Doc.: IEEE 802.11-08/0508r1
IEEE P802.11
Wireless LANs
|Normative Text Proposal for LB#133 Comment Resolution on Co-Located Interference Reporting |
|Date: 2008-11-10 |
|Author(s): |
|Name |Company |Address |Phone |email |
|Jing Zhu |Intel |2111, NE 25th Ave., |+1 (503) 265 7073 |jing.z.zhu@ |
| | |Hillsboro, OR 97124 | | |
|Jon Rosdahl |CSR |Highland, UT | |jrosdahl@ |
Introduction
Wireless communication systems which operate in overlapping or adjacent regions of spectrum may be mutually interfering when co-located. The common example of this interference is between IEEE 802.11 [1] and Bluetooth [4] (or IEEE 802.15.1) transceivers operating in the un-licensed 2.4 GHz Industrial Scientific and Medical (ISM) band, however other combinations are relevant such as Ultra-Wide Band (UWB) and IEEE 802.11 in the 5 GHz band, or IEEE 802.16(e) (WiMAX/Mobile WiMAX) and IEEE 802.11 operating in the 2.4 GHz band.
The severity of interference depends on the degree of co-location. When sufficient physical separation can be achieved between transmitter and receiver, RF isolation means that interference is normally limited to cases of direct spectral overlap, and probability of information loss is dependent on relative signal strengths at the respective receivers. Mutually interfering transceivers integrated into a converged device may be co-located on the same circuit board, or even the same die. In such situations the front-end overload mode of interference generally dominates, where the large ratio of local interferer power to desired receive signal strength has the net effect of severely desensitising the co-located receiver.
An 802.11 station (STA) which is co-located with another mutually interfering transceiver may be subject to periods of time when it is either:
a) not permitted to transmit in order to protect the reception of a communication to the co-located transceiver, or
b) unable to receive due to normal or front-end overload interference caused by a transmission from the co-located transceiver, or
c) unable to either transmit or receive due to the use by the co-located transceiver of a shared component requiring mutually exclusive access (e.g. a switched antenna).
Depending on the nature of the non-802.11 co-located transceiver and the traffic which it is communicating, the pattern of interference to which the 802.11 STA is subjected may be predictable. Examples of technologies which can impose predictable interference patterns on an 802.11 STA include Bluetooth using Synchronous Connection-Oriented (SCO), Extended SCO (eSCO), or the sniff low-power mode, and WiMAX with its fixed length Time Division Duplex (TDD) frame structure.
In such cases, knowledge of interference patterns at peer 802.11 STAs can enable scheduling of communications with the co-located STA to avoid periods of interference. Even if the interference is stochastic or continuous, awareness of this at the peer 802.11 STA is beneficial in enabling more intelligent Adaptive Modulation and Coding (AMC) and Transmit Power Control (TPC) decisions. Though no explicit provision for exchange of such information is made in the base IEEE 802.11 standard, the draft IEEE 802.11v amendment [2] specifies such a mechanism for co-located interference reporting between 802.11 STAs.
The 802.11v amendment provides for co-located interference reporting through the definition of two new management action frame formats and description of their use. We herein propose changes to the amendment to allow stations that can identify the type of interference to which they are subject, to communicate this to a peer in the Co-located Interference Response frame.
Discrimination of Receive and Transmit Interference
An 802.11 STA which is co-located with another transceiver may be subject to modes of interference which prevent it from receiving, transmitting, or both. Reception at the 802.11 STA can be prevented by receiver desense caused by a co-located transmission, or lack of access to a shared antenna which is switched between the co-located transceivers on the occasion where the other transceiver has been given priority. Transmission at the 802.11 STA can be blocked by a Packet Traffic Arbiter (PTA) [3] to protect reception at a co-located transceiver, or may be prevented by lack of access to a shared antenna which is switched between the co-located transceivers on the occassion where the other transceiver has been given priority.
Interference, or front-end arbitration preventing reception at the 802.11 STA will be herein referred to as receive desense interference, and PTA or front-end arbitration decisions preventing transmission STA will be herein referred to as transmit inhibition interference, with the terms used reflecting the net effect on the co-located 802.11 STA as observed by a peer.
STAs subject only to transmit inhibition interference at a given time can still receive transmissions from a peer STA, however transmit inhibition will prevent positive acknowledgement of received unicast frames with immediate acknowledgement policy. Broadcast or multicast frames and unicast frames which have a QoSNoAck policy or allow a delayed block acknowlegement may still be transmitted to the co-located STA by the peer STA. Further, if the duration of the period of transmit inhibition interference is known by the peer STA (having been communicated using a Co-located Interference Response frame) then the peer STA may commence transmission of a unicast frame requiring acknowledgement if transmission of the acknowledgement will not be required until after the period of transmit inhibition has lapsed[1].
To allow STAs to take advantages of this we propose to add a new 1-bit field into Co-located Interference Response frames to indicate that its 802.11 PHY receive functionalities (e.g. Receive PLCP) are able to perform without degradation regardless of the reported co-located interference.
References
1] IEEE Std 802.11-2007, “IEEE Standard for information technology – Telecommunications and information exchange between systems – Local and metropolitan area networks – Specific requirements – Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”. Jun. 2007.
2] IEEE P802.11v/D2.00, “Draft standard for information technology – Telecommunications and information exchange between systems – Local and metropolitan area networks – Specific requirements – Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications – Amendment 9: Wireless Network Management”. Mar. 2008.
3] IEEE Std 802.15.2-2003, “IEEE recommended practice for information technology – Telecommunications and information exchange between systems – Local and metropolitan area networks – Specific requirements – Part 15.2: Coexistence of Wireless Personal Area Networks with Other Wireless Devices Operating in Unlicensed Frequency Bands”. Aug. 2003.
4] “Specification of the Bluetooth System: Wireless Connections Made Easy. Version 2.1 + EDR”. Jul. 2007.
5] IEEE P802.11s/D1.08, “Draft standard for information technology – Telecommunications and information exchange between systems – Local and metropolitan area networks – Specific requirements – Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications – Amendment: Mesh Networking”. Jan. 2008.
6] IEEE 802.11-08/0233r2, Co-located Interference Reporting
Proposed Text Change
7.3.2.80 Co-located Interference Report element
Change Figure v69 of 7.3.2.80 as follows:
| | | | | | |
| |Element ID |Length |Report Period |Interference Level |Interference Level |
| | | | | |Accuracy/Interference |
| | | | | |Index / Receive |
| | | | | |Indicator |
|Octets: |1 |1 |1 |1 |1 |
| | | | | | |
| |Interference |Interference Burst|Interference Start Time |Interference Center |Interference Bandwidth |
| |Interval |Length | |Frequency | |
|Octets |4 |4 |4 |2 |2 |
Figure v69: Co-located Interference Report element format
Change Figure v70 of 7.3.2.80 as follows:
| |B0-B3 |B4-B6 |B7 |
| |Expected Accuracy |Interference Index |Receive Indicator |
|Bits |4 |4 3 |1 |
Figure v70—Interference Level Accuracy/Interference Index/Receive Indicator field format
Add a new 9th paragraph as follows:
Option 1: [The bit field set to 1 indicates that the performance degradation of the STA is only caused by the impact of the reported co-located interference on its 802.11 PHY transmit functionalities (e.g. Transmit PLCP). Otherwise, the bit is set to 0.]
Option 2: [The bit field set to 1 indicates its 802.11 PHY receive functionalities (e.g. Receive PLCP) are able to perform without degradation regardless of the reported co-located interference, and the performance degradation of the STA is caused by the impact of the reported co-located interference on its 802.11 PHY transmit funcitonlaities (e.g. Transmit PLCP) or other reason. The value of 0 is reserved.]
Option 3: [The bit indicates the nature of co-located interference. If set, the bit indicates that the interference causes transmit inhibition only, meaning that the transmitting STA can be addressed while subject to the interference, but will be unable to respond.]
Co-located Interference Reporting
Change the 5th paragraph as follows:
A STA accepting a request for automatic Co-located Interference reporting shall send a Co-located Interference Response frame to the requesting STA if it detects that a co-located radio or another co-located interferer is causing performance degradation to its 802.11 receiver the STA. The STA that has not received any Colocated Interference Request frame may send a Co-located Interference Response frame autonomously with the Dialog Token field set to zero. The Dialog Token field is set to the nonzero value received in the Colocated Interference Request frame which was used to enable automatic responses. If co-located interference is present, the reporting STA shall send Co-located Interference Response frames with interval indicated by the Report Period field or if the level of the interference caused by co-located interferer is significantly changing or if the time characteristics of the interference is significantly changing. The Report Period timer shall restart whenever the reporting STA sends out a Co-Located Interference Response frame. The criteria a reporting STA uses for determining significant changes are internal to the reporting STA and outside the scope of this standard.
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[1] These ideas can be trivially extended to other automated control responses.
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Abstract
This submission contains the normative text to resolve IEEE 802.11v LB#133 comments with CID 302~308.
The text is aligned with P802.11v-D3
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