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Storage and transmission of spatial sound signals
Published in Bosun Xie, Spatial Sound, 2023
A DAB-transmitted signal consists of a multiplex of several independent audio and other data, which simultaneously allow several digital services. Figure 13.37 illustrates the block diagram of the transmission system of DAB. Each PCM audio input is coded independently in the source coding stage. The MUSICAM (e.g., the MPEG-1 Layer II in Section13.5.1) is used for audio source coding. Each source-coded audio data stream is further coded by a channel coder (and interleaved in the time domain). Multiple channel-coded audio data and other services are multiplexed (and interleaved in the frequency domain). An orthogonal frequency division multiplexing (OFDM) is applied through which the multiplexed bit stream is divided into a large number of bit streams with a low bit rate, and each low-bit-rate stream is used to modulate individual orthogonal subcarriers. The modulated carriers are transposed to appropriate radio frequency band and then transmitted.
Operational Amplifiers
Published in Michael Olorunfunmi Kolawole, Electronics, 2020
In digital signal processing (DSP), clipping occurs when the range of a chosen representation restricts the signal. For example, suppose a system uses 8-bit integers, and the amplitude of the sample signal is 120 bits. Fundamentally, the system will have the largest positive value of 127 (i.e. 27 − 1) that can be represented. If during signal processing the amplitude of the signal doubled, the available sample values of 120 bits would become 240 bits. However, instead of the sample signals reaching 240 bits, they are truncated (clipped) to the system’s maximum of 127. Clipping may be seen as a form of distortion that limits a signal once it exceeds a threshold, but it has been suggested as an effective peak-to-average power ratio reduction scheme for orthogonal frequency-division multiplexing (OFDM) system [3,4]. OFDM is a modulation technique used in many new and emerging broadband technologies including Internet, digital audio, and video broadcasting. It is a spectrally efficient method, which mitigates the severe problem of multipath propagation that causes massive data errors and loss of signal, particularly in the microwave and ultra-high frequency (UHF) spectrum. OFDM is not discussed in this book.
Coding Techniques to Improve Bit Error Rate in Orthogonal Frequency Division Multiplexing System
Published in Rajeshree Raut, Ranjit Sawant, Shriraghavan Madbushi, Cognitive Radio, 2020
Rajeshree Raut, Ranjit Sawant, Shriraghavan Madbushi
The telecommunications industry is in the midst of a veritable explosion in wireless technologies [1]. Once exclusively military, satellite and cellular technologies are now commercially driven by ever more demanding consumers, who are ready for seamless communication from their home to their car, to their office, or even for outdoor activities. With this increased demand comes a growing need to transmit information wirelessly, quickly, and accurately. To address this need, communication engineers have combined technologies suitable for high-rate transmission with forward error correction techniques. The latter are particularly important as wireless communications channels are far more hostile as opposed to wire alternatives, and the need for mobility proves especially challenging for reliable communications. Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation technique in which a single high rate data stream is divided into multiple low rate data streams and is modulated using subcarriers that are orthogonal to each other.
Comprehensive Analysis of PAPR Reduction in OFDM, UFMC and Signal Scrambling UFMC Technique using Shuffled Frog Leaping Algorithm
Published in IETE Journal of Research, 2023
K. Krishna Kishore, P. Rajesh Kumar
OFDM is acknowledged as the competent and most advanced waveform for 4G communications with high data rates. However, moving to the 5G communications some uncertainties of OFDM make it stand as a challenge [3]. The improvements in 5G communication have special targets like IoT (Internet of Things), V2 V (Vehicle to Vehicle) communication, M2X (machine to any) communication and Cognitive Radios. OFDM has the following limitations: Since OFDM is sensitive to CFO [4], it will show a significant drawback during the implementation of V2 V of communication systems.OFDM suffers from cyclic prefix [5], which will lead to poor resource utilization.The high PAPR in OFDM [6] makes High Power Amplifier (HPA) shift towards the non-linear region causing OOB (Out of Band) emission.High Spectral Regrowth in the side-lobes of OFDM leads to interference with adjacent carriers.
Reduction of PAPR in OTFS using rooting companding techniques
Published in International Journal of Electronics Letters, 2022
Hanumantharao Bitra, Palanisamy Ponnusamy, Srinivasarao Chintagunta
Fifth-generation (5 G) wireless systems that use the orthogonal frequency division multiplexing (OFDM) modulation technique are incapable of supporting high mobility scenarios such as high-speed trains, unmanned aerial vehicles, the Internet of things, vehicle-to-vehicle communications, mobile communications on board aircraft, low-Earth orbit satellites, and so on (Hadani & Monk, 2018; Tusha et al., 2021). Due to high Doppler shifts in time-varying channels, it is impractical to use OFDM due to loss of orthogonality in subcarriers, resulting in inter carrier interference and significant performance degradation (Hadani & Monk, 2018; Shi et al., 2021). A novel resilient modulation technique called orthogonal time frequency space (OTFS) has recently (Hadani et al., 2017) been developed to avoid the necessity for subcarrier orthogonality.
Performance of modified and low complexity pulse shaping filters for IEEE 802.11 OFDM transmission
Published in Journal of Information and Telecommunication, 2019
Tulsi Pawan Fowdur, Louvi Doorganah
Inter Symbol Interference (ISI) is a problem that is encountered in most communication systems including 802.11a/g. ISI occurs when the symbols in OFDM overlap with each other in bandlimited channels. As a result, the probability of error due to distortion effects increases and the performance of the OFDM system degrades. Pulse shaping filters are therefore used to limit the effects of ISI and improve the error performance of the OFDM system. Pulse shaping filters have several conditions to satisfy to curb the ISI effects (Nyquist, 1928). The main condition is that the equivalent impulse response of the transmitting and receiving filters should have zero crossings at multiples of the symbol period, T (Nyquist, 1928). Several works have proposed enhanced pulse shaping filters to solve the problem of ISI and to improve the performance of OFDM. An overview of the current pulse shaping filters is given next.