doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 1 OBSS Simplification Date: Authors:

doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 2 Abstract Overlapping BSS is a big issue for 11aa because of the popularity of television and the limited number of non- overlapping channels. There have been many presentations highlighting the complexity of trying to solve the OBSS issue. This presentation contains a summary of our research on OBSS and proposes a pragmatic simplification to reduce the complexity the OBSS issue.

doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 3 Project History Started looking at video distribution within the home about 5 years ago –Aim of allowing every home to distribute video to any room in the house and allow every home to do so simultaneously –Considered both wired and wireless options Wired –Re-use existing (coax, powerline) cable –Installing Ethernet twisted pair cabling Wireless –Looked at many options, e.g. DVB-T, UWB, DECT, IEEE – was the closest fit at a sensible price point

doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 4 RF Study Commissioned study in to RF propagation within the home TR LOSLOS

doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 5 RF Simulations Static modelling for RF in the home environment –Link losses in various types of home (based upon Defense Advanced Research Projects Agency (DARPA) results) –Required transmit power –Zone of interference outside of each home –Number of channels required for every home to be active simultaneously Ray-tracing –How realistic were the Rayleigh model assumptions in the static model? Dynamic modelling –Using mathematical model to calculate link losses and apply this to a dynamic model of the MAC –Allows dynamic simulations of a variety of home layouts and options within

doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 6 Dynamic Modelling Results 2.4GHz becomes over-crowed at fairly modest traffic levels when every home operates simultaneously –Difficult to reliably stream a couple of streams at 3MBit/sec or higher without DLS or TPC 5GHz much better, but can have problems reaching whole home –On some channels due to regulatory power limits –IC design power limits –Building materials attenuation higher at 5GHz

doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 7 Example Domestic Application Multiple dwelling unit Many homes within radio range of each other Homes share channels either due to insufficient channels or imperfect channel selection

doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 8 Typical UK Housing Stock: Houses Sufficient power to reach all parts of the home will radiate in to neighbouring properties Estimate other homes will be affected At least 8 channels needed for scalable solution

doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 9 Real-World Tests 5 different access points and 3 different NICs In our homes and those of friends & family Reception characteristics were recorded for each access point in multiple rooms and also whilst mobile

doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 10 Experimentation Conclusions 2.4GHz is practically a lost cause in terms of improving the OBSS issue –Only 1 channel with 11n 5GHz band much more encouraging –In a (mythical) “perfect” channel plan, each BSS only has to share with one other BSS –In reality probably needs to be a robust solution for 2 to 3 overlapping BSS.

doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 11 OBSS Chains If we can bound the problem to 2 or 3 OBSS, that makes the problem easier to solve But what happens if this causes a chain of BSS?

doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 12 Breaking chains Several proposals have discussed the concept of “leader” APs –Either first on the channel or by election Could we “rig” the election of leaders to reduce chains to manageable proportions?

doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 13 Proposal Use an election process to choose leaders Election is triggered every time an AP starts to use a channel Election process is designed to reduce chain length If chain length is over a set limit (e.g. 3), drop back to existing (11e) features

doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 14 EDCA Admission Control A lot of focus has been applied to OBSS in relation to HCCA –Probably because HCCA CAPs are particularly impacted by OBSS However, EDCA-AC is also an issue to consider Total consumed medium time is not simply the sum of each BSS –Not every STA overlaps –Some traffic can happen simultaneously without causing impairment.

doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 15 BSS1 BSS2BSS3 AP 1 AP 2 AP 3 Proposal Use neighbour reports to “over allocate” EDCA-AC when there is some separation between BSS, otherwise use a simple summation of medium time

doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 16 BSS1 BSS2 BSS3 AP 1 AP 2 AP 3 In this example there is more overlap with each BSS and therefore the EDCA-AC medium time is close to BSS1 + BSS2 + BSS3 This only works if chains can be broken in to manageable links

doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 17 Conclusions Several presentations have given estimates of BSS overlap in various housing configurations –Estimates of 1 or 2 overlaps in most configurations The amount of overlap outside of the 2.4GHz band could be reasonably manageable The problem becomes significantly more complex if chains of overlaps need to be supported So let’s architect our solution to break chains in to manageable portions

doc.: IEEE /0045r0 Submission Jan 2009 Alex Ashley, NDS LtdSlide 18 References r2 OBSS Analysis of Channel Requirements