Research And Implementation Of TDMA Mechanism Based On IEEE 802.11

In the current development of industrial Internet and intelligent manufacturing background,more and more devices have entered the network,and the network traffic is getting larger and larger,which posed new challenges to wireless communication technologies.In the field of control,wireless technologies based on the IEEE 802.15.4 standard are mainly used.However,the IEEE 802.15.4 standard is applicable to low-power,low-rate application scenarios and cannot cope with future high-rate and large-data traffic situations.The Wi-Fi network based on IEEE 802.11 standard has many advantages such as high speed and high reliability.However,the IEEE 802.11 standard adopts a contention-based CSMA/CA mechanism as a basic access mechanism,which uses frame aggregation to improve efficiency,so the Wi-Fi network cannot provide real-time guarantee for data transmission.This article focused on improving the real-time performance of Wi-Fi networks.By replacing the existing CSMA/CA mechanism with TDMA mechanism,Wi-Fi can provide real-time guarantee so that it can be applied to the control field.Based on common hardware and software platform,we designed and implemented a TDMA mechanism that can support dynamic time slot scheduling,then we analyzed,verified,and evaluated this mechanism.The experimental results show that the TDMA mechanism we designed in this paper can provide high rate support.Compared with the CSMA/CA mechanism,our TDMA mechanism can guarantee real-time performance.The main work of this article is as follows:(1)We designed and implemented the TDMA mechanism of this paper on the existing hardware and software platforms.In this mechanism,the AP controls the access slots of each site and supports dynamic time slot scheduling for both uplink and downlink.Firstly,we analyze the transmission and reception principle of the existing wireless driver.Based on this principle,we design the TDMA mechanism,including time slot structure,timing transmission and time slot scheduling three parts.Finally,by disabling the CSMA/CA mechanism,multiplexing SWBA timers,and broadcasting timeslot scheduling information by Beacon frames,we implements this TDMA mechanism.(2)For the environment where TDMA networks and CSMA/CA networks coexist,we proposed a model to analyze the interference between the CSMA/CA mechanism and the TDMA mechanism,then,we use this model to calculate the access delay of TDMA stations in this mixed network environment.Finally,we verified this model by simulation,the experiment show that our model is correct,and we discussed the main factors that affecting the access delay.(3)We verified and evaluated the hardware TDMA mechanism implementations of this article.Firstly,we implemented a uniform slot allocation algorithm,by sniffing 802.11 packets,we validated the clock synchronization and time slot scheduling in our TDMA mechanism.Then we evaluated the TDMA mechanism and the CSMA/CA mechanism in a basically interference-free environment.The experimental results show that our TDMA mechanism can provide 5Mbps throughput.Compared with the uncertain delay of CSMA/CA mechanism,our TDMA mechanism can guarantee more than 99%data delay in 1ms,85%data delay in 350us,whether delay or delay jitter are much better than CSMA/CA mechanism,which can meet the real-time requirements of data in the control system completely.