相關資料
國立中山大學視覺與智慧系統實驗室 李宗南教授
沈錳坤、李素瑛﹐視覺資訊系統中內容擷取技術之研究與發展
Data Mining
Data Management in a Wireless Environment
- Introduction
Why do we care about wireless data management?
- Information is the core of business success.
- The internet has changed the way information is accessed.
- Wireless network are in place.
- Mobile devices are available in the market.
- Users like to go mobile and get ubiquitous access of information.
- Wireless Networks
- Cellular Systems
- Analog systems.
- CDMA digital systems.
- Data Services: Dial-up, Circuit Switched
- Coverage areas: 60% of US
- Roaming: Depend upon carrier
- Internet access: Yes
- Type of data support: Dial-up at 14.4 Kbps
- TDMA digital systems.
- Data Services: Nothing available today
- Coverage areas: 50% of US
- Roaming: Depend upon carrier
- Internet access: N/A
- Type of data support: ???
- Personal Communication Services (PCS)
- CDMA and TDMA system.
- GSM system.
- Data Services: Dial-up, Circuit Switched
- Coverage areas: 50% of US
- Roaming: Depend upon carrier
- Internet access: Yes
- Type of data support: Dial-up at 9.6 Kbps
- Satellite Systems
- Wireless local Area Networks
- IEEE 802.11 Wireless LAN Standard based systems,
e.g., Lucent WaveLan.
- Data Services: IP packets
- Coverage areas: Offices, buildings, campuses
- Roaming: Within deployed systems
- Internet access: via LAN
- Type of data support: Data at near LAN speed.
- Packet Data Networks
- ARDIS
- RAM
- Cellular Digital Packet Data (CDPD)
- Private Networks
- Wireless Data
Data can be everywhere
- Computers
- LAN
- Internet
- Air!
Wireless Data Management
- Characteristics and Assumptions
- Limited and asymmetric bandwidth
- Limited battery power on clients
- Client machines have power managerment facility
- A channel can be used either for on-demand, point-to-point
service or broadcast service
- Unlike Internet, bandwidth is a regulated and controlled
system resource
- Performance Criteria
- Access time:
the time elapsed from the moment a MH issues a query
to the moment the answer is received by the MH
- Tune-in time:
the time spent by a MH staying active in order to
acquire the requested data
- Goals:
to make mobile client access time and tune-in time low
while indexing efficiency high
- Wireless Data Dissemination
- Many applications involve dissemination of data to large
group of users, e.g., stock quotes, sport tickers and
news delivery
- Wireless dissemination of data is enabled by advances in
Internet, data availability and wireless communications
- An important issue: Scalability!
- Data push and pull
Services in Mobile Environment
- Broadcast Services
- push-based
- shared (serve an arbitrary number of users
simultaneously)
- On-Demand Services
- pull-based
- requests sent through an up-link channel
- on-demand data delivered (access to any data item)
- point-to-point communications
(bi-directional)
- through broadcast (by multiplexing with
broadcast data)
- Broadcast Scheduling
- Broadcast scheduling is to arrange the order and frequency
of data items in a broadcast channel, in order to
improve the client access time.
- A common idea is to arrange the broadcast of data itmes
based on their client access frequencies.
- Scheduling Approaches
- Flat Broadcast
- Broadcast every data item once per broadcast cycle
- Multi-level broadcast
- Data itmes are grouped together based on their
client access frequencies
- Groups of data itmes are broadcast based on their
group weight
- Data items in the same group are broadcast equally
- Channel Management
- Exclusive on-demand channel allocation is desirable when
the number of clients is small compared to the number
of channels available
- Exclusive broadcast channel allocation is great when a
small number of data itmes are of interest to a large
group of users
- Channel Allocation Medthods
- With the limited and fixed bandwidth available in a cell,
it's necessary to mix the broadcast and on-demand
channels in order to compensate the weaknesses of the
exclusive medthods and to improve the overall system
performance
- Mixed channel allocation methods
- Hybird Channel Allocation
- Dynamic Channel Allocation
- Caching
- Main ideas: use cache to reduce access time
- Caching policy: cache the most frequently accessed pages
- Broadcast disk caching policy: pages are not arriving at
the same time, so cache the important pages that are
far away
- Indexing
- To estimate the arrival of a requested data item, the
client can select between broadcast and on-demand data
services to reduce the access time
- Cached schedule: the complete broadcast schedule
is broadcast at the beginning of each cycle, each
active client should monitor the channel for the
schedule
- Integrated signature
Wireless Application Technologies
- Wireless Application Protocol (WAP)
- Wireless Application Environment (WAE)
- Wireless Markup Language (WML)
Conclusion
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