Let us give an overview how wireless technology takes a smooth coarse from singlecarrier to OFDMA to understand the necessity for robust communication and better efficiency.
To date, single-carrier modulation was the prominent transmission scheme for cellular networks. It is important to know how single-carrier is susceptible to wireless multipath channel distortion. Multipath may cause delay in some paths and arrival may coincide with successor signals. This is called delay spread in the literature and overlay of delayed signal onto current is known as intersymbol-interference.
In single-carrier systems, as data rate increases symbol time decreases from Nyquist-Shannon theorem; significant delay caused by multipath on the order of few symbol times may spill the delayed symbol into later symbols. Each multipath arrives with an amplitude change and phase shift. And when combined in the receiver, some frequencies within the signal experience constructive and destructive interference. These induce increase in the error rate.
KeywordsPower Allocation Multiple Input Multiple Output Adaptive Modulation OFDM Symbol Subcarrier Allocation
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