SNR

What Is SNR?

SNR stands for signal-to-noise ratio, a metric utilized to gauge communication reliability. While SNR focuses solely on the ratio of signal to noise, SINR, which stands for signal-to-interference-plus-noise ratio, considers the presence of interference in addition to noise when evaluating communication quality.

Classification of SNR

The SNR is a crucial technical metric for evaluating communication reliability and is relevant across various fields.

• Communication SNR: In signal modulation, SNR usually represents the ratio of the average power of carrier signals at the receiver's end of a channel to the average noise power within that channel. This can also be termed the carrier-to-noise ratio (CNR). In analog systems, SNR typically measures the ratio of average signal power to average noise power at the output of a demodulator. For digital systems, it often denotes the ratio of the average signal energy per digital bit to the noise power within a specific frequency band at the output of a digital demodulator or decoder. This is also known as normalized SNR or energy SNR.

• Audio SNR: This refers to the ratio of the strength of the desired audio signal to the strength of background noise during playback. A lower SNR means that noise significantly impacts audio quality, especially with weaker signals.

• Image SNR: Similar to its application in images, SNR in this context measures the ratio of video signal strength to noise strength. Higher SNR results in clearer images, while a lower SNR can cause noticeable static noise.

• Web Page SNR: Originally from the electroacoustic field, this concept measures the ratio of the clear text content on a web page to the noise created by HTML tags. In web page optimization, a higher web page SNR means a greater proportion of readable text compared to HTML code, making it easier for search engines to index the page.

This article document mainly focuses on the application of SNR in the wireless communication sector.

SNR vs SINR

• SNR

SNR measures the ratio of signal power to noise power within a system, typically expressed in decibels (dB). The decibel is a unit used to indicate the relative difference in power or intensity between two signals, defined as ten times the common logarithm of the ratio of their levels. Here, a signal is an external electronic input that a device processes, while noise consists of irregular, extraneous signals not originally present, and is generally constant regardless of the original signal. Distortion, another form of extraneous signal, differs from noise in that it is regular and predictable, whereas noise is irregular.

For instance, in a crowded room where two people are talking, the conversation is the signal, and the voices of others are the noise. SNR reflects how surrounding noise affects communication, indicating the need for the speakers to overcome this noise for clearer communication.

• SINR

SINR measures the ratio of the signal strength to the combined strength of interference and noise. It considers not only noise but also interference from other sources.

Key Difference Between SNR and SINR

Both SNR and SINR are used to assess communication quality. The key difference is that while SNR focuses solely on the ratio of signal to noise, SINR includes the impact of interference as well. Interference, such as co-channel or multipath interference, originates from both the system and external sources. A higher SINR, like a higher SNR, indicates better signal quality.

Impact of the SNR on WLANs

SNR is not merely a ratio but represents the decibel difference between the received signal and the background noise, also known as the noise floor. The noise floor of a channel is influenced by factors such as the noise figure, temperature, and channel bandwidth of the RF component used in the radio system. If the difference between the received signal and background noise is too small, data integrity is compromised, leading to retransmissions which can negatively affect throughput and increase delays in WLANs.

SNR is a key indicator of radio signal quality, taking into account the noise floor of the environment. For instance, if a signal measures –65 dBm and the background noise is –90 dBm, the SNR is 25 dB, indicating good signal quality. Conversely, if the background noise is –80 dBm, the SNR drops to 15 dB, suggesting poorer signal quality due to higher noise. For optimal performance, it is recommended that the SNR be at least 20 dB for data networks and 25 dB or higher for voice applications. In WLANs, an SNR above 30 dB is necessary to ensure a satisfactory user experience.

Enhancing the SNR on a WLAN

Enhancing the SNR is a key strategy for improving communication quality. To boost the SNR on a WLAN, consider the following actions:

• Steer clear of channels with high signal strength and heavy usage to avoid contention.

• Position access points (APs) as close as possible to stations (STAs) to prevent signal attenuation through walls.

• Regulate the power levels of nearby APs to ensure they cover distinct areas without causing interference to users in adjacent zones.