Editing Received signal strength indicator

{{Short description|Measurement of the power in a radio signal}}
[[File:Signal Strength -74 dBm 66 asu LTE Golan Telecom Signal Bars EN.jpg|thumb|Cellular signal strength of -74dBm (or 66 {{abbr|asu|arbitrary signal unit}}) displayed on a smartphone. Also shown: signal bars of two cellular networks, and signal bars of a Wi-Fi network.]]
In [[telecommunications]], '''received signal strength indicator''' or '''received signal strength indication'''<ref name="Usage of received signal strength indicator v. received signal strength indication in literature">{{cite web |url=https://books.google.com/ngrams/graph?content=received+signal+strength+indicator%2Creceived+signal+strength+indication&year_start=1800&year_end=2019&corpus=en-2019&smoothing=3 |website=Google Ngram Viewer |title= Usage of received signal strength indicator v. received signal strength indication in literature}}</ref> ('''RSSI''') is a measurement of the [[Electric power|power]] present in a received [[radio]] signal.<ref>{{Cite book
 |author=Martin Sauter |year=2010 |title=From GSM to LTE: An Introduction to Mobile Networks and Mobile Broadband |chapter=3.7.1 Mobility Management in the Cell-DCH State |type=eBook |publisher=[[John Wiley & Sons]] |page=160 |isbn=9780470978221 |accessdate=2013-03-24 |chapter-url=https://books.google.com/books?id=uso-6LN2YjsC&q=received%20signal%20strength&pg=PA160 }}</ref>

RSSI is usually invisible to a user of a receiving device. However, because signal strength can vary greatly and affect functionality in [[Wireless LAN|wireless networking]], [[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 [[Direct-conversion receiver|zero-IF systems]], it is derived in the baseband signal chain, before the baseband amplifier.<ref>{{Cite book |last1=Foerster |first1=Anna |url=https://books.google.com/books?id=wgmhDwAAQBAJ |title=Emerging Communications for Wireless Sensor Networks |last2=Foerster |first2=Alexander |date=2011-02-07 |publisher=BoD – Books on Demand |isbn=978-953-307-082-7 |page=241 |language=en}}</ref> RSSI output is often a DC analog level. It can also be sampled by an internal [[analog-to-digital converter]] (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 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 [[Wireless LAN|wireless networking]] card to determine when the amount of radio energy in the channel is below a certain threshold at which point the network card is [[IEEE 802.11 RTS/CTS|clear to send]] (CTS). Once the card is clear to send, a [[packet (information technology)|packet]] of information can be sent.  The [[end-user]] 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]], [[Kismet (software)|Kismet]] or [[Inssider]]. As an example, [[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]]. 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 [[dBm|decibels referenced to one milliwatt (dBm)]]. Vendors and chipset makers provide their own accuracy, granularity, and range for the actual power (measured as milliwatts, which can be expressed in terms of decibels relative to one milliwatt) and their range of RSSI values (from 0 to RSSI maximum, in arbitrary signal units "asu").<ref>{{cite conference|last1=Lui|first1=Gough|last2=Gallagher|first2=Thomas|last3=Binghao|first3=Li|conference=2011 International Conference on Localization and GNSS (ICL-GNSS)|title=Differences in RSSI readings made by different Wi-Fi chipsets: A limitation of WLAN localization|pages=53–57|doi=10.1109/ICL-GNSS.2011.5955283|isbn=978-1-4577-0186-3|year=2011|s2cid=16846238|hdl=1959.4/unsworks_47285|hdl-access=free}}</ref> One subtlety of the 802.11 RSSI metric comes from how it is sampled{{mdash}}RSSI is acquired during only the preamble stage of receiving an 802.11 frame, not over the full frame.<ref name=":0" />

As early as 2000, researchers were able to use RSSI for coarse-grained location estimates.<ref name=bahl-infocom2000>{{cite conference|last1=Paramvir|first1=Bahl|last2=Padmanabhan|first2=Venkata|title=RADAR: An In-Building RF-based User Location and Tracking System|url=https://www.microsoft.com/en-us/research/publication/radar-an-in-building-rf-based-user-location-and-tracking-system/|book-title=Proceedings IEEE INFOCOM 2000. Conference on Computer Communications. Nineteenth Annual Joint Conference of the IEEE Computer and Communications Societies|doi=10.1109/INFCOM.2000.832252|access-date=19 December 2014|url-access=subscription}}</ref> More recent work was able to reproduce these results using more advanced techniques.<ref name="sev-mobisys2013">{{cite conference|last1 = Sen|first1 = Souvik|last2 = Lee|first2 = Jeongkeun|last3 = Kim|first3 = Kyu-Han|last4 = Congdon|first4 = Paul|title = Avoiding Multipath to Revive Inbuilding WiFi Localization|url = http://dl.acm.org/citation.cfm?id=2464463|book-title = MobiSys '13: Proceeding of the 11th annual international conference on Mobile systems, applications, and services | year=2013 | pages=249–262 | doi=10.1145/2462456.2464463 | isbn=9781450316729 | s2cid=16251944 |accessdate = 19 December 2014|url-access = subscription}}</ref> Nevertheless, RSSI does not always provide measurements that are sufficiently accurate to properly determine the location.<ref name=parameswaran-srds2009>{{cite conference |last1=Parameswaran |first1=Ambili Thottam |last2=Husain |first2=Mohammad Iftekhar |last3=Upadhyaya |first3=Shambhu |title=Is RSSI a Reliable Parameter in Sensor Localization Algorithms – An Experimental Study |url=http://www.cse.buffalo.edu/srds2009/F2DA/f2da09_RSSI_Parameswaran.pdf |date=27 September 2009 |location=Niagara Falls, New York |conference=28th IEEE Symposium On Reliable Distributed Systems |conference-url=https://cse.buffalo.edu/srds2009/ |access-date=12 March 2025}}</ref> 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.<ref name=abdullah2016>{{cite journal|url=https://www.researchgate.net/publication/309257981 |last1=Alhasanat|first1=Abdullah|last2=Sharif|first2= Bayan |last3= Tsemendis|first3= C. |title=Efficient RSS-based collaborative localisation in wireless sensor networks|date=January 2016 |journal=International Journal of Sensor Networks |volume=22 |issue=1 |pages=27–36 |doi=10.1504/IJSNET.2016.079335}}</ref>

=== 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<ref name=":0">{{cite web|url=http://standards.ieee.org/getieee802/802.11.html |archive-url=https://archive.today/20100813230349/http://standards.ieee.org/getieee802/802.11.html |url-status=dead |archive-date=August 13, 2010 |title=IEEE 802.11-2012 |publisher=IEEE |date=2012-03-29 |accessdate=2013-02-11}}</ref> measure of the received [[radio frequency]] [[Power (physics)|power]] in a selected [[Channel (communications)|channel]] over the preamble ''and'' the entire received [[Frame (telecommunications)|frame]], and has defined absolute levels of accuracy and resolution. RCPI is exclusively associated with [[802.11]] 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]]).

== Uses in indoor localization ==

=== RSSI-based distance estimation ===
RSSI is commonly used in wireless communication protocols, such as [[Bluetooth]] and [[Zigbee|ZigBee]], to estimate the distance between nodes.{{cn|date=January 2024}} This estimation is essential for indoor localization and is often preferred due to its simplicity and the lack of need for synchronization or timestamping, as required in other methods like [[Time of arrival|Time of Arrival]] (TOA).

=== Localization algorithms ===
Various localization algorithms, such as anchor-based algorithms, employ RSSI. Anchor-based algorithms use nodes with known positions (anchors) to determine the location of an unknown node. The accuracy of these algorithms is enhanced by using a higher number of known nodes, as they rely on the [[Time of arrival|Time of Arrival]] (TOA) and [[Angle of arrival|Angle of Arrival]] (AOA) of the signal for estimating the distance between the known nodes and the unknown node. However, the accuracy of these algorithms can be affected by environmental factors, such as signal interference, obstacles, and the density of nodes in the area.{{cn|date=January 2024}}

=== Effect of environmental factors and antenna type ===
Factors like diffraction, reflection, scattering, and antenna type can significantly influence RSSI values. These variables need consideration for accurate indoor localization using RSSI.<ref>{{cite web|title=RSSI-based method in Indoor Asset Tracking: Benefits, Drawbacks and Comparison with AoA, Navigine|url=https://navigine.com/blog/rssi-based-method-in-indoor-asset-tracking/}}</ref>

=== RSSI-with-Angle-based Localization Estimation (RALE) ===
The RALE approach offers several advantages for indoor localization:

* Does not require complex infrastructure or prior scene surveys.
* Low cost and simple execution, making it accessible for various applications.
* Only requires RSSI values and angular measurements, eliminating the need for more sophisticated measurements.

== See also ==
* [[Signal strength in telecommunications]]
* [[Log-distance path loss model]]
* [[Wi-Fi_positioning_system#Signal_strength_based|Signal strength based Wi-Fi positioning system]]
* [https://www.orbit6.com/rssi-to-dbm-calculator/ RSSI to dBm Calculator]

== References ==
{{reflist|30em}}

{{DEFAULTSORT:Received Signal Strength Indication}}
[[Category:IEEE 802.11]]
[[Category:Radio communications]]