Research On Fined-grained Multichannel Communication And Access Control Technology On NC-OFDM

In recent years,wireless network has made great progress in various fields for its flexibility,low cost and easily installation.At the same time,the increasing number of users and the interference between the users of the wireless network,and the contention of public spectrum resources between nodes has produced a large number of collisions and backoff,the limited spectrum resources are becoming increasingly scarce.Therefore,the subcarrier nulling technology based on non-contiguous orthogonal frequency division multiplexing(NC-OFDM)has been widely studied by scholars.The basic requirement of subcarrier nulling technology is allocating the spectrum resource and communication channel by subcarrier as the granuIarity.The unauthorized sub users can use the channel that has been authorized to the main user but not occupied,thus effectively improving the spectrum utilization.So,more and more researchers start the multichannel communication technology.The implementation of multichannel communication technology based on software radio is closer to reality than software simulation,and it is an effective way to evaluate the performance of subcarrier nulling technology.This paper aims at improving the reliability and anti-interference of multichannel communication by multichannel communication and access technology based on non-contiguous orthogonal frequency division multiplexing,and studies the design and optimization of the physical layer algorithm based on the non-contiguous orthogonal frequency division multiplexing and the dynamic access protocol based on the IEEE 802.11 DCF.The main work includes:Firstly,a heterogeneous network coexistence mechanism based on subcarrier nulling technology is designed to solve the common channel interference problem between the main user and the subuser.In this mechanism,when the secondary user node detects the main user node working on the same channel,it only uses the channel that does not overlap the channel of the main user node,5o that the main user and the secondary user do not overlap on the spectrum to achieve the purpose of the signal parallel transmission.At the same time,an adaptive synchronization based on preamble is proposed to synchronize the NC-OFDM receiver and identify the subcarrier transmission mode used by the transmitter to correct the frequency offset and phase deviation of each symbol in real time,and then be able to decode correctly.Secondly,a multichannel media access control(Medium Access Control,MAC)protocol is designed for the application of heterogeneous network coexistence scenarios in NC-OFDM physical layer.This MAC protocol innovation includes three parts:a carrier sensed function matched with the fine-grained multichannel communication system.It can dynamically and accurately monitor the state of each subchannel and set a reasonable transmission mode for the physical layer;a improved distributed channel access mechanism for heterogeneous network coexistence scenarios;a self-adaption scheme designed to guarantee node to access channels and transmit data in time when there are differences between channel environments.Finally,in view of the above problems,a verification platform is built on the GNURadio/USRP software radio platform,which validates the synchronization and recognition algorithm of physical layer and the feasibility of the MAC protocol,and tests the feasibility and time performance of the technology through a reasonable test method,Providing support for the application and popularization of the technology.Experimental results show that the recognition algorithm has more than 95%correct rate for subcarrier transmission pattern,which makes the experimental environment closer to reality.This MAC protocol can support the coexistence of heterogeneous networks on the basis of ensuring better performance of the subcarrier nulling techmology,thus ensuring the connectivity and quality of service in complex communication environments.