DOI: 10.21227/k75x-1f76
title: CRAWDAD mannheim/compass (v. 2006-09-13)

description: COMPASS is a positioning system based on 802.11 and digital compasses. We apply an two-stage fingerprinting approach: In the training phase, we sample the signal strength of neighboring access points for selected orientations at each reference point and store the data in a database. During the positioning phase, the orientation of the user is utilized to preselect a subset of the training data and based on this data compute her position.last modified :2006-11-14release date :2006-09-13date/time of measurement start :2006-02-11date/time of measurement end :2006-03-09collection environment :Positioning systems are one of the key elements required by
location-based services. We design and implement a positioning system 
called COMPASS which is based on 802.11-compliant network infrastructure 
and digital compasses. On the mobile device, COMPASS samples the signal 
strength values of different access points in its communication range 
and utilizes the orientation of the user to preselect a subset of 
the training data. The remaining training data is used by a probabilistic 
positioning algorithm to determine the position of the user.

While prior systems show limited accuracy due to blocking effects
caused by the human body, we apply digital compasses to detect
the orientations of the users so that they can deal with these blocking
effects. After a short period of training the COMPASS system achieves 
an average error distance of less than 1.65 meters in the experimental 
environment of 312 square meters.network configuration :The test environment is equipped with five Linksys / Cisco WRT54GS and 
four Lancom L-54g access points. All access points support 802.11b and 
802.11g. One Lancom and all Linksys access points are located on the same 
floor as our testing area whereas three Lancom access point are located 
in other places inside the building. The exact position of the access points 
located inside the testing area is marked by squares in the floor plan 
(see the download link below).data collection methodology :We deployed our positioning system in the hallway of an office
building on the campus of the University of Mannheim. The operation
area is nearly 15 meters in width and 36 meters in length,
covering an area of approximately 312 square meters. The floor
plan of the testing area is shown in the floor plan figure 
(see the download link below).  The large hallway in the left part of 
the map is connected by two narrow hallways that are separated by rooms 
such as archives and a kitchen.

We marked the floor plan (see the download link below) with markers 
depicting the grid of the reference points (light-colored dots) and 
the online measurement points (dark dots). The access points are 
marked by squares.

As a client, we used a Lucent Orinco Silver PCMCIA network
card supporting 802.11b. We collected the signal strength samples
on an IBMThinkpad R51 running Linux kernel 2.6.13 and Wireless
Tools 28pre.

To obtain the orientation of the user we used the Silicon Laboratories
C8051F350 Digital Compass Reference Design Board. This device provides 
a USB-to-Serial bridge to access the data and is powered by the USB 
electricity supply. We calibrated the compass in the middle of the operation 
area. In a closer area around the calibration point we measured a variation of 
1 degree. However, variations up to 23 degree were rarely detected at a few 
points of the testing area. These measurement errors occured always close 
to electromagnetic objects such as high-voltage power lines and electronic devices.Tracesetmannheim/compass/signalstrengthA traceset of signal strength collected from 802.11 APs for the COMPASS positioning system.files: offline.tar.gz, online.tar.gzdescription: A traceset of signal strength collected from 802.11 APs for the location estimation used by the COMPASS positioning system.measurement purpose: Location-aware Computing, Positioning Systemsmethodology: The grid of reference points applied to the operation area includes 166 points with a spacing of 1 meter (see the light-colored dots in the floorplan figure). During the offline phase, the signal strength was measured at reference points for different orientations. We then randomly selected 60 coordinates and orientations for the online phase.last modified: 2006-11-14dataname: mannheim/compass/signalstrengthversion: 20060913change: the initial versionrelease date: 2006-09-13date/time of measurement start: 2006-02-11date/time of measurement end: 2006-03-09mannheim/compass/signalstrength Tracesoffline: A trace of signal strength values from 802.11 APs measured at reference points for different orientations.configuration: During the offline phase, the signal strength was measured at reference points for different orientations. We collected 110 signal strength measurements at each reference point and for each orientation. This leads to 146,080 measurements for the offline phase. We spent over 10 hours to collect all the data.format: t="Timestamp"; id="MACofScanDevice"; pos="RealPosition"; degree="orientation"; "MACofResponse1"="SignalStrengthValue","Frequency","Mode"; ... "MACofResponseN"="SignalStrengthValue","Frequency","Mode" t: timestamp in milliseconds since midnight, January 1, 1970 UTC id: MAC address of the scanning device pos: the physical coordinate of the scanning device degree: orientation of the user carrying the scanning device in degrees MAC: MAC address of a responding peer (e.g. an access point or a device in adhoc mode) with the corresponding values for signal strength in dBm, the channel frequency and its mode (access point = 3, device in adhoc mode = 1)description: A trace of signal strength values from 802.11 APs measured at reference points for different orientations for the offline phase of the COMPASS positioning system.last modified: 2006-11-14dataname: mannheim/compass/signalstrength/offlineversion: 20060913change: the initial versionrelease date: 2006-09-13date/time of measurement start: 2006-02-11date/time of measurement end: 2006-03-09url: /download/mannheim/compass/offline.tar.gzonline: A trace of signal strength, which is derived from mannheim/compass/signalstrength/offline.configuration: We randomly selected 60 coordinates and orientations for the online phase. The only condition to select a point inside the testing area as an online set point is that it is surrounded by four reference points. Again, we collected 110 signal strength measurements for each online set point, leading to 6,600 measurements in total. In Figure 3 the online set points are marked by dark dots.format: t="Timestamp"; id="MACofScanDevice"; pos="RealPosition"; degree="orientation"; "MACofResponse1"="SignalStrengthValue","Frequency","Mode"; ... "MACofResponseN"="SignalStrengthValue","Frequency","Mode" t: timestamp in milliseconds since midnight, January 1, 1970 UTC id: MAC address of the scanning device pos: the physical coordinate of the scanning device degree: orientation of the user carrying the scanning device in degrees MAC: MAC address of a responding peer (e.g. an access point or a device in adhoc mode) with the corresponding values for signal strength in dBm, the channel frequency and its mode (access point = 3, device in adhoc mode = 1)description: A trace of signal strength, which is derived from mannheim/compass/signalstrength/offline for online phase of the COMPASS positioning system.last modified: 2006-11-14dataname: mannheim/compass/signalstrength/onlineversion: 20060913change: the initial versionrelease date: 2006-09-29date/time of measurement start: 2006-02-11date/time of measurement end: 2006-03-09url: /download/mannheim/compass/online.tar.gz