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VDL4 Radio, Toulouse/(xx)2000-06-13/FQ

Radio

Radio link design


Overview

• VDL Mode 4• A (radio) communication system• The radio channel• Channel access


VDL Mode 4 Ground station

VHF TransceiverCommunication

Processor GNSS reference receiver


VHF TransceiverCommunication

Processor

VDL Mode 4 Transponder

GNSS receiver


VDL Mode 4 Superframe - 1 minute - 4,500 slots = 75 slots/s

13.33 msSlot 1 Slot 4500

Slot 4501 Slot 9000

Current superframe

Current superframe + 1


VDL-4 Summary

• Avionics data link– Communication, navigation and

surveillance

• Based upon STDMA (By Håkan Lans)• 108-137 MHz, 25 kHz channels• 19200 bit/s, FSK• ≈10 W Tx power• 200 nmi range (≈370 km)


Communication layers

Physical

Data link

Network

Transport

Presentation

OSI LAN examples

HTTP, FTP

TCP

IP

Ethernet, ATM

Twisted pair

Data delivery

Packets

Frames

Raw bits

VDL4

xx

xx

vv

STDMA

VHF channel

Session

Application

Process

Transform /translate

User interface Web browser... CDTI(Cockpit display of traffic information)

ADS-B

TIS-B

DLS


Power level units

• dB: Logarithmic level ratio:– 3 dB ↔ double power– 10 db ↔ 10 * power

• dBm: Power level, 0 dBm = 1 mW• dBi: Antenna gain, 0 dBi => isotropic ant• dBc: Power level, 0 dBc => carrier level• dBµV: Voltage level, 0dBµV = 1 µV• dBµV/m: Field strength


The radio spectrum

100 MHz 1 GHz 10 GHz

FM radio VDL-4 GSM 900

1 MHz 1015Hz1 kHz0Hz 1 GHz 1 THz 1018Hz 1021Hz 1024Hz

VLF LF MF HF VHF UHF SHF EHF Infrared Visible Ultraviolett Gamma-ray Cosmic-ray

Infrasonics Sonics

Ultra sonics Microwaves Infrared X-ray Cosmic-ray

Radio spectrum3 kHz 300 GHz

NG W-LAN5.8±0.752.45±0.5

BluetoothW-LAN

1160 * 25 kHz channels 108MHz 137MHz

. . .

Spectrum mask

1:st 2:nd 4:th 32:nd2 dBm -28 dBm -38 dBm -53 dBm≈45 dBm


Frequency issues

• Attenuation ~ f2 ( Pr/Pt = GrGtλ2/(4πr)2 )– 81 times more power required at 900MHz

for same received power as at 100MHz

• Antenna size ~ f– Typically 70 cm for FM λ/4 antenna (100

Mhz)– ≈ 8 cm for 900 MHz λ/4 antenna– Efficient (VHF) antenna can have ≈ 0 dBi

(typical aircraft antenna ≈-4 dBi)


Noise

• Thermal background noise– -174 dBm/Hz @ 290K (0 dB NF)

• Sky temperature– Significant (NF ≈ 5-10 dB) at low

frequencies (< 200 MHz)

• Other systems (man made)– Impulse and continuous signal (CW)

• Noise figure NF = 10log(1+T/290)Temperature T in Kelvin


Noise

100 MHz 1 GHz

NF dB

1

2

3

4

5Typical sky temperature

Thermal noise floor (-174 dBm/Hz @ 290K)0


Noise

• CCI: Co-channel interference– In-band interference– Typically 6-20 dB CCI rejection– Interference from other similar units using

same channel– Low CCI ratio => more efficient frequency

reuse– 10 dB CCI protection will be required for

VDL-4


Digital modulation

• Symbol: Bit or collection of bits• Modifying parameters of a carrier

– Amplitude (ASK), 1 bit/symbol– Frequency (FSK ), 1 bit/symbol

• Constant envelope (no amplitude variations) canbe implemented

– Phase (PSK ), 1-3 bit/symbol– Amplitude and phase (QAM ), 4-8 bit/symbol– Multi-carrier (OFDM), 50-16000 bit/symbol


Metrics

• Power efficiency– Signal power to achieve a particular BER

for a given modulation scheme– Signal energy per bit / noise spectral

density: Eb / N0

• Bandwidth (spectral) efficiency– Possible data rate for given bandwidth– Data rate typically 0.5-4 bit/s/Hz– Shannon limit: C = B * log2(1+s/n)


Constellation: Vectornotation

• Representing amplitude and phaseusing polar coordinates

• I = M*cosθ, M: Amplitude, θ: Phase• Q = M*sinθ

I

Q

M

θIn-phase component

Quadrqture component


Using the vector notation

• ”Detectability”• Crest factor (amplitude variations)• Power and bandwidth efficiency

Peak powerDistance ~ detectability

Log2(number of signals) = bits/symbol ~ bits/s/Hz

Transitions: Indicates amplitude variations


Transceiver structure

Error controlcoding

Modulator Mixer

RF osc

Filter

Power amp

LNA

PLL

Digital (DSP) Digital and/or analog Analog

Errorcorrection

Demodulator


Analog design issues

• Filters– Attenuation– Phase linearity

• Mixers and amplifiers– Dynamic range

• Spurious products• Noise

• Oscillators– Phase noise

ffc

Phase noise


Implementation issues

• For analog components:– Performance costs:

• Money• Size• Power


Constant envelopemodulation

• FSK, MSK (h=0.5)• Features:

– Frequency reuse (CCI)– Power efficient– Non-linear transmitter

GMSK GFSK(h=0.25)

BPF VCOBits RF

Signalmapping

Filter

Filter

90 degFcBits RF

I

Q


• D8PSK, QPSK• Features

– High throughput (1.5-3 bit/s/Hz)

D8PSK π/4 DQPSK

Phase modulation

Signalmapping

Filter

Filter

90 degFcBits RF

• Edge (upgraded GSM)(Uses π/16 offset )

• Tetra• IS-54 (NA Dig Cellular)• Japanese Dig Cellular• Japanese PHP


• 16 QAM, 64 QAM, 256 QAM• Features

– High throughput (3-8 bit/s/Hz)16 QAM

Phase/Amplitudemodulation

Signalmapping

Filter

Filter

90 degFcBits RF

• Microwave links


Multi-carrier modulation

• OFDM, COFDM, MC-CDMA• Multiple orthogonal carriers, typically

PSK or QAM modulated• Coding in the frequency dimension• For N carriers, symbol time increases

by N– Less ISI (intersymbol interference)

• Less sensitive to multipath interference


DS-CDMA modulation

• Direct sequence CDMA– Spreading gain W/R– Rake receiver (“ISI-free”)

Carrier Spreadingsequence

Power amp

BPSK

W/R = 10 log(1.2288 MHz/9600Hz) = 21 dB (IS-95 CDMAW = Spreading bandwidth, R = data rate


Performance

• Spectrum use Error rates

Power

ffc

SNR

BER

10-1

10-2

10-3

10-4

10-5

10-0

2 4 6 8 10 12 14

Typ. ≈1-1.5 * symbol rate FEC gain ≈ 2-10 dB

FECNo FEC


-3 dB

Gt: -2 dB Gr: -2 dB

-3 dB

Att: 127 dB

PALNA

•Antenna gain: -2dBi (Tx and Rx)•Cable loss: 3dB (Tx and RX)•Thermal noise: -174dBm/Hz•Sky temp: NF∼4dB•Man-made noise 16dB ENR•U=4,359 * 106 * Er * √GR / f•U= √PR

•Bandwidth: 25 kHz = 44 dB•Rx Input NF: 12dB•Rx SNR required: 12 dB

•Distance 200 nmi (370 km)•Carrier frequency: 137 MHz•Signal attenuation: 127dB

Link budget

NF: 12dB

Power ?


Link budget

PA power: 29+2+3=34dBm (2.5W)Required signal level into antenna: -103+2+3= -98dBm

Noise into RX antenna: Man-made + Sky temp: Tenr=11835K, Tsky=1018K, Tot: 12853K => 4064K at LNA

LNA NF (12 dB) => Teq= (1012/10-1)*290 = 4306K

Cascaded noise factor: Feq = F1 + (F2-1)/G1 + (F3-1)/G1G2+ … + (Fn-1)/G1G2 … Gn-1

Cascaded noise temperature: Teq = T1 + T/G1 + T3/G1G2+ … + Tn/G1G2 … Gn-1

Te = (10NF/10 -1) T0 NF = Noise figure, T0 =290K, Te=equivalent noise tempTenr = (10ENR/10+1) T0

Total T at LNA = 4306+4064=8370K => F=30 (NF=15dB)

Noise power at LNA = -174+44+15= -115dBm

Signal level at LNA: -115+12 = -103dBm for 12 db SNR

A= -3 dB

Gt: -2 dBGr: -2 dB

A= -3 dB

Att: 127 dB

PALNA

NF=12dB

Transmitted power: -98+127=29dBm


Multi-access system FDMA

Time

Frequency •Central coordination

•Analog systems•POTS, FM-radio, VHF


Multi-access system “Aloha”

Time

User•No coordination•Low channelutilization

•Mode-S, UAT


Multi-access system CSMA

Time

User•No central coordination•Medium channelutilization

•Ethernet, VDL mode 2,3


Multi-access system TDMA

Time

•Coordination of slots

•GSM, DECT...•VDL4 (STDMA)


Multi-access system FH-CDMA

Time

Frequency •Coordination by codes

•Bluetooth, Radio-LAN•Military systems


Multi-access system DS-CDMA

Time

Frequency

•Coordination by codes

•IS-95 (US CDMA), GPS• Users use different spreadingsequences with low cross-correlation


SECTRA Wireless Technologies 2000SECTRA Wireless Technologies 2000http://www.http://www.sectrasectra.se/wireless.se/wireless

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Radio - Engineering Class Home Pages · Radio Radio link design. VDL4 Radio, Toulouse/Page 2 ......

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