1. <month year>
<month year>
doc.: IEEE <doc#>
doc.: IEEE <doc#>
08/07/2010
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [ Potential Channel Tracking Limitations in OFDM Mode]
Date Submitted: [ July 2010 ]
Source: [Charles Razzell]
Company: [Maxim Integrated Products] [
Re: [ TG4g comments on LB51 (e.g., #1422)]
Abstract:
Purpose: Provide data to assess potential limitations of the proposed OFDM pilot scheme
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
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2. 08/07/2010
Background
A specific OFDM pilot scheme has been proposed for g
This document seeks to estimate the limits of the channel disturbances that can be successfully tracked using the proposed pilot scheme
Decision directed tracking is not considered at this time.
Knowing these limitations should inform any discussion about the merits of the existing scheme.
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3. Pilot Scheme for Option 2
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Pilot Scheme for Option 2
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4. Pilot Scheme Overlaid with 8us 2-tap Channel
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Pilot Scheme Overlaid with 8us 2-tap Channel
8us * C = 2.4km flight time difference.
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5. Pilot Scheme Overlaid with 8us 2-tap Channel
08/07/2010
Pilot Scheme Overlaid with 8us 2-tap Channel
8us * C = 2.4km flight time difference.
Under-sampled
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6. Pilot Scheme Overlaid with 8us 2-tap Channel
08/07/2010
Pilot Scheme Overlaid with 8us 2-tap Channel
8us * C = 2.4km flight time difference.
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7. Rate of change of channel
<month year>
doc.: IEEE <doc#>
08/07/2010
Rate of change of channel
If the channel is quasi-stationary over 9 OFDM symbols, the additional frequency domain samples can be “safely” used without additional processing.
Assume we will allow 6 of rotation over 9 x 120us, time allowed for full rotation is 360/6 * 9 * 120 = 64.8ms  Fdmax <= 23Hz.
This could be considered the approximate limit for zero-order hold interpolation.
To get higher Doppler tolerance, sophisticated 2- dimensional interpolation is required over the time and frequency, preferably using Weiner filtering.
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Conclusions
For delay spreads exceeding 3.5 ms, more than one pilot tone set must be incorporated in the estimation to avoid under- sampling.
When all 3 sets of pilot tones are used, the upper limit of delay spread tolerance is approximately 9.6 ms.
Simple zero-order interpolation in the time domain will not suffice in the presence of Doppler reflectors moving at typical automotive speeds.
A 2-dimensional interpolator using Weiner estimation in both time and frequency dimensions has the potential to yield sufficiently robust channel estimation to both Doppler and Delay spread effects.
Detailed simulations are recommended to evaluate the performance limitations of such interpolation schemes beyond the first-order limitations shown here.
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9. Thank you <month year> doc.: IEEE 802.15-<doc#> 08/07/2010
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