Impact of IEEE 802.11n Operation On IEEE 802.15.4 Performance

1
Impact of IEEE 802.11n Operation On IEEE 802.15.4
Performance

• Date 2008-11-02

Authors
Notice This document has been prepared to assist
IEEE 802.19. 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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Abstract

• In this presentation, we evaluate the impact of
  IEEE 802.11n operation on IEEE 802.15.4
  performance via test bed experiments. The IEEE
  802.15.4 performance is measured in terms of
  packet loss rate and the latency for successfully
  delivered packets.

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IEEE 802.15.4 Overview

• A MAC/PHY layer protocol for low power, low data
  rate (lt 250 kbps) wireless sensor applications
• Based on CSMA/CA

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The CSMA/CA algorithm in (unslotted) 802.15.4

• The source node backoffs for a random number of
  slots between 0 and (2BE) 1
• BE is Backoff Exponent
• After the backoff, the source node does the clear
  channel assessment (CCA)
• If the channel is not idle (CCA Failure), the
  source node increments BE and repeat the process
  up to 4 times
• The initial BE value is 3 and max BE value is 5

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The CSMA/CA algorithm in (unslotted) 802.15.4

• If the CCA fails even after 4th retry, the source
  node declares channel access failure (CAF) and
  abandons the packet transmission
• If the CCA succeeds, the source node transmits
  the packet.
• On receiving the packet, the destination
  optionally sends an acknowledgement back

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Collisions and Retransmissions

• If the packet or the ack suffers a collision, the
  source node waits for a certain time duration and
  then repeat the (backoff transmission) process
  up to 3 more times.
• If the ack is not received even after the 3rd
  retry, the source node declares a collision
  failure and abandons the packet.

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Packet Loss in IEEE 802.15.4

• Channel access failure
• channel access failure occurs after 5
  back-to-back CCA failures during a try.
• Collision failure
• occurs after failure to receive the ack even
  after 4 tries.
• Note that a channel access failure causes
  abandonment of packet transmission attempt even
  if 4 tries have not been made.

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Impact of IEEE 802.11n operation on IEEE 802.15.4
Performance

• IEEE 802.15.4 performance is measured in terms of
  the packet loss rate and latency for successfully
  delivered packets.
• In the following graphs, we plot the increase in
  average loss rate/latency values for IEEE
  802.15.4 nodes due to the presence of an IEEE
  802.11n network.

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Traffic in IEEE 802.15.4 Network

• 15 nodes sending packets to the coordinator.
• The packet size is 112 bytes.
• Each node sends on average one packet per second
  (poisson distributed) for 15 minutes
• IEEE 802.15.4 network uses a 3 MHz wide channel
  centered at 2425 MHz (Channel 15)
• Power level 10dBm

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Traffic in IEEE 802.11n Network

• An iperf client sends a UDP stream to an iperf
  server over an IEEE 802.11n network
• Power level 17dBm
• Packet size 1470 bytes
• Client generates traffic at rates 1, 2, 5, 10,
  15, 20 Mbps.

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IEEE 802.11n Channels Used

• Scenario 1 Channel 1, 20 MHz wide, no overlap
  with IEEE 802.15.4 channel
• Scenario 2 Channel 6, 40 MHz wide (extends
  towards channel 11), no overlap with IEEE
  802.15.4 channel
• Scenario 3 Channel 1, 40 MHz wide, extends into
  the channel used by IEEE 802.15.4 network
• Scenario 4 Channel 4, 20 MHz wide, overlaps the
  channel used by IEEE 802.15.4 network

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Scenario 1 IEEE 802.11n on Channel 1, 20 MHz wide
2425 MHz
2412 MHz
22MHz
3MHz
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Scenario 1 Impact of IEEE 802.11n Operation on
IEEE 802.15.4 Loss Rate
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Scenario 1 Impact of IEEE 802.11n Operation on
IEEE 802.15.4 Latency
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Scenario 2 IEEE 802.11n on Channel 6, 40 MHz wide
2425 MHz
2437 MHz
3MHz
44MHz
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Scenario 2 Impact of IEEE 802.11n Operation on
IEEE 802.15.4 Loss Rate
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Scenario 2 Impact of IEEE 802.11n Operation on
IEEE 802.15.4 Latency
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Scenario 3 IEEE 802.11n on Channel 1, 40 MHz wide
2425 MHz
2412 MHz
3MHz
44MHz
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Scenario 3 Impact of IEEE 802.11n Operation on
IEEE 802.15.4 Loss Rate
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Scenario 3 Impact of IEEE 802.11n Operation on
IEEE 802.15.4 Latency
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Scenario 4 IEEE 802.11n on Channel 4, 20 MHz wide
2425 MHz
2427 MHz
3MHz
22MHz
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Scenario 4 Impact of IEEE 802.11n Operation on
IEEE 802.15.4 Loss Rate
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Scenario 4 Impact of IEEE 802.11n Operation on
IEEE 802.15.4 Latency