Communication Theory-2 Assoc. Prof. Hakan DOĞAN Department of Electrical and Electronics Engineering
Source Destination Telephone, Radio, Television, Radar, Sonar, Telemeter,...
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted. In telecommunications, modulation is the process of conveying a message signal, for example a digital bit stream or an analog audio signal, inside another signal that can be physically transmitted. Modulation of a sine waveform is used to transform a baseband message signal into a passband signal, for example low-frequency audio signal into a radio-frequency signal (RF signal).
Transmitting very low frequencies require antennas with miles in wavelength When free space is the communication channel, antennas radiate and receiver the signal. Theory shows that the antennas operate effective only when their dimensions are of the order of the magnitude of wavelength of the signal being transmitted.
The condition for resonance in a linear dipole antenna is usually that the electrical length be equal to a multiple of a half-wavelength, λ/2, while for a monopole antenna it is a multiple of a quarter-wavelength, λ/4. Vertical Dipole: Monopole, Quarter-wavelength, Marconi
In simplest terms, the antenna current must be zero at both ends of a half wave antenna, these are called the current nodes. But where the current nodes are zero, the voltage anti-nodes are at maximum. So you have voltage maximums at both ends of the half wave antenna causing the maximum possible antenna current to flow and the maximum amount of electromagnetic radiation from the antenna. For that reason the half wave antenna is considered to be the most efficient. In general, an antenna should not be shorter than a half wavelength long, but you will find exceptions to this especially at very low frequencies and long wavelengths where even a half wave antenna would be too long to be physically practical. One solution is to use a quarter wave antenna and ground one end, letting the ground act as the other quarter wave, so you still have a half wave antenna. This is known as the Marconi antenna.
A monopole antenna is a class of radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some type of conductive surface, called a ground plane.
Audio is in the range approx. 30-20 khz. If an electromagnetic signal with a frequency of 30 Hz is transmitted it will have a wavelength of (speed of light /frequency) = 300,000/30 km = 10,000 km. To pick up this signal an aerial of size approx. 2,500 km will be required impractical. If this signal is used to modulate a carrier of 1 MHz the wavelength will be 300,000/1,000,000 km = 300 m, and an aerial of 75 m will suffice. If the carrier is 100 MHz, the wavelength is 3 m and a 75 cm aerial is sufficient.
So, then the connection between the frequency and the size of the antenna, the higher the frequency the lower the antenna size. Therefore, modulation is necessary in order to shift frequency components of the baseband signal around the frequency of the carrier signal
The ability of different users sharing a medium (multiple access) A large number of radio transmitters are trying to transmit at the same time. It is necessary for the receiver to pick up only the wanted signal and to reject the rest. One way to do to this is to assign a carrier with a known frequency to each transmitter, modulate this carrier with the signal, and then design the receiver to pick up only that known carrier frequency and reject the rest, using appropriate filtering methods. Then the original signal is removed from the received carrier.
Frequency division multiplexing (To support multiple transmissions via a single channel). To avoid interference
Amplitude modulation
Telemetre A telemeter is a device used to remotely measure any quantity. It consists of a sensor a transmission path and a display, recording, or control device Radar(Radio Detecting And Ranging) Radar is an object detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. Sonar (Sound Navigation And Ranging) Sonar is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels.
Some factors for Wireless Communication The total number of sources The total number of users Distance Mobility Security
Input Signal Transmitted Signal Received Signal Output Signal Input Transducer Transmitter Transmission Medium Receiver Output Transducer Input Message Source Unwanted effects Ouput Message Destination
Representation of Modulation Signals Bandpass signals (signals with small bandwidth compared to carrier frequency) can be represented in any of three standard formats:
Converts a nonelectrical input message into an electrical input signal (microphone, video camera, photocell, thermocouple, displacement gauge, etc.) The input signal can also be referred as the baseband signal Microfon Output Transducer: Converts the electrical signals into its Original form as needed by the user. A loudspeaker and a picture tupe are the most familiar examples of the output transducer.
Modifies the the baseband signal for efficient transmission Analog Modulation : AM, FM, PM Digital Modulations: BPSK, QPSK, 16-QAM, 64 QAM output is sent. The medium through which transmitter Responces the signal from the channel modifications made at the transmiter and the channel. by undoing the signal
Twisted pair Twisted pair cabling is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from unshielded twisted pair (UTP) cables, and crosstalk between neighboring pairs. It was invented by Alexander Graham Bell.
Coaxial cable, or coax, has an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing a geometric axis. Coaxial Cable
Waveguide : A waveguide is a structure which guides waves, such as electromagnetic waves. The original and most common meaning is a hollow conductive metal pipe used to carry high frequency radio waves, particularly microwaves.
An Optical Fiber Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information
Wireless communication is the transfer of information between two or more points that are not connected by an electrical conductor. The most common wireless technologies use electromagnetic wireless telecommunications, such as radio. With radio waves distances can be short, such as a few metres for television remote control, or as far as thousands or even millions of kilometres for deep-space radio communications. IEEE.802.11 IEEE.802.16
IEEE 802.11 is a set of standards for implementing wireless local area network (WLAN) computer communication in the 2.4 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee (IEEE 802). 802.11g 2.4-2.5 GHz 19 Mbit/s 54 Mbit/s 35 meter 110 meter The Institute of Electrical and Electronics Engineers (IEEE, read I-Triple-E) is a professional association headquartered in New York City that is dedicated to advancing technological innovation and excellence IEEE 802.16 is a series of Wireless Broadband standards authored by the Institute of Electrical and Electronics Engineers (IEEE). The IEEE Standards Board established a working group in 1999 to develop standards for broadband for Wireless Metropolitan Area Networks.
Wireline Wireless
LIMITS 1- Noise 2- Distortion 3- Signal to Noise Ratio-SNR 4- Attenuation 5- Channel 6- Interference
A distortion is the alteration of the original shape (or other characteristic) of waveform. Attenuation is an important consideration in the modern world of wireless telecommunication. Attenuation limits the range of radio signals and is affected by the materials a signal must travel through (e.g., air, wood, concrete, rain). Path loss (or path attenuation) is the reduction in power density (attenuation) of an electromagnetic wave as it propagates through space. Path loss is a major component in the analysis and design of the link budget of a telecommunication system.this term is commonly used in wireless communications and signal propagation.
In physics, interference is a phenomenon in which two waves superimpose to form a resultant wave of greater or lower amplitude. Co-channel interference or CCI is crosstalk from two different radio transmitters using the same frequency. There can be several causes of co-channel radio interference; Adjacent-channel interference (ACI) is interference caused by extraneous power from a signal in an adjacent channel. ACI may be caused by inadequate filtering (such as incomplete filtering of unwanted modulation products in FM systems), improper tuning or poor frequency control (in the reference channel, the interfering channel or both).
Noise : AWGN (Additive White Gaussian Noise) internal noise sourses *Thermal noise *Shot noise Signal to Noise Ratio (SNR) external noise * Solar intergalactic radiation *Thunderbolts and lightninings *Fluorescent lamps *Running electrical motor