LTE Q&A

 the difference between FDD and TDD?
In FDD there will be pair of frequencies assigned in the downlink and uplink directions and hence transmissions from multiple subscribes can happen at the same time but on different frequencies as mentioned.
In TDD, one single frequency will be used at different time instants by multiple subscriber terminals (UEs). Both frame versions of LTE will have 1 ms sub-frame duration and 0.5 ms slot duration.

What is Modulation?

Modulation basically is used to convert information (digital bit stream or analog audio signal) in the form that can be physically transmitted over the air or cable. Information is referred as baseband or modulating signal. 

The device which performs modulation operation is called modulator and the resulting waveform or output of modulator is called as modulated signal. The device which performs inverse of modulation is called demodulator and the operation is named as demodulation. 

The most complex digital modulation techniques used now-a-days are BPSK, QPSK and QAM.