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Quadrature Amplitude Modulation

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  • Last Updated : 17 Aug, 2022
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Quadrature Amplitude Modulation (QAM) is a modulation technique that can be utilized in Analog modulation concepts and digital modulation concepts. It is a combination of ASK and PSK. So, in this article, we will discuss QAM, Analog QAM, Digital QAM, and many more. 

Quadrature Amplitude Modulation:

Quadrature Amplitude Modulation (QAM) can be defined as a modulation technique that can be used to combine two amplitude modulated waves into a single channel to increase the channel bandwidth.

  • Quadrature amplitude Modulation is a modulation technique that can be utilized in Analog modulation concepts and digital modulation concepts.
  • Depending upon the input signal form, it has two types: Analog and digital modulation schemes.
  • In QAM, we can modulate two individual signals and transmit them to the receiver level and by using the two input signals, the channel bandwidth also increases.
  • QAM is capable to transmit two message signals over the same channel.
  • This QAM technique is also known as “Quadrature carrier multiplexing”.

PSK is limited by the ability of the equipment to differentiate the small differences in phase. This factor limits its potential bit rate. Quadrature Amplitude Modulation is a combination of ASK and PSK.

Bandwidth for QAM: ASK/PSK transmission and QAM transmission require the same minimum bandwidth. QAM has the same advantages as PSK over ASK.

Advantages of QAM:

  • Supports high data rate.
  • Noise immunity is very high therefore, noise interference is very less.
  • Low probability of error value.
  • It expertly uses channel bandwidth.

Disadvantages of QAM:

  • The receiver is more complex compared to receivers of other modulation types.
  • QAM requires coherent demodulation with the same phase and frequency.
  • As QAM uses the amplitude component of the signal to represent binary data, linearity needs to be maintained; hence linear amplifier is required which consumes more power.

Analog QAM:

They are used to allow more than one signal to be carried. Analog QAMs and AM (Amplitude Modulation) are the same with two carrier signals transmitted together but are out of phase by 90 degrees.

Digital QAM:

Digital QAMs are generally described as a “ Quantized QAM ” and they’re generally used in radio dispatches systems ranging from cellular technology to Wi-Fi. Digital QAM can carry advanced data rates compared to both amplitude and phase-modulated schemes.

QAM in Wi-Fi: 

Progressing into the latest standard of Wi-Fi 6, QAM technology can handle more data than it has handled ever before. As the world upgrades to the new Wi-Fi 6 standard, the preface of the rearmost QAM technology for wireless routers also emerges to the market. 1024 QAM is a large enhancement from the former 256 QAM in Wi-Fi 5, quadrupling the data outturn per modulation cycle. Still, with,1024 people packed into the proverbial party room, this is a delicate task, especially with factors like background noise or other interferences. Maximizing the benefits of this enhancement requires a stronger signal than any of QAM’s former duplications or a more sensitive receiver to pick up details of fainter signals.

This also means that further data is packed into each transmission, which makes for an advanced threat, advanced price model than former generations of QAM in home networking. Smaller packets mean smaller chances for collision. Still, in the script a data collision was to do, a 1024 QAM would lose further data compared to a 256 QAM. But considering the progress in stability from previous technologies and a 75% reduction in chances for collision, the adoption of this technology allows for an overall enhancement.

As for the future of internet service providers, advancements in QAM technology will equate to further data transfer effectiveness from point-to-point links, which can allow for further guests per link and even higher speeds per client. As the market awaits the appearance of WiFi-6 devices, understanding how QAM technology works behind the scenes to restate data uncovers just how important this new standard can be.

Amplitude Shift Keying (ASK): 

In amplitude shift keying, the amplitude of the carrier signal is changed to create signal elements. The amplitude changes but the frequency and the phase remain constant.

Binary ASK (BASK): When ASK is implemented with only two levels, it is referred to as binary amplitude shift keying (BASK) or on-off keying. The peak amplitude of one signal level is 0; the other is the same as the amplitude of the carrier frequency.

Advantages of ASK:

  • It offers high bandwidth efficiency.
  • Simple receiver design.
  • ASK modulation can be used to transmit digital data over optic fiber.
  • Modulation and demodulation processes are comparatively inexpensive.

Disadvantages of ASK:

  • It offers low power efficiency.
  • Very susceptible to noise interference because noise affects the amplitude.
  • It is not suitable for high-bit-rate data transmission.

Phase Shift Keying (PSK): 

It is a digital modulation technique that conveys data by changing the phase of a constant frequency reference signal. This modulation is accomplished by varying the sine and cosine inputs at a precise time. In phase shift keying, the phase of the output signal gets shifted depending upon the input. If the m(t) baseband signal is =1 then the carrier signal within the phase will be transmitted. Similarly, if the baseband signal m(t)=0 then the carrier signal by out of phase is transmitted. The applications mainly include wireless LANs, bio-metric, contactless operations, satellite communications, etc. 

Binary PSK (BPSK): This is also known as 2-phase PSK or Phase Reversal Keying. In this technique, the sine wave carrier takes two phase reversals such as 0° and 180°. BPSK is basically a Double Side Band Suppressed Carrier modulation scheme.

Advantages of PSK:

  • It allows information to be transmitted in radio communication in a more efficient way as compared to that of FSK.
  • Less prone to error.
  • A high rate of data transmission is achieved.
  • It is also more power-efficient as compared to other techniques.

Disadvantages of PSK:

  • Significantly less bandwidth as compared to ASK.
  • It is a type of non-coherent reference signal.
  • Extremely difficult algorithms are used in decoding the binary information which is transmitted during PSK.
  • Sometimes they are susceptible to phase differences.
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