Lohan, Alén-Savikko, Chen, Järvinen, Leppäkoski, Kuusniemi, and Korpisaari
296
While such a scheme can be directly applied on a 5G mobile device with a WiFi
chipset by relying solely on the WiFi signal, a direct application of it to the RSS of 5G
signals is not obvious. To enable it, the 5G networks should support some passive
beacon modes, which are currently not found in 5G white papers.
2) Definition 2 (mostly encountered in e‐health related research) [109,122]: Passive
positioning may also refer to the device‐free positioning schemes, where the user is
not required to do anything in order to be positioned by the network. In contrast,
active positioning means a positioning mechanism where the user carries some positioning device with him/her (e.g. mobile phone, wearable devices, etc,) and may be
required to take some active steps to perform the positioning, such as turning on the
GNSS or WiFi engine on his/her mobile device. A video‐based positioning and a
tactile floor are typical examples of passive positioning according to this second definition. This definition is in fact the opposite to the previous definition of passive
positioning, and is not the one adopted in this chapter.
Clearly, the passive positioning schemes according to the first definition above can
fully preserve the user location privacy. Another example of passive positioning, this
time with TDOA, is discussed in [20]. The mobile device computes the TDOA from at
least four ANs in range and computes its position based on some hyperbolic equations.
The signaling sequences are not discussed in [20]. Again, such a downlink signaling
only solution in 5G is highly unlikely, as the 5G network has to first verify the user
identity for allowing access to the network and it is likely to use various location‐aware
mechanisms where the knowledge about the user location is a must [55,70,91].
In conclusion, passive positioning schemes in 5G remain are in contrast with the 5G
targets of location‐aware communications, mobility management in 5G and detection
and tracking of Primary Users (PU). Thus, the passive positioning schemes are not
likely to be a gaining technology in 5G.
13.8 Physical‐Layer Based Security Enhancements
Mechanisms for Positioning in 5G
This section focuses on the description of the main methods proposed so far at the
physical layer to mitigate or eliminate the vulnerabilities and security threats in 5G
positioning. Such methods include the reliability monitoring and outlier detection algorithms, the methods for detecting and locating interference signals, and backup systems.
13.8.1 Reliability Monitoring and Outlier Detection Mechanisms
From the reliability monitoring point of view, 5G positioning based on TOA has similarities to GNSS based positioning. Due to the dense network of ANs, it is likely that the
TOA from the user is measured by 5 or more ANs, which makes the system of positioning equations over‐determined. As the typical range of TOA estimation errors is also
small compared to the TOA measurements, the redundancy in the over‐determined
equation system can be used to detect measurement errors in the positioning processing similarly as is used in integrity monitoring with GNSS signals [37]. However, there
are also differences between 5G based positioning and GNSS. With GNSS, the positioning geometry is significantly different, as the distances to the satellites are much longer
296
While such a scheme can be directly applied on a 5G mobile device with a WiFi
chipset by relying solely on the WiFi signal, a direct application of it to the RSS of 5G
signals is not obvious. To enable it, the 5G networks should support some passive
beacon modes, which are currently not found in 5G white papers.
2) Definition 2 (mostly encountered in e‐health related research) [109,122]: Passive
positioning may also refer to the device‐free positioning schemes, where the user is
not required to do anything in order to be positioned by the network. In contrast,
active positioning means a positioning mechanism where the user carries some positioning device with him/her (e.g. mobile phone, wearable devices, etc,) and may be
required to take some active steps to perform the positioning, such as turning on the
GNSS or WiFi engine on his/her mobile device. A video‐based positioning and a
tactile floor are typical examples of passive positioning according to this second definition. This definition is in fact the opposite to the previous definition of passive
positioning, and is not the one adopted in this chapter.
Clearly, the passive positioning schemes according to the first definition above can
fully preserve the user location privacy. Another example of passive positioning, this
time with TDOA, is discussed in [20]. The mobile device computes the TDOA from at
least four ANs in range and computes its position based on some hyperbolic equations.
The signaling sequences are not discussed in [20]. Again, such a downlink signaling
only solution in 5G is highly unlikely, as the 5G network has to first verify the user
identity for allowing access to the network and it is likely to use various location‐aware
mechanisms where the knowledge about the user location is a must [55,70,91].
In conclusion, passive positioning schemes in 5G remain are in contrast with the 5G
targets of location‐aware communications, mobility management in 5G and detection
and tracking of Primary Users (PU). Thus, the passive positioning schemes are not
likely to be a gaining technology in 5G.
13.8 Physical‐Layer Based Security Enhancements
Mechanisms for Positioning in 5G
This section focuses on the description of the main methods proposed so far at the
physical layer to mitigate or eliminate the vulnerabilities and security threats in 5G
positioning. Such methods include the reliability monitoring and outlier detection algorithms, the methods for detecting and locating interference signals, and backup systems.
13.8.1 Reliability Monitoring and Outlier Detection Mechanisms
From the reliability monitoring point of view, 5G positioning based on TOA has similarities to GNSS based positioning. Due to the dense network of ANs, it is likely that the
TOA from the user is measured by 5 or more ANs, which makes the system of positioning equations over‐determined. As the typical range of TOA estimation errors is also
small compared to the TOA measurements, the redundancy in the over‐determined
equation system can be used to detect measurement errors in the positioning processing similarly as is used in integrity monitoring with GNSS signals [37]. However, there
are also differences between 5G based positioning and GNSS. With GNSS, the positioning geometry is significantly different, as the distances to the satellites are much longer