1. 80MHz and 160MHz channel access modes
Month Year
doc.: IEEE yy/xxxxr0
80MHz and 160MHz channel access modes
Date:
Authors:
John Doe, Some Company

2. Multichannel non contiguous transmissions
Interests of multi-channel
Multi-channel is an efficient solution to increase the probability to transmit at 80MHz and ensure an increase of single-user throughput compared to 11n.
In [1], we presented the gains that can be obtained with the most favored solution: synchronous non contiguous
We concluded that this solution provided a clear increase of the probability to reach the desired bandwidth
In this presentation, we discuss the need for contiguous or non contiguous modes for 80MHz and 160MHz transmissions
Slide 2

3. 11n 40MHz channel access - 20MHz bandwidth unit BWU
- Classical contention on the primary channel (BWU1)
- CCA during PIFS on the secondary channel (BWU2)
BWU1
Primary Channel
AIFS + backoff
Ack
BWU2
time
Secondary Channel
Ack
time
PIFS 30 23 17
Primary
Slide 3

4. How does 11n work? 11n is a contiguous case and the transmitter can
Transmit at 40MHz when primary and secondary are idle or at 20MHz when primary channel only is idle or defer when the primary is busy
 Defer/20/40 mode
Transmit at 40MHz when both channels are idle or defer
 Defer/40 mode
Because of implementation issues, only the second mode is used: Defer/40 mode
Slide 4

5. 11ac 80MHz channel access - 20MHz bandwidth unit BWU as in 11n
- Classical contention on the primary channel (BWU1)
- CCA during PIFS on the secondary, tertiary, quaternary channel (BWU2,3,4)
BWU1
Primary Channel
AIFS + backoff
Ack
BWU2
time
Secondary Channel
Ack
BWU3
time
Tertiary Channel
PIFS
Ack
BWU4
time
Quaternary Channel
PIFS
Ack
time
PIFS
SIFS 30 23 17
Primary
Slide 5

6. 11ac 160MHz channel access
- 40MHz bandwidth unit instead of 20MHz bandwidth unit BWU
- Classical contention on the primary BWU
- CCA during PIFS on the secondary, tertiary, quaternary BWU
BWU1
Primary BWU
AIFS + backoff
Ack
time
Ack
time
BWU2
Secondary BWU
Ack
time
Ack
time
BWU3
Tertiary BWU
PIFS
Ack
time
Ack
time
BWU4
Quaternary BWU
PIFS
Ack
time
Ack
time
PIFS
SIFS 30 23 17
Slide 6

7. 11ac 80MHz channel access: non contiguous case (use of 2 segments or more)
BWU1
Primary Channel
AIFS + backoff
Ack
BWU2
time
Secondary Channel
Ack
time
PIFS
Segment 2
BWU3
Tertiary Channel
Ack
time
BWU4
Quaternary Channel
PIFS
Ack
time
PIFS
SIFS 30 23 17
Primary
Slide 7

8. 11ac 80MHz channel access: non contiguous case (use of 2 segments or more)
Contiguous (1 segment)
Non contiguous (2 or more segments)
Non contiguous mode also incorporates in this definition the case of contiguous segments 30 23 17
Segment 1
Segment 2 30 23 17 30 23 17
Slide 8

9. How would 11ac work with contiguous (1 segment) or non contiguous (2 segments)?
For contiguous case, we will be able to fill up the subcarriers between every channels
For non contiguous case, we won't be able to use the subcarriers between the two segments
4% gain for 40MHz, ~6% for 80MHz, ~4% for 160MHz
40MHz
40MHz
80MHz
108
108
80MHz
~230
80MHz
80MHz
~230
~230
160MHz
160MHz
Bandwidth
~478
Subcarriers
Slide 9

10. How would 11ac work with contiguous (1 segment) or non contiguous (2 segments)?
For contiguous case, we will be forced to do as in 11n
Transmit at 80MHz (160 with 160MHz case) when all channels are idle or defer
 Defer/80 mode: static selection of channels as in 11n and with a lower probability of transmission
 Defer/160 mode: static selection of channels as in 11n and with a much lower probability of transmission
For non contiguous case, we will have the degree of freedom provided by the 2 segments
Transmit at 80MHz (160 with 160MHz) when all channels are idle or transmit at 40MHz (80 with 160MHz) is first segment only is idle or defer
 Defer/40/80 mode: dynamic selection of channels (80MHz case)
 Defer/80/160 mode: dynamic selection of channels (160MHz case)
Slide 10

11. Simulation results We use the simulation plateform as presented in [1]
Equivalent bandwidth vs density curves
The equivalent bandwidth is the bandwidth that you could have 100% of the time
The density is the number of channels in the 5GHz band which are interfered with a fixed load (here 0,9)
We compare contiguous (1 segment) and non contiguous (2 segments) for 80MHz and 160MHz
For contiguous: defer/80 mode (or defer/160 mode for 160MHz)
For non contiguous: defer/40/60/80 mode (or defer/80/120/160 mode for 160MHz)
Slide 11

12. Performance results: 80 MHz, load 0.9
Non contiguous (2 segments) provides very important gain over contiguous (1 segment)
Even with the throughput degradation due to unfilled subcarriers between segments of 6%, as soon as for a density of 6
Slide 12

13. Performance results: 160 MHz, load 0.9
Non contiguous (2 segments) provides very important gain over contiguous (1 segment)
Even with the throughput degradation due to unfilled subcarriers between segments of 4%, as soon as for a density of 2
Slide 13

14. Performance results:
As soon as for a density of 2 with 160MHz, contiguous mode will be almost inefficient
This density of 2 can easily be reached because of
11a/n/ac OBSS,
Radars: especially static wheather radars which are located in one of the two available contiguous 160MHz band,
Channel reserved for high QoS: like bit intolerant
Slide 14

15. Conclusions
Non contiguous (2 segments) provides significantly better results than contiguous (1 segment), even with the throughput degradations due to unfilled subcarriers between segments
For 160MHz, it's not worth allowing contiguous transmission. We should only use non contiguous (2 segments).
For 80MHz, we should define contiguous (1 segment) and non contiguous (2 segments of 40MHz) modes
Slide 15

16. References
[1] Cariou, L. and Benko, J., Gains provided by multichannel transmissions, IEEE /0103r1, Jan. 2010
Slide 16