operate at lower data rates, which decreases throughput. A SINR of 30 dB, for example, may allow an 802.11g client radio and access point to communicate at 24 Mbps; whereas, a SNR of 15 dB may only provide for 6 Mbps.

SINR Values

Use the table below as an indication.

Common sources of Wireless Interference

There are a wide variety of devices that can cause interference on your wireless network (Wifi or LTE).

If you suspect that your network is experiencing interference from other sources, look for items on this list as possible suspects.

Interference causing devices:

Microwave ovens
Cordless phones
Bluetooth devices
Wireless video cameras
Outdoor microwave links
Wireless peripherals
PDAs, cellphones
Zigbee - Wireless personal area network technology
Fluorescent lights
WiMAX
Other 802.11 networks - this is known as co-channel and adjacent channel interference. Since other 802.11 devices follow the same protocol, they tend to work cooperatively – i.e. two access points (APs) on the same channel will share the capacity of the channel.
Bad electrical connections can also cause broad RF spectrum emissions
Cordless phones
Radar
Perimeter sensors
Digital satellite

SINR and other measurements

As mentionned in summary, measurements like Signal Quality (SINR) 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 related articles:

EC/IO - Downlink carrier-to-interference ratio (signal quality) (dB) (2G, 3G & LTE)
RSSI - Received Signal Strength Indication (signal power) (dBm) (2G, 3G and LTE)
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)

SINR is mostly used in combinaition with other measurements such as RSRP/RSRQ and RSSI.

In the mean time a minimum of -20 dB SINR is needed to detect RSRP/RSRQ

There is for example following relationship between SINR and RSRQ (LTE only):

There is also a relationship between SINR and RSSI (2G, 3G and LTE):

RSSI is the signal strength of an AP that a client is seeing currently, Client always use this value to decide whether to roam to other AP or not.

In simple terms, greater the distance from radio, lesser the RSSI, lesser the SINR. At lower SINR, client switches to slower encoding/decoding mechansim (to reduce frame errors) which results in lower data rates. Click here for more details.

Data rate always depends on SINR and SINR depends on two factors

1. Distance from AP

2. Floor noise

Client will switch to lower data rate as per the support rate when is see poor SINR

To achieve a particular data rate, it is required to maintain a particular SINR as shown in the snapshot.