What is Modulation AM, FM and PM ?

-
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted.
In telecommunications, modulation is the process of conveying a message signal, for example a digital bit stream or an analog audio signal. Modulation of a sine waveform transforms a base-band message signal into a pass-band signal.
A modulator is a device that performs modulation. A demodulator (sometimes detector or demod) is a device that performs demodulation, the inverse of modulation.  

A modem (from modulator–demodulator) can perform both operations.
Amplitude Modulation (AM)
Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. In amplitude modulation, the amplitude (signal strength) of the carrier wave is varied in proportion to the waveform being transmitted.
Figure: Amplitude Modulation 
Frequency Modulation (FM)
In telecommunications and signal processing, frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. 
Frequency modulation is widely used for FM radio broadcasting. It is also used in telemetry, radar, seismic prospecting. In radio transmission, an advantage of frequency modulation is that it has a larger signal-to-noise ratio and therefore rejects radio frequency interference better than an equal power amplitude modulation (AM) signal. For this reason, most music is broadcast over FM radio.
Figure: Frequency Modulation 



Phase Modulation (PM)
Phase modulation (PM) is a modulation pattern that encodes information as variations in the instantaneous phase of a carrier wave.

Phase modulation is widely used for transmitting radio waves and is an integral part of many digital transmission coding schemes that underlie a wide range of technologies like WiFi, GSM and satellite television.

Phase modulation is closely related to frequency modulation (FM); it is often used as an intermediate step to achieve FM. Mathematically both phase and frequency modulation can be considered a special case of quadrature amplitude modulation (QAM).


Figure: Phase Modulation

Comments

Post a Comment

Popular posts from this blog

Symbol rate, Bandwidth and Bit rate Calculation

-
In satellite communication bandwidth (BW), symbol rate and bit rate are the most vital fact for proper signal transmission. There are many commercial software for BW, Symbol rate and bit rate calculation for TV signal transmission. But the equations of these parameter calculation are as follows. BW= (1+Roll of factor)* Symbol rate In general Roll of factor is 35% Symbol Rate =BW / (1+Roll of factor) and Bit Rate = Symbol rate * Modulation* FEC* (188/204)                                     [when 188 is encoder packet length] or Bit Rate = Symbol rate * Modulation* FEC* (204/188)                                     [when 204 is encoder packet length] Here, FEC = Forward Error Correction. In general FEC is in the range from 1/2 to 7/8. 188/204 = constant Unit ** BW= Hz, KHz, MHz, GHZ ** Symbol Rate= sps or baud, Ksps or Kbaud, Msps or Mbaud, Gsps or Gbaud ** Bit Rate= bps, Kbps, Mbps, Gbps Baud: U nit of signalling speed Baud rate: N umber of symbols transm
Read more

Terminology: EIRP, G/T, Input Back-Off, Output Back-Off

-
  EIRP:   Used to indicate the power transmitted from an antenna. EIRP=Power +Antenna Gain, Both EIRP and Power is expressed in dBW and Gain in dBi. G/T:   It is the figure of merit for an earth station and is expressed as dB/K (dB per K). G/T= Antenna Gain-10*Log (System Noise Temperature) The higher the better-G/T can be raised by using a higher gain antenna or a lower temperature LNA. The earth station G/T determines the received carrier to noise ration. Increasing station G/T will increase the C/N of the received carrier. Input Back-Off (IPBO):   The level of a signal at the input of an amplifier relative to that level at the input that would result in the maximum possible output level. For example, if an input level of -20dBm causes max output and the actual input level is -25dBm, the IPBO is 5dB. Both IPBO and OPBO are commonly used to determine the operating levels in a satellite transponder TWTA. Output Back-Off (OPBO)   The level of a signal at the output
Read more

Bit Error Rate (BER) and Roll Off Factor

-
Image
Roll Off  Factor W hen a digital signal is modulated the output would be a waveform with the shape of sin(x)/x. Now this has an infinite bandwidth. So in order to be able to transmit this signal over satellite we need to filter it to reduce the occupied bandwidth. This is done by applying a "raised cosine roll-off filter". This filter is present both at the modulator output stage and at the input of the demodulator (I believe one says these filters are then matched). The steepness and the resulting occupied bandwidth can be set by the parameter roll-off factor. In DVB-S2 it can be 0.20 (20%); 0.25 (25%) or 0.35 (35%) where the  Occupied bandwidth = symbol rate x (1 + roll-off factor). Figure: Occupied bandwidth, Roll off factor and symbol rate 
Read more

Followers