Research On Interference Alignment In Two-Way Relay Channels

In future wireless communication systems,interference will become an important factor to hinder the performance of current wireless networks,due to the spectrum scarcity and the surging users.Thus,an effective interference management scheme is urgently needed in wireless communications.Traditional methods handle the interference by providing each user with exclusive access to a fraction of wireless resources.However,these methods are complex and difficult to implement when the number of users is large.Recently,the interference alignment(IA)has been proposed in wireless networks as an efficient solution to the interference problem.It uses spatial beam-forming to divide the signal space into the desired signal subspace and the interference subspace at the receiver by multiple antennas.If all the interferences can be aligned into an interference subspace,it will not extend to the desired signal space.Now the desired signal does not fall into the interference subspace,and thus the receiver can easily attain its desired signal.For example,given K transmitter-receiver pairs in an interference channel,each pair has access to 1/ K of the resource with the traditional approach to interference management.But,using the IA scheme in each pair,it can have access to up to 1/ 2 of the resources simultaneously.For its impressive performance,IA has been applied to numerous networks,e.g.,two-way relay networks,cellular networks,HetNets,cognitive radio(CR)networks,LTE-A systems,D2 D systems,and underwater networks.To deal with the practical applications,relaying technique in wireless communications is popular,which has been identified as an effective method to both extend coverage areas and has robustly improved high speed data transmission with the reduction of power consumption.Compared with the one-way relay strategy,the two-way relay strategy provides higher spectral efficiency,benefiting from the emergement as a promising candidate.How to address the integration of two-way relay strategy with IA for higher degree of freedom and sum rate has become a hot topic in recent years.To the best of our knowledge,the research of alignment algorithm in the two-way relay channels is still seldom,where more problems are needed to be solved.For example,the traditional relay strategy has been widely used in two-way relay channel with IA by employing amplify-and-forward(AF).However,the rate performance of two-way multiple relays channels is usually ineffective,since this AF strategy leads to relays of both transmitted messages and noise.We also note that,to guarantee feasible solutions,IA strives to optimize some performance parameter in two-way relay channels.Here,both the pre-coding and interference suppression matrices are incorporated by using the channel state information.However,the designed optimal model under this condition is non-convex and intractable.The closed-form solution of the pre-coding and interference suppression matrices only can be found in some special cases.Moreover,the user and relay nodes in the two-way relay networks equip with multiple antennas.A complex broadcast channel in communication system is often impacted with the number of antennas at the transmitters/receivers.Hence,it is difficult to derive the rate expression of two-way relay channels with IA.On the other hand,interference in two-way relay channels can be effectively handle by interference alignment,which improves the network performance,but also increases the energy consumption of both receivers and transmitters,but the research on energy efficiency is less.To deal with the aforementioned problems,we build the corresponding IA models with several strategies,i.e.,computer-and-forward(CF),rank constrainted rank minimization(RCRM),large system analysis and simultaneous wireless information and power transfer based optimization strategies.As a result,our work can significantly enhance the capacity for the future wireless communication system.The main contributions and innovations of this dissertation are summarized as follows.First,interference alignment in two-way relay channels with compute-and-forward.Most IA methods in two-way relay channels proposed recently are based on amplify-and-forward,which leads to relays of both transmitted messages and noise.On the other hand,compute-and-forward(CF)is developed based on nested lattice to enable relays to decode linear equations of transmitted message using the noise linear combinations provided by the channel,and then only forward the desired message.In this paper,we analyze the interference alignment in both two-way single relay channels and two-way multiple relays channels via compute-and-forward.Then,interference alignment in two-way relay channels via rank constrainted rank minimization.The rank constrainted rank minimization means that interference spans the lowest dimensional subspace and the useful signal spans all available spatial dimensions.In this paper,we use rank constrained rank minimization(RCRM)to solve the IA problem of two-way relay channels.In particular,we proposes left reweighted nuclear norm minimization algorithm and selective coupling reweighted nuclear norm minimization algorithm to implement interference alignment in two-way relay channels.Next,large system analysis of two-way heterogeneous cellular networks with interference alignment.A complex broadcast channel is often impacted with the number of antennas at the transmitters/receivers,and thus the rate expression of two-way relay networks is difficult to obtain.In this paper,we resort to large system analysis(LSA)to obtain the average achievable rate in multiantenna two-way relay networks and derive the rate expressions under both equal power allocation and optimal power allocation.Stochastic geometry is a very powerful mathematical and statistical tool for the modeling,analysis,and design of wireless networks with random topologies.Further more,we also reaserch large system analysis of heterogeneous cellular networks with IA.In order to improve the performance of HCNs,we perform interference alignment via rank constrained rank minimization.The large system analysis is then used to compute the achievable rates in HCNs.In this paper,we derive the rate expressions of macro users and micro users through finding the asymptotic eigenvalue distribution of the channel gains with random matrix theory.Finally,interference alignment in energy harvest two-way relay channels.In SWIPT systems,the RF energy can be harvested from either ambient interfering signals opportunistically or desired information signals at the receiver-side.This provides a great convenience to energy-constrained wireless devices.In this paper,we propose novel IA in two-way relay channels by formulating a transceiver design problem to jointly design all transmit and receive precoding matrix to implement SWIPT,our objectives are to minimize the total transmit power of all transmitters,maximize the total harvested energy of all receivers and maximize the total signal to interference and noise ratio of all receivers respectively.