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GNSS Signals and Range Determination
Published in Basudeb Bhatta, Global Navigation Satellite Systems, 2021
In communication technology, a carrier wave, or carrier, is a waveform (shape and form of a signal) that is modulated (modified or changed) with an input signal for the purpose of conveying information: for example, voice or data, to be transmitted, by radio wave. A carrier wave has at least one characteristic such as phase, amplitude, or frequency that may be changed or modulated (Figure 4.4), for the purpose of carrying information. For example, the information, music, or speech received from an AM radio station is placed on the carrier wave by amplitude modulation (i.e., the amplitude is altered), and the information on the signal from a FM radio station is there because of frequency modulation (i.e., the frequency is changed). Any one of the several types of modulation may be used to carry the information.
128 Ears to Listen
Published in Ted G. Lewis, The Signal, 2019
Classical radio and TV signals operate in the 50 MHz to 1.0 GHz range, or in terms of wavelength, carrier wave peaks are up to 30 cm (11.8 in.) apart. The frequency of visible light is many orders of magnitude higher at 400–770 THz—peaks are one-millionth of an inch apart. Each country has rules governing its own allocation of spectrum to 5G, but they all restrict 5G signals to somewhere below visible light and somewhere above TV and radio, say one to several hundred GHz, which means a typical wave is less than a US postage stamp wide. This is important because an antenna must be long enough to capture at least 1/2 of a wavelength. So, the first feature of 5G signaling is the ability to transmit and receive signals from small antennas. This is often called mmwave signaling, because mm stands for millimeter size. Postage-stamp-sized antennas also fit nicely inside the small form factor of a smart phone.
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Published in Mário Marques da Silva, Cable and Wireless Networks, 2018
A modem implements modulation at the transmitter side, whereas the demodulation process is carried out at the receiver side. The modulation involves the process of encoding one or more source bits into a modulated carrier wave. An important advantage of using a modem, instead of line coding, relies on the ability to select a frequency band where the channel impairments are less destructive to the transported signal. Contrarily, line encoding techniques always transmit the signals in the baseband, even though if the level of distortion or attenuation is high. Let us consider a voice-graded twisted pair as an example, whose bandwidth is limited to the frequency range of 300 Hz to 3.4 kHz. Above this upper frequency, the attenuation level becomes too high, translating into a high level of distortion. If one intends to transmit a symbol rate whose bandwidth is higher than that required for voice, the solution is to select a carrier frequency to place the signal (band-pass signal) where the channel impairments are less intense than those experienced in baseband. A dial-up or a digital subscriber line modem typically implements this operation. A block diagram of a communication chain, including a modem, is plotted as shown in Figure 6.17. As can be seen, a modem typically has the error control capability embedded in itself, consisting of error correction or error detection (normally associated with retransmission). Error control techniques are covered in Chapter 12.
Fractional sequential likelihood ascent search detector for interference cancelation in massive MIMO systems in 5G technology
Published in International Journal of Electronics, 2021
Anju V. Kulkarni, Radhika Menon, Pramodkumar H. Kulkarni
Interference is considered as the major problem in the next-generation wireless systems to attain higher throughput. The interference in the signals causes an error or imprecise estimation of the channel for future 5 G transmissions. The main aim of the research is to model a technique that eradicates the interference produced in the massive-MIMO systems. At first, the input signals are transmitted to the encoder for converting the signals from one format to another format. Then, the modulation of the encoded signal is carried out for converting the radio waves by adding information to the signal. The obtained modulated signal is fetched using the transmitting antenna, which helps to transmit the signals and the receiver receives the signals at the receiver side. The obtained modulated signals are demodulated for extracting the original signal from the carrier wave. Finally, the decoding of the signal is done to convert the received signal into codes and is used for recovering the signals sent from the noisy channel. Here, the interference of the signals is eradicated by applying the proposed Fractional-SLAS, which is devised by integrating FC and SLAS algorithm. The proposed interference mitigation method helps to mitigate the interference produced from the signals without any delay or loss of quality of the transmitted signal.
Monitoring of pavement deflections using geophones
Published in International Journal of Pavement Engineering, 2020
Ngoc Son Duong, Juliette Blanc, Pierre Hornych, Fabien Menant, Yann Lefeuvre, Benoit Bouveret
The Hilbert transform of a signal x(t) is defined as the transform in which the phase angle of all components of the signal is shifted by ± 90 degrees. In this way, the application of the Hilbert transform to a sine signal gives a cosine signal with the same magnitude. So, in case of a demodulation operation, when a signal is combined with its Hilbert transform, the oscillations corresponding to the carrier wave can be removed and the 'envelope' of the signal can be extracted.