DTFT properties

We already know about what is DTFT. In this section, we will study some properties of  DTFT to know a better understanding of this topic. We know that x (n) and X (ω) are Fourier transform pair and denoted as given below,
             DTFT
If  x (n)   ↔   X(ω)  

1. Linearity :

Fourier transform of a linear combination of signals then it will be the same as the linear combination of the Fourier transform of each of the individual signals.
                 DTFT
If  x1 (n) is    ↔   X1(ω)  and  x2 (n) is   ↔  X2(ω)  then
              
                                      DTFT
a1 x1 (n)   +  a2 x2 (n) is    ↔    a1 X1 (ω)   + a2 X2 (ω)  

2. Time shifting : 

Time shifting shows that a shift in time is equivalent to a linear phase shift in frequency domain. Since the frequency content depends only on the shape of a signal generated, which is basically unchanged in a time shift, then only the phase spectrum will be altered. This   property is given below : 


 If 
            DTFT
x (n)  is    ↔    X(ω)  then 

              DTFT
x(n-k)  is   ↔    e –jωk  X(ω)  

3. Frequency shifting :

  If 

             DTFT                                           DTFT
x (n)  is   ↔    X(ω)  then  e –jω0n  x(n)   is   ↔    X ( ω - ω0)

4. Time reversal :

 If 
         DTFT
x (n)    ↔    X(ω) is  then 
   
            DTFT
x (-n) is    ↔    X(-ω)   

5. Differentiation :

It is a complicated differentiation equation, it is the easiest way to understand a better way to this topic, the equation is given below.  It is apparent with this property that converting to the frequency domain may allow the frequency domain may allow us to convert these complicated differential equations to easy simpler equations involving multiplication and addition. This property is given below :


If 
         DTFT
x (n)    ↔    X(ω)  then 

           DTFT
n x (n)    ↔    d/dω X(ω)  

6. Parseval's theorem : 


                DTFT                                 DTFT
If  x1 (n) is  ↔   X1(ω)  and  x2 (n)  is   ↔      X2(ω)  then

Parseval's relation tells us that the energy of a signal is totally equal to the energy of its Fourier transform.

  ∞                                                ∏
∑  x1 (n)   x2 (n)  is  = 1 /2∏  ∫  X1(ω)  X2(ω)  dω
n = - ∞                              -∏

7. Convolution theorem :

Convolution is one of the big reasons for converting signals to the frequency domain since convolution in time becomes multiplication in frequency domain.


                DTFT                                DTFT
If  x1 (n) is  ↔   X1(ω)  and  x2 (n) is    ↔     X2(ω)  then

                             DTFT
  x1 (n) * x2 (n)  is     ↔     X1(ω) . X2(ω) 

Space diversity

The space diversity method is also called the antenna diversity method. There was no guarantee of a direct path between the transmitter and receiver in the conventional method of wireless communications. Hence, the occurrence of Rayleigh fading signal was suspected. 

Now  let us talk about the different types of space diversity reception method given below :
  • Selective diversity
  • Feedback diversity
  • Maximal ratio combining
  • Equal gain diversity
1. Selective diversity :

Principle :

Selective diversity is one of the best signals among all the signals received from different branches at the receiving end.

In the selective diversity method, the branches that have the strongest received signal are combined and selected.

In this method suppose n number of the demodulator is used to provide n number of diversity branches. The gains of these n number of diversity branches can be adjusted to give the average signal to noise ratio for every diversity branch.

The antenna signal will be then sampled and the signal that possesses a good signal strength and the best signal is sent to the demodulator side.

2. Feedback diversity :

Principle :

The feedback diversity also referred to as the scanning type of diversity. In this method in a correct sequence n number of signals are scanned. The signals are continuously monitored so that they can pick up a signal in the sequence that is above some threshold value alpha.

For the signal received the process of scanning is initiated but the limitations of this method are that the decreases in the fading level were less than the diversity method.

The advantages of scanning diversity are easier implementation than other diversity techniques. It needs only one receiver.

3. Maximum ratio combining techniques :

Principle :

In this method is all the (N) branch signal are weighted with the necessary coefficients for each diversity branch signal and combined coherently in order that the decreases in fading will be more. This will improve the overall system of performance.

 In this method, the signal is also combining all the signals in a weighted manner and co-phased manner, so as to have the highest achievable signal to noise ratio (SNR) at the receiver at all the times.

Advantages :
  • The maximal ratio combiner produces as acceptable SNR value
  • The accuracy of this method is high
  • In this method also maximal ratio combiner results in best decreases in fading
4. Equal gain combiner :

In these techniques, all diversity branches are coherently added with the same weighting factor. These techniques also based on co-phases all the diversity branches and finally adds them up.

As the signal are co-phased from all branches they provide an equal number of gain factor. So in this method combining all the signal in a co-phased manner with the unity based weights for all signals levels, so as to have the highest achievable signal to noise ratio (SNR ratio) at the receiver at all the times.

Advantages :
  • Several diversity branches are allowed
  • Space diversity applicable to macroscopic diversity
  • No extra bandwidth or power is needed

Diversity concept

Diversity definition :

The simple concept of the terms of diversity is that even if a radio signal path experiences a deep face, there will be another independent signal path available for analysis. 

The concept of diversity encompasses acceptance and respect. It means understanding that each individual is unique, recognizing for our individual differences. 

Assume that there is two antenna with some specific separation between them. Both the antenna signal are located on the same terminal. As the mobile terminal moves the antennas signal side experience different fading levels.

The received signal level varies with their corresponding fading levels. Hence we need to select an antenna that has a higher signal level. This is done so that the probability of deep fading is to be avoided.

There are two kinds of diversity :
  • Microscopic diversity
  • Macroscopic diversity
1. Microscopic diversity :

The counteract small signal fading in the signal received under very small distance, microscopic, diversity can be used to exploit changing signal.

It can prevent the small signal fades in case of fewer antenna separations if two antennas are used.

By choosing the signal of higher strength most of the time, the receiver can reduce the fading effects.

2. Macroscopic diversity :

The signal strength is too much decreases in large scale fading because of the problems related to shadowing by selecting a base station that is not shadowed in comparison to the other base stations, the mobile unit in its forward path can get a better signal to noise ratio (SNR).

Such a diversity concept is used to decreases the large scale signal fades is called macroscopic diversity. At the base station receiver is to end, this diversity method is useful.

Advantages and disadvantages of nuclear power

The main uses of nuclear energy is electric power generation and it can be also used scientific research, space page, medicine, nuclear fission, food, and agriculture etc.  Here this article gives the information about advantages and disadvantages of nuclear power to know more details about it.

Advantages of nuclear power :
  • No green house gases
  • Conserves fossils fuel
  • Fuel has low cost
  • High density
  • Sustainable
  • Clean energy
  • High qualities
  • Contentiously generate electricity
  • A little makes a lot of  energy
  • High electricity output
  • Reliable
  • A small amount of fuel used so less transport needed
  • Cheap to run once built
  • No sulfur dioxide emission
  • No carbon dioxide emission
  • Safe under normal condition
  • Does no emit green house gases
Disadvantages of nuclear power :
  • Expensive to built and start to maintain power plants
  • High operating maintenance cost
  • Mining uranium cause pollution
  • The west of radioactive and also is harmful thus having to be disposed of carefully
  • Risk of disaster or accident
  • Safely concerns
  • Waste that remains toxic for many years
  • Supplies will run out in 50 years
  • No renewable
  • Expensive to decommission
  • A power station is at risk of being attacked
  • Link with cancer
  • Product radio active waste
  • If it is needed, it takes days to shut down a total power plant
  • In a nuclear meltdown, high dosages of radioactivity are exposed

Advantages and disadvantages of transformer

A transformer is a static electrical device which can transfer the electrical energy between two or more many circuits through electromagnetic induction. This article gives information about the advantages and disadvantages of a transformer to know more details about it.

Advantages of transformer :
  • A transformer will increase or decrease  basically AC voltage, current or independence 
  • It is efficient for high-frequency range
  • The available power cannot change but will slightly too much decrease depending on the efficiency of the transformer 
  • It has the advantage of preventing condensed flux leakage as well as iron loss
  • It offers good mechanical strength
  • The transformer is widely used in power transmission
Disadvantages of transformer :
  • A transformer will not work with DC voltage under any condition
  • The transformer size become un widely
  • The physical size of the transformer is directly related to the amount of power to be desired
  • It is not good to use outdoors
  • It can be noisy

Microphone advantages and disadvantages

A microphone can be used a telephone, hearing aids, public address system for the concert hall and public event, radio and television broadcasting, megaphone etc.  Here this article gives information about the advantages and disadvantages of a microphone to know more details about it. 

Advantages of a microphone :
  • In uses microphone greater freedom of movement for the artist or speaker 
  • Reduction of cable trip hazards in the depends upon performance space
  • Avoidance of cabling problems common with wired microphones, caused by constant moving as well as stressing the cables
  • It is faster to read in text than to type it in using a keyboard type
  • It can improve both safety and security when used in the voice activation system
  • Sound can be manipulated in real time rather than a recording done at the earlier stage
Disadvantages of a microphone :
  • Noise or dead spots 
  • The limited number of operating microphones at the same time and place
  • The limited number of radio channels 
  • Sound files can use up a lot of computer memory in a device
  • Voice recognition system software is not as accurate as typing manually 

Advantages and disadvantages of ac generators

AC generator stands for an alternating current generator, It is a device that produces an electromotive force. Here this article gives information about the advantages and disadvantages of AC generator to know more details about it.

Advantages of ac generators :
  • AC is very easy and efficient to transmit over a long distance rather than DC
  • The design of the AC generator is fairly simpler than DC generator type
  • No need for matching a voltage 
  • Cost of ownership is lower
  • They have a quiet operation
  • This also makes easier to maintain this generator 
  • An AC generator allows users to convert its current to other voltage with the use of transformers
  • AC generator is compatible only with an AC generator and not with a DC generator
  • AC motors do not have a smell that is very typical of DC motors; in the latter, this is caused by and also these are compatible with an AC generator and not with a DC generator type
 Disadvantages of ac generators :
  • This poses a challenge when it comes to handling because of the greater voltages needed to supply a fixed level of power
  • In these systems require additional insulation because of the greater voltages needed to supply a fixed level of power
  • In addition to all these risks, an AC generator is not as durable as a DC generator type
  • Working with alternating current system has some distinct risk and difficulties  as compared to what can be expected from DC motors
  • In addition to all these risks, an AC generator is not durable as a DC generator type

Advantages and disadvantages of FSK

FSK stands for Frequency shift keying. This technology is used for a communication system such as caller ID and emergency broadcast. Here this article gives information about the advantages and disadvantages of FSK to know more details about it. 

Advantages of  FSK :
  • It has a lower probability
  • Easy to implement
  • High data rate 
  • It has better noise immunity than ASK method, so the probability of error-free reception of data is high
  • Easy to decode
  • Operate in virtually any wires available
  • FSK transmitter, as well as FSK receiver implementations, are simple for low data rate application
  • It provides high SNR
  • Used in long-distance communication
  • Power requirement is constant
  • Good sensitivity
  • It has higher immunity to noise due to a constant envelope. Hence it is robust against variation in attenuation through a channel
  • Low noise
Disadvantages of FSK :
  • The BER performance in the AWGN channel is worse compared to PSK modulation
  • Extensively used in low-speed modems having bit rates below around 1200 bits/sec
  • This increases the channel bandwidth required to transmit the FSK signal type
  • It uses larger bandwidth compared to other modulation techniques like ASK and PSK. Hence it is not bandwidth efficient
  • FSK is not preferred for the high-speed modems because with increases in speed and also have the bit rate increases
  • When in the telecommunication media, the telephone lines have very low bandwidth, it is not possible to satisfy the bandwidth requirement of FSK at a too much higher speed. So in a method of FSK is preferred only for the low-speed problem
Explore more information:

Advantages and disadvantages of electricity

We all know that electricity is a set of physical phenomena associated with the presence and motion of electric charge. Here this article gives information about the advantages and disadvantages of electricity to know more details about it.

Advantages of electricity :
  • It is a clean, safe, cheap and convenient source of energy
  • Lower maintenance cost
  • More efficient
  • No tailpipe emission
  • We all know that it  can be set up in many sizes
  • It doesn't require as many employees
  • Reduces greenhouse emission
  • Makes barely any pollution compare to other ways of creating or generating electricity
  • Relatively low maintenance cost
  • Hydroelectric station are inexpensive to operate
  • Hydroelectricity produces no gas emissions or waste
  • A station can operate and run for long periods of time
  • It is renewable
Disadvantages of electricity :
  • More expensive than gasoline
  • Loss of fish species
  • Sometimes messes up wildlife
  • Dependent on precipitation
  • More power plants and more pollution
  • Damming can cause loss of land suitable for agriculture as well as recreation
  • Cost for construction
  • Change in river or stream quality
  • An electric vehicle is not completely emission free
  • In electricity, there are a limited number of feasible sites for a large number of dams
  • Drought can affect power production
  • Hydroelectric natural seasonal changes in river and ecosystems can be destroyed

Advantages and disadvantages of centrifugal pump

Centrifugal pump was fairly simple in nature. This article gives the information about the advantages and disadvantages of the centrifugal pump to know more details about it.

Advantages of centrifugal pump :
  • Simple in construction and cheap
  • Steady delivery
  • Handle liquid with a large amount of solid
  • Uniform pressure without shock or pulsation
  • Direct coupling to the motor
  • Maintenance cost is lower 
  • Can be mounted horizontally or vertically
  • No valve involve in pump operation
  • No metal to metal fit 
  • Discharge line may be closed
  • Therein almost no noise 
  • In these pumps, there is no drive seal so there is no leakage in the pump
  • It can pump hazards liquids
  • A pump has almost 100 % efficiency
  • This pump has minimum wear with respect to other
  • This pump is used magnetic coupling which breakup on high load eliminating the risk of damaging the motor
Disadvantages of centrifugal pump :
  • Can not handle viscous fluids efficiently
  • Can handle a small number of gases in liquids
  • Primary offer needed before startup
  • Can not be operated at a high head
  • Must be primed
  • This pump has not effective for high velocity but multistage configuration are expensive
  • Can not be operated at high discharge pressures
  • Maximum efficiency is to be hold over a narrow range of conditions

Advantages and disadvantages of switch

A switch is a network device which transfers data only to the host where it is being addressed. This article gives the information about the advantages and disadvantages of a switch to know more details about it.

Advantages of a switch :
  • It can make use CAM table for a port to MAP mapping
  • It helps in logical segmentation by supporting VLANs
  • The number of broadcast domains gets decreases
  • Support centralized management
  • They help in reducing the workload on individual host PCs
  • Permit multiple simultaneous conversations
  • Fairer than connection based technology
  • Switch interconnected individual node and also controlled access to media
  • Switches can be connected directly to work station
  • A network which uses switch will have fewer frame collisions
  • They increase the available bandwidth of the network
Disadvantages of a switch :
  • High cost 
  • Failure of switch bridge down the network
  • When we use a switch, a network connectivity problem can be difficult to trace through a switch
  • Broadcast traffic may be troublesome
  • While uses a limited broadcast, they are not as good as routers
  • Proper design and most important configuration is needed in order to handle multicast packets
  • If a switch is in promiscuous, they are vulnerable to security attacks
Explore more information:

Advantages and disadvantages of hub

Hub is a network device used to connect multiple Ethernet devices uses a twisted pair. Here this article gives information about the advantages and disadvantages of a hub to know more details about it.

Advantages of hub :
  • Easy to install
  • Very little delay
  • It is used for internal connectivity between the system
  • Can different media type
  • Cheaper
  • Hub device does not affect the performance of the network seriously
  • It can extend the total distance of the network
Disadvantages of hub :
  • It runs half-duplex
  • Can not filter information
  • It can not connect different type of network architecture such as a token ring and Ethernet extra
  • It does not have a mechanism to reduce the network traffic
  • Passes packet to all connected segment
  • Can not reduce network traffic
  • It will broadcast to all the port
  • Extend the collision
Explore more information:

Advantages and disadvantages of router

Router network can choose the best path across an internetwork using dynamic routing techniques. Here this article gives information about the advantages and disadvantages of the router to know more details about it. 

Advantages of the router :
  • It provides sophisticated routing, flow control, and traffic isolation
  • Reduce network traffic by creating collision domains
  • Reduce network traffic by creating broadcast domains
  • Can connect different network architecture, such as Ethernet and token ring
  • They are configurable which allows the network manager to make policy based on routing decisions
  • It can choose the best path across the internetwork using dynamic routing algorithms
  • It can reduce network traffic by creating collision domains and also by creating broadcast domains
  • Allow achieving loop so that redundant paths are available
Disadvantages of the router :
  • A router is more expensive than bridge or repeaters
  • Router only work with rotatable network protocol, not all protocol are routable
  • The router is slower than bridge or repeaters because they must analyze data transmission from the physical to the network layer
  • Dynamic router communication causes additional network traffic 
  • Are relatively complex device 
  • Can require a considerable amount of initial configuration 
  • They are protocol dependent devices which must understand protocol they are forwarding
Explore more information:

Advantages and disadvantages flowchart

Flowchart are widely used in programming tool that programmer or program designer used to design a solution to a problem. Flowchart allows you to layout a complex set of interactions in a way that is easier to digest. This article gives the information about advantages and disadvantages of flowchart to know more details about it.

Advantages  of flowchart :
  • Better way of communicating the logic of a system to all concerned so flowchart is convenient method of communication
  • Problem can be analysed in more effective way with the use of flowchart  
  • It promote the logical accuracy
  • It provide overview of the system and also demonstrates the relationship between various steps. 
  • Easy to draw
  • Easy techniques to understand logic
  • Easy to identify the mistake done by non computer person
  • Easy to branching and looping
  • It is easy to convert flowchart makes program or system maintenance easier 
  • It help the programmer to write a program code which is need for various purpose
  • Flowchart act as a guide or blueprint during the system analysis and program development phase
  • It helps in debugging process 
  • Facilitates troubleshooting 
 Disadvantages of flowchart :
  • Some task are difficult to represent using a flowchart
  • Quite costly and difficult to use and manage
  • People need to understand what the symbol mean
  • Time consuming and slow down the process of software development 
  • Sometime in complex flowchart other program might have a difficult time understanding the logic and the process of the flowchart
  • Difficult for modification
  • It is just visualization of program it cannot function like an actual program
  • As the flowchart symbols can't be type so that reproduction of flowchart becomes a problem

Advantages and disadvantages of tree topology

Tree topology is the combination of bus and star topology in a network device, this topology is best when a network is large and not for too small because of it is west of cable to use it. Here this article gives information about the advantages and disadvantages of tree topology to know more details about it.

Advantages of tree topology :
  • Point-to-point wiring for individual segment
  • Error detection and correction is easy
  • Each device is connected to the central device through a dedicated link type 
  • Expansion of the network is possible and easy 
  • If one segment is damaged other segment are not be affected 
  • All computers have access to larger and also their immediate networks 
  • We can the whole network into a segment, which can be easily managed and maintained
  • Supported by several  hardware and software vendors
Disadvantages of tree topology :
  • This topology is more difficult to configure and wire than other types of topologies
  • In this topology, relies heavily on the main bus cable, if it breaks the whole network is crippled
  • It requires more cabling
  • If the backbone link breaks, the entire segment totally goes down
  • As more and more nodes and segments are needed, the maintenance becomes difficult
  • The overall length of each segment is limited by the types of cabling used
  • The scalability of the network depends on the types of cable used
  • Heavily traffic cause the network and be it too slow
Explore more information:

Advantages and disadvantages of floppy disk

A floppy disk is a magnetic storage medium for a computer system. This article gives information about the advantages and disadvantages of a floppy disk.

Advantages of a floppy disk :
  • Floppy disks are Small and lightweight.
  • Easy to carry
  • Floppy disks are generally Cheap
  • Easy to transport and handle
  • Data on a floppy disk device can be write-protected from being changed accidentally
  • Floppy disk can be used to transfer data from one computer to another computer
  • Portable and inexpensive
  • Data on a floppy disk can be accessed randomly manner
  • Useful for transferring a small file
  • Security tab to stop data from being overwritten
Disadvantages of a floppy disk :
  • Easy to be damaged
  • The access time of floppy disks low
  • They have to handle more carefully
  • Floppies can be affected by heat
  • Small storage capacity
  • Also limited capacity
  • Many new computers don't have any floppy disk drive
  • Data can be erased if the disk comes into contact with a magnetic field side
  • Slow to access and retrieve data when compared to a hard-disk device

Explore more information : 

Full form of PCM

What is the full form of PCM?

Answer :
  • Pulse Code Modulation

What does PCM mean?

PCM is a digital scheme for transmitting analog data and converted into digital form. The signal in PCM is that there are only two possible states, represented by logic 1 and logic 0 form. Using PCM is possible to digitized all form of analog data, including full-motion video, voice, etc.

Explore more information:

Subscribe to: Comments (Atom)