Transcript 15-04-0476-00-004a-sensitivity-location-estimates-to-snr.ppt

September 10, 2004
doc.: IEEE 802.15-04-0476-00-004a
Project: IEEE 802.15 Study Group for Wireless Personal Area Networks (WPANs)
Submission Title: [On Sensitivity of Location Estimates to SNR]
Date Submitted: [10 September, 2004]
Source: [Shahriar Emami, Celestino A. Corral, Gregg Rasor]: Company1 [Freescale Semiconductor],
Address [8000 W. Sunrise Blvd., Plantation, FL 33322], Voice:[(954) 723-3854], FAX: [(954) 723-3883],
Re: [Accuracy of Location Estimates]
Abstract: [The relationship between SNR and location accuracy is explored. A region with reasonable
location accuracy is found.]
Purpose: [To gain an understanding of parameters that impact location accuracy of 802.15 TG4a. This
work should assist designers in predicting the location accuracy of their system.]
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.
Contribution
Slide 1
Shahriar Emami, Freescale Semiconductor
September 10, 2004
doc.: IEEE 802.15-04-0476-00-004a
On Sensitivity of Location Estimates
to SNR
Shahriar Emami, Celestino A. Corral and Gregg Rasor
Freescale Semiconductor
Contribution
Slide 2
Shahriar Emami, Freescale Semiconductor
September 10, 2004
doc.: IEEE 802.15-04-0476-00-004a
Outline
• Introduction
- Prior Art
- Open Issues
• Proposed Approach
- Root Raised Cosine (RRC) Pulse Shape
- Raised Cosine (RC) Pulse Shape
• Error Statistics & Achievable Accuracy
• Conclusions
Contribution
Slide 3
Shahriar Emami, Freescale Semiconductor
September 10, 2004
doc.: IEEE 802.15-04-0476-00-004a
Introduction
• The impact of AWGN on the accuracy of measurement
was previously investigated:
- R. Enns, “The Effect of AWGN on Accuracy of Time of
Arrival Detection,” IEEE802.15-04-0335-00-004a, July
2004.
• Outstanding questions:
- What is the desirable SNR in AWGN channels?
- Does pulse shaping impact the location estimates?
Contribution
Slide 4
Shahriar Emami, Freescale Semiconductor
September 10, 2004
doc.: IEEE 802.15-04-0476-00-004a
Approach
• Pulse shapes
- Root raised cosine
- Raised cosine
• Various roll-off factors
(0.15-0.85)
• A length 31 PN
sequence was utilized
• Peak detector at the
receiver
Contribution
Auto Correlation Function of RRC Shaped Stream
2500
2000
1500
1000
500
0
-500
-1000
-1000
Slide 5
-800
-600
-400
-200
0
200
Delay in Samples
400
600
800
1000
Shahriar Emami, Freescale Semiconductor
September 10, 2004
doc.: IEEE 802.15-04-0476-00-004a
RRC Pulse Shape -1
Root Raised Cosine (RRC) Shaped Pulses
140
Roll Off = 0.15
Roll Off = 0.5
Roll Off = 0.85
Mean Estimation Error in Samples
120
100
80
60
40
20
0
-25
-20
-15
-10
-5
SNR (dB)
0
5
10
15
Mean location estimate does not vary with roll-off factor
Contribution
Slide 6
Shahriar Emami, Freescale Semiconductor
September 10, 2004
doc.: IEEE 802.15-04-0476-00-004a
RRC Pulse Shape - 2
Root Raised Cosine (RRC) Shaped Pulses
10
Root Raised Cosine (RRC) Shaped Pulses
Roll Off = 0.15
Roll Off = 0.5
Roll Off = 0.85
8
7
6
Region 2
5
4
3
2
1
0
0.8
-20
0.6
-18
-16
-14
-12
-10
SNR (dB)
-8
-6
-4
-2
0
Region 1
Root Raised Cosine (RRC) Shaped Pulses
140
0.4
Roll Off = 0.15
Roll Off = 0.5
Roll Off = 0.85
120
Mean Estimation Error in Samples
Mean Estimation Error in Samples
1
Mean Estimation Error in Samples
• There are three distinct
regions:
Roll Off = 0.15
Roll Off = 0.5
Roll Off = 0.85
9
0.2
0
0
5
10
15
SNR (dB)
100
80
Region 3
60
40
20
-25
Contribution
Slide 7
-24.5
-24
-23.5
-23
-22.5
SNR (dB)
-22
-21.5
-21
Shahriar Emami, Freescale Semiconductor
September 10, 2004
doc.: IEEE 802.15-04-0476-00-004a
RRC Pulse Shape - 3
Root Raised Cosine (RC) Shaped Pulses
omni antenna
above house
Variance of Estimation Error in Samples
350
Roll Off = 0.15
Roll Off = 0.5
Roll Off = 0.85
300
250
200
150
omni antenna
near ground
100
50
0
-25
-20
-15
-10
-5
SNR (dB)
0
5
10
15
Variance of the location estimate does not vary with roll-off factor
Contribution
Slide 8
Shahriar Emami, Freescale Semiconductor
September 10, 2004
doc.: IEEE 802.15-04-0476-00-004a
RC Pulse Shape - 1
Dry
soil
Raised Cosine (RC) Shaped Pulses
Wet soil and
wet roof
140
200 m
Roll Off = 0.15
Roll Off = 0.5
Roll Off = 0.85
200 m
Mean Estimation Error in Samples
120
100
80
60
40
20
0
-25
-20
-15
-10
-5
SNR (dB)
0
5
10
15
Mean location estimate does not vary with roll-off factor
Contribution
Slide 9
Shahriar Emami, Freescale Semiconductor
September 10, 2004
doc.: IEEE 802.15-04-0476-00-004a
RC Pulse Shape - 2
Raised Cosine (RC) Shaped Pulses
Variance of Estimation Error in Samples
350
Dry soil
Wet soil
Roll Off = 0.15
Roll Off = 0.5
Roll Off = 0.85
300
250
200
150
100
50
0
-25
-20
-15
-10
-5
SNR (dB)
0
5
10
15
Variance of the location estimate does not vary with roll-off factor
Contribution
Slide 10
Shahriar Emami, Freescale Semiconductor
September 10, 2004
doc.: IEEE 802.15-04-0476-00-004a
Error Statistics
Dry soil
Dry soil
Mean and variance of estimation error when SNR = -5 dB
CDF
Histogram of Error
250
1
0.9
Number of Occurances
200
SNR = -5 dB
0.8
0.7
150
TX antenna
placed at 1.5m
height and at the side of
the house
0.6
0.5
100
0.4
0.3
50
0.2
0.1
0
-8
-6
Contribution
-4
-2
0
2
Estimation Error (Samples)
4
6
0
-1
8
Slide 11
0
1
2
3
4
Estimation Error (Samples)
5
6
7
Shahriar Emami, Freescale Semiconductor
September 10, 2004
doc.: IEEE 802.15-04-0476-00-004a
Achievable Location Accuracy
Chip Rate = 10 Mc/s and 100 samples/chip
- RRC pulse shaping
- Rc = 10 Mc/s
- 100 samples/chip
180
Resolution with 95% confidence (cm)
• Consider a UWB
transmitter with:
160
140
120
100
80
60
40
20
-10
-5
0
5
10
15
SNR (dB)
• Sub meter accuracy with SNR>0 dB
Contribution
Slide 12
Shahriar Emami, Freescale Semiconductor
September 10, 2004
doc.: IEEE 802.15-04-0476-00-004a
Conclusions
• There are three regions in terms of location
estimate accuracy.
• To have a good accuracy you need to operate in
region 1.
• Location accuracy appears to be independent of
pulse shape and roll-off factor.
• Sub-meter accuracy can be achieved if
SNR > 0 dB.
Contribution
Slide 13
Shahriar Emami, Freescale Semiconductor