Adaptive Modulation

Adaptive Modulation 

Wireless Communications

 

 I-The Use of Adaptive Modulation Not Fixed Modulation:

The reason is as the Fading channels confront us with the problem
of lost Packets and the need for frequent re-transmissions and 
Wireless communication systems are affected by changing weather conditions.

And if those effects not handled correctly, such systems may not be
able to cope with issues such as signal degradation thereby seriously 
endangering a Carrier’s ,quality of service obligations.
To overcome this effects making coding and interleaving to reduce
the effect of channel and weather effects but it reduces the 
throughput of  the channel, but we can “Dynamic Adaptive Modulation” 
which ensures maximum bandwidth most of the time with guaranteed 
critical services all the time .

II- Idea of Adaptive Modulation:

The basic idea of Adaptive Modulation is to adapt different 

order modulations that allow sending more bits per symbol

and thus achieving higher throughput or better spectral 

efficiencies However, it must also be noted that when using

a modulation technique such as 64-QAM, better signal-to-noise

ratios (SNRs) are needed to overcome any interference and 

maintain a certain bit error ratio (BER).

The use of adaptive modulation allows a wireless system to

choose the highest order modulation depending on

,the channel conditions then when

*The channel condition is good use 16-QAM or 64-QAM

*Bad channel condition use QPSK

*The channel is very bad do not send the data or use BPSK

In one word we can define Adaptive Modulation as 

the automatic modulation adjustment that a wireless system

can make to prevent weather-related fading from causing 

communication on the link to be disrupted.

From the figure, knowing the mean of the adaptive modulation

As the channel changes the modulation schemes also changes

(to maintain a constant BER (here its 10^-5

 The adaptive modulation try to use the time -variation in 

 channel conditions to increase the capacity of the system

not try to fight this effects only.

or can be  obvious from the following figures that the modulation

scheme changes due to weather changes or the distance form the a

antenna

The Block diagram of adaptive modulation: 

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Adaptive Modulation of wireless Communication channel,wireless Communications channel,

4G Communications,Adaptive Modulation of wireless Communications channel

Adaptive Modulation of wireless Communication channel,wireless Communication channel,

Adaptive Modulation of wireless Communications channel,wireless Communications channel,

Adaptive Modulation of wireless Communication channel in 4G communication,wireless Communication channel in 4G communication ,

Adaptive Modulation of wireless Communications channel in 4G communications,wireless Communications channel in 4G communications,

Adaptive Modulation of 4G wireless Communication channel,4G wireless Communication channel,