NEC Level-1 Training Session

Day-1

Haroon Goraya

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

Back to Basics

• WaveA wave is a disturbance that propagates (travels) through space and time, usually by transference of energy. For example, sound waves propagate via air molecules slamming into their neighbors, which push their neighbors into their neighbors (and so on); when air molecules collide with their neighbors, they also bounce away from them (restoring force). This keeps the molecules from actually traveling with the wave.

Waves travel and transfer energy from one point to another, often with no permanent displacement of the particles of the medium—that is, with little or no associated mass transport. They consist instead of oscillations or vibrations around almost fixed locations. Imagine a cork on rippling water, it would bob up and down staying in about the same place while the wave itself moves outward. 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 itself does not flow with it.

Back to Basics

• Types of WavesHere 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 is Wavelength.– Relationship b/w Frequency & Wavelength

• Speed of Wave = Frequency x Wavelength

Back to Basics

• Electromagnetic Waves (EM Waves)• Self-propagating waves that can travel in both Vacuum & Matter with speed of light

(Theoretically). • It comprises electric and magnetic field components, which oscillate in phase

perpendicular to each other and perpendicular to the direction of energy propagation.• EM radiation carries energy and momentum that may be imparted to matter with which it interacts.• According to Maxwell's equations, a spatially-varying electric field generates a time-varying

magnetic field and vice versa. Therefore, as an oscillating electric field generates an oscillating magnetic field, the magnetic field in turn generates an oscillating electric field, and so on. These oscillating fields together form an electromagnetic wave.

• When any wire (or other conducting object such as an antenna) conducts alternating current, electromagnetic radiation is propagated at the same frequency as the electric current.

• Depending on the circumstances, electromagnetic radiation may behave as a wave or as particles.• When EM radiation impinges upon a conductor, it couples to the conductor, travels along it, and

induces an Electric current on the surface of that conductor by exciting the electrons of the conducting material. This effect (the skin effect) is used in antennas.

Back to Basics• Electromagnetic Spectrum

Its is the range of all possible frequencies of electromagnetic radiation. The electromagnetic spectrum extendsfrom below frequencies used for modern radio to gamma radiation at the short-wavelength end, coveringwavelengths from thousands of kilometers down to a fraction of the size of an atom. The long wavelength limitis the size of the universe itself, while it is thought that the short wavelength limit is in the vicinity of the Plancklength, although in principle the spectrum is infinite and continuous.

Microwaves• Microwaves are electromagnetic waves with wavelengths ranging from as

long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz (0.3 GHz) and 300 GHz.

• Electromagnetic waves longer (lower frequency) than microwaves are called “Radio waves".

Why Microwaves?• Microwave Frequencies are being heavily employed in today’s

world for a million different purposes. Some of the reasons which make Microwave ideal for employment 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 & well above 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 while being 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 not thick enough.

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

Analog / Digital Transmission

Analog Transmission

• Analog Modulation Scheme is used to Modulate an Analog Baseband Signal on a High

Frequency Carrier for transmission over a Medium.

Digital Transmission

• Digital Modulation Scheme is used to Modulate an Analog Baseband Signal on a High

Frequency Carrier for transmission over a Medium.

Baseband Analog Signal

Analog Modulation

Analog Demodulation Analog Signal

Analog Transmission

Baseband Analog/ Digital

Signal

Digital Modulation

Digital Demodulation

Analog/ Digital Signal

Digital Transmission

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 or current.• The digital output may use different coding schemes, such as binary, Gray code or two's

complement binary.• The resolution of the converter indicates the number of discrete values it can produce over the

range of analog values. The values are usually stored electronically 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. The minimum change in voltage required to guarantee a change in the output code level is called the LSB (least significant bit, since this is the voltage represented by a change in the LSB). The resolution Q of the ADC is equal to the LSB voltage.

• The analog signal is continuous in time and it is necessary to convert this to a flow of digital values. It is therefore required to define the rate at which new digital values are sampled from the analog signal. The rate of new values is called the sampling rate or sampling frequency of the converter.

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

• Quantization error is due to the finite resolution of the ADC, and is an unavoidable imperfection in all types of ADC. The magnitude of the quantization error at the sampling instant is between zero and half of one LSB.

Analog-to- Digital (A/D) Converter

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 for pulse 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 representation of the input signal (shaded area) that can be easily encoded as digital data 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 by a purpose-specific digital signal processor or general purpose CPU.

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-band information, 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.

Modulation• Modulation is the process of varying one or more properties (Amplitude, Frequency, Phase)

of a high frequency periodic waveform, called the carrier signal, 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 of the Hop.

Analog Modulation• In analog modulation, the modulation is applied continuously in response to the analog

information signal.• Common analog modulation techniques are:• Amplitude modulation (AM) (here the amplitude of the carrier signal is varied in accordance

to the instantaneous amplitude of the modulating signal) – 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 is varied in

accordance to the instantaneous frequency of the modulating signal)– Phase modulation (PM) (here the phase shift of the carrier signal is varied in accordance

to the instantaneous phase shift of the modulating signal)

Analog Modulation

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, and the corresponding demodulation or detection as analog-to-digital conversion. The changes in the carrier signal are chosen from a finite number of M alternative symbols (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 two amplitudes are used.

Why Digital Modulation?

• Digital Modulation has several very important benefits over Analog Modulation. This is the main reason why Digital Modulation Schemes are being employed in our world extensively. Some of these benefits are as follows;– Data integrity. Repeaters take out cumulative problems in transmission. 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, eliminating cumulative errors. An

incoming (analog) signal is sampled, its value is determined, and the node then generates a new signal from the bit value; the incoming signal is discarded. With analog circuits, intermediate nodes amplify the incoming signal, noise and all.

– Information density. Digital systems can carry far more information in the same channel. This also implies that this information can be stored in less space.

Multiplexing• In Telecommunications Multiplexing is a process where multiple analog

message signals or digital data streams are combined into one signal over a shared medium. The aim is to share an expensive resource. For example, in telecommunications, several phone calls may be transferred using one wire

• A multiplexing technique may be further extended into a multiple access method or channel access method, for example TDM into Time-division multiple access (TDMA) and statistical multiplexing into carrier sense multiple access (CSMA). A multiple access method makes it possible for several transmitters connected to the same physical medium to share its capacity.

Types of Multiplexing• The group of multiplexing technologies may be divided into several types,

all of which have significant variations. Here are some of them;• Space Division Multiplexing (SDM)• Code Division Multiplexing (CDM)• Frequency Division Multiplexing (FDM)• Time Division Multiplexing (TDM)

Types of Multiplexing

Multiplexing Hierarchies

Plesiochronous Digital Hierarchy (PDH)• PDH or the Plesiochronous digital hierarchy is a popular technology that is widely used in

the networks of telecommunication in order to transport the huge amounts of data over the digital equipment for transportation like microwave radio or fiber optic systems.

• PDH helps in proper transmission of the data that generally runs at the similar rate but allows some slight variation in the speed than the nominal rate. The basic transfer rate of the data is 2048 kilobits per second. For instance, in each speech transmission, the normal rate breaks into different thirty channels of 64 kilobits per second along with two different 64 kilobits per second in order to perform the tasks of synchronization and signaling.

• The weaknesses that PDH faced paved way for the introduction and use of the SDH systems. Although the PDH proved to be a breakthrough in the field of digital transmission, the weaknesses that made 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.• PDH, if we talk as n x E1 G.703 lines to be transmitted, can be developed only up to 16

E1 lines

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 out the 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 also defined but in the end was not standardized. This digital multiplexing hierarchy is the European version of what is known as Plesiochronous Digital Hierarchy or PDH.

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 a frame alignment signal (FAS), with the difference that, at these levels, multiplexing is carried out bit-by-bit (unlike the multiplexing of 64 kbit/s channels in a 2 Mbit/s signal, which is byte-by-byte), thus making it impossible to identify the lower level frames inside a higher level frame.

Synchronous Digital Hierarchy (SDH)• Synchronous Optical Networking (SONET) or Synchronous Digital Hierarchy (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 an electrical interface. The method was developed to replace the Plesiochronous Digital Hierarchy (PDH) system for transporting larger amounts of telephone calls and data traffic over the same fiber wire without synchronization problems.

• Both SDH and SONET are widely used today. SONET in the U.S. and Canada 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 are tightly synchronized across the entire network, using atomic clocks. This synchronization system allows entire inter-country networks to operate synchronously, greatly reducing the amount of buffering required between elements in the network.

• The basic unit of framing in SDH is a STM-1 (Synchronous Transport Module 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 level of the synchronous digital hierarchy. The STM-1 frame is transmitted in exactly 125 microseconds, therefore there are 8000 frames per second on a fiber-optic circuit designated OC-3 (Optical Carrier-3).

Synchronous Digital Hierarchy (SDH)

• The STM frame is continuous and is transmitted in a serial fashion, byte-by-byte, row-by-row.

• STM–1 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 μsec– Bit rate : 155.520 Mbps (2430 octets x 8 bits x 8000 frame/s )or 270*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 right and top to bottom.

Synchronous Digital Hierarchy (SDH)

SDH STM1 Frame

Synchronous Digital Hierarchy (SDH)

SDH/ SONET Data Rates

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. E1 is such carrier system.

• E1 circuits are very common in most telephone exchanges and are used to connect to medium and large companies, to remote exchanges and 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 a method that avoids long periods without polarity changes. The line data rate is 2.048 Mbit/s (full duplex, i.e. 2.048 Mbit/s downstream and 2.048 Mbit/s upstream) which is split into 32 timeslots, each being allocated 8 bits in turn. Thus each timeslot sends and receives an 8-bit PCM sample, usually encoded according to A-law algorithm, 8000 times per second (8 x 8000 x 32 = 2,048,000). This is ideal for voice telephone calls where the voice is sampled into an 8 bit number at that data rate and reconstructed at the other end. The timeslots are numbered 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 start of each frame and match up each channel in turn. The standards allow for a full Cyclic Redundancy Check to be performed across all bits transmitted in each frame, to detect if the circuit is losing bits (information), but this is not always used.

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 Associated Signaling (CAS) where a set of bits is used to replicate opening and closing the circuit (as if picking up the telephone receiver and pulsing digits on a rotary phone), or using tone signaling which is passed through on the voice circuits themselves. More recent systems used Common Channel Signaling (CCS) such as ISDN or Signaling System 7 (SS7) which send short encoded messages with more information about the call including caller ID, type of transmission required etc. ISDN is often used between the local telephone exchange and business premises, whilst SS7 is almost exclusively used between exchanges and 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 E1 systems to be used equally well for circuit switch data calls, without risking the loss of any information.

E-Carrier System

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 are designed to carry 4 signals from the level below. Because of the necessity for overhead bits, and justification bits to account for rate differences between sections of the network, each subsequent level has a capacity greater than would be expected from simply multiplying the 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 individually demultiplex every single level down to the one that is required.

What does NEC IDU do?!

• NEC IDU is packaged & integrated with circuitry that enables it to do the following;a. Modulation/ Demodulationb. Multiplexing/ De-Multiplexingc. Switching Functionality

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/Out or 10BaseT5. NMS LAN: for PNMS with LAN interface6. Engineer’s Orderwire (EOW): receptacle for EOW headset

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

8. RESET: CPU reset switch for IDU

12 3 4 5 6 7

8

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

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)

What does NEC ODU do?!

• NEC ODU is packaged & integrated with circuitry that enables it to do the following;a. Conversion of IF (from IDU) to much higher Frequency

for Transmissionb. Conversion of the Received Signal frequency to IF for IDU

to work uponc. Direct reading of the Received Signal Power Level

Rear Side Front Side

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

The signal is transmitted by a radio broadcast tower.

Base station Room Micro wave antennas

Radio wave antennas

Radio Signal Propagation

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

Point-to-Point Microwave Connection

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.

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

Basic concept Free Space Basic Transmission Loss

P = TX Power

PTX

PowerLevel

Distance

GTX GRX

PRX

G = Antenna Gain

A0

A0 = Free Space Loss

M

Receiver Threshold

M = Fading Margin

System Characteristics

Example

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

– 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 used to transmit information in parallel and independently.

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 Receive Frequency.• Low site: Transmit Frequency is lower than Receive Frequency.

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

Link Budget Calculations

• Weather conditions (Rain, wind, etc.)

• At high rain intensity (150 mm/hr), the fading of an RF signal 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.

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 of the link.

Clear Line of Sight

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

Fresnel Zone

Fresnel Zone clear of obstacles

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!

Vertically PolarizedWaveguide

Horizontally PolarizedWaveguide

Vertical polarization

Horizontal polarization