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Paul Gorday, MotorolaSlide 1

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

Submission Title: [802.15.4 Multipath]

Date Submitted: [July 2004]

Source: [Paul Gorday] Company: [Motorola]

Address: [8000 W. Sunrise Blvd., Plantation, FL, 33322, USA]

Voice:[+1 561 723 4047], E-Mail:[paul.gorday@motorola.com]

Re: [ IEEE 802.15.4 ]

Abstract: [This contribution presents simulated performance of a simple 802.15.4 (2.4 GHz PHY)

receiver in multipath channel conditions.]

Purpose: [To encourage discussion.]

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 ofIEEE and may be made publicly available by P802.15.

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Paul Gorday, MotorolaSlide 2

Motivation

Proposed modifications to 868/915 MHz PHY

consider additional multipath tolerance for long-

range applications.

Provide benchmark simulation results for the 2.4

GHz PHY, which would also apply to the

proposed down-banded version.

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2.4 GHz PHY Simulation

Floating point simulation of optimum non-coherent

demodulator.

Detection based on largest correlation peak (largest path) No RAKE or equalizer.

Assume channel is constant throughout packet (quasi-

static) and uncorrelated from packet to packet.

Record average packet error rate (PER) vs. Eb/No.

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Paul Gorday, MotorolaSlide 4

2.4 GHz Channel Model

No channel model was specified by 802.15.4

Commonly used diffuse exponential model

802.11 Handbook [1]

802.15.3a Narrowband Model [2]

ETSI BRAN, HIPERLAN/2 [3]

Many textbooks [e.g., 4]

Detailed channel models are being developed by 802.15.4afor a variety of environments, but are not finished.

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Paul Gorday, MotorolaSlide 5

Diffuse Exponential Model

0 2 4 6 8 10 12 14 16 18 200

0.05

0.1

0.15

0.2

0.25 Diffuseeach delay bin

contains multipath energy

Exponentialaverage power

decays exponentially

Fading - each delay bin has

independent Rayleigh fading

Single Parameter:- RMS delay spread = - Mean excess delay

- Max excess delay (10 dB) 2.5

- Max excess delay (20 dB) 5k (Bin #)

NormalizedAveragePower 0,)(

/

kCekf s

kT

C = Normalization Constant

Ts = Simulation Sample Period

Depicted: = 4Ts

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Paul Gorday, MotorolaSlide 6

0 5 10 15 20 25 30 35 4010

-3

10-2

10-1

100

Eb/No (dB)

PER

No Fading

= 0 ns

= 100 ns

= 200 ns

= 300 ns

= 400 ns

= 500 ns

Results for 2.4 GHz PHY

Acceptable performance

for 400 ns

RMS delay spread = 400 ns

Mean excess delay 400 nsMax excess delay (10 dB) 1 s

Max excess delay (20 dB) 2 s

Results scale with chip rate

half-rate at 915 MHz would

tolerate RMS delay spreads

up to 800 ns

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Paul Gorday, MotorolaSlide 7

802.11a/HIPERLAN/2 Models [3]

Channel EnvironmentRMS Delay

Spread (ns)

A Typical office (NLOS) 50B Typical large open space (NLOS) 100

C Large open space indoor (NLOS) 150

D Large open space indoor/outdoor (LOS) 140

E Large open space outdoor (NLOS) 250

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IEEE 802.11 Handbook[1]

EnvironmentRMS Delay

Spread (ns)

Typical Home < 50

Typical Office ~ 100

Typical Manufacturing 200-300

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Paul Gorday, MotorolaSlide 9

Factory/Office Measurements [4]

Tx-Rx separation < 30 m

Location Type

Mean RMS

Delay Spread

(ns)

Max RMS

Delay Spread

(ns)

A Factory 16 40

B Factory 29 60

C Factory 52 152

D Factory 73 150

E Factory 33 146

F Office 16 48

G Office 39 55

H Office 55 146

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Paul Gorday, MotorolaSlide 10

Conclusions

802.15.4 (2.4 GHz PHY) with simple non-coherent demodulator can tolerate RMS delayspreads up to 400 ns sufficient for most WLAN

applications, more than enough for WPANapplications.

Down-banded, half-rate 2.4 GHz PHY wouldtolerate RMS delay spreads up to 800 ns.

Additional delay spread tolerance may beachievable with some increase in demodulatorcomplexity.

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Paul Gorday, MotorolaSlide 11

References

[1] B. OHara and A. Petrick,IEEE 802.11 HandbookA

Designers Companion, IEEE Press, 1999.

[2] J. Foester, Channel Modeling Sub-committee Report

(Final), IEEE P802.15-02/490r1-SG3a, Feb. 2003.

[3] J. Medbo and P. Schramm, Channel Models for

HIPERLAN/2, ETSI/BRAN doc. No. 3ERI085B, 1998.

[4] K. Pahlavan and A. Levesque, Wireless Information

Networks, John Wiley & Sons, 1995.