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Additional info for Antenna Compendium Volume 3
However, by truncating the pulse shape to a few symbol periods and delaying it, it is possible to use an approximate version of these rootraised cosine pulse shapes. 33 Raised cosine shape of the frequency response of the combined transmit and receive filters. tion will introduce some sidelobes. 2 is used in practice. Although the bandwidth of the transmitted signal is an important characteristic of a modulation scheme, it is also important to use the spectrum efficiently. The spectral efficiency of a modulation scheme is defined as the number of bits that can be transmitted per unit time per unit of frequency, normally measured in bits/ second/Hz.
117) We can see that the peak power depends on the sequence of transmitted symbols and on the pulse shape. 117) is maximized when |vn| is at its maximum value for all n. Let Emax = max |vn|2 be the maximum energy of any signal in the constellation. 119) and is usually expressed in decibels. 1. The factor of 2 is because we are considering the PAPR of a modulated bandpass signal. This factor would be missing from the PAPR of the corresponding baseband signal. 120) is the excess roll-off factor due to pulse shaping and depends only on the pulse shape, not the signal constellation.
48 An Introduction to Communication Systems pulse shape, the null-to-null bandwidth of the modulated signal is 2/T, whereas the bandwidth is (1 + a)/T when a root raised cosine pulse shape with roll-off factor a is used. 113) which increases as M increases. However, with FSK the bandwidth also depends on the modulation order, M. 114) which decreases quickly as M increases. One may be tempted to decrease the frequency separation in an attempt to improve the spectral efficiency, but this is futile.