Multicarrier Modulation and Multiple Access
The requirements for the IMT-Advanced mandate that the utilized multiple access technologies are backward compatible with IMT-2000 (3G) systems. To support different services, both contention and contention-free multiple access should be supported. In addition, as a step towards interference control, FR should be supported. At the same time, in order to accommodate heterogeneity in regulations between different regions, both TDD and FDD duplexing schemes should be supported as well, including half and full duplex FDD.
In order to abide by these requirements while achieving the promised levels of performance, LTE-Advanced as well as WiMAX resort to multicarrier techniques. In particular, three techniques are used, namely OFDM, SC-FDMA, and OFDMA. While WiMAX uses OFDMA in both the uplink and the downlink, LTE-Advanced uses OFDMA for the downlink only while using SC-FDMA uplink.
An advantage of multi-carrier access techniques is their robust communication and stable interference management. In fact, multicarrier techniques facilitate fractional FR which will be discussed in subsequent sections. In addition, they also allows exploiting multiuser diversity at smaller granularities than was ever possible in CDMA-based networks. Another advantage of multicarrier techniques is enhancing system throughput by mitigating the frequency-selective randomness, that is, frequency selective fading. This enhancement is achieved by modulating orthogonal ...
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