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Time and Frequency Synchronization Schemes for OFDM-Based Mobile Broadcasting
Published in Borko Furht, Syed Ahson, Handbook of Mobile Broadcasting, 2008
Xianbin Wang, Yiyan Wu, Jean-Yves Chouinard
Digital broadcasting involves the transmission of information in digital form from an information source to one or several destinations. In an ideal channel, there is no intersymbol interference (ISI) caused by multipath channel distortion, and error-free transmission can be achieved. However, this condition could not be satisfied with channel distortion as in a digital broadcasting environment due to the multipath propagation effects, including reflection and scattering. Equalization and channel control coding methods can be applied to achieve robust transmission. A time domain equalizer could be used to shorten the effective channel impulse response duration, or length, of a dispersive channel,9 and whose coefficients are updated with an adaptive algorithm like that of Kalman filtering or the gradient algorithm, for instance. However, adaptive equalization could considerably increase the system implementation complexity, and the convergence of such an equalizer is not guaranteed.
Audio routing and transmission
Published in John Watkinson, Audio for Television, 1997
Digital broadcasting is a technique in which the received radiation from the transmitter is decoded into discrete numerical values rather than as a continuous variable. Discrete decoding allows moderate noise levels to be rejected. As noise has a distribution of levels, the higher, yet infrequent, noise levels will cause data errors, but a suitable error correction system can correct the data to the original values. In an analog system the higher amplitude noise pulses are visible in the picture and audible in the sound. The only solution is to raise the power of the transmitter. In digital systems the infrequent noise peaks are eliminated by error correction. Consequently lower transmitter power can be used in digital transmission.
Spatial diversity for QAM OFDM RoFSO links with nonzero boresight pointing errors over atmospheric turbulence channels
Published in Journal of Modern Optics, 2019
M. P. Ninos, H. E. Nistazakis, E. Leitgeb, G. S. Tombras
In OFDM systems the information signal is conveyed by parallel subcarriers which are orthogonal to each other over the OFDM symbol duration (6–9,42–44). This technique has already been applied in many digital broadcasting services such as IEEE 802.16e, IEEE 802.11a, g, ac, ad, ax, ay, DTTV, LTE, visible light communications (VLC), etc, and is also considered as a potential candidate for the mobile wireless networks of next generation, i.e. the 5G, (2–6). Among its advantageous features is the high spectral efficiency, the robustness against frequency selective fading and the inter-symbol interference minimization. Also, simple time-domain equalization is needed. Nonetheless, the main drawback of the OFDM signal is its high peak-to-average power ratios (PAPR), imposing restrictions on its application to intensity modulation schemes such as optical communications (36–38). A dc bias is required so that clipping of the modulating signal can be avoided. It can lead to nonlinearities though, due to the finite spurious-free dynamic range (SFDR) of the transmitter laser diodes (LD), (1,2,6–8,42–44).