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Submission

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: [shannon.park@samsung.com]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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Submission

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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Submission

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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Submission

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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Submission

Thank You!