智慧型手機日漸普及。大部分的手機都含有各式各樣的感應器。手機上的定位系統、相機、錄音功能等等都可能被當成監控的工具。我們提出一個利用未接來電來傳達坐標的位置追蹤系統。監控端會用收到的未接來電的資料來解出發送出來的坐標。由於不可避免的基地台和手機系統的時間延誤，有時候會有解碼錯誤的情況。調整參數與加入能夠修補資料或偵測錯誤的編碼預計能提高資料傳輸的準確率。

Smartphones and tablets are getting more accessible to the common people with affordable price and wide selection of hardware specifications. Most of the mobile devices come with built-in cameras, microphones and GPS sensors that can be used as surveillance device. We propose a location tracking system that would track and send user's geographical coordinates stealthily in the background using multiple missed calls to a predefined phone number. The receiver would decode the location data using an agreed format of the duration of the missed calls. Delay in the internal message passing of Android and the latency of mobile cellular network base stations reduces the bandwidth that can be achieved by our prototype and also causes errors. There are cases where duration of a missed call is mis-categorized into unintended group. The grouping is used for coding of location data. We are able to send data up to 0.12bit/s with a modified phone application on Android operating system. The location of the user can be transmitted in 5 minutes. Subsequent location notification costs less time as only the changes in coordinates compare to previous update are sent. The proposed method of data transmission using missed calls can be easily replaced by internet connection or Short Message Service(SMS) but typically it would cost money to do so. Further fine-tuning of the missed call duration parameter should increase the bandwidth of the system. Inclusion of data detection or correction code should reduce the interpretation errors.

Chapter 1 Introduction ............................................................................. 1
Chapter 2 Background............................................................................... 3
2.1 Mobile Cellular Phone Network .......................................................... 3
2.1.1 Global System for Mobile Communications.......................... 4
2.2 Longitude and Latitude....................................................................... 6
2.3 Location Technologies ......................................................................... 7
2.3.1 Global Positioning System.................................................... 7
2.3.2 Wireless Positioning.............................................................. 7
2.3.3 IP Location........................................................................... 7
2.3.4 Cellular Identification ........................................................... 8
2.4 Android............................................................................................... 8
2.4.1 Platform Architecture........................................................... 9
2.4.2 Intents................................................................................... 10
2.4.3 Service................................................................................... 10
2.5 CyanogenMod...................................................................................... 11
Chapter 3 Related Work........................................................................... 12
3.1 Side Channel Spying............................................................................ 12
3.2 Location Tracking ............................................................................... 13
Chapter 4 Design........................................................................................ 14
4.1 Proposed System................................................................................. 14
4.2 Missed Calls Approach........................................................................ 15
4.2.1 Variable hangup duration ..................................................... 15
i
4.2.2 Binary form........................................................................... 16
4.2.3 Multiple phones .................................................................... 16
4.3 Coding of Geographical Coordinates................................................... 17
4.3.1 Conversion into Decimal Degree form................................... 18
4.3.2 Accuracy of Decimal places .................................................. 18
4.3.3 Fractions Representations..................................................... 19
4.3.4 Movement Representation..................................................... 20
4.3.5 Coding Approach.................................................................. 21
Chapter 5 Implementation........................................................................ 23
5.1 Explicit Tracking System .................................................................... 23
5.1.1 Client.................................................................................... 23
5.1.2 Server.................................................................................... 25
5.1.3 Incoming call state................................................................ 25
5.1.4 Outgoing call state................................................................ 26
5.1.5 Initiate outgoing call............................................................. 27
5.1.6 Terminate outgoing call........................................................ 28
5.1.7 User Interface........................................................................ 28
5.2 Stealth Tracking System ..................................................................... 30
5.2.1 Modified Phone App............................................................. 31
5.2.2 Stealth Client App................................................................ 31
5.2.3 Extra Outgoing Call State.................................................... 31
Chapter 6 Discussion ................................................................................. 34
Chapter 7 Conclusion ................................................................................ 36
7.1 Future Work........................................................................................ 37

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