From d4ac4dec204b552459bdb117cbaaa4ab3b429779 Mon Sep 17 00:00:00 2001 From: Jet Hughes Date: Tue, 21 Mar 2023 12:00:33 +1300 Subject: [PATCH] vault backup: 2023-03-21 12:00:33 --- content/notes/07-location-sensors.md | 223 +++++++++++++++++++++++++++ content/notes/cosc-301.md | 2 +- content/notes/info-305.md | 1 + 3 files changed, 225 insertions(+), 1 deletion(-) create mode 100644 content/notes/07-location-sensors.md diff --git a/content/notes/07-location-sensors.md b/content/notes/07-location-sensors.md new file mode 100644 index 000000000..f8b395bd4 --- /dev/null +++ b/content/notes/07-location-sensors.md @@ -0,0 +1,223 @@ +--- +title: "07-location-sensors" +tags: +- lecture +- info305 +--- + + +## Terminology + +- Precision vs. Accuracy +- 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): +- How many translational and rotational movements are possible? +- How many degrees of freedom in 3D space? + - 2 DoF? + - 3 DoF? + - 6 DoF? + - 9 DoF? + - Unlimited DoF? +- How many degrees of freedom in 2D space? + +![Degrees of Freedom](https://i.imgur.com/uWDwFsO.png) + +- (Tri)angulation: + - Based on angles between signals + - Referred to as angles of arrival + - 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) + +- (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) + +## Cell-based +- Positioning based on GSM cell ID +- Mobile Positioning System (MPS) by Ericsson to improve accuracy + - Few changes of infrastructure + - No changes of user devices +1. Cell Global Identity (CGI) for identification of the cell + - Uses GSM cell ID + - If sector-antennas used position can be narrowed to segment of the circle + - Angulation + +![](https://i.imgur.com/uzTcwTC.png) + +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) + +3. Uplink-Time Difference of Arrival (UL-TOA) + - Four base stations needed + - Measurement of signal propagation time at base stations + - Calculation of position based on lateration + - Accuracy 50 – 150m + - 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) + +- Integrated approach based on existing infrastructure +- Low costs (for user) +- Low power draw +- High availability +- Works indoor and outdoor (no direct line of sight needed) +- 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 +- Cell ID requires database with mapping WiFi cell ID to GPS or …. (e.g. created by Apple, Google) +- Lateration + - Requires accurate information about access point positions + - Measurement of signal strength of various access points + - At least three access points have to be available + - Measurements are influenced by obstacles like walls +- Improved approach: Fingerprinting + + +- Fingerprinting: + - 1st Phase: Radio Map Creation (Offline): + - Measurements of fingerprints at reference points -> stored in fingerprint DB + - Definition of reference points according to accuracy needs and building structure +- 2nd Phase: Radio Map Usage (Online): + - Fingerprint of current position is taken + - Search for closest matching reference point on radio map Position taken from that reference point or interpolated + + +- Fingerprint + - Location: lat,lon,floor + - VisibleAccessPoints{ + - Fingerprint DB + - AP1: + - SSID: eduroam + - MAC: 08:17:35:33:5f:80 + - signal strength: -64 + - AP2 + - SSID: VPN/WEB + - MAC: 08:17:35:33:5f:81 + - signal strength: -61 + - APn o... + +![](https://i.imgur.com/vJSirwu.png) + +Fingerprinting services using Wifi +- ~99% of queries use Google location database (Google Maps Geolocation API) + - https://developers.google.com/maps/documentation/geolocation + - Access is logged + - Used to improve DB + - Privacy issues (e.g. private routers) +- Alternatives (less coverage & accuracy) + - OpenCellID + - Mozilla Location DB +- Not available when offline, cell DB too large +- WLAN cells can move/change - frequent update required + +![](https://i.imgur.com/FowUq39.png) + + +- Cell structure: circular (theory), hexagonal (planning), irregular (reality) +- Neighbouring cells use different frequencies to minimise interference + - Some overlap inevitable +- Typical cell sizes: + - WiFi: 10m - 100m + - 3G (UMTS): 100m - 5km + - 2G (GSM): 100m - 35km + +![7-cell cluster (commonly used)](https://i.imgur.com/4s8Bv7g.png) +![cell characteristics](https://i.imgur.com/maI9ctM.png) + +## Proximity Sensors & Near Field Communication +- Different technologies for sensing proximity or exchanging data (often dual purpose) + - Stand-alone infrastructure approaches + - Not widely accepted due to special hardware requirements infrastructure costs (for tracking) +- Conceptually often similar to cell-based approaches but require extra infrastructure + +![](https://i.imgur.com/AdxaFMb.png) + + +- WIPS (Infrared) + - Beacons installed in the rooms sending unique ID + - User’s badges receive signals of local beacons + - Received beacon ID is sent to location server via WLAN + - Server maps received beacon ID to semantic location which is sent back to the user +- Active Badge (Infrared) + - Users carry badge sending specific user ID + - IR-receivers in the rooms receive those signals + - Position of user is tracked by central server + - Energy-efficient badges (sending short signals of 0,1s each 15s) + +![](https://i.imgur.com/y2wweyT.png) + + +- Bluetooth Low Energy LE (Bluetooth specification 4.0) +- Not to confuse with “classic” Bluetooth (e.g. used in headsets or for I/O devices) + - Optimized for battery powered sensors + - Months or years of battery liftetime + - Lower data rate (1MBIT/sec) + - Backwards compatible (same frequency and modulation) + +![](https://i.imgur.com/BKftnA4.png) + +- Two classes for peripherals: + - Beacons (pure static broadcasts: + - iBeacon simply broadcasts UUID + - Additional data possible on request + - Sensors (broad/unicast with sensor data) + - Different profiles temperature, gravity, hear rate, pressure, … + - Notification possible to avoid polling + - Bidirectional communication + - Not primarily focus, mostly for setting parameters + + +- Location and Proximity Sensing using Bluetooth LE + - One beacon (e.g. per room) + - Pure proximity sensing, looking for strongest signal + - E.g. Region monitoring to detect Beacon presence + - Many beacons (e.g. per room) + - Range calculation using Received Signal Strength Indicator (RSSI) and calibrated transmitter power (txPower = RSSI at 1m) + - Trilateration using several beacons but not very accurate +- Range different for beacons but typically between 20-50m (rarely 100m) + +![](https://i.imgur.com/Xqh7cp0.png) + + +- Different protocols on top of Bluetooth LE + - iBeacon (Apple) + - Broadcasts a UUID + - ID is used with database integrated in the app + - Further information on request (e.g. range information) + - Eddystone (Google) + - Beacons broacasts information about the beacon (telemetry frame e.g. battery or sensor information) + - Beacons broadcasts and redirects to an URL (physical web) + +![|200](https://i.imgur.com/jVfJF41.png) + diff --git a/content/notes/cosc-301.md b/content/notes/cosc-301.md index 39a270e1c..fd679ffb9 100644 --- a/content/notes/cosc-301.md +++ b/content/notes/cosc-301.md @@ -33,5 +33,5 @@ https://www.cs.otago.ac.nz/cosc301/schedule.php - [x] [[04-scripting-techniques]] - [x] [[05-filesystems]] - [x] [[06-network-system-administration]] -- [[07-system-installation]] +- [x] [[07-system-installation]] # Info diff --git a/content/notes/info-305.md b/content/notes/info-305.md index 642eeb891..315f65cab 100644 --- a/content/notes/info-305.md +++ b/content/notes/info-305.md @@ -21,5 +21,6 @@ tags: - [x] [[04-lens-studio]] - [x] [[05-pervasive-ubiquitious-2]] - [x] [[06-challenges-for-ubicomp-and-intro-to-sensors]] +- [ ] [[07-location-sensors]] # Info \ No newline at end of file