Multi-User MMSE-Based Frequency Synchronization in OFDMA Uplink

One of the key ideas in this paper is to merge frequency offset compensation into the FFT matrix. The new inverse transform matrix is used in lieu of regular FFT. In uplink of OFDMA, different users (subcarriers) may have different frequency offsets, which causes severe performance degradation. It is also difficult to estimate/compensate these frequency offsets in uplink case. Even if the frequency offsets are correctly estimated, the compensation of one subcarrier (or user) may worsen the inter-carrier interference from the frequency offsets of other subcarriers (users). A single MMSE-based transform is used to perform both inverse Fourier transform and frequency offset compensation. Compared to the conventional methods such as circular convolution, this approach has lower computational complexity with comparable performance.