November, 2005
Doc: IEEE 15-05-0669-00-004a
Project: IEEE P802.15 Working Group for Wireless Personal Area Networks
(WPANs)
Submission Title: [channel dependent initial backoff of CSMA]
Date Submitted: [November, 2005]
Source: [Bin Zhen, Huan-Bang Li, Ryuji Kohno, Company: National Institute of
Information and Communications Technology ]
Contact: Bin Zhen
Voice:+81 46 847 5445, E-Mail: [email protected]]
Abstract: [ Channel dependent multiple channel access method of 802.15.4a to
improve throughput and save power consumption]
Purpose: [Opportunistic channel access]
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.
TG4a
Slide 1
Bin, Li, Kohno (NiCT)
November, 2005
Doc: IEEE 15-05-0669-00-004a
Channel dependent initial
backoff of CSMA
Bin Zhen, Huan-Bang Li, and Ryuji Kohno
National Institute of Information and Communications Technology
(NiCT)
TG4a
Slide 2
Bin, Li, Kohno (NiCT)
November, 2005
Doc: IEEE 15-05-0669-00-004a
Motivations
• Time varying wireless channel
– Different users experience peaks in their channel
quality at different times
– Dense distribution of sensor nodes
• Multi-user diversity to maximize system capacity
– P. Knopp and P.A. Humblet, “Information capacity and
power control in single-use multiuser
communications,” ICC, 1995
– Not only solve collision, but also transmit when user
has favorable channel condition
• maximize system throughput
• minimize energy consumption
TG4a
Slide 3
Bin, Li, Kohno (NiCT)
November, 2005
Doc: IEEE 15-05-0669-00-004a
Contention in 15.4a
• Burst traffic
– An event is sensed and reported by more than one sensors
– Coordinator broadcasts pending data to more than one nodes.
All of them contend the channel
– All traffic can only occur during active period.
• 15.4a targets simple UWB sensor which is of limited
power and computing resource
– Limited candidate random set and simple algorithm
• Channel quality dependent multiple access
– Add a new random dimension
– Give node in favorable channel more transmission probabilities
TG4a
Slide 4
Bin, Li, Kohno (NiCT)
November, 2005
Doc: IEEE 15-05-0669-00-004a
Channel quality information
• Channel quality evaluation parameters
– IEEE 802.15.4 has defined Link Quality Indicator
• Received energy, SNR, or a combination of them
– BER, RSSI, noise measurements, interference
margin
• Channel quality sources
– Beacon from coordinator
• Coordinator broadcast beacon periodically for device to
evaluate channel quality
– Data exchange between nodes
TG4a
Slide 5
Bin, Li, Kohno (NiCT)
November, 2005
Doc: IEEE 15-05-0669-00-004a
Channel dependent initial backoff
• Initial backoff of CSMA is used to reduce collision in
beacon-enabled network
– Total randomly from 0 to 2BE-1
• Map channel state to initial backoff of CSMA
– initial backoff = channel dependent part + random part
Initial backoff
τ=f(γ)
τmax
τ1
Poor channel
γ1
TG4a
Slide 6
Channel state
Bin, Li, Kohno (NiCT)
November, 2005
Doc: IEEE 15-05-0669-00-004a
Suggested parameters
• The default value of
macMinBE is 3 when
BLE is not set.
• Channel dependent
initial CSMA
– Channel dependent
backoff: [0~3]
– Random backoff: [0~4]
TG4a
Slide 7
Bin, Li, Kohno (NiCT)
November, 2005
Doc: IEEE 15-05-0669-00-004a
Performance
Random initial backoff
Average BER= 0.59%
0.01
0.009
0.008
user BER
0.007
0.006
Channel dependent initial backoff
average BER= 0.35%
0.005
0.004
0.003
0.002
0.001
0
0
5
10
15
20
25
round
30
35
40
45
50
• Total 20 nodes with BERs from 0.1% to 1%.
• Randomly, 4 of them become active in a round
TG4a
Slide 8
Bin, Li, Kohno (NiCT)
November, 2005
Doc: IEEE 15-05-0669-00-004a
Conclusions
• Channel dependent carrier sense initial backoff
– Channel state evaluation before carrier sensing
– Channel dependent backoff + random backoff
• Fully backward compactable with 15.4 MAC
– Nodes in unfavorable channel wait for channel to
become good
– Time sensitive traffics are in GTS
• Benefits
– High throughput and low power consumption
• Ride on the peak of channel
TG4a
Slide 9
Bin, Li, Kohno (NiCT)