Research On Mutual Interference Suppression And Time Synchronization For Full-Duplex Ad Hoc Networks

Wireless ad hoc networks are gradually used in various military and civilian communication scenarios due to their flexibility and ease of deployment.In existing ad hoc networks,nodes use time division duplex(TDD)or frequency division duplex(FDD)to send or receive signals to avoid interference caused by their own transmitted signals.However,TDD or FDD modes require different time slots or frequencies to achieve bidirectional transmission of signals,reducing the spectral utilization of the network.With the development of co-time co-frequency full-duplex(CCFD)technology,sending and receiving signals simultaneously at the same frequency is possible.Applying CCFD technology to wireless ad hoc networks will improve spectrum utilization.Compared to TDD or FDD ad hoc networks,CCFD ad hoc networks allow the same node to transmit signals using the same frequency while receiving signals,resulting in more serious mutual interference.The mutual interference problem between nodes can be solved through mutual interference cooperative suppression,and a common time base is the foundation for cooperation among nodes.Additionally,network-wide time synchronization is also beneficial for transmission resource cooperative scheduling.Therefore,this dissertation mainly conducts research and experimental verification on mutual interference cooperative suppression and time synchronization technology in CCFD ad hoc networks.The main work of this dissertation is as follows:1.Using the network total spectrum utilization rate as a performance indicator,the network performance of the CCFD frequency-hopping ad hoc network in a fixed area is analyzed.First,the nodes in the network are divided into two groups.Nodes from these two groups perform CCFD communication pairewirely,and the received signal model of the reference node is established.Then,the definition of the network total spectrum utilization rate is given.The closed expression of the network total spectrum utilization rate is derived.Finally,the total spectrum utilization rate of the network under uniform distribution and equal circle packing distribution is analyzed and compared with the halfduplex ad hoc network.The simulation results show that the CCFD frequency-hopping ad hoc network can achieve a spectrum utilization rate twice that of the half-duplex ad hoc network when the number of nodes in the network is small,effectively improving spectrum utilization.However,as the number of nodes in the network increases,the total spectrum utilization rate of the CCFD frequency-hopping ad hoc network first increases and then decreases.The decreasing trend is more serious than the half-duplex ad hoc network.When the normalized communication distance is 0.08 and the number of nodes in the network exceeds 143,the CCFD frequency-hopping ad hoc network’s final total spectrum utilization rate is even lower than the half-duplex ad hoc network.When the number of nodes is large,the more serious mutual interference problem in CCFD networks,compared to half-duplex networks,is the primary reason for the total spectrum utilization rate being lower than that of half-duplex networks.2.Aiming at the mutual interference problem between communication nodes in the CCFD ad hoc networks,two mutual interference cooperative suppression methods are proposed,which are used for broadband known and narrowband random signals,respectively.The mutual interference model of broadband known signals considers the impact of power amplifiers and channel fading on the signals.The channel parameters are estimated using neural networks.The transmitted signals are reconstructed based on the estimated channel parameters to cancel the mutual interference signals at the receiving node.The sending node and receiving node of the narrowband random signals can receive the mutual interference signals at the same time.The sending node adjusts the amplitude and phase of the received mutual interference signals and transmits the adjusted signals to the receiving node so that the adjusted signals cancel the mutual interference signals at the receiving node.The simulation results show that the cancellation methods under both signal models can effectively suppress mutual interference signals.Under ideal conditions,the suppression ratio of broadband known signals can reach about 60 d B,and the suppression ratio of narrowband random signals can reach about 54 d B.The cancellation performance of the broadband known signals depends on the reconstructed signal’s time synchronization and amplitude error related to the mutual interference signals.The cancellation performance of the narrowband random signals depends on the path propagation difference between the adjusted signals and the mutual interference signals.3.Aiming at the problem of two-way time synchronization errors caused by relative motion between nodes in ad hoc networks,two time synchronization methods used in TDD and CCFD modes are proposed.The TDD time synchronization method increases the number of equations in the synchronization equation set by transmitting four synchronization messages.The solution of the synchronization equation set is derived under the premise of relatively uniform motion of the nodes.The CCFD time synchronization method fully uses the characteristics of CCFD,which can transmit and receive signals simultaneously at the same frequency.This method transmits synchronization messages twice in the same time slot,thus avoiding the unequal propagation delay of synchronization messages caused by node movement.Both proposed time synchronization methods do not require a priori information about the node movement.Simulation results show that TDD time synchronization can completely eliminate the system error caused by the change of propagation delay when nodes move at a constant speed,and CCFD time synchronization can achieve sub-nanosecond time synchronization accuracy under variable-speed motion.4.A CCFD ad hoc network system suitable for unmanned aerial vehicle scenarios is designed,and mutual interference cooperative suppression and time synchronization are experimentally verified.Based on the application scenarios and system index requirements,the hardware platform,wireless communication links,and networking protocols of the CCFD ad hoc network system,which can support 16 nodes,are designed.The mutual interference cooperative suppression and time synchronization performance are verified on the designed CCFD ad hoc network system.The experimental verification results show that mutual interference cooperative suppression can effectively suppress the mutual interference signals during the time synchronization process,and the nanosecond synchronization accuracy can be achieved during the high-speed movement of nodes.This dissertation aims at the mutual interference problem in CCFD ad hoc networks,studies the impact of mutual interference on the network total spectrum utilization rate of CCFD frequency-hopping ad hoc networks,explores the methods of mutual interference cooperative suppression and high-precision time synchronization under node movement,designs the CCFD ad hoc network system,experimentally verifies mutual interference cooperative suppression and time synchronization.The research results are significant in technical support and engineering guidance for solving mutual interference problems in CCFD ad hoc networks.