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