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CPFSK
CONTINUOUS PHASE MODULATION (CPM) is a method for modulation of data commonly used in wireless modems . In contrast to other coherent digital phase modulation techniques where the carrier phase abruptly resets to zero at the start of every symbol (e.g. M-PSK ), with CPM the carrier phase is modulated in a continuous manner. For instance, with QPSK
QPSK
the carrier instantaneously jumps from a sine to a cosine (i.e. a 90 degree phase shift ) whenever one of the two message bits of the current symbol differs from the two message bits of the previous symbol. This discontinuity requires a relatively large percentage of the power to occur outside of the intended band (e.g., high fractional out-of-band power ), leading to poor spectral efficiency . Furthermore, CPM is typically implemented as a constant-envelope waveform , i.e., the transmitted carrier power is constant
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Orthogonal Frequency-division Multiplexing
ORTHOGONAL FREQUENCY-DIVISION MULTIPLEXING (OFDM) is a method of encoding digital data on multiple carrier frequencies. OFDM has developed into a popular scheme for wideband digital communication , used in applications such as digital television and audio broadcasting, DSL internet access , wireless networks , power line networks , and 4G mobile communications. In COFDM CODED ORTHOGONAL FREQUENCY-DIVISION MULTIPLEXING forward error correction (convolutional coding) and time/frequency interleaving are applied to the signal being transmitted. This is done to overcome errors in mobile communication channels affected by multipath propagation and Doppler effects . COFDM was introduced by Alard in 1986 for Digital Audio Broadcasting
Digital Audio Broadcasting
for Eureka Project 147. In practice, OFDM has become used in combination with such coding and interleaving, so that the terms COFDM and OFDM co-apply to common applications
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Delta-sigma Modulation
DELTA-SIGMA (ΔΣ; or SIGMA-DELTA, ΣΔ) modulation is a method for encoding analog signals into digital signals as found in an analog-to-digital converter (ADC). It is also used to transfer high bit-count low frequency digital signals into lower bit-count higher frequency digital signals as part of the process to convert digital signals into analog as part of a digital-to-analog converter (DAC). In a conventional ADC, an analog signal is integrated, or sampled, with a sampling frequency and subsequently quantized in a multi-level quantizer into a digital signal. This process introduces quantization error noise. The first step in a delta-sigma modulation is delta modulation. In delta modulation the change in the signal (its delta) is encoded, rather than the absolute value. The result is a stream of pulses, as opposed to a stream of numbers as is the case with PCM
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Frequency-division Multiplexing
In telecommunications , FREQUENCY-DIVISION MULTIPLEXING (FDM) is a technique by which the total bandwidth available in a communication medium is divided into a series of non-overlapping frequency sub-bands, each of which is used to carry a separate signal. This allows a single transmission medium such as the radio spectrum , a cable or optical fiber to be shared by multiple independent signals. Another use is to carry separate serial bits or segments of a higher rate signal in parallel. The most natural example of frequency-division multiplexing is radio and television broadcasting , in which multiple radio signals at different frequencies pass through the air at the same time. Another example is cable television , in which many television channels are carried simultaneously on a single cable
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Multiplexing
In telecommunications and computer networks , MULTIPLEXING (sometimes contracted to MUXING) is a method by which multiple analog or digital signals are combined into one signal over a shared medium . The aim is to share a scarce resource. For example, in telecommunications, several telephone calls may be carried using one wire. Multiplexing originated in telegraphy in the 1870s, and is now widely applied in communications. In telephony , George Owen Squier is credited with the development of telephone carrier multiplexing in 1910. The multiplexed signal is transmitted over a communication channel such as a cable. The multiplexing divides the capacity of the communication channel into several logical channels, one for each message signal or data stream to be transferred. A reverse process, known as demultiplexing, extracts the original channels on the receiver end
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Wireless Modem
A MOBILE BROADBAND MODEM, also known as a connect card or data card, is a type of modem that allows a laptop, a personal computer or a router to receive Internet access
Internet access
via a mobile broadband connection instead of using telephone or cable television lines. A mobile Internet user can connect using a wireless modem to a wireless Internet Service Provider
Internet Service Provider
(ISP) to get Internet access
Internet access

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Pulse-width Modulation
PULSE-WIDTH MODULATION (PWM), or PULSE-DURATION MODULATION (PDM), is a modulation technique used to encode a message into a pulsing signal . Although this modulation technique can be used to encode information for transmission, its main use is to allow the control of the power supplied to electrical devices, especially to inertial loads such as motors. In addition, PWM is one of the two principal algorithms used in photovoltaic solar battery chargers, the other being maximum power point tracking . The average value of voltage (and current ) fed to the load is controlled by turning the switch between supply and load on and off at a fast rate. The longer the switch is on compared to the off periods, the higher the total power supplied to the load. The PWM switching frequency has to be much higher than what would affect the load (the device that uses the power), which is to say that the resultant waveform perceived by the load must be as smooth as possible
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Pulse-code Modulation
PULSE-CODE MODULATION (PCM) is a method used to digitally represent sampled analog signals . It is the standard form of digital audio in computers, compact discs , digital telephony and other digital audio applications. In a PCM stream , the amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps. LINEAR PULSE-CODE MODULATION (LPCM) is a specific type of PCM where the quantization levels are linearly uniform. This is in contrast to PCM encodings where quantization levels vary as a function of amplitude (as with the A-law algorithm or the μ-law algorithm ). Though PCM is a more general term, it is often used to describe data encoded as LPCM
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Modem
A MODEM (MOdulator-DEModulator) is a network hardware device that modulates one or more carrier wave signals to encode digital information for transmission and demodulates signals to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used with any means of transmitting analog signals, from light emitting diodes to radio . A common type of modem is one that turns the digital data of a computer into modulated electrical signal for transmission over telephone lines and demodulated by another modem at the receiver side to recover the digital data. Modems are generally classified by the maximum amount of data they can send in a given unit of time , usually expressed in bits per second (symbol BIT/S, sometimes abbreviated "bps"), or bytes per second (symbol B/S). Modems can also be classified by their symbol rate , measured in baud
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Angle Modulation
ANGLE MODULATION is a class of carrier modulation that is used in telecommunications transmission systems. The class comprises frequency modulation (FM) and phase modulation (PM), and is respectively based on altering the frequency or the phase of a carrier signal to encode the message signal. This contrasts with varying the amplitude of the carrier, practiced in amplitude modulation (AM) transmission, the earliest of the major modulation methods used widely in early radio broadcasting. CONTENTS * 1 Formalism * 2 Frequency modulation
Frequency modulation
* 3 Phase modulation
Phase modulation
* 4 See also * 5 References FORMALISMIn general form, an analog modulation process of a sinusoidal carrier wave may be described by the following equation: m ( t ) = A ( t ) cos ( t + ( t ) ) {displaystyle m(t)=A(t)cdot cos(omega t+phi (t)),}
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Polar Modulation
POLAR MODULATION is analogous to quadrature modulation in the same way that polar coordinates are analogous to Cartesian coordinates
Cartesian coordinates
. Quadrature modulation makes use of Cartesian coordinates, x and y. When considering quadrature modulation, the x axis is called the I (in-phase) axis, and the y axis is called the Q (quadrature) axis. Polar modulation makes use of polar coordinates, r (amplitude) and Θ (phase). The quadrature modulator approach to digital radio transmission requires a linear RF power amplifier which creates a design conflict between improving power efficiency or maintaining amplifier linearity. Compromising linearity causes degraded signal quality, usually by adjacent channel degradation, which can be a fundamental factor in limiting network performance and capacity
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Pulse-amplitude Modulation
PULSE-AMPLITUDE MODULATION (PAM), is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulse. It is an analog pulse modulation scheme in which the amplitudes of a train of carrier pulses are varied according to the sample value of the message signal. Demodulation is performed by detecting the amplitude level of the carrier at every single period
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Carrier Wave
In telecommunications , a CARRIER WAVE, CARRIER SIGNAL, or just CARRIER, is a waveform (usually sinusoidal ) that is modulated (modified) with an input signal for the purpose of conveying information. This carrier wave usually has a much higher frequency than the input signal does. The purpose of the carrier is usually either to transmit the information through space as an electromagnetic wave (as in radio communication), or to allow several carriers at different frequencies to share a common physical transmission medium by frequency division multiplexing (as, for example, a cable television system). The term is also used for an unmodulated emission in the absence of any modulating signal. Most radio systems in the 20th century used frequency modulation (FM) or amplitude modulation (AM) to make the carrier carry information. The frequency of a radio or television station is actually the carrier wave's frequency
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QPSK
Phase-shift keying
Phase-shift keying
(\'PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a reference signal (the carrier wave ). The modulation occurs by varying the sine and cosine inputs at a precise time. It is widely used for wireless LANs , RFID
RFID
and Bluetooth
Bluetooth
communication. Any digital modulation scheme uses a finite number of distinct signals to represent digital data. PSK uses a finite number of phases, each assigned a unique pattern of binary digits . Usually, each phase encodes an equal number of bits. Each pattern of bits forms the symbol that is represented by the particular phase. The demodulator , which is designed specifically for the symbol-set used by the modulator, determines the phase of the received signal and maps it back to the symbol it represents, thus recovering the original data
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Viterbi Algorithm
The VITERBI ALGORITHM is a dynamic programming algorithm for finding the most likely sequence of hidden states – called the VITERBI PATH – that results in a sequence of observed events, especially in the context of Markov information sources and hidden Markov models . The algorithm has found universal application in decoding the convolutional codes used in both CDMA
CDMA
and GSM
GSM
digital cellular, dial-up modems, satellite, deep-space communications, and 802.11 wireless LANs. It is now also commonly used in speech recognition , speech synthesis , diarization , keyword spotting , computational linguistics , and bioinformatics . For example, in speech-to-text (speech recognition), the acoustic signal is treated as the observed sequence of events, and a string of text is considered to be the "hidden cause" of the acoustic signal
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Gaussian Filter
In electronics and signal processing , a GAUSSIAN FILTER is a filter whose impulse response is a Gaussian function
Gaussian function
(or an approximation to it). Gaussian filters have the properties of having no overshoot to a step function input while minimizing the rise and fall time. This behavior is closely connected to the fact that the Gaussian filter
Gaussian filter
has the minimum possible group delay . It is considered the ideal time domain filter, just as the sinc is the ideal frequency domain filter. These properties are important in areas such as oscilloscopes and digital telecommunication systems. Mathematically, a Gaussian filter
Gaussian filter
modifies the input signal by convolution with a Gaussian function; this transformation is also known as the Weierstrass transform
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