1. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
Jan 2013
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Interframe Spacing and Turnaround Requirements]
Date Submitted: [Jan 10th, 2013]
Source: [Rick Powell]
Company [Microsemi]
Address [15822 Bernardo Center Dr, Ste B, San Diego, CA, 92127]
Voice:[ ]
FAX :[ ] ]
Re: [In response to TG4k Sponsor Ballot]
Abstract: [This presentation discusses the relationship between Interframe Spacing requirements and Turnaround requirements.]
Notice: This document has been prepared to assist the IEEE P It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P
Rick Powell (Microsemi)
Rick Powell (Microsemi)

2. Interframe Spacing and Turnaround Requirements
Jan 2013
Interframe Spacing and Turnaround Requirements
Jan 10, 2013
Rick Powell, Microsemi
Rick Powell (Microsemi)

3. July 2012
doc.: IEEE /0626r0
Jan 2013
Abstract
This presentation discusses the relationship between Interframe Spacing requirements and Turnaround requirements.
Rick Powell (Microsemi)
Rick Powell (Microsemi)

4. Jan 2013
Definitions
Turnaround Time – A PHY constant that defines how quickly a PHY must be capable of transitioning from Tx to Rx, and from Rx to Tx, from the end of the last chip/symbol of one PPDU to the beginning of the first chip on the next PPDU. This is defined as the “maximum” time that the PHY must be capable of making the transition, i.e., less that or equal to “aTurnaroundTime.”
Interframe Spacing (IFS) – The time interval between frames, from the end of the of one PPDU until the beginning of the next. Interframe Spacing is a MAC requirement, in that the MAC has “minimum” interval requirements between various frame transactions. IFS includes both back-to-back frames transmitted by the same device, and turnaround IFS, such as Data Frame to ACK Frame. In sub-clause , IFS is defined as “minimum” frame separation interval.
Rick Powell (Microsemi)

5. Issues with Turnaround Requirements
Jan 2013
Issues with Turnaround Requirements
In , sub-clause & 8.2.2, it states that both the Tx to Rx and Rx to Tx turnaround times are less than or equal to aTurnaroundTime.
If the Tx-Rx device is allowed aTurnaroundTime to prepare for the first symbol/chip, but the Rx-Tx device starts transmitting in less than that time (as is allowed by the definition) then the Tx-Rx device will miss part of the PPDU.
aTurnaroundTime
Device 1
Tx Data Frame
Receiver Ready
Device 2
Receiver Ready
Tx ACK Frame
Rx-TxTurnaround
IFS < aTurnaroundTime
Slide 5
Rick Powell (Microsemi)

6. Issues with Turnaround Requirements, cont.
Jan 2013
Issues with Turnaround Requirements, cont.
For proper reception of the ACK Frame, the turnaround of the Tx-Rx device must be less than or equal to the turnaround of the Rx-Tx device.
Another way to state this is: The IFS from Data Frame to Ack Frame must be greater than or equal to aTurnaroundTime, if the maximum allowable Tx to Rx turnaround interval is aTurnaroundTime.
Device 1
aTurnaroundTime
Tx Data Frame
Receiver Ready
Device 2
Receiver Ready
Tx ACK Frame
IFS >= aTurnaroundTime
Slide 6
Rick Powell (Microsemi)

7. Issues with Turnaround Requirements, cont.
Jan 2013
Issues with Turnaround Requirements, cont.
The IFS interval following an ACK to the next Data Frame is LIFS, if the previous MPDU was greater than 18 octets.
LIFS is defined as 40 symbol periods, but aTurnaroundTime is 12 symbols or 1 msec, both of which can be less than LIFS.
There are cases such as the LIFS below where the turnaround time must be greater than, aTurnaroundTime.
Does this violate the PHY turnaround requirement as defined in and 8.2.2?
tack
LIFS
Device 1
Long Frame
RxRdy
Long Frame
tack
LIFS
Device 2
Receiver Ready
ACK
Receiver Ready
LIFS> aTurnaroundTime
Slide 7
Rick Powell (Microsemi)

8. Issues with Turnaround Requirements, cont.
Jan 2013
Issues with Turnaround Requirements, cont.
Tack turnaround IFS is defined in sub-cause to be between SIFS and SIFS + aUnitBackoffPeriod.
Tack can be greater than aTurnaroundTime.
Does this violate the PHY turnaround requirement as defined in and 8.2.2?
tack
LIFS
Device 1
Long Frame
RxRdy
Long Frame
tack
LIFS
Device 2
Receiver Ready
ACK
Receiver Ready
LIFS> aTurnaroundTime
Slide 8
Rick Powell (Microsemi)

9. Jan 2013
Conclusions
The PHY requirement for turnaround needs to be modified. It should state that this “maximum” time is the capability of the PHY, but not necessarily the behavior of the PHY in all cases.
If an LIFS interval is required during a turnaround, then it should not imply a violation of the PHY turnaround requirement.
The actual turnaround time is variable, and should be controlled by the MAC based on its IFS requirements and the turnaround capability of the PHY.
If the MAC needs more processing time before transmitting an ACK or responding to a Data Request, this should be a defined as an IFS requirement, not a PHY turnaround requirement.
The requirements must also be written in such a way that it ensures that the Rx-Tx turnaround does not occur before the Tx-Rx turnaround.
MAC timeout requirements, such as macAckWaitDuration, should take into account both IFS and PHY turnaround requirements.
Slide 9
Rick Powell (Microsemi)