Yin C. Research and development of methods for evaluating the transmission efficiency of audio-visual information by means of wireless networks of the IEEE 802.11 standard

The dissertation is devoted to the solution of the actual scientific and technical problem - improvement of methods of forecasting of operational parameters of wireless computer networks of IEEE 802.11 standard. The basic principles of IEEE 802.11a /g /n / ac wireless networks operating in the 2.4 and 5 GHz frequency bands are analyzed. The reasons for limiting the operational parameters of such networks have been clarified. The shortcomings of the methods for evaluating the performance of IEEE 802.11 wireless networks based on the time slot concept are analyzed. The paper presents an improved mathematical model of the process of transmitting information streams via IEEE 802.11 wireless network in competitive access mode. An advanced mathematical model was developed based on the concept of a virtual contention window. This concept was proposed to determine the limit values of operational parameters in networks with saturated load of active stations. The basic idea behind the concept is that in saturated mode, when each station constantly tries to access a channel to transmit a data frame, the process of operating a wireless channel can be considered as a quasi-stationary random process. Due to this concept it possible to obtain functional dependencies for both a single station and the wireless network segment as a whole. The process of occurrence of collisions is investigated and calculated ratios for quasi-stationary regime are obtained. It is justified that, due to conflicts, the number of stations competing for radio access is less than the total number of active stations in the network. It was proposed equations to determine, channel bandwidth, frame transmit delay, irregularity of delay (jitter), number of collisions occurring during virtual competitive window implementation, probability of successful transmission of data frame, probability of frame loss as a result of network transmission. A method based on an improved mathematical model is proposed to predict performance of wireless network. Using this method, the performance characteristics of IEEE 802.11a / n networks with different number of active stations were investigated. Using this method, the performance characteristics of IEEE 802.11a / n networks with different number of active stations were investigated. The range of the stations number changing is from 2 to 14. The study was made for traffic whose data frames contain different payloads from 64 to 1500 bytes. The study was done for two types of TCP and UDP transport protocols. Two competitive network access modes are considered: unrivaled access mode and RTS and CTS frame mode. Compared to the channel bandwidth under ideal conditions in the event of collisions for UDP, bandwidth is reduced in RTS/CTS mode by 4.8% (frame load 1500 bytes) and 11.4% (frame load 64 bytes), and by 3% (1500) and 6.5% (64) for TCP. To evaluate the effectiveness of IEEE 802.11 wireless network resources using, a method based on payload coefficient using is proposed. Network payload coefficient is the ratio of the rate of transmission of useful information to the system connection speed. This coefficient allows you to evaluate the efficiency of using the technological capabilities of the wireless network. Thus, according to the results of the conducted studies, under favorable conditions for the mode with the bandwidth of the wireless channel 40 MHz and the system speed of 150 Mbps, kkn(1500) = 0,366, and for the mode with the bandwidth of the wireless channel 20 MHz, 72 Mbps with kkn(1500) = 0.308. The brackets show the approximate amount of payload in a single data frame. The effectiveness of the proposed methods is theoretically and experimentally proven. The results of theoretical and experimental studies are applied in the educational process.