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Spatial Queries in Wireless Broadcast Environments
沈俊宏 助理教授亞洲大學資訊傳播學系
台中市霧峰區http://infocom.asia.edu.tw
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大綱• 無線資料廣播相關技術
• 結合無線廣播與空間查詢
• Neighbor-Index Method
• 結論
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無線環境
FIXED NETWORK
PDA
FIXEDHOSTBASE
STATION
BASESTATION
BASESTATION
Mbps to Gbps
MOBILE HOST
WIRELESS LAN CELL2Kbps - 15Mbps
WIRELESS RADIO CELL9Kbps - 14Kbps
BASESTATION
PDA
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無線系統的特性• 傳輸的非對稱性
• 經常斷線
• 電力的限制
• 螢幕的尺寸
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傳輸的非對稱性• Wireless information channels consist of
two distinct sets of channels:– uplink (upstream) channels:
• from clients to servers
– downlink (downstream) channels:
• from servers to clients
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• In the environment under consideration, the downstream communication capacity is relatively much greater than the upstream one.
• In such an environment, the push-based data broadcast provides a good performance.
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Push-based Data Broadcast System
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Wireless channel
Mobile devices
屏東孔廟屏東大學 阿緱城門 孫立人將軍行館
Server
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為什麼要使用無線資料廣播• Scalability ( 可擴充性 ):
– The server only broadcasts data items on the channel which can be accessed by the clients, no matter the number of the clients.
– For example, the servicing cost of the server for 10 clients is the same as that for 100 ones.
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Microsoft® DirectBand™
• A wide-area wireless data broadcast network built and operated by Microsoft.
• Unused FM radio spectrum.
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相關產品• Complete Regional Weather Station with
MSN® Direct Weather Data Service
Photos courtesy of http://www.msndirect.com/10
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• Smart Watches
News Weather Stocks
Sports Lottery Horoscopes
Photos courtesy of http://www.msndirect.com/11
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Ambient’s Products
Photos courtesy of http://www.ambientdevices.com/12
Football SportsCast 7-Day Forecaster
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無線系統的特性• 傳輸的非對稱性
• 經常斷線
• 電力的限制
• 螢幕的尺寸
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選擇性聽頻道技術• Active mode ( 耗電模式 )
– More power consumption.
• Doze mode ( 省電模式 )– Less power consumption.
• Selective tuning is to remain the doze mode most of the time and go into the active mode only when the relevant information is present.
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: Index : Data
Time
: Desired Data
: Period of the active mode
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效能評比參數• Access Time ( 存取時間 ):
– The client waiting time for accessing the requested data.
• Tuning Time ( 實際聽頻道時間 ):– The amount of time spent by a client listening to the
channel.– This determines the client’s power consumption.
• There is a trade-off between the access time and the tuning time.
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T0 T1 T2 T3 T4 T5 T6 T7
Time
: Access Time : Tuning Time
• Access Time = (T7 – T0)
• Tuning Time = (T7 – T6) + (T5 – T4) + (T3 – T2) + (T1 – T0)
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空間查詢• Location-Dependent Spatial Query (LDSQ) in
the wireless environment is that mobile users query the spatial data items dependent on their current location.– Nearest Neighbor Query– k-Nearest Neighbors Query– Window Query
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Nearest Neighbor Query
• Show me the nearest convenient store.
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k-Nearest Neighbors Query
• Show me 2 nearest convenient stores.
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Window Query
• Show me the restaurants around me.
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Continuous Window Query
• Where are gas stations within this region along this segment?
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Linear Access on the Wireless Channel
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Neighbor-Index Method
Jun-Hong Shen, Ching-Ta Lu and Ming-Shen Jian, "Neighbor-Index Method for Continuous Window Queries over Wireless," Applied Mechanics and
Materials, Vol. 284-287, pp. 3295-3299, Jan. 2013. (EI)
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Motivation
• For a continuous window query, answer spatial objects may be neighbors of each other.
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• Therefore, we propose a neighbor-index method, NI, to efficiently support the continuous window queries over wireless data broadcast.
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System Architecture
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Mobile clients
Spatial objects
Spatial index
+
Server
A broadcast cycle
Wireless downlink channel Broadcasting
Update access patternsvia the uplink channel
Tune in & retrieve
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Neighbor-Index Method
• Spatial objects are broadcast once in a cycle in the sequence of the Hilbert curve of order n.
• The spatial objects covered by the same value of the Hilbert curve of order (n-1) are put in the same group.
• An index bucket containing information about neighbors and the objects in this group is allocated before each group.
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Hilbert Curve
0
1
0
2
3
0 1
23
4
5 6
7 8
9 10
11
1213
14 15
Order 1
Order 2
Good locality
0
1 2
3 4 5
67
8 9
101112
1314
15
16 17
1819
20
21 22
23 24
25 26
27
2829
30 31 32 33
3435
36
37 38
39 40
41 42
43
4445
46 47
48
4950
515253
54 55
5657
58 59 60
61 62
63
Order 3
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Spatial Objects
• Hilbert curve of order 3
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Grouping
• The objects having the same Hilbert-curve value of order (n – 1) are allocated to the same group.
31
5 6
4 7
9 10
8 11
3 2
0 1
13 12
14 15
8
29
0
1 2
48
49
21 41 42
32
23
• Hilbert curve of order 2
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Neighbor Index Construction
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1. procedure NeighborIndexConstruction(h(n-1))
2. current_h ←h(n-1) /*current_h is the current processing block.*/
3. for i ← (n-1), 1 do
4. Call procedure NeighborInformation(current_h)
/* Calculate the Hilbert-curve value of the previous order. */
5. current_h ←
6. end for
7. Call procedure IndexEntryShrink
8. Add the index entries pointing to those spatial objects in the same
group to the index bucket for this group
9. end procedure
4/_ hcurrent
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Neighbor Index
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5 6
4 7
9 10
8 11
3 2
0 1
13 12
14 15
8
29
0
1 2
48
49
21 41 42
32
23
3
21
0 8
29
0
1 2
48
49
21 41 42
32
23
• Hilbert curve of order 2 • Hilbert curve of order 1
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o0 o1 o2 o29 o32 o41o8 o42o21 o23NI1 NI2 NI3 NI4 NI5
o48 o49NI6 NI7
Index bucket Data bucket
(29, 29, NI4)
(0, 2, NI1')
(32, 32, NI5)
(32, 42, NI5)
(48, 49, NI7)
(21, 29, NI3)
Neighbor indexes of order 2
Neighbor indexes of order 1
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Index Entry Shrink
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o0 o1 o2 o29 o32 o41o8 o42o21 o23NI1 NI2 NI3 NI4 NI5
o48 o49NI6 NI7
Index bucket Data bucket
(29, 29, NI4)
(0, 2, NI1')
(32, 32, NI5)
(32, 42, NI5)
(48, 49, NI7)
(21, 29, NI3)
Neighbor indexes of order 2
Neighbor indexes of order 1
Index entry shrink(29, 29, NI4)
(0, 2, NI1')
(32, 42, NI5)
(48, 49, NI7)
(21, 29, NI3)
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A Broadcast Cycle with Neighbor Indexes
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o0 o1 o2 o29 o32 o41o8 o42o21 o23
(29, 29, NI4)
(32, 42, NI5)
(48, 49, NI7)
(21, 29, NI3)
NI1 NI2 NI3 NI4 NI5o48 o49
NI6 NI7
(0, 2, NI1')
(29, 29, NI4)
(32, 42, NI5)
(48, 49, NI7)
(0, 8, NI1')
(32, 42, NI5)
(48, 49, NI7)
(0, 8, NI1')
(8, 8, NI2')
(21, 23, NI3')
(8, 8, NI2)
(21, 29, NI3)
(32, 42, NI5)
(48, 49, NI7)
(0, 8, NI1')
(41, 42, NI6)
(48, 49, NI7)
(8, 8, NI2')
(21, 29, NI3')
(29, 29, NI4')
(48, 49, NI7)
(0, 8, NI1')
(21, 29, NI3')
(32, 32, NI5')
(0, 8, NI1')
(21, 29, NI3')
(32, 42, NI5')
Index bucket Data bucket
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Continuous Window Query
• Targeted segments – (8, 11)– (31, 35)– (53, 53)
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o0 o1 o2 o29 o32 o41o8 o42o21 o23
(29, 29, NI4)
(32, 42, NI5)
(48, 49, NI7)
(21, 29, NI3)
NI1
NI2
NI3 NI4 NI5o48 o49
NI6 NI7
(0, 2, NI1')
(29, 29, NI4)
(32, 42, NI5)
(48, 49, NI7)
(0, 8, NI1')
(32, 42, NI5)
(48, 49, NI7)
(0, 8, NI1')
(8, 8, NI2')
(21, 23, NI3')
(8, 8, NI2)
(21, 29, NI3)
(32, 42, NI5)
(48, 49, NI7)
(0, 8, NI1')
(41, 42, NI6)
(48, 49, NI7)
(8, 8, NI2')
(21, 29, NI3')
(29, 29, NI4')
(48, 49, NI7)
(0, 8, NI1')
(21, 29, NI3')
(32, 32, NI5')
(0, 8, NI1')
(21, 29, NI3')
(32, 42, NI5')
Index bucket Data bucket
Tune in here
• After examining NI2– (8, 11) -> (8, 8)– (31, 35) -> (32, 35)– (53, 53) -> ()
• V = {o8, NI5} -> V = {NI5}
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o0 o1 o2 o29 o32 o41o8 o42o21 o23
(29, 29, NI4)
(32, 42, NI5)
(48, 49, NI7)
(21, 29, NI3)
NI1
NI2
NI3 NI4 NI5o48 o49
NI6 NI7
(0, 2, NI1')
(29, 29, NI4)
(32, 42, NI5)
(48, 49, NI7)
(0, 8, NI1')
(32, 42, NI5)
(48, 49, NI7)
(0, 8, NI1')
(8, 8, NI2')
(21, 23, NI3')
(8, 8, NI2)
(21, 29, NI3)
(32, 42, NI5)
(48, 49, NI7)
(0, 8, NI1')
(41, 42, NI6)
(48, 49, NI7)
(8, 8, NI2')
(21, 29, NI3')
(29, 29, NI4')
(48, 49, NI7)
(0, 8, NI1')
(21, 29, NI3')
(32, 32, NI5')
(0, 8, NI1')
(21, 29, NI3')
(32, 42, NI5')
Index bucket Data bucket
Tune in here End here
• After examining NI5– (32, 35) -> (32, 32)
• V = {o32} -> V = {}
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有效區間• The Minkowski region has the same size as the
query window and centers at the answered object.
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效能模擬比較• We compare our proposed method, NI, with
distributed spatial index (DSI).
B. Zheng, W.C. Lee, C.K. Lee, D.L. Lee, and M. Shao: A distributed spatial index for error-prone wireless data broadcast, The VLDB Journal, 18(4) (2009) 959-986.
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空間資料• There are two cases of the data distributions:
(a) uniform and (b) the real map (Greece).
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(a) (b)
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Parameters
• The simulation parameters
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Parameter Description
WinSideRatio The ratio of the side length of a window query to that of the search space
QueryLengthRatio The ratio of the length of a query line segment to the side length of the search space
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System Model
• The start position of a continuous window query is randomly picked, and its corresponding moving direction is randomly picked between 0 and π/2.
• In our simulation, 10,000 points are uniformly generated in a square Euclidean space (28 28).
• In our simulation, 10,000 queries with a square of 28*WinSizeRatio 28*WinSizeRatio are randomly issued.
HCDI - 44
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存取時間
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• Uniform
100
110
120
130
140
150
160
170
0.02*0.02 0.05*0.05 0.1*0.1 0.2*0.2
Acc
ess t
ime
x 10
0000
WinSizeRatio*QueryLengthRatio
NIDSI
30
32
34
36
38
40
42
44
0.02*0.02 0.05*0.05 0.1*0.1 0.2*0.2
Acc
ess
tim
e x
1000
00WinSizeRatio*QueryLengthRatio
NI
DSI
• Real
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實驗聽頻道時間
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-
5
10
15
20
25
0.02*0.02 0.05*0.05 0.1*0.1 0.2*0.2
Tu
nin
g ti
me
x 10
0000
WinSizeRatio*QueryLengthRatio
NIDSI
-
2
4
6
8
10
0.02*0.02 0.05*0.05 0.1*0.1 0.2*0.2
Tu
nin
g ti
me
x 10
0000
WinSizeRatio*QueryLengthRatio
NIDSI
• Uniform • Real
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耗電程度的比較
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-
1,000
2,000
3,000
4,000
5,000
0.02*0.020.05*0.05 0.1*0.1 0.2*0.2
Pow
er c
onsu
mpt
ion
WinSizeRatio*QueryLengthRatio
NI
DSI-
500
1,000
1,500
2,000
0.02*0.020.05*0.05 0.1*0.1 0.2*0.2
Pow
er c
onsu
mp
tion
WinSizeRatio*QueryLengthRatio
NIDSI
• Uniform • Real
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LEA - 48
結論• To speed up the query processing and reduce
power consumption of mobile devices, our proposed method interleaves neighbor information of spatial objects among a wireless broadcast cycle.
• Experimental results show that our proposed method outperforms DSI on the average access time, tuning time and power consumption.
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Thanks for your attention.
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