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Wireless LAN Technology for the Factory Floor: Challenges and Approaches
Published in Richard Zurawski, Networked Embedded Systems, 2017
An immediate result of reflection, diffraction, and scattering is that multiple copies of a signal may travel on different paths from T to R. Since these paths usually have different lengths, the copies arrive at different times (delay spread) and with different phase shifts at the receiver and overlap. This has two consequences: Overlapping signals can interfere constructively or destructively. Destructive interference may lead to up to 40 dB loss of received power. Such a situation is often called a deep fade.Delay spread leads to inter-symbol interference, since signals belonging to neighbored information symbols overlap at the receiver.
Wireless LAN Technology for the Factory Floor: Challenges and Approaches
Published in Richard Zurawski, Industrial Communication Technology Handbook, 2017
An immediate result of reflection, diffraction, and scattering is that multiple copies of a signal may travel on different paths from T to R. Since these paths usually have different lengths, the copies arrive at different times (delay spread) and with different phase shifts at the receiver, where they are superposed. This has two consequences: Overlapping signals can interfere constructively or destructively. Destructive interference may lead to up to 40 dB loss of received power. Such a situation is often called a deep fade.Delay spread leads to intersymbol interference, since signals belonging to neighbored information symbols overlap at the receiver.
Performance modelling of turbo-coded non-ideal single-carrier and multi-carrier waveforms over wide-band Vogler-Hoffmeyer HF channels
Published in Amir Hussain, Mirjana Ivanovic, Electronics, Communications and Networks IV, 2015
Fatih Genç, Mustafa Anil Reşat, Asuman Savaşçabes, Özgür Ertuğ*
OFDM and SC-FDE are similar in many ways. However, there are explicit differences that make the two systems perform differently. As shown in Figure 5, the main difference between OFDM and SC systems is the placement of the IFFT block. In SC systems, it is placed on the receiver side to transform the frequency domain equalized signals, thus compensating for channel distortion, bringing back to the time domain R3. All the other blocks are formed with the same manner like OFDM system at the both sides of the transmission. In the OFDM system, symbols are exposed to an additional transformation by using the IFFT, x(n)=IFFT{X[k]}, but in the SC-FDE system no transformation is used. The frame of SC-FDE is transmitted during the time instant after the Turbo encoder, 16-QAM modulation, pilot insertion and CP insertion are applied, respectively, and the receiver maps received data into the frequency domain in order to equalize. When the channel delay spread is large it is more efficient computationally to equalize in the frequency domain.
Interference Cancellation in Wireless Communications: Past, Present, and Future
Published in IETE Journal of Education, 2022
S. M. Zafaruddin, Pranay Bhardwaj
High bit-rate transmissions over multi-path channels may cause inter-symbol interference (ISI) if the symbol duration becomes comparable or less than the delay spread of the channel. A naive approach may be to lower the data rate transmissions sufficiently to account for the ISI. However, channel equalization is a potential technique to suppress the ISI and render the demand for high data rates in modern communication systems [11]. Channel equalization compensates for the distortion in the transmitted signal due to the frequency-selective channel. There are many equalization techniques for ISI mitigation such as linear equalizer, adaptive equalizer, decision feedback equalizer, and maximum-likelihood sequence estimator [12]. On the other hand, multicarrier modulation divides a wideband channel into multiple low-rate orthogonal sub-channels with negligible ISI [13]. A popular implementation of multicarrier modulation for wireless systems is orthogonal frequency division multiplexing (OFDM). However, OFDM is sensitive to the carrier frequency offset (CFO), which may be caused due to differences in the carrier frequencies of transmitter and receiver.
Deep Learning Techniques for OFDM Systems
Published in IETE Journal of Research, 2021
M. Meenalakshmi, Saurabh Chaturvedi, Vivek K. Dwivedi
One of the major issues of wireless communication is ISI, which is caused by the multipath propagation and delay spread of the channels. The problem of ISI in OFDM system has been addressed by CP insertion between adjacent symbols, but it decreases the spectral efficiency of the system. A CP removal technique can be applied to improve the spectral efficiency, but it affects the received pilots and channel estimation in the OFDM receiver. To address the problem of channel estimation and SD in the CP-free OFDM system, an AI-aided receiver was introduced in [14].