All About Electronics

Global System for Mobile Communications

GSM (Global System for Mobile Communications) is a Digital Wireless Technology used for cell phone in the world that is, it is a cellular technology used for transmitting mobile voice and data services. It was developed by the European companies.

Features Of GSM

It is 2G Technology
GSM is a circuit-switched technology
Uses GMSK [Gaussian Minimum Shift Keying] Modulation
It supports FDMA & TDMA
It uses SIM card so u can easily switch your SIM card between phones
International roaming is easier on a GSM network
In GSM every user requires a separate frequency channel for communication
GSM accounts for 80% of total mobile phone technologies market

The Frequency Band(range) in GSM
The frequency of the carrier is very important, because it determines the Size, power, efficiency of your mobile phones.

It supports FDMA & TDMA as Multiple Access Techniques

Date Published: Mar 12, 2012 - 9:35 am

Radio Frequency - RF Spectrum

Radio signals are transmitted through electromagnetic waves, also called radio waves, in radio communication system. The radio waves have a wide frequency range starting from a few ten kilo Hertz (kHz) to several thousand Mega Hertz (MHz). This wide range frequencies is called the radio spectrum or RF spectrum.

The RF spectrum is classified according to the applications of the spectrum in different service areas. The classification of the RF spectrum is given in below table along with the associated applications in communication system.

Date Published: Mar 09, 2012 - 4:10 am

Digital Microwave Communication

Microwave is a kind of electromagnetic wave. In a broad sense, the microwave frequency range is from 300 MHz to 300 GHz. But In microwave communication, the frequency range is generally from 3 GHz to 30 GHz.

Concept of Digital Microwave Communication

Digital microwave communication is a way of transmitting digital information in atmosphere through microwave or radio frequency (RF).

Microwave communication refers to the communication that use microwave as carrier.

Digital microwave communication refers to the microwave communication that adopts the digital modulation.

The baseband signal is modulated to intermediate frequency (IF) first . Then the intermediate frequency is converted into the microwave frequency.

The baseband signal can also be modulated directly to microwave frequency, but only phase shift keying (PSK) modulation method is applicable.

Date Published: Mar 09, 2012 - 4:01 am

Multiplexing Vs Multiple Access

Multiplexing

Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link.

Multiple Access

If the physical links are shared by more than two nodes/users, it is said to be Multiple Access.

Categories of Multiplexing

a. Frequency Division Multiplexing (FDM)

b. Time Division Multiplexing (TDM)

c. Wave Division Multiplexing (WDM)

Categories of Multiple Access Methods

a.Frequency Division Multiple Access (FDMA) - flexible and simple

b.Time Division Multiple Access (TDMA) - popular

c.Code Division Multiple Access (CDMA Spread Spectrum) - highly secure

Date Published: Jan 07, 2012 - 3:42 am

Market Analysis of Pak's Cellular Mobile Phone Companies

Currently, six cellular mobile phone companies are operating in pakistan namely, InstaPhone, Paktel(Zong), Mobilink, Ufone, Al-Warid and Telenor. All the cellular mobile phone service providers work under the executive control of Pakistan Telecommunication Authority (PTA) through its Mobile Policy. It initiates new access code for each cellular service provider if it reaches the limit of 5 million subscribers. PTA keeps a visionary watch on the services of the cellular mobile phone service providers to ensure quality services and prevent those providing bad services to the subscribers. If any service provider is not up to the mark in terms of connectivity, voice quality etc…, it is charged for by heavy fine according to the rules and regulations. A brief description of each of these cellular mobile service providers is given below.

§ INSTAPHO is the first cellular service provider company which started its operations in Pakistan. It was established in 1990 and started its operations on September 1990.

Currently, InstaPhone is providing its services with CDMA Technology. From the inception, InstaPhone network had been using Analog Mobile Phone System (AMPS) Technology but, with the advancement in technology it converted its networks to D-MPS Technology which is also referred to as Time Division Multiple Access (TDMA) Technology.

§ PAKTEL:

Paktel is the second cellular service provider company in Pakistan. It was established in 1992 and started its operations in the end 1992. It was set up by cable & wireless and carried out AMPS services until 2004. Later on the company launched GSM services as well. Currently Paktel is providing its services with both Analog Mobile Phone System (AMPS) and Global System for Mobile Communication (GSM) based technologies.It has no GPRS and MMS services.

§ MOBILINK:

Mobilink is the third cellular service provider in Pakistan. It is the subsidiary of ORASCOM telecom. It was established in 1994 and started its operation in early 1994.Mobilink is the first GSM (Global System for Mobile communication) cellular based network of Pakistan. Prior to this, other companies namely InstaPhone and Paktel were using AMPS technology for mobile communication. GSM technology provides higher capacity for data transfer than AMPS technology, and is based on SIM technology. Mobilink, came into the market and became very popular among the users because it was the first SIM based GSM network.

§ Ufone-PTML:

Ufone-PTML (Pakistan Telecom Mobile Limited) is the fourth cellular service provider in Pakistan. Ufone network was established in January 2001.Ufone network also uses state of the art SIM based GSM technologY.

§ AL-WARID:

Warid Telecom is the fifth cellular service provider in Pakistan.Al-Warid network uses state of the art SIM based GSM technology.Warid telecom is providing services like GPRS for internet access, SMS, MMS, and International roaming with very competitive prices to its customers. Besides these, it is also providing free roaming throughout Pakistan, free SMS via internet and the newly introduced 30 second billing system for the first time in Pakistan.

§ TELENOR:

Telenor is the sixth cellular service provider in Pakistan. It was established in 1992 and started its operations in the end of 1992.It was the first cellular network that had introduced a new idea of easy load which is an excellent way of recharging......;)

Date Published: Dec 06, 2011 - 12:38 am

MXB7843 interfacing with Microcontroller - Block Diagram

MXB7843TOUCHSCREENINTERFACINGBLOCKDIAGRAM

Before you read on further, read the working of 4 wire resistive touch screen. This post is for the newbies; technicalities will be addressed later.

It is always better to use a dedicated controller for touch screens, instead of designing your own. The best option according to me is to use one of the product of MAXIM, MXB7843.

MXB7843 is controller dedicated for 4 wire resistive touch screens. It has a configurable ADC of 8/12 bit resolution. Overall pictorial representation says that to interface a 4 wire resistive touch screen, what you have to have a microcontroller apart from touch screen controller and a touch screen itself. Touch Screen is directly connected to the microcontroller. The microcontroller which is controlling all the affairs gets the coordinates of the touch screen, whenever it is interrupted, via SPI communication. SPI communication is used for high speed synchronous communication. Once the data is received in 8 or 12 bit format, you can play around as you desired.

The schematic of MXB7843 is given below:

More to follow!

Date Published: Nov 11, 2011 - 8:03 pm

8051 LCD interfacing Command Codes

Before you interface an LCD with any microcontroller , say 8051 or AVR, you should have a knowledge of basic LCD commands. These commands or codes are used to get the LCD perform some particular task, for example, clearing the LCD display screen ornshifting entire data to the right etc. I have gathered here some the commands that might prove for you an important data, because once I was doing 8051 LCD interfacing it really helped me a lot. Here are some of it :-

01H : Clear Display Screen
02H : Return Home
04H: Decrement Cursor
06H : Increment Cursor
05H : Shift Dis[;ay Right
07H : Shift Display Left
08H : Display off, Cursor off
AH : Display off, Cursor on
CH : Display on, Cursor off
EH : Display on, Cursor Blinking
FH : Display on, Cursor Blinkinf
10H: Shift Cursor position to left
14H: Shift Cursor position to right
18H: Shift the entire display to left
1CH: Shift the entire display to right
80H: Force cursor to begin from the Ist line
C0H:Force cursor to begin from the 2nd line
38H: 2 lines and 5 x 7 matrix

More to folow for 8051 LCD interfacing

Date Published: Oct 17, 2011 - 4:49 am

Finding order of Butterworth IIR filter in Matlab GUI

Order of filter is very important as far as the characteristics of filter design is concerned. This particular GUI is for all Butterworth IIR filters. Order of butterworth filter is given by :

where Ap and As are passband and stopband attenuations in dB and wsp is the prototype stopband edge frequency of digital filter and wpp is the prototype passband edge frequency i-e cutoff of frequency of the digital filter to be designed.

You may calculate from the above formula but as far as designing of the problems for student is concerned, it may take a long time to take correct values out of the calculator. There you need an easy interface to get your work done. This assignment was given to us by our Professor, S K Hasnain who is the author of two books on Signals and Systems and Digital Signal Processing. Below you can download the M-File and Fig File. But if you dont have the basic idea about Graphical User Interface, see how to make a simple calculator in MATLAB GUI.

Download N.m

Download N.fig

GUI looks like

Date Published: Oct 17, 2011 - 4:45 am

Basic Concept of FDM and TDM

Why do we need Multiplexing technique?

In communication, under the simplest conditions, a medium can carry only one signal at any moment in time.For multiple signals to share one medium, the medium must somehow be divided, giving each signal a portion of the total bandwidth. This is where the concept of Multiplexing comes!

Multiplexing means “sharing a medium”. It is a form of data transmission in which one communication channel carries several transmissions at the same time. In simple words, the method of dividing a single channel into many channels so that a number of independent signals may be transmitted on it is known as Multiplexing.

Multiplexing techniques can be divided into two basic categories:

Frequency Division Multiplexing-FDM

Time Division Multiplexing-TDM

Frequency Division Multiplexing-FDM

In FDM the available bandwidth is divided into a number of smaller independent logical channels with each channel having a small bandwidth. It assigns “frequency ranges” to each “user” or “signal” on a medium. Thus, all signals are transmitted at the same time, each using different frequencies.The method of using a number of carrier frequencies, each of which is modulated by an independent signal is in fact frequency division multiplexing.

Time Division Multiplexing-TDM

In TDM, sharing is accomplished by dividing available “transmission time” on a medium/channel among users.

Each user of the channel is allotted a small time interval during which he transmits a message. Total time available in the channel is divided, and each user is allocated a time slice. In TDM, users send message sequentially one after another. Each user can use the full channel bandwidth during the period he has control over the channel.

Date Published: Oct 10, 2011 - 9:13 am

Multiplexer

The term Multiplexing means "sharing of a resource/medium" .Resource could be time, frequency, space or any physical medium .Multiplexer is a communication device that multiplexes (combines) several signals for transmission over a single medium.

It helps different sources of data to use a single medium for transmitting their data.Basically the aim is to share an expensive resource

In more simple words, Multiplexer also called as Mux is a device that selects one of several analog or digital input signals and forwards the selected input into a single line.A multiplexer of 2^ⁿ inputs has n select lines, which are used to select which input line to send to the output.

A device that performs the reverse process is called a Demultiplexer (DEMUX).

Follow this tutorial for more understanding of Multiplexer

http://www.wisc-online.com/Objects/ViewObject.aspx?ID=DIG5604

The Operation of a Multiplexer/Demultiplexer Circuit

http://www.wisc-online.com/Objects/ViewObject.aspx?ID=DIG5804

Date Published: Oct 07, 2011 - 8:03 pm

E-books

Follow the following simple steps to download a big collection of e-books, of every field!

1-Creat your account :

http://library.nu/

2-Login and search your required book

3-Click on "ifile.it" in the bottom

4-Click on "Request download ticket"

5-and last, click on "Download "

Date Published: Oct 06, 2011 - 8:10 am

Basics of Channel Coding

Environmental interference and physical defects in the communication medium can cause random bit errors during data transmission. Channel coding also known as Error coding is a method of detecting and correcting these errors to ensure that information is transferred from its source to its destination reliably.

The idea behind channel coding is, to make the data more secure and error free. Channel Coding is done to ensure that the signal transmitted is recovered with very low probability of error at the destination. You can think channel coding as a “Security guard” for data .

What happens If Channel coding is not used?

If data is transmitted without channel coding ,and an error occurs in data , the receiver will inform the transmitter that an error has occurred in data, therefore transmit it again.Transmitter will have to retransmit the whole data ! A question may arise in your mind that, incase of error, data will be retransmitted so, what’s the need of using channel coding?

The reason is, if transmitter retransmits the whole data definitely there will be wasteage of power,and delay in communication. Therefore to avoid these factors it is necessary to implement channel coding.

In channel coding extra bits are added along with actual data bits. These extra bits are termed as “Redundant bits” because they actually cause redundancy in data. They ensure minimal or no error.

Error coding uses mathematical formulas to encode data bits at the transmitter or source into longer bits for transmission. The "coded data " is then decoded at the destination to retrieve the information. These bits help the the destination or receiver to determine if the communication medium introduced errors, if yes correct them so that the data need not be retransmitted.

Error coding is used in satellite and deep space communications, network communications, cellular telephone networks, magnetic and optical data storage media, and almost any other form of digital data communication.

Date Published: Oct 05, 2011 - 9:09 am

What is Bit Error Rate ?

When data is transmitted to its destination over a communication channel there is a possibility of errors being introduced into the the data. In digital communication performance of the system is assessed by a term called as bit error rate, BER. BER is also known by the term Probability of Error.

In simple words, it is actually the ratio of number of bits in error to the total number of bits transmitted.

BER = Bits in Error/Total Number of Bit transmitted

For instance, If 10 bits were transmitted, and 5 bits get in error,then :

BER=5/10

=0.2

In BER curve if a value is mentioned, say 0.01, it means ,out of 100 transmitted bits, 1 bit got error [1/100=0.01]

Example:

Let's consider an example, assume a transmitted bit sequence:

0 1 1 0 0 0 1 0 1 1

and the following received bit sequence:

0 0 1 0 1 0 1 0 0 1,

The number of bit errors (the underlined bits) is in this case 3. The BER is 3 incorrect bits divided by 10 transmittedbits, resulting in a BER of 0.3 or 30%.

Date Published: Oct 03, 2011 - 11:13 am

M-PSK Modulation

Uptill now, we have discussed the basic concepts of digital modulation techniques.Let’s move one step ahead!

In digital modulation two commonly used terms are Symbols n Modulation order(M) Symbol:

It is actually a combination of bits.For instance, So and S1 are two symbols.Where ,So=00,S1=11 etc

Modulation order-M:

It refers to the number of states used in modulation,or the number of symbols.If M=2 it means two distinct states are being used in modulation. States could be different frequencies, amplitudes, or phase angles.If M is represented in power of ‘2’, that shows the number of bits per symbol.

For M=4

There will be 4 symbols(S0, S1, S2, S3).4=2^2.Therefore ,each symbol will be represented by Two bits.S0=00,S1=01,S2=10,S3=11

Keeping in view the ‘M’ factor, let’s restate the modulations techniques as:

M-PSK,M-FSK,M-ASK, and M-QAM

M-PSK:

For M=2: It is called as BPSK,(where B stands for Binary).Number of symbols are two. S0 and S1.As 2=2^1, so each symbol is represented by a single bit, therefore we wil have, S0=0 and S1=1

For M=4: It is called as 4-PSK.Number of symbols are Four.S0,S1,S2,and S3.As 4= 2^2,so each symbol is a combination of two bits,so we will have,S0=00,s1=01,s2=10,s4=11

So on and so forth for M=8,16,32,64

As PSK is phase modulation ,therefore the number of states actually refer to distinct Phase angles.These phase angles are used to modulate the carrier.

For M=2 , we have 2 phases/states
Total angle is 360 degree

360/M =180 deg

So.’S0’ will b represented by 0 degree and ‘S1’ will be represented by 180(phase difference of 180 between symbols).That is, if 0 bit appears in signal, it will modulate the carrier wave with 0 degree, and 1 bit will modulate the carrier with 180 deg phase.

For M=4, we have 4 distinct phases

360/4 =90

So, Symbols will be represented as:

S0=0 deg,S1=90 deg,S2=135 deg,S3=180 deg

As we have the following symbols ,S0=00,s1=01,s2=10,s4=11.So, if 00 bits appear in signal, they will modulate the carrier wave with 0 degree,01 will modulate the carrier with 90 deg phase.10 will modulate the carrier with 135 deg n 11 will modulate it with 180 deg.

For M=8,we have 8 phases

360/8=45 deg

So,So=0deg,S1=45 deg,S2=90 deg,S3=135 deg,S4=180 deg,S5=225 deg,S6=270deg deg,S7=360 deg

Each symbol is represented by three bits here,

S0=000,S1=001,S2=010,S3=011,S4=100,S5=101,S6=110,S7=111

So, 000 bits will indicate 0 degree phase shift ,001 will represent 90 deg phase.010 will modulate the carrier with 135 deg ,0 11 will refer to 180 deg, n so on .

Similarly, for M-FSK, M frequencies are used to modulate a carrier and for M-ASK , M amplitude levels will be used.

Date Published: Oct 03, 2011 - 7:04 am

Introduction to FDM, OFDM, OFDMA

Frequency Division Multiplexing (FDM)

In FDM system, signals from multiple users/transmitters are transmitted simultaneously (at the same time slot) over multiple frequencies. That is each user is assigned a different frequency for communication. Each frequency range is called as sub-carrier, n it is modulated separately by different data stream, that is there are different sources of data (users/transmitters) for each subcarrier frequency. A spacing (guard band) is placed between sub-carriers to avoid signal overlap.

Orthogonal Frequency Division Multiplexing (OFDM)

Like FDM, OFDM also uses multiple sub-carriers but the sub-carriers are closely spaced to each other without causing interference, removing guard bands between adjacent sub-carriers. This is possible because the frequencies (sub-carriers) are orthogonal. In OFDM multiple subcarriers are modulated by single source of data. If I am a transmitter, n using OFDM technique, my data will be modulated by multiple subcarrier frequencies , instead of single carrier frequency ,as it happens in normal modulation .if I assume that 3 subcarriers are being used for modulation so, they will modulate the data of just one Transmitter ,unlike FDM where 3 frequencies will b used to modulate three different sources of data (three transmitters).

In an OFDM system, a very high rate data stream is divided into multiple parallel low rate data streams. Each smaller data stream is then mapped to individual data sub-carrier and modulated using some sorts of PSK or QAM modulation . let’s assume that I have a high rate data stream, X=[abcdefghi] ,

I divide it into three low rate data streams [p=abc, q=def, r=ghi ].Assume that there are three sub-carrier frequencies: f1,f2 n f3

Each low data rate stream will be modulated individually by each sub-carrier,that is data stream ‘p’ will be modulated by carrier f1, data stream ‘q’ by f2 n similarly data stream ‘r’ by f3 and finally all are combined.If it were FDM technique ,the data stream X would have been modulated by a single carrier frequency instead of multiple carriers.Therefor OFDM is called as multi-carrier modulation

Orthogonal Frequency Division Multiple Access (OFDMA)

Like OFDM, OFDMA employs multiple closely spaced sub-carriers, but the sub-carriers are further divided into groups of sub-carriers. Each group is named a sub-channel, different colors in figure show a different sub channel. The sub-carriers that form a sub-channel need not be adjacent. Sub-channels actually used for multiple access (multi users communication). Each sub-channel consists of multiple carrier frequencies. For instance I have two sub-channels, S1 n S2. S1 has carrier frequencies f1 ,f2,f3, and S2 has carrier frequencies, f4,f5, n f6 . sub-channel 1 will b used to entertain one user/transmitter and sub-channel 2 will b used by another user/transmitter.

Date Published: Oct 02, 2011 - 6:48 pm

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