Downlink transmission of broadband OFCDM Systems-part II: effect of Doppler shift
Downlink transmission of broadband OFCDM Systems-part II: effect of Doppler shift
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DOI：
10.1109/tcomm.2006.876872
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发表时间：
2006-06
影响因子：
8.3
通讯作者：
Yiqing Zhou;Jiangzhou Wang;M. Sawahashi
中科院分区：
文献类型：
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作者：
Yiqing Zhou;Jiangzhou Wang;M. Sawahashi
具有二维扩频（时域和频域扩频）的正交频分码分复用（OFCDM）系统正成为未来宽带无线通信系统的一种有希望的候选方案。OFCDM比正交频分复用（OFDM）更有吸引力，因为它引入了频域扩展以提供频率分集和时域扩展以提供灵活的数据速率。为了提供高速移动的业务，多码传输与OFCDM结合使用。在高斯或平坦衰落信道中，多码信道是正交的。然而，在现实的无线信道中，正交性不再保持。因此，造成多码干扰（MCI）。研究了多普勒频移对高速移动的OFCDM系统下行链路传输的影响。提出了一种基于码复用导频信道的信道估计算法，用于跟踪衰落信道的变化。本文提出了一种在频域消除MCI的有效方法，即混合MCI消除和最小均方误差（MMSE）检测。分析了在信道估计不理想的情况下，信道估计窗口大小、多普勒频移、混合检测级数、导频信道与数据信道的功率比、扩频因子等参数对系统性能的影响
The orthogonal frequency and code division multiplexing (OFCDM) system with 2-D spreading (time- and frequency-domain spreading) is becoming a promising candidate for future broadband wireless communication systems. OFCDM is more attractive than orthogonal frequency-division multiplexing (OFDM) both by introducing frequency-domain spreading for frequency diversity provision and time-domain spreading for flexible data rate provision. To provide high-speed mobile services, multicode transmission is employed in conjunction with OFCDM. In a Gaussian or flat-fading channel, multicode channels are orthogonal. However, in a realistic wireless channel, the orthogonality no longer maintains. Thus, multicode interference (MCI) is caused. This paper focuses on the investigation of the effect of Doppler shift on the downlink transmission of high-speed mobile OFCDM systems. A practical channel estimation algorithm based on a code-multiplexed pilot channel is employed to track the variations of fading channels. Hybrid MCI cancellation and minimum mean-square error (MMSE) detection proposed by the authors is employed as an efficient way to eliminate the MCI in the frequency domain. The system performance is analytically studied with imperfect channel estimation to show how it is affected by parameters such as the window size in the channel estimation, Doppler shift, the number of stages of the hybrid detection, the power ratio of pilot to data channels, spreading factor, and so on