Wireless Systems

1. Wireless Systems Lecture no. 1

2. Introduction • The world is revolutionized by the advancements that have taken place in various fields. • Examples of such areas are computers specially internet, communication particularly telecommunication and information technology. • Just imagine the technology today, it is beyond imaginations. • You have high speed technology and devices that are capable to operate on high data rates. What makes devices to have these qualities embedded?

3. Data and Signals • You must know the difference between Analog and Digital Signals. • Periodic and Non Periodic Signals. • Representation of Analog and Digital Signals. • How to calculate Peak Amplitude? • Example is: The power we use at home has a frequency of 60 Hz. How can you determine the period of this wave? The answer to the above example is 0.0166 x 10 Power 3 milliseconds.

4. Transmission Impairment • Signal Travels through transmission media which are not perfect. • This imperfection cause signal impairments, that means that the signal at the beginning of the medium is not same as the signal received at the end of the medium. • It will be more worst if the medium is wireless. • What information you have sent is not received and the factors can be attenuation, distortion and noise.

5. Diagrammatic Representation of Impairment

6. Attenuation • It means Loss of Energy. • Whenever a signal travel through medium it losses some of its energy in overcoming the resistance of the medium. • That is the reason a wire carrying electric signal gets warm. • To compensate this loss amplifiers are used to amplify the signal.

7. Decibel • To demonstrate whether a signal has lost or gained strength, Engineers use the unit of decibel. • The dB means the relative strengths of two signals. Or it can be one signal at two different points. • Note that dB is negative if the signal is attenuated and positive if the signal is amplified. NB: Power is square of voltage.

8. Examples • Suppose a signal travels through a transmission medium and its power is reduced to one half, how will you calculate the power loss? • A signal travels through an amplifier, and its power is increased 10 times. How can you calculate the amplification? • In first example the answer will be negative because it is attenuation and the second example answer will be Positive because of the amplification.

9. Why Decibels • One of the reasons why engineers use dB to measure the changes in strength of the signal is that dB numbers can be added or subtracted, when we measure several points. • Have a look in the example below and you will find how easy it is to find the attenuation or amplification of the overall system.

10. Distortion • Distortion means if the signal changes its form or shape. If you have a composite signal made of different frequencies than it will cause distortion. • Every signal has its own propagation speed through a medium and therefore it will cause its own delay while receiving at the final destination.

11. Noise • There are so many types of Noise. It can be thermal, induced noise, cross talk, and impulse noise. • Thermal noise is the random motion of electrons in a wire which creates an extra signals not created by a transmitter. • Induced noise comes from sources such as motors and appliances. These devices act as a sending antenna. • Cross talk is the effect of one wire over another. One wire act as a sending antenna and other as receiving. • Impulse noise is a spike (A Signal with High Energy in a Very short Time) it comes from power lines, lightning etc.

12. Types of Information • Categorically speaking all information can be either Analog/ Digital • If I say the systems are Digital and the real time signals are Analog, Am I right or wrong. Can you justify that? • Here we need to have a debate what are the advantages of Analog and Digital Signals? • You all have your notebooks, please write at least 3 disadvantages of Analog Information and 3 advantages of digital information. I am not asking to compare just individual advantages.

13. Advantages of Digital Information • A Digital Signal which comprises bits can be easily processed by computers. Once the computers are involved in processing, much of the work by humans are avoided. • For instance to manipulate a beautiful drawing you need to have drawing masters. If it is a computer even a kid can make it as he/ she likes. The condition is if the kid knows how to operate or use the system. • The Digitized information can easily be copied and the copies also have the originality of it.

14. Advantages of Digital Information (Continued) • The noise that interrupts the information and it is always in analog form if we are considering the wireless transmission and reception can’t modify the digitized information. • The network like internet and intranet are available to transmit the digital information to a long distance. You have High speed digital systems these days they are capable to operate on high data rates. • Example is ISDN, Integrated Services Digital Networks Technique.

15. Radio Basics • Once we talk about wireless systems most of the time we deal with RF Signals, Can anyone tell what are RF Signals? • The Radio Spectrum is a term that scientists, engineers and policymakers use to classify a vast and otherwise undifferentiated swath of EM Energy that exists in the Universe. • This form of Energy makes possible the development and use of technology such as broadcast radio and TV, Remote controlled Toy Air Planes, Geographic Positioning System (GPS) and Mobile Phones etc.

16. Radio Basics (Continued) • In 20th Century, the entrepreneurs developed first reliable radio system and the spectrum quickly became recognized as a radically new mean by which human being can communicate. • Initially there was comparatively little or no need to differentiate between various sections of radio spectrum because there was relative modest demand. • Modest demand means there was less products available at that time. • But with the passage of time problem was created and the problem was?

17. Need to Divide Radio Spectrum • One reason for dividing is that the number of frequencies available for transmission are limited and we have to manage them properly. • Just think about mobile networks. Even in Pakistan you have different providers. Are they operating on the same frequency (we are not talking about the frequency band we are discussing the spectrum allocation) • Things will get clearer in the coming lecture so don’t worry for the time being 

18. Electromagnetic Energy • To begin to understand how radio energy is used for human communication it is helpful to start with a simple rule of physics: when material vibrate they transfer energy to surroundings. • There can be different form of waves, For the time being we just say that energy is transferred in the form of waves. • If we take the example of sound wave, it is transmitted through the air by means of ‘compression’ wave like for example when we speak our mouth expels air from our lungs.

19. Electromagnetic energy (continued) • In the previous analogy air act as a medium that enables that Compressional waves to propagate from one place to another. • Not necessarily sound waves only travel through air. Just think about a real time scenario while you are speaking and other person is listening is there only air that is capable to pass on the sound wave to the receiver or there are other objects as well?

20. Frequency and wavelength • I expect that you all know about wavelength and frequency. • The length of the radio wave is a property that allows us to classify the radio spectrum according to the frequency. • During transmission or reception, the number of energy vibrations reaching an antenna each second is measured as the frequency of the signal. • One vibration per second is known by the term HZ, Hertz.

21. Units of Frequencies