CHAPTER VII

Radio Aspects, Cell Sites and

Antenna Subsystem

by

Miftadi Sudjai, Ir., MSc., MPhilLab. Antena

Jurusan Teknik Elektro

STTTELKOM

Cellular Radio Access System

MSC

PSTN

Packet/IPNetwork

BTS1/cell site 1

BTS1/cell site n

Radio (Tx & Rx) System

• Signal Source: Informasi & Baseband Processing.• Tx-er: Modulator, Channel Encoder, Interleaver, etc.• PA: Power Amplifier.• Feedline: Cable, Connector and Jumper.• Pre-Amp: LNA.• Rx-er: Demodulator, Channel Decoder, De-Interleaver, etc.

RxerPASignalInformation

Txer

SignalSource(Voice, data, etc)

propagation

feedlineTx filter Rx filter Pre-Amp

Structure of Transmitter

• BB Processing: to process analog signal into digital signal & other processing• Mod: translate from BB freq. To RF freq depend on type of cellular system being

used e.g. G-MSK modulator for GSM.• Power Amp:

- Class A: high linearity- Class B: greater output power more efficient than Class A, but less linear- Class AB: combined adv. of class A & B become widely used in wireless.- Class C: more power efficient widely used in wireless

BBProcessing

Mod PAInfoSignal

Jumper

Jumper

Cable

Connector

Depend ontype of Mod used

Generic Structure of Rxer

• Block diagram of Rxer varies depend on type of modulation, encoder, and/ or base band processing.

• Parameters to be considered are:- frequency range- dynamic range- sensitivity- distortion- noise- tuning speed

12...

N

ChanelEncoder

PAData/Signal

filter

jumper

Multicoupler/RF Distributor

X IF

LOfeedline

Antenna

IF

Rxer

• Antenna: to convert electromagnetic energy from atmosfer electric energy and transfer it to feed line

• Feed line

Receiver Components

Jumper Cable Jumper

• Filter & Pre-Amplifier:- Filter: to pass the wanted signal & attenuated the interference designed to work according to the intended bands- Pre-Amplifier is used to increased S/N of received signals.

= Connector

Jumper to ease maintenance and installation

Receiver Components

• Multicoupler:- used for RF distribution- many signals/users can share the same receive antenna:

1 : 4Splitter

1 : 4Splitter

# 1

# 2

# 3

# 4

1 : 4Splitter

# 13

# 14

# 15

# 16

RFin

signal

Performance Criteria of Receivers

• Sensitivity:- ability to detect a weak signals, measured by minimum discernible signal (MDS).- MDS is measured by turning off the AGC, input a signal with correct BW, and increasing the signal output from generator until S + N = 3 dB higher than 0 when there is no signal.- Sensitivity incorporate thermal noise, NF and BW, defined as:

Sen = 10 log (kTB) + 10 log (Channel BW) + NF

where: 10 log (kTB) = -174 dBm/Hz for T = 25oC,

B = 840 MHz and k = 1.38 x 10-23 J/K

Sen = -174 + 10 log(W) + NF

where: W = Channel Bandwidth

e.g. for IS-9 W = 1.23 MHz

S = -174 + 10 log (1.23 x 106) + 4 = 109.1 dBm

GSM W = 200 kHz

S = -174 + 10 log (2 x 105) + 4 = -117 dBm

Performance Criteria of Receiver• Dynamic Range

- a range of levels of the signal that receiver can handle accurately.- blocking DR is defined from MDS to 1 dB compression point.- spurious free DR (SFDR) is defined from MDS to a specified 3rd order

intermodulation level.

Linear operation

Signal slope

Spurious free dynamic range

Third order

Intercept point

Noise level

Input power, dBm

Input powercausing burnout

Out

put p

ower

, dB

m

1-dB compression

- e.g. a range from -13 to -104 dBm DR = 91 dB

Performance Criteria of Receiver• SINAD = signal to noise and distortion:

dBDN

DNSSINAD

• Noise = thermal noise + other noises:

affect overall performance of receiver

quantified by Noise Figure, NF:

• Selectivity:

- a measure of protection from off channel interference.

- depend upon filtering.

- greater selectivity means better rejection to unwanted signal however if too selective, the signal could be distorted.

NS

NS

NF

output

inputlog10

4 Basic Antenna System

G=2.14 dBi

a. Dipole

G=4 dBi

b. monopole

Ground plane

c. Loop

Ground plane

conductorFeed point

d. Microstrip/ patch

dielectric

Base Station Antenna• Use antenna with higher gain• Could be omnidirectional or sectoral depending on cell type• Collinear antenna:

S

2

2

4

feeder

line

OmnidirectionalRadiationPattern

boresight

main lobe

side lobe(elevation)

• Log periodic dipole array (LPDA)

Base Station Antenna

DipolesTransmissionline

- BW is smaller than LPDA- typical gain 12 – 14 dB

Reflector Driven element (dipole)Directors

• Yagi antenna

Directional RadiationPattern

main lobe

main lobeside lobeback lobe

- very wide BW, with constant SWR- typical gain 10 dBi

SWR of Antenna

• SWR = Vmax/Vmin, define the matching level between antenna and feeder line

• Reflection coefficient:

1

1

SWR

SWR2

2log10Re Lossturn

where represent a percent of reflected power defined by:

SWR of Antenna

Amplitude

Vmax

Vmin

Performance Criteria of Antenna

• Antenna pattern, defined at azimuth and elevation orientation either omni or bidirectional antenna

• Main lobe & side lobe, the lower side lobe the better resistance to interference

• Input impedance, usually complex matching input ipedance and feeder line impedance is very critical to have maximum power transfer from feeder to antenna

• Beamwidth, usually defined as angular separation where there is 3 dB reduction from bore-sight

• Directivity & Gain, is ratio of radiation intensity at wanted direction and coverage radiation intensity over all direction

• Bandwidth, define operating range of antenna, limited by SWR. A typical BW is for SWR 1:1.2 at the band edge.

• Polarization, defined by orientation of E

DG .

Performance Criteria of Antenna• Front to Back Ratio, is ratio between main lobe & back lobe,

very impotant for directional antenna.

• Spatial diversity:

Rx2 Rx1

h

d

)(835

11feet

fx

hd

where f is in MHz

Antenna Installation

a) Tower

Tx

Rx1Rx2

d

b) Roof Top, Edge of Buildingc) Roof Top

d

Rx1

Rx2Tx

d

Rx1

Rx2Tx

d) Wall Mounting

sector 1 Rx1

Rx2

Tx2

3

d

Antenna Installation Tolerance

• Apply to physical oriented & plumbness of its installation

• For omnidirectional antenna, it is unnecessary. But for directi-onal antenna it is very critical

• Usually taken +/- 5% from antenna horizontal/azimuth pattern.

Azimuth/Horizontal Pattern Tolerance from Bore Sight

110O +/- 5.5o

92O +/- 4.5o

60O +/- 3.0o

40O +/- 2.0o

Table: Horizontal Antenna Tolerance

Antenna Isolation

a. vertical

y

Tx

Rx

ywhere

dBy

VI log4028

c. slant

y

angleslantwhere

dBHIHIVISIo

90

Tx Rx

x

b) horizontal

10

log2022

xwhere

dBx

HI

Link Budget

TXer RXer

Txercomponent

Rxercomponent

link budget component

path loss

Link Budget – Up Link

• Frequency range, MHz

• Mobile parameters- Tx PA output (max)- Cable loss- Antenna gain-------- (Subsc. ERP max, dB)

• Environmental margins- Fading margin- Environmental attenuation- Cell overlap

-------------------- (dB)

• Base station parameters

- Rx ant. gain Rx jumper loss

- Rx tower top amp gain (net)

- Rx cable loss

- Rx ligthning arrester loss

- Rx duplexer loss

- Rx diversity gain

- Rx coding gain

- Rx sensitivity

------- Up-link budget, dB

Link Budget – Down Link• Frequency range, MHz

• Base station parameters

- Tx PA output power

- Tx combiner loss

- Tx duplexer loss

- Tx ligthning arrester loss

- Tx cable loss

- Tx jumper loss

- Tx tower top amp gain

- Tx antenna gain

(Cell ERP, dB)

• Environmental margins- Tx diversity gain- Fading margin- Environmental attenuation- Cell overlap

(dB)• Mobile parameters

- Antenna gain - Rx diversity gain- Antenna cable loss- Coding gain- Rx sensitivity

---------- Down-link budget, dB

Type of Cell Site/BTS (1)

Monopole

Rx2Rx1

Tx

Roof Top

Rx2Rx1 Tx

a) Omni cell b) 3 Sectors

Rx12

Tx1

Rx11

Rx21

Tx2

Rx22

Rx32

Tx3

Rx31

1

2

3

120o

Type of Cell Site/BTS (2)

c) 6 sectors

T

R

R

R

RR

R

RR R

R

R

R

T

T

T

T

T

1

2

3

4

5

6

d) Microcell or picocell

Traffic light

Micro- or pico-cell antenna

60

Cell Site Design (1)

Site Qualification Test(SQT)

Planning andZoning Board

SiteAccepted?

EMF Compliance

Site activation

Search area

Cell Site Design (2)

• Search Area:- searching area to place cell site/BTS that meet the specifications- plot the propagation path, including clearance- mapping the area for planning & documentation

• SQT:- to assure the area is a viable candidate for a cell site by measurements- include a sketch of the location, antenna type, height, ERP, path clearance,

and do callibration

• Site acceptance:- if SQT is positive then the area is accepted to place a cell site- if not, then area is rejected- both site acceptance and rejection should be documented

Cell Site Design (3)

• Planning and zoning board:- why the site is needed- how the site will improve the network- drawing the sketch of site

• Electromagnetic Force (EMF) Compliance:- EMF identify the source of EM from the site itself and surrounding area- to ensure it complies with personal safety and government regulation- incorporated the type of Txer, power, frequency range, etc- method for calculating EMF, e.g. IEEE C95.1 – 1991 standard

• Site activation:- when every steps above is OK, the cell site/BTS could be placed and turn on

Conclusion

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The End