Quadrature amplitude modulation (QAM) is a technique that transmits two baseband signals simultaneously by modulating them onto carriers that are 90 degrees out of phase. At the receiver, synchronous detection using two local carriers in quadrature allows the two channels to be separated. Any error in the phase or frequency of the carrier at the demodulator can result in loss of signal, distortion, and interference between the channels. Phase-locked loops can be used to synchronize the local oscillator and acquire carrier synchronization in systems with suppressed carriers like QAM.
Angle modulation techniques were explored to help reduce static noise in communications. It was initially thought that frequency modulation (FM), where the carrier frequency varies proportionally to the message, could reduce bandwidth and thus noise. However, experimental results did not match expectations. The concept of instantaneous frequency was then developed to better understand angle-modulated signals. Different angle modulation techniques like frequency shift keying (FSK) and phase shift keying (PSK) were also introduced. Narrowband angle modulation can be achieved by ensuring the modulation index is small, while wideband modulation requires accounting for higher order terms in the modulation equation.
This document discusses amplitude modulated communication systems. It describes how a carrier signal is modulated by a baseband modulating signal to allow for information exchange over a channel. There are different types of modulation including continuous wave, pulse, and digital modulation. Amplitude modulation varies the amplitude of the carrier signal based on the instantaneous value of the modulating signal. This allows for multiplexing of multiple messages and use of more practical antenna sizes. Specific amplitude modulation techniques are described like conventional AM, DSB-SC, SSB, and VSB along with their tradeoffs in terms of carrier suppression, bandwidth, cost, and applications.
This document discusses analog and digital communication, specifically vestigial sideband modulation and angle modulation techniques like frequency modulation and phase modulation. It provides definitions and equations to describe these modulation schemes. Vestigial sideband modulation is described as a technique where one sideband is passed almost completely while just a trace of the other sideband is retained. For frequency and phase modulation, the carrier frequency and phase respectively are varied in accordance with the modulating signal. The difference between the two is also explained.
This document discusses digital communication systems and various digital modulation techniques. It begins with an overview of digital communication systems and their advantages. It then covers different digital modulation schemes including PAM, FSK, PSK, and QAM. It discusses how these schemes work, their bandwidth and power requirements, and how to demodulate the signals. It also covers more advanced topics like differential PSK and M-ary modulation schemes, examining how their bandwidth and power scale with increasing symbol sizes. The document provides detailed explanations of key digital modulation concepts and tradeoffs.
This document discusses various digital modulation techniques including:
- Coherent and non-coherent detection methods for baseband and broadband signals
- Phase-locked loops used in frequency demodulation
- Digital modulation techniques where binary symbols modulate the carrier phase, including BPSK where the carrier phase is shifted by 180 degrees to represent 1s and 0s
- BFSK where the carrier frequency is shifted according to the binary symbols while keeping the phase unchanged
- ASK where the carrier amplitude is shifted according to the binary symbols to keep the frequency constant
- Pulse modulation techniques where pulse amplitude, width, or time is varied to transmit analog data.
This document discusses types of amplitude modulation, including single sideband modulation (SSB) and vestigial sideband modulation. It provides details on SSB modulation such as using Hilbert transforms to generate an SSB signal from a baseband signal and information carried in upper and lower sidebands. Methods for generating SSB signals including selective filtering and phase shifting networks are described. The document also discusses vestigial sideband modulation, demodulation of SSB signals, and applications to telephone channel multiplexing.
This document discusses types of amplitude modulation, including single sideband modulation (SSB) and vestigial sideband modulation. It provides details on SSB modulation such as how it contains information from only one sideband, reducing the required bandwidth. Methods for generating SSB signals like selective filtering and phase shifting networks are described. The document also discusses vestigial sideband modulation and compares SSB and AM modulation.
Angle modulation techniques were explored to help reduce static noise in communications. It was initially thought that frequency modulation (FM), where the carrier frequency varies proportionally to the message, could reduce bandwidth and thus noise. However, experimental results did not match expectations. The concept of instantaneous frequency was then developed to better understand angle-modulated signals. Different angle modulation techniques like frequency shift keying (FSK) and phase shift keying (PSK) were also introduced. Narrowband angle modulation can be achieved by ensuring the modulation index is small, while wideband modulation requires accounting for higher order terms in the modulation equation.
This document discusses amplitude modulated communication systems. It describes how a carrier signal is modulated by a baseband modulating signal to allow for information exchange over a channel. There are different types of modulation including continuous wave, pulse, and digital modulation. Amplitude modulation varies the amplitude of the carrier signal based on the instantaneous value of the modulating signal. This allows for multiplexing of multiple messages and use of more practical antenna sizes. Specific amplitude modulation techniques are described like conventional AM, DSB-SC, SSB, and VSB along with their tradeoffs in terms of carrier suppression, bandwidth, cost, and applications.
This document discusses analog and digital communication, specifically vestigial sideband modulation and angle modulation techniques like frequency modulation and phase modulation. It provides definitions and equations to describe these modulation schemes. Vestigial sideband modulation is described as a technique where one sideband is passed almost completely while just a trace of the other sideband is retained. For frequency and phase modulation, the carrier frequency and phase respectively are varied in accordance with the modulating signal. The difference between the two is also explained.
This document discusses digital communication systems and various digital modulation techniques. It begins with an overview of digital communication systems and their advantages. It then covers different digital modulation schemes including PAM, FSK, PSK, and QAM. It discusses how these schemes work, their bandwidth and power requirements, and how to demodulate the signals. It also covers more advanced topics like differential PSK and M-ary modulation schemes, examining how their bandwidth and power scale with increasing symbol sizes. The document provides detailed explanations of key digital modulation concepts and tradeoffs.
This document discusses various digital modulation techniques including:
- Coherent and non-coherent detection methods for baseband and broadband signals
- Phase-locked loops used in frequency demodulation
- Digital modulation techniques where binary symbols modulate the carrier phase, including BPSK where the carrier phase is shifted by 180 degrees to represent 1s and 0s
- BFSK where the carrier frequency is shifted according to the binary symbols while keeping the phase unchanged
- ASK where the carrier amplitude is shifted according to the binary symbols to keep the frequency constant
- Pulse modulation techniques where pulse amplitude, width, or time is varied to transmit analog data.
This document discusses types of amplitude modulation, including single sideband modulation (SSB) and vestigial sideband modulation. It provides details on SSB modulation such as using Hilbert transforms to generate an SSB signal from a baseband signal and information carried in upper and lower sidebands. Methods for generating SSB signals including selective filtering and phase shifting networks are described. The document also discusses vestigial sideband modulation, demodulation of SSB signals, and applications to telephone channel multiplexing.
This document discusses types of amplitude modulation, including single sideband modulation (SSB) and vestigial sideband modulation. It provides details on SSB modulation such as how it contains information from only one sideband, reducing the required bandwidth. Methods for generating SSB signals like selective filtering and phase shifting networks are described. The document also discusses vestigial sideband modulation and compares SSB and AM modulation.
Single Sideband Suppressed Carrier (SSB-SC)Ridwanul Hoque
Single-sideband suppressed carrier (SSB-SC) modulation improves spectral efficiency by transmitting only one sideband. It requires a bandwidth equal to the signal bandwidth. SSB-SC can be detected coherently using multiplication by the carrier. Quadrature amplitude modulation (QAM) transmits two baseband signals over the same bandwidth using in-phase and quadrature carriers that are 90 degrees out of phase. Vestigial sideband (VSB) modulation is a compromise between DSB and SSB that inherits advantages of both while requiring only slightly greater bandwidth than SSB. It is used for broadcast television transmission.
This document discusses frequency modulation (FM) generation and demodulation. It describes how FM can be generated by varying the capacitance in an LC oscillator circuit using a varactor diode, causing the oscillator frequency to vary with the modulating signal. It also discusses Armstrong's indirect method of generating FM by combining a DSB-SC signal with a quadrature carrier. Frequency multiplication is described as a way to increase the frequency deviation of an FM signal. Demodulation of FM signals is also briefly mentioned.
The document discusses phase-shift keying (PSK) modulation techniques. It begins with an introduction to PSK and how it uses phases to encode digital data. It then discusses binary phase-shift keying (BPSK) which uses two phases separated by 180 degrees to encode one bit per symbol. BPSK is robust but has a low data rate. Quadrature phase-shift keying (QPSK) is then introduced, which uses four phases separated by 90 degrees to encode two bits per symbol, doubling the data rate of BPSK. Implementations of BPSK and QPSK modulators and demodulators are provided along with diagrams of their constellation plots.
This document provides information about phase-shift keying (PSK) modulation techniques. It begins with an introduction to PSK and discusses how it conveys data by changing the phase of a carrier signal. It then describes the basic PSK techniques of binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK). BPSK uses two phases separated by 180 degrees to encode one bit per symbol, while QPSK uses four phases separated by 90 degrees to encode two bits per symbol. The document discusses the implementation, modulation, demodulation, and advantages of these PSK techniques.
Modulation techniques allow data to be transmitted using a carrier signal. Analog modulation varies properties of the carrier continuously, while digital modulation makes the carrier take on discrete states. Common digital modulation techniques include ASK, FSK, PSK, and higher-order schemes like QPSK that encode multiple bits per symbol. Demodulation recovers the data by synchronizing to the carrier and detecting the modulated signal. Higher order modulations can achieve greater bandwidth efficiency but require more complex transmissions and receivers.
1. The document discusses various methods of FM demodulation including balanced slope detector, Foster-Seeley discriminator, phase locked loop demodulator, and ratio detector.
2. It provides details on the basic principles and circuit operations of each method. The balanced slope detector uses three tuned circuits which makes it difficult to tune. The Foster-Seeley discriminator and ratio detector have better linearity due to their use of phase relationships.
3. The phase locked loop demodulator tracks the instantaneous frequency of the input signal using a voltage controlled oscillator and error signal in a feedback loop. It has good performance even at low signal-to-noise ratios.
1. The document discusses amplitude modulation (AM) techniques such as AM double sideband full carrier (AMDSB-FC), AM double sideband suppressed carrier (AMDSB-SC), and single sideband (SSB) modulation.
2. It explains that AMDSB-FC and AMDSB-SC use two sidebands which contain redundant information, wasting channel bandwidth. SSB modulation suppresses one sideband to improve bandwidth efficiency.
3. Key aspects of envelope detection and its use in demodulating AM signals are covered, along with the need for coherent detection of AMDSB-SC to avoid phase errors.
This paper proposes three kinds of single stage RF front-end, called quadrature LMVs (QLMVs), by merging LNA, single-balanced mixer, and quadrature voltage-controlled oscillator (VCO) exploiting a series LC (SLC) network. The low intermediate frequency (IF) or baseband signal near dc can be directly sensed at the drain nodes of the VCO switching transistors by adding a simple resistor-capacitor (RC) low-pass filter (LPF). Using a 65 nm CMOS technology, the proposed QLMVs are designed. Oscillating at around 2.4 GHz band, the proposed QLMVs achieve the phase noise below ‒107 dB/Hz at 1 MHz offset frequency. The simulated voltage conversion gain is larger than 30 dB. The double-side band (DSB) noise figure (NF) of the proposed QLMVs is below 10 dB. The QLMVs consume less than 0.51 mW dc power from a 1-V supply.
Discusses basic television broadcasting system and standards. Explains TV transmission principles used in Broadcasting. Modulation type and advantage of negative modulation. Explains VSB modulation in TV transmitters.
Analog modulation involves representing analog information as an analog signal. It is needed when the transmission medium is bandpass in nature or only a bandpass channel is available. There are three main types of analog modulation: amplitude modulation (AM), which changes the amplitude of the carrier signal; frequency modulation (FM), which changes the frequency; and phase modulation (PM), which changes the phase. AM encodes the modulating signal as variations in the envelope of the carrier signal. This results in a spectrum with the carrier frequency flanked by upper and lower sidebands. The bandwidth required is twice that of the modulating signal.
What property of PN code makes them suitable for use in spread spect.pdfaquacosmossystems
What property of PN code makes them suitable for use in spread spectrum communication?
Solution
Pseudo random noise is used in some electronic musical instruments, either by itself or as an
input to subtractive synthesis, and in many white noise machines.
In spread-spectrum systems, the receiver correlates a locally generated signal with the received
signal. Such spread-spectrum systems require a set of one or more \"codes\" or \"sequences\"
such that
Like random noise, the local sequence has a very low correlation with any other sequence in the
set, or with the same sequence at a significantly different time offset, or with narrow band
interference, or with thermal noise.
Unlike random noise, it must be easy to generate exactly the same sequence at both the
transmitter and the receiver, so the receiver\'s locally generated sequence has a very high
correlation with the transmitted sequence.
In a direct-sequence spread spectrum system, each bit in the pseudorandom binary sequence is
known as a chip and the inverse of its period as chip rate; comparebit rate and symbol rate.
In a frequency-hopping spread spectrum sequence, each value in the pseudo random sequence is
known as a channel number and the inverse of its period as thehop rate. FCC Part 15 mandates at
least 50 different channels and at least a 2.5 Hz hop rate for narrow band frequency-hopping
systems.
GPS satellites broadcast data at a rate of 50 data bits per second – each satellite modulates its
data with one PN bit stream at 1.023 million chips per second and the same data with another PN
bit stream at 10.23 million chips per second. GPS receivers correlate the received PN bit stream
with a local reference to measure distance. GPS is a receive-only system that uses relative timing
measurements from several satellites (and the known positions of the satellites) to determine
receiver position.
Other range-finding applications involve two-way transmissions. A local station generates a
pseudo random bit sequence and transmits it to the remote location (using any modulation
technique). Some object at the remote location echoes this PN signal back to the location station
– either passively, as in some kinds of radar and sonar systems, or using an active transponder at
the remote location, as in the Apollo Unified S-band system.[4] By correlating a (delayed version
of) the transmitted signal with the received signal, a precise round trip time to the remote
location can be determined and thus the distance..
This document discusses radio channel modeling and the effects of multipath fading. It describes narrowband and wideband channel modeling approaches. Narrowband channels cause signal fading due to destructive interference from multiple propagation paths. Wideband channels cause signal dispersion in addition to fading. Channel characteristics like delay spread, Doppler spread, and coherence bandwidth are defined. Common fading distributions like Rayleigh and Rice are also summarized. Techniques to mitigate fading effects in narrowband and wideband systems are outlined.
This slide describe the techniques of digital modulation and Bandwidth Efficiency:
The first null bandwidth of M-ary PSK signals decrease as M increases while Rb is held constant.
Therefore, as the value of M increases, the bandwidth efficiency also increases.
This document summarizes the results of an indoor channel measurement experiment using USRP boards and GnuRadio. A spread spectrum channel sounder was implemented using a PN sequence transmitted from one USRP and correlated at a receiving USRP. Measurements were taken at different stations in a lab room with LOS and NLOS configurations. The data showed shifting of LOS peaks over time due to unsynchronized clocks between USRPs. With synchronized clocks, distinct multipath components were observable. The experiment demonstrated basic properties of PN sequences and their use in channel sounding.
The document discusses various types of amplitude modulation including double sideband full carrier (DSB-FC), double sideband suppressed carrier (DSB-SC), and single sideband suppressed carrier (SSB-SC). It also covers power in amplitude modulation, noting that the carrier contains most power while each sideband contains half the carrier power. Finally, it defines modulation index as the ratio of the modulating signal to the unmodulated carrier signal, which should not exceed 1 or 100% modulation to avoid signal distortion.
Digital modulation techniques change aspects of a carrier signal to transmit information. This document discusses various digital modulation methods including:
- Amplitude modulation (AM) which varies the amplitude (A) of the carrier.
- Frequency modulation (FM) which varies the frequency (ω) of the carrier.
- Phase modulation (PM) which varies the phase (φ) of the carrier.
It then discusses specific modulation techniques including amplitude shift keying (ASK), frequency shift keying (FSK), phase shift keying (PSK) and their variants like quadrature phase shift keying (QPSK). The document provides illustrations of the modulated signals and discusses their bandwidth efficiency and performance in noise.
This document provides an overview of analog communications and amplitude modulation (AM). It discusses the key components of a communication system including the input/output transducers, transmitter, channel, and receiver. For AM, it describes how the input signal is used to vary the amplitude of the carrier signal. It also examines the frequency spectrum of AM signals and discusses different forms of AM including double sideband suppressed carrier modulation. Coherent detection requires synchronization of both frequency and phase between the transmitter and receiver for DSB-SC due to the absence of the carrier signal.
This document provides an overview of phase locked loops (PLL). It describes the basic blocks of a PLL including a phase detector, low pass filter, error amplifier, and voltage controlled oscillator (VCO). The phase detector compares the input and feedback signals and produces sum and difference frequencies. The low pass filter removes the sum frequency, and the error amplifier amplifies the difference frequency to control the VCO. The VCO then adjusts its frequency to reduce the difference between the input and feedback signals until they are locked. The document also discusses digital and analog phase detectors, VCO design using the LM566 IC, and formulas for output frequency.
Telecommunications, also known as telecom, is the exchange of information over significant distances by electronic means and refers to all types of voice, data and video transmission. This is a broad term that includes a wide range of information-transmitting technologies and communications infrastructures, such as wired phones; mobile devices, such as cellphones; microwave communications; fiber optics; satellites; radio and television broadcasting; the internet; and telegraphs.
A complete, single telecommunications circuit consists of two stations, each equipped with a transmitter and a receiver. The transmitter and receiver at any station may be combined into a single device called a transceiver. The medium of signal transmission can be via electrical wire or cable -- also known as copper -- optical fiber, electromagnetic fields or light. The free space transmission and reception of data by means of electromagnetic fields is called wireless communications.
Types of telecommunications networks
The simplest form of telecommunications takes place between two stations, but it is common for multiple transmitting and receiving stations to exchange data among themselves. Such an arrangement is called a telecom network. The internet is the largest example of a telecommunications network. On a smaller scale, examples include the following:
corporate and academic wide area networks (WANs);
telephone networks;
cellular networks;
police and fire communications systems;
taxi dispatch networks;
groups of amateur (ham) radio operators; and
broadcast networks.
Data is transmitted in a telecommunications circuit by means of an electrical signal called the carrier or the carrier wave. In order for a carrier to convey information, some form of modulation is required. The mode of modulation can be categorized broadly as analog or digital.
In analog modulation, some aspect of the carrier is varied in a continuous fashion. The oldest form of analog modulation is amplitude modulation (AM), which is still used in radio broadcasting at some frequencies. Digital modulation actually predates AM; the earliest form was Morse code. Modern telecommunications use internet protocols to carry data across underlying physical transmissions.
Telecommunications industry and service providers
Telecommunications systems are generally run by telecommunications service providers, also known as communications service providers. These providers historically offered telephone and related services and now offer a variety of internet and WAN services, as well as metropolitan area network (MAN) and global services.
In many countries, telecom service providers were primarily government-owned and -operated. That is no longer the case, and many have been privatized. The International Telecommunication Union (ITU) is the United Nations (UN) agency that administers telecommunications and broadcasting regulations, although most countries also have their own government agencies to set and enf
Redefining brain tumor segmentation: a cutting-edge convolutional neural netw...IJECEIAES
Medical image analysis has witnessed significant advancements with deep learning techniques. In the domain of brain tumor segmentation, the ability to
precisely delineate tumor boundaries from magnetic resonance imaging (MRI)
scans holds profound implications for diagnosis. This study presents an ensemble convolutional neural network (CNN) with transfer learning, integrating
the state-of-the-art Deeplabv3+ architecture with the ResNet18 backbone. The
model is rigorously trained and evaluated, exhibiting remarkable performance
metrics, including an impressive global accuracy of 99.286%, a high-class accuracy of 82.191%, a mean intersection over union (IoU) of 79.900%, a weighted
IoU of 98.620%, and a Boundary F1 (BF) score of 83.303%. Notably, a detailed comparative analysis with existing methods showcases the superiority of
our proposed model. These findings underscore the model’s competence in precise brain tumor localization, underscoring its potential to revolutionize medical
image analysis and enhance healthcare outcomes. This research paves the way
for future exploration and optimization of advanced CNN models in medical
imaging, emphasizing addressing false positives and resource efficiency.
Single Sideband Suppressed Carrier (SSB-SC)Ridwanul Hoque
Single-sideband suppressed carrier (SSB-SC) modulation improves spectral efficiency by transmitting only one sideband. It requires a bandwidth equal to the signal bandwidth. SSB-SC can be detected coherently using multiplication by the carrier. Quadrature amplitude modulation (QAM) transmits two baseband signals over the same bandwidth using in-phase and quadrature carriers that are 90 degrees out of phase. Vestigial sideband (VSB) modulation is a compromise between DSB and SSB that inherits advantages of both while requiring only slightly greater bandwidth than SSB. It is used for broadcast television transmission.
This document discusses frequency modulation (FM) generation and demodulation. It describes how FM can be generated by varying the capacitance in an LC oscillator circuit using a varactor diode, causing the oscillator frequency to vary with the modulating signal. It also discusses Armstrong's indirect method of generating FM by combining a DSB-SC signal with a quadrature carrier. Frequency multiplication is described as a way to increase the frequency deviation of an FM signal. Demodulation of FM signals is also briefly mentioned.
The document discusses phase-shift keying (PSK) modulation techniques. It begins with an introduction to PSK and how it uses phases to encode digital data. It then discusses binary phase-shift keying (BPSK) which uses two phases separated by 180 degrees to encode one bit per symbol. BPSK is robust but has a low data rate. Quadrature phase-shift keying (QPSK) is then introduced, which uses four phases separated by 90 degrees to encode two bits per symbol, doubling the data rate of BPSK. Implementations of BPSK and QPSK modulators and demodulators are provided along with diagrams of their constellation plots.
This document provides information about phase-shift keying (PSK) modulation techniques. It begins with an introduction to PSK and discusses how it conveys data by changing the phase of a carrier signal. It then describes the basic PSK techniques of binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK). BPSK uses two phases separated by 180 degrees to encode one bit per symbol, while QPSK uses four phases separated by 90 degrees to encode two bits per symbol. The document discusses the implementation, modulation, demodulation, and advantages of these PSK techniques.
Modulation techniques allow data to be transmitted using a carrier signal. Analog modulation varies properties of the carrier continuously, while digital modulation makes the carrier take on discrete states. Common digital modulation techniques include ASK, FSK, PSK, and higher-order schemes like QPSK that encode multiple bits per symbol. Demodulation recovers the data by synchronizing to the carrier and detecting the modulated signal. Higher order modulations can achieve greater bandwidth efficiency but require more complex transmissions and receivers.
1. The document discusses various methods of FM demodulation including balanced slope detector, Foster-Seeley discriminator, phase locked loop demodulator, and ratio detector.
2. It provides details on the basic principles and circuit operations of each method. The balanced slope detector uses three tuned circuits which makes it difficult to tune. The Foster-Seeley discriminator and ratio detector have better linearity due to their use of phase relationships.
3. The phase locked loop demodulator tracks the instantaneous frequency of the input signal using a voltage controlled oscillator and error signal in a feedback loop. It has good performance even at low signal-to-noise ratios.
1. The document discusses amplitude modulation (AM) techniques such as AM double sideband full carrier (AMDSB-FC), AM double sideband suppressed carrier (AMDSB-SC), and single sideband (SSB) modulation.
2. It explains that AMDSB-FC and AMDSB-SC use two sidebands which contain redundant information, wasting channel bandwidth. SSB modulation suppresses one sideband to improve bandwidth efficiency.
3. Key aspects of envelope detection and its use in demodulating AM signals are covered, along with the need for coherent detection of AMDSB-SC to avoid phase errors.
This paper proposes three kinds of single stage RF front-end, called quadrature LMVs (QLMVs), by merging LNA, single-balanced mixer, and quadrature voltage-controlled oscillator (VCO) exploiting a series LC (SLC) network. The low intermediate frequency (IF) or baseband signal near dc can be directly sensed at the drain nodes of the VCO switching transistors by adding a simple resistor-capacitor (RC) low-pass filter (LPF). Using a 65 nm CMOS technology, the proposed QLMVs are designed. Oscillating at around 2.4 GHz band, the proposed QLMVs achieve the phase noise below ‒107 dB/Hz at 1 MHz offset frequency. The simulated voltage conversion gain is larger than 30 dB. The double-side band (DSB) noise figure (NF) of the proposed QLMVs is below 10 dB. The QLMVs consume less than 0.51 mW dc power from a 1-V supply.
Discusses basic television broadcasting system and standards. Explains TV transmission principles used in Broadcasting. Modulation type and advantage of negative modulation. Explains VSB modulation in TV transmitters.
Analog modulation involves representing analog information as an analog signal. It is needed when the transmission medium is bandpass in nature or only a bandpass channel is available. There are three main types of analog modulation: amplitude modulation (AM), which changes the amplitude of the carrier signal; frequency modulation (FM), which changes the frequency; and phase modulation (PM), which changes the phase. AM encodes the modulating signal as variations in the envelope of the carrier signal. This results in a spectrum with the carrier frequency flanked by upper and lower sidebands. The bandwidth required is twice that of the modulating signal.
What property of PN code makes them suitable for use in spread spect.pdfaquacosmossystems
What property of PN code makes them suitable for use in spread spectrum communication?
Solution
Pseudo random noise is used in some electronic musical instruments, either by itself or as an
input to subtractive synthesis, and in many white noise machines.
In spread-spectrum systems, the receiver correlates a locally generated signal with the received
signal. Such spread-spectrum systems require a set of one or more \"codes\" or \"sequences\"
such that
Like random noise, the local sequence has a very low correlation with any other sequence in the
set, or with the same sequence at a significantly different time offset, or with narrow band
interference, or with thermal noise.
Unlike random noise, it must be easy to generate exactly the same sequence at both the
transmitter and the receiver, so the receiver\'s locally generated sequence has a very high
correlation with the transmitted sequence.
In a direct-sequence spread spectrum system, each bit in the pseudorandom binary sequence is
known as a chip and the inverse of its period as chip rate; comparebit rate and symbol rate.
In a frequency-hopping spread spectrum sequence, each value in the pseudo random sequence is
known as a channel number and the inverse of its period as thehop rate. FCC Part 15 mandates at
least 50 different channels and at least a 2.5 Hz hop rate for narrow band frequency-hopping
systems.
GPS satellites broadcast data at a rate of 50 data bits per second – each satellite modulates its
data with one PN bit stream at 1.023 million chips per second and the same data with another PN
bit stream at 10.23 million chips per second. GPS receivers correlate the received PN bit stream
with a local reference to measure distance. GPS is a receive-only system that uses relative timing
measurements from several satellites (and the known positions of the satellites) to determine
receiver position.
Other range-finding applications involve two-way transmissions. A local station generates a
pseudo random bit sequence and transmits it to the remote location (using any modulation
technique). Some object at the remote location echoes this PN signal back to the location station
– either passively, as in some kinds of radar and sonar systems, or using an active transponder at
the remote location, as in the Apollo Unified S-band system.[4] By correlating a (delayed version
of) the transmitted signal with the received signal, a precise round trip time to the remote
location can be determined and thus the distance..
This document discusses radio channel modeling and the effects of multipath fading. It describes narrowband and wideband channel modeling approaches. Narrowband channels cause signal fading due to destructive interference from multiple propagation paths. Wideband channels cause signal dispersion in addition to fading. Channel characteristics like delay spread, Doppler spread, and coherence bandwidth are defined. Common fading distributions like Rayleigh and Rice are also summarized. Techniques to mitigate fading effects in narrowband and wideband systems are outlined.
This slide describe the techniques of digital modulation and Bandwidth Efficiency:
The first null bandwidth of M-ary PSK signals decrease as M increases while Rb is held constant.
Therefore, as the value of M increases, the bandwidth efficiency also increases.
This document summarizes the results of an indoor channel measurement experiment using USRP boards and GnuRadio. A spread spectrum channel sounder was implemented using a PN sequence transmitted from one USRP and correlated at a receiving USRP. Measurements were taken at different stations in a lab room with LOS and NLOS configurations. The data showed shifting of LOS peaks over time due to unsynchronized clocks between USRPs. With synchronized clocks, distinct multipath components were observable. The experiment demonstrated basic properties of PN sequences and their use in channel sounding.
The document discusses various types of amplitude modulation including double sideband full carrier (DSB-FC), double sideband suppressed carrier (DSB-SC), and single sideband suppressed carrier (SSB-SC). It also covers power in amplitude modulation, noting that the carrier contains most power while each sideband contains half the carrier power. Finally, it defines modulation index as the ratio of the modulating signal to the unmodulated carrier signal, which should not exceed 1 or 100% modulation to avoid signal distortion.
Digital modulation techniques change aspects of a carrier signal to transmit information. This document discusses various digital modulation methods including:
- Amplitude modulation (AM) which varies the amplitude (A) of the carrier.
- Frequency modulation (FM) which varies the frequency (ω) of the carrier.
- Phase modulation (PM) which varies the phase (φ) of the carrier.
It then discusses specific modulation techniques including amplitude shift keying (ASK), frequency shift keying (FSK), phase shift keying (PSK) and their variants like quadrature phase shift keying (QPSK). The document provides illustrations of the modulated signals and discusses their bandwidth efficiency and performance in noise.
This document provides an overview of analog communications and amplitude modulation (AM). It discusses the key components of a communication system including the input/output transducers, transmitter, channel, and receiver. For AM, it describes how the input signal is used to vary the amplitude of the carrier signal. It also examines the frequency spectrum of AM signals and discusses different forms of AM including double sideband suppressed carrier modulation. Coherent detection requires synchronization of both frequency and phase between the transmitter and receiver for DSB-SC due to the absence of the carrier signal.
This document provides an overview of phase locked loops (PLL). It describes the basic blocks of a PLL including a phase detector, low pass filter, error amplifier, and voltage controlled oscillator (VCO). The phase detector compares the input and feedback signals and produces sum and difference frequencies. The low pass filter removes the sum frequency, and the error amplifier amplifies the difference frequency to control the VCO. The VCO then adjusts its frequency to reduce the difference between the input and feedback signals until they are locked. The document also discusses digital and analog phase detectors, VCO design using the LM566 IC, and formulas for output frequency.
Telecommunications, also known as telecom, is the exchange of information over significant distances by electronic means and refers to all types of voice, data and video transmission. This is a broad term that includes a wide range of information-transmitting technologies and communications infrastructures, such as wired phones; mobile devices, such as cellphones; microwave communications; fiber optics; satellites; radio and television broadcasting; the internet; and telegraphs.
A complete, single telecommunications circuit consists of two stations, each equipped with a transmitter and a receiver. The transmitter and receiver at any station may be combined into a single device called a transceiver. The medium of signal transmission can be via electrical wire or cable -- also known as copper -- optical fiber, electromagnetic fields or light. The free space transmission and reception of data by means of electromagnetic fields is called wireless communications.
Types of telecommunications networks
The simplest form of telecommunications takes place between two stations, but it is common for multiple transmitting and receiving stations to exchange data among themselves. Such an arrangement is called a telecom network. The internet is the largest example of a telecommunications network. On a smaller scale, examples include the following:
corporate and academic wide area networks (WANs);
telephone networks;
cellular networks;
police and fire communications systems;
taxi dispatch networks;
groups of amateur (ham) radio operators; and
broadcast networks.
Data is transmitted in a telecommunications circuit by means of an electrical signal called the carrier or the carrier wave. In order for a carrier to convey information, some form of modulation is required. The mode of modulation can be categorized broadly as analog or digital.
In analog modulation, some aspect of the carrier is varied in a continuous fashion. The oldest form of analog modulation is amplitude modulation (AM), which is still used in radio broadcasting at some frequencies. Digital modulation actually predates AM; the earliest form was Morse code. Modern telecommunications use internet protocols to carry data across underlying physical transmissions.
Telecommunications industry and service providers
Telecommunications systems are generally run by telecommunications service providers, also known as communications service providers. These providers historically offered telephone and related services and now offer a variety of internet and WAN services, as well as metropolitan area network (MAN) and global services.
In many countries, telecom service providers were primarily government-owned and -operated. That is no longer the case, and many have been privatized. The International Telecommunication Union (ITU) is the United Nations (UN) agency that administers telecommunications and broadcasting regulations, although most countries also have their own government agencies to set and enf
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2. Quadrature Amplitude Modulation
2
Prepared By: Mohsin Yousuf, FAST NU, LHR
DSB signals occupy twice the bandwidth required for the
baseband, i.e., 2B for a signal of bandwidth B Hz.
This disadvantage can be overcome by transmitting two
DSB signals using carriers of the same frequency but in
phase quadrature.
Phase
Shifters
3. Quadrature Amplitude Modulation
3
Prepared By: Mohsin Yousuf, FAST NU, LHR
If the two baseband signals to be transmitted are 𝑚1(𝑡) and
𝑚2(𝑡), the corresponding QAM signal 𝜑𝑄𝐴𝑀(𝑡), the sum of
the two DSB-modulated signals, is
𝜑𝑄𝐴𝑀 𝑡 = 𝑚1 𝑡 cos 𝜔𝑐𝑡 + 𝑚2 𝑡 sin 𝜔𝑐𝑡
Both modulated signals occupy the same band. Yet two
baseband signals can be separated at the receiver by
synchronous detection using two local carriers in phase
quadrature, as shown in Figure.
The upper arm of the receiver also known as in-phase (I)
channel can be demultiplexed as;
𝑥1(𝑡) = 2𝜑𝑄𝐴𝑀 𝑡 cos 𝜔𝑐𝑡
= 2[𝑚1 𝑡 cos 𝜔𝑐𝑡 + 𝑚2 𝑡 sin 𝜔𝑐𝑡] cos 𝜔𝑐𝑡
= 𝑚1(𝑡) + 𝑚1(𝑡) cos 2𝜔𝑐𝑡 + 𝑚2(𝑡) sin 2𝜔𝑐𝑡
4. Quadrature Amplitude Modulation
4
Prepared By: Mohsin Yousuf, FAST NU, LHR
The lower arm of the receiver is the Quadrature (Q)
channel.
QAM is somewhat of an exacting scheme. A slight
error in the phase or the frequency of the carrier at the
demodulator in QAM will not only result in loss and
distortion of signals, but will also lead to interference
between the two channels.
To show this let the carrier at the demodulator be
2 cos(𝜔𝑐𝑡 + 𝜃). In this case,
This is co-channel interference after LPF.
6. 6
SSB Coherent Demodulation
Prepared By: Mohsin Yousuf, FAST NU, LHR
SSB signals without any additional carrier, hence,
they are suppressed carrier signals (SSB-SC)
7. 7
Time-Domain Representation of SSB
Prepared By: Mohsin Yousuf, FAST NU, LHR
USB: 𝑀+(𝜔)
LSB: 𝑀−(𝜔)
𝑀+ 𝜔 = 𝑀 𝜔 𝑢(𝜔)
𝑀− 𝜔 = 𝑀 𝜔 𝑢(−𝜔)
Let 𝑚+(𝑡) and 𝑚−(𝑡) be the
inverse Fourier Transforms of
𝑀+(𝜔) and 𝑀−(𝜔).
8. 8
Time-Domain Representation of SSB
Prepared By: Mohsin Yousuf, FAST NU, LHR
USB: 𝑀+ 𝜔 = 𝑀 𝜔 𝑢(𝜔)
LSB: 𝑀− 𝜔 = 𝑀 𝜔 𝑢(−𝜔)
𝑚+(𝑡) ⇔ 𝑀+(𝜔)
𝑚−(𝑡) ⇔ 𝑀−(𝜔)
Are 𝑀+(𝜔) and 𝑀−(𝜔) even
functions of 𝜔?
NO. 𝑀+(−𝜔) ≠ 𝑀+(𝜔)
• 𝑚+(𝑡) and 𝑚−(𝑡) can not
be real; they are complex.
𝑀+ −𝜔 = 𝑀−(𝜔) are equal
and 𝑀+ 𝜔 = 𝑀−
∗ (𝜔), hence
𝑚+(𝑡) and 𝑚−(𝑡) are
conjugates pairs.
14. Generation of SSB Signals
Selective-Filtering Method
Prepared By: Mohsin Yousuf, FAST NU, LHR 14
15. Generation of SSB Signals
Phase-Shift Method
Prepared By: Mohsin Yousuf, FAST NU, LHR 15
16. Envelope Detection of SSB Signals
with a Carrier (SSB+C)
Prepared By: Mohsin Yousuf, FAST NU, LHR 16
17. 17
AM: Vestigial Sideband (VSB)
Prepared By: Mohsin Yousuf, FAST NU, LHR
A gradual
cut-off of
one
sideband
18. 18
VSB Modulator and Demodulator
Prepared By: Mohsin Yousuf, FAST NU, LHR
What type of detector is in the Rx?
A synchronous detector
Can we recover it using Envelope
Detector?
Yes, if a large carrier is transmitted
with the VSB signal
• 𝑯𝒊(𝝎) is VSB Shaping Filter
• VSB Signal Spectrum is
• The bandwidth of VSB signal
is typically 25 to 33 % higher
than that of the SSB signals.
21. Use of VSB in Broadcast TV
Prepared By: Mohsin Yousuf, FAST NU, LHR 21
22. Carrier Acquisition
In the suppressed-carrier amplitude-modulated system
(DSB-SC, SSB-SC, and VSB-SC), one must generate a local
carrier at the receiver for the purpose of synchronous
demodulation.
Ideally, the local carrier must be in frequency and phase
synchronism with the incoming carrier. Any discrepancy in
the frequency or phase of the local carrier gives rise to
distortion in the detector output.
Consider a DSB-SC case where a received signal is
𝑚 𝑡 cos 𝜔𝑐𝑡 and the local carrier is 2 cos[ 𝜔𝑐 + ∆𝜔 𝑡 + 𝛿].
The local-carrier frequency and phase errors in this case are
∆𝜔 and 𝛿, respectively.
Prepared By: Mohsin Yousuf, FAST NU, LHR 22
23. Carrier Acquisition
Prepared By: Mohsin Yousuf, FAST NU, LHR 23
The product of the received signal and the local carrier is 𝑒(𝑡), given by
Case-I: ∆𝜔 = 0
Case-II: 𝛿 = 0
Attenuation
Attenuation + Distortion at
beat frequency ∆𝜔
Distortion if 𝛿 = 𝑓(𝑡)
24. Carrier Acquisition
To ensure identical carrier frequencies at the transmitter and the
receiver, we can use quartz crystal oscillators, which generally are
very stable. Identical crystals are cut to yield the same frequency
at the transmitter and the receiver.
At very high carrier frequencies, where the crystal dimensions
become too small to match exactly, quartz-crystal performance
may not be adequate.
In such a case, a carrier, or pilot, is transmitted at a reduced level
(usually about -20 dB) along with the sidebands. The pilot is
separated at the receiver by a very narrow-band filter tuned to
the pilot frequency. It is amplified and used to synchronize the
local oscillator.
The phase-locked loop (PLL), which plays an important role in
carrier acquisition, will now be discussed.
Prepared By: Mohsin Yousuf, FAST NU, LHR 24
25. Phase-Locked Loop (PLL)
The phase-locked loop (PLL) can be used to track the phase and
the frequency of the carrier component of an incoming signal. It
is, therefore, a useful device for synchronous demodulation of AM
signals with suppressed carrier or with a little carrier (the pilot).
It can also be used for the demodulation of angle-modulated
signals, especially under low SNR conditions.
For this reason, the PLL is used in such applications as space-
vehicle-to-earth data links, where there is a premium on
transmitter weight, or where the loss along the transmission path
is very large; and, more recently, in commercial FM receivers.
A PLL has three basic components:
1. A voltage-controlled oscillator (VCO)
2. A multiplier, serving as a phase detector (PD) or a phase comparator
3. A loop filter H(s)
Prepared By: Mohsin Yousuf, FAST NU, LHR 25
26. Phase-Locked Loop (PLL)
Prepared By: Mohsin Yousuf, FAST NU, LHR 26
The operation of the PLL is similar to that of a feedback system shown above. In a typical
feedback system, the signal fed back tends to follow the input signal. If the signal fed back
is not equal to the input signal, the difference (known as the error) will change the signal
fed back until it is close to the input signal.
A PLL operates on a similar principle, except that the quantity fed back and compared is
not the amplitude, but the phase. The VCO adjusts its own frequency until it is equal to
that of the input sinusoid. At this point, the frequency and phase of the two signals are in
synchronism (except for a possible difference of a constant phase).
27. Voltage Controlled Oscillator (VCO)
Prepared By: Mohsin Yousuf, FAST NU, LHR 27
An oscillator whose frequency can be controlled by an external voltage is a voltage-
controlled oscillator (VCO). In a VCO, the oscillation frequency varies linearly with the
input voltage. If a VCO input voltage is 𝑒𝑜(𝑡), its output is a sinusoid of frequency 𝜔 given
by;
𝜔 𝑡 = 𝜔𝑐 + 𝑐𝑒𝑜(𝑡)
where 𝑐 is a constant of the VCO and 𝜔𝑐 is the free-running frequency of the VCO [the
VCO frequency when 𝑒𝑜(𝑡) = 0]. The multiplier output is further low-pass-filtered by the
loop filter and then applied to the input of the VCO. This voltage changes the frequency of
the oscillator and keeps the loop locked.
28. How the PLL Works:
Prepared By: Mohsin Yousuf, FAST NU, LHR 28
Input 1: 𝐴 sin(𝜔𝑐𝑡 + 𝜃𝑖) and
Input 2: 𝐵 cos 𝜔𝑐𝑡 + 𝜃𝑜 which is an output of VCO
The multiplier output: 𝑥 𝑡 = 𝐴𝐵 sin(𝜔𝑐𝑡 + 𝜃𝑖) cos 𝜔𝑐𝑡 + 𝜃𝑜
=
𝐴𝐵
2
[sin 𝜃𝑖 − 𝜃𝑜 + sin 2𝜔𝑐𝑡 + 𝜃𝑖 + 𝜃𝑜 ]
𝑒𝑜 𝑡 =
𝐴𝐵
2
sin 𝜃𝑒 , 𝜃𝑒 = 𝜃𝑖 − 𝜃𝑜
29. How the PLL Works:
Prepared By: Mohsin Yousuf, FAST NU, LHR 29
𝑒𝑜 𝑡 =
𝐴𝐵
2
sin 𝜃𝑒 ,
𝑃𝑎𝑠𝑒 𝐸𝑟𝑟𝑜𝑟; 𝜃𝑒 = 𝜃𝑖 − 𝜃𝑜
30. Some Definitions:
Prepared By: Mohsin Yousuf, FAST NU, LHR 30
Hold-in / Lock Range:
Thus, the PLL tracks the input sinusoid. The two signals are said to
be mutually phase coherent or in phase lock. The VCO thus tracks
the frequency and the phase of the incoming signal. A PLL can track
the incoming frequency only over a finite range of frequency shift.
This range is called the hold-in or lock range.
Pull-in / Capture Range:
Moreover, if initially the input and output frequencies are
not close enough, the loop may not acquire lock. The frequency
range over which the input will cause the loop to lock is called the
pull-in or capture range. Also if the input frequency changes too
rapidly, the loop may not lock.
31. Carrier Acquisition in DSB-SC
Prepared By: Mohsin Yousuf, FAST NU, LHR 31
Signal-Squaring Method:
Works for Analog Signals
because of the sign
ambiguity in the carrier
generated.
33. Carrier Acquisition in SSB-SC
Prepared By: Mohsin Yousuf, FAST NU, LHR 33
Similar argument can be
given for VSB-SC
34. SUPERHETERODYNE AM RECEIVER
Prepared By: Mohsin Yousuf, FAST NU, LHR 34
The RF section is basically a tunable
filter and an amplifier that picks up
the desired station by tuning the filter
to the right frequency band.
35. SUPERHETERODYNE AM RECEIVER
Prepared By: Mohsin Yousuf, FAST NU, LHR 35
Frequency mixer (converter), translates the carrier
from 𝜔𝑐 to a fixed IF frequency of 455 kHz. For this
purpose, it uses a local oscillator whose frequency 𝑓𝐿𝑂
is exactly 455 kHz above the incoming carrier
frequency 𝑓𝐶; i.e.,
𝑓𝐿𝑂 = 𝑓𝐶 + 𝑓𝐼𝐹 𝑤ℎ𝑒𝑟𝑒, 𝑓𝐼𝐹 = 455 𝑘𝐻𝑧
Note that this is up-conversion.
36. SUPERHETERODYNE AM RECEIVER
Prepared By: Mohsin Yousuf, FAST NU, LHR 36
• The tuning of the local oscillator and the
RF tunable filter is done by one knob.
Tuning capacitors in both circuits are
ganged together and are designed so that
the tuning frequency of the local
oscillator is always 455 kHz above the
tuning frequency of the RF filter.
• This means every station that is tuned in
is translated to a fixed carrier frequency
of 455 kHz by the frequency converter.
The reason for translating all stations to a
fixed carrier frequency of 455 kHz is to
obtain adequate selectivity.
37. SUPERHETERODYNE AM RECEIVER
Prepared By: Mohsin Yousuf, FAST NU, LHR 37
• IF amplifier is a three-stage amplifier,
which does have good selectivity. This is
because the IF frequency is reasonably
low, and, second, its center frequency is
fixed and factory-tuned.
• The IF section can effectively suppress
adjacent-channel interference because of
its high selectivity. It also amplifies the
signal for envelope detection.
38. SUPERHETERODYNE AM RECEIVER
Prepared By: Mohsin Yousuf, FAST NU, LHR 38
• The main function of the RF section is
image frequency suppression.
• Mixer, or converter output is;
𝑓𝐼𝐹 = 𝑓𝐿𝑂 − 𝑓𝐶
• Example:
𝑓𝐶 = 1000 𝑘𝐻𝑧
𝑓𝐿𝑂 = 𝑓𝐶 + 𝑓𝑅𝐹 = 1000 + 455 = 1455 𝑘𝐻𝑧
• But another carrier, 𝑓𝐶
′
= 1455 + 455 =
1910 𝑘𝐻𝑧, will also be picked up because
the difference, 𝑓𝐶
′
− 𝑓𝐿𝑂 is also 455 𝑘𝐻𝑧.
39. SUPERHETERODYNE AM RECEIVER
Prepared By: Mohsin Yousuf, FAST NU, LHR 39
• The station at 1910 𝑘𝐻𝑧 is said to be the
image of the station of 1000 𝑘𝐻𝑧.
• Station that are 2 𝑓𝐼𝐹 = 910 𝑘𝐻𝑧 apart are
called image stations and would both
appear simultaneously at the IF output if
it were not for the RF filter at receiver
input.
The RF filter may provide poor selectivity
against adjacent stations separated by
10 𝑘𝐻𝑧, but it can provide reasonable
selectivity against a station separated by
910 𝑘𝐻𝑧. Thus, when we wish to tune in a
station at 1000 𝑘𝐻𝑧, the RF filter, tuned to
1000 𝑘𝐻𝑧, provides adequate suppression of
the image station at 1910 𝑘𝐻𝑧.