Chapter 3:

This chapter, presents an overview of different indoor localization technologies and techniques used in wireless communication technology based indoor localization.

The chapter is organized as follow. The first section gives an overview of indoors localization based wireless communication technologies and discusses the wireless communication technology that has been used for indoor localization. We will compare the advantages and disadvantages of each wireless communication technology as an indoor localization technology. In second section, we will introduce five basic mathematical techniques used in most kinds technology for indoor localization based wireless communication.

2. Overview of Wireless Based Indoor Localization

3. Wireless Technologies for Indoor Localization

• 3.1 Long Distance Wireless Technology

◦ Localization based on FM

◦ Localization based on GSM/CDMA

• 3.2 Middle Distance Wireless Technology

◦ Localization based on Wi-Fi

◦ Localization based on  ZigBee

• 3.3 Short Distance Wireless Technology

◦ Localization based on Bluetooth

◦ Localization based on UWB (Ultra-Wide Band)

◦ Localization based on RFID (Radio Frequency Identification

4. Mathematical Techniques for Wireless Based Indoor Localization

4.1. Cell Identifier (CID)

4.2 Localization technique based Angle of Arrival (AOA)

4.3 Localization technique based Angle of Arrival (TOA)

4.4 Localization technique based of Time Difference of Arrival TDoA

4.5.Localization technique based received signal strength (RSS)

4.6 Localization technique based Fingerprint

5 Localization algorithms

5.1 Trilateration and multilateration

5.2 Triangulation method

6. Conclusion

Overview of most technologies and techniques  used in indoor location environment

A lot of studies and researches are still going in order to create a very efficient system that can provide us with an exact accurate  indoor localization ,various technologies have been studied,some of them just were incapable of responding to the expectations , other were really good ,but demand big efforts or huge budgets to be installed and maintained .

In my research I will be treating the Wireless communication technology (RF, Ultrasonic) as a technique for indoor location systems .As I mentioned before these technologies have weaknesses , and some of them can become brakes on their deployment, including the consumption of the energy, cost and the installation complexity ,the price of certain components in these systems sometimes hinder the deployment of the technology, especially when we speak about Vision Based Indoor Localization, Wireless Based Indoor localization, acoustic based localization and other totally different methods like Mechanical ( MEMS sensor)) localisation technology.

•                  Vision Based Indoor Localization Visual information can be collected and practiced in indoor navigation in many kinds of literature. In [Zufferey0-6] the micro-flyer is installed with two miniature cameras, which can shoot photos of the specific mark (texture) on the wall. By analyzing each individual marks, the system can derive its locations from the walls, that help to prevent the micro-flyer from crashing into the surrounding walls. The Unmanned Aerial Vehicle UAV can predict its distance from ground and walls by the laser beams shoot from [Mohamede11] to the surrounding to detect and analyze the position. However, vision based localization will use up more computing resource (image processing) and power. In robot navigation systems, the robot is required to wander on the floor for a long period of time to determine its potential locations. Hence, the application of the camera will higher the cost, and fails the scalability of the system.
•                  Wireless communication technology Based Indoor localization one of the advantages of wireless technology is that it can get through obstacles (doors, walls) and cover the whole building with a stable signal. In wireless communication technology the distance to a known points is calculated using characteristics of the received signal strength then used to get the location of the current point. . The implementation of the system is easy and waves don’t stop human activities in the building. Wireless chips are very affordable and much cheaper than cameras and other technology. The power and computing resource consumption also less than processing the image.
•                  Acoustic based localization

Acoustic is a mechanical vibration transmitted over solid, liquid, and air, ultrasonic is a sound with a frequency out of human hearing rang. Being significantly simple and cheap are the main advantages of ultrasound systems, and unlike Wireless based technologies, ultrasound does not penetrate walls but they reflect on most obstacles. In order to obtain an estimation of the distance between a transmitter and a receiver, most of ultrasound indoor systems are combined with other technologies. The receiver will catch both the ultrasonic wave and the other selected wave (eg RF) [12, 13, 80, 68, 100, 60, and 2].

The Advantages of using acoustic to identify the location of the user in indoor environment. Transmission is confined by walls limiting the signals in an enclosed area. No extra hardware is required as almost every COTS smartphone has integrated speakers and microphones, nodes can be manufactured to produce ultrasound signals at little cost, And The behavior of sound is much more predictable than Infrared and radio waves. Infrared needs direct line of sight and does not work in sunlight and under bright lights Radio waves on the other hand can be adversely affected by interferences and cannot pass through obstacles  [1].

It can provide more control over the range of transmission,

• Other localization technology

There are many exiting technologies using other techniques for indoor localization, some of them use sensors (campus, accelerometer, and gyroscope) to detect the movement of the user. the position can be calculated as the previous location adding the movement this method is insured by adopting a dead-reckon algorithm.

This chapter will give us an overview on different indoor localization technologies based on RF waves, I will be discussing their advantages and disadvantages, then I will briefly introduce some applications of indoor location system then conclude with the techniques that could potentially be used for a Hybrid indoor location system.

The choice of a suitable technology must be based on four main parameters (factors):

Observing localization technique’s accuracy isn’t enough if we are trying to judge its performance. Referring to [21] and considering the difference between the indoor and outdoor wireless geolocation, we find that the following parameters are the performance benchmarking for indoor wireless location system: Accessibility, accuracy, robustness, and cost. Thereafter, we make a comparison among different systems and solutions

•                Accessibility (SmartPhone):Refers to the ability of the technology to be available, or accessed by a consumer or business. No matter what the technology, to determining location always requires some infrastructure: like transmitter and receiver. Some technology requires carrying an extra hardware. Now the more highly accessible technology Is GPS because there is a single global standard for satellite transmitters, and all smart phone can act as receivers. In our case should this this technology supported by smartphone or pad, because the smartphone are very important in our life
•                Coverage: Coverage means the area covered for accurate localization. Since different wireless technology has different distance, hence short-range wireless technology might need more devices to cover the same area.
•                Accuracy: Accuracy (location error) usually the most important requirement in indoor and outdoor localization system in environment is the distance between the real location and estimation location.
•                Power consumption :It is a very important requirement now low power consumption means having cheaper infrastructure.
•                Cost: The Cost of a localization system may depend on many factors includes the expense of setting up, using and maintaining the systems. Time, space, weight, and energy. The time factor is related to installation and maintenance e etc.

3 Wireless Based Indoor Localization Technologies

Radio frequency (RF) spectrum refers to the frequency that is less than 300GHz electromagnetic spectrum. RF signal is being utilized for wireless communication over hundreds of years. There are various usage for different radio frequency, and the usage of spectrum is regulated by The Federal Communications Commission (FCC). There are numerous applications created with various wireless communication protocols and standards.

The wireless technology used for indoor localization can be classified by the frequency it uses. As the frequency of the wireless technology affects its abilities like coverage, penetration wall, and resistance to obstacles. In this chapter, we classify them into three categories: long range wireless communication technology, Medium Range Wireless Communication technology and short range wireless Communication technology.

3.1 Long range wireless communication technology

Global Navigation Satellite System GNSS, are positioning systems using satellites emitting signals as reference points for positioning a receiver terminal. These systems work on frequency L. The L band, as defined by the IEEE, is the 1 GHz to 2 GHz range of the radio frequency spectrum. Using repeater beacons, it is possible to improve the received signal in GNSS and use the same system that GNSS positioning. This method, called Assisted GPS, can significantly improve indoor positioning. For users, it is one of the most natural solutions because this system is transparent to all applications that use satellite tracking. Furthermore, the service provider must supply all interior repeater beacons.

Frequency Modulation FM is used worldwide for regional radio transmission. the majority of countries, they are using   87.5  ~ 108.0 MHz radio frequency spectrum. by  Using the very high frequency VHF which is far less than the Wi-Fi and other modern wireless technology, FM signal is less affected by weather or obstacles like buildings, walls, and tree.

Since the ubiquity of FM, there is no need to build extra hardware infrastructure using FM for indoor localization. FM receiver is cheap and has less power consumption thus better battery life. However, the FM base station is very far away and FM signal has a long wave length around 3m, which means that the receiver signal strength  RSS of FM signal does not dramatically change in short distance. Therefore FM signal works better for a large area. due different FM stations use Frequency division multiple access  FDMA to share the spectrum, Each channel occupies a different band of the frequency spectrum which can be used to reduce the variance of error introduced by single channel signal [Popleteev13-].

GSM/CDMA has been used in cellular network communication. The GMS/CMDA frequencies in different regions are different. Generally GMS/CMDA it operates in bands 850MHz, 900MHz, 1800MHz and 1900MHz. The GSM/CDMA network is already covered in most buildings, thus there is no or less need for extra infrastructure and has good propagation is less affected by weather or obstacles like buildings, walls, and tree. Contrary FM, GSM, on the other hand, has a relatively small propagation distance in the indoor environment [5]. Unfortunately, GSM/CDMA is heavily patented, so it is hard to do modification or extensions based on GSM/CDMA which limits the future development on it.

3.2 Medium Range Wireless Communication technology

WiFi is one of the most used wireless technologies. Therefore, there are plenty of base stations that can be used as a access point, It follows a series of standards in WLAN (IEEE 802.1). It uses two licence-exempt frequency bands: 2.4 GHz, and 5 GHz. Now, most commercial products, like smartphones, laptops, and tablets support WI-FI. Nowadays most buildings such as mall, airport, train station and office building have already deployed Wi-Fi hotspots that provide whole building coverage as network access point. That means the infrastructure cost and user device cost can be very low. Additionally, Wi-Fi based localization can be easily adopted by buildings and users. The disadvantage of this technology is that high power consumption and interfere with other technology use same band

.ZigBee is a specification based on IEEE 802.15.4 standard for low or low-rate WPANs. It uses 784 MHz band in China ,915 MHz band in the USA and Australia, 868 MHz band in Europe, and 2.4 GHz in other regions. ZigBee is used for long distance transmission between devices in wireless networking. rates vary from 20 kbit/s for 868 MHz band to 250 kbit/s for 2.4 GHz band . It has low data transfer rate, low cost, low power consumption, short latency time, comparing to Wi-Fi standards. In IEEE 802.15.4 standard Link Quality Indication LQI is defined to indicate the quality of the link and can be used to derive RSS. And there are integrated chips such as Ti   CC2530/CC2531 [Hu11-] been manufactured to get the RSS, which makes the implementation of the system easier. Unfortunately this technology it is not integrated into commercial products, like smartphones, laptops, and tablets which mean that the user should hold an extra hardware and also interfere with other technology use same band like Wi-Fi

3.3 short range wireless Communication technology.

Short-range communication networks is the most widely used technologies for indoor localization, it make possible to locate the user within buildings with an accuracy of a few centimeters. There are several categories of location interfaces.

Bluetoothis a wireless technology for exchanging data over short range. It follows a series of standards IEEE 802.15.1 personal area network standard. It also uses 2.4 GHz band as Wi-Fi does. Bluetooth is widely used for short range communication technology like smart phones, headset, etc… the Bluetooth consumption is very low especial Bluetooth low energy 4.0 BLE 4.0 and therefore the coverage of Bluetooth is shorter range than Wi-Fi and other WLAN technology. Hence, Bluetooth is suit for localization for small area. In IEEE 802.15.1 standard Link Quality Indication LQI is defined to indicate the quality of the link and can be used to derive RSS. And there are integrated chips such as Instruments TI CC2540/CC2541 been manufactured to get the RSS, and also is opened source code, which makes the implementation of the system easier. Bluetooth BLE ibeacon technology  : are a low-cost piece of hardware — small enough to attach to a wall or countertop — that use battery-friendly, low-energy Bluetooth connections to transmit messages or prompts directly to a smartphone or tablet.The biggest advantage of Bluetooth technology is that the devices are small, easy to integrate in the PDA, PC and mobile phone, easy to find equipment and signal transmission without affecting the time horizon of the technology for short-range indoor positioning. Its drawback is that the price of Bluetooth devices and equipment is more expensive, but also for the stability of the complex space environment, the Bluetooth system somewhat less affected by great noise signal interference.

Ultra-Wide Band UWB is a novel wireless personal area network technology It follows a series of standards IEEE 802.15.3, uses a sub nanosecond radio pulse to transmit very large information data of bandwidth normally greater than 480 MHz/s achieved over a short distance of few meters. Its transmission can be regarded as background noise to other wireless communication technology, hence, it can use any spectrum without interfering with other users. It uses transmission power -41.4dBm/MHz, which is limited by Federal Communications Commission FCC, The power consumption is low. Another advantage of UWB is its immune to multipath problems [Gonzalez07]. The positioning error of this technology is very low compared other wireless communication technology, but unfortunately, today’s smartphone doesn’t have incorporated such technology. But there are signs that this technology will soon be incorporated into the smartphone [6].

Radio Frequency Identification RFID uses radio electromagnetic fields to transfer Data [2], It composes of two parts reader and tag. The reader uses radio frequency electromagnetic field to read and write the data in the tag and get the identification of the object the tag attached too. There is two type tags in the market can either active tag or passive tag. The passive tag can be very cheap and can use for a long time, which is ideal for cost sensitive scenario. However, the passive tag suffers from both tag collision and reader collision problems, RFID Tag collision happens when a reader reads multiple passive RFID tags, and RFID reader collision happens when the coverage of two readers interfere and read the tag at the same time. The communication range of the RFID is very small distance between 1cm~2m, which increases the labor works for pre-deployment to cover the big area. This system gives completely accurately, but unfortunately require specific terminals, so it is not appropriate for the case study of this project, and not easy to integrate into other systems, so that there are some limitations positioning technology.

In order to summarize all theses wireless communication technologies used in literatures, A comparison of the technology mentioned are done in the following table 1 from a point of view of indoor localization. Which different technology has different transmission range, different indoor environment needs a dedicated infrastructure, Accessibility, power consumption and cost. In the following section, we will discuss the most techniques used for indoor localization. The same technique can use in several different wireless technologies and have different performance (accuracy and precision) based on the characteristics of the wireless communication technology itself.

	GPS	FM	GSM	UWB	Wi-Fi	BLE	ZigBee	RFID	Ultrasonic
Signal	RF	RF	RF	RF	RF	RF	RF	RF	Acoustic
FrequencyBand	1575.42 MHz