Research On Key Technologies In Full Duplex Communication Systems

With the increasing quest for high speed communication,mobile communication networks expend rapidly.To avoid self-interference(SI),traditional wireless communication systems usually adopt half du-plex(HD)mode,such as frequency division duplex(FDD)and time division duplex(TDD).Unlike HD systems,full duplex(FD)systems are capable to transmit and receive on the same spectrum simultaneously with efficient SI cancellation technologies.As a result,FD can achieve almost double spectrum efficiency with comparison to HD.It is quite essential to investigate the system performance when combining FD with other key communication technologies.Based on FD mode,we primarily study the channel estimation prob-lem in FD relay systems,physical-layer secrecy of FD systems,and performance of FD ad hoc networks,respectively.The second section of the dissertation mainly focuses on the channel estimation problem in FD relay systems.In the considered multiple-input multiple-output(MIMO)FD relay system,both source node and relay node work on the FD mode.While broadcasting signals,the relay node also receives transmission signals from the source node.Through monitoring the broadcast signals,the source node could estimate the channel state information(CSI)required for precoder design.We first propose a channel estimation algorithm without requirement of feedback from the relay node.Based on the algorithm,we further derive the bias and Cramer-Rao lower bound(CRLB)of the estimator.Additionally,we propose another modified channel estimation algorithm which addresses the antenna number constraint of the original algorithm.At last,we demonstrate that both algorithms are efficient and effective via comparison between theoretical analysis and numerical simulations.The third section of the dissertation considers the secret key distribution in FD systems.In order to cancel the SI efficiently,either circulator or separate antennas are applied for the legitimate users,resulting in non-perfect reciprocity of forward and backward channels.In this section,we propose two practical physical-layer based secret key generation schemes for MIMO wireless links over non-reciprocal physical channels.One is pilot assistant secret key(PASKey)generation and the other is eigenvalue based secret key(EVSKey)generation.In PASKey,both legitimate users estimate the same composite channel while EVSKey exploits properties of eigenvalues to generate secret bits.Both are effective against secrecy key theft by eavesdroppers.Furthermore,without adopting public training signals,EVSKey manages to generate secret bits even when nearby eavesdroppers collude.Our two schemes are shown to be more efficient and can achieve lower key error ratio(KER)than existing methods.In the fourth section of the dissertation,we investigate the performance evaluation of FD ad hoc net-works.Unlike the more traditional HD nodes,FD wireless equipments can exchange data simultaneously over the same spectrum band.While FD transmission represents a promising mechanism to improve spec-trum efficiency,the inevitable rise of interference from more transmitting nodes can also lower the rate of successful transmissions in ad hoc full duplex networks.We study the transport capacity of ad hoc FD net-works by analyzing the successful packet decoding rate in both physical and protocol link models.We derive a new upper bound and a new lower bound for the network transport capacity,which can be used to lower complexity approximate analysis of the network transport capacity.We further determine the optimal packet access probability for maximizing network throughput and quantify the potential benefit of full duplex nodes in wireless ad hoc networks.In both physical and protocol link models,our analysis shows that full duplex networks can nearly double the transport capacity against half duplex only when the paired link distance is rel-atively small.As the paired link distance grows,the transport capacity gain of full duplex networks begins to degrade under the constraint of successful packet decoding rate.Our numerical simulation results corroborate the analytical results.