Research On Diffusion-Based Molecular Communication Theory And Technology

Due to the constraints of transceiver size and energy consumption,traditional electromagnetic communication can not be directly applied to nanoscale devices.In recent years,with rapid development of nanotechnology,bioengineering and synthetic biology,microscale and nanoscale devices have become a reality.The reliable communication between microscale devices is still an open and new subject.In nature,there are a large number of biological nanomachines,such as cells,which can exchange information through biochemical molecules and cooperate to form efficient and reliable biological nanonetwork.Since biologically inspired molecular communication(MC)is suitable for many specific scenarios,such as in an organism,and has the advantages of biocompatibility,small size,high energy efficiency and low energy consumption.It is generally believed that molecular communication is one of the feasible communication technologies to realize nanonetwork and as a supplement to the existing communication systems in nanoscale.Free diffusion is the most common molecular transmission mechanism in intracellular and intercellular.This transmission system has the advantages of simple and the ability to realize fast and short distance information transmission because it does not need additional energy sources and communication facilities.Therefore,diffusion-based molecular communication is a hot topic in MC research and has broad application prospects in biomedicine,military,environmental monitoring,industry and other fields.In diffusion-based molecular communication,the propagation time is proportional to the square of the distance.If the transmission distance is far,the communication process may fail.In order to improve the reliability and performance of communication link,relay is a good choice.Information transport is governed by diffusion through a fluid medium.The achievable data rates are very low compared to the radio communication system,since diffusion is a slow process.MIMO technique can effectively improve the data transmission rate.This dissertation mainly focuses on the research of theory and technology of diffusion-based molecular communication.A two-hop molecular communication system is constructed,and a relay binding in discrete time(BIND)channel is proposed.Combining the ligand receptor binding mechanism in signal transduction system with decode and forward(DF)two-hop molecular communication system,the bit error probability(BER)performance of the relay network is analyzed.Diffusion-based molecular MIMO communication system is studied,including system modeling,channel modeling and receiver design.The main contributions of this dissertation are as follows:(1)The information theory of signal transduction in two-hop MC system is studied.According to the interdisciplinary research of biology and information theory,the signal transduction based on the cyclic adenosine monophosphate(c AMP)is introduced.For signal transduction,we extend from point-to-point communication network to two-hop communication network,and propose the relay BIND channel.For binary finite input alphabets,binary channel state,and binary output,a discrete-time finite state Markov channel is modelled.We show how to calculate the mutual information(MI)of the relay BIND channel.Further,our simulation and analytical results show that the relay BIND channel can improve the molecular communication capacity between two nanomachines using the relay.(2)Performance analysis of a decode-and-forward(DF)relay-assisted diffusion-based molecular communication system is presented.The system consists of one nanotransmitter,one nanoreceiver and one nanotransceiver acting as relay.We consider cases using one molecule in our two-hop network(1M2H),and using two molecules(2M2H).Inspired by the biological signal transduction systems,the ligand-receptor binding mechanism is introduced for the receptors on the surface of receiver.Inter-symbol interference(ISI)and self-interference(SI)can be identified as the performance-limiting effects in our relaying network.The number of received molecules can be approximated by the normal distribution,and using this approximation,a closed-form expression of bit error probability for the relay-assisted network is derived.Then,we put forward an optimization problem for minimizing the bit error probability,and solve it using an algorithm based on the gradient descent to find the optimal detection threshold.In addition,the expression of channel capacity is obtained for two-hop molecular communication with ligand receptors.Numerical results show that the 2M2 H network has greater capacity than the 1M2 H network.(3)The channel modeling and high-level receiver design of diffusion-based molecular MIMO system are analysed.Diffusion-based communication refers to the transfer of information using molecules as message carriers whose propagation is based on the law of molecular diffusion.In order to improve the data rate,we propose a novel paradigm for diffusion-based molecular MIMO communications.First,we establish the communication mode of molecular MIMO system.Then,since the receptors are not independent of each other,we develop a channel model for the MIMO system by considering the possible transmission routes and use it to determine inter-symbol interference(ISI).Moreover,a high-level scheme is proposed for the receiver design,consisting of three parts: a concentration processor,a detector,and a data fusion centre.A low-complexity signal processing technique is proposed for detecting molecular concentration,where the global pulse peak time is calculated and used to suppress ISI.For the design of the detector,the Neyman-Pearson test is used to obtain the optimal detection performance.Analytical results show that the performance of the ISI cancellation processing outperforms the sampling processing.MIMO with fusion is better than MIMO with selection combining in terms of BER.Moreover,with the increase of the number of molecules and symbol duration,the BER performance of each detection scheme is improved.