Scalable Orthogonal Frequency Division Multiple Access (SOFDMA or S-OFDMA)

Larger FFT size is provided to wider channels, while smaller FFT size to lower bandwidth channels. SOFDMA makes the sub-carrier frequency spacing constant, which lowers the system complexity of smaller channels and also enhances the efficiency of wider channels.

Basic principles of SOFDMA

• The sub-carrier spacing does not depend on bandwidth
• The volume of sub-carriers scales with bandwidth
• The smallest unit of bandwidth allocation, depending on the idea of sub-channels, is fixed and bandwidth independent
• The volume of sub-channels scales with bandwidth, and the ability of every individual sub-channel remains constant

As well as variable FFT sizes, SOFDMA supports the following features:

• Advanced Modulation and Coding (AMC)
• Multiple-Input-Multiple-Output (MIMO) in DL and UL
• High-efficiency uplink sub-channel structures
• Hybrid Automatic Repeat Request (H-ARQ)
  
• Other default features including a range of sub-carriers allocation in addition to diversity schemes.

Spectral efficiency, and combating Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI) are two major benefits of SOFDMA, while requirement for strict synchronization and Peak-to-Average Power Ratio (PAPR) are two disadvantages.