Transmission Reliability Based On Data Link Layer Enhancement In Wireless Local Area Network

With the rise of the Cyber-Physical Systems(CPS)industry,there is increasing interest in CPS in the application of real-time wireless technologies.In the current TDMA scheduling protocol,it provides real-time,high-speed,and predictable data transmission to meet the time-demanding industrial needs,but there is no clear reliability of the implementation mechanism.TDMA scheduling protocol due to noise and other interference caused by uncontrolled packet loss,or suffer from inefficient use of communication channels,the reliability of the performance needs to be further improved.Much of the current research has been to increase reliability at the expense of data transfer rates,which is clearly unacceptable for control applications where data transfer has tight timing requirements.In wireless local area network control system,the perception of information transmission rate and transmission reliability control system is the crucial two objectives,users depend on reliable data transmission based on timely and make decision.It is a great research significance to improve the transmission reliability in wireless networks.Based on the full analysis of the research on TDMA scheduling mechanism at home and abroad,this dissertation explicitly considers the interference of WiFi and non-WiFi interference sources and proposes two effective solutions based on the TDMA scheduling protocol.The main research contents and innovations are as follows:(1)Based on the existing carrier interception collision avoidance(CSMA / CA)and stop-waiting protocols in the IEEE802.11 protocol,each station accesses the communication link in a competing manner with an uncertain delay and can not Complete real-time data transfer.In response to this problem,this paper studies the reliability based on the existing TDMA scheduling protocol.Combined with Linux open source wireless network card driver Ath9 k and mac80211,add custom modules such as timer,channel access control and link scheduling to complete the data link layer structure based on TDMA scheduling mechanism and implement it on commercial IEEE802.11 hardware Build real-time WiFi platform.(2)Based on the TDMA scheduling protocol,a new rate adaptive algorithm is designed to determine the condition of the channel by continuously receiving or losing the ACK acknowledgment frame under different channel conditions,so that the "S" search scheme intelligently adjust different sending rates.When sending data,the sender performs sending data and probing a new data rate that may exceed the current rate,comparing the new data rate with a better transmission quality with the currently used sending rate,and selecting one of the best Item,Finally,the rate of switching.(3)On the basis of rate adaptation and TDMA scheduling mechanism,consider how to improve the reliability of data transmission in the face of common non-WiFi interference sources.This paper designs a real-time rate adaptive derivation retry chain algorithm,as well as short-cycle priority scheduling algorithm.Real-time rate adaptive export retry chain algorithm is used to derive a retry chain that meets the minimum time budget under the delivery success rate.On all scheduled links,each link has its own cycle,which takes short-cycle-first scheduling so that short cycles can be scheduled many times throughout the scheduling period.Under the TDMA scheduling mechanism,the data transmission of each scheduled link may not be transmitted once,and may need to be transmitted multiple times.Therefore,when scheduling time is set,multiple retransmissions should be considered.Based on real-time rate adaptive derivation retry chain algorithm and short-cycle priority scheduling algorithm,intra-slot retransmission is combined to improve the reliability of data transmission in non-WiFi interference environment.(4)Based on the TDMA scheduling protocol,consider how to improve the reliability of data transmission in the face of WiFi interference sources.In the environment of WiFi interference,the CSMA / CA mechanism of the TDMA scheduling network needs to be turned on.This ensures that TDMA networks can intercept each other when they coexist with normal WiFi and avoid unnecessary collisions.And a retry chain derived according to the rate adaptively.If the number of retransmissions is not fully used,the remaining unused retransmission times are reserved in advance for the next link to which data is to be sent.By scheduling the mini-slots in the scheduling link in advance,the unused mini-slots in the links that have already been transmitted successfully are reserved in advance for the next link to be scheduled,so as to further improve the schedulability of the link.While shortening the TDMA inter-frame space(IFS)to improve the priority of the TDMA network,and finally sharing the unused bandwidth of the TDMA network to the normal WiFi network.