submission doc.: ieee 802.11-13/0801r1 akira kishida, ntt issues of low-rate transmission date:...
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Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
Issues of Low-Rate Transmission
Date: 2013-07-18
Name Company Address Phone email Akira Kishida NTT 1-1 Hikari-no-oka,
Yokosuka, Kanagawa 239-0847 Japan
+81 46 859 3254
Masashi Iwabuchi +81 46 859 8692
Yasuhiko Inoue +81 46 859 5097
Yusuke Asai +81 46 859 3494
Yasushi Takatori +81 46 859 3135
Toshiyuki Shintaku +81 46 859 3463
Tetsu Sakata +81 46 859 3259
Akira Yamada NTT DOCOMO 3-5, Hikarino-Oka, Yokosuka-shi, Kanagawa, 239-8536, Japan
+81-46-840-3175
Authors:
Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
Introduction
• Since so many WLAN devices have been already deployed in many places, we need to consider the impact of those legacy devices in the HEW usage models.▫ Some discussions are in progress concerning the impact of low-rate
transmissions by these legacy devices [1].
• Compared with high-rate transmissions, low-rate transmissions by legacy STAs, especially 802.11b devices, consume more wireless channel time. It results to degrade the performance of STAs complying with latter standards.
• This presentation introduces current situations of the use of 802.11b low-rate transmissions from the results measured in Tokyo. Besides, some experiments show how low-rate transmissions degrade throughput of high-rate transmissions.
Slide 2
July 2013
Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
Issues of Low-Rate Transmission
• A large number of low-rate management frames degrade efficiency in dense scenario▫ The newer standard comes, the larger the Beacon size become.
▫ In fact, the size of the 11n Beacon is approximately from 2 to 2.5 times larger than that of 11g. (See Appendix.A)
• Low-rate transmissions by legacy STAs consume more wireless channel time▫ The chance of transmission for all STAs shall become impartial
according to the policy of IEEE802.11.
▫ In dense environment, data traffic will be saturated and these low-rate transmissions will prevent high-rate transmissions because of the policy.
Slide 3
July 2013
Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
Condition of Packet Capture in Tokyo
• Packet capture is conducted in dense environment:▫ Date: June 28▫ Location: Shinagawa Station▫ Measured Channel: ch 1 (2.4GHz)▫ Measured Time: 5m25s▫ The number of all captured packets:160,574▫ The number of measured SSIDs:20 (at ch 1)
• The whole 2.4GHz channel condition at the location
Slide 4
July 2013
Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
74%
18%
8%
All frames categorized by stds.
11/11b
11g
11n 20MHz
Results of Packet Capture in Tokyo [1]
• More than 70% of the whole captured frames are 802.11/11b format▫ Most of the frames are transmitted in 1Mbps of 802.11/11b.
▫ Those frames are mainly management or control frames transmitting to correspond to 802.11/11b.
Slide 5
July 2013
84%
2%1%
13%
11/11b frames categorized by rate1Mbps2Mbps5.5Mbps11Mbps
18%
20%62%
0%
11/11b frames categorized by type
Data
Control
Management
Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
Results of Packet Capture in Tokyo [2]
• Most management frames are 802.11/11b format▫ Most management frames are 802.11b format in order to ensure
interoperability and to reach farther distance.
▫ In control frames, the ratio of 11b and 11g is in halves.
Slide 6
July 2013
49%51%
0%
Control frames categorized by stds.
11/11b
11g
11n 20MHz
99%
1% 0%
Management frames categorized by stds.
11/11b 11g
11n 20MHz
Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
23%
30%
46%
All frames categorized by type
Data
Control
Management
Results of Packet Capture in Tokyo [3]
• More than 50% of the data frames are 802.11/11b format▫ 11g or 11n STAs use 11b mode if their RSSI is low due to distance,
interference, or fading.
Slide 7
July 2013
57%
9%
34%
Data frames categorized by stds.
11/11b
11g
11n 20MHz
Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
The effect of Low-Rate Beacons:Experimental Result [1]
• An experiment was conducted in order to measure degradation of FTP file transfer by a large number of Beacons.
• System configuration▫ FTP data was continuously transmitted from the FTP server to the PC via the 11n (or 11g) AP.
▫ 2~30 APs without any connected device were located in 5 meter distance from the target AP.
▫ Under the condition, the throughput of the FTP transmission was observed.
Slide 8
July 2013
BSS1 (11n or 11g) [Target]
SW 6ch/20MHz Fixed
AP
Server
PC1
FTP file (50Mbyte) transfer
・・・APs
(2 ～ 30 units)
10m
6ch
5m
The ratio of the number of 11n APs and 11g APs was equal (See Appendix.A).
Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
The effect of Low-Rate Beacons:Experimental Result [2]
• Experimental result▫ The FTP throughput decreases by about 50% when 30 APs just exists.
▫ Consumption of the wireless channel time by a number of low-rate Beacons is not negligible in the dense scenario.
Slide 9
July 2013
0
20
40
60
80
100
0 5 10 15 20 25 30
The number of APs
Th
rou
ghpu
t [M
bp
s]
11n11g
0.4
0.6
0.8
1.0
0 5 10 15 20 25 30Number of APs
Th
rou
ghp
ut
(rel
ativ
e)
11n
11g
Throughput Characteristics Throughput Characteristics (Normalized)
Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
BSS2 (11b or 11n) [Interference]
BSS1 (11n) [Target]
The effect of Low-Rate Transmissions:Experimental Results [1]
• Experiments were conducted in order to measure degradation of FTP file transfer by single low-rate transmission
▫ Two BSSs were set to measure the effect of low-rate transmission via FTP transfer.
▫ The BSS1 was target to measure and used 11n mode for its transmission.
▫ The BSS2 using 11b or 11n mode was the source of interference.
• System configuration
Slide 10
July 2013
SW 6ch/20MHz Fixed
AP1
AP2
Server
PC1
FTP file (50Mbyte) transfer
10m
FTP file (50Mbyte) transfer
6ch/20MHz Fixed
PC2
Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
The effect of Low-Rate Transmissions:Experimental Results [2]
Slide 11
July 2013
Throughput of each BSS (BSS2:11n)
• Experimental results▫ Throughput when BSS2 adopted 11b mode greatly decreased.▫ This problem might occur in the case not only with 11b STAs but also
with low-rate transmission by distant APs or STAs.Throughput of each BSS (BSS2:11b)
96% decrease45% decrease
Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
Summary and Next Steps
• Our field investigation shows that there are still a lot of low-rate transmissions in current situations.▫ Most of management frames are broadcasted in 1Mbps.
▫ More than 50% of the data frames are 802.11/11b format
• In the HEW, coexistence with legacy devices should be considered in usage model.▫ A number of low-rate Beacons consume much wireless channel time in dense
scenarios.
▫ Even a single low-rate transmission is not negligible.
• It should be considered to minimize the impact of a lot of low-rate management frames or low-rate transmissions.▫ It should be considered not to support 11b STAs in the HEW.
▫ Some techniques that raise MAC Efficiency irrespective to the existence of legacy STAs is necessary.
Slide 12
July 2013
Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
Reference
[1] 11-13-0416-03-000m-cid-32-11b-is-poison.pptx
Slide 13
July 2013
Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
Appendix.A• List of Beacon size for each SSID using the experiment
Slide 14
July 2013
SSID StandardMAC Header+Frame Body+FCS
[oct]Beacon frame length[μs]
SSID1 11g 108 1056SSID2 11g 117 1128SSID3 11g 117 1128SSID4 11g 117 1128SSID5 11g 117 1128SSID6 11g 129 1224SSID7 11g 130 1232SSID8 11g 130 1232SSID9 11g 130 1232SSID10 11g 130 1232SSID11 11g 130 1232SSID12 11g 130 1232SSID13 11g 157 1448SSID14 11g 176 1600SSID15 11n 206 1840SSID16 11n 242 2128SSID17 11n 242 2128SSID18 11n 242 2128SSID19 11n 250 2192SSID20 11n 259 2264SSID21 11n 259 2264SSID22 11n 259 2264SSID23 11n 259 2264SSID24 11n 262 2288SSID25 11n 262 2288SSID26 11n 262 2288SSID27 11n 262 2288SSID28 11n 300 2592SSID29 11n 308 2656SSID30 11n 362 3088
Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
Backup Slides
Slide 15
July 2013
Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
wait waitwait
Issue of Low-Rate Transmission
• Unfairness of the medium time by a low-rate transmission
Slide 16
July 2013
High-rate STAs
Low-rate STA
wait wait wait
Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
BSS2 (11b) [Interference]
BSS1 (11n) [Target]
The effect of Low-Rate Transmissions:Experimental Results [3]
• Experiment was conducted in order to measure degradation of FTP file transfer by low-rate web browsing by a mobile gaming machine
▫ A mobile gaming machine was deployed as the interference instead of the PC2.
▫ Due to limitations of feature of the gaming machine, manual web browsing was conducted instead of FTP transmission.
• System configuration
Slide 17
July 2013
SW 6ch/20MHz Fixed
AP1
AP2
Server
PC1
FTP file (50Mbyte) transfer
10m
Web Browsing
6ch
GamingMachine
The InternetThe Internet
Submission
doc.: IEEE 802.11-13/0801r1
Akira Kishida, NTT
The effect of Low-Rate Transmissions:Experimental Results [4]
Slide 18
July 2013
Throughput of BSS1 (BSS2:11b)
• Experimental result▫ Throughput decreased by about 50%.
▫ Even a single low-rate transmission is not negligible.
48% decrease