Reliability
 improvement for an
RFID-based psychiatric
 patient localization
       system
Reference

 Chieh-Ling Huang, Pau-Choo Chung, Ming-Hua Tsai,
 Yen-Kuang Yang, Yu-Chia Hsu Reliability improvement
 for an...
Outline

 Introduction
 System overview
 Reliability improvement with field generator scheduling
 Experiments
 Conclus...
Introduction

 Psychiatric patients often cannot control their actions,
  occasionally resulting in dangerous behavior
 ...
System overview
 The Department of Psychiatry, National Cheng Kung University
  Hospital (NCKUH) uses an RFID-based psych...
System overview




                  6
Reliability improvement with
     field generator scheduling
 This system relies on the Tag correctly receiving signal fro...
Reliability improvement with
 field generator scheduling




                               8
Transform the relationships among
  all Field Generators into a graph
 The relationships among Field Generators are
 tran...
Vertex deletion

 When the range of one Field Generator, FGx, is
 completely covered by other Field Generators, the
 func...
Vertex merging

 The entire overlapping region is covered by a union of
 Field Generators, so other Field Generators can ...
Vertex coloring

 A coloring algorithm is applied to the trimmed graph, in
  which connected vertices are assigned differe...
Operation slot allocation

 A weighted TDMA is applied to assign time slots for
  operation to each group
 Consider that...
Experiments

 Elucidating system performance


 Fixed-points test


 Route test




                                   ...
15
16
Elucidating system performance




                                 17
Elucidating system performance

 Tags
  send out responses periodically (reciprocated regularly)
  only when triggered ...
Elucidating system performance

 More than two Tags are sending reports back to the
 Reader simultaneously             Re...
Elucidating system performance

 Time in field (TIF) time: a Tag can be programmed with
 a TIF Time (TTIF) that specifies t...
Elucidating system performance
 Trep + TTIF is defined as one round; if one of the six
  responses in one round is receive...
Fixed-points test

 positions 1–6 reside in single Field Generator range
 positions 7–10 are located in the overlapping ...
Fixed-points test




                    23
Fixed-points test




                    24
Fixed-points test




                    25
Route test

 5 routes
 (a) Route1 is the path passing the 15 representative points
 (b) Route2 is the path connecting w...
 (a) The route
  connecting 15
  representative
  points
 (b) The route
  connecting the
  lowest reliability
  points
...
Route test




             28
Route test




             29
Route test




             30
Route test




             31
Experiments

 position 3: The Field Generator has difficulty reaching
  this sharp corner and the Tag cannot reach the Read...
Reliability comparison for original system and the
     system with proposed GCMD algorithm




                          ...
Conclusion

 The RFID devices that are small and relatively cheap are
  very appropriate for use in localizing psychiatri...
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Reliability Improvement For An Rfid Based Psychiatric Patient Localization

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Reliability Improvement For An Rfid Based Psychiatric Patient Localization

  1. 1. Reliability improvement for an RFID-based psychiatric patient localization system
  2. 2. Reference  Chieh-Ling Huang, Pau-Choo Chung, Ming-Hua Tsai, Yen-Kuang Yang, Yu-Chia Hsu Reliability improvement for an RFID-based psychiatric patient localization system IEEE Computer Communications 31 (2008) 2039–2048 2
  3. 3. Outline  Introduction  System overview  Reliability improvement with field generator scheduling  Experiments  Conclusion 3
  4. 4. Introduction  Psychiatric patients often cannot control their actions, occasionally resulting in dangerous behavior  RFID technology has been utilized in various applications, including supply chain management, entry and exit control  Localizing moving objects, e.g., freight localization or human localization is a challenging and relatively unexplored task  presents a novel graph coloring with merging and deletion (GCMD) algorithm 4
  5. 5. System overview  The Department of Psychiatry, National Cheng Kung University Hospital (NCKUH) uses an RFID-based psychiatric patient localization system  The second floor serves as a clinic for psychiatric patients, and the third floor is an activity area  Nurses : scheduling daily activities and providing basic care  Doctors : medical treatment  This RFID-based psychiatric patient localization system uses a ultra high frequency (UHF) long range tracker. The Field Generators operate on 433 MHz when triggering the Tag to respond, and the Tag replies to a Reader with 916 MHz signal once it is triggered  Psychiatric patients in the care center wear watch-like Tags, Tag transmits information, including Tag ID and Field Generator ID 5
  6. 6. System overview 6
  7. 7. Reliability improvement with field generator scheduling  This system relies on the Tag correctly receiving signal from the Field Generators to estimate the Tag location  Two Field Generators with overlapping transmission ranges simultaneously issuing trigger signals to a Tag causes signal interferences in the overlapped region  This interference results in loss of signal and, therefore, decreases localization accuracy  Transform the relationships among all Field Generators into a graph  Vertex deletion and merging  Vertex coloring  Operation slot allocation 7
  8. 8. Reliability improvement with field generator scheduling 8
  9. 9. Transform the relationships among all Field Generators into a graph  The relationships among Field Generators are transformed into an undirected graph G, whereas V and E are sets of vertices and edges, respectively. Where V and E are derived based on the Field Generators and their signal region overlapping situations, respectively 9
  10. 10. Vertex deletion  When the range of one Field Generator, FGx, is completely covered by other Field Generators, the function of FGx can be replaced by a combination of these other Field Generators 10
  11. 11. Vertex merging  The entire overlapping region is covered by a union of Field Generators, so other Field Generators can cover the overlapping region  Consequently, the two vertices associated with the two Field Generators can be merged, and no special care is required to avoid signal interference from the two Field Generators 11
  12. 12. Vertex coloring  A coloring algorithm is applied to the trimmed graph, in which connected vertices are assigned different colors  The Field Generators with the same color are assigned to the same group, and, therefore, can transmit signals simultaneously  Conversely, the Field Generators with different colors are assigned to different groups; scheduling must be applied to avoid signal conflict 12
  13. 13. Operation slot allocation  A weighted TDMA is applied to assign time slots for operation to each group  Consider that each partitioned group can occupy different levels of importance  Another consideration is the size of an area covered by a group of Field Generators  The importance factor for each group wi can be approximated  The time slot ratio for each group 13
  14. 14. Experiments  Elucidating system performance  Fixed-points test  Route test 14
  15. 15. 15
  16. 16. 16
  17. 17. Elucidating system performance 17
  18. 18. Elucidating system performance  Tags send out responses periodically (reciprocated regularly) only when triggered by Field Generators  A patient’s location is computed based on the communication range of the patient’s Tag within the Field Generators with respect to ranges of reference Tags 18
  19. 19. Elucidating system performance  More than two Tags are sending reports back to the Reader simultaneously Repetitive transmission  Repetitive transmission times are set at 6 and the associated lasting time is Trep 19
  20. 20. Elucidating system performance  Time in field (TIF) time: a Tag can be programmed with a TIF Time (TTIF) that specifies the time duration before the Tag can be triggered again A Reader receives two consecutive reports from the same Tag. How can the Reader determine whether the two reports are issued due to two separate triggers, or whether the two reports are due to a repetitive response trigger? Another aim of TIF time is to prevent Tags from wasting energy replying to the same trigger from a Field Generator 20
  21. 21. Elucidating system performance  Trep + TTIF is defined as one round; if one of the six responses in one round is received, this round is regarded as successfully received  lost rate of responses L as the total number of lost rounds divided by the total number of rounds that should trigger the Tag: r denotes the number of rounds that the Reader successfully received Tag’s reply signal and T represents time cost  In this system, it takes roughly three rounds for a patient to move from the building exit to the main gate. Under this scenario, we define response rate Rn as: n is the number of rounds – 3 in this case 21
  22. 22. Fixed-points test  positions 1–6 reside in single Field Generator range  positions 7–10 are located in the overlapping region of two Field Gen-erators  positions 11–14 are in the overlapped region for three Field Generators  position 15 is in the overlapping region of four Field Generators  people wearing Tags stand at each fixed position for 1 min  group1 is assigned 2 s for operation and group2 is assigned 1s 22
  23. 23. Fixed-points test 23
  24. 24. Fixed-points test 24
  25. 25. Fixed-points test 25
  26. 26. Route test  5 routes  (a) Route1 is the path passing the 15 representative points  (b) Route2 is the path connecting with poor reliability in the fixed-point test  (c) Route3 is the path connecting points with high reliability  (d) Route4 is the path of shortest distance from the building exit to the main gate and  (e) Route5 is a route tracing through a region that is rarely covered by routes (a–d) 26
  27. 27.  (a) The route connecting 15 representative points  (b) The route connecting the lowest reliability points  (c) The route connecting the highest reliability points  (d) The route having the shortest path from exit to main gate  (e) The route tracing a region not tested in (a–d) 27
  28. 28. Route test 28
  29. 29. Route test 29
  30. 30. Route test 30
  31. 31. Route test 31
  32. 32. Experiments  position 3: The Field Generator has difficulty reaching this sharp corner and the Tag cannot reach the Reader. Thus, a Reader is added at position 10  Experimental results: response rate for position 3 improves from 0% to 57.81% in the unscheduled original system, and from 14.26% to 83.36% using GCMD scheduling  Transmission time slots should be based on group importance  For group covering important regions or large areas should be allocated increased time periods 32
  33. 33. Reliability comparison for original system and the system with proposed GCMD algorithm 33
  34. 34. Conclusion  The RFID devices that are small and relatively cheap are very appropriate for use in localizing psychiatric Patients  In this study, a GCMD scheduling model is utilized for scheduling Field Generator transmissions in an RFID-based psychiatric patient localization system, thereby reducing interference caused by Field Generators located near one another  Experimental results demonstrated that the system is highly effective when using the proposed scheduling algorithm 34

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