Chapter 5 - Analog Transmission PPT, Data Communications and Networking, ECE - Computer Science Engineering (CSE) PDF Download

Figure 5.3  Binary amplitude shift keying

Data Communications and Networking -------------------------- Next slide -------------------------- Forouzan

Figure 5.4  Implementation of binary ASK

Data Communications and Networking -------------------------- Next slide -------------------------- Forouzan

Example 5.3

We have an available bandwidth of 100 kHz which spans from 200 to 300 kHz. What are the carrier frequency and the bit rate if we modulated our data by using ASK with d = 1?

Solution

The middle of the bandwidth is located at 250 kHz. This means that our carrier frequency can be at                 f_c = 250 kHz. We can use the formula for bandwidth to find the bit rate (with d = 1 and r = 1).

Data Communications and Networking -------------------------- Next slide -------------------------- Forouzan

Example 5.4

In data communications, we normally use full-duplex links with communication in both directions. We need to divide the bandwidth into two with two carrier frequencies, as shown in Figure 5.5. The figure shows the positions of two carrier frequencies and the bandwidths. The available bandwidth for each direction is now 50 kHz, which leaves us with a data rate of 25 kbps in each direction.

Data Communications and Networking -------------------------- Next slide -------------------------- Forouzan

Figure 5.5  Bandwidth of full-duplex ASK used in Example 5.4

Data Communications and Networking -------------------------- Next slide -------------------------- Forouzan

Frequency Shift Keying

Data Communications and Networking -------------------------- Next slide -------------------------- Forouzan

Bandwidth of FSK

B = (1+d)xS + 2Δf

Data Communications and Networking -------------------------- Next slide -------------------------- Forouzan

Example 5.5

We have an available bandwidth of 100 kHz which spans from 200 to 300 kHz. What should be the carrier frequency and the bit rate if we modulated our data by using FSK with d = 1?

Solution

This problem is similar to Example 5.3, but we are modulating by using FSK. The midpoint of the band is at 250 kHz. We choose 2Δf to be 50 kHz; this means

Data Communications and Networking -------------------------- Next slide -------------------------- Forouzan

Coherent and Non Coherent

Data Communications and Networking -------------------------- Next slide -------------------------- Forouzan

Example 5.6

We need to send data 3 bits at a time at a bit rate of 3 Mbps. The carrier frequency is 10 MHz. Calculate the number of levels (different frequencies), the baud rate, and the bandwidth.

Solution

We can have L = 2³ = 8. The baud rate is S = 3 Mbps/3 = 1 Mbaud. This means that the carrier frequencies must be 1 MHz apart (2Δf = 1 MHz). The bandwidth is B = 8 × 1M = 8M. Figure 5.8 shows the allocation of frequencies and bandwidth.

Data Communications and Networking -------------------------- Next slide -------------------------- Forouzan

Figure 5.8  Bandwidth of MFSK used in Example 5.6

Data Communications and Networking -------------------------- Next slide -------------------------- Forouzan

Phase Shift Keyeing

B = (1+d)xS

Data Communications and Networking -------------------------- Next slide -------------------------- Forouzan

Figure 5.9  Binary phase shift keying

Data Communications and Networking -------------------------- Next slide -------------------------- Forouzan

Figure 5.10  Implementation of BASK

Data Communications and Networking -------------------------- Next slide -------------------------- Forouzan

Quadrature PSK