What is power electronics

History of Power electronics  :

The development of the mercury arc rectifier began with the development of power electronics. This article gives a brief description of power electronics historical review and also have power electronics used, advantages as well as disadvantages. It was invented by Peter copper Hewitt in the year 1902 used to convert alternating current into direct current. after in the year of 1993 selenium rectifier were invented.

 After that in the year of 1947, the BJT was invented by Walter H. Brattain and John Bardeen under the direction of William Shockley at bell laboratory. In 1956 the SCR  was introduced by general electric applications. In 1976 Power MOSFET became commercially available and finally the year of 1982 the insulated gate bipolar transistor was introduced. The history of power electronics is so vast so that it is impossible to review it within a few pages.


What is the power electronics?


Power electronics is the application of solid-state electronics to control and conversion of electric power. The first high power electronics started with the development of the mercury arc rectifier. 

 For detailed information 
Read more >>  Power electronics systems   
Read more >> PCBA

Advantages of power electronics

  • Long life
  • Flexibility
  • High reliability
  • High efficiency
  • Less maintenance
  • Less weight
  • High-quality power
  • Small size

Disadvantages of power electronics 

  • Complected design
  • Overload capacity
  • generate harmonics
For detailed information 
Read more >>  Power electronics advantages and disadvantages   

Power electronics applications :

  • SMPS
  • UPS
  • HVDC
  • Static switch
  • Static circuit breaker
For detailed information 
Read more >>  Power electronics applications 

 Power Electronics is the study of electrical energy flow control using electronic circuits. 
  • Power electronics belongs partly to power electronic engineers. Power engineering primarily concerned with generation transmission, distribution, and utilization of electric energy at high efficiency.
  • On the other hand, electronics engineering is the production, transmission, and reception of data and signals of very low power levels of the order of few watts without much regard to efficiency.
  • In addition, power engineering devices are based primarily on electromagnetic principles, while in electronics engineering they are based on physical phenomena in vacuum, gas, and semiconductors.
  • The main focus of Power Electronics is the application of electronic principles to a situation that is rated at the power level rather than at the signal level and also deals with appliances and equipment based on the electronics principle.

Advantages and disadvantages of TDMA

TDMA full form is Time Division Multiple Access uses time instead of frequency. It is used to facilitate channel sharing without interference. Different user shares the same time slot of the complete time available. Each user to allocate a time slot in which the user can access the channel and in each slot, only one user is allowed to transmit or receive. 

TDMA was more used by Europe, Japan, and Asian countries, whereas CDMA is widely used in North and South America. But nowadays both technologies are very popular throughout the world. 


Advantages of TDMA :

  • TDMA can easily adapt to the transmission of data as well as voice communication.
  • It has the ability to carry 64 kbps to 120 Mbps of data rates.
  • No interference from simultaneous transmission.
  • TDMA is the cost-effective technology to convert an analogue system to digital.
  • Share a single carrier frequency with multiple users
  • Mobile assisted handoff possible
  • TDMA provides the user with extended battery life since transmitting the only portion of the time during conversations
  • Flexible bit rate
  • No frequency guard band required
  • No need of a precise narrowband filter
  • TDMA separates users according to time ensures that there will be no interference from the simultaneous transmission. 
  • TDMA allows the operator to do services like fax, voiceband data, SMS as well as applications such as multimedia and video conferencing.  
  • TDMA offers substantial savings in base-station equipment, space, and maintenance, an important factor as cell sizes grow ever smaller. 
  • Dual-band 800/1900 MHz.
  • It is the only technology that offers an efficient utilization of hierarchal cell structures like pico, micro, and macro. 

Disadvantages of TDMA :

  • In TDMA each user has a predefined time slot so that users roaming from one cell to another are not allotted a time slot. Thus, if all the time slots in the next cell are already occupied, a cell might well be disconnected. In the same way, if all the time slots in the cell in which a user happens to be in are already occupied, a user will not receive a dial tone. 
  • It is subjected to multipath distortion. A signal coming from a tower and receive to handset might come from any one of several directions so on the road signal bounced off several different buildings before arriving which can cause interference. 
  • Network and spectrum planning is intensive. 
  • Too few users result in ideal channels rural versus urban environment. 
  • High synchronization overhead.
  • Frequency/slot allocation is to be complex in TDMA. 
  • Equalization was necessary for high data rates. 
  • Demands high peak power on the uplink in transient mode.
  • Signal processing is required for matched filtering and correlation detection.
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What is digital signal

The signal is a physical quantity, which contains some information. The signal is an electrical current or electromagnetic field used to carry data from one place to another. 

The signal can be two types :


 1. Analog signal
  2.Digital signal

What is a digital signal?  


 A digital signal is a signal that is being used to represent data as a sequence of discrete values at any given time and it can take only one of a finite number of values. 

 Digital signals can be sent for long-distance and suffer less interference than an analog signal. 

Digital signals are easily represented by a computer because It described as using binary (  0s and 1s) and therefore, cannot take on any fractional values. Each sample can be with a series of bits that are either in the state of on (1) or off (0).

Difference between Bluetooth and WiFi

We are all familiar with the two technologies known as Wi-Fi and Bluetooth. Both of them are wireless technologies which make use of radio waves and a free open atmosphere as a communication channel. The main difference between Bluetooth and Wi-Fi is the purpose behind their design. Bluetooth is essentially used to connect short-range devices for sharing data and Wi-Fi provides high-speed internet access. 

Wi-Fi officially launched in the year 1997 was set in the year of 1990 which was head by, victor hayes who is also known as the father of WiFi Bluetooth technology invention has been credited to Ericsson, which in the year of 1994 launched it as a wireless communication alternative to  RS232. 

So now let us check out the difference between Bluetooth and WiFi to know more understanding about Bluetooth and WiFi.

Difference between Bluetooth and WiFi 

  • Bluetooth was initially defined under IEEE 802.15.1 standard but is now taken care of by a special interest group SIG, on the other hand, Wi-Fi is defined under 802.11X where X is a, b, c etc series of protocols and is currently maintained under the same. 
  • Bluetooth updated several versions such as Bluetooth 2.0, 2.1, and Bluetooth 3.0 and the latest Bluetooth 4.0 added technologies such as Enhanced Data Rate (EDR), alternate MAC/PHY, and low energy protocols have been implemented in these updates whereas Wi-Fi updates are quite different such as IEEE 802.11 standard such as IEEE 802.11a, b, c etc. These versions vary in terms of security protocols, radio frequency used for data exchange, maximum speed for data exchange, the bandwidth occupied etc. 
  • Bluetooth works at the frequency range of 2.400 GHz and 2.483 GHz while Wi-Fi works in the range of 2.4 GHz and 5 GHz. 
  • The latest updates of Bluetooth promise data transfer rates of up to 25 Mbps while the latest Wi-Fi updates can reach up to 250 Mbps of data transfer rates. 
  • Bluetooth-based wireless connection's maximum range is 30m while Wi-Fi, it can extend well up to 100m. In Wi-Fi, the range depends on the version of the Wi-Fi protocol and antennas in the wireless communication system. 
  • In Bluetooth, up to 7 devices can be connected to each other while in Wi-Fi maximum connections depend on a Wi-Fi router which can accommodate several connections at a time. 
  • Bluetooth is fairly simple as there is just a simple key-matching process for connecting two devices while Wi-Fi needs expertise in configuration and security passcode matching process so the Wi-Fi connection process is much more complex than Bluetooth.
  • New versions of Bluetooth were encryption and even now Bluetooth security is limited to key matching whereas Wi-Fi security standards have been raised with the inclusion of new versions. Wireless Equivalent Privacy (WEP) and Wi-Fi Protected Access (WPA) are the two most used security accesses used in Wi-Fi. 
  • Wi-Fi is able to work at longer distances and is loaded with high-quality security protocols making them more power-consuming than Bluetooth. 
  • Wi-Fi is more used in connecting computers to routers or internet gateways also used to connect with each other while Bluetooth is used to connect peripherals to a computer such as keyboards, mice, headsets etc. 
  • Bluetooth used low bandwidth of 800 Kbps while Wi-Fi used a high bandwidth range of around 11 Mbps.
  • Bluetooth is less secure and Wi-Fi security issues already being debated. 
  • The latency of Bluetooth is 200ms and Bit-rate is 2.1 Mbps and Wi-Fi latency is 150 ms and Bit-rate is 600 Mbps. 
  • Bluetooth use modulation technique is GFSK (Gaussian frequency shift keying) and OFDM (Orthogonal frequency division multiplexing) and QAM (Quadrature amplitude modulation) used by Wi-Fi. 
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What is digital signal processing

Before we learn about digital signal processing first let is check it out what is form of DSP. In a digital communication system, the word 'Signal' is very commonly used. Therefore we must know its exact meaning.

Signal system must be describe as a function of one or more independent variables.

What is digital signal processing?


Digital signal processing is the process of analyzing and modifying a signal to optimize or improve its efficiency or performance. It involves applying various mathematical and computational algorithms to analog and digital signal to produce a signal that is of higher quality than the original signal.

 Digital signal processing take real-world signal like audio, video, pressure, voice that have been digitized and then mathematically manipulate them. Mathematical processing algorithm can be easily implement using DSP. 

Using digital signal processing; much better accuracy is obtained to refers various techniques. 

In processing digital signal converting analog transmission into digital signal. i.e. The audio signal are processed in real time. This conversion method uses digital conversion software to receive and process the signal. So the output results in a number of different sound effect. This type of processing is present a number of audio devices such a mp3 players, radio sound system. Compare to analog signal digital signal are more versatile, more accurate.

Now a days, digital signal processing used in various application like image processing, Scanners, robotics, military, speech recognition, power line monitors, voice command, television, and music system etc.

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Advantages and disadvantages digital filter

A system that performs the mathematical operation in signal processing on a sampled signal to reduce or enhance certain aspects of that signal is known as a digital filter. Its main objective is to remove the unwanted parts of the signal. This article gives information about the advantages and disadvantages of the digital filter to know more about it. 

Advantages of digital filter : 

  • Digital filter has characteristic like linear phase response.
  • The performance of the digital filter does not vary with environmental parameters.
  • Digital filters used at very low frequencies, for example in a biomedical application so-called as an adaptive filter because the frequency response can be possible to adjust automatically with an implementation of the programmable processor. 
  • The digital filter is highly flexible possible to filter several input sequences without any hardware reapplication. 
  • From unit to unit the performance of the digital filter is repeatable.
  • In the case of the analogue filter maintenance is frequently required but for digital filters is not required.
  • It is used where the use of an analog system is impractical due to its operating level is at low frequency.  
  • The digital filters are portable.
  • In the case of the digital filter; since the filtering is done with the help of a digital computer, both filtered and unfiltered data can be saved for further use.
  • The hardware of digital filters can be reduced similarly, thus the power consumption can be reduced.
  • Digital filter is easily designed, tested and implemented on a general-purpose computer or work-station. 
  • Digital filters do not suffer from drift and dependent on temperature so they are extremely stable with respect to both time and temperature. 

Disadvantages of digital filter :

  • It is expensive.
  • The signal bandwidth of the input signal is limited by ADC and DAC. 
  • The bandwidth of the digital filter is much lower than an analogue filter.
  • Quantization noise is present.
  • The accuracy of the digital filter depends on the word length used to encode them in binary form. 
  • It required more design and development time compared to an analogue filter.

Advantages and disadvantages of digital signal processing

Digital signal processing the word itself says it is a process of analyzing the digital signal. The DSP is a microprocessor chip with optimized architecture to support the processing of complete algorithms at high speed in less time. Using DSP you can filter signals more accurately, and extract other signals from the information such as frequency components easily. Now we can check the advantages and disadvantages of digital signal processing to know more about it. 

Advantages of digital signal processing 
  • DSP offers high accuracy. Hence, filters designed in DSP have tighter control over the output accuracy.
  • Comparatively cheaper than an analog counterpart.
  • Reconfiguration is very easy and only code or DSP program needs to be flashed after changes as per requirement. Reconfiguration of an analog signal is difficult.
  • DSP offers various interface types such as UART, I2C helps in interfacing other ICs with the DSP.
  • DSP can be interfaced with FPGA helps in the design of a protocol stack of the entire wireless system such as WiMAX and LTE.
  • Digital system can be cascaded without any loading problem. 
  • The digital circuits can be reproduced easily in large quantities at a comparatively lower cost. 
  • The digital circuits are less sensitive to a tolerance of component values. 
  • DSP are easily transported because digital signals can be processed offline. 
  • Current computers can't process analog data so digitalization is necessary. 
  • Enables transmission of signals over a long distance. 
  • DSP use less bandwidth so that you can cram more information into the same space. 
  • DSP enables multi-directional transmission very easily. 
  • In DSP easier to translate human audio and video signals and other messages into machine language. 
  • Universal compatibility is possible in DSP compared to ASP. 
  • Mathematical processing algorithms can be easily implemented in DSP. 
  • Generally, all application needs standard hardware thus the operation of DSP is mainly dependent on software. 

Disadvantages of digital signal processing 

  • DSP requires an anti-aliasing filter before ADC and re-construction filter after DAC so it requires ADC and DAC modules. 
  • DSP dissipates higher power compared to ASP because DSP processed signals at high speed and moreover it consists of higher internal hardware resources. 
  • DSP chips are very costly and hence one needs to use the appropriate ICs as per requirement. 
  • The hardware architectures and software instructions of each DSP are different so training on DSP in order to program for various applications. Hence, Highly skilled engineers can only work on the device. 
  • A typical DSP chip contains more than 4 lakhs transistors thus power dissipation is more in DSP. 
  • DSP is costly for small applications as compared to ASP. 
  • DSP requires greater bandwidth to transmit the same information of ASP. 
  • Downgrading the quantity of data is possible but increasing the bit rate is also possible beyond the certain level. 
  • The detection of digital signals requires the communication system to be synchronized whereas there is no case in ASP. 

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What is GSM | History | Features | Network | Advantages

Basic details of GSM : 


 GSM full form Global System for Mobile Communications is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation cellular networks. It was first established in Finland in December 1991. As of 2014, it has over 90% of market share, operating in over 193 countries and territories. 

 GSM is a digital cellular technology used for transmitting mobile voice and data services by use of narrowband TDMA technique owned by GSM Association. 

 GSM digitalizes and compress data, then sends it down through a channel with two other streams of user data, each in its own time slots. 

History of GSM : 


1983 - European Conference of Postal and Telecommunications Administrations set up the GSM committee and after that provided a permanent technical support group based in Paris. 

 1986 - Check the different radio techniques recommended for the air interface to do executed field test.  

 1987 - 15 representatives of 13 European countries signed a memorandum of understanding MoU and TDMA is chosen as the access method

 1987 - Europe produced very first GSM technical specification. 

 1989 -  The group CEPT was given the responsibility to European Telecommunications Standards Institute (ETSI). 

 1991 - World's first GSM DCA 900 delivered by Telenokia and Siemens and operated by Radiolinja. 

 1992 - Coverage spreads to larger cities and airports and addition of the countries also signed the GSM MoU. 

 1993 - The first GSM standard to the 1800 MHz frequency band became operational in the UK called GSM DCA 1800. 

 1994 - The number of a network rises to 69 to 43 countries by the end of 1994 and data transmission capabilities launched. 

 1995 - Fax, Data and SMS messaging services were launched commercially and GSM subscribers worldwide exceeded 10 million.

 1995 - GSM Association formed and phase 2 of GSM specification occurs. 

 1996 - GSM SIM cards were launched and 133 networks in 81 countries operational. 

 1997 - 200 network in 109 countries operational around 44 million subscribers worldwide. 

 1998 - GSM subscriber passed to 100 million. 

 1999 - Wireless Application Protocol (WAP) came into existence and become operational in 130 countries with 260 million subscribers.

 2000 - First commercial GPRS was launched. 

 2001 - First UMTS (W-CDMA) network was launched and Worldwide touched 500 subscribers. 

 2002 - The first multimedia message (MMS) was introduced. 

 2003 - EDGE service first became operational. 

 2004 - GSM subscribers exceeded 1 billion. 

 2005 - The first HSDPA-capable network also became operational and reached to 1.5 billion subscribers. 

 2007 - The first HSUPA network launched. 

 2008 - Worldwide 3 billion subscribers. 

 2010 - GSM standard served 80% of the mobile market and 5 billion subscribers across more than 212 countries. 

 GSM standards do not include the 3G UMTS and CDMA technology nor the 4G LTE and OFDMA technology standards issued by the 3GPP. 

 2016 - Australia shut down its 2G GSM network. 

 After that many advanced technologies came into existence so that GSM technology got older and their users are continuously decreased and updated in 3G and 4G technology services. 

GSM Features : 


  • Supports more subscriber capacity in the given spectrum.
  • Supports smaller handsets.
  • Rapid call setup.
  • Use the same phone in different networks.
  • SIM phonebook management. 
  • Supports fixed dialing number ( FDN ).
  • Real-time clock with alarm management. 
  • Improved spectrum efficiency.
  • Low-cost mobile sets and base stations. 
  • Supports new services. 
For detailed information : 
Read more >> Features of GSM 

 GSM networks :
  • T-Mobile
  • AT&T
  • Indigo wireless 
  • Pine cellular
  • TerreStar

Advantages of GSM : 

  • More suitable network with robust features.
  • No roaming charges on International calls. 
  • Worldwide connectivity and extensive coverage. 
  • SAIC and DAIC techniques used in GSM provide very high transmission quality. 
  • The phone works based on the SIM card so that it is easy to change the different varieties of phones by users. 
  • GSM signals don't have any deterioration. 
  • Easy to integrate GSM with other wireless technology such as CDMA and LTE.
  • It has the ability to use repeaters. 
  • Because of the pulse nature of transmission talk time is generally high.

Disadvantages of GSM : 

  • Bandwidth lag because of multiple users shares the same bandwidth so the transmission can encounter interface. 
  • It can interfere with certain electronics, such as hearing aids that are due to pulse transmission technology. As a result, many locations, such as hospitals, airports and petrol pumps require cell phones to be turned off. 
  • To increase coverage repeaters are required to be installed. 
  • It provided limited data rate capability so for high data rate advanced version of GSM devices are used. 
  • Many of GSM technology is patented by Qualcomm thus license needs to be obtained from them. 
  • Manufacturers are not releasing IS-95 devices due to the lack of a big market so IS-95 is normally installed in the small tower. 
  • GSM has fixed maximum call sites range up to 35 km that is very limited. 
  • There is no end-to-end encryption of user data. 
  • Several incompatibilities within the GSM standards. 
  • Electromagnetic radiation is more with the use of GSM.
  • Macrocells affected by the multipath signal loss. 
For detailed information : 
Read more >> Advantages and disadvantages of GSM 

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  1. What is GPRS?

What is GPRS | History | Features | Goal | Service | Protocol | Advantages

What is GPRS?


 GPRS full form General Packet Radio Service is a packet-oriented mobile data standard on 2G and 3G cellular communication network's global system for mobile communication accessible to GSM and IS-136 mobile phones users. 

 GPRS based wireless communication service that promises data rates from 56 up to 114 Kbps and continuous connection to the Internet for mobile and computers. 

GPRS is third generation step towards internet access. GPRS also was known as GSM-IP the Global System Mobile Communication Internet Protocol.

Who owns GPRS?


The GPRS specification was written by European Telecommunication Standard Institute (ETSI) and American National Standard Institute.

History of GPRS : 



 1991-1992 - The CELLPAC protocol developed. 
1993 - The CELLPAC voice and data functions introduced in ETSI workshop
2000 - GPRS opened as a packet-switched data service embedded to the channel-switched cellular radio network GSM. GPRS extends the reach of internet access to mobile terminal worldwide. 

 Successor system to GPRS like CDMA and LTE reply on key GPRS function for mobile internet access as introduced by CELLPAC. 

Basic details :



GPRS network allows the network operators to implement an IP based core architecture for data application, so that will continue to be used and expanded for 3G services for data application.

GPRS offers fast connection set up a mechanism to offer a perception of being "Always ON". Hence, It referred to as "always connected".

GPRS always short bursty traffic like email, web browsing etc and no dial-up modem connection is essential for GPRS.

GPRS allows other services like :
  • Unicast
  • Multicast
  • Broadcast
The GPRS core network allows 2G, 3G and CDMA mobile networks to transmit IP packets to external networks such as the Internet. 

 GPRS extends the GSM packet circuit switched data capabilities and it makes the following services possible. 

Services of GPRS :

  • Messaging SMS and broadcasting 
  • Always ON Internet access
  • Multimedia message services (MMS)
  • Push-to-talk over cellular (PoC)
  • Wireless village 
  • Internet applications for mobile and computers through wireless application protocol 
  • Point to point services 
  • Inter-networking with the Internet (IP)
  • Point to multipoint services 

Protocols of GPRS :

  • Internet protocol (IP)
  • Point to point protocol (PPP)
  • X.25

Goals of GPRS :


GPRS is the first step towards the end to end wireless infrastructure. 
  • Open architecture
  • Same infrastructure for different air interface 
  • Consistent IP services
  • Leverage industry investment in IP
  • Service innovation independent of infrastructure
  • Integrated telephony 
  • Internet infrastructure 

Features of GPRS : 

  • The always online feature 
  • An upgrade to existing systems
  • An integral part of future 3G systems  

Advantages of GPRS :

  • Provide high-speed data service
  • Support bursty application like email, traffic, telemetry, broadcast service, and web browsing
  • GPRS offers fast connection set up a mechanism to offer a perception of being always on hence the GPRS devices are referred to as always connected
  • GPRS based network has high bandwidth
  • Provide point to point services
  • Mobility provides wireless internet access
  • GPRS is not possible to troubleshoot in case of issues
  • Deployment is easier
  • Communication via GPRS is cheaper than through the regular GSM networks
  • Constant connection to the internet 
  • GPRS provides wireless access to the internet from any location where there is a network signal so that you can surf the internet on your laptop or phone, even in remote areas
  • GPRS is still faster than the old WAP ( Wireless Application Protocol ) data is transferred at speeds ranging from 9.6 kilobytes per second up to 114 kbps
  • When you surfing the internet it doesn't block incoming calls enables you to make or receive voice calls while you are browsing the internet or downloading data. So that users can have both voice call and data call together

 Disadvantages of GPRS : 

  • Limited capacity for all users
  • Speed much lower in reality 
  • Data rates supported are slower compared to the latest wireless standards such as LTE or LTE-advanced. 
  • Mobile station using GPRS can't receive direct GPRS calls
  • A network can be affected when a large number of users in the same area utilize the GPRS services at the same time. 
  • Users may decide to charge based on time rather than volume
  • GPRS could be consumed by the public during the public emergency
  • Can have high latency, especially text messaging
  • Can not troubleshoot means works or doesn't
  • Expensive to add terminal above 4
  • Slower 72 Kbps vs 11 Mbps
  • Transit delay

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What is orthogonal frequency division multiplexing

OFDM is a modulation format that is being used for many of the latest wireless and telecommunication technology. First, let us check it out the full meaning of OFDM.

 OFDM has been adopted in the Wi-Fi arena where the standards like 802.11a and many more. It has also been adopted by cellular telecommunication standards LTE and LTE-A. It also used for a number of broadcast standards such as DAB digital radio to digital video broadcast standards. 

Definition of OFDM : 


OFDM is a special form of multi-carrier modulation, patented in 1970 is particularly suited for transmission over a dispersive channel. An OFDM signal consists of a number of closely spaced modulation carrier. When modulation in the form of voice or data is applied to a carrier, then sidebands spread out either side. As a result, when signals are transmitted close to one another they must be spaced so that the receiver can separate them using a filter and must be a guard band between them. 

It is used to obtain a higher data rate in the multipath fading environment of mobile communication. It also used in Wi-Fi, DSL internet access, 4G wireless communications, and digital television and radio broadcast services. 

 The selection of digital modulation is dependent on three parameters are listed below :

  • Narrower bandwidth 
  • Efficient power utilization
  • Elimination of intermodulation products

How OFDM works? 

Orthogonal means "unrelated or independent of each other". The subcarriers for each radio channel are orthogonal to one each other and spaced close to each other without guard bands. To know how OFDM works, first of all, we will look at the receiver. The receiver acts as a demodulators bank, translating each carrier down to DC. This resulting signal is integrated over the symbol period to regenerate the data from that carrier. When the carrier spacing equal to the reciprocal of the symbol period so that they will have a whole number of cycles in the symbol period and their contribution will sum to zero thus there is no interference contribution. 

Detailed Analysis : 


OFDM uses data bursts to reduce the intersymbol interference many symbols are sent in parallel. Hence, the symbol rate decreases.

When the symbol duration increases, the intersymbol interference effects that were produced by Rayleigh fading are reduced.

The principle of orthogonality can be obtained by dividing the carrier signal with an integer multiple that is capable of making the inverse of symbol duration of the parallel bit stream.

The OFDM method is applied to reduce the frequency selective fading and burst errors generated by a wideband fading signal in wireless communication. It is robust in a narrow band interference environment.

Block diagram of OFDM :


In OFDM block diagram basically two parts : Transmitter and Receiver.

 Assume that the system is operating on the downlink so that the transmitter is in the BS and receiver is in the mobile. BS is sending streams of bits to different mobile. It modulates each bit stream independently, using a different modulation scheme then passes each symbol stream through a serial-to-parallel converter to divide it into sub-streams. The number of sub-streams for each mobile depends on the data rate. The resulting information is the amplitude and phase of each sub-carrier in the form of a function of frequency. We can compute the in-phase and quadrature components of the corresponding time-domain waveform by passing it through an inverse FFT. This can be digitized, filtered and mixed up to radio frequency for transmission. The mobile reverse the process, starts by sampling the incoming signals, filtering it, and converting it down to baseband. After that passes the data through a forward FFT to recover the amplitude and phase of each sub-carrier. Using this knowledge, the mobile selects the require sub-carriers, recover the transmitted information and discarding the reminder. 

Block diagram of OFDM


Advantages of OFDM : 

  • Immunity to selective fading 
  • Resilience to interference
  • High spectrum efficiency 
  • Very resilient to inter-symbol and inter-frame interference 
  • Adequate channel coding and interleaving possible to recover symbols which are lost due to frequency selectivity of the channel and narrow-band interference. 
  • Simpler channel equalization 

Disadvantages of OFDM : 

  • High peak to average power ratio 
  • Sensitive to carrier offset and drift 
  • Loss of efficiency caused by cyclic prefix or guard interval 
For detailed information : 


OFDM variants : 

  • COFDM : 
COFDM stands for coded orthogonal frequency division multiplexing. It is the form of OFDM where error correction coding is incorporated into the signal. 
  • Flash OFDM : 
This variant was developed by Flarion. It is a fast hopped form of OFDM. 
  • OFDMA : 
OFDMA stands for orthogonal frequency division multiple access. It is used to provide multiple access capability for applications such as cellular telecommunications. 
  • VOFDM : 
VOFDM stands for vector OFDM. It uses the concept of MIMO technology. It is being developed by CISCO systems. 
  • WOFDM :
WOFDM stands for wideband OFDM. It uses a degree of spacing between the channels that is large enough that any frequency errors between transmitter and receiver don't affect the performance. This variant was particularly applicable to Wi-Fi systems. 

Features of GSM

There are many features associated with GSM technology because it is the most leading mobile communication technology in the world today. It is facilitated with high speed integrated data, voice data, fax, mail, and also SMS features. Let us check some more features of GSM technology listed below.  

Features of GSM technology :

  • Supports more subscriber capacity in the given spectrum.
  • Supports smaller handsets.
  • Rapid call setup.
  • Supports call forwarding, calls on hold, conference facility.
  • Use the same phone in different networks.
  • Allows data transmission and data reception across GSM networks at 9600 bps.
  • The encrypted conversions cannot be tapped.
  • Supports calling number identification presentation.
  • The short message service allows the GSM subscriber to transmit and receive a character text message.
  • Supports fully international roaming capability.
  • Compatibility with ISDN for supplementary services.
  • SIM phonebook management. 
  • Supports fixed dialing number ( FDN ).
  • Real-time clock with alarm management. 
  • Improved spectrum efficiency.
  • Low-cost mobile sets and base stations. 
  • Supports new services. 
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