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Doc: IEEE 15-05-0383-02-004a19 July 2005

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)(WPANs)

Submission Title: [Non-coherent ranging results with a-priori knowledge of noise variance]Date Submitted: [24 June 2005]Source: [Ismail Guvenc, Zafer Sahinoglu, Andy Molisch, Philip Orlik, Mitsubishi Electric]Contact: Zafer SahinogluVoice:[+1 617 621 7588, E-Mail: zafer@merl.com]Abstract: [This document provides performance results of non-coherent ranging

receivers, under the assumption that noise variance is accurately estimated and available a-priori]

Purpose: [To help objectively evaluate ranging proposals under consideration]

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.

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Doc: IEEE 15-05-0383-02-004a19 July 2005

Outline

• Signal waveforms• Receiver architectures• Threshold and search back• Simulations• Summary• Recommendations

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Objective

• Study feasibility of non-coherent ranging• Evaluate ranging performance of various proposals

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Signal Parameters

Signal Energy ConditionerChannel

Characteristics

Signal Energy Collector

Signal

TOAEstimate

Signal Energy Edge Detector

Generic Architecture for Ranging

• Received signal energy is collected• Energy vector is processed to suppress noise artifacts and enhance signal containing

parts• Edge detection is performed

channel

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4 pulses

One Bit

Always EmptyAlways Empty Always Empty

4-pulses

Option-III (Ternary Sequences)

…………………………

1 2 3 314 5 6 7 8 30

Pulse Repetition Interval ~ 62.5ns

Option-IV (Pulse PPM)

Tp = 4ns

Tf = ~125ns

PRP ± TH

Option-I (Burst PPM) The Other Bit

Proposed System Parameters (With Same # Pulses per unit time)

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Technical Differences and CommonalitiesPulse OOK (option-III) Burst PPM (option-I) Pulse OOK (option-IV)

Energy Integration period (for ranging)

2~4ns 2~4ns 2~4ns

Type of receiver that can receive this Common signaling preamble

Coherent, differential & energy detector

Coherent, differential & energy detector

Coherent, energy detector

Symbol Duration 2us 2us 2us

Pulses per symbol 16 16 16

Pulses per microsecond 8 8 8

Edge per symbol 16 4 16

# of edges per us 8 2 8

Power per pulse P P P

Peak to Side Lobe Ratio (PSLR) - periodic

0 (at the cost of increased noise variance)

N/A 1/N

Peak Signal to Interference Ratio 6dB N/A 3dB

Zero Correlation Zone (periodic) Yes (symbol wide) N/A Yes (fraction of a symbol)

Noise Variance (noise only region) in 2us of preamble

32 Units 4 Units 16 Units

Noise Floor Level 1 Unit (16+, 15- in the bipolar correlation

template)

4 Units 16 Units

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Energy Detection Receiver Architectures

TOA Estimator

BPF

( )2

LPF / 2-4ns

integrator

ADC

1D to 2D Conversion

Length-3 Vertical Median or Minimum Filtering

Removes interference

2D to 1D Conversion with Energy Combining

Energy image generation

"Path-arrival dates" table

1D to 2D Conversion

Assumption path synchronization

Matrix

Filtering + Assumption/path

selectionTime base 1-2ns accuracy

Time stamping

Analog comparator

Sliding Correlator

Energy combining across symbols

interference suppression

1D-2D Conversion

2D-1D Conversion

Energy image generation

Bipolar template

MERL

I2R

FT R&D

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LOS Before and After Square-Law

• A 500MHz pulse (4ns duration) is passed through a channel sampled at 8GHz

• Received signal energy is collected at 4ns intervals• Strong LOS is lost

First arriving energy block

Strongest energy block

First arriving and strongest path

Channel realization

Energy collection at 4ns

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Another exampleChannel realization

Energy collection at 4ns

With a search back window of 32ns, in this realization the first energy block is missed (the error was 4 energy blocks (2ns +3*4ns = 14ns)

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Threshold Selection

• Assume that µn and σn2 mean and the variance of the

noise respectively• Probability that a noise only sample greater than a

threshold ε is

• Probability of threshold crossing within K consecutive noise only samples

• The corresponding threshold is

)()(n

nQxP

K

n

nfa QP

)(11

nK

fan PQ /11 )1(1PFA ε

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Fixed Search Back

• Fixed search back window length is not very efficient

p

Strongest energy block

x

First signal energy

z

Fixed search back window

t

threshold

y

First threshold crossing within 430 (TOA estimate)

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Adaptive and Iterative Search Back

• K-iterative search back deals with K consecutive noise only blocks• As long as a cluster is detected backward, the search back continues

z

Strongest energy block

x

First signal energy

p

noise dependent thresholdy

Iterative search back

0123nn+1n+2n+3 Energy block index

Wednesday, April 19, 2023

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Ts3 = 2048ns*

Ts1 = Ts

4 = 512ns

TOA Ambiguity = 256ns

Observation window = 512ns

Option 3(16 pulses per 2us)

Option 1 **(16 pulses per 2us)

Option 4 (16 pulses per 2us)

* Since option-3 uses 31 chip sequences, 1984ns symbol duration is used for option-3 to have multiples of 4ns sampling duration. However, total energy used within 4ms duration are identical for all cases.** A training sequence of all 1’s are used. Random training sequence will introduce self interference that will degrade the performance.

Simulation Settings

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Results

• PFA = 0.01, TB = 4ns

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Results

• PFA = 0.005, TB = 4ns

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Results

• PFA = 0.001, TB = 4ns

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Results

• PFA = 0.05, TB = 2ns

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Results

• PFA = 0.01, TB = 2ns

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Results

• PFA = 0.005, TB = 2ns

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TransmittedTime-hoppingSequence

ACF of the TransmittedTime-hoppingSequence

Zero Correlation Zone

Received energysamples (after processed with the time-hopping code)

Multipath components

Peak

Search-back the leading edge

Leading Edge

Anomaly in Option-4

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Summary

• A-priori knowledge of noise variance improved ranging performance• Threshold is set according to the noise variance and

probability of missing a block, not according to the percentage of the highest signal energy block– This made option-4 suffered.

• Option-1 performed the best both in terms of 3ns confidence level and mean absolute error (MAE).– Increasing the sampling rate gained us 2dB

• 3ns 90% confidence level around 13dB at 2ns sampling interval• The MAE is appr. 2ns at 13dB with 2ns sampling interval

• In order to have SOP support, symbol duration should be prolonged in option-1– This lowers the achievable bit rate (<1Mbps)

• Coherent processing is faster with burst PPM

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Recommendation to the IEEE 802.15.4a TG

• Lower the bit rate from 1Mbps to 500Kbps– This will provide

• Non-coherent with option-1 with better SOP support

• Better non-coherent ranging

• Adopt option-1 waveform in preamble

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Backup Slide

• EBN0 = 22dB, Interference and desired equidistant to the receiver

• Strong SOP interference is easily suppressed by the way the image is created and by means of length-3 minimum filtering (in ranging)

Desired User EnergyMulti-user Interference

Block Index

Sym

bo

l In

de

x Minimum Filtering {Length 3 Vertical}

Sym

bo

l In

de

x

Block Index