中文摘要：

多用户分集是多用户无线通信中固有的分集，而它受制于用户信道的动态范围，为此可通过随机波束形成技术（OBF）来增大信道变化的动态范围，从而提高多用户分集。本文中我们讨论了现有的几种随机波束形成方案：传统的随机波束形成，多权重随机波束形成，基于信道记忆的随机波束形成和更为简单的随机相位波束形成。在此基础上，也得出基于记忆和多权重的随机相位波束形成，并通过仿真比较其和常规OBF的性能。

英文摘要：

Multiuser diversity is an inherent diversity form in wireless communication network, but it is limited by the dynamic range of the users＇ channel fluctuations. Opportunistic beamforming （OBF） can induce large and fast channel fluctuations and thus increase the multiuser diversity. In this paper, some existing opportunistic beamforming schemes, such as OBF, OBF based on multiple weighting vectors, memory-based OBF, and opportunistic cophasing （OC）, etc., are introduced. Newly schemes, OC based on multiple weighting vectors and memory, are purposed and compared with the existing schemes via computer simulations.