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Spectral Efficiency
Spectral efficiency, spectrum efficiency or bandwidth efficiency refers to the information rate that can be transmitted over a given bandwidth in a specific communication system. It is a measure of how efficiently a limited frequency spectrum is utilized by the physical layer protocol, and sometimes by the medium access control (the channel access protocol). Guowang Miao, Jens Zander, Ki Won Sung, and Ben Slimane, Fundamentals of Mobile Data Networks, Cambridge University Press, , 2016. Link spectral efficiency The link spectral efficiency of a digital communication system is measured in '' bit/ s/ Hz'', or, less frequently but unambiguously, in ''(bit/s)/Hz''. It is the net bit rate (useful information rate excluding error-correcting codes) or maximum throughput divided by the bandwidth in hertz of a communication channel or a data link. Alternatively, the spectral efficiency may be measured in ''bit/symbol'', which is equivalent to ''bits per channel use'' (''bpcu''), i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Information Rate
In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction with an SI prefix such as kilo (1 kbit/s = 1,000 bit/s), mega (1 Mbit/s = 1,000 kbit/s), giga (1 Gbit/s = 1,000 Mbit/s) or tera (1 Tbit/s = 1,000 Gbit/s). The non-standard abbreviation bps is often used to replace the standard symbol bit/s, so that, for example, 1 Mbps is used to mean one million bits per second. In most computing and digital communication environments, one byte per second (symbol: B/s) corresponds roughly to 8 bit/s. However if stop bits, start bits, and parity bits need to be factored in, a higher number of bits per second will be required to achieve a throughput of the same number of bytes. Prefixes When quantifying large or small bit rates, SI ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
OFDM
In telecommunications, orthogonal frequency-division multiplexing (OFDM) is a type of digital transmission used in digital modulation for encoding digital (binary) 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/ 5G mobile communications. OFDM is a frequency-division multiplexing (FDM) scheme that was introduced by Robert W. Chang of Bell Labs in 1966. In OFDM, the incoming bitstream representing the data to be sent is divided into multiple streams. Multiple closely spaced orthogonal subcarrier signals with overlapping spectra are transmitted, with each carrier modulated with bits from the incoming stream so multiple bits are being transmitted in parallel. [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase-shift Keying
Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency carrier wave. The modulation is accomplished by varying the sine and cosine inputs at a precise time. It is widely used for wireless LANs, RFID and 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. This requires the receiver to be able to compare the phase of the received signal to a reference signal such a system is termed coherent (an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amplitude-shift Keying
Amplitude-shift keying (ASK) is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave. In an ASK system, a Symbol rate, symbol, representing one or more bits, is sent by transmitting a fixed-amplitude carrier wave at a fixed frequency for a specific time duration. For example, if each symbol represents a single bit, then the carrier signal could be transmitted at nominal amplitude when the input value is 1, but transmitted at reduced amplitude or not at all when the input value is 0. Method Any digital modulation scheme uses a wikt:finite, finite number of distinct signals to represent digital data. ASK uses a finite number of amplitudes, each assigned a unique pattern of bit, binary digits. Usually, each amplitude encodes an equal number of bits. Each pattern of bits forms the Symbol (data), symbol that is represented by the particular amplitude. The demodulator, which is designed specifically for the symbol-set used by the mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Superheterodyne Receiver
A superheterodyne receiver, often shortened to superhet, is a type of radio receiver that uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original carrier frequency. It was invented by French radio engineer and radio manufacturer Lucien Lévy. Virtually all modern radio receivers use the superheterodyne principle. Precursors Early radio Early Morse code radio broadcasts were produced using an alternator connected to a spark gap. The output signal was at a carrier frequency defined by the physical construction of the gap, modulated by the alternating current signal from the alternator. Since the output frequency of the alternator was generally in the audible range, this produces an audible amplitude modulated (AM) signal. Simple radio detectors filtered out the high-frequency carrier, leaving the modulation, which was passed on to the user's headphones as an audible signal of do ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Undersampling
In signal processing, undersampling or bandpass sampling is a technique where one samples a bandpass-filtered signal at a sample rate below its Nyquist rate (twice the upper cutoff frequency), but is still able to reconstruct the signal. When one undersamples a bandpass signal, the samples are indistinguishable from the samples of a low-frequency alias of the high-frequency signal. Such sampling is also known as bandpass sampling, harmonic sampling, IF sampling, and direct IF-to-digital conversion. Description The Fourier transforms of real-valued functions are symmetrical around the 0 Hz axis. After sampling, only a periodic summation of the Fourier transform (called discrete-time Fourier transform) is still available. The individual frequency-shifted copies of the original transform are called ''aliases''. The frequency offset between adjacent aliases is the sampling-rate, denoted by ''fs''. When the aliases are mutually exclusive (spectrally), the original transf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Passband
A passband is the range of frequency, frequencies or wavelengths that can pass through a Filter (signal processing), filter. For example, a radio receiver contains a bandpass filter to select the frequency of the desired radio signal out of all the radio waves picked up by its antenna. The passband of a receiver is the range of frequencies it can receive when it is tuned into the desired frequency as in a radio station or television channel. A band-pass filter, bandpass-filtered signal (that is, a signal with energy only in a passband), is known as a bandpass signal, in contrast to a baseband signal. The bandpass filter usually has two stopband, band-stop filters. Filters In telecommunications, optics, and acoustics, a passband (a band-pass filtered signal) is the portion of the frequency spectrum that is transmitted (with minimum relative loss or maximum relative Gain (electronics), gain) by some filtering device. In other words, it is a ''band'' of frequencies which ''pa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intersymbol Interference
In telecommunications, intersymbol interference (ISI) is a form of distortion of a signal in which one symbol interferes with subsequent symbols. This is an unwanted phenomenon as the previous symbols have a similar effect as noise, thus making the communication less reliable. The spreading of the pulse beyond its allotted time interval causes it to interfere with neighboring pulses. ISI is usually caused by multipath propagation or the inherent linear or non-linear frequency response of a communication channel causing successive symbols to blur together. The presence of ISI in the system introduces errors in the decision device at the receiver output. Therefore, in the design of the transmitting and receiving filters, the objective is to minimize the effects of ISI, and thereby deliver the digital data to its destination with the smallest error rate possible. Ways to alleviate intersymbol interference include adaptive equalization and error correcting codes. Causes Multip ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pulse-amplitude Modulation
Pulse-amplitude modulation (PAM) is a form of signal modulation in which the message information is encoded in the amplitude of a pulse train interrupting the carrier frequency. Demodulation is performed by detecting the amplitude level of the carrier at every single period. Types There are two types of pulse amplitude modulation: * In ''single polarity PAM'', a suitable fixed DC bias is added to the signal to ensure that all the pulses are positive. * In ''double polarity PAM'', the pulses are both positive and negative. Pulse-amplitude modulation is widely used in modulating signal transmission of digital data, with non- baseband applications having been largely replaced by pulse-code modulation, and, more recently, by pulse-position modulation. The number of possible pulse amplitudes in analog PAM is theoretically infinite. Digital PAM reduces the number of pulse amplitudes to some natural number. Uses Ethernet Some versions of the Ethernet communication standard are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Line Coding
In telecommunications, a line code is a pattern of voltage, current, or photons used to represent digital data transmitted down a communication channel or written to a storage medium. This repertoire of signals is usually called a constrained code in data storage systems. Some signals are more prone to error than others as the physics of the communication channel or storage medium constrains the repertoire of signals that can be used reliably. Common line encodings are unipolar, polar, bipolar, and Manchester code. Transmission and storage After line coding, the signal is put through a physical communication channel, either a transmission medium or data storage medium.Karl Paulsen"Coding for Magnetic Storage Mediums".2007. The most common physical channels are: * the line-coded signal can directly be put on a transmission line, in the form of variations of the voltage or current (often using differential signaling). * the line-coded signal (the '' baseband signal'') u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Baseband
In telecommunications and signal processing, baseband is the range of frequencies occupied by a signal that has not been modulated to higher frequencies. Baseband signals typically originate from transducers, converting some other variable into an electrical signal. For example, the electronic output of a microphone is a baseband signal that is analogous to the applied voice audio. In conventional analog radio broadcasting, the baseband audio signal is used to modulate an RF carrier signal of a much higher frequency. A baseband signal may have frequency components going all the way down to the DC bias, or at least it will have a high ratio bandwidth. A modulated baseband signal is called a passband signal. This occupies a higher range of frequencies and has a lower ratio and fractional bandwidth. Various uses Baseband signal A ''baseband signal'' or ''lowpass signal'' is a signal that can include frequencies that are very near zero, by comparison with its highest ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
