Chapter 2

ASK Advantage:

• It is used for transmitting digital data through fiber. • Less energy is needed to transmit the information.

Other amplifiers are:

• Vacuum tube amplifiers • Transistors amplifiers • Operational amplifiers • Video amplifiers • Microwave amplifiers

Various PSK techniques are:

Binary Phase Shift Keying (BPSK) Differential Phase Shift Keying (QOSK) Quadrature Phase Shift Keying (QPSK)

ASK Disadvantage:

• It requires extra bandwidth, hence the wastage of power.

Disadvantages of FM:

• More Bandwidth is required. • Receiver and transmitter are more complicated.

Circuit-based networks:

The communication channel is fixed and is a dedicated end-to-end connection in circuit- based telephone networks. All the users can avail the resources.

Ultra Wideband

Ultra Wideband is a short-range wireless technology. It is used for transmitting digital data on large scale over a wide spectrum of frequency for a short distance. As Ultra wideband requires low power than normal or background noise, there is no chance of interference at any frequency band which is in use. UWB transmits the digital signals that are timed correctly on a carrier signal across a broad spectrum at a same time.

Filter:

A Filter is an electronic circuit that performs signal processing functions, and mainly used to either accept or block a radio frequency signal. Low-pass filter High-pass filter Band-pass filter

Mixer:

A Mixer is a nonlinear device that combines two radio frequency inputs to produce a single output.

Amplitude Shift Keying

Amplitude Shift Keying (ASK) is the binary modulation technique which is same as Amplitude modulation. In this modulation, by keeping the frequency and phase constant, the amplitude of the carrier signal is changed with the discrete values of modulating signal. The peak amplitude of signal during each bit is always constant and the value depends on the bit (0 or 1). In this modulation NRZ coding is used, i.e. 1 bit has a carrier signal, while the '0' bit is represented by no signal, which represents ON/ OF F Keying (0oK). Same as AM, it is affected by noise and distortion. Both modulation and demodulation techniques are low cost.

Filter

Filter is an electronic circuit which changes the frequency spectrum of signals passing through it. It removes the unwanted signals. It either passes or rejects the frequencies above or below the cutoff frequency.

Frequency Hoping Spread Spectrum

In Frequency Hoping Spread Spectrum (F 1188), instead of sending the signal on a single frequency, it applies the range of frequencies. Frequencies get changed during the transmission of signal. In FIISS, transmission is done in burst; a small burst is transmitted on one frequency, after another burst is transmitted on another frequency. This process is continued until the end of transmission. In F 1188, the receiver must know the hoping code, for correctly receiving the transmitted signal. During the transmission, if interference occurs on frequency, then that burst is transmitted over the next frequency. The F IISS signal gets affected by the interfering signal when both are transmitted at same time and at the same frequency.

Quadrature Phase Shift Keying (QPSK):

It is also known as 4PSK. QPSK has 4 phases (0, 90, 135 and 180 degree). By this 4 phase QPSK encodes 2 bit of information. It is a multilevel modulation technique. The bandwidth of QPSK is half than the bandwidth of PSK.

Bandpass Filter:

It is the combination of high-pass and low-pass filter. It passes the frequencies between certain ranges and rejects the frequencies outside of that range.

Classification of filter by technology

Passive filter: Filters which are not dependent on external power supply are known as passive filter. RC, RL, LC, RLC all are passive filters.

Switching

Switching involves moving the signal from one frequency to another. Two types of signal switching are possible: Packet-switching and Circuit-switching.

Signal-to-Noise Ratio (SNR):

The measure of signal strength relative to background noise SNR: (PSignal/PNuisc) = (ASignal/ANoisc)2 Where P, is the power and A, is the amplitude of the signal Dynamic range: Amount by which the signal's maximum intensity exceeds its minimum detectable level.

Active Filter:

These filters are designed by using amplifying components. Generally, operational amplifier is used for design of active filter.

Wireless Signals:

Wireless transmissions do not use the visible media; instead they travel using electromagnetic waves.

Various digital modulation techniques are:

• Amplitude Shift Keying (ASK): It is a binary modulation technique in which value of amplitude is changed depending on 0 or 1, frequency while the phase is kept constant. • Frequency Shift Keying (FSK): It is a binary modulation technique that changes the value frequency depending on 0 or 1, amplitude while the phase remains constant. • Phase Shift Keying (PSK): It is a binary modulation technique similar to PM but phase gets changed depending on the value 0 or 1.

Analog modulation can be further divided into:

• Amplitude modulation: Amplitude of carrier waves changes according to change in characteristics of modulating signal. • Frequency modulation: Frequency of the carrier waves changes according to the variation in modulating signal. • Phase modulation: Phase of carrier waves changes according to the variation in modulating signal.

Digital modulation is categorized into:

• Amplitude shift keying • Frequency shift keying • Phase shift keying

Characteristics of amplifiers:

• Gain: Gain means how much level of input signal is to be increased; it is measured in decibels (dB). • Output dynamic range: It is the range between lowest useful output and highest useful output. • Bandwidth and rise time: Bandwidth of amplifier is defined as the difference between the upper and lower half power points (Half power point is the frequency at which the output power has dropped to half of its mid-band level). • Slew rate: It is the maximum rate of change of output signal. • Noise: It is an unwanted distortion created during amplification process. • Efficiency: It is the amount of input power required to amplifiers output.

Advantages of DSSS

• If interference occurs, while sending the chipping code rather than single bit, then statistical technique in receiver side recovers the original data instead of retransmission. • If the third user accepts the signal, then it appears as less powered noise, and hence gets rejected. • It is more secured to send chipping code than single bit. • WLAN uses the DSSS.

Frequency:

"For an oscillating or varying current, frequency is the number of complete cycles per second in alternating current direction. The standard unit of frequency is the hertz, abbreviated Hz. If a current completes one cycle per second, then the frequency is 1 Hz; 60 cycles per second equals 60 Hz."

Bandwidth:

"In electronic communication, bandwidth is the width of the range (or band) of frequencies that an electronic signal uses on a given transmission medium. In this usage, bandwidth is expressed in terms of the difference between the highest-frequency signal component and the lowest frequency signal component. Since the frequency of a signal is measured in hertz (the number of cycles of change per second), a given bandwidth is the difference in hertz between the highest frequency the signal uses and the lowest frequency it uses."

Amplifier:

Amplifier is the electronic device which can be used for increasing the voltage, current or power of the signal to be transmitted. It improves the quality of the input signal and transmits it to the receiver. The transfer function used is generally the ratio of input to output.

Amplitude Modulation (AM)

Amplitude modulation (AM) is a modulation technique, in which amplitude of the carrier wave is changed in direct proportion to the characteristics of modulating signal. Amplitude modulation is used in radio frequencies. The AM generates the modulated signal which has double bandwidth than the modulating signal. It is generated by multiplying sinusoidal data signal by constant factor of the carrier signal. This product generates three sinusoidal components: Carrier, lower sideband and upper sideband having same bandwidth as modulating signal. Simple sine wave of carrier signal is given by c (t) = Csin (ωϵt) Where, ωϵ: Frequency of Carrier Signal C: Amplitude of Carrier Signal The equation for the simple sine wave of frequency com is: m (t) = Msin (ωmt + Φ) Where, Φ: phase offset relative to c (t). ωm :Frequency of modulating Signal M: Amplitude of modulating Signal Amplitude modulation is performed simply by adding m(t) to C. The amplitude-modulated signal is then y (t) = (C + Msin (ωmt + (p)) sin (ωet) The formula for y(t) above may be: y(t) : Csin(ωct) + M (cos⁡(O-(ωm-ωc)t))/2-M (cos⁡(0+(ωm+c)t))/2

Amplifier:

An amplifier is a device that increases a signal's intensity or strength. • Class A • Class B • Class C • Class D

Analog Signals

Analog signals are uninterrupted electrical signals. These signals vary with time and amplitude. These signals are easy to create and transfer from one place to other. But if the pattern is changed due to unwanted noise or distortion, then the output is not the same as the input. For example, the old fashion telephone uses the analog signals.

Transmission Direction

Data can be transferred from one point to another. Data transmission can be categorized into three types depending on the direction of flow of data: • Simplex Transmission: Data is transferred in only one direction • Half-duplex: Data is transferred in two ways but not simultaneously • Full-duplex Transmission: Data is transferred in both ways at a time

Digital Modulation:

Digital modulation is also known as discrete modulation. In this modulation, modified format of carrier signal can take only discrete values. The analog signal gets converted into number format for the transmission purpose. Modulated digital signal gets transmitted through cable, satellite or via. Microwave. Digital modulation has the capacity to transmit large scale of data than analog.

Digital Signals:

Digital signals are interrupted signals; they change in each step. They contain a pattern of bits of information, and pulses with discrete levels or digits with values as well. The value of pulse is constant but value of digit changes rapidly. Digital signals have two amplitude levels known as nodes. The value of each node varies between 1 and 0, true and false, high and low and so on.

Direct Sequence Spread Spectrum

Direct Sequence Spread Spectrum (DSSS) is the best technique of spread spectrum. In this technique, instead of sending the one bit, numbers of bits are transmitted. For a signal bit, DSSS uses the spreading code; in other words, it uses different sequence of bits. That code is known as 'chipping code'. This chipping code spreads the signal across large frequency band; it spreads the signal in direct proportion to the number of bits used. If for a single bit, ten bit of spreading code is used then the bandwidth of the signal is ten times than the single bit.

Frequency Shift Keying

Frequency Shift Keying (FSK) is the modulation technique which is same as FM. In this modulation, amplitude and phase remains constant. The value of frequency gets changed according to the discrete values of modulating signal. Different frequencies are used for denoting bit 0 and 1, so the frequencies are transmitted in opposite direction avoiding the overlapping of frequencies. It avoids most of the problem from noise. It is less susceptible to noise as compared to ASK.

Frequency modulation (FM)

Frequency modulation (FM) is the modulation technique, in which amplitude is kept constant and the frequency of the carrier wave gets changed according to the variation in modulating signal. FM is a technique of impressing data onto the AC wave by changing the frequency of wave immediately. In analog FM, frequency of carrier wave gets changed in proportion to the amplitude of carrier signal, while in digital modulation frequency gets shifted.

Packet-based networks:

In packet-based network, the data is fragmented into packets that are transmitted from one point to another. The packets are reassembled at the other end. All the data packets follow the same path to reach the destination network. The packet-based networks are connectionless.

Simplex Transmission

In simplex transmission data transmission is unidirectional; in other words data is transferred in only one direction. Simplex transmission is not generally used, because it is not possible to send the reply to the transmitter end. For example: Television set. In this, signals are transmitted from transmitter but it is not possible to send reply.

Infrared Light

Infrared light are a type of electromagnetic radiation with wavelength larger than visible light but less than radio waves. The wavelength of Infrared light lies between 700 nanometers and 1 millimeter. The wavelength of 'Near infrared' light is nearest to the wavelength of visible light, while the wavelength of 'Far infrared' light is nearest to microwave region of electromagnetic spectrum. Far infrared waves are thermal; we realize it in the form of heat like heat from sun or fire. On the other hand, we cannot feel the 'Near infrared' waves as these are not hot. They are generally used by TV's remote control.

Binary Phase Shift Keying (BPSK):

It is a simple form of PSK. In this PSK, two various phases i.e. 0 and 180 are used, hence known as 2-PSK or binary PSK (BPSK). In BPSK the alternative sine waves are used for encoding the bits. The bandwidth is the same as the bandwidth of ASK. In BPSK Signaling rate is equal to the bit rate. This is more robust compared to other PSKs. It is generally used in satellite communication.

Differential Phase Shift Keying (QOSK):

It is a simple form of coding. In this PSK, the modulating signal is not the binary code, but this code determines the variations in the binary code. Here, the two phases of successive symbols are compared for determining the data rather than doing demodulation. When such differential encoding is used, then it is known as DPSK. The demodulator is necessary to determine the changes in the incoming signal. The PSK signal is changed to a DPSK signal by the following rules: A '1' in the PSK signal is indicated by no change in the DPSK A '0' in the PSK signal is indicated by a change in the DPSK signal

Spread Spectrum

It is a wireless communication technique, which uses the narrow signal and spreads it over broad areas. This spectrum is challenging to outside interference, because interference can affect small part of a signal rather than the entire signal.

High-pass Filter:

It is the filter which passes the high frequencies but rejects the frequencies below the cutoff frequency.

Low-pass Filter:

It is the filter which passes the low frequencies but rejects the frequencies above than cutoff frequency.

Analog Modulation

It is the modulation technique in which carrier analog signals such as amplitude, frequency and phase change according to the immediate values of modulating analog signal. In this modulation, contents of data are not changed. Instead, the modulating signal mixed with the carrier signal of higher frequency and the modulated output signal defines the bandwidth same as the carrier signal. In digital data communication, analog modulation requires to change the analog data to digital before the transmission of modulated signal. Depending on: • Carrier waveform (sinusoidal or pulse) • Type of transmission (analog or digital) • Types of modulation depends on change of (Amplitude, frequency and phase of modulating signal)

Digital Filter:

It performs the digital math operation on the signals. SAW (Surface Acustic Wave) Filter: It is electromechanical device used for radio frequency purpose.

Mixer -

Mixer is a non-linear device used for frequency conversion. It combines two or more input frequency to produce a single output. It changes the RF power at one frequency to RF power at another frequency for making signal processing simple and low-cost. This frequency conversion allocates amplification of received signal at a frequency other than RF or audio frequency.

Modulation

Modulation is the process of changing the carrier signal in such a way that it can be used for transmitting the information. In modulation, the information can be added to the carrier signal by varying the amplitude, frequency and phase to get the modulated signal. A device which performs the modulation is known as modulator, while the device which performs demodulation is known as demodulator. The device that performs both the operations is known as modern. There are two main types of modulation: • Analog modulation • Digital modulation

Phase Shift Keying

Phase Shift Keying (PSK) is a binary modulation technique same as PM. In this technique, both the peak amplitude and frequency remains constant while the phase gets changed, according to the value 0 or 1. In this modulation, the current phase is compared with the phase of the previous state. The minimum bandwidth required for PSK transmission is same as ASK. It is used in WLAN.

Phase modulation (PM)

Phase modulation (PM) is sometimes used as the alternative for FM. In PM technique, the amplitude and the frequency of carrier signal remain constant, but as the amplitude of modulating signal changes the phase of carrier wave gets changed. This phase changes the starting point of the cycle, but the change can occur only when bits get transmitted change from 1 to 0 bit, or vice versa. PM is a technique of impressing the data onto AC waveform by changing the phase of wave. In analog PM, frequency of carrier wave gets changed in proportion to the amplitude of carrier signal, while in digital modulation frequency gets shifted. PM is not generally used, because it needs more complex hardware receiver.

Radio Waves:

Radio waves are a kind of electromagnetic radiation. The wavelength of radio waves is the longest wavelength in electromagnetic spectrum. These waves can be generated easily. The AM radio waves use the Medium frequency band; therefore they can easily pass through the building. These waves can travel long distances of approximately 1000km. These waves transmit the information in all direction; therefore it is not necessary that the transmitter and the receiver may be in a direct line of sight. The radio waves used for communication are modulated in two ways: • Amplitude modulation (waves vary according to wavelength amplitude) • Frequency modulation (waves vary according to wavelength frequency)

Band rate:

The baud rate is a measure of changes in the signal state during its transmission in a channel. The signal state can change with respect to strength, frequency, voltage, phase angle. A measure of one baud implies the change in signal for one time. Therefore, 200 baud implies that the signal has been changed 200 times in a second.

Components of a Radio System

The components that allow communication through radio frequency are filters, mixers, and amplifiers.

Transmission Speed

The speed at which data is transmitted over a channel is called the transmission speed. The units of transmission speed are measured in kilobits, kbps, 10005 of bits per second, or megabits, Mbps, millions of bits per second. The bps and baud rate are generally used to express the transmission rate.

Signal Strength

The strength of a signal is measured at a distance (called the reference point) from where the signal is actually transmitted. The signal strength can be measured in terms of its voltage. It determines the strength at which the signal is transmitted, received or predicted. The units for signal strength are: V/m2, mV/m2, dBuV/m2, based on the intensity of the signal.

Analog modulation for analog signal is categorized into:

• Amplitude modulation • Frequency modulation • Phase modulation

The Analog modulation is divided into:

• Analog modulation for analog signal • Analog modulation for digital signal

Summary

• Analog signals are continuous electrical signals that vary in both time and amplitude. • Digital signals are non-continuous, quantized signals that consist of patterns for bits of information. • A Filter is an electronic circuit that performs signal processing functions, and mainly used to either accept or block a radio frequency signal. • Mixer is a nonlinear device that combines two radio frequency inputs to produce a single output. • Based on the direction of flow of data, the transmission of data can be classified into: o Simplex Transmission o Half-duplex Transmission o Full-duplex Transmission o Ultra wideband is a wireless technology for transmitting large amounts of digital data over a wide spectrum of frequency bands with low power for a short distance. o An Amplitude Shift Keying (ASK) is a digital modulation format where information is conveyed in the amplitude of a carrier signal.

Amplifiers are generally classified into:

• Cass A: In this amplifier, efficiency is not so considered. It amplifies all part input signal. • Cass B: Each output device conduct only half wave of input signal. • Cass AB: It transmits between 180 and 360 degrees. • Class C: It amplifies less than 180 degree of input signal. Its efficiency is greater than A • AB and B but poor linearity. • Cass D: It mainly depends on Pulse Width Modulation (PWM). It has high efficiency.

Radio waves are used in:

• Cellular phone to transfer the information • Sound and Video for TV carry through Radio waves

Advantages of FHSS

• Eavesdroppers hear only meaningless blips, because F 1188 appears for a very short duration. • If any frequency gets jammed, only that part of the frequency gets affected rather than whole signal. • Affected part of signal is again retransmitted.

It uses two different methods

• Frequency Hoping Spread Spectrum (F IISS): Most of the signals use the digital technique known as the Frequency hoping. Signal is broadcast over number of radio frequencies. • Direct Sequence Spread Spectrum (DSSS): Each bit is represented by multiple bits in the transmitted signal.

Advantages of FM over AM:

• Improved signal to noise ratio with respect to man-made interference (up to 25dB). • In FM, there is smaller geographical interference between neighboring stations. • Less radiated power. • Well-defined service areas for given transmitter power.

Features of Ultra VVideBand

• It can transmit large amount of data over a short distance up to 230 feet. • It requires very low power up to 0.5 milli watts. • UWB has the capacity to transmit the signals through doors and other barriers which reflect the signal with more bandwidth and high power.

FSK Advantage:

• It is suitable for Full-duplex transmission, and is denoted by Digital F M (DFM). • It is used in radio broadcasting transmission. • Less bandwidth is required, so F SK supports 1200 bps or more bit rate. • It is used in low speed asynchronous application of data transmission. • It is used in LAN by using broadcast network.

Advantages of digital modulation over Analog modulation:

• It makes better use of bandwidth. • It requires less power for transmission purpose. • When signal gets interfered with other signal, DM handles it in a better way. • Error correcting techniques are friendlier with other digital systems.

Applications of infrared light

• Night vision equipment: Infrared light is used as night vision, when there is no sufficient visible light available to see any object. • Thermography: Thermography is the process, in which we calculate the temperature of object by using the infrared radiation. • Heating: Infrared radiation can apply to heat the occupants in infrared saunas. It is used for de-icing purpose means to remove the ice from wings of aircraft. • Communication: Infrared radiation is used in small range of communication, such as communication between PDA (Personal Data Assistant) and computer devices. • Spectroscopy: It is related with the infrared portion of electromagnetic spectrum. In this method, IR is used for calculating the percentage of organic compound in a given sample.

Spread Spectrum Advantages:

• Signal gets spread over a broad frequency band, so less Power spectral density is required, and so it does not affect the other communication system. • Interference limited operation: All frequency spectrums are used in any condition. • Users can use their transmission at any random time. • Using spread spectrum involves the reduction of multi-path effects. • It has good anti-jam performance.

Applications of UVVB

• UWB used in radar, in which the signal goes through nearby surfaces but reflects surfaces that are farther away, and allows objects to be detected. • It requires less power and low-cost signals to transmit a large amount of voice and data using digital signal.

One DSSS method

• Use the spreading code for each bit, combine that spreading code with the input bit by using the X-OR operation. • If input bit is '1' then it inverts the spreading code, while if it is '0' then it does not make any change to the spreading code. • The bits which are to be obtained are transmitted as a signal to the receiver. • The data rate is equal to the original spreading code.