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Project: IEEE P802.15 Working Group for Wireless Personal Area NProject: IEEE P802.15 Working Group for Wireless Personal Area Networks (etworks (WPANsWPANs))
Submission Title: [Distributed TDMA Scheduling for SOP]Date Submitted: [4th May, 2009]Source: [Seung-Hoon Park / Jeongsik In / Sridhar Rajagopal / Eui-Jik Kim / Ranjeet Kumar Patro / Noh-Gyoung Kang / Chihong Cho / Giriraj Goyal / Ashutosh Bhatia / Thenmozhi Arunan / Kiran Bynam / ArunNaniyat / Farooq Khan / YongSuk Park / Eun-Tae Won] Company [Samsung Electronics Co. Ltd.]Address [416, Maetan-3dong, Yeongtong-gu, Suwon-si, Gyeonggi-do, 443-742, Korea]Voice: [+82-31-279-4579], FAX: [+82-31-279-5130], E-Mail: [[email protected]]Re: [Responses to Call for Intent in Wireless Body Area Networks]
Abstract: [This document proposes the method to schedule time resource for SOP of BAN]
Purpose: [To propose scheduling algorithm for SOP to support BAN high data rate applications]Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.
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Distributed TDMA Scheduling for SOP
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doc.: IEEE 802.15-09-0321-00-0006
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Motivation
High data rate service [1]– Streaming service with see-through goggle– Video recording & storage
BAN piconet environment– Frequent encounter with other piconets
Time resource sharing is required – QoS requirement
Collision affects packet error rate– UWB band opened globally is narrow [2]
A few number of frequency bands
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Possible Solutions for SOP
FDMA– How to allocate bands ?
Frequent change of band makes the system complexDirect spread spectrum, frequency hopping, or time hopping– Only low data rate can be supported
Contention-based access (CSMA)– Not delay bounded– Hidden node– Channel sensing is not easy at UWB, implant (MICS) or body
shadowing conditionContention free allocation (TDMA, polling)– Bandwidth efficient with dynamic slot allocation
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Inter-piconet Collision
Collision types– Piconet A ↔ Piconet B– TDMA↔ TDMA
Can not avoid collision without any control
– TDMA↔ CSMAPiconet B can reduce collision ratio by channel sensinglow receiver sensitivity is required
– CSMA↔ CSMASame as the condition of CSMA in single piconet
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CSMA/CA Performance
1 2 3 4 50
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000CSMA/CA Throughput Performance
# of piconets
Thro
ughp
ut [k
bps]
Rx.Sen. -98 dBmRx.Sen. -108 dBmRx.Sen. -118 dBm
1 2 3 4 50
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1CSMA/CA PER Performance
# of piconets
PE
R
Rx.Sen. -98 dBmRx.Sen. -108 dBmRx.Sen. -118 dBm
* Rx. Sensitivity of 802.15.4a UWB PHY is 85dBm (for 1Mbps) or 91dBm (for 250kbps).
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TDMA
Contention free allocationPros– Guaranteed QoS– High channel efficiency– Very low power consumption
Cons– Inter-piconet collision induces much performance
degradationHow to sync and schedule ?
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TDMA Performance
1 2 3 4 50
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000TDMA Throughput Performance
# of piconets
Thro
ughp
ut [k
bps]
TDMA 100% Duty CycleTDMA 20% Duty Cycle
1 2 3 4 50
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1TDMA PER Performance
# of piconets
PE
R
TDMA 100% Duty CycleTDMA 20% Duty Cycle
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Centralized Piconet Merging
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Centralized Piconet MergingSuperframe
CSMA TDMA
Timer Offset
Approach
Sync Root
Sync Root
Superframe
Time sync unification
Unified Sync Root
TDMA reschedule
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Problems of Centralized Piconet Merging
BAN Piconet– Piconet is moving– High density in the specific location
Fine synchronization is very difficultCentralized approach is apt to failed– Sync root node is changed frequently– Low scalability
Long latencyLarge signal overhead
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Problems of Centralized Piconet Merging
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Resolving Approach
Distributed scheduling– Only local consensus is required
No sync root– Exchanging time information between
neighboring piconetsLoose synchronization– Just avoiding slot allocation over the slot
duration allocated by neighboring piconet– No need to fitting at slot level
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Distributed TDMA SchedulingSuperframe
TDMA reschedule without Time sync unification
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Local Time Offset Exchange
A
B
C
T1
T2 T3
STA
STB
STC
DA DC
DB
Addr # hop
0
1
1
Offset
0
T1
T2
Slot Start
STA
STB + T1
STC + T2
Slot Dur
DB
DA
DC
A
B
C
Addr # hop
1
0
1
Offset
0
Slot Start
STA – T1
STB
STC – T3
Slot Dur
DB
DA
DC
A
B
C
Addr # hop
1
1
0
Offset
T3
0
Slot Start
STA – T2
STC
Slot Dur
DB
DA
DC
A
B
C
STB + T3
– T1
– T3
– T2
ATDMA schedule Table
B C
Addr # hop Slot Start Slot Dur
TDMA Schedule Advertisement MessageSeqno
SNB
SNA
SNC
Seqno
SNB
SNA
SNC
Seqno
SNB
SNA
SNC
Seqno
TDMA schedule Table TDMA schedule Table
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Offset Calculation
Existing synchronization method– IEEE 802.11
Time stamping– IEEE 802.15.4
Beacon Tx. time control
Any method can be used
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TDMA Schedule Table Calculation
Addr # hop
0
1
Offset
0
T1
Slot Start
STA
STB + T1
Slot Dur
DA
DC
A
B
C
A
Seqno
SNB
SNC
Hop distance between A and B.
( TDMA sched info can be propagated in multi
hop )
1
Timer value of A – Timer value of C.
( Timer values can be communicated using any existing sync method )
T2
The slot start time received from C can be converted into the equivalent
time of A’s timer by adding the offset with respect to C, T2.
Received from C
STC + T2 Slot duration does not change node to
node.
DB
Sequence number is used to reject obsolete information
delivered through another path.
SNA
TDMA schedule Table
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Simulation Setup
10Mbps system# of nodes = 8CSMA/CA parameters– CCA threshold = 10dB– Rx. Sensitivity = -98dBm
Time information broadcasting– Sent at beacon time with robust coding
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Simulation Results
1 2 3 4 50
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000Comparison of Throughput Performance
# of piconets
Thro
ughp
ut [k
bps]
TDMA 100% Duty CycleTDMA 20% Duty CycleCSMA Rx.Sen. -98 dBmproposed DTS
1 2 3 4 50
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1Comparison of PER Performance
# of piconets
PE
R
TDMA 100% Duty CycleTDMA 20% Duty CycleRx.Sen. -98 dBmproposed DTS
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doc.: IEEE 802.15-09-0321-00-0006
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Conclusion
TDMA– Bandwidth efficient– Dynamic bandwidth allocation possible– Delay bounded– Mixable with other types of channel access mechanisms
CSMA, low duty cycle overlapping, or etcDistributed TDMA scheduling– Support dynamically changing multiple piconets
Uncoordinated interference problem– When two piconets are out of the communication range
while still in the interference range of each other– Partially solved with multi hop coordination– Fundamentally solved with two level Tx power control
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Welcome Merger
Super-frame– CFP (Contention Free Period)– CAP (Contention Access Period)
Partial proposal– Only SOP criteria is covered– Other companies are invited for
collaboration
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References
[1] “802.15.6 Call for Applications - Response Summary”, 15-08-0407-05-0006-tg6-applications-summary.doc[2] “IEEE standard for information technology - telecommunications and information exchange between systems - local and metropolitan area networks - specific requirement part 15.4: Wireless medium access control (MAC) and physical layer (PHY) specifications for low-rate wireless personal area networks (WPANs),” IEEE Std 802.15.4a-2007 (Amendment to IEEE Std 802.15.4-2006), pp. 1–203, 2007.
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Thank You!