11-11-0306-01-00ac-comment-resolution-tpc
IEEE P802.11
Wireless LANs
Abstract
Submission for Draft P802.11ac_D0.1 comment resolution. The document addresses various comments related to transmit power limit configuration for wider bandwidth such as 80MHz, 160MHz, and non-contiguous 80+80Mhz channel bandwidths.
Submission addresses Draft P802.11ac_D0.1 comments 559, 1030, 1031, 1032, 1453, 1454, 1455, and 1525.
Introduction
Interpretation of a Motion to Adopt
A motion to approve this submission means that the editing instructions and any changed or added material are actioned in the TGac Draft. This introduction is not part of the adopted material.
Editing instructions formatted like this are intended to be copied into the TGac Draft (i.e. they are instructions to the 802.11 editor on how to merge the text with the baseline documents).
TGac Editor: Editing instructions preceded by “TGa c Editor” are instructions to the TGa c editor to modify existing material in the TGac draft. As a result of adopting the changes, the TGac editor will execute the instructions rather than copy them to the TGac Draft.
Submission Note: Notes to the reader of this submission are not part of the motion to adopt. These notes are there to clarify or provide context.
Discussion:
With the support of very wide bandwidths in VHT, the transmission signal may be subject to various transmit power constraint given by the regulatory body. For example in US the transmit power for UNII-1 and UNII-2 are different, where the 160MHz transmission signal can be transmitted across these bands.
20 MHz
Tx Power Limit: 800mW (20/40/80MHz), 80mW (80+80MHz)
Figure 1. Example of transmission in different transmit power regulatory domains
There are two components to limiting transmission power for 802.11, the first is the transmit power information given by the Country information element, and the second is power constraint element which give further restrictions on top of the maximum transmit power specified by the Country IE.
Since the VHT transmission can be also transmitted in non-contiguous manner and also support dynamic switching between 20, 40, 80, 160/80+80 MHz bandwidths, we must be able to indicate non-contiguous bands which are backward compatible. Figure 1 shows some examples of how the transmit power may change for
different transmission bandwidths.
After some discussion the use of Country IE, we received comments where there might be issues with legacy STAs interpreting the Country IE with operating triplet with operating extension identifier with 201 or above. Because of this we propose to define new information element with the needed information. In the proposed text we call this information element ‘VHT Transmit Power Envelope element ’.
The three fields ‘Channel Center Frequency Segment ’, ‘Segment Channel Width’, and
‘Maximum Transmit Power ’ are repeated as needed, as determined by the ‘Number of Segments ’ field.
Octets: 1
1
1
1
1
1
The power constraint element contains the local maximum transmit power in the current channel. This element can be used in both contiguous and non-contiguous transmission signals, but if the wide band signal is being transmitting in multiple regulatory transmit power limit domains, then we may need to further indicate how differentiate the transmit power limit for smaller bandwidth and large bandwidths. For this we propose to add one element which extends the power constraint element. We propose to extend it by also including bandwidth information so that VHT devices can understand for which bandwidths the local power constraint applies. Since if the operating channel bandwidth is either 20 or 40 MHz, there is no need for this extended power constraint element,
we propose only to signal the extended power constraint element if the AP is operating in channel widths lager than 80MHz or above.
Octets: 1 1 1
Table 2. Extended Power Constraint element
The two fields ‘Channel Width’and ‘Local Power
Constraint’ are repeated as needed, as determined by the
length field.
Octets: 1 1 1 1
It may be possible to extend the Channel Power Management element used in 11af to inform the transmit power limits but the said information element provides various TV White Space specific functionalities. The functionalities included in the CPM element are signaling of changes of channel availability, signaling of Maximum Transmit Power switching from the regulatory database, and signaling of Channel (and Power) switching. The support of such element with all the functionalities therein in the 5GHz is rather not clear and may cause additional implementation needed for VHT 5GHz only support devices.
To keep the channel switch mechanism simple and considering the VHT is only supported in the 5GHz, we propose to extend the existing transmit power and power capabilities information element to support wider bandwidths. Proposed Resolution:
Agree in principle to finalize the TBD fields as described in Draft P802.11ac_D0.1 comments 559, 1030, 1031, 1032, 1453, 1454, 1455, and 1525.
Editing instructions:
7.2.3.1 Beacon frame format
TGac editor: Insert the VHT Transmit Power Envelope element and the Extended Power Constraint element in Table 7-8 Beacon frame body after order 41 and before order Last:
7.2.3.9 Probe Response frame format
TGac editor: Insert the VHT Transmit Power Envelope element and the Extended Power Constraint element in Table 7-15 Probe Response frame body after order 39 and before order Last-l:
7.3.2 Information elements
TGac editor: Insert the following row in table 7-16, and renumber the reserved values accordingly:
Table 7-16—Element IDs
TGac editor: Insert the following VHT Transmit Power Envelope element section to the last subsection of 7.3.2: 7.3.2.64 VHT Transmit Power Envelope element
The VHT Transmit Power Envelope element contains the information necessary to convey the maximum transmit power for various transmission bandwidth of VHT devices. The format of the VHT Transmit Power Envelope element in shown in Figure 7-95o27b (VHT Transmit Power Envelope element format).
The three fields ‘Channel Center Frequency
Segment’, ‘Segment Channel Width’, and
‘Maximum Transmit Power’ are repeated as needed,
as determined by the ‘Number of Segments’ field.
Octets: 1 1 1 1 1 1
Figure 7-95o27b—VHT Transmit Power Envelope element format
The Number of Segments field which is 1 octet in length defines the number of segment triplets (Channel Center Frequency Segment, Segment Channel Width, and Maximum Transmit Power).
The Channel Center Frequency Segment field which is 1 octet in length is set to n, the channel number corresponding to the channel center frequency of bandwidth segment.
The Segment Channel Width field which is 1 octet in length is set to the number of channels in the bandwidth segment.
The Maximum Transmit Power field defines the maximum transmit power limit of the transmission bandwidth defined by the VHT Transmit Power Envelope element. The Maximum Transmit Power field is a signed number and is 1 octet in length. It indicates the local maximum power, in dBm, allowed to be transmitted. In case the VHT Transmit Power Envelope element format contains more than 1 segment then the multiple Maximum Transmit Power field all indicate the same maximum transmit power field which applies to the entire operating BSS channel width.
TGac editor: Change the following section 7.3.2.15 Power Constraint element as follows:
7.3.2.15 Power Constraint element
The Power Constraint element contains the information necessary to allow a STA to determine the local maximum transmit power in the current primary 20MHz and primary 40MHz channel. The format of the Power Constraint element is shown in Figure 7-52 (Power Constraint element format).
TGac editor: Insert the following section 7.3.2.15a after section 7.3.2.15 Power Constraint element:
7.3.2.15a Extended Power Constraint element
The Extended Power Constraint element contains the information necessary to allow a STA to determine the local maximum transmit power in each of the operating channel bandwidths. The format of the Power Constraint element is shown in Figure 7-52a (Extended Power Constraint element format).
These two fields are
repeated, as determined by
Octets:
Figure 7-52a—Extended Power Constraint element format
The Channel Width field is coded with the identical coding and meaning as Channel Width subfield of the VHT operational Information element fields in section 7.3.2.62 (VHT Operation element). The unspecified values in the Channel Width field are reserved.
The Local Power Constraint field is coded as an unsigned integer in units of decibels. The local maximum transmit power for a channel is thus defined as the maximum transmit power level specified for the channel in the VHT Transmit Power Envelope element minus the local power constraint specified for the channel (from the MIB) in the Extended Power Constraint element.
The Extended Power Constraint element is included in Beacon frames, as described in 7.2.3.1 (Beacon frame format), and Probe Response frames, as described in 7.2.3.9 (Probe Response frame format). The use of Extended Power Constraint elements is described in 11.8.2 (Specification of regulatory and local
maximum transmit power levels).
TGac editor: Change the following section 11.8.2 as follows:
11.8.2. Specification of regulatory and local maximum transmit power levels
A STA shall determine a regulatory maximum transmit power for the current channel. The STA shall use the minimum of the following:
— Any regulatory maximum transmit power received in a Country element from the AP in its BSS or another STA in its IBSS and
— Any regulatory maximum transmit power for the channel in the current regulatory domain known by the STA from other sources.
A STA shall determine a local maximum transmit power for the current channel by selecting the minimum of the following:
— Any local maximum transmit power received in the combination of a Country element and a Power Constraint element from the AP in its BSS or another STA in its IBSS and
— Any local maximum transmit power received in the combination of a VHT Transmit Power Envelope element and a Extended Power Constraint element from the AP in its BSS or another STA in its IBSS and
— Any local maximum transmit power for the channel regulatory domain known by the STA from other sources.
The Local Power Constraint field of any transmitted Power Constraint element and Extended Power Constraint element shall be set to a value that allows the mitigation requirements to be satisfied in the current channel.
Any calculation of the local maximum transmit power for the channel shall ensure the mitigation requirements for the channel in the current regulatory domain can be satisfied. The conservative approach is to set the local maximum transmit power level equal to the regulatory maximum transmit power level minus the mitigation requirement. However, it may be possible to satisfy the mitigation requirement using a higher local maximum transmit power level. A lower local maximum transmit power level may be used for other purposes (e.g., range control, reduction of interference).
The regulatory and local maximum transmit powers may change in a STA during the life of a BSS. However, network stability should be considered when deciding how often or by how much these maximums are changed. The regulatory and local maximum transmit powers shall not change during the life of an IBSS.
An AP in a BSS and a STA in an IBSS shall advertise the regulatory maximum transmit power for that STA’s operating channel in Beacon frames and Probe Response frames using a Country element. An AP in a BSS and a STA in an IBSS shall advertise the local maximum transmit power for that STA’s operating channel in Beacon frames and Probe Response frames using either the combination of a Country element and a Power Constraint element or the combination of a VHT Transmit Power Envelope element and an Extended Power Constraint element.
Where TPC is being used for radio measurement without spectrum management, the inclusion of a Power Constraint element and an Extended Power Constraint element in Beacon and Probe Response frames shall be optional.