Molecular transceiver design and performance study in diffusive molecular communications

Abstract

Molecular communication (MC) is inspired by the nature, where chemical or biological molecules are used to transmit information instead of electronic or electromagnetic signals in the traditional wireless communications. Due to non toxic material and possible energy-efficient signal propagation, MC has been recognised to be the naturally fitting methods to provide communication inside the living bodies and other biological environments, including the applications in biomedical, industrial and consumer goods, military, environmental, etc. In this thesis, we focus on the diffusion-based molecular communication (DMC), where information molecules are only driven by the Brownian motion.

In this thesis, we first provide an introduction for the research and development of DMC, as well as address the background in the research and development of DMC, including channel model, modulation schemes, receiver design, detection algorithm and multiple access technique. Based on the background, we realize that there is strong inter-symbol interference (ISI) in DMC systems due to the slow propagation speed and random movements of information molecules. Furthermore, it can be shown that on-off keying (OOK) modulation is lack of the capability to reduce ISI effect and is also hard to implement in practice. On the other hand, binary molecule shift keying (BMoSK) is a promising modulation technique, which employs some embedded capability to reduce ISI. Therefore, in this thesis we first propose a low-complexity ISI cancellation (ISIC) to improve the performance of DMC systems with either OOK or BMoSK modulation. In order to investigate the achievable performance of the DMC systems with OOK and BMoSK modulation and with/without ISIC, we then analyse the bit-error rate (BER) performance of DMC systems by introducing different analytical approaches. Specifically, we first consider the Poisson modelling of the DMC systems as the exact approach to analyse the BER of the DMC systems with OOK or BMoSK modulation. Then, the Gaussian and Gamma approximation approaches are introduced to reduce the computation complexity. Moreover, the simplified Poisson, simplified Gaussian and MonteCarlo approaches are proposed to further reduce the computation burden for BER. We demonstrate that all the approximation and simplified approaches can provide near-accurate estimation of the BER performance of DMC systems.

As ISI is a main factor affecting the performance of DMC systems, following the above studies, a range of linear equalisers, including matched-filter (MF), zero-forcing (ZF) and minimum mean- square error(MMSE) equalisers, are introduced to the BMoSK-modulated DMC systems, in order to mitigate the effect of ISI. Our studies show that ZF and MMSE equalisers can significantly reduce the effect of ISI.

Furthermore, we propose and study a molecular code-division multiple access (MoCDMA) systems with BMoSK modulation, in order to allow multiple nano-machines to simultaneously communicate with an access-point receiver. We mirror the proposed MoCDMA to the conventional radio-based CDMA with binary phase-shift keying (BPSK) modulation, based on which we derive the various expressions for received signals, so that the information conveyed by different nano-users can be flexibly detected on either symbol-by-symbol or block-by-block basis. For signal detection in MoCDMA systems, a range of detectors are proposed, which include the symbol-based, block-based and frequency-domain detectors that are operated in the principles of MF, ZF, and MMSE. Furthermore, the performance of the MoCDMA systems with various detection schemes is studied and compared, showing that the MoCDMA with these detection schemes are capable of providing required communications in multiple user environments. Finally, we conclude the thesis and propose some possible future research issues.

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Identifiers

ORCID for Lie-Liang Yang: orcid.org/0000-0002-2032-9327

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