introduction to Telecommunication RF part 1

8/9/2019 introduction to Telecommunication RF part 1

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GSM900

DCS1800

Introduction to Telecommunication Systems


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Describe the major components of the networkand their interrelationships.Describe how your voice is converted toelectrical signals and transmitted over the

network.

Objectives

Network Overview


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A system of interconnected elements

A system of various departments tosupport these elements

Traffic is the flow of information ormessages throughout the network

Definition of a network:


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A system of interconnectedelements linked by facilities (i.e.,physical connections) over whichtraffic will flow.

The traffic may be conversations,information, or complex video oraudio services. Thetelecommunications networkmust also be able to control theinterconnected elements

What is a telecommunications network?


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Physical components required fortelecommunication network

Transmission Facilities

Local Loop

IOF - Interoffice facilities

Switching Systems

Customer Premise Equipment(CPE)

Network Components and Architecture


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In its simplest form, a transmission facility is acommunication between two end points. Thiscommunication path can also be referred to as:

ChannelCircuit

TrunkFor telephony purposes, the communicationpath (also known as network facilities) can beclassified into two broad categories:

Local LoopInteroffice Facilities (IOF)/Trunk

Transmission Facilities


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The local loop: is a circuit that connects a

customer to the telephonenetwork.

provides the customer withaccess to the switchingsystem.

The term "loop" is derived fromthe pair of wires that forms theelectrical path between thecustomer and the central office.

The local loop is also referred toas the subscriber loop.

A simple local loop architecture isdepicted in Figure

Transmission Facilities..


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The primary functions of switchingsystems are to provide:

Call setup and routingCall supervisionCustomer I.D. and phonenumbers

These are accomplished byinterconnecting facilitiesSwitching systems located at thecentral office (CO) that are used toprovide dial tone and ringing arereferred to as end offices or local

switches. These switches can also beinterconnected with other switches.Another type of switch, tandem, isused as a hub to connect switches andprovide routing. (No dial tone isprovided to the customer.)

Switching Systems


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Three components of anytransmission system are the

The transmitterThe receiverThe communication path

In its simplest form, the CPE orcustomer premises equipment, is thetransmitter and receiver. The media(twisted pair copper, coaxial cable,optical fiber, radio waves) thatconnects the CPE is the path.

Components for Transmission


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Many customers' telephones areconnected to the central office by apair of wires within a cableWhy two wires?

Because your telephone is anelectro-mechanical instrument, itrequires a battery source and aground source.

The battery source is supplied fromthe central office equipment to yourtelephone set by a wire called the ringlead. The ground source is transmittedfrom the central office by a wire called

the tip lead. Together, the tip and ringof the telephone set are commonlyreferred to as a cable pair.

Telephone Connection to the Central Office


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Analog and Digital Transmission


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Describe a carrier system.Describe the major differences between analog anddigital signals.Describe the analog to digital and digital to analogconversion process.Compare and contrast Frequency Division Multiplexingand Time Division Multiplexing.

Objectives

Analog and Digital Transmission


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The telecommunications network can transmit a variety ofinformation, in two basic forms, analog and digital. In thislesson we will examine both. This information may betransmitted over a circuit/channel or over a carrier system.Where: A circuit/channel is a transmission path for a singletype of transmission service (voice or data) and is generallyreferred to as the smallest subdivision of the network. Acarrier, on the other hand, is a transmission path in which oneor more channels of information are processed, converted toa suitable format and transported to the proper destination.

The two types of carrier systems we will be discussing in thislesson are:1. FDM (Frequency Division Multiplexing) -- analog2. TDM (Time Division Multiplexing) - digital

Introduction


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Multiplexing is the process of transmitting two or moreindividual signals over a common path. In effect, it increasesthe amount of information transmitted, while decreasing therequirement for the physical media (no longer a 1:1 ratio).

Frequency Division Multiplexing The first type of multiplexing was an analog multiplexing

technique. Frequency Division Multiplexing (FDM). In FDM, thebandwidth of the transmission path serves as the frame of

reference for all of the information being transmitted. The totalbandwidth is divided into subchannels consisting of smallersegments of the available bandwidth Each subchannel iscapable of carrying a separate signal. Signals are transmittedsimultaneously. Thus, with FDM each channel is:

Assigned a different frequency Separated into channels 4000 Hz. wide.

The different channels are then stacked and transported over acommon path. In other words, each channel occupies a portionof the total frequency bandwidth.

Multiplexing


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Digital Transmission, demanded by our customers, hascontinually increased since its introduction in 1962. This is due, inlarge part, to the fact that more of our customers require a highdegree of accuracy in the information they are transmitting overour network. And with a digital transmission (as opposed toanalog) system we are able to manage the quality of the signalby managing the previously discussed transmission impairments.

Thus, digital systems: 1). are a better switching interface 2.) areeasier to multiplex 3.)produce clearer signals

Digital Signals A digital signal is a discrete signal. It is depictedas discontinuous -- Discretely variable (on/off) as opposed to ananalog signal which is continuously variable (sine wave) A digitalsignal has the following characteristics:

1.) Holds a fixed value for a specific length of time2.) Has sharp, abrupt changes3.) A preset number of values allowed

Why Digital Transmission?

Th P l C d M d l i (PCM) P


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Pulse Code Modulation (PCM) converts analog signals to a digital format (signal).

This process has four steps

The Pulse Code Modulation (PCM) Process

St O Filt i


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Frequencies below 300 Hz and above3400 Hz (Voice Frequency range) arefiltered from the analog signalThe lower frequencies are filtered outto remove electrical noise induced fromthe power lines.

The upper frequencies are filtered outbecause they require additional bitsand add to the cost of a digitaltransmission system.The actual bandwidth of the filteredsignal is 3100 Hz (3400 - 300). It is

often referred to as 4 kHz.

Step One: Filtering

St T S li


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The analog signal is sampled 8000

times per second. The rate at which theanalog signal is sampled is related tothe highest frequency present in thesignal. This is based on the Nyquistsampling theorem. In his calculations,Nyquist used a voice frequency rangeof 4000 Hz (which represents the voice

frequency range that contains"intelligent" speech). Thus, thestandard became a sampling rate of8000 Hz, or twice the bandwidth. Thesignal that is the result of the samplingprocess contains sufficient informationto accurately represent the informationcontained in the original signal. Theoutput of this sampling procedure is aPulse Amplitude Modulated, or PAM,signal.

Step Two: Sampling

St Th d F Q ti i d E di


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In the third step of the A/D conversionprocess, we quantize the amplitude ofthe incoming samples to one of 255amplitudes on a quantizing scaleThus, in this step the sampled signalis matched to a segmented scale. The

purpose of step three is to measure theamplitude (or height) of the PAM signaland assign a decimal value that definesthe amplitude. Based on the quantizingscale, each sampled signal is assigneda number between 0 and +127 to

define its amplitude.

Step Three and Four: Quantizing and Encoding

In the fourth step of the A/D conversion process, the quantized samples areencoded into a digital bit stream (series of electrical pulses).

Ti di i i lti l i (TDM)


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Time division multiplexing (TDM) is a digital multiplexingtechnique. In TDM, a number of low rate channels are fedinto a multiplexer (e.g., D Bank), which combines theminto one high rate digital signal. Each of the 24 VF(voicefrequency)/DS0 channels is assigned a specific time slotby the TDM(Time Division Multiplexer). Thus, TDM is aprocess by which several digital signals are combinedonto a single path and sent sequentially. Relating thisback to the PAM process: The analog signal is sampled8000 times a second. There will be 8,000 eight-bit words

transmitted per second. These words will be 1/8000second (or 125 microseconds) apart.

Time division multiplexing (TDM)

Digital Hierarchy


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The digital hierarchy represents thestandard rates by which digitalcommunications are sent in NorthAmerica.The basic building block of the digitalhierarchy is the DS0 rate at 64 Kbps.Remember that multiplying 8-bit wordsby the sampling rate of 8000times/second produces the 64,000 bpsrate. With Time Division Multiplexing,multiplexing by an additional 24 timeslots and including 8000 framing bits

for timing information produces the1,544,000 bps or 1.544 Mbs. DS1 isconsidered the beginning of highcapacity digital transmission rates.

Digital Hierarchy


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Introduction to Switching

Fundamentals of Switching


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Identify the major functions of switching.State the meaning of electronic switching systems (ESS)and stored program control (SPC) switching systems.

Describe how this family of switches differs from earlierswitches. Describe the major components of a digitalswitch and the main functions of those components.Identify and describe the basic traffic measurements.

Objectives

Fundamentals of Switching

Functions of a Switch


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The purpose of a switch is to provide a path for the call. Toprocess a call the switch performs three main functions:

1) Identifies the customer2) Sets up the communication path3) Supervises the call

Functions of a Switch

Identify the Customers


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Initially customers were identified by the

jack position they occupied on theswitchboard. With the introduction ofelectromechanical switches, customerswere as signed telephone numbers. (Alsocalled line or station numbers.) Thecustomer's cable pair is terminated and

cross-connected to the office equipment atthe main distributing frame. Officeequipment terminated on the MDFrepresents a physical location in the switchand a specific telephone number. With theintroduction of electronic switches, atelephone number is no longer wired to a

specific component of the switch. Thetelephone number is now associated with acustomer record which exists in thetranslations (or memory) of the switch.

Identify the Customers

Set Up the Path


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Early in the processing of a call, theswitch needs to determine what type ofa call is being made. By analyzingeither the first digit (is it a 0 or a 1?) orthe first three digits (prefix), the switchwill determine whether the call is

intraswitch or inter-switch. If the callbeing processed is an intra-switch call,the path that the switch will allocate iscalled a line (i.e., "on the line side ofthe network"). If the call is an inter-switch call, the path that the switch will

allocate is a trunk.

Set Up the Path

Supervise the Call


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The supervision functions of the switchtend to be overlooked because they aretransparent to the customer. They are,however, extremely important becausethey directly impact the efficientfunctioning of the switch itself.

Supervise the Call


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Wireless Fundamentals

BASIC Telephony


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Off Hook

Dial Tone

Dialing Digits

RBT

Conversation

RingOff Hook &

Conversation

Signaling

TrafficSWITCH / EXCHANGE

BASIC Telephony

Wireless Telephony


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BSCBTS BTS

Mobile

Subscriber...

MSC

Wireless Telephony

Different Standards Worldwide


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Till 1982 Cellular Systems were exclusively Analog Radio Technology.

Advanced Mobile Phone Service (AMPS)

U.S. standard on the 800 MHz Band

Total Access Communication System (TACS)

U.K. standard on 900 MHz band

Nordic Mobile Telephone System (NMT)

Scandinavian standard on the 450 & 900 MHz band




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Analog Mobile Telephony


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End of 1980s Analog Systems unable to meet continuing demands

Severely confined spectrum allocations Interference in multipath fading environment

Incompatibility among various analog systems

Inability to substantially reduce the cost of mobile terminals and

infrastructure required

Analog Mobile Telephony

Digital Mobile Telephony


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Spectrum space - most limited and precious resource

Solution - further multiplex traffic (time domain)

Can be realized with Digital Techniques only

Digital Mobile Telephony

Cellular Communication


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A cellular system links Mobile subscribers to Public

Telephone System or to another Mobile subscribers.

It removes the fixed wiring used in a traditional telephone installation.

Mobile subscriber is able to move around, perhaps can travel

in a vehicle or on foot & still make & receive call.

Advantage of Cellular Communication


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Mobility

Flexibility

Convergence

Greater QOS

Network Expansion

Revenue/Profit

g

First Mobile Radio Telephone (1924)


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Courtesy of Rich Howard

p ( )

First Generation


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Advanced Mobile Phone Service (AMPS) US trials 1978; deployed in Japan (79) & US (83)

800 MHz band two 20 MHz bands TIA-553

Still widely used in US and many parts of the world

Nordic Mobile Telephony (NMT) Sweden, Norway, Demark & Finland

Launched 1981; now largely retired

450 MHz; later at 900 MHz (NMT900) Total Access Communications System (TACS)

British design; similar to AMPS; deployed 1985

Some TACS-900 systems still in use in Europe

Second Generation 2G


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Digital systems

Leverage technology to increase capacity

Speech compression; digital signal processing Utilize/extend Intelligent Network concepts

Improve fraud prevention

Add new services

There are a wide diversity of 2G systems IS-54/ IS-136 North American TDMA; PDC (Japan)

iDEN DECT and PHS

IS-95 CDMA (cdmaOne)

GSM

D-AMPS/ TDMA & PDC


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Speech coded as digital bit stream Compression plus error protection bits

Aggressive compression limits voice quality Time division multiple access (TDMA)

3 calls per radio channel using repeating time slices

Deployed 1993 (PDC 1994) Development through 1980s; bakeoff 1987

IS-54 / IS-136 standards in US TIA

ATT Wireless & Cingular use IS-136 today Plan to migrate to GSM and then to W-CDMA

PDC dominant cellular system in Japan today NTT DoCoMo has largest PDC network

iDEN


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Used by Nextel

Motorola proprietary system

Time division multiple access technology Based on GSM architecture

800 MHz private mobile radio (PMR) spectrum

Just below 800 MHz cellular band

Special protocol supports fast Push-to-Talk

Digital replacement for old PMR services Nextel has highest APRU in US market due to Direct Connect

push-to-talk service

DECT and PHS


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Also based on time division multiple access

Digital European Cordless Telephony Focus on business use, i.e. wireless PBX

Very small cells; In building propagation issues

Wide bandwidth (32 kbps channels)

High-quality voice and/or ISDN data

Personal Handiphone Service Similar performance (32 kbps channels)

Deployed across Japanese cities (high pop. density)

4 channel base station uses one ISDN BRI line

Base stations on top of phone booths

Legacy in Japan; new deployments in China today

North American CDMA (cdmaOne)


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Code Division Multiple Access

All users share same frequency band

Discussed in detail later as CDMA is basis for 3G Qualcomm demo in 1989

Claimed improved capacity & simplified planning

First deployment in Hong Kong late 1994

Major success in Korea (1M subs by 1996)

Used by Verizon and Sprint in US Simplest 3G migration story today

cdmaOne IS-95


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TIA standard IS-95 (ANSI-95) in 1993

IS-95 deployed in the 800 MHz cellular band

J-STD-08 variant deployed in 1900 MHz US PCS band Evolution fixes bugs and adds data

IS-95A provides data rates up to 14.4 kbps

IS-95B provides rates up to 64 kbps (2.5G)

Both A and B are compatible with J-STD-08

All variants designed for TIA IS-41 core networks (ANSI 41)

GSM


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Groupe Special Mobile , later changed to Global System for Mobile

Joint European effort beginning in 1982 Focus on seamless roaming across Europe

Services launched 1991 Time division multiple access (8 users per 200KHz)

900 MHz band; later extended to 1800MHz

Added 1900 MHz (US PCS bands)

GSM is dominant world standard today Well defined interfaces; many competitors

Network effect (Metcalfes law) took hold in late 1990s

Tri-band GSM phone can roam the world today


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Multiple Access Technologies

1G Separate Frequencies


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30 KHz

30 KHz

30 KHz

30 KHz

30 KHz

30 KHz

30 KHz

30 KHzFreque

ncy

FDMA Frequency Division Multiple Access

2G TDMA Time Division Multiple Access


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Freque

ncy

Time

200 KHz

200 KHz

200 KHz

200 KHz

One timeslot = 0.577 ms One TDMA frame = 8 timeslots

2G & 3G CDMA Code Division Multiple Access


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Spread spectrum modulation

Originally developed for the military

Resists jamming and many kinds of interference Coded modulation hidden from those w/o the code

All users share same (large) block of spectrum

One for one frequency reuse

Soft handoffs possible

Almost all accepted 3G radio standards are based on CDMA

CDMA2000, W-CDMA and TD-SCDMA

Multi-Access Radio Techniques


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Courtesy of Petri Possi, UMTS World

3G Vision


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Universal global roaming

Multimedia (voice, data & video)

Increased data rates 384 kbps while moving

2 Mbps when stationary at specific locations

Increased capacity (more spectrally efficient)

IP architecture

Problems No killer application for wireless data as yet

Vendor-driven

International Standardization


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ITU (International Telecommunication Union)

Radio standards and spectrum

IMT-2000

ITUs umbrella name for 3G which stands for InternationalMobile Telecommunications 2000

National and regional standards bodies are collaborating

in 3G partnership projects ARIB, TIA, TTA, TTC, CWTS. T1, ETSI - refer to reference

slides at the end for names and links

3G Partnership Projects (3GPP & 3GPP2)

Focused on evolution of access and core networks

IMT-2000 Vision


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Satellite

MacrocellMicrocell

UrbanIn-Building

Picocell

Global

Suburban

Basic TerminalPDA Terminal

Audio/Visual Terminal

IMT-2000 Radio Standards


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IMT-SC* Single Carrier (UWC-136): EDGE GSM evolution (TDMA); 200 KHz channels; sometimes called 2.75G

IMT-MC* Multi Carrier CDMA: CDMA2000 Evolution of IS-95 CDMA, i.e. cdmaOne

IMT-DS* Direct Spread CDMA: W-CDMA New from 3GPP; UTRAN FDD

IMT-TC** Time Code CDMA New from 3GPP; UTRAN TDD

New from China; TD-SCDMA IMT-FT** FDMA/TDMA (DECT legacy)

* Paired spectrum; ** Unpaired spectrum

CDMA2000 Pros and Cons


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Evolution from original Qualcomm CDMA

Now known as cdmaOne or IS-95

Better migration story from 2G to 3G

cdmaOne operators dont need additional spectrum

1xEVD0 promises higher data rates than UMTS, i.e. W-CDMA

Better spectral efficiency than W-CDMA(?)

Arguable (and argued!)

CDMA2000 core network less mature

cmdaOne interfaces were vendor-specific

Hopefully CDMA2000 vendors will comply w/ 3GPP2

W-CDMA (UMTS) Pros and Cons


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Wideband CDMA

Standard for Universal Mobile Telephone Service (UMTS)

Committed standard for Europe and likely migration path forother GSM operators

Leverages GSMs dominant position

Requires substantial new spectrum

5 MHz each way (symmetric)

Legally mandated in Europe and elsewhere

Sales of new spectrum completed in Europe

At prices that now seem exorbitant

TD-SCDMA


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Time division duplex (TDD)

Chinese development

Will be deployed in China Good match for asymmetrical traffic!

Single spectral band (1.6 MHz) possible

Costs relatively low

Handset smaller and may cost less

Power consumption lower TDD has the highest spectrum efficiency

Power amplifiers must be very linear

Relatively hard to meet specifications

Migration To 3G


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CDMA

GSM

TDMA

PHS(IP-Based)

64Kbps

GPRS

115Kbps

CDMA 1xRTT

144 Kbps

EDGE

384Kbps

cdma2000

1X-EV-DV

Over 2.4 Mbps

W-CDMA

(UMTS)

Up to 2Mbps

2G

2.5G

2.75G 3G

1992 - 2000+2001+

2003+

1G

1984 - 1996+

2003 - 2004+

TACS

NMT

AMPS

GSM/

GPRS

(Overlay)115 Kbps

9.6 Kbps

9.6 Kbps

14.4 Kbps

/ 64 Kbps

9.6 Kbps

PDC

Analog Voice

Digital VoicePacket Data

IntermediateMultimedia

Multimedia

PHS

TD-SCDMA

2 Mbps?

9.6 Kbps

iDEN

(Overlay)

iDEN

Source: U.S. Bancorp Piper Jaffray

Mobile Standard Organizations


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Mobile

Operators

GSM, W-CDMA,

introduction to Telecommunication RF part 1

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