有人懂相位旋转吗？帮解答一下

对抗幅度噪声性能更好？ 瞎猜的

【 在 Dave 的大作中提到: 】 : 对抗幅度噪声性能更好？ : 瞎猜的 汗！

An alternate way to attain diversity is to build in the diversity into the modulation. This idea is illustrated in Fig. 15. On the left is the usual QPSK modulation and on the right is a rotated QPSK modulation. Suppose we transmit information on the real and imaginary parts through independent fading channels. Then, we can view the transmission as being over two independent channels and the maximal diversity order attainable is 2. According to the criterion developed in Section III-C, the uncoded transmission would obtain diversity order dependent on whether the codewords (in this case we have four codewords) are different in each of the dimensions. Clearly, the unrotated modulation has a built-in diversity of 1 whereas the rotated modulation in Fig. 15 has a diversity of 2. This basic idea was proposed in [42], [158] and developed for higher dimensional lattices in [43] and references therein. Therefore, one can construct modulation schemes with built-in diversity, with the caveat that the constellation size is actually increasing. This is because the projections of the constellation points are now distinct and, therefore, the modulation scheme has to deal with a larger number of transmit levels. The main point to note here is that the Theorem 3.9 refers to rate versus diversity tradeoff for a given constellation size. Therefore, in order to consider the efficiency of coding schemes based on the rotated constellations, one needs to take into account the expansion in the constellation size. For example, transmit diversity using such rotated constellations is described in [77] and [91] and space–time codes designed using rotated constellations are given in [75].

Great Expectations: The Value of Spatial Diversity in Wireless Networks 【 在 Dave 的大作中提到: 】 : An alternate way to attain diversity is to build in the diversity : into the modulation. This idea is illustrated in Fig. 15. On : the left is the usual QPSK modulation and on the right is a : ...................

好像有些序列靠这个来获得正交特性吧。