A frequency offset compensation method for OFDM-FDMA, that can correct offsets after the DFT via circular convolution, is proposed as an alternative to the direct method that corrects frequency offsets by multiplying the complex exponents of the offset estimates before the DFT. In contrast to the direct method whose complexity increases proportional to the number of users, the computational load of the proposed scheme decreases as the number of users increases. It is shown that the proposed method is simpler to implement than the direct method when the number of users is greater than two. Furthermore, the former can outperform the latter, because a frequency offset compensation for one user after the DFT does not affect the data of other users. Computer simulation results demonstrate the advantage of the proposed method.

The 10-Gigabit Ethernet (10GbE) is emerging as an alternative for solving the bottleneck of wide area network (WAN) links. Currently, the choice of line codes is being an issue in the 10GbE standardization. We review the candidates for the 10GbE line code, and propose a new line code, MB810, for 10GbE. Its spectrum is bounded within the Nyquist band and has no DC component. This code can improve the transmission rate-distance limitation of the optical fiber. We describe the design concept of the MB810 and its design procedure, and compare its characteristics with the NRZ and 8B/10B codes.