We are in the age of technology, where every human activity involves automation. Information Technology has brought such a revolution to the planet that the integration and communication of several wireless devices perform our daily tasks more efficiently than man. That is where the Internet of Things (IoT) has overridden traditional telecommunication channels. This article discusses RSSI-based indoor localization with the Internet of Things.
IoT refers to the interconnection of computer networks with physical devices to collect and share data. Since IoT is an aggregation of indoor telecommunication devices, it finds its application in communication in buildings and homes. Thus, we can equip the routinely used devices with wireless connectivity.
The sensor node’s location must be known for better sharing among various wireless connectivities. Also, a sensor node’s localization will make the information production valid. Global Positioning System (GPS) is used for its ease of implementation and accuracy of up to five meters but only in outdoor localization systems. It doesn’t suit the localization in IoT due to the limited space that comes with performing localization of indoor environments and the large number of obstacles found indoors. Therefore we will discuss RSSI-based indoor localization with the Internet Of Things.
What is meant by localization?
Localization study has been a trend in finding and assessing a node. We can define localization as estimating or finding a position of a node. Global Positioning System (GPS) is one of the straightforward methods to obtain a localization position but requires a direct line of sight (LOS).
Techniques in localization
There are two techniques in localization.
- Range-based Techniques
- Range-free techniques.
We categorize the Received Signal Strength Indicator (RSSI) localization method in a range-based technique along with the Time of Arrival, Time Difference of Arrival, and Angle of Arrival.
Why is Indoor localization necessary?
An indoor localization system has many applications in a variety of areas. It proves beneficial as indoor localization provides the added benefit of safety and security and can also improve efficiency in the working environment. One example is hospitals where indoor localization finds its application for tracking patients. Doctors become able to know exactly where a patient resides inside the building without needing to provide constant supervision. Another example is in emergencies, where first responders could use indoor localization to help quickly guide them to anyone in distress without needing to know the exact layout of the building.
Hindrance to performing Indoor localization
Experts could not develop a standard model for indoor localization so far due to obstacles, floor layouts, and reflections of signals that can occur. Unfortunately, indoor localization suffers from many complications not present in outdoor localization. For instance, there are many more obstacles indoors, including people, furniture, and walls, which can reflect the signals produced, increasing multipath effects. There are also many wireless electronic devices utilizing Wi-Fi and BLE that are accessing the medium and transmitting information, which could make noise affecting the system’s performance.
Indoor localization is possible with IoT Devices.
Due to the small size of most IoT devices, their hardware is often quite limited. They contain low storage, minimal processing power, and basic communication capabilities. Therefore, any localization algorithms that IoT uses need to accommodate these devices’ capabilities. For an indoor localization system to be successful, multiple targets will need to be tracked at once while continuously updating when any targets are added, moved, or removed from the system.
Technologies employed in Indoor localization
Several different wireless technologies have been proposed and tested in the literature when performing indoor localization. The most common technologies are
- Radio Frequency Identification (RFID)
- Ultra-Wide Band (UWB)
However, each has its advantages and disadvantages when used for localization.
Due to the high availability of access points in buildings, Wi-Fi has become the most straightforward option, as any additional hardware needed is minimal. Unfortunately, Wi-Fi access points are often placed to maximize signal coverage, not for localization. Wi-Fi also consumes a large amount of power, which, if used for tracking, would quickly deplete a device’s battery, which is not ideal for most localization systems.
With the recent emergence of Bluetooth Low Energy (BLE) and beacons, it has become more feasible to place inexpensive beacons around an environment than rearrange existing hardware and use that for localization. In contrast, the main disadvantage of using beacons is that most require batteries to function. Once the battery is depleted, the beacon will no longer work, and either the beacon or the battery it contains will need to be replaced.
As different as all the wireless technologies seem, they also contain a commonality: they can follow the same positioning algorithms if required.
Models used in localization systems
As I told you earlier, no standard indoor localization model has been developed. Some of the most common models that we use in localization systems are:
- Angle of Arrival (AoA)
- Time of Arrival (ToA)
- Time Difference of Arrival (TDoA)
- Received Signal Strength Indicator (RSSI)
These are all Range-based Techniques of localization. Now, we shall discuss the RSSI-based Indoor localization with the Internet Of Things.
RSSI-based Indoor localization with the Internet Of Things
In the era of smart cities, there are many applications where the localization of indoor environments is essential, from monitoring and tracking smart buildings to proximity marketing and advertising in shopping malls. The success of these applications is based on the development of a robust real-time, cost-efficient system capable of accurately localizing objects.
What is RSSI?
RSSI is an acronym that stands for Received Signal Strength Indicator. Here is an explanation of what each part of this acronym means:
- Received: A Wi-Fi router typically sends wireless signals, and Wi-Fi devices receive them, such as laptops, smartphones, wireless security cameras, and others. The word ‘received’ indicates that RSSI is concerned with wireless signals at the time when WiFi-enabled devices receive them.
- Signal strength: RSSI measures the strength or power present in a radio signal when it gets received. In other words, it measures Wi-Fi signal strength.
- Indicator: Just another word for “measurement,” which is what RSSI is.
Signal strength power measurement, commonly known as the received signal strength identifier (RSSI), is a technique for calculating the distance between two UAVs or wireless nodes. Signal strength varies as the distance between nodes changes.
RSSI is an estimated measure of the power level that an RF client device is receiving from an access point or router. Signal strength varies as the distance between nodes changes.
At more considerable distances, the signal gets weaker, and the wireless data rates get slower, leading to lower overall data throughput. Receive Signal Strength Indicator (RSSI) measures the signal, which in most cases indicates how well a particular radio can hear the remotely connected client radios.
RSSI stands for Received Signal StrengthRSSI, or “Received Signal Strength Indicator,” which measures how well your device can hear a signal from an access point or router. It helps determine if you have enough movement to get a good wireless connection.
Because an RSSI value is pulled from the client device’s Wi-Fi card (hence “received” signal strength”), it is not the same as transmitting power from a router or AP.
What is the RSSI Level?
Wi-Fi signals start gradually losing power from the moment they are transmitted. Therefore, RSSI is always negative, indicating a signal has lost how much of its power since it represents a measurement of received signal strength.
In the real world, it is impossible to achieve an RSSI of 0, but you want to get as close to 0 as possible. Therefore, vendors and chipset makers typically break down RSSI values into many levels to tell you how close you are.
Each RSSI level represents a certain power level in milliwatts or decibels referenced to one milliwatt (dBm). Therefore, when you test Wi-Fi signal strength, you should always strive to discover your RSSI level. You can then use the information to determine the room for improvement.
RSSI values represent the relative quality of a signal a device receives.
RSSI indicates the power level after any possible loss at the antenna and cable level. The higher the RSSI value, the stronger the signal will be. When measured in negative numbers, the number closer to zero typically means better signal strength. It implies an RSSI closer to 0 is more potent, and closer to –100 is weaker. You want your RSSI to be as high as possible for the best performance. A helpful thumb rule is that if the RSSI is less than –70 dBm, you are unlikely to have good performance over Wi-Fi for bandwidth-intensive tasks. For example, -50 is a pretty good signal, -75 – is relatively reasonable, and -100 is no signal.
|Desired RSSI||-40 dBm to -50 dBm|
|Usable RSSI||-35 dBm to -70 dBm|
(Signal is too strong, saturated amplifiers)
(Signal is too weak, subject to an external interference)
Acceptable RSSI Signal Strength
1. -50 dBm
The highest signal strength level that a device can achieve in real-world conditions. If you reach an RSSI value of -50, one would have absolutely no trouble enjoying the internet connection to its full potential.
2. -60 dBm
Status: Very good
While not perfect, an RSSI value of -60 is still outstanding, and most people who don’t know what RSSI is would never guess their signal strength could be any better.
3. -70 dBm
With an RSSI of -70, you could enjoy most online activities without significant slowdowns and connection drops. However, one may notice that a video is buffering a bit longer than usual from time to time. One may also see a file that takes a while to download.
4. -80 dBm
It is where things start to get nasty. When one’s RSSI drops to -80, one’s download and upload speeds will likely suffer considerably, and one’s latency with them. Sending emails or browsing the web should not be a problem, but don’t expect to enjoy online games or high-definition video streaming without significant issues.
5. -90 dBm
Status: Very Low
Most people find an RSSI of -90 unacceptable for anything beyond minor bandwidth-intensive tasks. You can encounter frequent connection drops and issues with lost data packets at this signal strength level.
6. -100 dBm
Status: No signal
The more RSSI nears the value of -100, the closer one gets to not having any signal whatsoever.
Why does RSSI matter?
Now that you understand the RSSI meaning, briefly discuss why RSSI matters in the first place.
Many Wi-Fi users rely on internet speed tests to determine how fast their internet connection is. While quick and handy, internet speed tests do not tell the whole story because many factors affect your upload and download speeds.
One of these factors is the strength of the radio signal that a device receives, where the RSSI signal strength measurement comes in, and why it is so helpful to know. Because internet speed tests can not tell you your RSSI, you must equip yourself with a capable Wi-Fi signal strength Mac app or a Windows Wi-Fi signal strength app.
Why is localization necessary for Indoor IoT systems?
In Internet Of Things (IoT) applications, sensor data must not only be obtained. The sensor node’s location inside the building also needs to be known for the information produced to be valid. Therefore, all devices must efficiently determine the location of smart buildings’ residents in real-time with minimal knowledge of their surroundings. If a centralized server becomes unaware of the device’s positions, the information those devices make becomes irrelevant, and their limited resources are wasted. Therefore, indoor localization is often performed to determine a position. It increases efficiency and improves the experience of those who reside in smart buildings.
Why do we not prefer GPS-based Indoor Localization to RSSI-based Indoor Localization with the Internet Of Things?
Indoor localization is a system used to locate objects or devices in an environment where the Global Positioning System (GPS) is not applicable. It may suit outdoors, where there is plenty of space, but indoors this is not feasible due to limitations in the size of the environment. Therefore, we often use GPS in outdoor localization systems as it is the simplest method. However, it consumes a lot of energy and can be expensive to implement for every node in an extensive network. Therefore, when performing localization indoors, we require accuracy of less than one meter for a proper localization system. Hence, we prefer other methods, such as RSSI-based indoor localization with the Internet Of Things, to determine a device’s location.
Why is GPS not suitable for Indoor localization?
Most outdoor localization systems use Global Positioning System (GPS) due to its ease of implementation and accuracy of up to five meters. However, GPS is not a suitable option due to the limited space that comes with performing localization of indoor environments and the large number of obstacles found indoors. Hence, accurately and efficiently locating objects is a significant challenge in indoor environments. Moreover, we cannot use GPS indoors due to a dependency on Line-of-Sight (LOS) between GPS satellites and receivers. Additionally, GPS only provides maximum accuracy of up to five meters. Hence, RSSI-based indoor localization with the Internet Of Things finds its application here.
Moreover, look at another scholarly article on interoperability is a weakness in cloud computing.