China
Africa
Explore chapters and articles related to this topic
Guided-Wave Photonic Transmitters
Published in Le Nguyen Binh, Optical Modulation, 2017
Two arms of the dual-drive MZM modulator are biased at Vπ/2 and −Vπ/2 and driven with data and data¯. Phase-shaping driving sources can be a periodic triangular voltage source in case of linear MSK generation or simply a sinusoidal source for generating a non-linear MSK-like signal which also obtains a linear phase trellis property but with small ripples introduced in the magnitude. The magnitude fluctuation level depends on the magnitude of the phase shaping driving source. High spectral efficiency can be achieved with tight filtering of the driving signals before modulating the electro-optic MZMs. Three types of pulse shaping filters are investigated including Gaussian, raised cosine and squared-root raised cosine filters. The optical carrier phase trellis of linear and non-linear optical MSK signals are shown in Figure 4.29.
From the Top Down: The Physical Layer–FM OFDM
Published in David P. Maxson, The IBOC Handbook, 2007
Identical RRC filters are placed at the transmitter and receiver; this is called a matched filter. (In practice, the filter at the receiver is the complex conjugate of the transmitter's filter, with matching amplitude and complementary phase characteristics.) If the goal of the filtering were simply to control spectrum occupancy, the RC filter would be placed entirely at the transmitter. However, on its way to the receiver, the signal picks up delayed reflection energy in the guard times, and realizes a general increase in noise. To better control the spectral energy in the pulse arriving at the receiver, and maximize the likelihood of recovering the waveform now compromised by the propagation channel, it is valuable to have a pulse shaping filter at the receiver as well(as long as it is also synchronized in the time domain to correctly shape the incoming flow of symbols). Recall that the raised cosine shaped pulse provides an ideal sinc-like function for OFDM orthogonality. It stands to reason that placing the two RRC filters in the path between transmitter and receiver is like placing one RC filter somewhere in the path. In the time domain, the matched pulse shapers multiply the passing signal by their characteristic impulse responses. Thus, the effect of the first RRC filter at the transmitter is multiplied by the second RRC filter at the receiver. RRC × RRC = RRC2 = RC. The second trace on the inset of Figure 7.14 is the multiplication of two RRC pulse shapes in the time domain—an RC pulse shaper. The receiver's RRC pulse shaper helps reform the pulse shape in the presence of noise, providing the DFT the window it requires to demodulate the symbol.
Data Transmission
Published in Goff Hill, The Cable and Telecommunications Professionals' Reference, 2012
Stuart D. Walker, Emilio Hugues-Salas, Rouzbeh Razavi, Tahmina Ajmal
An ideal square wave requires that the signal changes from the high to the low state instantaneously. This requires infinite harmonics to be added and would need infinite bandwidth for transmission. In fact, transmitting a signal at a high modulation rate through a band-limited channel can create Intersymbol Interference. Therefore, a pulse is shaped before its transmission. The purpose of pulse shaping is to make the transmitted signal better suited to the communication channel by limiting the effective bandwidth of the transmission. By filtering the transmitted pulses this way, the intersymbol interference caused by the channel can be kept in control.
Time Domain Auto Pulse Shaping Operation
Published in IETE Journal of Education, 2018
P. Hari Krishna Prasad, L. Anjaneyulu
Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier digital modulation technique [1–2] that offers several advantages. InterCarrier Interference (ICI) and Peak-to-Average Power Ratio (PAPR) [3] are the two major concerns of an OFDM system. Pulse shaping is one of the methods of reducing the effect of ICI in OFDM systems [1–3]. A number of pulse shaping functions have been proposed in the literature [3–7]. Pulse shaping involves multiplying a basic pulse (usually sinc pulse) by a window function. The window function has the property that it has maximum amplitude for frequencies up to the frequency where the first zero crossing of the basic pulse occurs and ideally zero amplitude beyond that frequency. This observation led to the idea that better windowing functions can be derived from pulse shapes such as Gaussian, triangle and raised cosine pulse by extending the region of maximum amplitude and relatively reducing that portion over which the amplitude falls to zero value. The operation that achieves this objective is referred to as “Auto pulse shaping (APS)”.