doc.: IEEE /0916r0 Submission September 2005 Slide 1 Adjacent channel interference and its impact on the Mesh MAC Date: Authors: Notice: This document has been prepared to assist IEEE 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 grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE Working Group. If you have questions, contact the IEEE Patent Committee Administrator at. Syed Aon Mujtaba Agere Systems Mathilde Benveniste Avaya Labs 233 Mt Airy Road Basking Ridge, NJ American Parkway, Allentown, PA

doc.: IEEE /0916r0 Submission September 2005 Slide 2 Adjacent channel interference What is it? Adjacent channel interference (ACI) is caused by energy on channels that are adjacent in the RF spectrum –ACI is serious when the receiver is close to a transmitter on an adjacent channel 2.4 – GHz // 5 GHz band Adjacent Channels Frequency

doc.: IEEE /0916r0 Submission September 2005 Slide 3 ACI in a WLAN Why ACI is not a problem in a WLAN BSS –BSS stations use a single radio; all radios in a BSS use the same channel, but at different times to transmit and receive ACI in neighboring BSSs –Stations in different BSSs may use adjacent channels –ACI becomes a problem if the interfering signal exceeds a certain threshold, which is data rate dependent, and is shown in the table on the next slide. –Typically, this means that the interferer is closer to the receiver than the desired transmitter

doc.: IEEE /0916r0 Submission September 2005 Slide 4 Receiver Performance Requirements (from a spec) ACI Threshold

doc.: IEEE /0916r0 Submission September 2005 Slide 5 Transmit Spectrum Mask (from a spec) Desired Adjacent Alternate

doc.: IEEE /0916r0 Submission September 2005 Slide 6 Multi-radio mesh points For large meshes, multi-radio MPs are needed closer to the portal of the mesh –Traffic increases geometrically with the number of hops Load =x Load =3x Portal Load =7x Load =15x Load =31x

doc.: IEEE /0916r0 Submission September 2005 Slide 7 Adjacent channel interference in WiFi bands A multi-radio MP cannot use two adjacent channels in the same unlicensed WiFi band to receive and transmit on two radios at the same time [1, 2, 3]: –TX power can be 20 dBm (or higher) –RX sensitivity can be as low as -82 dBm (or lower) –Transmit spectral mask only drops the adjacent channel by 28 dB (alternate by 40 dB) –The system – as is – will not work!!! –{Unless there is at least 46 (30) dB isolation between RX and TX for adjacent (alternate) channels.} ([2] shows 35 dB isolation) – directional antennas, or the radios are time synchronized) s needs to consider this issue

doc.: IEEE /0916r0 Submission September 2005 Slide 8 References [1] R. Draves, J. Padhye, and B. Zill, “Routing in multi-radio, multi-hop wireless mesh networks,” MobiCom’04. [2] J. Robinson, K. Papagiannaki, C. Diot, N. Gao, and L. Krishnamurthy, “Experimenting with a multi-radio mesh networking testbed,” WiNMee [3] J. H. Winters, “Smart antennas and their application to wireless ad hoc networks,” PIMRC’05.