transmitter Archives

In the previous post on transmit filtering using Nyquist pulse, we had briefly learned that the information symbol $a_m$ with a symbol period $T$ can be transmitted without inter symbol interference (ISI) by using Nyquist pulse,

$g(t) = \frac{sin(\pi t/T)}{\pi t/T},\mbox{ } t=-\infty \mbox{ to } +\infty$ .

The resultant waveform is ideally bandlimited to frequencies from $-\frac{1}{2T}$ Hz to $+\frac{1}{2T}$ Hz.

However, in typical transmission schemes, we do not hear of pulse shaping using sinc() filters. Rather, pulse shaping using raised cosine filter is frequently used. In this post, objective is to understand the motivation behind using raised cosine filtering for pulse shaping.

Continue reading “Raised cosine filter for transmit pulse shaping”

In the previous post on I-Q modulator and de-modulator, we had briefly mentioned that the a baseband PAM transmission can be modelled as

$s(t) = \sum_{m=-\infty}^{\infty}a_mg(t-mT)$ , where

$T$ is the symbol period,

$a_m$ is the symbol to transmit,

$g(t)$ is the transmit filter,

$m$ is the symbol index and

$s(t)$ is the output waveform.

In this post, the objective is to understand the properties of the transmit filter $g(t)$ i.e. to find out a filter which occupies the minimum required bandwidth while ensuring inter-symbol-interference (ISI) free transmission of the information symbol $a_m$ .

Continue reading “Transmit pulse shaping filter – rectangular and sinc (Nyquist)”