نشریه مهندسی مخابرات جنوب
پیاپی 28 (تابستان 1397)

With the expansion of societies and the increasing daily needs of human beings for fast communication and high speed information transfer and proper security, there is a need for a suitable platform for sending and receiving information, which is the Internet. This method is the most powerful tool ever invented for information exchange. Since the Internet became commercialized in 1990, the world has entered a new arena of new communications. Dial-up, ADSL, DSL, Wireless, Satellite and Wimax are some of the types of internet connection methods. This article discusses one of the new methods of IPL Internet data transmission. The transmission of Internet information through distribution lines is called IPL power networks. In this article, during the introduction of IPL technology, the technical-economic evaluation of Internet information transmission through distribution lines is compared to other methods and its effectiveness, profitability, and future are expressed. Becomes. Then its applications in the field of automation, telemetry, and control telephoto are introduced.

One of the wireless networks that have been studied in recent years is the WiMAX network. Multi-antenna techniques are used in WiMAX systems to increase coverage and reliability of transmission and reception. The design of multiple antennas provides many benefits such as array gain, diversification gain, and elimination of co-channel interference. Multi-antenna technology support is a key feature of WiMAX compared to other wireless broadband technologies (such as HSDPA). To increase coverage and reliability, IEEE 802.16-2004 standard WiMAX systems support multiple antenna techniques such as space-time coding (STC), array antenna systems (AAS), and MIMO systems. In this paper, we focus on techniques that do not require channel information in the transmitter, such as STC and MIMO and compare the results.

The range of operation of compressors is limited by the surge phenomenon. Surge control is inevitable to deal with this phenomenon. In this paper, a solution to control it with a fuzzy controller using a surge control line and a surge line using a remote control. The speed of the compressor is also expressed using the anti-surge valve (in combination). A fuzzy controller is designed to stop the surge according to the compressor model with a high degree of safety. Simulations show the use of these simple controllers compared to classical controllers and their efficiency.

This paper examines the application of FACTS devices to increase the voltage stability margin in power systems. Most of the proposed methods for allocating FACTS devices consider only the normal state of the network. However, the mains voltage usually breaks down due to an unforeseen accident. Therefore, in this paper, the strategy of locating FACTS devices based on possible (unpredictable) studies is proposed. Using medal analysis, a possible index is defined that can be used to classify system buses based on their effect on improving system voltage stability, under all possible probabilities. This method has been shown to lead to integrated reactive power supply. As a result, it can be more effective in the event of a further error. The IEEE standard 14-bus network has been used to demonstrate the proposed achievement in locating parallel FACTS devices. The results show that the allocation of FACTS devices by the proposed method improves the system voltage stability under the conditions of error probability.

Office systems that are connected to the Internet are constantly exposed to a variety of computer viruses. One of the main factors that significantly increases the risk of malware is the desire to give system administrator capabilities to users. When a user logs in as an administrator, all the programs they run also have access to the administrator. One of the ways that can protect the system from attacks is the lack of access to the system administrator mode for ordinary users. In this article, this issue has been studied and at the same time, the experiments that have been done in order to create a situation of minimum access for users and its results have been studied. Malware that can attack the system in the presence of strong and up-to-date antivirus software is analyzed.

Increasing communication through digital media has made the issue of security very important. Steganography is a way to hide communication through cover media. Hiding information in JPEG images is very attractive because these types of images are the most widely used images on the Internet. There are many ways to detect the presence of hidden information in JPEG format, which are also very accurate, and so far there is no method that can be called secure. Due to the loss of JPEG compression and the effects that this type of compression has on images, it has become impossible to use the spatial field for embedding easily. Embedding in the DCT coefficients of the JPEG algorithm has also been discovered in any of the proposed methods. This paper presents a recursive method for embedding in the conversion domain before JPEG compression, which uses blocking other than the usual JPEG blocking. Embedding is done in such a way that JPEG compression does not cause any errors when extracting data. These properties make the security and capacity of the method good.