基于大规模天线的多用户MISO下行链路频谱效率分析

Analysis of spectral efficiency of multiuser MISO downlink based on large-scale antennas

在大规模天线时分双工通信系统中,分析了多用户MISO下行链路的频谱效率。假定用户数固定且基站天线数M无限增大,通过理论推导分析发现,当基站发送功率减小到单天线基站的1/M时,随着M的增加系统频谱效率趋于一个恒值;并且简单的预处理即可消除用户间干扰和快衰落的影响。虽然多小区系统会受导频污染的影响,致使小区间干扰不能被完全消除,但是降低后的发送功率可使系统由干扰受限转变为噪声受限。采用迫零单位预编码与采用最大比发送单位预编码的系统频谱效率极限表达式相同。最后给出采用空时分组码的多用户下行链路的频谱效率下限值,并通过仿真分析证实了以上结论的正确性。

The spectral efficiency of the downlink of multi-user multiple-input and single-output （MU-MISO） was ana- lyzed in the time-division duplex （TDD） communication systems with large-scale antennas. Assuming that the number of users was fixed and the antenna number （M） of base station （BS） increases without limit, the conclusions through theo- retical derivations and analyses were drawn that, when the transmit power of the BS reduces to 1/M of that of BS with single antenna, the system spectral efficiency tends to a constant value with the increase of M if the BS acquires the per- fect channel state information （CSI）. The adverse effects of the inter-user interferences and the fast fading could also be eliminated through simple pre-processings. Although the multicell system is affected by the pilot contamination, which is the reason why the inter-cell interferences cannot be eliminated, the reduced transmit power makes the system changed from interference-limited to noise-limited. The limit expression of the system spectral efficiency using zero-forcing （ZF） normalized precoding is equal to that using maximum ratio transmission （MRT） normalized precoding. Finally, the lower bound of the spectral efficiency of multi-user downlink applying space time block code was presented and the correctness of the above conclusions was confirmed by the simulation analyses.