| 查看: 132 | 回复: 0 | |||
| 当前主题已经存档。 | |||
zzgyb荣誉版主 (文坛精英)
小木虫警察局局长
|
[交流]
【转贴】A Mathematical Theory of Communication
|
||
|
T HE recent development of various methods of modulation such as PCM and PPM which exchange bandwidth for signal-to-noise ratio has intensified the interest in a general theory of communication.A basis for such a theory is contained in the important papers of Nyquist1 and Hartley2 on this subject.In the present paper we will extend the theory to include a number of new factors,in particular the effect of noise in the channel,and the savings possible due to the statistical structure of the original message and due to the nature of the final destination of the information. The fundamental problem of communication is that of reproducing at one point either exactly or ap- proximately a message selected at another point.Frequently the messages have meaning;that is they refer to or are correlated according to some system with certain physical or conceptual entities.These semantic aspects of communication are irrelevant to the engineering problem.The significant aspect is that the actual message is one selected from a set of possible messages.The system must be designed to operate for each possible selection,not just the one which will actually be chosen since this is unknown at the time of design. If the number of messages in the set is finite then this number or any monotonic function of this number can be regarded as a measure of the information produced when one message is chosen from the set,all choices being equally likely.As was pointed out by Hartley the most natural choice is the logarithmic function.Although this definition must be generalized considerably when we consider the influence of the statistics of the message and when we have a continuous range of messages,we will in all cases use an essentially logarithmic measure. The logarithmic measure is more convenient for various reasons: 1.It is practically more useful.Parameters of engineering importance such as time,bandwidth,number of relays,etc.,tend to vary linearly with the logarithm of the number of possibilities.For example, adding one relay to a group doubles the number of possible states of the relays.It adds 1 to the base 2 logarithm of this number.Doubling the time roughly squares the number of possible messages,or doubles the logarithm,etc. 2.It is nearer to our intuitive feeling as to the proper measure.This is closely related to(1)since we in- tuitively measures entities by linear comparison with common standards.One feels,for example,that two punched cards should have twice the capacity of one for information storage,and two identical channels twice the capacity of one for transmitting information. 3.It is mathematically more suitable.Many of the limiting operations are simple in terms of the loga- rithm but would require clumsy restatement in terms of the number of possibilities. [ Last edited by laizuliang on 2007-9-29 at 07:07 ] |
回复此楼» 猜你喜欢
研究生做的很差，你们会让毕业吗？
已经有9人回复
-
求碳排放博导；方向是LCA、生命周期可持续发展以及碳排放
已经有7人回复
-
2026博士申请求助
已经有4人回复
-
2026博士或科研助理转27年博士
已经有7人回复
-
急招2026年9月份入学博士
已经有3人回复
-
26申博
已经有3人回复
-
申博自荐
已经有7人回复
-
26年博士申请自荐-电催化
已经有7人回复
-
2026年博士申请求捞
已经有3人回复
-
国自科送审了吗
已经有11人回复
