Diversity Technique In 4G Wireless communications
4G Communications
The diversity is a technique that combating the fading by ensuring that there will be many copies of the transmitted signal which effected with different fading over time, frequency or space.
Diversity types:
1. Time (temporal) diversity.
2. Frequency diversity.
3. Spatial (antenna) diversity.
1-Time diversity:
In this type of diversity we averaging the fading of the channel over time by using the channel coding and interleaving to let every part of the codeword affected by different fading along the time so if a deep fading occurs only part of the codeword will being missing not all the codeword to explain this we will see an example:
2-Frequency diversity:
a) Frequency hop spread-spectrum
b) Direct sequence spread-spectrum
3-Spatial (antenna) diversity:
In this type of diversity we assures that we will have many copies of the transmitted signal or a coded versions effects with different fading over the space as we use multi antenna systems at the transmitter or the receiver to have finally at the receiver many copies of the transmitted signal suffers from different fading and the type of the diversity defined by where the multi antenna system so we have this types of the spatial diversity.
a) MISO (transmit diversity):
We use multi antenna at the transmitter. The receiver will receiving two (in our case) signals one from each antenna to the same transmitted data so if one of them has a deep fading he can get the information from the second one
b) SIMO (Receive diversity):
We use multi antenna at the receiver. Here the receiver will has many copies of the transmitted signal at its antennas as each one of them will effecting with different fading.
c) MIMO (Multiple Input Multiple Output):
Here the diversity order is equal to the number of the transmitter antennas multiplies with the number of receiver antennas (MT×MR ) which is the number of independent possible paths between the transmitter and receiver so each antenna of transmitter antennas will
transmitting a copy of message which will passing through different paths to reach the receiver antennas.
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d) MIMO multi-user (MIMO-MU):
The main difference here with the MIMO system is that we have many receivers each one has an antenna.
Notes:
The diversity order in the SIMO & MISO systems is the same in case of we use the same number of antennas but it is found that the SIMO performance is better than the MISO.
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4G Communications,Diversity technique In 4G wireless Communications channel
Diversity technique In 4G wireless Communication channel,wireless Communication channel,
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