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Link budgetClaus Rmer Andersen

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Simple transmitter and receiver

Demodulator

Matching&

Filter

Casing

Modulator

Matching&

Filter

Casing

Path Loss

Example: 868 MHz FSK

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Estimating minimum energy per bit, Eb

= hh

TkEQBER

eff

b

2)2sin(1

Acceptable BER defined as 10-6

h = 0.715 (modulation index) k = 1.38*10-23 J/K (Boltsmanns constant) Teff = 290 K (Room temp., antenna direktiviy of 0 dBi)

Eb = 7.43*10-20 W/Hz = -161.3 dBm/Hz

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Link budget for 868 MHz FSK systemTransmitterTx power (dBm) 16.0Antenna gain (dBi) 0.0Cable losses (dB) 0.2Casing losses (dB) 1.0EIRP (dBm) 14.8

DemodulatorRequired Eb (dBm/Hz) -161.3Datarate (kbps) 220Req. demodulator power (dBm) -107.9

ReceiverReq. demodulator power (dBm) -107.9Antenna gain (dBi) 0.0Cable losses (dB) 0.2Casing losses (dB) 1.0Required received power (dBm) -106.7

dBdBitdBmtdBm LossesGPEIRP += ,,

( )bHzdBmbdBmin REP log10/,, +=

dBdBirdBmindBmr LossesGPP += ,,,

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PropagationEIRP, Tx (dBm) 14.8Required received power (dBm) -106.7Fast fading margin (dB) 7.5Polarisation loss (dB) 3.0Log normal fading margin (dB) 0.0Building penetration loss (dB) 0.0Max. allowed path loss (dB) 111.0

Max. range Max. allowed path loss (dB) 111.0Frequency (MHz) 868.3Max. range,free space - N=2 (m) 9717.1

Link budget for 868 MHz FSK system

( )20

2

04

NRL =

dBdBmrdBmdB LossesPEIRPPL = ,

Almost 10 kM!

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Simple non-ideal path loss modelExpected rangePath loss exponent (N) 2 3 4 5 6 8Expected range (m) 9717.1 455.4 98.6 39.4 21.3 9.9

Range vs. path loss exponent

1

10

100

1000

10000

2 3 4 5 6 7 8

Path loss exponent, N

R

a

n

g

e

[

m

]

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WLAN: ch. 11, 16, 21 & 26 @ DELTA offices

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The big trade-off

Modulationsorder, M

Low DatarateLow Datarate

Low RangeLow Range

High BERHigh BER

High DatarateHigh Datarate

High RangeHigh Range

Low BERLow BER

Low High

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Common technologies

Name Frequency Datarate Tx power Range Max. nodes

Bluetooth 2.1, Class 1 2.4 GHz 1-3 Mbps 100 mW 100 m

7 slaves per master

ZigBee, 2.4 GHz 2.4 GHz 250 kbps 1 mW 10-100 m 4090 nodes

ZigBee, 868 MHz (EU) 868 MHz 20 kbps 1 mW 10-100 m 4090 nodes

Z-Wave 868 MHz 9.6/40 kbps 1 mW 30-100 m 232 nodes

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When should you list your requirements?

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Why are we doing this?

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Claus Rmer AndersenDELTA - EMC & Wirelesscra@delta.dk+45 7219 4419

Link budgetSimple transmitter and receiverEstimating minimum energy per bit, EbLink budget for 868 MHz FSK systemLink budget for 868 MHz FSK systemSimple non-ideal path loss modelWLAN: ch. 11, 16, 21 & 26 @ DELTA officesThe big trade-offCommon technologiesWhen should you list your requirements? Why are we doing this?