Lecture-1
R.C. JoshiAssot. ProfessorECE Department
A.D.Patel Institute of Technology
Introductory session
Course Outline
• Random variable and Processes • Overview of Wireless Communication • Propagation through channel and diversity• Digital Modulation and Detection• Channel Coding• Spread Spectrum Communication
Seminar/Journal/Term Project/Assignment
• Practical exam evaluate based on three entities
(1) Seminar/Assignment (25%)(2) Journal(25%)(3) Term Project (50%)
Power measurements decibel: is a logarithmic unit or transmission
measurement unit used to express relative Gains and Losses.
• dB (decibel)• dBm (decibel pre mili watt)• dBµ (decibel per micro watt)• dBi (decibel per isotropic antenna)• dB-SPL (decibel Sound Pressure Level)
1010 log ( )0.001 )
PdBmW
=
1010 log ( )0.000001
PdBµ =
Example-1Three stage system comprise of two amplifiers and one filter. The input power Pin = 0.1mW. The absolute power gains are Ap1 = 100, Ap2 = 40, Ap3 = 0.25. Determine
(a) the input power in dBm(b) output power (Pout) in watts and dBm(c) The dB gain of each of the three stages(d) The overall gain in dB
Answer
• (a) -10dBm• (b) Pout = 0.1W, 20dBm• (c) 20dB, 16dB, -6dB• (d) 30dB
Example-2
• Determine the Total power when a signal with a power level of 20dBm is combine with a second signal with a power level of 21dBm
Answer
• 23.5dBm
Bandwidth and Information Capacity
• The bandwidth of an information signal is simply the difference between the highest and lowest frequencies contain in the information.
• Information Capacity (Shanon’s Equation)
2log (1 )I B S N= +
Noise
• Electrical Noise is defined as any undesirable electrical energy that falls within the pass band of the signal
• Noise can be divided in two general categories:
(1) correlated(2) uncorrelated
Uncorrelated Noise
• Uncorrelated noise is present regardless of whether there is signal present or not
• Uncorrelated noise can further divided in two categories
• external Noise: noise that is generated outside the device or circuit.
• Internal Noise: is a electrical interference generated within a device or circuit.
External Noise• Atmospheric Noise: Atmospheric noise is
commonly called as a static electricity- lightening effect- Explosive sounds- Friction sounds- Extraterrestrial Noise: Extraterrestrial noise
consist of electrical signal that originates outside earth’s atmosphere
- Milky way- Other galaxies- Sun
• Man-Made Noise: Noise that is produced by mankind
- Commutators in electric motors- Automobile ignition system- AC power generating and switching
equipments- Fluorescent lights
Internal Noise
• Shot Noise: shot noise is caused by random arrival of carriers at the output of the element of an electronic device like diode, transistor etc..
- Shot noise is sometimes called as a transistor noise and is additive with thermal noise.
• Transit time Noise: any modification to a stream of carrier as they pass from input to the output of the device produce an irregular , random variations categorized as a transit time noise.
• Thermal Noise : Thermal noise is associated with the rapid and random movement of electrons within a conductor due to thermal agitation
N KTB=
Correlated Noise• Correlated noise is a form of noise that is
mutually related with signal. Correlated noise is also known as a nonlinear distortion
• Harmonic Distortion: Harmonic distortion occurs when unwanted harmonics produced due to non linear amplification of the signal.
- Harmonics are integer multiples of fundamental frequency
% 100higher
fundamental
VTHD
V= ×
2 2 22 3higher nV V V V= + +
Example
• Determine(a) 2nd, 3rd, 12th harmonics for 1-KHz wave(b) Percent second order, third order and
total harmonic distortion for fundamental frequency with amplitude of 8 Vrms , a second harmonic amplitude 0.2 Vrms , and third harmonic amplitude is 0.1 Vrms
Answer
• (a) 2KHz, 3KHz, 12KHz• (b) 2.5%, 1.25%, 2.795%
• Intermodulation Noise: is the generation of unwanted sum and difference frequencies produced when two or more signals applied to the non linear device
• Sum and difference frequencies also known as a cross product of the signals
• Cross product = 1 2mf nf±
Example
• For a non linear amplifier with two input frequencies 3KHz, 8KHz determine
(a) First three harmonics present in the output for each fundamental frequency
(b) Cross-product frequencies produced for values of m and n of 1 and 2
(a) 3KHz and 8KHz, 6KHz and 16KHz, 9KHz and 24KHz
(b) 5KHz and 11KHz, 2KHz and 14KHz, 13KHz and 19KHz, 10KHz and 22KHz
(for m,n = 11,12,21,22)
Important terms to estimate noise effect in the system
• noise floor• Signal to noise ratio• noise factor/noise figure• noise margin