信息论与编码 曹雪虹 张宗橙 清华大学出版社 课

x3x4x5x6x7 X x1x2

5.1设信源 = 0.20.190.180.170.150.10.01 ()PX

(1)求信源熵H(X)；

(2)编二进制香农码；

(3)计算平均码长和编码效率。

解：(1)

H(X)= ∑p(xi)log2p(xi)

i=

1

7

= (0.2×log20.2+0.19×log20.19+0.18×log20.18+0.17×log20.17+0.15×log20.15+0.1×log20.1+0.01×log20.01)=2.609bit/symbol

K=∑kip(xi)=3×0.2+3×0.19+3×0.18+3×0.17+3×0.15+4×0.1+7×0.01

i

=3.14

η=

H(X)H(X)2.609

===83.1%R3.14K

x3x4x5x6x7 X x1x2

5.2对信源 =

0.20.190.180.170.150.10.01 编二进制费诺码，计算编码效率。PX()

=∑kip(xi)=2×0.2+3×0.19+3×0.18+2×0.17+3×0.15+4×0.1+4×0.01

i

=2.74

H(X)H(X)2.609η====95.2%

R2.74K