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Publication: Using spatial partitioning to reduce the bit error rate of diffusion-based molecular communications

By 19th March 2020 No Comments

Molecular communication is an emerging field which focuses on realising communication between nano-scale devices  and especially the internet of bio-nano things. A key characteristic of molecular communication is the use of molecules as the information carrier. This paper considers diffusion-based molecular communications. The receiver is an important component in any communications system. We can divide the techniques for improving receiver performance of diffusion-based molecular communications into two categories. The first category of work uses signal processing techniques. Some examples in this category are: the paper designs a receiver based on minimum mean square error method; uses multiple samples per symbol and maximum likelihood method to design a receiver; designs a matched filter to maximise the signal-to-interference-plus-noise ratio; studies the design of estimate-and-forward relay nodes; and, uses data fusion of decisions from multiple receivers. The second category of work uses physical or chemical properties to improve communications performance. Some examples are: uses enzyme in the medium to reduce interference;  uses flow to improve the performance of the weighted sum detector at the receiver;  uses chemical reactions in the transmission medium to reduce interference.

This paper proposes to use the physical mechanism of spatial partitioning to improve communication performance. Our work is inspired by the fact that receptors on the cell membrane are organized into spatially separated clusters of receptors. In this paper, we  assume that the receiver uses receptors which can be activated by the signalling molecules. We propose to segregate these receptors into a number of clusters separated spatially. We consider two configurations: partitioned and mixed. In the partitioned configurations, spatial isolation is perfect and receptors cannot move between clusters; however, in mixed configurations, which can be considered as imperfect isolation, receptors can diffuse between the clusters. For both configurations, we derive the maximum-a-posteriori (MAP) demodulator by leveraging our earlier work on designing demodulators for diffusion-based molecular communications using a Markovian approach. This paper also removes a limitation of our earlier work in where the receiver is assumed to be a small cubic volume called a voxel. In this paper, we assume that the receiver consists of multiple voxels and the union of these voxels define the shape of the receiver. This method of modelling a 3-dimensional volume is similar to that in finite difference method. In this paper, we extend the method of demodulator design in to the multi-voxel case.

We study the impact of dr i.e. inter-voxel diffusion rate on the BER (bit error rate). Three different values for dr are used: 0, 0.5 and 1. The SSA simulations is performed up to time 2.5. Fig. 9 shows the BER for Symbols 0 and 1. It can be seen that a lower dr leads to a lower BER. The results in Figs. a and b show the BER for, respectively, Symbols 0 and 1. We witness the same trend that the BER increases with dr. This means that spatial partitioning leads to reduction in BER.

Authors: M.Usman Riaz, Hamdan Awan Chun Tung Chou
Journal: IEEE Transactions on Communications