1. Extension Channel CCA Proposed Solutions
May 2006
doc.: IEEE /0608r2
May 2006
Extension Channel CCA Proposed Solutions
Date:
Authors:
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Srinivas Kandala, Airgo Networks, Inc.
Srinivas Kandala, Airgo Networks, Inc.

2. May 2006
doc.: IEEE /0608r2
May 2006
Abstract
In this presentation, we study the possible solutions to improve the co-existence between an IEEE n network in the 40 MHz and a legacy IEEE network in the extension channel. Three alternative solutions are provided and through simulations we show the effect on the network throughput due to each of the co-existence mechanisms.
Srinivas Kandala, Airgo Networks, Inc.
Srinivas Kandala, Airgo Networks, Inc.

3. Three Alternatives May 2006
1. Major / Significant Impact on Legacy Operation in Ext Ch
Slight Impact on Legacy Operation in Ext Ch
3. Minimal Impact on Legacy Operation in Ext Ch
No CCA on extension channel
Mandatory independent CCA on both Control and extension channel (ED CCA for ext ch)
Mandatory to avoid 40MHz transmissions when ext ch CCA is busy
Mandatory independent CCA on both Control and extension channel (ED CCA for ext ch)
Mandatory to avoid 40MHz transmissions when ext ch CCA is busy
Independent back-off counters for both Control and Ext Channels
Dramatic negative impact on throughput of both HT and Legacy devices
Relatively Fair Sharing of Medium
Including back off counter for ext ch provides some improvements in favor of legacy networks over alt. 2
ED = Energy Detect, CCA = Clear Channel Assessment
Srinivas Kandala, Airgo Networks, Inc.

4. Simulations The three alternatives are studied using simulations.
May 2006
Simulations
The three alternatives are studied using simulations.
For each alternative, the simulations are set up in the following manner:
Run one UDP flow from a 20/40 MHz to another 20/40 MHz station.
Run two UDP flows from a 20 MHz legacy station to another 20 MHz legacy station
Vary the offered load on the legacy UDP flows.
Srinivas Kandala, Airgo Networks, Inc.

5. Simulation scenarios Scenario 1 (No CCA on Extension Channel):
May 2006
Simulation scenarios
Scenario 1 (No CCA on Extension Channel):
20/40 station contends for the channel based on the backoffs (and CCA) performed on the control channel. The carrier of the extension channel is not sensed
20 MHz stations contend for the extension channel based on the backoffs (and CCA)
20 MHz stations are also assumed to be capable of detecting a 40 MHz transmission and backoff if the (extension) channel is busy
Srinivas Kandala, Airgo Networks, Inc.

6. Simulation scenarios Scenario 2 (CCA on Extension Channel):
May 2006
Simulation scenarios
Scenario 2 (CCA on Extension Channel):
20/40 station contends for the channel based on the backoffs (and CCA) performed on the control channel. In parallel, the station keeps track of the CCA on extension channel.
When the backoff on the control channel expires and the extension channel has been idle for at least a duration of PIFS, the 20/40 stations transmits using a 40 MHz signal.
When the backoff on the control channel expires and the extension channel is busy or extension channel is idle only for a duration of less than the PIFS, the station transmits using the 20 MHz signal
20 MHz stations contend for the extension channel based on the backoffs (and CCA)
20 MHz stations are also assumed to be capable of detecting a 40 MHz transmission and backoff
Srinivas Kandala, Airgo Networks, Inc.

7. Simulation scenarios Scenario 3 (Backoff on Extension Channel):
May 2006
Simulation scenarios
Scenario 3 (Backoff on Extension Channel):
20/40 station contends for the channel based on the backoffs (and CCA) performed on the control channel. In parallel, the station runs a separate backoff engine based on the CCA on the extension channel.
When the backoff on the control channel expires and if the backoff counter on the extension channel has counted down to 0 and the channel has been idle for at least a duration of PIFS, the 20/40 stations transmits using a 40 MHz signal.
When the backoff on the control channel expires and the extension channel is busy or is in a backoff or the extension channel is idle only for a duration of less than the PIFS, the station transmits using the 20 MHz signal
20 MHz stations contend for the extension channel based on the backoffs (and CCA)
20 MHz stations are also assumed to be capable of detecting a 40 MHz transmission and backoff
Srinivas Kandala, Airgo Networks, Inc.

8. Simulation Parameters
May 2006
Simulation Parameters
Parameter
Value
CWmin/CWmax
15/1023
Retry Limit 7
40 MHz HT Data rate
270 Mbps
20 MHz HT Data rate
130 Mbps
20 MHz extension Data rate (No QoS)
54 Mbps
AIFSN (on 11n STA transmissions) 3
TXOP Size (on 11n STA Transmissions)
Number of MPDUs in A-MPDU (in 11n STA transmissions)
5 or 10
Number of UDP flows in 40 MHz
1 (others are also simulated)
Number of UDP flows in extension
1 or 2 (others are also simulated)
PER on either transmissions 1%
Srinivas Kandala, Airgo Networks, Inc.

9. May 2006
Impacts of CCA and Back-Off on Extension Channel Operation (Fully Loaded Networks, A-MPDU=5, One flow on Legacy Network)
Max Goodput for 40MHz .11n (138Mbps)
Max Goodput for 20MHz .11n (87Mbps)
Max Goodput for Legacy (30Mbps)
Simulation Assumptions: TXOP = O, One 40MHz UDP flow fully loaded, One 20 MHz UPD flow on extension channel in legacy network fully loaded, A-MPDU = 5, Random PER 1%
Srinivas Kandala, Airgo Networks, Inc.

10. May 2006
Impacts of CCA and Back-Off on Extension Channel Operation (20% loading of Legacy Network, A-MPDU=5, One flow on legacy network)
Max Goodput for 40MHz .11n (138Mbps)
Max Goodput for 20MHz .11n (87Mbps)
Max Goodput for Legacy (6Mbps)
Simulation Assumptions: TXOP = O, One 40MHz UDP flow fully loaded, One 20 MHz UPD flow on extension channel in legacy network fully loaded, A-MPDU = 5, Random PER 1%
Srinivas Kandala, Airgo Networks, Inc.

11. May 2006
doc.: IEEE /0608r2
May 2006
Impact of CCA and Back-Off in Extension Channel (A-MPDU=5, One flow on legacy network, multiple legacy network traffic loading scenarios)
Simulation Assumptions: TXOP = O, One 40MHz UDP flow fully loaded, One 20 MHz UPD flow on extension channel in legacy network 20%, 40%, 60%, 80%, 100% loaded, A-MPDU = 5, Random PER: 1%
Srinivas Kandala, Airgo Networks, Inc.
Srinivas Kandala, Airgo Networks, Inc.

12. May 2006
doc.: IEEE /0608r2
May 2006
Conclusions
Alternatives 2 and 3 clearly allow the IEEE n stations to share the channel with legacy transmissions on the extension channel in a fair manner
Alternative 3 is clearly the fairest
When the load on the extension channel is light or even moderate, the benefits of using IEEE n using 40 MHz can be achieved.
We welcome further discussion regarding finding a solution for the 40Mhz interoperability / coexistence problem, based on the results from these simulations
Srinivas Kandala, Airgo Networks, Inc.
Srinivas Kandala, Airgo Networks, Inc.

13. May 2006
Back Up
Srinivas Kandala, Airgo Networks, Inc.

14. May 2006
Impacts of CCA and Back-Off on Extension Channel Operation (Fully Loaded Networks, A-MPDU=5, 2 flows on Legacy Network)
Max Goodput for 40MHz .11n (138Mbps)
Max Goodput for 20MHz .11n (87Mbps)
Max Goodput for Legacy (30Mbps)
Simulation Assumptions: TXOP = O, One 40MHz UDP flow fully loaded, 2 x 20 MHz UPD flow on extension channel in legacy network fully loaded, A-MPDU = 5, Random PER 1%
Srinivas Kandala, Airgo Networks, Inc.

15. May 2006
Impacts of CCA and Back-Off on Extension Channel Operation (20% loading ofLegacy Network, A-MPDU=5, 2 flows on legacy network)
Max Goodput for Legacy (6Mbps)
Max Goodput for 40MHz .11n (138Mbps)
Max Goodput for 20MHz .11n (87Mbps)
Simulation Assumptions: TXOP = O, One 40MHz UDP flow fully loaded, 2 x 20 MHz UPD flow on extension channel in legacy network fully loaded, A-MPDU = 5, Random PER 1%
Srinivas Kandala, Airgo Networks, Inc.

16. May 2006
Impact of CCA and Back-Off in Extension Channel (A-MPDU=5, multiple legacy network traffic loading scenarios)
Simulation Assumptions: TXOP = O, One 40MHz UDP flow fully loaded, 2 x 20 MHz UPD flow on extension channel in legacy network 20%, 40%, 60%, 80%, 100% loaded, A-MPDU = 5, Random PER: 1%
Srinivas Kandala, Airgo Networks, Inc.

17. May 2006
Impacts of CCA and Back-Off on Extension Channel Operation (Fully Loaded Networks, A-MPDU=10)
Simulation Assumptions: TXOP = O, 1 40MHz UDP flow fully loaded, 2 x 20 MHz UPD flow on extension channel in legacy network fully loaded, A-MPDU = 5, Random PER 1%
Max Goodput for Legacy (30Mbps)
Max Goodput for 40MHz .11n (179Mbps)
Max Goodput for 20MHz .11n (102Mbps)
Srinivas Kandala, Airgo Networks, Inc.

18. May 2006
Impacts of CCA and Back-Off on Extension Channel Operation (20% loading ofLegacy Network, A-MPDU=10)
Impact of CCA and Back Off on Ext Channel on .11n
40MHz and Legacy Operation (UDP goodput in Mbps)
- 20% Loading of Extension Channel Legacy Network (6Mbps), A-MPDU = 10
180
Max Goodput for 40MHz .11n (179Mbps) -
151.8
160
135.2
140
120
40MHz
Operation
100
Max Goodput for 20MHz .11n (102Mbps)
79.0 80 60
Legacy 20 40
MHz
Operation 20
5.0
Max Goodput for Legacy Operation (6Mbps)
5.9
5.9
No CCA on Ext Ch
CCA on Ext Ch
CCA and Back-Off on
Ext Ch
Simulation Assumptions: TXOP = O, 1 40MHz UDP flow fully loaded, 2 x 20 MHz UPD flow on extension channel in legacy network fully loaded, A-MPDU = 10, Random PER 1%
Srinivas Kandala, Airgo Networks, Inc.

19. May 2006
Impact of CCA and Back-Off in Extension Channel (A-MPDU=10, multiple legacy network traffic loading scenarios)
Simulation Assumptions: TXOP = O, 1 40MHz UDP flow fully loaded, 2 x 20 MHz UPD flow on extension channel in legacy network 20%, 40%, 60%, 80%, 100% loaded, A-MPDU = 10, Random PER: 1%
Srinivas Kandala, Airgo Networks, Inc.

20. May 2006
References
Srinivas Kandala, Airgo Networks, Inc.