Modulation index(m) = V_m/V_c
= (8/12)*100
= 66.66.

Kirchhoff’s Voltage Law
Kirchhoff’s Voltage Law (KVL) is Kirchhoff’s second law that deals with the conservation of energy around a closed circuit path.

Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier signal. The technology is used for communication systems such as telemetry, weather balloon radiosondes, caller ID, garage door openers, and low frequency radio transmission in the VLF and ELF bands. The simplest FSK is binary FSK (BFSK). BFSK uses a pair of discrete frequencies to transmit binary (0s and 1s) information. With this scheme, the “1” is called the mark frequency and the “0” is called the space frequency.

T=100ms
= (100)10^-3 sec
=10^-1 sec
F=1/T
F=1/10^-1 Hz
F=1/(10^-1 *10³) KHz
F = 10^-2 KHz

→ ECL is the fastest of all logic families. High speed in ECL is possible because transistors are used in difference amplifier configuration, in which they are never driven into Saturation.
→ Emitter-coupled logic (ECL) is a high-speed integrated circuit bipolar transistor logic family. ECL uses an overdriven BJT differential amplifier with single-ended input and limited emitter current to avoid the saturated (fully on) region of operation and its slow turn-off behavior.
→ As the current is steered between two legs of an emitter-coupled pair, ECL is sometimes called current-steering logic (CSL), current-mode logic (CML) or current-switch emitter-follower (CSEF) logic.[

Mobile computing main applications:
1.Portability
2. Connectivity
3.Social Interactivity
4. Individuality
5. IMobility
Travelling of salesman applicable to mobility of application.
Location awareness services applicable to Connectivity.

There are 2 popular GSM methods.
1. GSM-900
2. GSM-1800
GSM-900 uses 890 – 915 MHz to send information from the Mobile Station to the Base
Transceiver Station (uplink) and 935 – 960 MHz for the other direction (downlink), providing 124 RF channels (channel numbers 1 to 124) spaced at 200 kHz. Duplex spacing of 45 MHz is used.

The cluster size N = 7 and the frequency reuse factor is 1/7 since each cell contains one-seventh of the total number of available channels.
Total cells=7*3
=21
Frequency reuse concept, cells with the same letter use the same set of frequencies. A cell cluster is outline in blue color and replicated over the converge area.

→ Interim Standard 95 (IS-95) was the first ever CDMA-based digital cellular technology.
→ The IS-95 standards describe an air interface, a set of protocols used between mobile units and the network.
→ IS-95 is widely described as a three-layer stack, where L1 corresponds to the physical (PHY) layer, L2 refers to the Media Access Control (MAC) and Link-Access Control (LAC) sublayers, and L3 to the call-processing state machine.

→ In CDMA, multiple users share a 1.25 MHz channel by using orthogonal spreading codes (Walsh codes)
→ IS-95a standard designed for AMPS cellular band
→ Each cellular provider is allocated 25 MHz spectrum and ten 1.25-MHz CDMA duplex channels if A AMPS Band provider, 9 if B band provider

Multiplexing is a method by which multiple analog or digital signals are combined into one signal over a shared medium. It can share a medium without interference.

→ Wireless LANs are use high frequency radio waves instead of cables for connecting the devices in LAN. Users connected by WLANs can move around within the area of network coverage. Most WLANs are based upon the standard IEEE 802.11 or WiFi.
→ A wireless access point (WAP), or more generally just access point (AP), is a networking hardware device that allows other Wi-Fi devices to connect to a wired network.
→ Wireless access point in 802.11 WLAN services are association, association and Integration.

Given data,
— 4 channels are multiplexed using TDM
— Multiplex 1 byte per channel. So, total 4 bytes=4 channels.
— Each channel sends 100 bytes/sec
— Bit rate=?
Bit rate= 100 * 4 bytes(1 byte=8 bits)
= 100 * 4 *8 (we are converting into bits because we are finding bit rate)
= 3200 bps

— Mobile phone system with hexagonal( equals to 6) cells
— 840 frequencies are available.
— How many can be used in a cell?
In this we need maximum 3 unique cells are required.

Total cells used with frequency is = 840/3
= 280 frequencies

Option-A:​ This is the maximum number of distinct tuples that you can form with p distinct values per dimensions.
Option-B:​ You need at least p tuples to contain p distinct values per dimension. In this case no tuple shares any value on any dimension.
Option-C:​ The minimum number of cells is when each cuboid contains only p cells, except for the apex, which contains a single cell.
Option-D:​ We have p+1 because in addition to the p distinct values of each dimension we can also choose ∗.

Decibel (dB), unit for expressing the ratio between two physical quantities, usually amounts of acoustic or electric power, or for measuring the relative loudness of sounds. One decibel (0.1 bel) equals 10 times the common logarithm of the power ratio

Sampling is the process of recording an analog signal at regular discrete moments of time.
sampling is the reduction of a continuous-time signal to a discrete-time signal. A common example is the conversion of a sound wave (a continuous signal) to a sequence of samples (a discrete-time signal).
Quantization in digital signal processing, is the process of mapping input values from a large set (often a continuous set) to output values in a (countable) smaller set, often with a finite number of elements.
The sampling rate fs is the number of samples per second.
The time interval between samples is called the sampling interval T_s=1/f_s

● A multivibrator is a one type of electronic circuit, that is used to implement a two state system like flip-flops, timers and oscillators.
● Multivibrators are classified into three types based on the circuit operation, namely Astable multivibrators, Bistable multivibrators and Monostable multivibrators.
● The astable multivibrator is not stable and it repeatedly switches from one state to the other. In monostable multivibrator, one state is stable and remaining state is unstable.
● When the power is turned ON consider the flip flop is cleared initially, then the o/p of the inverter will be high. The charging of the capacitor will be done using two resistors R1& R2. When the voltage of the capacitor goes above 2/3 Vcc, then the output of the higher comparator will be High, it changes the control flip flop

A multivibrator is an electronic circuit used to implement a variety of simple two-state devices such as relaxation oscillators, timers and flip-flops. It consists of two amplifying devices (transistors, vacuum tubes or other devices) cross-coupled by resistors or capacitors.

A transceiver is a device comprising both a transmitter and a receiver that are combined and share common circuitry or a single housing. When no circuitry is common between transmit and receive functions, the device is a transmitter receiver.

Limitation of single-sideband modulation being used for voice signals and not available for video/TV signals leads to the usage of vestigial sideband. A vestigial sideband (in radio communication) is a sideband that has been only partly cut off or suppressed. Television broadcasts (in analog video formats) use this method if the video is transmitted in AM, due to the large bandwidth used. It may also be used in digital transmission, such as the ATSC standardized 8VSB.
Vestigial sideband (VSB) is a type of amplitude modulation ( AM ) technique (sometimes called VSB-AM ) that encodes data by varying the amplitude of a single carrier frequency . Portions of one of the redundant sidebands are removed to form a vestigial sideband signal – so-called because a vestige of the sideband remains.

→ The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source.
→ The Doppler effect is observed whenever the source of waves is moving with respect to an observer.
→ The Doppler effect can be described as the effect produced by a moving source of waves in which there is an apparent upward shift in frequency for observers towards whom the source is approaching and an apparent downward shift in frequency for observers from whom the source is receding.

→ Digitization is the process of converting information into a digital format . In this format, information is organized into discrete units of data (called bit s) that can be separately addressed (usually in multiple-bit groups called bytes).
→ sampling is the reduction of a continuous-time signal to a discrete-time signal. A common example is the conversion of a sound wave (a continuous signal) to a sequence of samples (a discrete-time signal).
→ “fidelity” denotes how accurately a copy reproduces its source

Moore’s law is the observation that the number of transistors in a dense integrated circuit doubles about every two years.

● The Bistable Multivibrator is another type of two state device.
● Bistable Multivibrators have TWO stable states (hence the name: “Bi” meaning two) and maintain a given output state indefinitely unless an external trigger is applied forcing it to change state.

→ An eight-bit D/A converter have 2​ ⁸​ -1 resolvable levels which is nothing but 255 levels.
→ Percentage resolution is (1/255)×100=0.39%

●The generic term waveform means a graphical representation of the shape and form of a signal moving in a gaseous, liquid, or solid medium.
●For sound, the term describes a depiction of the pattern of sound pressure variation (or amplitude) in the time domain
● The temporal frequencies of sound waves are generally expressed in terms of cycles (or kilocycles) per second. The simplest waveform is the sine wave, since it has only one frequency associated with it. The sound waves associated with, say, music, are constantly varying.

● Reverberation, in psychoacoustics and acoustics, is a persistence of sound after the sound is produced.
● A reverberation, or reverb, is created when a sound or signal is reflected causing a large number of reflections to build up and then decay as the sound is absorbed by the surfaces of objects in the space – which could include furniture, people, and air.

Digital sampling is the recording of a sound using a string of numbers to represent the sound. 1s and 0s. These numbers are called samples.

In MOSFET fabrication channel length is defined during Poly-Silicon gate patterning process

An ideal op-amp lead us to an op-amp with input resistance is infinite, so no current flows into either input terminal (the “current rule”) and that the differential input offset voltage is zero (the “voltage rule”).
Ideal operational amplification will have
➝ High input impedance ( R _in = ∞ ) and low output impedance ( R _out = 0 )

➝ R _in = ∞ , so zero input current
➝ Infinite voltage gain
➝ So, it is a voltage controlled voltage source device.

→ Microwave signals are often divided into three categories:
1)Ultra high frequency (UHF) (0.3-3 GHz);
2)Super high frequency (SHF) (3-30 GHz); and
3)Extremely high frequency (EHF) (30-300 GHz).
→ In addition, microwave frequency bands are designated by specific letters.
→ The term “P band” is sometimes used for ultra high frequencies below the L-band. For other definitions, see Letter Designations of Microwave Bands
→ Lower Microwave frequencies are used for longer links, and regions with higher rain fade. Conversely, Higher frequencies are used for shorter links and regions with lower rain fade.

In signal processing, independent component analysis is a computational method for separating a multivariate signal into additive subcomponents. This is done by assuming that the subcomponents are non-Gaussian signals and that they are statistically independent from each other.

The T-carrier system, introduced by the Bell System in the U.S. in the 1960s, was the first successful system that supported digitized voice transmission. The original transmission rate (1.544 Mbps) in the T1 line is in common use today in​ Internet service provider (ISP) connections to the Internet. Another level, the T3 line, providing 44.736 Mbps, is also commonly used by Internet service providers.
The T-carrier system is entirely digital, using pulse code modulation (PCM) and time-division multiplexing (TDM). The system uses four wires and provides duplex capability (two wires for receiving and two for sending at the same time). The T1 digital stream consists of 24 64-Kbps channels that are multiplexed.

A low-pass filter (LPF) is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. The exact frequency response of the filter depends on the filter design.

● Pulse code modulation (PCM) is a digital scheme for transmitting analog data. The signals in PCM are binary; that is, there are only two possible states, represented by logic 1 (high) and logic 0 (low). This is true no matter how complex the analog waveform happens to be. Using PCM, it is possible to digitize all forms of analog data, including full-motion video, voices, music, telemetry, and virtual reality (VR).
● sampling is the reduction of a continuous-time signal to a discrete-time signal. A common example is the conversion of a sound wave (a continuous signal) to a sequence of samples (a discrete-time signal).
● Quantization in digital signal processing, is the process of mapping input values from a large set (often a continuous set) to output values in a (countable) smaller set, often with a finite number of elements.
● The encoder encodes the quantized samples. Each quantized sample is encoded into an 8-bit code word by using A-law in the encoding process.

JPEG( Joint Photographic Experts Group) is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality
MPEG (Moving Picture Experts Group): It is a method of lossy compression for coding audio-visual information (e.g., movies, video, music).
Arithmetic coding is a form of entropy encoding used in lossless data compression. Normally, a string of characters such as the words “hello there” is represented using a fixed number of bits per character, as in the ASCII code. When a string is converted to arithmetic encoding, frequently used characters will be stored with fewer bits and not-so-frequently occurring characters will be stored with more bits, resulting in fewer bits used in total.

Line coding→ Process of converting digital data to digital signal

Block coding→ Provide redundancy to ensure synchronization and inherits error detection

Scrambling→ Provides synchronization without increasing number of bits

Pulse code modulation→ A technique to change analog signal to digital data

Transmission rate over a noisy channel:

→ H(X) is the amount of information per symbol at the input of the channel.

→ H(Y) is the amount of information per symbol at the output of the channel.

→ H(X|Y) is the amount of uncertainty remaining on X knowing Y.

The information transmission is given by:

I(X;Y) = H(X)−H(X|Y) bits/channel use

For an ideal channel X = Y, there is no uncertainty over X when we observe Y. So all the information is transmitted for each channel use: I(X;Y) = H(X) If the channel is too noisy, X and Y are independent. So the uncertainty over X remains the same knowing or not Y, i.e. no information passes through the channel: I(X;Y) = 0.

Capacity of a noisy channel:

Quadrature Amplitude Modulation means changing both amplitude and phase of the carrier.

→ TDM:
1. TDM stands time division multiplexing.
2. Cross talk like problem not occurs in TDM.
3. TDM requires channel synchronization
4. TDM has greater noise immunity.
→ TDM is a non-priority peer/peer protocol.

→ TDMA sets cellular apart from all preceding mobile/radio systems.
→ TDM:
1. TDM stands time division multiplexing.
2. Cross talk like problem not occurs in TDM.
3. TDM requires channel synchronization
4. TDM has greater noise immunity.
→ TDM is a non-priority peer/peer protocol.

The Unlicensed National Information Infrastructure (U-NII) radio band is part of the radio frequency spectrum used by IEEE 802.11a devices and by many wireless ISPs. It operates over following ranges:

Cellular CDMA systems can use N=1(it means the same frequency is used in all cells)

The VLF and LF bauds use ground propagation for communication.
Propagation methods are 3 types
1. Ground
2. Sky
3. Line of sight

→ Very low frequency or VLF is for radio frequencies (RF) in the range of 3 to 30 kilohertz (kHz), corresponding to wavelengths from 100 to 10 kilometers, respectively.
→ The low-frequency signals travel in all directions from the transmitting antenna.