The 3G LTE uses 3 Quadrature Amplitude Modulations (QAMs) depending on the radio quality.
QAM uses both the amplitude and the phase.
The LTE supports in DL and UL the following modulations:
- QPSK, the most robust but the less efficient
- 16-QAM
- 64-QAM, the less robust but the most efficient
QAM is a modulation method modifying the phase and the amplitude of the carrier signal.
QAM symbols are represented by the carrier signal being transmitted with specific phase / amplitude (dictated by the message), for finite periods of time.
One symbol is identified by a Q and an I value.
Transmission channels with a limited bandwidth limit the amount of symbols per second (Baud rate) that can
be transmitted.
To increase the bit per sec (bps) capacity of a channel, while keeping the Baud rate at the low values imposed
by the channel bandwidth, the symbols carry (represent) more than one single bit.
Symbols will represent a number of n bits, increasing the channel capacity by a factor of n.
The price paid is the presence of multiple symbols in the channel, increasing the probability of incorrect
symbol identification at the receiver.
QAM symbols are represented by the carrier signal being transmitted with specific phase / amplitude (dictated by the message), for finite periods of time.
One symbol is identified by a Q and an I value.
Transmission channels with a limited bandwidth limit the amount of symbols per second (Baud rate) that can
be transmitted.
To increase the bit per sec (bps) capacity of a channel, while keeping the Baud rate at the low values imposed
by the channel bandwidth, the symbols carry (represent) more than one single bit.
Symbols will represent a number of n bits, increasing the channel capacity by a factor of n.
The price paid is the presence of multiple symbols in the channel, increasing the probability of incorrect
symbol identification at the receiver.