Video over 802.11 Research Date: 2007-05-10 Authors: May 2007 May 2007 doc.: IEEE 802.11-yy/xxxxr0 May 2007 Video over 802.11 Research Date: 2007-05-10 Authors: Notice: This document has been prepared to assist IEEE 802.11. 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 802.11. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures <http:// ieee802.org/guides/bylaws/sb-bylaws.pdf>, 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 stuart@ok-brit.com 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 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at <patcom@ieee.org>. Alex Ashley, NDS Ltd Alex Ashley, NDS Ltd

May 2007 doc.: IEEE 802.11-yy/xxxxr0 May 2007 Abstract A description of our research in to streaming video over IEEE 802.11 networks in the domestic environment. Alex Ashley, NDS Ltd Alex Ashley, NDS Ltd

May 2007 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 (satellite) cable Installing Ethernet twisted pair cabling Wireless Looked at many options, e.g. DVB-T, UWB, DECT, IEEE 802.11 802.11 was the closest fit at a sensible price point Alex Ashley, NDS Ltd

May 2007 doc.: IEEE 802.11-yy/xxxxr0 May 2007 RF Study Commissioned a paper study in to RF propagation within the home T R LOS Alex Ashley, NDS Ltd Alex Ashley, NDS Ltd

RF Simulations Static modelling for RF in the home environment May 2007 RF Simulations Static modelling for RF in the home environment Link losses in various types of home 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 are 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 802.11 MAC Allows dynamic simulations of a variety of home layouts and options within 802.11 Alex Ashley, NDS Ltd

Static Modelling Results May 2007 Static Modelling Results Digital AV services can be successfully and safely transmitted in typical UK housing stock Frequency allocation to avoid interference with nearby homes is a big issue Alex Ashley, NDS Ltd

Ray Tracing Modelling Results May 2007 Ray Tracing Modelling Results Significant amount of signal at receiver is multi-path Using Rayleigh channel modelling in the static model was the correct choice Compared to dynamic aspects such as noise and movement, differences between ray-tracing results and static model results were minor Alex Ashley, NDS Ltd

Dynamic Modelling Results May 2007 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 5GHz has problems reaching whole home On some channels due to regulatory power limits Building materials attenuation much higher at 5GHz Alex Ashley, NDS Ltd

Dynamic Modelling Results (2) May 2007 Dynamic Modelling Results (2) EDCA becomes non-linear at about 2 x 3 MBit/sec Alex Ashley, NDS Ltd

Real-World Tests 4 different access points and 2 different NICs May 2007 Real-World Tests 4 different access points and 2 different NICs In our homes and those of friends & family Reception characteristics were recorded for each access point in 4 different rooms and also whilst mobile Packet error rate Bit error rate Error rate post FEC correction, using only valid packets Error rate post FEC correction, also using packets with invalid FCS Alex Ashley, NDS Ltd

Real-World Test Results May 2007 Real-World Test Results Marked difference between 11g and 11a Frames received, but with incorrect FCS more common at 5GHz In frames with incorrect FCS, roughly 1-2% of bytes are in error At 2.4GHz packets tended to be completely lost Similar performance amongst 11g equipment Higher gain aerial improved BER but only small PER improvement Antenna diversity produced results similar to 11a / 11g trend Errors seam to occur in bursts Alex Ashley, NDS Ltd

Error Correcting Codes May 2007 Error Correcting Codes Video is latency and jitter sensitive Retransmissions built in to 802.11 are problematic One option is to not retransmit But packet losses cause lousy video quality Adding Forward Error Correction information can deal with the packet losses But increases the bitrate and adds (a fixed) latency Server Forward error correction encoding and data interleaving De-interleaving and FEC decoding Client Wireless network Alex Ashley, NDS Ltd

Error Correction Codes May 2007 doc.: IEEE 802.11-yy/xxxxr0 May 2007 Error Correction Codes Error free without re-transmissions Alex Ashley, NDS Ltd Alex Ashley, NDS Ltd

May 2007 Future FEC Work May be desirable to use a hybrid system with FEC plus a limited amount of retransmission Need to decide how decide when to use retransmissions Fixed maximum number of retransmissions Maximum amount of time between packet arrival at the wireless network and its successful transmission Only request a retransmission if the FEC cannot correct the error May be possible to improve FEC performance Populate known data such as IP headers and repeated data such as MPEG PSI tables to reduce error rate before FEC Alex Ashley, NDS Ltd

Current & Future Work Improved Inter-network coexistence May 2007 Current & Future Work Improved Inter-network coexistence Co-operation between BSS (time sharing) Better transmit power control (reduce BSS overlap) Using FEC on an encrypted BSS Using frames with failed FCS gives huge gain to FEC, but does not work if frame was encrypted after FEC was applied Investigate use of multicast Most current APs only use basic rate for multicast traffic How to negotiate “best” rate (esp with all the modes in 11n!) Are errors correlated (all STAs loose the same packet) or different per STA? Alex Ashley, NDS Ltd

VTS PAR / 5 Criteria Need for the project Broad Market Potential May 2007 VTS PAR / 5 Criteria Need for the project 802.11 becomes over-crowed at fairly modest video traffic levels when every home operates simultaneously Slightly below bitrates commonly used for SD broadcasts Using 11n will probably solve this But we also want to do HD video Broad Market Potential TV almost ubiquitous (e.g. >94% in many regions) Technical Feasibility We have found some MAC layer modifications that seem to help Alex Ashley, NDS Ltd

May 2007 References Alex Ashley, NDS Ltd