On The Integration And Extension Of Known-interference Cancellation In Wireless Ad Hoc Networks

With the increasing number of wireless terminals and their frequent movements,wireless ad-hoc network that is of easy deployment is an important networking mode.However,open wireless channel causes the interferences between concurrent transmissions,and further brings the low efficiency of wireless networks.Known interference cancellation(KIC)can improve the efficiency of wireless networks through employing the openness of wireless channel.The idea of KIC is that if a node sent,overheard or received a packet,it known the content of this packet.Hence,if the node receives an interfering signal that carries this packet,the interference can be cancelled by this node.KIC can be used in many scenarios,such as,conventional network coding(CNC)and physical-layer network coding(PNC)for two-hop topology and two flows,overlapped transmission(OT)for two-hop topology and single flow,and full-duplex transmission(FD).Existing work on KIC has three main problems:greedy employment of KIC(excessively using KIC leads that the space-reusing gain is low,which reduces the transmission efficiency),limited application scenarios,and the lack of practical transmission schemes.To tackle these problems,this thesis aims to improve the efficiency of existing KIC schemes,extend the application scenarios of KIC and propose practical transmission schemes for KIC.For the first problem,this thesis develops the idea of relaying method adaptation,which selects the best relaying method according to channel conditions,instead of preferential-ly selecting KIC-based relaying method.For the second problem,this thesis extends existing KIC techniques to support multi-hop unidirectional or bidirectional flows.Nodes in a multi-hop unidirectional or bidirectional flow can simultaneously transmit with the new KIC techniques.For the third problem,this thesis designs channel-sharing principles(i.e.MAC protocols)to support relaying method adaptation and the proposed KIC techniques.These protocols are close-coupled with physical and networks layers,to enhance the advantage of KIC in wireless Ad Hoc networks.The contributions of this thesis can be summarized as:(1)Relaying method adaptation and its application in rate-fixed network.Star-shaped topology is the basic unit of wireless network.This thesis first focuses on the star-shaped topology(with only one relay node),and then,extends the results into multi-hop network.The involved relaying methods mainly include plain routing(PR),CNC,and PNC.According to the channel conditions,the relaying method that can offer the maximal transmit rate is selected as the optimal relaying method.In this study,this thesis firstly formulates the maximal transmit rates of different relaying methods.Then,this thesis finds that this optimization problem can be formulated as the well-known set partition problem,which is NP-hard.A heuristic algorithm is designed to tackle this challenge,which is based on the problem of minimum-weight perfect matching(MWPM).The proposed algorithm is of polynomial time complexity(specifically,O(n3))and its throughput performance is close to that of the optimal method based on set partition.To apply the proposed idea of relaying method adaptation into practice,this thesis designs a new transmit scheme,i.e.overhearing-supported PNC-MAC(OPNC-MAC)protocol.This protocol supports physical-layer network coding with opportunistic overhearing and a two-level relaying method selection.The first selection level is the preliminary decision based on the topology,while the second level is the accurate decision based on the signal level and the state of nodes.(2)The application of relaying method selection in multi-rate network.Realizing the benefit of rate adaptation,this thesis further designs a scheme to support the relaying method selection in multi-rate network.In this study,this thesis firstly designs an algorithm to optimize the transmission rate and power of PNC,which is a challenging job because of superposed signals and interferences caused by concurrent transmissions.Then,this thesis designs a MAC protocol(rate-and-power-adaptation OPNC-MAC(RPOPNC-MAC))to support multiple flow patterns,multiple transmission rates,and multiple relaying methods.This MAC protocol can obtain topology information from network layer and channel information from physical lay-er,and select the optimal relaying method through jointly considering different information.RPOPNC-MAC lays a foundation for KIC's application,and also show a feasible example for the study of other promising physical techniques that need cooperations.(3)End-to-end KIC(E2E-KIC).Existing work on KIC mainly focuses on single-hop or two-hop networks,with PNC and FD communications as typical examples.This thesis extends the idea of KIC to general multi-hop networks,and proposes an end-to-end KIC(E2E-KIC)transmit method together with its MAC design.With E2E-KIC,multiple nodes in a flow pass-ing through a few nodes in an arbitrary topology can simultaneously transmit and receive on the same channel.According to different application scenarios,E2E-KIC has two types:bidi-rectional E2E-KIC(BE2E-KIC)for bidirectional multi-hop flow and unidirectional E2E-KIC(UE2E-KIC)for unidirectional multi-hop flow.This thesis firstly presents a theoretical analysis on the effectiveness of E2E-KIC(including BE2E-KIC and UE2E-KIC)in an idealized case.Then,to support E2E-KIC in multi-hop networks with arbitrary topology,this paper proposes two E2E-KIC-supported MAC protocols to support both types of E2E-KIC.(4)Performance analysis of KIC-based transmit schemes.Performance analysis can be used to understand the principle of transmit schemes and guide the design of transmit schemes.Because involving more nodes that concurrently transmit,UE2E-KIC and its MAC scheme is taken as an example to show the performance analysis of KIC-based transmit schemes.In the analysis,each node has a state,which is represented by the number of remaining backoff timeslots,and the state transition of a node is modeled as a Markov chain.The throughput is formulated through discussing the stationary distribution of the Markov chain and the channel-sharing principles of UE2E-KIC MAC.The proposed transmit schemes in this thesis are evaluated in our discrete-time simulator developed with MATLAB and C.The results show that the proposed schemes can further im-prove the performances of wireless networks in comparison with existing KIC schemes,and at the same time,the analysis results are very consistent with the simulation results.