1. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
SEP 2007
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [performance-analysis-reservation-based-low-power-function]
Date Submitted: [September 18, 2007]
Source: [Chang Sub Shin*, Gangja Jin*, Yuan Dao**, Yoh-Han Lee**, SeungHyun Whang**]
Company [*ETRI, **SNR Inc]
Address [161 Gajeong-dong Yuseong-gu, Daejeon, Korea]
Voice:[ ], FAX: [ ],
Re: []
Abstract: [performance analysis for reservation-based-low-power-function in low rate WPAN mesh.]
Purpose: [to discuss low power function]
Notice: This document has been prepared to assist the IEEE P 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 P
<shincs>, <ETRI>
<author>, <company>

2. May 2007
Performance Analysis of Reservation based Low Power Function (Low Power Support for low-rate IEEE )
ChangSub Shin*, Gangja Jin*,
Yuan Dao**, Yoh-Han Lee**, Seung-Hyun Whang**
* ETRI, ** SNR Inc
<author>, <company>

3. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
May 2007
Contents
Overview of previous proposal
Additional issue
Time synchronization
MAC PIB value
Frame Format
Performance Analysis
Implementation result of synchronization
Implementation result of low power function
Reference of performance analysis
<author>, <company>
<author>, <company>

4. Overview of previous proposal - 1
<month year>
doc.: IEEE <doc#>
May 2007
Overview of previous proposal - 1
Synchronous and Reservation method for end-to-end multi-hop transmission
Consist of active period and sleep period
If a node have a packet, It transmit its REQ control packet in active period and then transmit data in sleep period
REQ control packet : inform next node to transmit and prevent other neighbor node’s transmission
RSP control packet : respond to REQ or RSP sender and inform next hop node to transmit
<author>, <company>
<author>, <company>

5. For one-hop unicasting
<month year>
doc.: IEEE <doc#>
May 2007
For one-hop unicasting
Other neighbor
nodes
Listen
Sleep
Sleep
Data
REQ
RSP
Sender node
(A)
Sleep
Ack Frame
Data
REQ
RSP
Destination node
(B)
Sleep
RSP
Other node
(C)
Listen
Sleep
Sleep
Other node
(D)
Listen
Sleep
Listen Period
Sleep Period
Duty Cycle
<author>, <company>
<author>, <company>

6. For broadcasting or multicasting
<month year>
doc.: IEEE <doc#>
May 2007
For broadcasting or multicasting
Listen
Sleep
Data
Sender node
(A)
Sleep
Data
Neighbor node #1
Sleep
Data
Neighbor node #2
Sleep
Data
Neighbor node #3
Sleep
Listen Period
Sleep Period
Duty Cycle
<author>, <company>
<author>, <company>

7. for multi-hop unicasting
<month year>
doc.: IEEE <doc#>
May 2007
for multi-hop unicasting
other neighbor
nodes
Listen
Sleep
Sleep
Data
(1)
REQ
RSP
Sender node
(A)
Sleep
Sleep
Data
Data
(2)
REQ
RSP
RSP
1st Forward node
(B)
Sleep
Sleep
Data
Data
(3)
RSP
RSP
RSP
2nd Forward node
(C)
Listen
Sleep
Listen
Sleep
Data
Listen
RSP
RSP
Destination node
(D)
Sleep
Listen
Sleep
Ack Frame
Listen Period
Sleep Period
Duty Cycle
<author>, <company>
<author>, <company>

8. Multi-hop low power and minimum end-to-end latency
<month year>
doc.: IEEE <doc#>
May 2007
Multi-hop low power and minimum end-to-end latency
<author>, <company>
<author>, <company>

9. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
May 2007
Contents
Overview of previous proposal
Additional issue
Time synchronization
MAC PIB value
Frame Format
Performance Analysis
Implementation result of synchronization
Implementation result of low power function
Reference of performance analysis
<author>, <company>
<author>, <company>

10. Time synchronization - methods
<month year>
doc.: IEEE <doc#>
May 2007
Time synchronization - methods
Using MAC Primitive with timestamp value
MCPS-DATA.confirm : transmitted time
MCPS-DATA.indication : received time
Methods
Method 1 : unicast 3 way message exchange
Method 2 : broadcast 3 way message exchange
Method 3 : 2 successive synch packet broadcast
Method 4 : 1 synch packet broadcast
<author>, <company>
<author>, <company>

11. Timestamp of IEEE802.15.4 Timestamp of IEEE802.15.4 Length : 3 bytes
Unit : 16 us (1 symbol)
Maximum interval : 4.5 minutes
Timestamp interrupt signal timing in PPDU frame
Timestamp interrupt Signal timing

12. Time synchronization – method 1B T1 T4 A
(1)
(2)
(3) with T1, T4 time value B
(4) Synch with A’s timer T2 T3

13. Time synchronization – method 2B C D
TA4-TC3
TA4-TD3
TA1
TA4-TB3
(5) with TA1, TA4-TB3,
TA4-TC3, TA4-TD3 time value A
(1)
(2) B
(6) Synch with A’s timer
(3)
TB2
TB3 C
(6) Synch with A’s timer
TC2
TC3
(4) D
(6) Synch with A’s timer
TD2
TD3

14. Time synchronization – method 3
TA1
TA2 A A
(1)
(2) with TA1 time value B
(3) Synch with TA1 and TB1
TB1
TB2 B C D C
(3) Synch with TA1 and TC1
TC1
TC2 D
(3) Synch with TA1 and TD1
TD1
TD2

15. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
May 2007
MAC PIB value
Default MAC PIB during Listen period
macMaxCSMABackoffs = 4
macMinBE = 3
Temporal MAC PIB during Sleep period
macMaxCSMABackoffs = 2
macMinBE = 0
using MLME-SET.request primitive to change value
<author>, <company>
<author>, <company>

16. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
May 2007
Frame Format
<author>, <company>
<author>, <company>

17. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
May 2007
Contents
Overview of previous proposal
Additional issue
Time synchronization
MAC PIB value
Frame Format
Performance Analysis
Implementation result of synchronization
Implementation result of low power function
Reference to performance analysis
<author>, <company>
<author>, <company>

18. Test environment of time synch - 1
(1)
(2)
(3)
(4) 1 2 3 4
Coordinator
Level 1
Level 2
Level 3
Level 4
Time synch event node
Time synch event node

19. Test environment of time synch - 2

20. Test environment of time synch - 3
Hardware platform
MCU : MSP430
RF : CC2420
Oscillator max skew : 20 ppm
Synch packet interval
every 8 second test
every 3 minute test
test packet interval
Every 1.1 second test
test result graph
y-axis is sync error in microsecond unit,
x-axis is in 1.1 second unit

21. Test scenario Multi-hop time synch procedure Synch error measurement
Coordinator send synch packet to level 1 node.
Level 1 node receiving synch packet will forward it to next level
Subsequently, every each level nodes receiving synch packet will forward it to next level.
Synch error measurement
Periodical multi-hop time synch procedure
Event node broadcast event packet to simulate an event happen at a certain time(every 8s and every 4 min)
All nodes including coordinator receive the broadcast packet at the same time, and send receiving timestamp back to event node.
Event node prints out the timestamps via RS232 for synch error analysis

22. Synchronization error
synchronization error (8s interval)
Synchronization error
Level 1 2 3 4
Average
Standard deviation

23. Absolute synchronization error
absolute synchronization error (8s interval)
Absolute synchronization error
Level 1 2 3 4
Average
Standard deviation
Maximum

24. synch error analysis (8second interval)
error unit is us
synch packets are sent every 8 seconds, and event samples are taken every 1.1 second.
Theoretically, average synch error should be zero, but the skew difference will cause the average synch error deviate from zero.
the standard deviation of synch error which reflects the jitter tells more about the synch accuracy. It shows the synch error is accumulated every hop.

25. synchronization error (4minutes interval)

26. synchronization error (4minutes interval)

27. synch error analysis (4minutes interval)
<month year>
doc.: IEEE <doc#>
May 2007
synch error analysis (4minutes interval)
The difference on clock skew will slowly take effect when synch interval increases.
Once synch packet is sent, synch errors reduce to zero. When time passes, each local timers of the nodes in each level increases at a slightly different rate. This rate uncertainty is caused by the frequency uncertainty of crystal oscillator which is 20 ppm according to the datasheet.
In the following picture, node3 is slower than the coordinator, and other nodes are faster than coordinator at different speed.
It’s possible to use skew compensation to reduce the long term drift effect caused by skew difference. But it requires extra computation overhead. 
However, if the synchronization interval is very small, the synch error caused by the skew uncertainty can be negligible
<author>, <company>
<author>, <company>

28. Test environment of low power function
Test value
Chain topology based 4 nodes test
5% Duty Cycle
Period : 500, 1000, 2000, 5000 msec (4 cases)
 2.5% Duty Cycle
Period = 1000, 2000, 5000 msec (3 cases)
procedure of multi-hop low power function
Periodical multi-hop time synch procedure
All nodes make synch
Source node generate packet
measurement
Every node have timer for power consumption measurement
Calculate active time and sleep time
Result : end-to-end delay, power consumption

29. Implementation result of low power function - 1
<month year>
doc.: IEEE <doc#>
May 2007
Implementation result of low power function - 1
<author>, <company>
<author>, <company>

30. Implementation result of low power function -2
<month year>
doc.: IEEE <doc#>
May 2007
Implementation result of low power function -2
<author>, <company>
<author>, <company>

31. Reference of performance analysis - 1
Refer to “Li, J., Blake, C., Couto, D., Lee, H.I., Morris, R.: Capacity of ad hoc wireless networks. In: ACM MobiCom (2001)”
MAC interference among a chain of nodes. The solid-line circle denotes a node’s valid transmission range. The dotted-line circle denotes a node’s interference range. Node 4’s transmission will corrupt node 1’s transmissions at node 2.
Effective capacity of a forwarding chain topology becomes just 1/3 of the effective capacity of a single-hop connection

32. Reference of performance analysis - 2
Refer to “Tony Sun, Ling-Jyh Chen, Chih-Chieh Han, Guang Yang and Mario Gerla: Measuring effective capacity of IEEE beaconless mode”
Results on Multihop forwarding chain testbed
effective end-to-end capacity of a chain topology decreases as the hop length increases