Adaptive pilot distribution for OFDM systems in time-variant channels
Adaptive pilot distribution for OFDM systems in time-variant channels
复制标题
时变信道中 OFDM 系统的自适应导频分配
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
A. Omar
中科院分区：
文献类型：
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作者：
Ali Ramadan;A. Balalem;Tariq Jamil Khanzada;Jan Machac;A. Omar
研究了时变环境下基于ofdm的无线局域网系统。使用最大延迟扩展为550ns的4-抽头和2-抽头通道。使用未编码的QPSK符号，并假设完全同步。一个更现实的假设是让通道的变化水平在快速和非常缓慢之间变化。自适应导频系统选择了6个多普勒频散阈值。图2中的仿真结果显示，当信道是静态或缓慢变化时，比特率会增加。而在快速变化的情况下，比特率下降到传统的（24 Mbps）。在图2中，比特率每500个符号被平均。结果表明，自适应方法提高了系统的总容量。对于缓慢变化和静态信道，吞吐量的增益是明显的。我们注意到，通过选择合适的阈值水平，自适应系统的误码率性能与传统系统相当。
An OFDM-based WLAN system in time-variant environment has been considered. 4-tap and 2-tap channels with a maximum delay spread of 550ns were used. Uncoded QPSK symbols were used and perfect synchronization was assumed. A more realistic assumption is to let the level of variation of the channel changes between fast and very slow. Six threshold levels of the Doppler spread have been chosen for the adaptive pilot arrangement. The simulation results in Fig. 2 show an increase in the bit rate when the channel is static or slowly varying. Whereas in the rapidly varying cases the bit rate falls down to the conventional one (24 Mbps). In Fig. 2 the bit rate has been averaged every 500 symbols. It was shown that the adaptive method increases the total capacity of the system. The gain in the throughput is noticeable for slow varying and static channels. We noticed that, by choosing proper threshold levels, the adaptive system is comparable in the BER performance with the conventional one.