Digital Communications

6Baseband Transmission

In Chapter 5 we considered the conversion of analog signals into digital by an ADC and baseband modulation techniques (see Figure 5.1). The line codes used for symbol transmission require infinite transmission bandwidth, as shown in Figure 5.26. Since frequency spectrum is a scarce resource, its economic use is of paramount importance. Therefore, the frequency components with negligible power of the transmitted signals are filtered out at the transmitter output.

On the other hand, in addition to the intended copy of the transmitted signal, its echos with different amplitude, phase and delay also arrive to the receiver. Hence, the original signal may be spread in time and frequency‐domains at the receiver input. On the other hand, the receiver filters out signals and noise outside its bandwidth for mitigating interference and noise. Therefore, the receiver should be able to cope with all these inconveniences to estimate the received pulses with minimum error.

This chapter will address the issues related to the reception of pulses at the receiver after transmission through a linear baseband channel.

6.1 The Channel

Let us consider the transmission of a pulse g(t) through a linear channel, as shown by Figure 6.1, characterized by its impulse response h(t) and the corresponding channel transfer function H(f). The signal x(t) at the channel ouput may be expressed as the convolution of the input pulse g(t) and the channel impulse response h(t). The output ...