RSSI (Received Signal Strength Indicator)
RSSI (Received Signal Strength Indicator) is a measurement of the strength of a radio signal received by a two-way radio or other wireless device.
RSSI is commonly used by radio engineers and networkA Network is a connected system of radios, equipment and infrastructure that allows users to communicate across a defined area. Radio networks can range from simple radio-to-radio systems to large multi-site networks. systems to assess signal strength, identify coverageRadio Coverage is the geographical area in which a two-way radio system can provide reliable communication. Coverage depends on the radios, antennas, frequency, terrain, buildings and system infrastructure. areas and help diagnose communication problems.
RSSI is normally expressed as a numerical value, often in dBm (decibels relative to one milliwatt). Because dBm values for received signals are normally negative, a value closer to zero generally represents a stronger received signal.
For example:
−50 dBm → Stronger signal
−90 dBm → Weaker signal
The exact RSSI scale and interpretation can vary between radio manufacturers and systems.
What does RSSI measure?
RSSI indicates the strength of the radio-frequency energy being received by a device.
It can help determine whether a radio is receiving a strong or weak signal from:
- Another radio
- A repeaterA Repeater receives a two-way radio transmission and retransmits it, usually from an elevated location, to extend the coverage and reliability of a radio communication system.
- A base stationA base station is a fixed two-way radio installed at a permanent location, allowing an operator to communicate with handheld or mobile radios across a site or operating area.
- A radio network
- A wireless access point
RSSI measures signal strength; it does not, by itself, indicate whether the communication will be clear or reliable.
RSSI and received signal strength
The received signal becomes weaker as the radio moves further away from the transmitter, although the relationship is affected by the environment.
Factors affecting RSSI can include:
- Distance
- Transmitter powerAn antenna transmits and receives radio-frequency signals, allowing a two-way radio to communicate. Antenna type, frequency, height and location can all affect radio performance and coverage.
- AntennaAn antenna transmits and receives radio-frequency signals, allowing a two-way radio to communicate. Antenna type, frequency, height and location can all affect radio performance and coverage. performance
- Antenna height
- FrequencyAn antenna transmits and receives radio-frequency signals, allowing a two-way radio to communicate. Antenna type, frequency, height and location can all affect radio performance and coverage.
- Terrain
- BuildingsAn antenna transmits and receives radio-frequency signals, allowing a two-way radio to communicate. Antenna type, frequency, height and location can all affect radio performance and coverage.
- Obstacles
- InterferenceRadio interference occurs when unwanted radio-frequency signals or electrical noise disrupt two-way radio communications, causing distorted audio, broken transmissions, reduced coverage or loss of communication.
RSSI and dBm
RSSI is frequently represented using dBm.
Because dBm is a logarithmic measurement, small numerical changes can represent meaningful differences in signal power.
Typical examples might be:
| RSSI | General indication |
|---|---|
| −40 dBm | Very strong |
| −50 dBm | Strong |
| −60 dBm | Good |
| −70 dBm | Moderate |
| −80 dBm | Weak |
| −90 dBm | Very weak |
These values are illustrative rather than universal thresholds. The acceptable RSSI level depends on the radio technology, receiverA Receiver is the part of a two-way radio that detects and processes incoming radio signals, converting them into audible voice or usable data for the user. sensitivity and operating environment.
RSSI and receiver sensitivity
Receiver Sensitivity describes the weakest signal a receiver can reliably detect under specified conditions.
RSSI describes the strength of the signal being received.
For example:
RSSI = −75 dBm
This tells you approximately how strong the received signal is.
It does not necessarily tell you whether −75 dBm is sufficient for reliable communication on that particular system.
RSSI and signal quality
Signal strength and signal quality are not the same thing.
A radio can receive a relatively strong signal while still experiencing poor communication because of:
- Interference
- Noise
- Multipath effects
- Adjacent-channel signals
- Distortion
- Digital errors
RSSI should therefore be considered alongside other measurements when diagnosing radio performance.
RSSI and interference
A high RSSI reading does not necessarily mean that the wanted radio signal is strong.
The measurement can be affected by unwanted RF energy.
For example, a receiver could report strong received energy because of a nearby interfering transmitter while the desired signal remains difficult to decode.
This is why RSSI alone should not be used to determine radio coverage.
RSSI and noise
The Noise Floor is the background level of RF energy present when the wanted signal is absent.
The difference between the wanted signal and the noise floor contributes to the Signal-to-Noise Ratio (SNR).
A strong RSSI combined with a high noise floor may still result in poor communication.
RSSI and SNR
RSSI and Signal-to-Noise Ratio (SNR) provide different information.
RSSI: How much received RF energy is present.
SNR: How much stronger the wanted signal is than the background noise.
SNR can therefore provide a better indication of signal quality in some circumstancesAn antenna transmits and receives radio-frequency signals, allowing a two-way radio to communicate. Antenna type, frequency, height and location can all affect radio performance and coverage..
RSSI and SINR
In some digital and cellular systems, SINR (Signal-to-Interference-plus-Noise Ratio) is used to assess signal quality.
SINR considers both interference and noise, whereas RSSI primarily represents received signal strength.
The appropriate measurement depends on the radio technology.
RSSI and analogue radio
In an analogue radioAnalogue radio uses continuously varying radio signals to transmit voice communication. It remains widely used for reliable two-way communication across business, industry, events, security and other applications.radio systemA Radio System is a complete communication solution comprising two-way radios and, where required, equipment such as repeaters, antennas, base stations, mobile radios and network infrastructure., RSSI can help engineers understand the strength of a received signal.
However, acceptable communication quality depends on factors such as:
- Signal strength
- Noise
- Interference
- Receiver performance
- Audio quality
A strong RSSI reading does not guarantee clear analogue audio.
RSSI and digital radio
Digital radio systems can use RSSI as one of several indicators of RF conditions.
A digital radio may continue to produce clear audio while the received signal remains above the system’s usable threshold.
Once the signal becomes sufficiently poor, digital communication can degrade rapidly.
RSSI and DMR
In Digital Mobile Radio (DMR)Digital Mobile Radio (DMR) is an ETSI digital radio standard for professional two-way communications, supporting voice, group calling, data and other features on compatible radio systems. systems, RSSI can be used during testing and troubleshooting to assess the strength of signals received from radios or repeaters.
It can help engineers identify areas where the received signal is becoming weaker.
However, DMR performance should also be assessed using appropriate digital-radio measurements rather than RSSI alone.
RSSI and repeaters
RSSI can be particularly useful when assessing a Repeater system.
An engineer can measure the signal received from a repeater at different locations to establish how the signal changes across the coverage area.
This can help identify:
- Coverage boundaries
- Weak-signal areas
- Dead spots
- Antenna problems
- Potential interference
RSSI and radio coverage
RSSI measurements can be used during a Site SurveyA Site Survey is an assessment of a location to determine whether a two-way radio system will provide the required coverage, reliability and performance. to map the strength of received radio signals.
An engineer can take measurements at multiple locations and identify areas where signal strength falls below the required level.
A coverage map may therefore show RSSI values across a site.
RSSI and dead spots
A Dead SpotA Dead Spot is an area where two-way radio communication is weak, unreliable or unavailable. Dead spots can be caused by buildings, terrain, distance, interference or inadequate radio coverage. is an area where reliable radio communication cannot be maintained.
Low RSSI can be one cause of a dead spot.
However, a dead spot can also result from interference, building attenuation or other RF conditions.
RSSI and buildings
Building materials can significantly affect received signal strength.
Concrete, reinforced structures, metal and certain specialist materials can attenuate radio signals.
RSSI measurements can help identify how much signal strength is being lost as a radio moves through a building.
RSSI and terrain
Hills, valleys and other geographical features can affect radio propagation.
RSSI measurements can help identify how terrain affects coverage.
This is particularly useful for:
- Agriculture
- Utilities
- Outdoor events
- Construction
- Transport
- Large estates
RSSI and antennas
A poor or damaged antenna can result in reduced received signal strength.
Possible causes include:
- Damaged antenna
- Incorrect antenna
- Poor connector
- Damaged coaxial cable
- Poor installation
RSSI can therefore be useful when investigating antenna-system problems.
RSSI and transmitter power
Increasing transmitter power can increase the received signal strength at another radio.
However, transmitter power is only one factor affecting RSSI.
Antenna height, antenna gain, terrain and frequencyFrequency is the number of cycles a radio wave completes each second, measured in Hertz. In two-way radio, frequency determines where a transmission operates within the radio spectrum. can have a major influence on the received signal.
Increasing power is therefore not automatically the best solution to a coverage problem.
RSSI and frequency
Radio frequency affects how signals propagate through an environment.
VHF and UHF systems can produce different coverage characteristics depending on the environment and system design.
RSSI measurements can help engineers assess the actual performance of a particular frequency and installation.
RSSI and roaming
RSSI can play a role in RoamingRoaming allows a compatible two-way radio to move between different radio sites or coverage areas, automatically selecting an appropriate site as the user moves. systems.
A multi-site radio may monitor available sites and use signal conditions as part of the process of determining when another site should be selected.
The exact roaming algorithm depends on the radio system.
RSSI and multi-site radio
In a multi-site radio network, RSSI measurements can help engineers compare the strength of signals from different sites.
This can assist with:
- Site planning
- Coverage optimisation
- Roaming configuration
- Fault diagnosis
RSSI and radio network planning
RSSI can be collected during radio network planning to establish whether proposed sites and antennas provide sufficient signal strength.
Measurements can be taken across the intended coverage area and compared with the system’s requirements.
RSSI and radio system design
RSSI is one of several technical factors considered when designing a professional radio system.
System designers may assess:
- RSSI.
- Receiver sensitivity.
- Signal-to-noise ratio.
- Interference.
- Antenna performance.
- Transmitter power.
- Frequency.
- Terrain.
- Building attenuation.
- Required coverage reliability.
RSSI and site surveys
A radio site survey can use RSSI measurements to create a picture of actual RF coverage.
Measurements may be taken:
- Inside buildings
- Outside buildings
- Across large sites
- Around boundaries
- At different floors
- In vehicles
- At known problem areas
This provides more useful information than relying solely on theoretical coverage predictions.
RSSI and radio troubleshooting
RSSI can help engineers determine whether a reception problem is related to signal strength.
For example:
Low RSSI at one location → Possible coverage problem
Normal RSSI but poor audio → Investigate interference or equipment
Low RSSI everywhere → Investigate antenna, receiver or system
These are diagnostic starting points rather than definitive conclusions.
RSSI and radio hire
RSSI can be useful when deploying temporary Radio HireRadio Hire is the temporary rental of two-way radios and related communication equipment for events, projects and operational requirements, providing professional communication without purchasing the equipment. systems.
For a large event or construction project, engineers can measure received signal strength across the operating area to confirm that the temporary radio system provides suitable coverage.
Where weak areas are identified, the repeater or antenna arrangement may be adjusted.
RSSI and events
Large events can have complex RF environments because of:
- Large crowds
- Temporary structures
- Buildings
- Production equipment
- Multiple radio systems
- Other wireless equipment
RSSI measurements can help engineers assess the actual performance of the radio system across the event site.
RSSI and construction
Construction sites change as buildings and structures are erected.
This can alter radio propagation and therefore received signal strength.
RSSI measurements can be repeated as the site develops to identify new weak areas.
RSSI and security
Security teams operating across large buildings or outdoor sites can benefit from reliable radio coverage.
RSSI measurements can help identify areas where communication may become unreliable.
RSSI and vehicle radios
RSSI can also be measured from mobile radios installed in vehicles.
The vehicle’s antenna position, bodywork and surrounding environment can all affect received signal strength.
RSSI and GPS
RSSI and GPS (Global Positioning System)GPS is a satellite-based positioning system that allows compatible two-way radios to determine their location. GPS data can support tracking, dispatch, fleet management and Geo-Fencing. can be used together in some radio systems.
GPS provides the location of the radio, while RSSI can indicate the strength of a received radio signal at that location.
This can allow engineers to associate signal measurements with specific geographical positions.
RSSI monitoring
Some radio systems can report RSSI information automatically.
Depending on the system, this information may be available through:
- Radio displays
- Diagnostic software
- Network-management systems
- Engineering tools
- Coverage-monitoring systems
The availability and accuracy of RSSI reporting varies between manufacturers and technologies.
RSSI limitations
RSSI should not be treated as a complete measure of radio performance.
It does not necessarily tell you:
- Whether speech is intelligible
- How much interference is present
- Whether a digital signal is error-free
- Whether a system has sufficient capacity
- Whether a radio will maintain communication while moving
Other measurements and practical testing are often required.
RSSI and radio system optimisation
Engineers can use RSSI measurements to help optimise a radio system.
Potential improvements may include:
- Relocating a repeater
- Improving antenna height
- Changing antenna configuration
- Correcting damaged cabling
- Addressing interference
- Adding additional radio infrastructureRadio infrastructure is the equipment and supporting systems behind a professional two-way radio network, including repeaters, antennas, base stations, network connections, power systems and dispatch equipment.
The appropriate solution depends on the cause of the weak signal.
RSSI and DCS
DCS can use radio coverage testing and signal-strength measurements such as RSSI when assessing professional two-way radio systems.
Where coverage is important, RSSI can form part of a wider site survey and system assessment to identify weak areas and determine whether changes to antennas, repeaters or system configuration are required.
