In OFDMA system, each user has its own time offset and CFO (carrier-frequency offset), so the synchronization has became a multiple-parameter estimation problem, and the compensation of time offset and CFO has also became more difficult.

• 因为在OFDMA系统当中，叠加在一起的不同用户的信号具有不同的符号定时偏移和载波频率偏移，这样同步估计问题就由原来的单参数估计演变为多参数估计，同时同步估计结果的补偿也变的更加困难。