science

Received signal strength indicator

Received signal strength indicator is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Received signal strength indicator rather than just read about it. In short: In telecommunications, received signal strength indicator or received signal strength indication (RSSI) is a measurement of the power present in a received radio signal. RSSI is usually invisible to a user of a receiving device.

Key takeaways

Received signal strength indicator belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Received signal strength indicator to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Received signal strength indicator from memory before moving on to harder problems.

Reference excerpt

In telecommunications, received signal strength indicator or received signal strength indication (RSSI) is a measurement of the power 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, 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 (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 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 clear to send (CTS). Once the card is clear to send, a 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 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 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"). One subtlety of the 802.11 RSSI metric comes from how it is sampled—RSSI 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 power in a selected channel over the preamble and the entire received 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, to estimate the distance between nodes. 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 (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 (TOA) and 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.

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.

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 Signal strength based Wi-Fi positioning system RSSI to dBm Calculator

References

Illustrations

Worked examples

Example 1 — a first encounter with Received signal strength indicator

Start with the simplest possible case. Write down what Received signal strength indicator claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Received signal strength indicator before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Received signal strength indicator ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Received signal strength indicator

In research: Received signal strength indicator appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Received signal strength indicator in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Received signal strength indicator is common in secondary-school and first-year university syllabi. It links to neighbouring topics IEEE 802.11, Radio communications, so understanding it makes those chapters shorter.
In everyday life: Look for Received signal strength indicator outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Received signal strength indicator in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Received signal strength indicator means in your own words.
Compare your version with the excerpt and mark what you missed.
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Frequently asked questions

What is Received signal strength indicator in simple terms?

Why does Received signal strength indicator matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Received signal strength indicator?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Received signal strength indicator.