Modulation in Mobile Computing

Modulation is a process of mixing signals with a sinusoid to produce a new form of signals. The newly produced signal has certain benefits over an un-modulated signal. Mixing of low-frequency signal with a high-frequency carrier signal is called Modulation.

In other words, you can say that "Modulation is the process of converting one form of signals into another form of signals." For example, Analog signals to Digital signals or Digital signals to Analog signals.

Modulation is also called signal modulation.

Example: Let's understand the concept of signal modulation by a simple example. Suppose an Analog transmission medium is available to transmit signals, but you have a digital signal that needs to be transmitted through this Analog medium. So, to complete this task, you have to convert the digital signal into an analog signal. This process of conversion of signals from one form to another form is called Modulation.

Need for Modulation/ Why Use Modulation?

The baseband or low-frequency signals are not such strong and compatible signals that can be used for direct transmission. To make these signals travel longer distances, we have to increase their strength by modulating them with a high-frequency carrier wave. This process doesn't affect the parameters of the modulating signal.

Modulation is used to make the message carrying signal strong to be transmitted over a long distance and establish a reliable communication. A high-frequency signal can travel up to a longer distance without getting affected by external disturbances. In Modulation, these high-frequency signals are used as a carrier signal to transmit the message signal. This process is called Modulation. In Modulation, the carrier signals' parameters are changed according to the instantaneous values of the modulating signal.

Another reason to modulate a signal is to allow a smaller antenna as we know that a low-frequency signal would need a huge antenna. An antenna needs to be about 1/10th the length of the wavelength of the signal to be efficient. Modulation converts the low-frequency signal into a much higher frequency signal, which has much smaller wavelengths and allows a smaller antenna.

Advantages of Modulation

Following is the list of some advantages of implementing Modulation in the communication systems:

By implementing Modulation, the antenna size gets reduced. Before modulation technology, the antenna used for transmission had to be very large. The range of communication gets limited as the wave cannot travel to a distance without getting modulated.
The range of communication has increased.
The reception quality is immensely improved.
Receivers are allowed to adjust to the bandwidth.
Multiplexing of signals occurs.
No signal mixing occurs.

Types of Modulation

Primarily Modulation can be classified into two types:

Digital Modulation
Analog Modulation

Digital Modulation

Digital Modulation is a technique in which digital signals/data can be converted into analog signals. For example, Base band signals.

Digital Modulation can further be classified into four types:

Amplitude Shift Key(ASK) Modulation
Minimum Shift Key (MSK) Modulation
Frequency Shift Key (FSK) Modulation
Phase Shift Key (PSK) Modulation

Amplitude Shift Key (ASK) Modulation

As the name suggests, in Amplitude Shift Key or ASKS Modulation, the amplitude is represented by "1," and if the amplitude does not exist, it is represented by "0".
Using Amplitude Shift Key Modulation is very simple, and it requires a very low bandwidth.
Amplitude Shift Key Modulation is vulnerable to inference or deduction.

Minimum Shift Key (MSK) Modulation

The Minimum Shift Key or MSK Modulation is the most effective technique of Modulation and can be implemented for almost every stream of bits. It is easy and effective than Amplitude Shift Key, Frequency Shift Key and Phase Shift Key.
MSK is mostly used because of its ability and flexibility to handle "One(1)" and "Zero(0)" transition of binary bits.

Frequency Shift Key (FSK) Modulation

In Frequency Shift Key or FSK Modulation, different notations f1 and f2 are used for different frequencies.
Here, f1 is used to represent bit "1," and f2 represents bit "0".
It is also a simple modulation technique but uses different frequencies for different bits; bandwidth requirement becomes high.

Phase Shift Key (PSK) Modulation

In Phase Shift Key or PSK Modulation, the phase difference is used to differentiate between the "1" and "0" bits.
If the bit is "1", a simple wave is drawn, and if the bit becomes "0", the phase of the wave is shifted by "180 or π".
PSK Modulation is more complicated than ASK and FSK Modulation, but it is robust too.

Analog Modulation in Mobile Computing

Analog modulation is a process of transferring analog low-frequency baseband signal such as an audio or TV signal over a higher frequency carrier signal such as a radio frequency band. Baseband signals are always analog to this modulation.

In other words, you can say that "Analog Modulation is a technique which is used in analog data signals transmission into digital signals."

An example of Analog Modulation is Broadband Signals.

There are three properties of a carrier signal in analog modulation i.e., amplitude, frequency and phase. So, the analog modulation can further be classified as:

Amplitude Modulation (AM)
Frequency Modulation (FM)
Phase Modulation (PM)

Difference between Digital and Analog Modulation

Both digital and analog modulation are used to vary or transform signals from one for to another, but the difference is that an analog-modulated signal is demodulated into an analog baseband waveform. On the other hand, in digital modulation, a digitally modulated signal contains discrete modulation units, called symbols, that are interpreted as digital data.

Amplitude Modulation

Amplitude modulation or AM is a modulation technique that is used in electronic communication. It is most commonly used for transmitting messages with a radio carrier wave. It varies the instantaneous amplitude of the carrier signal or waves according to the message signal's instantaneous amplitude.

If we denote the message signal as m(t) and c(t)= Acosw_ct, then amplitude modulation signal F(t) will be written as:

F(t)= Acosw_ct+m(t) cosw_ct

F(t)=[A+m(t)] cosw_ct

History of Amplitude modulation

Amplitude modulation was the earliest modulation technique used for transmitting audio in radio broadcasting. It was developed during the first quarter of the 20th century and was based on the Roberto Landell De Moura and Reginald Fessenden's radiotelephone experiments proposed in 1900.

Advantages of Amplitude Modulation

Amplitude Modulation is easy to implement. It is the simplest type of modulation.
Amplitude Modulation, we can easily do Demodulation by using few components and a circuit.
The hardware design of both the transmitter and receiver is very simple, that's why it is cost-effective.
The receiver used for Amplitude Modulation is very cheap.

Disadvantages of Amplitude Modulation

Amplitude Modulation is not a very power efficient technique.
Amplitude Modulation requires a very high bandwidth that is equivalent to that of the highest audio frequency.
Amplitude Modulation is very susceptible to noise. You can easily notice the noise.

Usage of Amplitude Modulation

Amplitude Modulation is used in AM radio communication. AM radio broadcast is an example of Amplitude Modulation.

Frequency Modulation

Frequency Modulation or FM is the process of encoding the information in a carrier wave by varying the instantaneous frequency of the wave. It varies the instantaneous frequency of the carrier signal according to the instantaneous amplitude of the message signal.

If we denote the message signal as m(t) and c(t)= Acosw_ct, then Frequency modulation signal F(t) will be written as:

F(t)= Acos(w_c t+k_f ∫m(α)dα)

Advantages of Frequency Modulation

Frequency Modulation is widely used for FM radio broadcasting.
It is also used in telemetry, sound synthesis, seismic prospecting, radar, and monitoring newborns for seizures via EEG, two-way radio systems, magnetic tape-recording systems and some video-transmission systems.
The main advantage of using frequency modulation in radio transmission is that it has a larger signal-to-noise ratio. That's why it rejects radio frequency interference better than an equal power amplitude modulation (AM) signal. This is the main reason why most music radio channels prefer to broadcast over FM radio.
In FM, Modulation and Demodulation do not receive any channel noise.

Disadvantages of Frequency Modulation

FM consists of a complicated circuit than AM for modulation and Demodulation.

Usage of Frequency Modulation

The main example of Frequency Modulation is FM radio broadcasting.

Phase modulation (PM)

Phase modulation or PM is the technique of varying the carrier signal's instantaneous phase according to the instantaneous amplitude of the message signal. It encodes the message signal as changes occurred in the instantaneous phase of a carrier signal.

If we denote the message signal as m(t) and c(t)= Acosw_ct, then Phase modulation signal F(t) will be written as:

F(t)= Acos(w_ct+k_pm(t))

Advantages of Phase modulation

Phase Modulation is mainly used for transmitting radio waves. It is also used in many digital transmission coding schemes and technologies such as Wi-Fi, GSM and satellite television.
In PM, Modulation and Demodulation do not receive any channel noise.

Disadvantages of Phase modulation