Title: Impact of IEEE 802.11n Operation On IEEE 802.15.4 Performance
1Impact of IEEE 802.11n Operation On IEEE 802.15.4
Performance
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.
2Abstract
- 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.
3IEEE 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
4The 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
5The 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
6Collisions 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.
7Packet 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.
8Impact 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.
9Traffic 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
10Traffic 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.
11IEEE 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
12Scenario 1 IEEE 802.11n on Channel 1, 20 MHz wide
2425 MHz
2412 MHz
22MHz
3MHz
13Scenario 1 Impact of IEEE 802.11n Operation on
IEEE 802.15.4 Loss Rate
14Scenario 1 Impact of IEEE 802.11n Operation on
IEEE 802.15.4 Latency
15Scenario 2 IEEE 802.11n on Channel 6, 40 MHz wide
2425 MHz
2437 MHz
3MHz
44MHz
16Scenario 2 Impact of IEEE 802.11n Operation on
IEEE 802.15.4 Loss Rate
17Scenario 2 Impact of IEEE 802.11n Operation on
IEEE 802.15.4 Latency
18Scenario 3 IEEE 802.11n on Channel 1, 40 MHz wide
2425 MHz
2412 MHz
3MHz
44MHz
19Scenario 3 Impact of IEEE 802.11n Operation on
IEEE 802.15.4 Loss Rate
20Scenario 3 Impact of IEEE 802.11n Operation on
IEEE 802.15.4 Latency
21Scenario 4 IEEE 802.11n on Channel 4, 20 MHz wide
2425 MHz
2427 MHz
3MHz
22MHz
22Scenario 4 Impact of IEEE 802.11n Operation on
IEEE 802.15.4 Loss Rate
23Scenario 4 Impact of IEEE 802.11n Operation on
IEEE 802.15.4 Latency