Multiple carrier frequency offsets exist in the orthogonal frequency-division multiple access (OFDMA) uplink receivers, and consequently induce inter-carrier interference and multiple-access interferences simultaneously. We therefore propose a joint carrier frequency offset (CFO) and channel estimation scheme by leveraging the characteristic of transmission signals in the OFDMA uplink systems. A fully loaded assignment of subcarriers to active users is also supported by the proposed method. By modeling the system in a Hadamard product form, we develop an iterative algorithm wherein a closed-form estimate of CFO and channel is applied in each updating iteration. Different from the traditional expectation-maximization type methods, which update only a single CFO and channel of one user while keeping the other users’ CFOs and channels constant in each iteration, our proposed scheme updates the CFOs and channels of all active users simultaneously. Therefore, the proposed CFO and channel estimator enjoys faster convergence and lower complexity. Through numerical results, the proposed scheme is demonstrated to be robust to large CFOs and perform comparably well to the conventional approaches.

正交频分多址（OFDMA）上行链路接收机中存在多个载波频偏，因此会同时引起载波间干扰和多址干扰。因此，我们通过利用OFDMA上行链路系统中传输信号的特性，提出了一种联合载波频率偏移（CFO）和信道估计方案。所提出的方法还支持将副载波的满载分配给活动用户。通过以Hadamard产品形式对系统进行建模，我们开发了一种迭代算法，其中在每次更新迭代中均采用了CFO和渠道的闭式估计。与传统的期望最大化类型方法不同，该方案仅更新一个用户的单个CFO和渠道，而在每次迭代中保持其他用户的CFO和渠道不变，因此，我们提出的方案可同时更新所有活动用户的CFO和渠道。因此，所提出的CFO和信道估计器具有更快的收敛性和更低的复杂度。通过数值结果，证明了该方案对大型CFO具有鲁棒性，并且与常规方法相比性能良好。