Research and Analysis of Digital Baseband Transmission System Based on MATLAB

Transcription

1 Journal of Secure Communication and Sytem (017) Original Reearch Article Reearch and Analyi of Digital Baeband ranmiion Sytem Baed on MALAB Jianwen Chai,Yinghui Nie Phyic and Electronic Intitute, Hanzhong Univerity, Shaanxi, China ABSRAC hi paper mainly tudie the baic concept of baeband tranmiion of digital ignal and the tranmiion proce of digital ignal baeband tranmiion and how to deign digital baeband tranmiion ytem with MALAB oftware imulation. hi paper firt introduce the theoretical bai of thi ubject, including digital communication, the compoition of digital baeband tranmiion ytem and digital baeband ignal tranmiion proce. hen the paper introduced the characteritic of digital baeband tranmiion ytem, including digital PAM ignal power denity and common line pattern, and by comparing chooing the final bipolar zero return code. hen we introduced the MALAB imulation oftware. he condition of the bet reception of the digital baeband ignal are decribed and how the waveform of the baeband ignal i oberved by an ocillocope. Finally, according to the baic tep of imulation proce, the imulation proce of digital baeband tranmiion ytem i realized by MALAB imulation tool, and the ytem i analyzed. KEYWORDS: digital baeband tranmiion ytem MALAB computer imulation Citation: Chai JW and Nie YH. Reearch and Analyi of Digital Baeband ranmiion Sytem Baed on MALAB, Journal of Secure Communication and Sytem (017); 1(1): *Correpondence to: Jianwen Chai, Phyic and Electronic Intitute, Hanzhong Univerity, Shaanxi, China, herohere@ gmail.com. 1. Introduction Compared with analog communication, digital communication ha many excellent feature, it main drawback i that the equipment i complex and require a larger tranmiion bandwidth. In recent year, with the advent of large cale integrated circuit, the complexity and technical difficulty of digital ytem have been greatly reduced, and the ue of high-capacity tranmiion media uch a efficient tranmiion compreion technology and fiber i gradually becoming a olution to the bandwidth problem. A a reult, digital tranmiion i gaining popularity. Communication principle computer imulation experiment, i the imulation of digital baeband tranmiion ytem. he imulation tool i MALAB programming language. MALAB i an advanced high-tech programming language, mainly ued for numerical calculation and viual graphic proceing. It i characterized a high efficient programming tool, integrating numerou function uch a numerical analyi, matrix computing, graphic, image proceing and imulation into an extremely interactive environment of peudo-cientific reearch, engineering deign, and many dicipline. Uing MALAB, digital baeband tranmiion ytem can be more comprehenively tudied. In order to make the undergraduate tudent learn communication coure, through the coure deign we conducted a pilot imulation of the content of the coure of communication principle.. ext.1. Digital baeband tranmiion ytem he flexibility of digital proceing make digital information tranmitted in a digital tranmiion ytem either from variou digital code uch a computer, televiion and other data terminal, or from digitally proceed pulecode modulation (PCM) ignal from analog ignal. In principle, the digital information can be directly expreed and tranmitted in digital code equence, but in the actual tranmiion, depending on the ytem requirement and channel condition, generally need different way of coding and the ue of a et of limited dicrete waveform. hee dicrete Copyright 017 Chai JW and Nie YH. hi i an Open Acce article ditributed under the term of the Creative Common Attribution- NonCommercial 4.0 International Licene ( permitting all non-commercial ue, ditribution, and reproduction in any medium, provided the original work i properly cited. 37

2 Reearch and Analyi of Digital Baeband ranmiion Sytem Baed on MALAB waveform may be unmodulated electrical ignal or modulated ignal. he pectrum occupied by the unmodulated digital ignal tart from zero or very low frequency and i called a digital baeband ignal. In ome wired channel with low pa characteritic, the baeband ignal can be tranmitted directly without carrier modulation, epecially if the tranmiion ditance i not too far. For example, bae pule are tranmitted directly in the computer' local area network. hi ytem, which doe not directly tranmit digital baeband ignal without carrier modulation, i called a digital baeband tranmiion ytem. And the tranmiion ytem including the modulation and mediation proce i called a digital bandpa (or band) tranmiion ytem. At preent, although the digital baeband tranmiion ytem i not a widely ued a bandpa tranmiion, but it i till meaningful for the reearch of baeband tranmiion ytem. hi i becaue, firtly, ymmetrical cable contituting hort-range data communication ytem i till widely ued in thi tranmiion. Secondly, with the development of digital communication technology, baeband tranmiion ha a rapid development trend, not only for low-peed data tranmiion, but alo for high-peed data tranmiion. hirdly, the baeband tranmiion contain many baic problem of band-pa tranmiion, that i, many problem of baeband tranmiion ytem i alo problem to be conidered in band-pa tranmiion ytem. Latly, theoretically it can be proved that any one of the band-pa tranmiion ytem with linear modulation can be equivalent to a tudy of baeband tranmiion ytem. he digital baeband tranmiion ytem model hown in Figure 1-1, which mainly include the code converter, end filter, channel, receive filter, equalizer/ampling deciion and other part. Figure 1. Digital baeband tranmiion ytem model In hort, the information of the ource i tranmitted from the ender through the channel to the receiver at the receiving end in the form of a digital baeband ignal. he ytem i called a digital baeband tranmiion ytem. 1) Channel ignal generator (tranmiion filter) It function i to generate a baeband ignal waveform uitable for channel tranmiion. Becaue the input ignal i uually generated by the code encoder tranmiion code, the correponding baic waveform i uually a rectangular pule with a wide pectrum. hi i not conducive to tranmiion, hence the tranmiion filter i ued to compre the input ignal band, converting the input code into appropriate baeband ignal waveform to tranmit over the channel. ) Channel A channel i a medium that allow baeband ignal to pa through, typically wired channel uch a twited pair, coaxial cable and many more. he tranmiion characteritic of the channel are generally not atifying nonditorted tranmiion condition and contain additive noie (tn, which can caue the tranmiion waveform ditortion.) he digital baeband tranmiion ytem tudied in thi paper adopt the zero mean white Gauian noie channel, i.e AWGN channel. 3) Receiving filter It i ued to receive the ignal, a far a poible to filter out channel noie and other interference, and counter balance the channel, o that the output of the baeband waveform i conducive to for ampling deciion. 4) Sampling decider he ampling decider ample output waveform of the receiving filter at a predetermined time (controlled by the bit timing pule). When the background of the tranmiion characteritic i not ideal with noie background, it decide to recover or reproduce the baeband ignal. 5) iming pule and ynchronou extraction he timing pule ued for ampling i extracted from the received ignal by the ynchronou extraction circuit. he accuracy of the bit timing pule will directly affect the deciion reult. 38

3 Chai JW and Nie YH.. Digital baeband ignal..1 Baic baeband ignal waveform he digital baeband ignal i an electrical repreentation of digital information, which can repreent the correponding meage code with a different level or pule. here are many type of digital baeband ignal. Here are ome baic baeband ignal waveform. (1) Unipolar waveform hi i one of the implet baeband ignal waveform. It correpond to the binary code '1' and '0', repectively, with poitive and zero level, or '1' and '0' with pule, preent or abent in one ymbol time. he waveform i characterized by no gap between the electrical pule, the polarity i ingular, eay-to-ue L and CMOS circuit generated. he diadvantage are it i a DC component and requiring tranmiion line with DC tranmiion capacity, which i not uitable for AC coupling long-ditance tranmiion. It i only uitable for internal or very cloe tranmiion of the computer. () Bipolar waveform It denote the '1' and '0' of the binary code with poitive and negative pule, repectively. Since the magnitude of the poitive and negative level i equal and the polarity i oppoite, when there i no tributary component uch a '1' and '0', it i advantageou to tranmit in the channel and the deciion level of the recovery ignal at the receiving end i zero in value, which i not affected by change in channel characteritic. It anti-interference ability i alo trong. (3) Unipolar zero return waveform he o-called zero return waveform i it electrical pule width i le than the ymbol width, that i, the ignal voltage in a ymbol before the end of time alway return to zero level. In general, the zero-hift waveform ue the half-occupied code, that i, the duty ratio ( / ) of 50%. he non-polar RZ waveform can directly extract the timing information, which i a tranition waveform that i often ued by other code extraction bit ynchronization information. Correponding to the zero return waveform, the above unipolar waveform and bipolar waveform are non-return to zero waveform, it duty ratio, / i 100%. (4) Bipolar zero return waveform It i a zero-form of bipolar waveform. It ha both bipolar and zeroed waveform. Becaue there i a zero potential interval between adjacent pule, it i eay for the receiver to recognize the tart and end of each ymbol, o that both partie can keep the correct ynchronization. (5) Differential waveform hi waveform i repreented by the tranition of the level of adjacent ymbol and the invariant repreentation of the meage code, irrepective of the potential or polarity of the ymbol itelf. Since the differential waveform i repreented by the relative change of the adjacent pule level, it i alo called the relative code waveform, and the correponding unipolar or bipolar waveform i the abolute code waveform. he ue of differential waveform to tranfer code can eliminate the impact of the initial tate of the device, epecially in the correponding modulation ytem can be ued to olve the carrier phae blurring problem. (6) Multi-level waveform here are only two level of the above waveform, that i, a binary relative code correpond to a pule. In order to improve the band utilization, multi-level waveform or multi-value waveform can be ued. Since a pule of multilevel waveform correpond to multiple binary code, the bit rate i improved under the ame baud rate, o multi-level waveform i widely ued in high-peed data tranmiion ytem with limited band... Common pattern for baeband tranmiion (1) AMI code he full name of the AMI code i Alternate Mark Inverion code. Encoding rule: he '1' code in the ymbol equence i changed to the tranmiion code + 1, -1, + 1, -1,... which are alternately changed in polarity, and the '0' code in the ymbol equence remain unchanged. E.g: Meage code: AMI code:

4 Reearch and Analyi of Digital Baeband ranmiion Sytem Baed on MALAB AMI code correponding to the waveform i a poitive, negative, zero three level of pule equence. It can be een a a ingle-pole waveform ditortion, that i, '0' till correpond to zero level, and '1' alternately correpond to poitive and negative level. Advantage: No DC component. It low frequency and high frequency component are leer, energy concentrated at the frequency of 1/ peed. Codec circuit i imple, and can ue the polarity of the exchange of the law to oberve the error ituation. If it i AMI-RZ waveform, a long a the full-wave undergoe rectification, it can become a unipolar RZ waveform, from which can be extracted timed component. Diadvantage: When the ymbol equence appear long with '0', the ignal level doe not jump for a long time, cauing timed ignal extraction difficultie. () HDB3 code HDB3 code full name i the High Denity Bipolar Order 3 code. It i to overcome the tranmiion waveform appear in the long '0' code cae deigned to improve the AMI code. (1) Check the number of '0' in the meage code. When the number of '0' i le than or equal to 3, HDB3 code and AMI code the ame. () if there are four or more '0' in a tring, then form every 4 with '0' into a ection, defined a B00V, known a the broken ection, where V i called the damage pule, and B the regulation pule. (3) V i the ame a the previou non-'0' pule polarity, and the polarity between adjacent V code mut be alternated. V ha a value of +1 or -1. (4) he value of B i optional 0, + 1, -1, o that V atifie both of the two requirement in (3) at the ame time. (5) Paport polarity behind the V code hould alo be alternating. E.g: Meage code: AMI code: HDB3 code: V V B 0 0 V +B 0 0 +V -1 Where the pule and pule are the ame a the pule waveform, and the purpoe of the V or B ymbol i to indicate that the nonzero code i tranformed from the '0' of the original code. HDB3 code coding rule, although are more complex, the decoding i relatively imple. A can be een from the coding proce, each V code i alway the ame a it previou non-zero code (including B code). Hence from the received code equence we can eaily find the damage point V code, o the V code and it firt three code are '0' code. We then ubtitute all the -1 into +1, the original information code can be retored. HDB3 code i obviou, making it to be able to retain the AMI code without DC component, to facilitate direct tranmiion, alo overcome the long tring 0 (even the number of 0 up to 3). HDB3 code pectrum eliminate DC and very low frequency component, at the ame time eliminate the high frequency component in the quare wave, making it very uitable for baeband tranmiion ytem. herefore, HDB3 code i currently the mot widely ued in the actual ytem code. Although the HDB3 code i better than the AMI code, it till belong to the 1B1 pattern. (3) Dual phae code Dual code i alo called Mancheter code. It repreent the ymbol '0' with a poitive and negative ymmetrical quare wave of a cycle, and ue it inverted waveform to repreent the ymbol '1'. Encoding rule: '0' code with '01' two-bit code, '1' code with '10' two-bit code. E.g: Meage code: Dual phae code: hi code ha a level tranition at the center of each ymbol, thu facilitating the extraction of the timing ynchronization ignal, and the ize of the timing component i not affected by the tatitical characteritic of the ource. In Mancheter code, becaue the poitive and negative pule each half, o there i no DC component, but frequency band occupied ha doubled. he Mancheter code i uitable for tranmiion over a hort ditance of coaxial cable channel. 40

5 Chai JW and Nie YH (4) Differential biphae code In order to olve the decoding error caued by the polarity inverion of the biphaic code, the concept of the differential biphae code can be ued. he biphae code i ynchronized and the code i repreented by a level tranition in the middle of each ymbol duration. In the differential biphae code, the level tranition in the middle of each ymbol are ued for ynchronization, and code can be determined via an extra tranition at the beginning of each ymbol. (5) Miller code Miller code, alo known a delay modulation code, i a ditortion of the biphae code. Encoding rule: '1' code i repreented with a ymbolic center point jump, that i, '10' or '01'. '0' code ha two cae: for a ingle '0', the ymbol duration doe not appear level jump, and with the adjacent ymbol doe not jump on the border. During continuou '0', there are two level tranition at the boundary of the '0' code, that i, alternated by '00' and '11'. (6) CMI code CMI code i the abbreviation of the coded mark inverion, imilar to the biphae code, it i alo a bipolar two-level code. Encoding rule: '1' code alternately with '11' and '00' two-bit code; '0' code fixed with '01'. Figure. CMI coding equence diagram 41

6 Reearch and Analyi of Digital Baeband ranmiion Sytem Baed on MALAB.3. Experimental principle.3.1 Digital baeband tranmiion ytem model Auming a n i the input ymbol equence of the tranmit filter, in the cae of binary, the value of the ymbol n i 0, 1 or -1, + 1. For the ake of analyi, we repreent the baeband ignal correponding to thi equence d ( t) a ( t n ) n=- n hi ignal i a equence coniting of a unit impule function at time interval, and the intenity of each of them i determined by n. When the tranmit filter i energized by, the tranmit filter generate a large output ignal Where: '*' i a convolution ymbol; i a ingle action of to end the baic waveform, that i, the impule repone of the filter. he tranmiion characteritic of the tranmiion filter i,i.e,determined by the following equation g ( t) 1 - G ( ) e j t d If the tranmiion characteritic of the re-etablihment channel i, the tranmiion characteritic of the reception filter i R, the total tranmiion characteritic of the baeband tranmiion ytem hown in Fig. 1- he unit impule repone i R 1 j t h( t) = H ( ) e d - h(t) i the ingle influence under, the formation of the output waveform H ( ). herefore, under the action of the impule pule equence, the output filter output ignal can be expreed a r( t) = d( t) * h( t) + n ( t) = a h( t - n ) + n ( t) R - In the formula, n R (t) i the noie generated by the additive noie n(t) n R after received by the filter. he ample deciion maker then make a ampling deciion to determine the tranmitted digital information equence i a. For example, in order to determine the value of the kth ymbol k, we hould firt ample at the moment n t k S + = to determine the value of at that point. Hence the formula i t 0 r( k + t0 ) = ak h( t0 ) + å anh[( k - n) + t 0 ] + nr ( k + t0 ) n¹ k Where a ( t k h 0 ) i the ummation of the kth received ymbol waveform, which i the bai for the determination of k ; i the um of the other ymbol waveform other than the kth ymbol at the kth ampling å a nh[( k - n) + t0] n¹ k time, which i the um of the current ymbol. It play the role of interference on the deciion of k, alo known a inter-code crotalk value, becaue n i probability of occurrence, o the inter-code crotalk value i uually a random variable; nr ( k + t0) i the output noie at the ampling moment, it i a random interference, will alo affect the correct deciion of the k-th ymbol. 4

7 Chai JW and Nie YH.3. ranmiion condition for inter-code crotalk If there i no interymbol interference between the ymbol tranmiion rate R (Bd), theoretically the minimum ytem bandwidth required i R / (Hz). he condition of the minimum ytem bandwidth i that the ytem tranfer function H i a rectangular function a hown in -5 (b). he impule repone of the ytem i the Fourier tranform of H (f) to h (t) = inc ( / ), a hown in Figure -5 (a) ( = 1 / R), inc (t / ) i called the ideal Nyquit pule. 3. MALAB oftware introduction 3.1. Software introduction MALAB i releaed by the mathwork company of United State, mainly for cientific computing, viualization and interactive programming high-tech computing. It integrate numerical analyi, matrix computing, cientific data viualization, and modeling and imulation of nonlinear dynamic ytem into an eay-to-ue window interface for cientific reearch, engineering deign, and numerou cientific tudie that mut be validated. he field provide a comprehenive olution and, to a large extent, out of the traditional non-interactive programming language (uch a C, Fortran) editing model, repreenting the advanced level of today' international cientific computing oftware. MALAB, Mathematica, and Maple are three major math oftware. It i econd to none in numerical application in mathematical technology application. MALAB can perform matrix operation, draw function and data, implement algorithm, create uer interface, and connect other programming language program. It i mainly ued in engineering computing, control deign, ignal proceing and communication, image proceing, ignal detection, financial modeling deign/analyi and other field. MALAB baic data unit i a matrix. It intruction and expreion are commonly ued in the form imilar to the ue in mathematic and engineering. Hence, uing MALAB i much impler to olve the problem than with C, FORRAN and other language, and MALAB alo aborbing the advantage of oftware uch a Maple, making MALAB a powerful math oftware. In the new verion, C, FORRAN, C + +, JAVA upport are available and can be directly called. he uer can alo write their own procedure into the MALAB function library to facilitate their future call, in addition to many of the MALAB enthuiat have prepared ome claic procedure, uer can download directly can be ued. he MALAB family of product can be ued to perform the following tak: numerical analyi Numeric and ymbolic calculation Engineering and Scientific Drawing Deign and imulation of control ytem Digital image proceing technology Digital ignal proceing technology Communication ytem deign and imulation MALAB ha a wide range of application, including ignal and image proceing, communication, control ytem deign, teting and meaurement, financial modeling and analyi, and computational biology and many other application. he additional toolbox (a eparate et of pecialized MALAB function) extend the MALAB environment to addre pecific type of problem in thee application. In the 1970, Cleve Moler, director of the Department of Computer Science at the Univerity of New Mexico, wrote the earliet MALAB in FORRAN in order to reduce the burden on tudent programming. In 1984, MathWork, founded by Little, Moler and Steve Bangert, formally introduced MALAB to the market. By the 1990, MALAB ha become the tandard oftware for international control. 3.. Feature of Matlab language 1, high programming efficiency, eay to ue 3, expanion ability 4, imple language, rich content 5, efficient and convenient matrix and array operation 43

8 Reearch and Analyi of Digital Baeband ranmiion Sytem Baed on MALAB 6, convenient drawing function 4. Experimental content 4.1. Ideal low-pa characteritic Meeting the Nyquit firt criteria, there are many way. he eaiet to think of a limit ituation, i for Impule repone tranmiion characteritic he main drawback of ideal low-pa ignal: A. Engineering and phyically difficult to achieve; Figure 3. Ideal low-pa tranmiion ytem characteritic B. ail decay low (impule repone h (t) waveform convergence rate i low, mear to 1 / t rate of attenuation, when timing error will bring more interference) If the ampling time lightly deviated, evere inter-code crotalk occur. 4.. Coine roll-off characteritic In order to olve the problem of the ideal low-pa characteritic, the edge of the ideal low-pa filter characteritic can be lowly lowered, which i called 'roll-off'. A long a the H ( ) at amplitude of the center of the roll i in the odd ymmetry of the amplitude, it will be able to meet the Nyquit firt criteria, achieving inter-coding crotalk tranmiion. he tranfer function H ( ), which i rolled by the coine characteritic, can be expreed a H ( ì ï ï ï ) = í ï ï ï ïî 0 é ê1 + in êë æ ç è - öù ú øúû < 1 + ³ < 1 + h t It correponding i in t = t co 1-4 t t In the formula, = f D f N i the roll-off coefficient i ued to decribe the degree of roll-off. It i defined a 44

9 Chai JW and Nie YH Where, N i the Nyquit bandwidth; i the amount of expanion beyond the Nyquit bandwidth Coine roll-off ytem baed on Matlab procedure and imulation reult Coine roll ytem baed on matlab imulation, the ource code i a follow: = 1;% ampling interval N = 17;% Sampling point Dt = / N;% time ampling interval Df = 1.0 / (0.0 * ); = -10 * : dt: 10 * ; F = - / : df: / ; A = [0,0.5,1]; For n = 1: length (a) For k = 1: length (f) End If ab (f (k))> 0.5 * (1 + a (n)) / Xf (n, k) = 0; Ele if ab (f (k)) <0.5 * (1-a (n)) / Xf (n, k) = ; (Ab (f (k)) * (1-a (n)) / (a (n) + ep) * (ab (f (k) ))); End Xt (n): inc (t / ). * (Co (a (n) * pi * t / ))./ (1-4 * a (n) ^ * t. ^ / ^ + ep); End Subplot (11); Plot (f, xf); Axi ([ ]); Xlabel ('f / ');% plu x axi intruction Ylabel ('the pectrum of the raied coine roll ytem');% plu y-axi decription ('Α = 0', 'α = 0.5', 'α = 1');% plu the legend Subplot (1); Plot (t, xt); Axi ([ ]); Xlabel ('t');% plu x axi intruction Ylabel ('time-domain waveform of the raied coine roll-off ytem');% plu y-axi decription ('Α = 0', 'α = 0.5', 'α = 1');% plu the legend 5. Concluion In the above reult we can ee that the frequency domain waveform at the center of the roll frequency i at the center of the odd ymmetry to meet the Nyquit firt criterion. he graph how that the larger the roll-off coefficient, the greater the amount of expanion beyond the Nyquit bandwidth and the increaed bandwidth. In the time domain waveform, the greater the roll-off coefficient, the fater the run-down attenuation of the waveform, the lower the bit-time accuracy requirement. 45

10 Reearch and Analyi of Digital Baeband ranmiion Sytem Baed on MALAB Mathematical analyi how that the lift coine roll-off ytem not only atifie the tranmiion condition of codele crotalk on the ampling value, but alo add a zero point between the ample value, and it tail attenuation i fater, which i beneficial to reduce the inter-code crotalk and bit timing error. However, thi ytem occupie twice the bandwidth of the ideal low-pa ytem, the band utilization rate i 1 B Hz, half of maximum utilization of the bae tation ytem. he experiment i mainly uing MALAB oftware to carry out digital baeband communication ytem imulation. In the whole experiment proce, there are everal problem. 1, In the beginning I wa not very familiar of the overall compoition of the ytem. Later communication with other tudent I undertood more the compoition of the entire ytem, the tep and procee of programming., Becaue we are unkilled for the ue of Matlab oftware, o there i no imulink imulation. I will continue to tudy and effort in the next experiment. 3, In view of a large program of writing, there will alway be problem in the operation, the reult do not run out. I tarted run in different egment, change the mitake one after another, and later through the effort of other tudent, I learned to ue breakpoint to find the wrong and ingle-tep operation of the program, which i great help for any future experiment. 4, here are no general concept of the reult of the whole experiment before the imulation, leading me difficult to judge correctly on the imulation reult are. Becaue of the lack of knowledge, o that in the proce of programming there i miundertanding. In the future, we need to have a olid foundation and be well aware of the ytem procee. When we encounter the unknown, firt check their own olution on the book, if till unreolved then we will dicu with each other. hroughout the coure deign, we have learned a lot of theoretical and practical knowledge, which ummarized a follow: 1, Unmodulated digital ignal occupied by the pectrum began from zero or very low frequency, known a the digital baeband ignal., Without the carrier modulation and direct tranmiion of digital baeband ignal ytem, known a the digital baeband tranmiion ytem. he tranmiion ytem including the modulation and mediation proce i called a digital bandpa (or frequency band) tranmiion ytem. 3, Coine roll-off ytem frequency domain waveform in the center of the roll-off ection of the odd ymmetry characteritic meet the Nyquit firt criteria. he greater the roll-off coefficient, the greater the amount of expanion beyond the Nyquit bandwidth and the increae of bandwidth. 4, he coine roll-off ytem not only atifie the tranmiion condition of the inter-code crotalk on the ampling value, but alo add a zero point between the ampling value, and it tail attenuation i fater, which i beneficial to reduce the impact of inter-code crotalk and bit timing error. Reference 1. Fan Changxin. Principle of Communication (3rd Edition), Electronic Engineering Pre.. Liu Shutang. Modern communication ytem (firt edition), Xi'an Jiaotong Univerity Pre. 3. Lucky R W. Automatic Equalization for Digital Communication. Bell Syt. ech. J., 1965, (44) 4: John G. Proaki. Digital Communication. hird Edition Ma Hongjie. Data communication. Beijing: China Railway Publihing Houe, ~ Ding Yumei, Gao Xiquan, Peng Xueyu. Digital Signal Proceing. Xi'an: Xi'an Univerity of Electronic Science and echnology Pre, ~ Guo Liyun, Liu Zengji, Wang Xinhai, Zhan Daoyong, Yang Qia. Data tranmiion. Beijing: People' Pot and elecommunication Pre, ~ Shi Yang, Yan Weiheng, Li Jun, Zheng Huiyong. MALAB language eential and dynamic imulation tool SIM ULINK. Xi'an: Northwetern Polytechnical Univerity Pre, ~