1. Backward compatibility of 11aj with 11ad
March 2013
Backward compatibility of 11aj with 11ad
Date:
Authors:
Name
Affiliations
Address
Phone
Carlos Cordeiro
Intel Corp.
Brian Hart
Cisco
Sai Shankar
Tensorcom
Payam Torab
Broadcom
Chao-Chun Wang
MediaTek
Kazu Takahashi
Panasonic
Gal Basson
Wilocity
Su-Khiong Yong
Marvell
Brad Lynch
Peraso
Multiple co-authors

2. March 2013
Purpose
This presentation tackles the requirement of backward compatibility of 11aj with 11ad devices in the 60 GHz band
An 11aj PAR requirement
Only way to prevent thrashing of the 60 GHz band with incompatible devices
Backward compatibility has proven to be key to the success of n/g/a and it will not be different for 11aj
Here we revisit the principle of backward compatibility and bring up a proposal on how this can be accomplished by 11aj
Multiple co-authors

3. The principle of backward compatibility
March 2013
The principle of backward compatibility
The 11aj PAR states: “The amendment shall maintain backward compatibility with ad when it operates in the GHz frequency band.”
The principle of backward interoperability is well established in 11ac/n/a/g/b
Legacy STAs do not interfere with frame exchanges using next-gen PPDUs between next-gen STAs, and next-gen STAs do not interfere with frame exchanges using legacy PPDUs between legacy STAs. As a result, legacy and/or next-gen STAs are allowed to coexist with each other.
This same principle should apply to 11aj!
Multiple co-authors

4. March 2013
References from
From within (9.23 Protection mechanisms): “These protection mechanisms cause a STA that is a potential interferer to defer any transmission for a known period of time. When these mechanisms are used, non-ERP STAs do not interfere with frame exchanges using ERP PPDUs between ERP STAs and non-HT STAs do not interfere with frame exchanges using HT PPDUs between HT STAs. As a result, non-ERP and/or non-HT STAs are allowed to coexist with ERP and/or HT STAs.”
See also (9.7 Multirate support)
Multiple co-authors

5. March 2013
Comments on 11/ r0
In slide 6 of 11/ r0, 3 coexistence “modes” of n are presumed, labeled: Legacy mode, Mixed mode and Greenfield mode
Then, the following proposal is made based on the authors’ understanding of the 11n Greenfield mode:
“Exclusive Mode
No backward compatibility to ad device”
This is a misunderstanding:
11n does not have modes: 11n has PHY formats (legacy, HT-MM, HT-GF) with associated usage rules to ensure backwards compatibility
Greenfield “mode” does NOT imply that there is no backward compatibility
Greenfield allows data transmissions in a BSS to be restricted to a given mode (e.g., HT), but backward compatibility still exists
Use of HT-GF format is subject to an array of restrictions to minimize backwards compatibility issues. E.g., review the HT Protection, Nongreenfield HT STAs Present and OBSS Non-HT STAs Present fields in the HT Operation element, and associated normative text
Multiple co-authors

6. Applying the principle of backward compatibility to 11aj: a proposal
March 2013
Applying the principle of backward compatibility to 11aj: a proposal
Mechanisms must be defined to ensure that 11aj is backward compatible with 11ad
Some proposed mechanisms:
Support of 11ad MCS0, which is used to transmit several basic frames (see 9.7)
11aj STAs shall follow the same frame transmissions rules during the BTI, A-BFT and ATI portions of the beacon interval that are applicable to DMG STAs
During the DTI, 11aj stations may use 11aj specific modes after ensuring appropriate protection (e.g., similar to HT-GF protection rules in n)
Additional mechanisms might still be needed to meet the backward compatibility requirement of the 11aj PAR
Multiple co-authors

7. March 2013
Under this proposal (slide 6), how could 11aj STAs use 11aj specific modes?
There are possibly several alternatives for 11aj STAs to use 11aj specific modes during the DTI
For example, to support the smaller BW channel desired by 11aj, possible extensions can include:
Extending the Extended Schedule element to signal the channel BW
Extending the RTS/DMG CTS frames to signal the channel BW (e.g., transmitting DMG CTS-to-self)
Extending the frames used during the SLS to also signal the channel BW
Other?
Multiple co-authors

8. March 2013
Summary
Backward compatibility of 11aj with 11ad is critical not only because it is in the 11aj PAR, but also because it:
Ensures equitable and fair use of the 60 GHz band
Leverages all the implementation efforts made into 11ad
Increases the chances of 11aj success in the marketplace
We propose that 11aj follows the same principle of backward compatibility that is incorporated in other .11 amendments
The backward compatibility proposal made in this presentation follows this principle
Multiple co-authors