Doc.: IEEE 802.15-04/315r0 Submission July 2004 Celestino A. Corral et al., MotorolaSlide 1...
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Transcript of Doc.: IEEE 802.15-04/315r0 Submission July 2004 Celestino A. Corral et al., MotorolaSlide 1...
July 2004
Celestino A. Corral et al., MotorolaSlide 1
doc.: IEEE 802.15-04/315r0
Submission
Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Multi-Band OFDM Interference on In-Band QPSK Receivers]Date Submitted: [13 July, 2004]Source: [Celestino A. Corral, Shahriar Emami, Gregg Rasor] Company [Motorola]
Address [8000 W. Sunrise Blvd., Plantation, Florida, USA 33322]Voice:[954-723-3864], FAX: [954-723-3883]
Re: []
Abstract: [This document provides simulation and theoretical results that demonstrate MB-OFDM is an extremely harmful type of interference to wideband in-band QPSK systems such as TVRO receivers. A MB-OFDM interference model is derived based on simulation and analytical results.]
Purpose: [For discussion by IEEE 802.15 TG3a.]Notice: This document has been prepared to assist the IEEE P802.15. 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 P802.15.
July 2004
Celestino A. Corral et al., MotorolaSlide 2
doc.: IEEE 802.15-04/315r0
Submission
Multi-band OFDM Interference on In-Band QPSK Receivers
Celestino A. Corral, Shahriar Emami and Gregg Rasor
Motorola8000 W. Sunrise Blvd.
Plantation, Florida
July 13, 2004
July 2004
Celestino A. Corral et al., MotorolaSlide 3
doc.: IEEE 802.15-04/315r0
Submission
Motivation Goal: To characterize the impact of Multi-band OFDM UWB
interference on in-band broadband wireless system like C-band satellite receivers.
Note: Multi-band OFDM (MB-OFDM) and Multi-band UWB (MB-UWB) requires power scaling of the waveform to compare competing technologies based on interpretation of FCC rules.
Model of MB-OFDM interference derived. This model is bounded by periodically gated AWGN and impulsive MB-OFDM interference.
Reconcile observed test results of MB-OFDM interference on satellite receivers as presented in ABQ meeting.
July 2004
Celestino A. Corral et al., MotorolaSlide 4
doc.: IEEE 802.15-04/315r0
Submission
Multi-band UWB Power FCC states power spectral
density for UWB devices must be -41.2 dBm/MHz in band between 3.1 and 10.6 GHz
Since multi-band signals hop over a selected band of frequencies, the power spectrum is scaled by the hop and averaged over the band.
The resulting power spectral density is made equal to a system over any arbitrary band.
PSDlevel
Multi-band spectrum
Integrate the spectrum over band and average by band
To implement equal PSD over hop bandwidth, we need
requiring a power scaling.
f1 f2fx
July 2004
Celestino A. Corral et al., MotorolaSlide 5
doc.: IEEE 802.15-04/315r0
Submission
Multi-band UWB Power
Equatepower
Both systems transmit with equal power at a given range.
Assuming DS-UWB bandwith is 2 GHz and MB-OFDM bandwidth is 528 MHz.
Actual MB-OFDM PSD over its transmission bandwidth.
July 2004
Celestino A. Corral et al., MotorolaSlide 6
doc.: IEEE 802.15-04/315r0
Submission
In-band Receiver Filters
fc > 3 GHz
BW < 40 MHz
Q > 50 typical
Band-passFilterFrequencyResponse
High-Q band-pass filter can be approximated by [1]:
complex frequency of band-pass filter
complex frequency of low-pass prototype filter
Step response of band-pass filter has low-pass impulse response envelope:
[1] A. Papoulis, The Fourier Integral and its Application, Chap. 7, New York: McGraw-Hill, 1962.[2] G. E. Valley, Jr., and H. Wallman, Vacuum Tube Amplifiers, New York: McGraw-Hill, 1948.
Temporal characteristics of high-Q band-pass filter determined by low-pass prototype. This includes rise time, which obeys the following relation [2]:
Rise time of band-pass filter determined by 3dB bandwidth of low-pass prototype.
Not a function of filter approximationor order
July 2004
Celestino A. Corral et al., MotorolaSlide 7
doc.: IEEE 802.15-04/315r0
Submission
In-band Receiver FiltersBand-pass filter rise time for 40 MHz bandwidth.
Received power:
Filter responds quite fast and observes virtually full power of filtered MB-OFDM signal.
Portion due to filter bandwidth Portion due to temporal response
Filter with slower response.
in dB
July 2004
Celestino A. Corral et al., MotorolaSlide 8
doc.: IEEE 802.15-04/315r0
Submission
Coherent Detection QPSK Simulation
Detector
WindowMatched
Filter
Block Diagram of Simulator
• Assume perfect synchronization
• Assume perfect phase estimation
• Input filter bandwidth wide enough so rise time not a factor
• Interference bandwidth is very large relative to filter bandwidth and approaches thermal noise as in [3].
[3] J. Brandao, “Interference effect on the performance of PSK and QAM systems,” IEE Proceedings I, vol. 138, pp. 331—337, Aug. 1991.
• QPSK system at 27.05 Msym/sec, similar to Dubai EDTV at 4020 MHz.
• 0 < Eb/No < 30 dB.
• 1000 symbols, 500 packets per Eb/No set.
• Sample rate: 120 samples/QPSK symbol.
• Multi-band OFDM and all gated noise is 896 samples long.
NoiseSource
July 2004
Celestino A. Corral et al., MotorolaSlide 9
doc.: IEEE 802.15-04/315r0
Submission
Simulation Results: Gated Noise
3 dB
July 2004
Celestino A. Corral et al., MotorolaSlide 10
doc.: IEEE 802.15-04/315r0
Submission
Simplified Theoretical ReasonProbability of symbol error for QPSK [4]
Q-function for communication
Gated noise duty cycle: Np is time interference is present, Ns is time interference is silent.
Probability of error is due only to when the noise is present Pep; for the case it is silent Pes = 0:
Q is very sensitive to under high signal-to-noise (SNR), meaning small changes in duty cycle will impact probability of error when minor changes in bit energy is most significant.
equivalent “quasi-fading” of bit energy relative to fixed noise power No
Actual error must be scaled by duty cycle as this is time interference is present
[4] J. G. Proakis, Digital Communications, 4th Ed., Boston, MA: McGraw-Hill, 2001.
July 2004
Celestino A. Corral et al., MotorolaSlide 11
doc.: IEEE 802.15-04/315r0
Submission
Theoretical vs. Simulated Results: Gated Noise
Simulated
July 2004
Celestino A. Corral et al., MotorolaSlide 12
doc.: IEEE 802.15-04/315r0
Submission
Simulation Results: MB-OFDM
9 dB
3 hops
AWGN
July 2004
Celestino A. Corral et al., MotorolaSlide 13
doc.: IEEE 802.15-04/315r0
Submission
Simulation Results: Impulsive MB-OFDM
Theory
Worst-case peak-to-average power assumed for each MB-OFDM symbol
?? dB
July 2004
Celestino A. Corral et al., MotorolaSlide 14
doc.: IEEE 802.15-04/315r0
Submission
Simulation Results: 3 hops
Gated AWGN lower bound
Impulsive MB-OFDM upper bound
MB-OFDM
July 2004
Celestino A. Corral et al., MotorolaSlide 15
doc.: IEEE 802.15-04/315r0
Submission
MB-OFDM Interference Model
Amplitude distribution of AWGN Amplitude distribution of MB-OFDM Amplitude distribution of Impulsive MB-OFDM
Multi-band OFDM transmissions can be long or bursty:
• Long transmissions have amplitude distribution that approaches AWGN• Bursty transmissions can be potentially impulsive• We need to combine the Gaussian and impulsive characteristics
July 2004
Celestino A. Corral et al., MotorolaSlide 16
doc.: IEEE 802.15-04/315r0
Submission
MB-OFDM Interference ModelClass A Model [5]: Interference has “gaps” in time; i.e., non-zero probability of
time during which there is no interference in the receiver.
Interference time Receiver bandwidth
Model Incorporates Gaussian and Impulsive Factors:
impulse index
Peak factor (PAP)Carrier-to-noise ratio
for M-ary QAM
std. dev.
mean power ratio
Average symbol error rate:
[5] D. Middleton, “Non-Gaussian noise models in signal processing for telecommunications: New methods and results for class A and class B noise models,” IEEE Trans. Inform. Theory, vol. 45, pp. 1129—1149, May 1999.
July 2004
Celestino A. Corral et al., MotorolaSlide 17
doc.: IEEE 802.15-04/315r0
Submission
MB-OFDM Model
Simulated Model
July 2004
Celestino A. Corral et al., MotorolaSlide 18
doc.: IEEE 802.15-04/315r0
Submission
Filtered MB-OFDM40 MHz
9 subcarriers
The filtered waveform is generated and then scaled to obtain same power as AWGN over the packet.
The waveform is then scaled by a factor of 9/128 (in number of subcarriers) to reduce the level to a filtered amount. This is almost the same amount as 40/528 (in MHz), which corresponds to the desired power reduction relative to the full bandwidth of the 128-subcarrier symbol:
Received power:
Assumed 0 dB9/128 factor(40/528 factor)
July 2004
Celestino A. Corral et al., MotorolaSlide 19
doc.: IEEE 802.15-04/315r0
Submission
Simulation Results: Filtered MB-OFDM
July 2004
Celestino A. Corral et al., MotorolaSlide 20
doc.: IEEE 802.15-04/315r0
Submission
Conclusions Multi-band OFDM and Multi-band UWB equate power spectral
density by scaling power in the hop and averaging over the entire hop bandwidth. This equates the transmitted power of a Multi-band system with DS-UWB over a fixed bandwidth.
Probability of symbol error shows gated noise is akin to quasi-fading of bit energy relative to fixed AWGN level.
The gated and scaled interference is more harmful than AWGN depending on the hop depth. Gated noise interference produces performance 3 dB from theory; MB-OFDM produces performance 8 dB from theory.
Multi-band OFDM can be impulsive. Under worst-case peak-to-average power Multi-band OFDM is a significant interferer to in-band coherent detection QPSK receivers.
MB-OFDM model was derived based on combination of Gaussian and impulsive characteristics of MB-OFDM.
July 2004
Celestino A. Corral et al., MotorolaSlide 21
doc.: IEEE 802.15-04/315r0
Submission
Narrowband Filter Response
Wideband Filter Response
Only upper portion of response captured
Narrowband Filter Response
• Fast rise time
• Delay applies across entire response
• Full level of interference reached within response time of the filter, and present for most of the interference time.
• Total power captured
• Slow rise time
• Delay applies across entire response
• Full level of interference not reached within response time of the filter.
• Total power can be captured if rise time and interference time are about equal.
Narrowband filters “favor” narrow pulsed interference; full level of interference is not captured.
July 2004
Celestino A. Corral et al., MotorolaSlide 22
doc.: IEEE 802.15-04/315r0
Submission
Backup: Gated Noise Results for Other Hops
Increasing hop depth results in more degradation at high SNR.
3 713
July 2004
Celestino A. Corral et al., MotorolaSlide 23
doc.: IEEE 802.15-04/315r0
Submission
Backup: MB-OFDM Results for Other Hops
Increasing hop depth results in more degradation at high SNR.
3 7
13
July 2004
Celestino A. Corral et al., MotorolaSlide 24
doc.: IEEE 802.15-04/315r0
Submission
Backup: Impulsive MB-OFDM Results for Other Hops
Increasing hop depth results in more degradation at high SNR.
37
13
July 2004
Celestino A. Corral et al., MotorolaSlide 25
doc.: IEEE 802.15-04/315r0
Submission
Backup: Gated Noise Theoretical Results for Other Hops
3 713
July 2004
Celestino A. Corral et al., MotorolaSlide 26
doc.: IEEE 802.15-04/315r0
Submission
Backup: MB-OFDM Class A Model Results for Other Hops
July 2004
Celestino A. Corral et al., MotorolaSlide 27
doc.: IEEE 802.15-04/315r0
Submission
Properties of Q and Quasi-Fading Working with Q(x) directly is difficult. We use approximation
[4] P. L. Borjesson and C-E. W. Sundberg, “Simple approximations of the error function Q(x) for communication applications,” IEEE Trans. Commun., vol. COM-27, pp. 639—643, March 1979.
where [4]:
as then so decays more rapidly
Decay factor:
Value
July 2004
Celestino A. Corral et al., MotorolaSlide 28
doc.: IEEE 802.15-04/315r0
Submission
Peak-to-Average Power “Tracking”
Peak-to-average of AWGN and MB-OFDM “track” over different hop depths.