Thus each tap h can be modeled as a sample value of a random variable H which is the sum of a large number of small complex random variables each of uniformly distributed phase.By根据中心极限定理，be be modeled symmetric complex Gaussian.rv.'s-CN(O,o).这样，Hx的幅度R=Ha|是服从 Rayleigh分布的随机变量： Px(r)= r2】 r20 (7.11) 这个模型描述的信道即为Rayleigh衰落信道。The squared magnitude is exponentially distributed with density exp r20 (this is the power distribution.) Note that the word Rayleigh is almost universally used for this model,but the assumption is that the tap gains are circularly symmetric complex Gaussian random variables. ●Rician fadin When the line of sight(LOS)path (often called a specular path)is large and has a known magnitude,and there are also a large number of independent paths,theat least for one value ofl,can be modeled as 1 Cv(0) (7.12) with the first term corresponding to the specular path arriving with uniform phase 6 and the second term corresponding to the aggregation of the large number of reflected and scattered paths,independent of The parameter k(so-called K-factor)is the ratio of the energy in the ehin thd ths the arger the mor eteminsi is the The of such a random variable is said to have a Rician distribution.Its density has the form as (7.13) where is the average power in the non-LOS mulipath component and s2=is the power in the LOS component./o()is the zero order modified Bessel function of the first kind. The parameter k in (7.12)is then given by 11 11 Thus each tap hl,k can be modeled as a sample value of a random variable Hl,k which is the sum of a large number of small complex random variables each of uniformly distributed phase. By 根据中心极限定理，it can be easily shown that Hl,k can be modeled as circularly symmetric complex Gaussian r.v.’s 2 (0, )    l . 这样，Hl,k的幅度 , | | R H  l k 是服从 Rayleigh分布的随机变量： 2 2 2 ( ) exp , 0 2 R l l r r pr r           (7.11) 这个模型描述的信道即为 Rayleigh 衰落信道。 The squared magnitude 2 , | | l k h is exponentially distributed with density 2 2 1 exp , 0 l l r r           (this is the power distribution.) Note that the word Rayleigh is almost universally used for this model, but the assumption is that the tap gains are circularly symmetric complex Gaussian random variables.  Rician fading When the line of sight (LOS) path (often called a specular path) is large and has a known magnitude, and there are also a large number of independent paths, the l k, h , at least for one value of l, can be modeled as   1 2 ( ) 0, 1 1 j ll l hm e            (7.12) with the first term corresponding to the specular path arriving with uniform phase  and the second term corresponding to the aggregation of the large number of reflected and scattered paths, independent of . The parameter k (so-called K-factor) is the ratio of the energy in the specular path to the energy in the scattered paths; the larger k is, the more deterministic is the channel. The magnitude of such a random variable is said to have a Rician distribution. Its density has the form as 2 2 2 22 0 ( ) exp , 0 2 R l ll r r s rs pr I r               (7.13) where 2 2 0 2 [] n n  E     is the average power in the non-LOS multipath component and 2 2 0 s   is the power in the LOS component. I0(.) is the zero order modified Bessel function of the first kind. The parameter k in (7.12) is then given by