Start Searching the Answers
The Internet has many places to ask questions about anything imaginable and find past answers on almost everything.
From Wikipedia, the free encyclopedia. The modulation index (or modulation depth) of a modulation scheme describes by how much the modulated variable of the carrier signal varies around its unmodulated level. It is defined differently in each modulation scheme.
For a perfect modulation, the value of modulation index should be 1, which means the modulation depth should be 100%. For instance, if this value is less than 1, i.e., the modulation index is 0.5, then the modulated output would look like the following figure.
The RF carrier wave has peak amplitude “A”, while the modulation wave has peak amplitude “B”. The modulation index “K” is given by: K = B / A, and is a measure of the depth of modulation. If K = 1, the RF Carrier Wave is said to be 100 % modulated. Figure 4.1 Continuous Amplitude – Modulated Wave.
Modulation index is defined as the ratio of the fundamental component amplitude of the line-to-neutral inverter output voltage to one-half of the available DC bus voltage. From: Power Electronics Handbook (Fourth Edition), 2018.
If the modulation index is greater than 1, then we call this condition over modulation. In such cases, the baseband signal is not preserved in the envelope of the AM signal and therefore, the recovered signal is distorted at the output of the receiver.
Angle Modulation Types There are two types of angle modulation, and they are frequency modulation and phase modulation. Phase modulation: It is defined as the process in which the phase of the carrier signal varies linearly with respect to the message signal.
Angle Modulation is the process in which the frequency or the phase of the carrier varies according to the message signal. This is further divided into frequency and phase modulation. Frequency Modulation is the process of varying the frequency of the carrier signal linearly with the message signal.
Angle modulation is a class of carrier modulation that is used in telecommunications transmission systems. The class comprises frequency modulation (FM) and phase modulation (PM), and is based on altering the frequency or the phase, respectively, of a carrier signal to encode the message signal.
Angle modulation has several advantages over the amplitude modulation such as noise reduction, improved system fidelity and more efficient use of power. But there are some disadvantages too such as increased bandwidth and use of more complex circuits.
Angle modulation is resistant to propagation-induced selective fading because amplitude variations are unimportant. 2. Angle modulation is very efficient in rejecting interference (i.e., it minimizes the effect of noise on the signal transmission).
These modulation techniques are classified into two major types: analog and digital or pulse modulation.
Modulation is the addition of information to an electronic or optical carrier signal. In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, the carrier signal, with a modulating signal that typically contains information that is to be transmitted.
Frequency modulation is more effective in terms of noise tolerance and more suited for data transmission than AM. Phase modulation is more complex and costly but is relatively immune to noise and theoretically makes the best use of bandwidth for a given transmission rate.
The signals within 20 Hz to 20 kHz frequency range can travel only a few distances. To send the message signal, the length of the antenna should be a quarter wavelength of the used frequency. Thus, modulation is required to increase the frequency of the message signal and to enhance its strength to reach the receiver.
Advantages of Modulation
QPSK has advantages of having double data rate compare to BPSK. This is due to support of two bits per carrier in QPSK compare to one bit per carrier in the case of BPSK. While QPSK is used for data transmission to provide higher data rate.
QPSK, or Quadrature Phase-Shift Keying, uses four distinct phase-shifts to encode data. In contrast, 8PSK, or Eight Phase-Shift Keying, uses eight distinct phase-shifts. These occur at 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees.
QPSK provide very good noise immunity. It provides low error probability. Bandwidth is twice efficient is compared to BPSK modulation. For the same BER, the bandwidth required by QPSK is reduced to half as compared to BPSK.