(BAB II) Intro Wireless Technology.v1

Introduction Introduction

Wireless TechnologyWireless Technology

PT. Aplikanusa LintasartaPT. Aplikanusa Lintasarta

• Dalam perambatannya, sinyal radio sebagai gelombang Dalam perambatannya, sinyal radio sebagai gelombang elektromagnetik dapat mengalami proses :elektromagnetik dapat mengalami proses :

– PembiasanPembiasan

– DifraksiDifraksi

– HamburanHamburan

– PantulanPantulan

• Fenomena tersebut menyebabkan gelombang :Fenomena tersebut menyebabkan gelombang :– DibelokkanDibelokkan

– DiredamDiredam

– DihamburkanDihamburkan

Dimana efek-efek tersebut secara umum berubah terhadap lokasi maupun waktunya.Dimana efek-efek tersebut secara umum berubah terhadap lokasi maupun waktunya.

• Sehingga secara umum kanal wireless bersifat :Sehingga secara umum kanal wireless bersifat :– Kanal wireless merupakan kanal yang bersifat Kanal wireless merupakan kanal yang bersifat time varyingtime varying– Secara umum, fluktuasi kanal berubah menurut lokasi dan waktu.Secara umum, fluktuasi kanal berubah menurut lokasi dan waktu.

– Sinyal radio akan melalui daerah Sinyal radio akan melalui daerah propagasi redamanpropagasi redaman dan daerah dan daerah multipath multipath fadingfading..

Lingkungan WirelessLingkungan Wireless

Deskripsi Lingkungan WirelessDeskripsi Lingkungan Wireless

Daerah redaman propagasi Daerah multipath

fading

Redaman Propagasi & Multipath FadingRedaman Propagasi & Multipath Fading

Redaman PropagasiRedaman Propagasi• Perambatan gelombang radio dipengaruhi oleh penghalang yang terletak pada Perambatan gelombang radio dipengaruhi oleh penghalang yang terletak pada

jalur lintasan gelombang. Pengaruh tersebut dapat berupa pantulan, hamburan, jalur lintasan gelombang. Pengaruh tersebut dapat berupa pantulan, hamburan, redaman.redaman.

• Sehingga dalam perencanaan adanya penghalang harus benar-benar Sehingga dalam perencanaan adanya penghalang harus benar-benar diperhitungan untuk menentukan tinggi antena, dan pemilihan alokasi antena.diperhitungan untuk menentukan tinggi antena, dan pemilihan alokasi antena.

Multipath FadingMultipath Fading• Adalah naik-turunnya sinyal karena bertemunya gelombang langsung dengan Adalah naik-turunnya sinyal karena bertemunya gelombang langsung dengan

gelombang pantul di penerima.gelombang pantul di penerima.

• Besar fading tergantung pada beda fasa dan amplitude kedua jenis sinyal. Besar fading tergantung pada beda fasa dan amplitude kedua jenis sinyal. Multipath fading dapat menyebabkan kedalaman fading melebihi 20 dB.Multipath fading dapat menyebabkan kedalaman fading melebihi 20 dB.

Rugi-rugi Redaman Ruang BebasRugi-rugi Redaman Ruang Bebas

Gt Grd

Pengirim Pt

Penerima PrPt : Daya kirim

Pr : Daya terima

Gt : Gain antena kirim

Gr : Gain antena terima

d : Jarak antara pengirim dan penerima

: Panjang gelombang

Pr = Pt(/4d)2.Gt.Gr

• Faktor (/4d)2 merupakan bagian yang berkontribusi dalam penurunan daya dan harganya bergantung pada jarak dan panjang gelombang sinyal.

• Faktor rugi-rugi ini disebut sebagai rugi-rugi akibat redaman ruang bebas (free space loss)

• Dalam dB, free space loss diekspresikan sebagai :

Lf = 20 log ( / 4d ) [dB]

Rugi-rugi Redaman Ruang BebasRugi-rugi Redaman Ruang Bebas

Pr = S(d) . As = Pt/4d2 . 2/4

• Received power with a given antenna effective aperture, and for an isotropical antenna especially :

• Free space loss == > Lo = Pt/Pr = ( 4d/)2

• In dB (decibels) Lo = 32,44 + 20 log f [MHz] + 20 log d [km]

or Lo = 92,45 + 20 log f [GHz] + 20 log d [km]

Ideal LOS LinkIdeal LOS Link

• PR = Ae.GT.PT/(4r2)

• As will be shown later

Ae = GR. 2/(4)

• Hence

PR = PT.GT.GR.2/(4r)2

this is called the FRIIS Formula

• When expressed in dBs

PR(dBm) = PT(dBm) + GT(dB) + GR(dB) + 20 log(/4r)

= PT(dBm) + GT(dB) + GR(dB) + 20 log(C/4fr)

C = speed of light = 3 x 108 mps, f = frequency in Hz

• Thus

PR (dBm) = PT(dBm) + GT(dB) + GR(dB) – 20 log(r) – 20 log(f) – 32.44

• With f expressed in MHz and r in Km.

Rugi-rugi Redaman Akibat Pantulan PermukaanRugi-rugi Redaman Akibat Pantulan Permukaan

d

ht

hr

Direct wave

reflected wave

ht : tinggi antena pengirim

hr : tinggi antena penerima

d : jarak antara pengirim dan

penerima

Hubungan antara daya terima dengan daya kirim :

Pr = Pt . ( ht . hr / d2 )2. Gt . Gr

• Faktor ( ht.hr/d2 )2 merupakan bagian yang berkontribusi dalam penurunan daya akibat adanya pantulan dan harganya bergantung pada ketinggian antena pengirim, penerima dan jarak antara pengirim dan penerima.

• Redaman akibat pantulan tersebut tidak bergantung pada panjang gelombang sinyal.

• Dalam dB diekspresikan sebagai :

Lf = 20 log ( ht.hr / d2 ) [dB]

Rugi-rugi Redaman Akibat DifraksiRugi-rugi Redaman Akibat Difraksi

h1 : tinggi antena base station

h2 : tinggi antena mobile station

d1 : jarak antena base station ke bukit

d2 : jarak antena mobile ke bukit

hp : tinggi bukit

h1

h2

d1d2

hp

Besar redaman akibat difraksi ini mengikuti teori Kirchoff :

Ld = 0 dB ; 1 < V

Ld = 20 log ( 0.5 – 0.62 V ) ; 0 < V < 1

Ld = 20 log ( 0.5 e 0.95V ) ; -1 < V < 0

Ld = 20 log ( 0.4 – [0.1184 – (0.1V + 0.38)2]1/2 ; -2.4 < V < -1

Ld = 20 log ( -0.225 / V ) ; V < -2.4Dengan :

V = - hp { 2( 1/r1 + 1/r2 ) } 1/2

Contoh Beberapa Kondisi DifraksiContoh Beberapa Kondisi Difraksi

Tx Rxhm

dT dRTx Rx

hm

dT dR

Tx Rx Tx Rx

Karakteristik Lintas Jamak Suatu Gelombang RadioKarakteristik Lintas Jamak Suatu Gelombang Radio

T

Short term fading r (t)

Long term fading m (t)

Signal Strength (dB)

Time (t)

Short-term FadingShort-term Fading

• Fading cepat terjadi karena adanya lintasan ganda akibat dipantulkannya gelombang oleh benda-benda seperti rumah, gedung, kendaraan, pohon, dan benda-benda lain

• Karena perbedaan panjang lintasan yang ditempuh oleh lintasan pantul dan lintasan langsung, maka akan menyebabkan perbedaan amplitudo dan fasa dari kedua sinyal tersebut

• Frekuensi ikut mempengaruhi fading cepat, adapun pengaruh frekuensi terhadap pola fading cepat yaitu frekuensi yang semakin tinggi akan menghasilkan fluktuasi lebih cepat dibandingkan dengan frekuensi yang lebih rendah pada interval jarak sama.

• Penyebab utama :

• Adanya variasi penghambur selama pergerakan MS

• Adanya pergerakan penghambur selama MS diam

• Sifat :

• Secara statistik terdistribusi Rayleigh

• Sifat fading cepat berpengaruh dalam penentuan laju transmisi, panjang paket, dan skema coding.

Long-term FadingLong-term Fading

• Fading lambat disebabkan oleh adanya perubahan konfigurasi alam antara base station dan stasiun pelanggan yang akan menyebabkan fluktuasi path loss (redaman lintasan) akibat efek bayangan dari penghalang alam.

• Fading Lambat sering disebut dengan shadowing

• Penyebab utama :

• Adanya penghalang di sepanjang lintasan

• Variasi kotur bumi

• Sifat :

• Secara statistik terdistribusi Log-normal

Distribusi Rayleigh Distribusi Log-normal

Analisis Power BudgetAnalisis Power Budget• Tujuan : Menyeimbangkan antara level uplink dengan downlink

• Arti penting :

• Bila level downlink > uplink, maka :

• Jangkauan BS akan lebih besar daripada jangkauan MS

• Terjadi kegagalan panggilan setelah inisialisasi atau handoff

• Bila level uplink > downlink, maka :

• Jangkauan MS akan lebih besar daripada jangkauan BS

• MS akan boros dalam pemakaian batterai

• Perhitungan :

• Komponen downlink

• Daya pancar BS : EIRPbs

• Sensitivitas penerimaan MS : Sms

• Rugi-rugi redaman maksimum : DL = EIRPbs - Sms

• Komponen uplink

• Daya pancar MS : EIRPms

• Sensitivitas penerimaan BS : Sbs

• Rugi-rugi redaman maksimum : UL = EIRPms – Sbs

• Penyeimbangan downlink dan uplink : DL = UL

Analisis Power BudgetAnalisis Power Budget• Perhitungan EIRP

• Daya pancar pengirim (dBm)

• Rugi-rugi saluran transmisi (dB)

• Gain antena (dBi = dBd + 2.15)

Tx (Pout) Cable (Ltx)

Gain antena (Gtx) EIRP

Analisis Power BudgetAnalisis Power Budget

Contoh :

Path loss pada jarak 10 km dari suatu kawasan metropolitan diketahui berharga 160 dB. Parameter yang digunakan dalam pengukuran tersebut adalah :

• Tinggi antena BS : 30 m

• Tinggi antena MS : 3 m

• Frekuensi kerja : 1 GHz

• Tipe antena : dipole ½ lamda

Bandingkan hasil pengukuran tersebut dengan model prediksi yang dikembangkan oleh Okumura-Hatta dan Lee !

• Model Okumura-Hatta

L = 69.55 + 26.16 log 1000 – 13.82 log 30 – a (hr) + (44.9 – 65.55 log 30) . log 10 dB

a(hr) = 3.2 (log 11.75 x 3)2 – 4.97 dB

= 2.69 dB

L = 69.55 + 78.48 – 20.41 – 2.69 + 35.22 = 160.15 dB

• Model Lee

Untuk daerah urban : Lo ~ 118 dB, ~ 40 dB

F1 = (30 / 30.5)2 = 0.9675; F2 = F3 = F4 = 1; F5 = (1000 / 900)2 = 1.23

Fo = 0.9675 x 1 x 1 x 1 x 1.23 = 1.19 dB

L = 118 + 40 log 10 + 1.19 = 159.19 dB

Model Prediksi Rugi-rugi RedamanModel Prediksi Rugi-rugi Redaman

• Pendahuluan :

• Tidak ada satupun model yang secara universal dapat diterapkan pada semua situasi.

• Keakuratan model prediksi bergantung kesesuaian parameter antara model dengan daerah yang ditinjau.

• Ada beberapa model : yang populer antara lain…

• Model Lee

• Model Okumura - Hatta

Model LeeModel Lee• Didasarkan pada data hasil pengukuran di Amerika Serikat

• Frekuensi kerja : 900 MHz

• Model bisa digunakan untuk penerapan prediksi area to area atau point to point

• Sesuai untuk daerah urban, sub-urban, dan rural.

Persamaan Prediksi Lee :

Dengan: Fo = F1 . F2 . F3 . F4 . F5

F1 = faktor koreksi ketinggian antena BS

F2 = faktor koreksi daya pancar BS

F3 = faktor koreksi gain antena BS

F4 = faktor koreksi ketinggian antena MS

F5 = faktor koreksi frekuensi kerja

Parameter acuan :

• Frekuensi kerja = 900 MHz

• Tinggi antena BS = 30.5 m

• Tinggi antena MS = 3 m

• Daya pancar : 10 W

• Gain antena BS = 6 dB terhadap dipole ½ lambda

L = Lo + g log d + Fo

Lingkungan Lo (dB) Free Space 91.3 20

Open 91.3 43.5

Sub-urban 104 38

Urban    

Tokyo 128 30

Philadelphia 112.8 36.8

Newark 106.3 43.1

Model Okumura - HattaModel Okumura - Hatta

• Didasarkan pada data hasil pengukuran di Tokyo

• Frekuensi kerja : 1.9 GHz

• Sesuai untuk daerah urban dan quasi urban seperti Tokyo

• Hanya valid untuk daerah terrain yang rata

• Model prediksi dibedakani untuk daerah urban, sub-urban, dan open.

Persamaan Prediksi Okumura - Hatta :

• Daerah Urban : L = 69.55 + 26.16 log f – 13.83 log ht – a (hr) + [44.9 – 6.55log ht] log d dB

• Untuk kota kecil atau menengah : a(hr) = (1.1 log f – 0.7) hr – (1.56 log f – 0.8) dB, 1 < hr < 10m

• Untuk kota besar : a (hr) = 8.29 (log 1.54 hr)2 – 1.1 dB, f < 200 MHz

a (hr) = 3.2 (log 11.75 hr )2 – 4.97 dB, f < 400 MHz

• Daerah sub-urban : L = L urban – 2 [ log (f/28)2 – 5.4] dB

• Daerah open : L = L urban – 4.78 [ log f]2 + 18.33 log f – 40.94 dB

Perhitungan Sensitivitas & Metode Penteimbangan Downlink dan UplinkPerhitungan Sensitivitas & Metode Penteimbangan Downlink dan Uplink

Perhitungan Sensitvitas

• Gain antena (dBi)

• Rugi-rugi saluran transmisi (dB)

• Sensitivitas perangkat peneriaan itu sendiri (dBm)

Metode Penyeimbangan Downlink dan Uplink

• Perubahan daya pancar pada BS atau MS

• Penambahan diversity antena

• Penambahan LNA (Low Noise Amplifier)

Cable (Lrx)Rx (Pin)

Gain antena (Grx)Sensitivitas

Fresnel ZonesFresnel Zones

• The 1st Fresnel zone lies around the line-of-sight and contains components amplifying the sinusoidal field.

• The 2nd Fresnel zone contains components attenuating the field.

• This continues so that the odd-numbered zones amplify the received field, and the even-numbered zones attenuate the field.

• The outer radius of each ellipsoidal shell (at the same time the inner radius of following zone) is determined by the excess electrical path length

L1 + l2 = d + n /2 RFn = {n..d1.d2/(d1 + d2)}1/2

Fresnel ZonesFresnel Zones

• The power the 1st Fresnel zone is twice the power the power in free space. As the order of the zone increases, the resultant field from two adjacent zones approaches zero

• It is important the keep 1st Fresnel Zone free from obstacles

d1 d2

Tx Rx

Fresnel Zone (example)Fresnel Zone (example)

Line of sight path

First Fresnel zones at 10 GHz

First Fresnel zones at 100 MHz

Radius of 1st Fresnel zone :

Frequency distance

  2.5 km 5 km 10 km 20 km

2 GHz 9.7 m 13.7 m 19.4 m 27.4 m

7 GHz 5.2 m 7.3 m 10.4 m 14.6 m

18 GHz 3.2 m 4.6 m 6.5 m 9.1 m

38 GHz 2.2 m 3.1 m 4.4 m 6.3 m

Fresnel Zone vs. Near FieldFresnel Zone vs. Near Field

• Fresnel Zones are valid in the antenna far field only

• The lower limit for a reflector antenna far field is roughly

• e.g. for

D = 3 m f = 2 GHz r = 120 m

D = 60 cm f = 18 GHz r = 43 m

D = 30 cm f = 38 GHz r = 23 m

r = 2 D2 /

Calculation of Fade MarginCalculation of Fade Margin

Calculation of Fade marginCalculation of Fade margin

• Calculate the received power taking into account

• Tx power Ptx

• Feeder, branching & connector losses

• Antenna gain

• Free space loss

• Possible obstacles

• Compare the result to “receiver threshold power”

(=power needed to achieve BER 10-3 ----> for Voice)

Fade Margin

Tx power PTx power Ptxtx

• Transmitter power may vary according to system

• Normally only a few options available

e.g., normal power and reduced power

• Sometimes there may be continously changing, adaptive Tx power

• Typical values are between about 10 dBm – 30 dBm

Feeder, Connector losses & BranchingFeeder, Connector losses & Branching

• Feeder losses depend on frequency, cable type, and cable diameter

• Below 3 GHz feeder lines are normally coaxial cables

• Above 3 GHz they are typically waveguides

• Attenuation figure (dB/km) can be found in manufacture’s references (a few decibels/100m)

• Connector losses are typically of the order of 0.5 dB per feeder line (i.e. per site)

Lc = a(lver + lhor) + Lcon

• Branching loss depends on the system configuration (single, HSB, diversity etc)

• Can be found in manufacturers specs

• Typically from a couple of decibels up to about 12 dB

Free Space LossFree Space Loss

• The free space loss can be calculated from the dimensioned formula below

• Where Lo is the free space loss (dB), d is the path length (km) and f is the radio frequency (GHz)

Lo = 92.5 + 20 log(d) + 20 log(f)

• Exact formula :

Lo = 10 log (4.d/)2

Calculated Fade MerginCalculated Fade Mergin

• Fade Margin M

• Hop loss

M = Ptx - Lho - Prxth

• Where :

• Lo is the free space loss

• Lad is the additional obstruction loss (diffraction loss)

• Lbr is the branching loss (both ends summed)

• Lc is the sum of feeder loss (including connector)

• Ga is The antenna gain

All values in decibels

Lho = Lo + Lad + Lbr + Lc – Ga1 – Ga2

Power Levels and MarginsPower Levels and Margins

• P is the received power during normal conditions

• P th is the receiver threshold at given BER (ussually 10-3 Voice)

• Y is the threshold degradation (due to interference)

is the fade margin

P1

P2

Pth1

Pth2

Y1 Y2

Interference CalculationsInterference Calculations

Source of InterferenceSource of Interference

1

2

3 4

5

6

7

1. Cochannel or adjacent channel signal from different direction

2. Opposite hop front-to-back reception

3. Adjacent channel over the same hop

4. Cross polarized signal over the same hop

5. Front-to-back radiation

6. Over-reach (3 hops)

7. Terrain reflections (“radar effect”)

Types of InterferenceTypes of Interference

• Correlated(wanted signal and interfering signals fade approximately in the same manner)

• 3, 4 and 5 on the previous slide

• Uncorrelated(wanted signal and interference fade independently)

• 1, 2, 6 and 7 on the previous slide

• 1 (and 2) are the most important in correctly planned networks

Uncorrelated interference is often the worst(one must be prepared that the wanted signal fades all the fade margin while the interference remains at its normal value)

Passive RepeaterPassive Repeater

• Change polarization == > diminish interference

V

H

Interference between two hopsInterference between two hops

• Protection is given by the antenna gain patterns at direction and

• Distance dint affects also the amount of interference

d int

d want

Tx Int

Tx want

Rx want

Nonpreferred use of radio channelsNonpreferred use of radio channels

• Normally both transmitters should use channels with or without prime (i.e.channels of the same half band)

• Sometimes arrangements according to the figure must be used. Then :

• try to use maximally n frequency spaced channels (e.g. f1 and f3)

• use different polarizations when possible

• try to increase the vertical separation between antennas

• minimize the transmitter powers – use only the minimum necessary

f3f1

Link Budget CalculationsLink Budget Calculations

Ideal LOS Link (Example)Ideal LOS Link (Example)

• A microwave communications link is required between a satellite and a space craft. The satelite transmitter power output is 20 dBm and the sensitivity of the receiver on the spacecraft is -100dBm. A frequency is 25GHz is to be used with antennas of 50dB gain at either end of the link. What is the maximum communictions range ?

• PR (dBm) = PT(dBm) + GT(dB) + GR(dB) – 20 log(r) – 20 log(f) – 32.44

• -100 = 20 + 50 + 50 – 20 log(r) – 20 log(25x103) – 32.44

• 99.6 = 20 log(r)

• r = 104.98 km

• r = 95,499 km

System Planning of Radio Local Loop radio LinkSystem Planning of Radio Local Loop radio Link

• P tx is the transmitter power level, dBm

• L tx is the transmitter duplex filter and the antenna feeder total loss, dB

• G tx is the transmitter antenna gain, dBi

• L ch = Lo + L is the radio path loss, dB

• Lo = 32,5 + 20 log d (km) + 20 log f (MHz) is the free space loss

• L is additional loss due to the path profile and planning method

• G rx is the receiver antenna gain, dBi

• L tx is the receiver duplex filter and the antenna feeder total loss, dB

• P rx is the received power level, dBm, which should be larger than the receiver sensitivity level. This depends on the required bit error performance, modilation method, transmission rate, receiver noise figure, and implementation quality

Radio link power budget

Prx = Ptx – Ltx + Gtx – Lch + Grx – Lrx

Basic link structure

Tx RxPtx Prx

Gtx Grx

Ltx Lrx

Lch

d

System Planning of Radio Local Loop radio LinkSystem Planning of Radio Local Loop radio Link

f = 3.5 GHz

Ltx = 2.0 dB

G tx = 7.0 dBi

G rx = 18.0 dBi

L rx = 3.0 dB

Example : Determine the transmit power level so that the SES- objective is fulfiled with following system parameters :

F rx = 6.0 dB 4.0

Modulation method 4PSK

R b = 512 kbit/s

Implementation margin SNR = 1.5 dB

d = 3 km

In the test measurements is observed that the average receive level is 10 dB below free space loss, and the signal fading is Rice-distributed, = 4 ( 6 dB)

Calculations : The bit error probability of QPSK in the AWGN-channels :

BER = Q { [ E/No * 10 -0,1 SNR ]1/2} = Q { [ Prx / (FkToRs) * 10 -0,1 SNR ]1/2}

System Planning of Radio Local Loop radio LinkSystem Planning of Radio Local Loop radio Link

For the SES-objective :

BER = 10-3 = [ Prx / (FkToRs) * 10 -0,1 SNR ]1/2 = 3.09

P rx = 3.09 2. FkToRs . 10 -0,1 SNR = 9.55 . 10 0.6 . 4 . 10-21 . 512000/2 . 10 0.15

= 5.49 . 10-14 W = 5.49 . 10-14 mW -102.6 dBm

Free space loss :

Lo = 32.5 + 20 log 3 + 20 log 3500 = 112.9 dB

L = L + L = 10 dB + L

L is obtained from the Rice distribution graph

For the SES-objective BER > 10-3 with the probability 1.5 . 10-4 L=27.8 dB

System Planning of Radio Local Loop radio LinkSystem Planning of Radio Local Loop radio Link

Needed transmit power :

BER = 10-3 = [ Prx / (FkToRs) * 10 -0,1 SNR ]1/2 = 3.09

P tx = P rx + L tx – G tx + Lo + L + L – G rx + L rx

= -102.6 + 2.0 – 7.0 + 112.9 + 10 + 27.8 – 18.0 + 3.0

= 28.1 dBm 0.65 W

L = L + L = 10 dB + L is obtained from the Rice distribution graph

For the SES-objective BER > 10-3 with the probability 1.5 . 10-4 L=27.8 dB