Research and Analysis of Digital Baseband Transmission System Based on MATLAB

This paper mainly studies the basic concept of baseband transmission of digital signal and the transmission processof digital signal baseband transmission and how to design digital baseband transmission system with MATLABsoftware simulation. This paper fi rst introduces the theoretical basis of this subject, including digital communication,the composition of digital baseband transmission system and digital baseband signal transmission process. Then thepaper introduced the characteristics of digital baseband transmission system, including digital PAM signal powerdensity and common line pattern, and by comparing choosing the fi nal bipolar zero return code. Then we introducedthe MATLAB simulation software. The conditions of the best reception of the digital baseband signal are describedand how the waveform of the baseband signal is observed by an oscilloscope. Finally, according to the basic stepsof simulation process, the simulation process of digital baseband transmission system is realized by MATLABsimulation tool, and the system is analyzed.

Local SDH transmission network design

We know that today's society is the information society. The highly developed information society requires thatthe communication network can provide a wide variety of telecommunication services. The amount of informationtransmitted, exchanged and processed through the communication network will increase, which requires the moderncommunication network to be digitalized, integrated, intelligent and personalized. The transmission system is animportant part of the communication network, directly restricting the development of the communication network.One of the most important developments in the world to develop the information superhighway, with one of thekey is to set up a large capacity transmission fiber network, continuously improve the transmission line on thesignal rate, widening the transmission band. It is like expanding capacity to accommodate a large number of traffi cin highways. At the same time the user wants the transmission network to have a worldwide interface standard, toaccess to global village, in where every user can easily communicate anytime and anywhere. Synchronous DigitalHierarchy (SDH) is a comprehensive information transmission network that integrates multiplexing, line transmissionand switching functions and is operated by a unifi ed network management system. It is a synchronous informationtransmission network developed by Bell Communication Technology Research Institute’s optical network (SONET).The International Telegraph and Telephone Advisory Committee (now ITU-T) received the SONET concept in 1988and renamed it SDH, making it a general technology system that applies not only to fiber but also to microwaveand satellite transmission. It is applied for eff ective management of network, real-time service monitoring, dynamicnetwork maintenance, interoperability between different vendors and other functions, greatly improves networkresource utilization, reduce management and maintenance costs, flexible and reliable and efficient networkoperation and maintenance. So it is in the center of attention in world's information fi eld of transmission technologydevelopment and application.

Current Situation and Development Trend of Mobile Communication Systems

This paper introduces the development background of mobile communication and the development of mobilecommunication. It introduces the application principle, network structure, main technology, the advantages anddisadvantages of the three generations of mobile communication system respectively, and introduces the currentthird generation mobile communication system, including its technical support and research direction, analysis andcomparison of the European WCDMA system, the United States CDMA2000 system and China's TD-SCDMA systemtechnical characteristics. Finally, the development trend and prospect of future mobile communication system arediscussed.

Design of Mobile Communication Indoor Distribution System

With the development of economy, the improvement of people's living standard has been increasing and theconstruction of buildings is becoming more demanding. These buildings are large in scale and of good quality andhave a strong shielding effect on mobile phone signals. In the middle of the large-scale buildings, undergroundshopping malls, underground parking and other environments, the mobile communication signal is weak hence thephone cannot be used normally and forming a mobile communication blind area and shadow area. In the middlefl oor, due to the surrounding diff erent base station signal overlap, the ping-pong eff ect, frequent switching of mobilephones and even dropped calls are seriously aff ecting the normal use of mobile phones. In the building's higher fl oors,due to the height of the base station antenna, it has abnormal coverage and there is also mobile communication blindspot. In addition, in some buildings, although the phone can answer normal call but the user density, base stationchannel congestion and mobile phone line is diffi cult. In particular, the network coverage, capacity and quality ofmobile communication are the key factors for operators to gain competitive advantage. Network coverage, networkcapacity and network quality fundamentally refl ects the mobile network service level and is the theme of all mobilenetwork optimization work. The indoor coverage system is produced under this background. According to the relevantstatistics in some areas of indoor traffi c in the total traffi c accounted for a higher proportion. Therefore, strengtheningthe indoor coverage is of great signifi cance to improve the quality of mobile communication.

Research on Secure Communication Based on QQ Chat Platform

QQ is China's most widely used instant messaging tool, its security for user security and network security has animportant impact. Once a QQ account is hacked, the harm and the impact is terrible, the user loses a lot of friend’sinformation and contact information in a short time and is diffi cult to completely recover. This article will analyzethe security of QQ’s landing agreement, analyze its security, and point out the security vulnerabilities which exist,and explain the possible attacks that QQ may suff er, and make suggestions for improvement and ways to enhance thesecurity of QQ communication. In addition, this article also conducts a corresponding study of QQ hacking, and putsforward precautionary approaches.