NEC_Level-1_Training_Presentation.ppt

7/27/2019 NEC_Level-1_Training_Presentation.ppt

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NEC Level-1 Training

Session

Day-1

Haroon

Gora a


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Presentation Contents:

Back to Basics

Microwaves Why Microwaves? Analog/ Digital Transmission Analog-to-Digital Converter Pulse Code Modulation

Modulation Analog Modulation Digital Modulation Why Digital Modulation? Multiplexing

Types of Multiplexing Multiplexing Hierarchies Plesiochronous Digital Hierarchy Synchronous Digital Hierarchy E-Carrier System E-Carrier Hierarchy Levels


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Back to Basics

WaveA wave is a disturbance that propagates (travels) through spaceand time, usually by transference of energy. For example, soundwaves propagate via air molecules slamming into their neighbors,which push their neighbors into their neighbors (and so on); whenair molecules collide with their neighbors, they also bounce awayfrom them (restoring force). This keeps the molecules fromactually traveling with the wave.

Waves travel and transfer energy from one point to another,often with no permanent displacement of the particles of the

mediumthat is, with little or no associated mass transport. Theyconsist instead of oscillations or vibrations around almost fixedlocations. Imagine a cork on rippling water, it would bob up anddown staying in about the same place while the wave itself movesoutward. When we say that a wave carries energy but not mass,we are referring to the fact that even as a wave travels outward

from the center (carrying energy of motion), the medium itselfdoes not flow with it.


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Back to Basics

Types of Waves

Here are some of the many famous types of waves;

Sound Waves

Standing Waves

Electromagnetic Waves

Microwaves

Properties of Waves

Frequency

Rate of oscillation of a wave is Frequency.

Wavelength

Distance between successive crests or successive troughs isWavelength.

Relationship b/w Frequency & Wavelength

Speed of Wave = Frequency x Wavelength


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Back to Basics Electromagnetic Spectrum

Its is the range of all possible frequencies of electromagnetic radiation. Theelectromagnetic spectrum extends

from below frequencies used for modern radio to gamma radiation at the short-wavelength end, covering

wavelengths from thousands of kilometers down to a fraction of the size of an atom. Thelong wavelength limit

is the size of the universe itself, while it is thought that the short wavelength limit is inthe vicinity of the Planck

length, although in principle the spectrum is infinite and continuous.


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Microwaves

Microwaves are electromagnetic waves with wavelengthsranging from as long as one meter to as short as one

millimeter, or equivalently, with frequencies between300 MHz (0.3 GHz) and 300 GHz.

Electromagnetic waves longer (lower frequency) thanmicrowaves are called Radio waves".


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Why Microwaves?

Microwave Frequencies are being heavily employed intodays world for a million different purposes. Some ofthe reasons which make Microwave ideal foremployment in Human World are; Microwave do not carry huge amounts of energy & therefore are

far less harmful to humans than X-Rays, Gamma Rays etc.

Microwave Frequencies fall below Visible Light spectrum & wellabove the Audible Sound levels & therefore can not be seen/heard by human beings.

Microwaves have ideal ratios of Frequency, Power Levels &Wavelengths which enable them to travel long distances whilebeing less prone to Man made/ Machine made interference.

Microwaves have enough penetration capability (Cm range)which enables them to pass through obstacles if they are notthick enough.

Microwaves when directed (Focused), can provide an ideal Point-to-Point link & hence the extensive usage in

Telecommunications.


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Analog / Digital Transmission

Analog Transmission

Analog Modulation Schemeis used to Modulate an

Analog Baseband Signal ona High Frequency Carrier

for transmission over aMedium.

Digital Transmission

Digital Modulation Schemeis used to Modulate an

Analog Baseband Signal ona High Frequency Carrier

for transmission over aMedium.

BasebandAnalog

Signal

AnalogModulation

AnalogDemodulati

on

AnalogSignal

AnalogTransmissi

on

BasebandAnalog/Digital

Signal

DigitalModulation

DigitalDemodulati

on

Analog/Digital

Signal

DigitalTransmissi

on


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Analog-to- Digital (A/D) Converter Typically, an ADC is an electronic device that converts an input analog voltage

(or current) to a digital number proportional to the magnitude of the voltage orcurrent.

The digital output may use different coding schemes, such as binary, Graycode or two's complement binary.

The resolution of the converter indicates the number of discrete values it canproduce over the range of analog values. The values are usually storedelectronically in binary form, so the resolution is usually expressed in bits.

For example, an ADC with a resolution of 8 bits can encode an analog input to

one in 256 different levels, since 28 = 256.

Resolution can also be defined electrically, and expressed in volts. Theminimum change in voltage required to guarantee a change in the output codelevel is called the LSB (least significant bit, since this is the voltagerepresented by a change in the LSB). The resolution Q of the ADC is equal tothe LSB voltage.

The analog signal is continuous in time and it is necessary to convert this to aflow of digital values. It is therefore required to define the rate at which newdigital values are sampled from the analog signal. The rate of new values iscalled the sampling rate or sampling frequencyof the converter.

Perfect reconstruction of the sampled signal is only possible if the SamplingRate is higher than twice the highest frequency of the Signal.

Quantization error is due to the finite resolution of the ADC, and is anunavoidable imperfection in all types of ADC. The magnitude of the


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Analog-to- Digital (A/D) Converter


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Pulse Code Modulation (PCM) PCM is a digital representation of an analog signal where the

magnitude of the signal is sampled regularly at uniform intervals,

then quantized to a series of symbols in a numeric (usually binary)code.

Modulation

. In the diagram, a sine wave (red curve) is sampled and quantized forpulse code modulation. The sine wave is sampled at regular intervals,shown as ticks on the x-axis. For each sample, one of the available

values (ticks on the y-axis) is chosen by some algorithm (in this case,the floor function is used). This produces a fully discrete representationof the input signal (shaded area) that can be easily encoded as digitaldata for storage or manipulation.

For the sine wave example at right, we

can verify that the quantized values at

the sampling moments are 7, 9, 11, 12,13, 14, 14, 15, 15, 15, 14, etc. Encoding

these values as binary numbers would

result in the following set of nibbles: 0111,

1001, 1011, 1100, 1101, 1110, 1110, 1111,

1111, 1111, 1110, etc. These digital values

could then be further processed or analyzed

-


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Pulse Code Modulation (PCM)

Encoding for transmission Pulse-code modulation can be either return-to-zero (RZ) or non-return-

to-zero (NRZ). For a NRZ system to be synchronized using in-bandinformation, there must not be long sequences of identical symbols,such as ones or zeroes. For binary PCM systems, the density of 1-symbols is called ones-density.


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Modulation

Modulation is the process of varying one or more properties (Amplitude,Frequency, Phase) of a high frequency periodic waveform, called the carriersignal, with respect to a modulating signal.

The aim of Modulation is to transfer a message signal (Baseband Signal,Digital Bit Stream) over a distance & be received at the Receiver Side ofthe Hop.


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Analog Modulation

In analog modulation, the modulation is applied continuously in responseto the analog information signal.

Common analog modulation techniques are:

Amplitude modulation (AM) (here the amplitude of the carrier signal isvaried in accordance to the instantaneous amplitude of the modulatingsignal)

Double-sideband modulation (DSB)

Double-sideband modulation with unsuppressed carrier (DSB-WC) (used on

the AM radio broadcasting band) Double-sideband suppressed-carrier transmission (DSB-SC)

Double-sideband reduced carrier transmission (DSB-RC)

Single-sideband modulation (SSB, or SSB-AM),

SSB with carrier (SSB-WC)

SSB suppressed carrier modulation (SSB-SC)

Vestigial sideband modulation (VSB, or VSB-AM)

Quadrature amplitude modulation (QAM)

Angle modulation

Frequency modulation (FM) (here the frequency of the carrier signal isvaried in accordance to the instantaneous frequency of the modulatingsignal)


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Analog Modulation

i i l d l i


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Digital Modulation

In digital modulation, an analog carrier signal is modulated by a digital bit stream.Digital modulation methods can be considered as digital-to-analog conversion, andthe corresponding demodulation or detection as analog-to-digital conversion. Thechanges in the carrier signal are chosen from a finite number of M alternativesymbols (the modulation alphabet).

These are the most fundamental digital modulation techniques:

In the case of PSK, a finite number of phases are used.

In the case of FSK, a finite number of frequencies are used.

In the case of ASK, a finite number of amplitudes are used.

In the case of QAM, a finite number of at least two phases, and at least twoamplitudes are used.


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Why Digital Modulation?

Digital Modulation has several very important benefits over Analog

Modulation. This is the main reason why Digital Modulation Schemesare being employed in our world extensively. Some of these benefitsare as follows;

Data integrity. Repeaters take out cumulative problems intransmission. This enables transmission over longer distances.

It is easy to Multiplex large channel capacities with Digital

Modulation. Encryption in Digital Modulation is easy to implement, hence

added security.

Digital amplifiers regenerate an exact signal, eliminatingcumulative errors. An incoming (analog) signal is sampled, its

value is determined, and the node then generates a new signalfrom the bit value; the incoming signal is discarded. With analogcircuits, intermediate nodes amplify the incoming signal, noiseand all.

Information density. Digital systems can carry far moreinformation in the same channel. This also implies that this

information can be stored in less space.


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Multiplexing

In Telecommunications Multiplexing is a process wheremultiple analog message signals or digital data streams are

combined into one signal over a shared medium. The aim isto share an expensive resource. For example, intelecommunications, several phone calls may betransferred using one wire

A multiplexing technique may be further extended into a

multiple access method or channel access method, forexample TDM into Time-division multiple access (TDMA)and statistical multiplexing into carrier sense multipleaccess (CSMA). A multiple access method makes it possiblefor several transmitters connected to the same physical

medium to share its capacity.


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Types of Multiplexing


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Plesiochronous Digital Hierarchy (PDH)

PDH or the Plesiochronous digital hierarchy is a popular technologythat is widely used in the networks of telecommunication in order to

transport the huge amounts of data over the digital equipment fortransportation like microwave radio or fiber optic systems.

PDH helps in proper transmission of the data that generally runs at thesimilar rate but allows some slight variation in the speed than thenominal rate. The basic transfer rate of the data is 2048 kilobits persecond. For instance, in each speech transmission, the normal rate

breaks into different thirty channels of 64 kilobits per second alongwith two different 64 kilobits per second in order to perform the tasksof synchronization and signaling.

The weaknesses that PDH faced paved way for the introduction anduse of the SDH systems. Although the PDH proved to be abreakthrough in the field of digital transmission, the weaknesses thatmade it less demanded includes:

Asynchronous structure that is rigid.

Restricted management capacity.

Non availability of world standard on the digital formats.

No optical interfaces world standard and without an optical level,networking is not possible.

Pl i h Di it l Hi h


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Plesiochronous Digital Hierarchy In the European system, the E1 signal constitutes the first level of a

hierarchy of signals that are each formed by successively carrying outthe TDM multiplexing of 4 lower level signals. This way we obtain

signals with the following formats: E2 (8.448 Mbit/s), E3 (34.368 Mbit/s)and E4 (139.264 Mbit/s). A fifth level, E5 (565.148 Mbit/s)m was alsodefined but in the end was not standardized. This digital multiplexinghierarchy is the European version of what is known as PlesiochronousDigital Hierarchy or PDH.

Higher Hierarchical Levels


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Higher Hierarchical Levels As is the case with level 1 of the Plesiochronous digital hierarchy (2

Mbit/s), the higher levels also use a frame structure that begins with aframe alignment signal (FAS), with the difference that, at these levels,

multiplexing is carried out bit-by-bit (unlike the multiplexing of 64 kbit/schannels in a 2 Mbit/s signal, which is byte-by-byte), thus making itimpossible to identify the lower level frames inside a higher level frame.


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Synchronous Digital Hierarchy (SDH)

Synchronous Optical Networking (SONET) or Synchronous DigitalHierarchy (SDH) are standardized multiplexing protocols that transfer

multiple digital bit streams over optical fiber using lasers or light-emitting diodes (LEDs). Lower rates can also be transferred via anelectrical interface. The method was developed to replace thePlesiochronous Digital Hierarchy (PDH) system for transporting largeramounts of telephone calls and data traffic over the same fiber wirewithout synchronization problems.

Both SDH and SONET are widely used today. SONET in the U.S. andCanada and SDH in the rest of the world.

Synchronous networking differs from Plesiochronous Digital Hierarchy(PDH) in that the exact rates that are used to transport the data aretightly synchronized across the entire network, using atomic clocks.This synchronization system allows entire inter-country networks tooperate synchronously, greatly reducing the amount of bufferingrequired between elements in the network.

The basic unit of framing in SDH is a STM-1 (Synchronous TransportModule level 1), which operates at 155.52 Mbps.

The STM-1 (synchronous transport module level - 1) frame is the basic

transmission format for SDH or the fundamental frame or the first levelof the s nchronous di ital hierarch . The STM-1 frame is transmitted in


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The STM frame is continuous and is transmitted in a serial fashion,

byte-by-byte, row-by-row. STM1 frame contains

1 octet = 8 bit

Total content : 9 x 270 octets = 2430 octets

overhead : 8 rows x 9 octets

pointers : 1 row x 9 octets

payload : 9 rows x 261 octets

Period : 125 sec

Bit rate : 155.520 Mbps (2430 octets x 8 bits x 8000 frame/s )or270*9*64Kbps : 155.52Mbps

Actual payload capacity : 150.336 Mbps (2349 x 8 bits x 8000 frame/s)

The transmission of the frame is done row by row, from the left to rightand top to bottom.

S h Di it l Hi h (SDH)


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SDH STM1 Frame

S nchronous Digital Hierarch (SDH)


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SDH/ SONET D R


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SDH/ SONET Data Rates

E C i S t


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E-Carrier System In digital telecommunications, where a single physical wire pair can be

used to carry many simultaneous voice conversations by time-division

multiplexing, worldwide standards have been created and deployed. E1is such carrier system.

E1 circuits are very common in most telephone exchanges and areused to connect to medium and large companies, to remote exchangesand in many cases between exchanges.

An E1 link operates over two separate sets of wires, usually twisted

pair cable. A nominal 3 Volt peak signal is encoded with pulses using amethod that avoids long periods without polarity changes. The linedata rate is 2.048 Mbit/s (full duplex, i.e. 2.048 Mbit/s downstream and2.048 Mbit/s upstream) which is split into 32 timeslots, each beingallocated 8 bits in turn. Thus each timeslot sends and receives an 8-bitPCM sample, usually encoded according to A-law algorithm, 8000 timesper second (8 x 8000 x 32 = 2,048,000). This is ideal for voicetelephone calls where the voice is sampled into an 8 bit number at thatdata rate and reconstructed at the other end. The timeslots arenumbered from 0 to 31.

One timeslot (TS0) is reserved for framing purposes, and alternately

transmits a fixed pattern. This allows the receiver to lock onto the startof each frame and match up each channel in turn. The standards allow

E C i S t


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E-Carrier System One timeslot (TS16) is often reserved for signaling purposes, to control

call setup and teardown according to one of several standard

telecommunications protocols. This includes Channel AssociatedSignaling (CAS) where a set of bits is used to replicate opening andclosing the circuit (as if picking up the telephone receiver and pulsingdigits on a rotary phone), or using tone signaling which is passedthrough on the voice circuits themselves. More recent systems usedCommon Channel Signaling (CCS) such as ISDN or Signaling System 7

(SS7) which send short encoded messages with more informationabout the call including caller ID, type of transmission required etc.ISDN is often used between the local telephone exchange and businesspremises, whilst SS7 is almost exclusively used between exchangesand operators.

Unlike the earlier T-carrier systems developed in North America, all 8

bits of each sample are available for each call. This allows the E1systems to be used equally well for circuit switch data calls, withoutrisking the loss of any information.

E C i S t


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E-Carrier System

E C i Hi h L l


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E-Carrier Hierarchy Levels The PDH based on the E0 signal rate is designed so that each higher

level can multiplex a set of lower level signals. Framed E1 is designed

to carry 30 E0 data channels + 1 signaling channel, all other levels aredesigned to carry 4 signals from the level below. Because of thenecessity for overhead bits, and justification bits to account for ratedifferences between sections of the network, each subsequent levelhas a capacity greater than would be expected from simply multiplyingthe lower level signal rate (so for example E2 is 8.448 Mbit/s and not

8.192 Mbit/s as one might expect when multiplying the E1 rate by 4). Note, because bit interleaving is used, it is very difficult to demultiplex

low level tributaries directly, requiring equipment to individuallydemultiplex every single level down to the one that is required.


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What does NEC IDU do?!

NEC IDU is packaged & integrated withcircuitry that enables it to do the following;

a. Modulation/ Demodulation

b. Multiplexing/ De-Multiplexing

c. Switching Functionality

PASOLINK V4 IDU (1/3)


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PASOLINK V4 IDU (1/3)

1. IF connector (to

ODU)2. 2Mbps interface (CH 9 to CH 16): impedance selector switch(75 or 120 ohms)3. LAN Interface for main traffic: Port 1 and Port 2

(Optional)4. WS/LAN: optional port for Wayside In/Outor 10BaseT5. NMS LAN: for PNMS with LAN

interface6. Engineers Orderwire (EOW): receptacle forEOW headset

7. CALL: call buzzer for calling the opposite site of thetransmission path

8. RESET: CPU reset switch for IDU

1

2 3 4 5 6 7

8

PASOLINK V4 IDU


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PASOLINK V4 IDU(2/3)

9. LED: PWR : that the power switch is on (Green)

MAINT: for the purpose of maintenance (Yellow)

ODU : that the ODU alarms occur (Red)

IDU : that the IDU alarms occur (Red)

10. FG : connecting Frame Ground terminal

11. ESD: Connecting terminal for Electro Static Discharge

12. 2Mbps interface (CH 1 to CH 8) ): impedance selector switch (75 or 120 ohms)

13. ALM/AUX ALM: connector for parallel alarms (relay contact) connector for Data

Input / Data Output

10 11 12 139

PASOLINK V4 IDU


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14. OW / DSC / ASC(1) Order wire

(2) Digital and Analog (VF) service channel

15. NMS / RA: for PNMS or remote access Local Craft Terminal (None PM Card)

16. LA Port: connector to PC for local access Local Craft Terminal or PNMT

17. Fuse: for primary DC line (be inserted in each plus and minus line)

14

18. 20SW : power switch

19. DC IN: connector for DC power in.

15 16 17 18 19

PASOLINK V4 IDU(3/3)


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What does NEC ODU do?!

NEC ODU is packaged & integrated withcircuitry that enables it to do the following;

a. Conversion of IF (from IDU) to much higherFrequency for Transmission

b. Conversion of the Received Signal frequencyto IF for IDU to work upon

c. Direct reading of the Received Signal PowerLevel


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Rear Side Front Side

IF connector to IDU RF interface to Antenna( PBR220)RX LEV MON


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The signal is transmitted by a radio broadcasttower.

Base station Room Micro wave antennas Radio wave antennas

R di Si l P ti


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Radio Signal Propagation


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HOP A radio-link connection with a pair of communicating terminals

Point-to-Point Microwave Connection

Gain of antenna


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Gain of antenna

])/(6.0lg[10 20

DG =

D: Diameter: Wavelength

More the Diameter, more is the Gain of Antenna.More the Diameter, more is the distance we can achieve in a

hop.


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FSL F l (dB)


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FSL = Free space loss (dB)

FSL = 92.4 + 20 lg D + 20 lg F FSL = Free Space Loss

D = Path Length in kilometers

F = Radio Frequency in Gigahertz

D Km F GHz


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Basic conceptFree Space Basic Transmission Loss

P = TX Power

PTX

Power

Level

Distance

GTX GRX

PRX

G = Antenna Gain

A0

A0 = Free Space Loss

M

Receiver Threshold

M = Fading Margin

System Characteristics


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System Characteristics

Example


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Example


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EIRP = Pout - Ct + Gt = 16 dBm

Pl = 92.4 + 20xLog F(GHz) + 20xLog R(Km)

Si = EIRP - Pl + Gr - Cr = -82 dBm

Frequency Carries/ Channels


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Frequency Carries/ Channels

The information from sender to receiver is carrier

over a well defined frequency band. This is called a channel

Each channel has a fixed frequency bandwidth (in

KHz) and Capacity (bit-rate)

Different frequency bands (channels) can be usedto transmit information in parallel and

independently.

Tx/ Rx Space & High/ Low Site


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Tx/ Rx Space & High/ Low Site

Tx/ Rx space

Determined by the state. Different frequency has different Tx/ Rx Space.

High/ Low site

High site: Transmit Frequency is higher than ReceiveFrequency.

Low site: Transmit Frequency is lower than ReceiveFrequency.

Note: High Site and Low Site are forbidden at one BTS Site.


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Link Budget Calculations


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Link Budget Calculations

Weather conditions (Rain, wind, etc.)

At high rain intensity (150 mm/hr), the fading of an RFsignal at 2.4 Ghz may reach a maximum of 0.02 dB/Km.Wind may cause fading due to antenna motion.

Interference: Interference may be caused by another system on the

same frequency range, external noise, or some other co-located system.


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The Line of Sight Concept

An optical line of sight exists if an imaginary straight line

can be drawn connecting the antennas on either side ofthe link.

Clear Line of Sight

A clear line of sight exists when no physical objects obstructviewing one antenna from the location of the other antenna. Aradio wave clear line of sight exists if a defined area round theoptical line of sight (Fresnel Zone) is clear of obstacles.

Fresnel Zone


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Fresnel Zone


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Fresnel Zone clear of obstacles


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Polarization

- The time varying direction and amplitude of the electric field vector of the

electromagnetic (radio) wave- Point- to- point microwave paths can be either vertically or horizontally

polarized

- Vertical to horizontal isolation is about 30 dB

Vertical polarization

E

Horizontal polarization

E

The polarization must be identical in one hop!


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Vertically Polarized

WaveguideHorizontally Polarized

Waveguide


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Horizontal polarization


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NEC_Level-1_Training_Presentation.ppt