Mobile Database Systems

1. Vijay Kumar Computer Sc. Telecommunications University of Missouri-Kansas City 5100 Rockhill Road Kansas City, MO 64110, USA kumar@cstp.umkc.edu Mobile Database Systems

2. Mobile Database Systems Outline • Fully Connected Information Space • Personal Communication System (PCS) • Mobile Database Systems (MDS) • Transaction Management • Data Caching • Query Processing • Data Classification • Conclusion

3. Mobile Database Systems Fully connected information space

4. Mobile Database Systems Fully connected information space • Each node of the information space has some communication capability. • Some node can process information. • Some node can communicate through voice channel. • Some node can do both

5. Mobile Database Systems Fully connected information space Can be created and maintained by integrating legacy database systems, and wired and wireless systems (PCS, Cellular system, and GSM)

6. Mobile Database Systems A system with the following structural and functional properties • Distributed system with mobile connectivity • Full database system capability • Complete spatial mobility • Built on PCS/GSM platform • Wireless and wired communication capability What is a Mobile Database System (MDS)?

7. Mobile Database Systems What is a mobile connectivity? A mode in which a client or a server can establish communication with each other whenever needed. Intermittent connectivity is a special case of mobile connectivity.

8. Mobile Database Systems What is intermittent connectivity? A node in which only the client can establish communication whenever needed with the server but the server cannot do so.

9. Personal Communication System (PCS) Part 1 • Architecture • Wireless communication • Bandwidth limitations • Frequency reuse

10. Personal Communication System (PCS) A system where wired and wireless networks are integrated for establishing communication.

11. Personal Communication System (PCS) PCS refers to variety of wireless access (communication) and personal mobility services provided through a small terminal at any place, and in any form. Business opportunities (E-commerce) for such services are tremendous, since every person, every organization, etc., could be equipped. Several PCS systems have been developed to meet rapid growth prompted by market demand. Most of them are connected toPublic Switched Telephone Network (PSTN)to integrate with the wired service. Two of the most popular PCS systems are: • Cellular telephony • Cordless and low-tier PCS telephony

12. Personal Communication System (PCS) Cellular telephony overview Four popular cellular telephony networks are: • Advanced Mobile Phone Service (AMPS) • Global System for Mobile Communication (GSM) • EIA/TIA IS-136 Digital Cellular System • EIA/TIA IS-95 Digital Cellular System

13. Personal Communication System (PCS) Cellular telephony overview Advanced Mobile Phone Service (AMPS) AMPS was the first cellular system, which was developed during the 1970s by Bell Lab. From 1974 to 1978, a large scale AMPS trial was conducted in Chicago. Commercial AMPS service has been available since 1983. It is based on frequency division multiple access (FDMA), AMP was designed as a high capacity system based on a frequency reuse scheme. A total of 50 MHz in the 824-849 MHz and 869-894 MHz bands is allocated for AMPS.This spectrum is divided into 832 full-duplex channels using 1664 discrete frequencies, that is, 832 downlinks and 832 uplinks. In AMPS, the typical frequency reuse plan employs either a 12-group frequency cluster using omnidirectional antennas or a 7-group cluster using three sectors per base stations. Thus, there are about 50 channels per cell.

14. Personal Communication System (PCS) Cellular telephony overview Global System for Mobile Communication (GSM) GSM is a digital cellular system developed by Groupe Special Mobile of Conference Europeenne des Postes et Telecommunications (CEPT) and its successor European Telecommunications Standard Institute (ETSI). GSM combines time divisioin multiple access (TDMA) and FDMA. With TDMA, the radio hardware in the base station can be shared among multiple users. In GSM the frequency carrier is divided into eight time slots where the speech coding rate is 13 Kbps. In a GSM base station, every pair of radio transceiver-receiver supports eight voice channels, whereas an AMPS base station needs one such pair for every voice channel. The GSM development process was similar to that of AMPS, except that no large scale trial was conducted.

15. Personal Communication System (PCS) Cellular telephony overview EIA/TIA IS-136 Digital Cellular System This system is also referred to as digital AMPS (DAMPS), American Digital Cellular (ADC), or North American TDMA (NA-TDMA), IS-136, the successor to IS-54, supports a TDMA air interface similar to that of GSM. IS-54 was renamed IS-136 when it reached revision C. It supports three voice channels, where the speech coding rate is 7.95 Kbps. IS-136 capacity is around three times that of AMPS. An existing AMPS system can be easily upgraded to IS-136 0n a circuit-by-circuit basis.

16. Personal Communication System (PCS) Cellular telephony overview EIA/TIA IS-95 Digital Cellular System This digital cellular system was developed by Qualcomm, and has been operating in USA since 1996. IS-95 is based on Code Division Multiple Access (CDMA) technology. It allows many users to share a common frequency/time channel for transmission. The channel bandwidth used by IS-95 is 1.25 MHz, which has been extended to 5 MHz in the third generation wideband CDMA proposal. The speech coding rate for IS-95 is 13 Kbps or 8 Kbps. IS-95’s capacity is estimated to be 10 times that of AMPS.

17. Personal Communication System (PCS) Cordless telephony technologies Cordless Telephone, Second Generation (CT2) Developed in Europe, and has been available since 1989. CT2 is allocated 40 FDMA channels with a 32-Kbps speech coding rate. For a user, both baseptop handset signals and handset-to-base signals are transmitted in the same frequency. The maximum transmit power of a CT2 handset is 10 mW. In the call setup procedure, CT2 moves a call path from one radio channel to another after three seconds of handshake failure. CT2 also supports data transmission rates of up to 2.4 Kbps through the speech code and up to 4.8 Kbps with an increased rate. CT2 does not support handoff and in a public CT2 system, call delivery is not supported.

18. Personal Communication System (PCS) Cordless telephony technologies Digital European Cordless Telephone (DECT) The Digital European Cordless Telephone has been replaced by Digital Enhanced Cordless Telephone to denote global acceptance of DECT. DECT supports high user density with a picocell design. There are 12 voice channels per frequency carrier. Sleep mode is employed to converse handset power. DECT also supports seamless handoff. DECT is typically implemented as a wireless-PBX (Private Brach Exchange) connected to PSTN. DECT can interwork with GSM to allow user mobility.

19. Personal Communication System (PCS) Low-tier PCS telephony overview Personal Handy Phone System (PHS) PHS is a standard developed by the Research and Development Center for Radio Systems (RCR), a private standardization organization in Japan. PHS is a low-tier digital PCS system that offers telecommunication services for homes, offices, and outdoor environment, using radio access to the public telephone network or other digital networks. PHS uses TDMA. Sleep mode enables PHS to support five hours of talk time, or 150 hours of standby time. PHS operates in the 1895-1918.1 MHz band. The bandwidth is partitioned into 77 channels, each with 300 KHz bandwidth. The band 1906.1-1918.1 MHz (40 channels) is designed for public systems, and the band 1895-1906.1 MHz (37 channels) is used for home/office applications.

20. Personal Communication System (PCS) Low-tier PCS telephony overview Personal Access Communications Systems (PACS) PACS is a low-power PCS system developed at Telcordia (formerly Bellcore). TDMA is used in PACS with eight voice channels per frequency carrier. In FDD mode, the PACS uplink and downlink utilizes differentRF carriers, similar to cellular systems.

21. Personal Communication System (PCS) Cordless and low-tier PCS telephony overview

22. Personal Communication System (PCS) Wireless Components Base Station (BS):A network element that interconnects the mobile station (or Mobile unit (MU)) to the network via the air interface. Each cell in the network has a BS associated with it. The primary function of a BS is to maintain the air interface, or medium, for communication to any mobile unit within its cell. Other functions of BS are call processing, signaling, maintenance, and diagnostics. The BS communicates to its mobile unit via the air interface, and to MTSO by dedicated communication link such as T1 trunks. Communication links on the BS to the MTSO interface are also classified into voice links and signaling link.

23. Personal Communication System (PCS) Wireless Components Mobile Units (MU):Also called Mobile Systems (MS) or Mobile Hosts (MH). It consists of three components: (a) transceiver, (b) antenna, and (c) user interface. The user interface exists only at MU, which consists of a display, a keypad for entering information, and an audio interface for speaking and hearing voice conversation. This can be a laptop, a palmtop, or a cell phone, or any other mobile device.A MU also stores (a) Mobile Identification Number (MIN), (b) Electronic Serial Number (EIN), and (C) Station Class Mark (SCM). These are transmitted upon power on, cell initiated sampling, and cell origination.

24. Personal Communication System (PCS) Wireless Components

25. Personal Communication System (PCS) Wireless channels are limited NMT: Nordic Mobile Telephone PDC: Pacific Digital Cellular PACS: Personal Access Communications System PHS: Personal Handyphone System PACS-UB: PACS Unlicensed Band JCT: Japanese Cordless Telephone (Taken from Mobile Communications by Jochen Schiller)

26. Personal Communication System (PCS) Limited channels must be utilized efficiently. It is done so by (a) Frequency reuse and (b) Mobile cell Frequency reuse The goal of every mobile service provider is to manage as many simultaneous calls as possible. In USA each cellular provider is allocated 25 MHz of spectrum, 12.5 MHz for transmitting (downstream) and 12.5 MHz for receiving (upstream). Cellular system is duplex because transmitting and receiving are allocated their own frequencies. A person on a mobile call only needs the allocated frequency of the cell, thus there is no reason somebody else on the other end of the town cannot be using the same frequency in a different cell. The concept of multiple users using the same frequency at the same time for communication is called frequency reuse.

27. Personal Communication System (PCS) Frequency reuse (continued) For frequency reuse to work correctly it is imperative that each base station has just sufficient power to reach its cell boundary. If it puts out too much power, then it will not only reach the intended cell site, it will reach unintended cell sites, which others may be using at the same frequency for a totally different conversation. This limitation on transmitted power, however, is also an advantage because the cellular phone’s battery will last longer.

28. Personal Communication System (PCS) Mobile cell Within the cellular allocation the USA is divided into Metropolitan Statistical Areas (MSAs) and Rural Statistical Areas(RSAs). There are six PCS service providers authorized to provide mobile service in each of these areas. Within their geographical region, each service provider divides their area into smaller segments called cells. Each of this cell has a Base Station. Ideally, the system has a large number of very small hexagons (cell). The greater the number of hexagons, the more simultaneous calls the system can handle. However, larger number of hexagons increases the cost of implementation. Thus, cell coverage is a dynamic activity, which is constantly changing in response to increases in demand.

29. Personal Communication System (PCS) Mobile cells

30. Personal Communication System (PCS) Mobile cells The entire coverage area is a group of a number of cells. The size of cell depends upon the power of the base stations.

31. D = distance between cells using the same frequency R = cell radius N = reuse pattern (the cluster size, which is 7). Thus, for a 7-cell group with cell radius R = 3 miles, the frequency reuse distance D is 13.74 miles. Personal Communication System (PCS) Frequency reuse

32. Personal Communication System (PCS) Problems with cellular structure • How to maintain continuous communication between two parties in the presence of mobility? Solution:Handoff • How to maintain continuous communication between two parties in the presence of mobility? Solution:Roaming • How to locate of a mobile unit in the entire coverage area? Solution:Location management

33. Personal Communication System (PCS) Handoff A process, which allows users to remain in touch, even while breaking the connection with one BS and establishing connection with another BS.

34. Personal Communication System (PCS) Handoff To keep the conversation going, the Handoff procedure should be completed while the MS (the bus) is in the overlap region.

35. Personal Communication System (PCS) Handoff issues • Handoff detection • Channel assignment • Radio link transfer

36. Personal Communication System (PCS) Handoff detection strategies • Mobile-Controlled handoff (MCHO) • Network-Controlled handoff (NCHO) • Mobile-Assisted handoff (MAHO)

37. Personal Communication System (PCS) Mobile-Controlled Handoff (MCHO) In this strategy, the MS continuously monitors the radio signal strength and quality of the surrounding BSs. When predefined criteria are met, then the MS checks for the best candidate BS for an available traffic channel and requests the handoff to occur. MACHO is used in DECT and PACS.

38. Personal Communication System (PCS) Network-Controlled Handoff (NCHO) In this strategy, the surrounding BSs, the MSC or both monitor the radio signal. When the signal’s strength and quality deteriorate below a predefined threshold, the network arranges for a handoff to another channel. NCHO is used in CT-2 Plus and AMPS.

39. Personal Communication System (PCS) Mobile-Assisted Handoff (MAHO) It is a variant of NCHO strategy. In this strategy, the network directs the MS to measure the signal from the surrounding BSs and to report those measurements back to the network. The network then uses these measurements to determine where a handoff is required and to which channel. MACHO is used in GSM and IS-95 CDMA.

40. Personal Communication System (PCS) Handoff types with reference to the network • Intra-system handoff or Inter-BS handoff The new and the old BSs are connected to the same MSC.

41. Personal Communication System (PCS) Intra-system handoff or Inter-BS handoff Steps • The MU (MS) momentarily suspends conversation and initiates the handoff procedure by signaling on an idle (currently free) channel in the new BS. Then it resumes the conversation on the old BS.

42. Personal Communication System (PCS) Intra-system handoff or Inter-BS handoff Upon receipt of the signal, the MSC transfers the encryption information to the selected idle channel of the new BS and sets up the new conversation path to the MS through that channel. The switch bridges the new path with the old path and informs the MS to transfer from the old channel to the new channel.

43. Personal Communication System (PCS) Intra-system handoff or Inter-BS handoff After the MS has been transferred to the new BS, it signals the network and resumes conversation using the new channel.

44. Personal Communication System (PCS) Intra-system handoff or Inter-BS handoff Upon the receipt of the handoff completion signal, the network removes the bridge from the path and releases resources associated with the old channel.

45. Personal Communication System (PCS) Handoff types with reference to the network • Intersystem handoff or Inter-MSC handoff The new and the old BSs are connected to different MSCs.

46. Personal Communication System (PCS) Handoff types with reference to link transfer • Hard handoff The MS connects with only one BS at a time, and there is usually some interruption in the conversation during the link transition. • Soft handoff The two BSs are briefly simultaneously connected to the MU while crossing the cell boundary. As soon as the mobile's link with the new BS is acceptable, the initial BS disengages from the MU.

47. Personal Communication System (PCS) Handoff types with reference to link transfer Hard handoff • MU temporarily suspends the voice conversation by sending a link suspend message to the old BS. • MU sends a handoff request message through an idle time slot of the new BS to the network. • The new BS sends a handoff ack message and marks the slot busy. • The MU returns the old assigned channel by sending a link resume message to the old BS.

48. Personal Communication System (PCS) Handoff types with reference to link transfer Hard handoff • MU continues voice communication while the network prepares for the handoff. • Upon receipt of a handoff request message, the new BS sends a handoff ack message and reconfigures itself to effect the handoff. • The MSC inserts a bridge into the conversation path and bridges the new BS. • Finally, the network informs the MU to execute the handoff via both the new and old BSs by sending the handoff execute message.

49. Personal Communication System (PCS) Handoff types with reference to link transfer Hard handoff • MU releases the old channel by sending an access release message to the old BS. • Once the MU has made the transfer to the new BS, it sends the network a handoff complete message through the new channel, and resumes the voice communication. The network removes the bridge from the path and frees up the resources associated with the old channel.

50. Personal Communication System (PCS) Handoff types with reference to link transfer Soft handoff • MU sends a pilot strength measurement message to the old BS, indicating the new BS to be added. • The old BS sends a handoff request message to the MSC. If the MSC accepts the handoff request, it sends a handoff request message to the new BS. • The BS sends a null traffic message to the MU to prepare the establishment of the communication link.