Design And Implementation Of The Data Link Layer Of The Physical Layer Network Coding Wireless Communication System

Physical-layer network coding(PNC)is applied to wireless networks,allowing multiple communications simultaneous transmission,which can produce higher throughput than traditional network coding.Physical-layer network coding has developed into a subfield of network coding with a wide concern and research.Software defined radio is a wireless technology,which is based on digital signal processing theory,implement as much function as possible in a software form on a general hardware platform.It has been widely used in wireless communication system,even deploy in commercial wireless network.At present,the research of physical-layer network coding mainly focuses on the physical layer,and the research on data link layer is relatively few.In order to achieve reliable real-time PNC(RPNC)applications,the design of the data link layer must be considered.This paper first introduces the key technology of RPNC physical layer,and then focuses on the design and implementation of data link layer for RPNC wireless communication system with two-way relay network as the model.Specifically,Beacon mode and Burst mode MAC protocol in RPNC system has the shortcomings of high cost and low system throughput,a low overhead XOR mode MAC protocol is proposed to schedule the transmission of nodes.The XOR mode MAC protocol uses the PNC downlink XOR packet to synchronize the transmission of nodes.In addition,on the basis of the traditional end-to-end TO-ARQ(Terminal-Only ARQ),a relay cooperative TR-ARQ(Terminal-Relay ARQ)tailored for PNC system to provide reliable data delivery at the link layer.In TR-ARQ,when the XOR packet rdecoded by the relay is wrong,it request endnode to retransmit the corresponding data packet by sending the NACK.Compared to TO-ARQ,The cooperation of the relay node in TR-ARQ can advance the left boundary of the transmission window as soon as possible.In this paper,using Universal Software Radio Peripheral(USRP)and GNU Radio SDR platform,a two-way relay network RPNC system was established.Using OFDM PNC as the prototype,new designs have been put forth and implemented into data link layer to enable the support of real TCP/IP applications.RPNC realizes the real-time transmission of two image data files between the two end nodes.This paper compares the throughput of RPNC with different MAC protocol.The results indicate that RPNC with XOR mode MAC protocol achieves the higher system throughput than other two modes,and it can better meet the real-time requirement.Meanwhile,we compare the throughput and delay performance of the RPNC with TR-ARQ and TO-ARQ repectively by experiment.The results show that RPNC with TR-ARQ has a lower delay and it can significantly improve the system throughput.