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content/notes/07-location-sensors.md
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@ -12,7 +12,6 @@ tags:
- How practical are systems that are:
- Precise but not accurate?
- Accurate but not precise?
![Accuracy vs. Precision](https://i.imgur.com/r0dRA8K.png)
- Degrees of Freedom (DoF):
@ -24,7 +23,6 @@ tags:
- 9 DoF?
- Unlimited DoF?
- How many degrees of freedom in 2D space?
![Degrees of Freedom](https://i.imgur.com/uWDwFsO.png)
- (Tri)angulation:
@ -33,16 +31,16 @@ tags:
- Angle to reference point determined by means of special antennas
- Positions of reference points have to be known
- 3D-positioning requires three reference points (triangulation)
![Angulation](https://i.imgur.com/8k8aD5h.png)
> [!INFO] if you have two reference points and the angle towards them, you can get the location
- (Tri)lateration
- Based on distances between device and reference points
- Calculated e.g. by time of arrival (ToA) or signal strength
- Positions of reference points have to be known
- 3D-positioning requires three reference points (trilateration)
![Lateration](https://i.imgur.com/KQTJDSH.png)
> [!INFO] siimilra to triangulation but you need three points and its calculated using distancees not angles. the distances can be calculated by time of arrival of a signal
## Cell-based
- Positioning based on GSM cell ID
@ -53,17 +51,18 @@ tags:
- Uses GSM cell ID
- If sector-antennas used position can be narrowed to segment of the circle
- Angulation
![](https://i.imgur.com/uzTcwTC.png)
> [!INFO] compute your position based on which cell tower you are connected to. each tower has a unique ID.
> used by emergency providers, they know where you last logged in
2. GSM based on FDMA (Frequency-division multiple access) and TDMA (Time-division multiple access)
- Exact timing required for the synchronization of uplink and downlink
- Timing Advance (TA)
- Device calculates distance based on signal propagation time
- Can be used for positioning in combination with CGI
![|200](https://i.imgur.com/zGMWd9E.png)
![](https://i.imgur.com/U2VHcye.png)
> [!INFO] "towers" use FDMA or TDMA [[21-data-link-layer#multiple access links and protocols]] Timing advance used for multiple access can be used to calculate time
3. Uplink-Time Difference of Arrival (UL-TOA)
- Four base stations needed
@ -73,8 +72,8 @@ tags:
- Network-based location technology,
- Can locate any type of mobile phone.
- Only available to the owner of the sensor network
![Uplink-Time Difference of Arrival](https://i.imgur.com/CI07t5Z.png)
> [!INFO]
- Integrated approach based on existing infrastructure
- Low costs (for user)
@ -84,14 +83,12 @@ tags:
- Information not always available to the user (often only network provider)
- Used for “Enhanced 911”
- But relatively low accuracy
![](https://i.imgur.com/oLITCmM.png)
- Other cell-based location approaches: WiFi/WLan-cells
- Integrated infrastructure approach
- WiFi/WLAN (cell-id, lateration, fingerprinting)
![](https://i.imgur.com/VSMfEqW.png)
- Based on already existing WLAN infrastructure, primarily installed for communication purposes