Signal Strength -74 dBm 66 asu LTE Golan Telecom Signal Bars EN

In telecommunications, received signal strength indicator (RSSI) is a measurement of the

power Power most often refers to: * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power * Power (social and political), the ability to influence people or events ** Abusive power Power may ...

present in a received radio signal. RSSI is usually invisible to a user of a receiving device. However, because signal strength can vary greatly and affect functionality in

wireless networking A wireless network is a computer network that uses wireless data connections between network nodes. Wireless networking is a method by which homes, telecommunications networks and business installations avoid the costly process of introducing c ...

, IEEE 802.11 devices often make the measurement available to users. RSSI is often derived in the intermediate frequency (IF) stage before the IF amplifier. In zero-IF systems, it is derived in the baseband signal chain, before the baseband amplifier. RSSI output is often a DC analog level. It can also be sampled by an internal

analog-to-digital converter In electronics, an analog-to-digital converter (ADC, A/D, or A-to-D) is a system that converts an analog signal, such as a sound picked up by a microphone or light entering a digital camera, into a digital signal. An ADC may also provide ...

(ADC) and the resulting values made available directly or via peripheral or internal processor bus.

In 802.11 implementations

In an IEEE 802.11 system, RSSI is the relative received

signal strength In telecommunications, particularly in radio frequency engineering, signal strength refers to the transmitter power output as received by a reference antenna at a distance from the transmitting antenna. High-powered transmissions, such as those u ...

in a wireless environment, in arbitrary units. RSSI is an indication of the power level being received by the receiving radio after the antenna and possible cable loss. Therefore, the greater the RSSI value, the stronger the signal. Thus, when an RSSI value is represented in a negative form (e.g. −100), the closer the value is to 0, the stronger the received signal has been. RSSI can be used internally in a

card to determine when the amount of radio energy in the channel is below a certain threshold at which point the network card is clear to send (CTS). Once the card is clear to send, a

packet Packet may refer to: * A small container or pouch ** Packet (container), a small single use container ** Cigarette packet ** Sugar packet * Network packet, a formatted unit of data carried by a packet-mode computer network * Packet radio, a form ...

of information can be sent. The

end-user In product development, an end user (sometimes end-user) is a person who ultimately uses or is intended to ultimately use a product. The end user stands in contrast to users who support or maintain the product, such as sysops, system administrato ...

will likely observe an RSSI value when measuring the signal strength of a wireless network through the use of a wireless network monitoring tool like

Wireshark Wireshark is a free and open-source packet analyzer. It is used for network troubleshooting, analysis, software and communications protocol development, and education. Originally named Ethereal, the project was renamed Wireshark in May 2006 du ...

, Kismet or

Inssider inSSIDer is a Wi-Fi network scanner application for Microsoft Windows and OS X developed by MetaGeek, LLC. It has received awards such as a 2008 Infoworld Bossie Award for "Best of Open Source Software in Networking",Cisco Systems cards have an RSSI maximum value of 100 and will report 101 different power levels, where the RSSI value is 0 to 100. Another popular Wi-Fi chipset is made by

Atheros Qualcomm Atheros is a developer of semiconductor Integrated circuit, chips for Computer network, network communications, particularly wireless chipsets. Founded under the name T-Span Systems in 1998 by experts in signal processing and VLSI desig ...

. An Atheros-based card will return an RSSI value of 0 to 127 (0x7f) with 128 (0x80) indicating an invalid value. There is no standardized relationship of any particular physical parameter to the RSSI reading. The 802.11 standard does not define any relationship between RSSI value and power level in milliwatts or decibels referenced to one milliwatt (dBm). Vendors and chipset makers provide their own accuracy, granularity, and range for the actual power (measured as milliwatts or decibels) and their range of RSSI values (from 0 to RSSI maximum). One subtlety of the 802.11 RSSI metric comes from how it is sampledRSSI is acquired during only the preamble stage of receiving an 802.11 frame, not over the full frame. As early as 2000, researchers were able to use RSSI for coarse-grained location estimates. More recent work was able to reproduce these results using more advanced techniques. Nevertheless, RSSI does not always provide measurements that are sufficiently accurate to properly determine the location. However, RSSI still represents the most feasible indicator for localization purposes as it is available in almost all wireless nodes and it does not have any additional hardware requirements.

Received channel power indicator

For the most part, 802.11 RSSI has been replaced with received channel power indicator (RCPI). RCPI is an 802.11 measure of the received radio frequency

in a selected channel over the preamble ''and'' the entire received

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, and has defined absolute levels of accuracy and resolution. RCPI is exclusively associated with

802.11 IEEE 802.11 is part of the IEEE 802 set of local area network (LAN) technical standards, and specifies the set of media access control (MAC) and physical layer (PHY) protocols for implementing wireless local area network (WLAN) computer commu ...

and as such has some accuracy and resolution enforced on it through IEEE 802.11k-2008. Received signal power level assessment is a necessary step in establishing a link for communication between wireless nodes. However, a power level metric like RCPI generally cannot comment on the ''quality'' of the link like other metrics such as travel time measurement ( time of arrival).

References

{{DEFAULTSORT:Received Signal Strength Indication IEEE 802.11 Radio communications

In 802.11 implementations

Received channel power indicator

See also

References