Editing 4G (section)

=== Multiplexing and access schemes ===
{{Importance section|date=May 2010}}
Recently, new access schemes like [[OFDMA|Orthogonal FDMA]] (OFDMA), [[SC-FDMA|Single Carrier FDMA]] (SC-FDMA), Interleaved FDMA, and [[Multi-carrier code-division multiple access|Multi-carrier CDMA]] (MC-CDMA) are gaining more importance for the next generation systems. These are based on efficient [[Fast Fourier transform|FFT]] algorithms and frequency domain equalization, resulting in a lower number of multiplications per second. They also make it possible to control the bandwidth and form the spectrum in a flexible way. However, they require advanced dynamic channel allocation and adaptive traffic scheduling.

[[WiMax]] is using OFDMA in the downlink and in the uplink. For the [[LTE (telecommunication)]], OFDMA is used for the downlink; by contrast, [[Single-carrier FDMA]] is used for the uplink since OFDMA contributes more to the [[Crest factor|PAPR]] related issues and results in nonlinear operation of amplifiers. IFDMA provides less power fluctuation and thus requires energy-inefficient linear amplifiers. Similarly, MC-CDMA is in the proposal for the [[802.20|IEEE 802.20]] standard. These access schemes offer the same efficiencies as older technologies like CDMA. Apart from this, scalability and higher data rates can be achieved.

The other important advantage of the above-mentioned access techniques is that they require less complexity for equalization at the receiver. This is an added advantage especially in the [[MIMO]] environments since the [[spatial multiplexing]] transmission of MIMO systems inherently require high complexity equalization at the receiver.

In addition to improvements in these multiplexing systems, improved [[modulation]] techniques are being used. Whereas earlier standards largely used [[Phase-shift keying]], more efficient systems such as 64[[QAM]] are being proposed for use with the [[3GPP Long Term Evolution]] standards.