Adopting a multicarrier approach for multiple access in LTE was the first major design choice. The choice of multiple-access schemes was made in December 2005, with OFDMA being selected for the downlink, and SC-FDMA for the uplink.
Both of these schemes open up the frequency domain as a new dimension of flexibility in the system, as illustrated schematically in Figure below
OFDMA extends the multicarrier technology OFDM to provide a very flexible multipleaccess scheme. In OFDMA, the subdivision of the available bandwidth is exploited in sharing the subcarriers among multiple users.
This resulting flexibility can be used in various ways:
• Different spectrum bandwidths can be utilized without changing the fundamental system parameters or equipment design.
• Transmission resources of variable bandwidth can be allocated to different users and scheduled freely in the frequency domain.
• Fractional frequency re-use and interference coordination between cells are facilitated.
SC-FDMA has a significantly lower PAPR. It therefore resolves to some extent the dilemma of how the uplink can benefit from the advantages of multicarrier technology while avoiding excessive cost for the mobile terminal transmitter and retaining a reasonable degree of commonality between uplink and downlink
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