1. Limitation of EDCA/HCCA for Video Transmission
July 2007
doc.: IEEE /xxxxr0
July 2007
Limitation of EDCA/HCCA for Video Transmission
Date:
Authors:
0:15
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Akira Yamada, NTT DoCoMo,
Akira Yamada, NTT DoCoMo.

2. July 2007
doc.: IEEE /xxxxr0
July 2007
Abstract
This presentation shows typical functional limitations of existing MAC protocols (EDCA and HCCA) for Video transmission
0:15 0:30
Akira Yamada, NTT DoCoMo,
Akira Yamada, NTT DoCoMo.

3. HCCA issue : Cell Overlapping
July 2007
doc.: IEEE /xxxxr0
July 2007
HCCA issue : Cell Overlapping
HCCA parameters are configured in each HCs
CFP / CP may differ among HCs
[1]
If CFP/CP differ between AP1 and AP2, packets may collide in cell overlapping area due to lack of inter-HC coordination
Control access phase
1:00 1:30
Akira Yamada, NTT DoCoMo,
Akira Yamada, NTT DoCoMo.

4. EDCA Issue : Packet collision with large number of STAs in same AC
July 2007
doc.: IEEE /xxxxr0
July 2007
EDCA Issue : Packet collision with large number of STAs in same AC
Prioritization access for RT traffic is realized by shorter AIFSN/CWmin than those of Non-RT traffic in EDCA
(Video) AIFSN = 2, CWmin = 7, (Voice) AIFSN = 2, CWmin = 3
Large number of STAs that belong to same AC makes higher collision probability by shorter CWmin!
Simulation : Effect of shorter CWmin
Topology
2min
802.11a 24Mbps / Only UL traffic / 12 STAs
CWmin : 3
CWmin : 7
CWmin : 15
Smaller CWmin increases packet collisions and retransmissions
Lower throughput
Large end-to-end delay
Akira Yamada, NTT DoCoMo,
Akira Yamada, NTT DoCoMo.

5. EDCA issue : Limited support of AC_VO
July 2007
EDCA issue : Limited support of AC_VO
EDCA defines four types of ACs
AC_VO, AC_VI, AC_BE, AC_BK
Video transmissions can be categorized to some types (e.g. ITU-T document [2])
Conversational Voice and Video (Video Phone/Bidirectional)
Duplex system
Carrying both voice and video
Delay sensitive
Streaming audio/video (One-way video)
No duplex
Not so stringent requirement for delay
Akira Yamada, NTT DoCoMo,

6. EDCA Issue : Limited support of AC_VO (Cont.)
July 2007
EDCA Issue : Limited support of AC_VO (Cont.)
However those applications have different performance targets for delay [3]
Video Phone : < 150 ms (Preferred) , <400 ms (Limit), <1% PLR
Streaming audio/video : < 10s, <1% PLR
In IEEE802.11e (EDCA), those two types of video are assumed to belong to same AC
Impossible to prioritize Video-phone by EDCA
Different Requirement for Delay
Figure 1/G.1010 – Mapping of user-centric QoS requirements
Akira Yamada, NTT DoCoMo,

7. Possible Approach for VTS-MAC
July 2007
Possible Approach for VTS-MAC
HCCA issue:
Lack of inter-AP coordination
High complexity
QoS Scheme
Intserv
HCCA
VTS-MAC
Lower complexity than HCCA
More effective QoS than EDCA
VTS-MAC?
Low
High
Complexity
EDCA
EDCA issue:
Packet collision with small CWmin
Limited support of AC_VO
Diffserv
Akira Yamada, NTT DoCoMo,

8. Summary Functional limitations in existing WLAN MAC protocols
July 2007
Summary
Functional limitations in existing WLAN MAC protocols
HCCA issue
Severe packet collision due to lack of Inter-AP Coordination
EDCA issue
Packet collision with large number of STAs
Cannot support multiple types of Video communication
Possible approach for VTS-MAC
Lower complexity than HCCA
More effective QoS than EDCA
Akira Yamada, NTT DoCoMo,

9. Reference [1] IEEE802.11e Standard
July 2007
Reference
[1] IEEE802.11e Standard
[2] ITU-T G.1010 End-user multimedia QoS categories
Akira Yamada, NTT DoCoMo,