Gerald Chouinard, CRC Slide 1 doc.: IEEE 802.22-11/0022r0 Submission February 2011 Best static tone locations for extracting upstream channel impulse response and fine ranging N am e C om pany A ddress Phone em ail G erald Chouinard Com m unications Research Centre, Canada 3701 Carling A ve. Ottaw a, Ontario Canada K 2H 8S2 (613)998-2500 [email protected]Authors: Notice: This document has been prepared to assist IEEE 802.22. 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://standards.ieee.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 Carl R. Stevenson <[email protected]> as early as possible, in written or electronic form, if patented Abstract This contribution presents the results of a parametric study conducted at CRC in order to identify the performance of a number of upstream static subcarriers sets in an attempt to maximize the dynamic range of echo detection capability while trying to maximize the echo delay range before aliasing starts to appear and maximize the bandwidth for a minimum number of static subcarriers in the P802.22 system upstream. This is in response to comment #209 to the P802.22 D1.0.
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Doc.: IEEE 802.22-11/0022r0 Submission February 2011 Gerald Chouinard, CRCSlide 1 Best static tone locations for extracting upstream channel impulse response.
doc.: IEEE /0022r0 Submission February 2011 Gerald Chouinard, CRCSlide 3 Outline 1.Extraction of the Complex Channel Impulse Response 2.Generation of the Prototype Function (i.e., High-resolution Complex Channel Impulse Response) 3.Channel deconvolution process 4.Some subcarrier patterns for channel deconvolution Examples of perfect Channel Impulse Responses Examples of Prototype Functions Resulting Channel Echo Functions for various subcarrier patterns 5.Summary of the exercise 6.Summary of the results 7.Observations on the results 8.Proposal
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Gerald Chouinard, CRCSlide 1
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Best static tone locations for extracting upstream channel impulse response and fine ranging
Notice: This document has been prepared to assist IEEE 802.22. 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://standards.ieee.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 Carl R. Stevenson <[email protected]> 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 <[email protected]>.
AbstractThis contribution presents the results of a parametric study conducted at CRC in order to identify the performance of a number of upstream static subcarriers sets in an attempt to maximize the dynamic range of echo detection capability while trying to maximize the echo delay range before aliasing starts to appear and maximize the bandwidth for a minimum number of static subcarriers in the P802.22 system upstream. This is in response to comment #209 to the P802.22 D1.0.
3. Channel deconvolution process4. Some subcarrier patterns for channel deconvolution
• Examples of perfect Channel Impulse Responses• Examples of Prototype Functions• Resulting Channel Echo Functions for various subcarrier patterns
5. Summary of the exercise6. Summary of the results7. Observations on the results8. Proposal
Gerald Chouinard, CRCSlide 23
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Subcarrier patterns for channel deconvolutionDownstream:• Frame preamble
– Long training sequence: 840 subcarriers (one every two subcarriers)– Maximum echo delay range without aliasing: 149.4 µsec
Upstream:• CDMA Ranging burst
– Extensive search was conducted to find the optimum set of unevenly spread 56 subcarriers that would allow a multipath detection range of 30 µsec (echoes appearing beyond this range on the right would create aliasing and start to appear on the left of the range as ‘close-in’ pre-echoes)
– The resulting perfect channel impulse response was found to be limited to 20 dB sidelobe rejection (see slide 30) which is insufficient (re.: 22-10-0178r1). The corresponding Prototype Function (see slide 35) reduced this rejection to 17 dB.
– It was decided to expand the search to 2, 3 and 6 sub-channels (56, 84 and 168 subcarriers) with evenly spread subcarriers to achieve better performance.
Gerald Chouinard, CRCSlide 24
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Outline1. Extraction of the Complex Channel Impulse Response2. Generation of the Prototype Function
3. Channel deconvolution process4. Some subcarrier patterns for channel deconvolution
• Examples of perfect Channel Impulse Responses• Examples of Prototype Functions• Resulting Channel Echo Functions for various subcarrier patterns
5. Summary of the exercise6. Summary of the results7. Observations on the results8. Proposal
Gerald Chouinard, CRCSlide 47
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Summary of the exercise
• The channel deconvolution process described in previous contributions was used to establish the relative performance of various sets of static subcarriers used on the upstream for the channel profile model B.
• Beyond the localization performance of the various prototype functions resulting from different sets of static subcarriers, the resulting Channel Echo Functions were studied.
• The performance of the Channel Echo Functions were analyzed in terms of the width of the impulses representing the channel echoes and the residual ringing where peaks could be interpreted as false echoes.
• Minimum false echo rejection values were noted to establish the dynamic range of the process to identify real echoes before false echoes, resulting from unwanted ringing, start to appear.
• Simulations were first done without noise but were repeated with SNR= 6 dB (i.e., the minimum SNR for operation of the system at QPSK, rate: 1/2) to verify the effect of additive white Gaussian noise.
Gerald Chouinard, CRCSlide 48
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Outline1. Extraction of the Complex Channel Impulse Response2. Generation of the Prototype Function
The iterative process to identify echoes• The exercise was repeated by using an iterative process
where each echo for which the amplitude and delay was identified was removed for the Channel Impulse Response to improve the detection performance of the process.
1. Largest echo, normalized to 1, is localized in the Channel Echo Function obtained from the correlation process (amplitude and delay are noted)
2. The values of the prototype function corresponding to this maximum echo are subtracted from the Channel Impulse Response
3. The resulting new Channel Impulse Response is correlated with the Prototype Function
4. The resulting new Channel Echo Function is scaled up to bring the second largest echo to an amplitude of 1 (scaling factor is recorded to note the amplitude difference)
5. Steps 1-4 are repeated until all echoes have been removed and what remains is noise.
6. The concatenated scaling factors represent the dynamic range of the iterative process.
Gerald Chouinard, CRCSlide 51
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Iterative echo detection process
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
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1Correlation Response for 84 subcarriers in 3.6 MHz
Precise time samples
Am
plitu
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84 subcarriers regularly spaced every 12 subcarriers
over 3.38 MHz
Gerald Chouinard, CRCSlide 52
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Iterative echo detection process
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Precise time samples
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1Subtraction of echo
Time samples
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84 subcarriers regularly spaced every 12 subcarriers
over 3.38 MHz
Gerald Chouinard, CRCSlide 53
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Iterative echo detection process
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
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Precise time samples
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10 20 30 40 50 60 70 80 90 100 110 1200
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1Subtraction of echo
Time samples
Rel
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84 subcarriers regularly spaced every 12 subcarriers
over 3.38 MHz
Gerald Chouinard, CRCSlide 54
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Iterative echo detection process
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
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Precise time samples
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10 20 30 40 50 60 70 80 90 100 110 1200
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1Subtraction of echo
Time samples
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e am
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de (d
B)
84 subcarriers regularly spaced every 12 subcarriers
over 3.38 MHz
Gerald Chouinard, CRCSlide 55
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Iterative echo detection process
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
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1Correlation Response for 84 subcarriers in 3.6 MHz
Precise time samples
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10 20 30 40 50 60 70 80 90 100 110 1200
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1Subtraction of echo
Time samples
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e am
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84 subcarriers regularly spaced every 12 subcarriers
over 3.38 MHz
Gerald Chouinard, CRCSlide 56
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Iterative echo detection process
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
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Precise time samples
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10 20 30 40 50 60 70 80 90 100 110 1200
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1Subtraction of echo
Time samples
Rel
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de (d
B)
84 subcarriers regularly spaced every 12 subcarriers
over 3.38 MHz
Gerald Chouinard, CRCSlide 57
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Iterative echo detection process
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
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Precise time samples
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10 20 30 40 50 60 70 80 90 100 110 1200
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Time samples
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84 subcarriers regularly spaced every 12 subcarriers
over 3.38 MHz Left over of earlier detected
echoes
Gerald Chouinard, CRCSlide 58
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Iterative echo detection process
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
x 104
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1Correlation Response for 84 subcarriers in 3.6 MHz
Precise time samples
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10 20 30 40 50 60 70 80 90 100 110 1200
0.1
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1Subtraction of echo
Time samples
Rel
ativ
e am
plitu
de (d
B)
84 subcarriers regularly spaced every 12 subcarriers
over 3.38 MHz Left over of the earlier detected
echoes
Gerald Chouinard, CRCSlide 59
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Iterative echo detection process
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
x 104
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1Correlation Response for 84 subcarriers in 3.6 MHz
Precise time samples
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10 20 30 40 50 60 70 80 90 100 110 1200
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1Subtraction of echo
Time samples
Rel
ativ
e am
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de (d
B)
84 subcarriers regularly spaced every 12 subcarriers
over 3.38 MHz Left over of the earlier detected
echoes
Gerald Chouinard, CRCSlide 60
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Iterative echo detection process
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
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1Correlation Response for 84 subcarriers in 3.6 MHz
Precise time samples
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10 20 30 40 50 60 70 80 90 100 110 1200
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1Subtraction of echo
Time samples
Rel
ativ
e am
plitu
de (d
B)
84 subcarriers regularly spaced every 12 subcarriers
over 3.38 MHz
Gerald Chouinard, CRCSlide 61
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Iterative echo detection process
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
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1Correlation Response for 56 subcarriers in 3 MHz
Precise time samples
Am
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56 subcarriers irregularly spaced every 10 subcarriers
over 2.8 MHz
Gerald Chouinard, CRCSlide 62
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Iterative echo detection process
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
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Time samples
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56 subcarriers irregularly spaced every 10 subcarriers
over 2.8 MHz
Gerald Chouinard, CRCSlide 63
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Iterative echo detection process
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
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Time samples
Rel
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e am
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56 subcarriers irregularly spaced every 10 subcarriers
over 2.8 MHz
Gerald Chouinard, CRCSlide 64
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Iterative echo detection process
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
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10 20 30 40 50 60 70 80 90 100 110 1200
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1Subtraction of echo
Time samples
Rel
ativ
e am
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de (d
B)
56 subcarriers irregularly spaced every 10 subcarriers
over 2.8 MHz
Gerald Chouinard, CRCSlide 65
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Iterative echo detection process
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
x 104
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1Correlation Response for 56 subcarriers in 3 MHz
Precise time samples
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10 20 30 40 50 60 70 80 90 100 110 1200
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1Subtraction of echo
Time samples
Rel
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56 subcarriers irregularly spaced every 10 subcarriers
3. Channel deconvolution process4. Some subcarrier patterns for channel deconvolution
• Examples of perfect Channel Impulse Responses• Examples of Prototype Functions• Resulting Channel Echo Functions for various subcarrier patterns
5. Summary of the exercise6. Summary of the results7. Observations on the results8. Proposal
Gerald Chouinard, CRCSlide 69
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Observations on the results
• Effective bandwidth occupied by static subcarriers– The effective bandwidth over which the static subcarriers are spread has only a small
influence on the width of the impulses in the Channel Echo Function. In other words, the accuracy achievable on the precise time position of the echoes reduces only slightly with a reduction of the effective bandwidth, i.e., the accuracy of the precise echo delays is preserved even in the case of narrower bandwidths.
– However, it should be remembered that larger effective bandwidths will reduce the effect of echo smearing due to the Nyquist limitation related to the capability to differentiate closely spaced echoes for a given signal bandwidth, i.e., echo discrimination and exact delay will be better preserved with a larger signal bandwidth.
• Maximum echo delay range that can be characterized without aliasing– The maximum echo delay range that can be covered without aliasing is linearly related
to the static subcarrier spacing: larger the spacing is, shorter the maximum delay range is.
– The delay ranges covered by the 802.22 system for cyclic prefix 1/4, 1/8, 1/16 and 1/32 are: 75, 37.5, 18.75 and 9.4 µs respectively. The delay range covered by the downstream preamble is 149.3 µs. This is to be compared to the delay ranges resulting from the various upstream training options which vary from 10 µs to 30 µs.
Gerald Chouinard, CRCSlide 70
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Observations on the results (Cont’d)
• Tradeoff between occupied bandwidth and available delay range– There is a tradeoff, for a given number of sub-channels allocated to static
subcarriers, between the effective bandwidth over which the static subcarriers are spread and the maximum echo delay range that can be characterized without aliasing
• Regular versus irregular subcarrier spacing– Regular subcarrier spacing give better and more predictable sidelobe levels as
compared to irregularly sub-sampled subcarriers in the frequency domain (see the second row of the 2 sub-channel group on slide 49).
• False echo rejection performance– The downstream LTS preamble occupying 30 sub-channels offers some 30 dB false
echo rejection (41 dB with the iterative process)– If 6 sub-channels were used in the upstream for static subcarriers, the false echo
rejection would still be around 30 dB but the rejection would decrease to 22-24 dB in presence of large amount of noise (SNR= 6 dB) (33 dB and 22 dB respectively with the iterative process)
Gerald Chouinard, CRCSlide 71
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Observations on the results (Cont’d)
• False echo rejection performance (cont’d)– The false echo rejection reduces from 29 dB to 11 dB for 3 sub-channels with the
decrease in subcarrier spacing. However, the highest values are achieved at the cost of a reduced maximum echo delay range. Lower rejection values are found when noise is present.
– The false echo rejection reduces from 16.3 dB to 4.2 dB for 2 sub-channels with the decrease in subcarrier spacing. Again, the highest values are achieved at the cost of a reduced maximum echo delay range (down to 15 delay range, a 10 µs delay range example was included for convenience but is clearly insufficient). Slightly lower rejection values are found when noise is present.
– However, when an iterative process is used to identify echoes (once an echo is identified, it is removed from the Channel Impulse Function to ease the identification of the next one), much better false echo performance can be achieved (between 25 and 40 dB) when using regularly spaced subcarriers.
– Such performance is limited at low SNR (SNR= 6 dB is used as the threshold fpr proper operation of the 802.22 WRAN system). Performance in the range of 16 to 20 dB can be achieved with the iterative process.
– Irregularly spaced ranging subcarriers has a limited performance even in the case of the iterative echo removal process (limited to 10 dB range independent of noise).
Gerald Chouinard, CRCSlide 72
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Outline1. Extraction of the Complex Channel Impulse Response2. Generation of the Prototype Function
3. Channel deconvolution process4. Some subcarrier patterns for channel deconvolution
• Examples of perfect Channel Impulse Responses• Examples of Prototype Functions• Resulting Channel Echo Functions for various subcarrier patterns
5. Summary of the exercise6. Summary of the results7. Observations on the results8. Proposal
Gerald Chouinard, CRCSlide 73
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
Proposal• It is proposed to use 3 sub-channels for the upstream CDMA static
carriers, with the following parameters:– Total number of subcarriers = 84– Subcarrier spacing = 16
• The performance of this upstream static subcarrier arrangement is:– Total effective bandwidth = 4.5 MHz (i.e., 80% of total bandwidth giving sufficient
protection against echo smearing)– Maximum echo delay range (before aliasing starts to appear) = 18.7 µs
(i.e., 63% of the 30 µsec echo delay range)
– Minimum false echo rejection = 19.6 dB (17.4 dB at SNR = 6 dB) 39.6 dB (19.2 dB at SNR = 6 dB) with
iterations• It is proposed to make the necessary modifications to section 8.6 of the
P802.22 D1.0 to reserve 3 sub-channels for the static subcarriers on the upstream and indicate the exact location of these static subcarriers in Table 201.
Gerald Chouinard, CRCSlide 74
doc.: IEEE 802.22-11/0022r0
Submission
February 2011
References1. IEEE P802.22™/ DRAFTv7.0 Draft Standard for Wireless Regional Area Networks Part 22:
Cognitive Wireless RAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Policies and procedures for operation in the TV Bands, December 2009
2. 22-06-0206-00-0000-ranging-with-ofdm-systems.ppt3. 22-10-0055-0000-Multicarrier-ranging.ppt4. 22-10-0054-02-0000_OFDM-based Terrestrial Geolocation.ppt5. 22-10-0178-01-0000 Updated set of CDMA ranging tones.doc