doc.: IEEE f Submission March, 2010 Andy Ward, UbisenseSlide 1 Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs) Submission Title: Integration lengths for extended-range PHY Date Submitted: 16 th March 2010 Source: Andy Ward, Ubisense Address: St Andrew’s House, St Andrew’s Road, Chesterton, Cambridge, CB4 1DL, ENGLAND Voice: , FAX: , Re: TG4f Call for Preliminary Proposals and Final Proposals, IEEE P f Abstract: Integration lengths for extended-range PHY Purpose:To be considered by TG4f Notice:This document has been prepared to assist the IEEE P 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 acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P

doc.: IEEE f Submission March, 2010 Andy Ward, UbisenseSlide 2 Integration lengths for extended-range PHY Andy Ward Ubisense

doc.: IEEE f Submission March, 2010 Andy Ward, UbisenseSlide 3 Overview Discuss trade-offs involved in selecting the pulse-to-symbol ratio Show how system frequency accuracy is important Discuss ‘state-of-the-art’ in cheap crystal technology

doc.: IEEE f Submission March, 2010 Andy Ward, UbisenseSlide 4 Extended-range UWB PHY Rather than using one pulse-per-symbol mapping, we use m pulses-per-symbol Still very simple for transmitter to generate Still relatively simple for receivers as well! Use a different PRF (2MHz) so that receivers can do tone detection to figure out what type of packet is coming Integrate the pulses at the receiver to increase signal to noise –For example, integration of four pulses increases SNR by 6dB (ideally) System will be average-power limited rather than peak-power limited –Long pulse trains will mean that ‘average in 1ms’ trick can’t be used –However, once you are average-power limited, there is no (regulatory) limit to the length of packet you can transmit at the same power

doc.: IEEE f Submission March, 2010 Andy Ward, UbisenseSlide 5 Ideal coherent integrator performance

doc.: IEEE f Submission March, 2010 Andy Ward, UbisenseSlide 6 System frequency accuracy The previous graph assumes perfect frequency sources throughout the system When the frequency sources differ, the pulses won’t line up perfectly in the coherent receiver –So the achievable gain is less As the number of pulses-per-symbol increases, frequency accuracy gets more important –You’re integrating over a longer time… –…so the amount of drift between the transmitter and receiver increases… –…so the pulses at the start and end of the integration period don’t line up so well

doc.: IEEE f Submission March, 2010 Andy Ward, UbisenseSlide 7 Effect of system frequency accuracy on integration gain

doc.: IEEE f Submission March, 2010 Andy Ward, UbisenseSlide 8 System frequency accuracy vs centre frequency There is some dependence of integration performance (with non-ideal frequency sources) on system centre frequency As CF increases, it takes less drift to make the pulses align less well in the coherent integrator –So you need a higher frequency accuracy to maintain integration gain at high pulse-to-symbol numbers

doc.: IEEE f Submission March, 2010 Andy Ward, UbisenseSlide 9 System frequency accuracy vs CF

doc.: IEEE f Submission March, 2010 Andy Ward, UbisenseSlide 10 What is a reasonable frequency tolerance to aim for? Remember – this is ONLY relevant to systems that want to do coherent integration. You don’t need a super crystal if you don’t care about this! Plain crystal – maybe 10ppm TCXO – maybe 0.3ppm 0.5ppm TCXOs over -40C to 85C are now readily available –Used for GPS/GSM –Very cheap Need to cope with other effects too: –Initial frequency accuracy (tune out at manufacture) –Crystal ageing (either tune out during use, or pre-age) As a data point (nothing more!), system frequency accuracy budget in current Ubisense systems is better than 2ppm –Better than 1ppm would be achievable at same cost today