1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Low duty cycle UWB piconet]
Date Submitted: [March, 2006]
Source: [Bin Zhen, Huan-Bang Li and Ryuji Kohno; Company: National Institute of Information and Communications Technology ]
Contact: Bin Zhen
Voice: ,
Abstract: [piconet level low duty cycle for coexistence.]
Purpose: [UWB coexistence]
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.
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2. Low duty cycle UWB piconet
by Bin Zhen, Huan-bang Li and Ryuji Kohno

3. Agenda for discussion in DOC. 06-0049-00-4a
Regulatory requirement is to ensure coexistence by reasonable interference reduction technology, e.g. DAA, LDC.
Regulatory issues
(1) Necessity of Interference reduction technology, e.g. DAA
(2) Introduction and discussion of feasible DAA
Doc a (Previous Doc.)
(3) Summary of issues in DAA for regulatory compliance
2. Coexistence issues
(1) Category of coexistence problem
(2) Solution for regulatory requirement, i.e. simple DAA, LDC
(3) Definition of LDC: necessary duty cycle in node & PCN etc
Doc a (This Doc.)

4. Solution for regulatory requirement, i.e. simple DAA, LDC
Necessity of the reason why LDC is good enough for suppression of interference to coexisting victim radio instead of DAA
The reason for using 1% duty cycle in 2.4GHz band is vague
Can LDC solve all coexistence problems? If no, what can we do for solution?
Why and how is the value of 1% selected?
Is the value guaranteed for a device-to-device link or a piconet?
If the value is valid for a device-to-device link, then how can we guarantee such a low duty cycle for multiple piconet environments?

5. LDC nodes
Currently, LDC refers activity of a device to be 5% over one second, 0.5% over one hour (EU definition)
Victim receivers are interfered as long as the UWB channel is active
The victim systems may cover larger area than 4a, e.g
Any LDC device in the piconet can be an interferers

6. High density of LDC nodes
In the case of high density of LDC nodes in a piconet, the aggregate interference from the piconet (channel) is still high
Assuming 0.5% node duty cycle of a pure ALOHA piconet
0.161 when there are 36 nodes
0.732 when there are 360 nodes
The channel free period is randomly segmented into small pieces which is hard to be used

7. Aggregate channel busy period
360 nodes in the piconets
36 nodes in
a piconet
Irregular free channel piece
Beacon
Busy channel
Free channel
… ….
time
Channel state
Victim packet

8. Low duty cycle piconet Low Duty Cycle piconet as interference metrics
For simple sensors, it is hard to detect victim receiver reliable for the reason of cost, power consumption, etc.
Maximal aggregate interference to victim receivers from a piconet can be controlled through total piconet active duration
Localize the interference period

9. Low duty cycle piconet (cont.)
LDC piconet is to control the aggregate active period and its distribution in the piconet level, which can be guaranteed by
control of active/inactive period to add segmented free channel pieces together
reduce traffic in the piconets
control number of devices through association
increase number piconets to cover the same local area
traffic shaping at coordinator and device
good MAC to reduce packet collision in the active period
channel dependent ALOHA
CSMA

10. Low duty cycle piconet (cont.)
Inactive period
Active period
Active period
time
… ….
Active/inactive period
CSMA or channel dependent ALOHA
Traffic shaping
Inactive period
Active period
Active period
time
Piconet in another channel band

11. Applying LDC piconet to 15.4a
Extend concept of active/inactive period to non-beacon enabled network
Active period is immediately after the beacon for synchronization
Application layer clock synchronization
Channel dependent ALOHA
whose transmission probability depends on channel condition, e.g. RSSI and LQI obtained from beacon
Transmission threshold set by application
Suggested parameters
At least active/inactive ratio = 1:1
Maximal offered traffic in active period of a piconet
0.18 for pure ALOHA
0.5 for CSMA

12. Conclusions Low duty cycle piconet
Policy based coexistence
Active/inactive period to non-beacon enabled network
Synchronization in application layer
We suggest to have coexistence annex to define the duty cycle of device and duty cycle of piconet
LDC device is below 1% (for example)
LDC piconet is below 20% for ALOHA network or 50% for CSMA network
Any application that cannot be implemented through LDC should adopt DAA

13. Backup: Analysis on aggregate channel busy period in an ALOHA network
Pure ALOHA MAC
time 1 2 1 2
Busy period
idle period
Normalized offered load
The last packet arrive at y after the reference packet.
That is no packet occurs in (1-y). The probability is
The average of busy period of channel is
The average of idle period of channel is