I am looking for some help with chapter 12 questions and pro

I am looking for some help with chapter 12 questions and problems from the book electronic communication systems (2nd edition ) by Roy Blake. not just the answers but also the way to solve them. I am trying to learn not just get the answers. Typed please, or legiable writing. Thank you!

1. What is the meaning of the term modem?

2. What parameters of a sine-wave carrier can be modulated?

3. Name the three most common basic types of digital modulation.

4. Which type of modulation is likely to be used for:

a. low data rates

b. moderate data rates

c. high data rates

5. What signal parameters are verified with QAM?

41. Consider a QPSK system that will transmit three bits of information per symbol

a. How many phase angles are needed?

b. Draw a vector diagram for such a system.

c. Would this system have any advantages compared with the dibit systems described in the text? Any disadvantage?

42. A constellation diagram for a modem is shown in figure 12.20

(\"plus sign\" four dots up, four dots down, four dots left and four dots right)

a. What type of modulation is this?

b. If the transmitted bit rate is 9600 b/s, what will the baud rate using this modem?

43. A microwave radio systems uses 256-QAM, that is, there are 256 possible amplitude and phase combinations.

a. how many bits per symbol does it use?

b. If it has a channel with 40-MHz bandwidth, what is its maximum data rate, ignoring noise?

44. Draw a constellation pattern for a modem that uses eight equally-spaced amplitude levels. If the modem operates at 4800 baud, what is its bit rate?

48. Calculate the maximum data rate that could be sent using simplex transmission in a voice-grade telephone channel having a bandwidth of 3 kHz and a modem that uses QAM modulation with four possible phase angles and two amplitude levels. Assume that the signal-to-noise ratio in the channel is 30 dB.

Solution

1.] A modem (modulator-demodulator) is a network hardware device that modulates one or more carrier wave signals to encode digital information for transmission and demodulates signals to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used with any means of transmitting analog signals, from light emitting diodes to radio. A common type of modem is one that turns the digital data of a computer into modulated electrical signal for transmission over telephone lines and demodulated by another modem at the receiver side to recover the digital data.

2.] Amplitude, Frequency and Phase

3.] Digital modulation:

4.] a] amplitude/ phase shift keying

b] frequency shift keying FSK

c] orthogonal frequency division mutiplexing OFDM/ Trellis coded modulation

5.]Quadrature amplitude modulation (QAM) is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing (modulating) the amplitudes of two carrier waves, using the amplitude-shift keying(ASK) digital modulation scheme or amplitude modulation (AM) analog modulation scheme. The two carrier waves of the same frequency, usually sinusoids, are out of phase with each other by 90° and are thus called quadrature carriers or quadrature components — hence the name of the scheme. The modulated waves are summed, and the final waveform is a combination of bothphase-shift keying (PSK) and amplitude-shift keying (ASK), or, in the analog case, of phase modulation (PM) and amplitude modulation. In the digital QAM case, a finite number of at least two phases and at least two amplitudes are used.