0122229现代数字通信与编码理论 September 1,2010 XDU.Fall 2010 Lecture notes Introduction Digital communication is a field in which theoretical ideas have had an unusually powerful impact on actual system design.The basis of the theory was developed 58 vears ago by Claude Shannon,and is called information theory.The goal of this course is to get acquainted with some of these ideas and to gain deep understanding on how to efficiently and reliably communicate through a channel,especially to better understand the advanced techniques for signal transmission and coding used in modern digital communication systems.We will focus on point-to-point systems consisting of a single transmitter,a channel and a receiver A.Block diag the ne Laboratorie oublished one of the V0827 423 and pp 623-656)laid the p.3793 scientific discinl digital communication system. Channel encoder 信源 信源编码器 CC编码器数字调制器 调制信道 信宿 信源译码器 CC译码器， 数字解调器 bits symbols waveform The source encoder involves the efficient representation of source signals.It has the function of converting the input from its original form,e.g.,speech waveforms,image waveforms,and text,into a sequence of bits.The objective of doing this is as efficiently as possible.i.e.,transmitting as few bits as possible,subject to the need to reconstruct the input adequately at the output.In this case source encoding is often ca ed data compression. Shannon s that t compres entropy of the source The chan box in the figure ab of mapping the binary sequ nne efor might t discrete seque o map at the bit rat ate th pp erfo is called tion etric oint,the modulation process may be thought of a two-step ocess:first mappir g 7 0122229 现代数字通信与编码理论 September 1, 2010 XDU, Fall 2010 Lecture Notes Introduction Digital communication is a field in which theoretical ideas have had an unusually powerful impact on actual system design. The basis of the theory was developed 58 years ago by Claude Shannon, and is called information theory. The goal of this course is to get acquainted with some of these ideas and to gain deep understanding on how to efficiently and reliably communicate through a channel, especially to better understand the advanced techniques for signal transmission and coding used in modern digital communication systems. We will focus on point-to-point systems consisting of a single transmitter, a channel and a receiver. A. Block diagram of a digital communication system In 1948, Claude E. Shannon of the Bell Telephone Laboratories published one of the most remarkable papers in the history of engineering. This paper (“A Mathematical Theory of Communication", Bell System Tech. Journal, Vol. 27, July and October 1948, pp. 379 - 423 and pp. 623 - 656) laid the groundwork of an entirely new scientific discipline, “information theory", in which Shannon first introduced the following figure to model a digital communication system. The source encoder involves the efficient representation of source signals. It has the function of converting the input from its original form, e.g., speech waveforms, image waveforms, and text, into a sequence of bits. The objective of doing this is as efficiently as possible. i.e., transmitting as few bits as possible, subject to the need to reconstruct the input adequately at the output. In this case source encoding is often called data compression. Shannon showed that the ultimate data compression is the entropy of the source. The channel encoder box in the figure above has the function of mapping the binary sequence at the source/channel interface into channel inputs. The channel inputs might be waveforms, or might be discrete sequences. The general objective here is to map binary inputs at the maximum bit rate possible into waveforms or sequences such that the channel decoder can recreate the original bits with low probability of error. One simple approach to performing this is called modulation and demodulation. From the geometric signal-space viewpoint, the modulation process may be thought of a two-step process: first mapping 信源 信源编码器 ECC 编码器 数字调制器 信 道 干 扰 信宿 信源译码器 ECC 译码器 数字解调器 调制信道 Channel decoder n(t) bits Channel encoder symbols waveform