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Novel Modulation Techniques using Isomers as Messenger Molecules for Nano Communication Networks via Diffusion
Na-Rae Kim, Chan-Byoung Chae
TL;DR
The paper addresses the lack of clearly specified practical messenger molecules for diffusion-based nano communication and the need to improve achievable-rate performance. It proposes three isomer-based modulation techniques and evaluates them against insulin-based concepts. The isomer-based techniques achieve higher performance, with reported SNR gains of about 7 dB and 7.5 dB, while messenger size and modulation order create a data-rate and reliability tradeoff.
Problem
Prior diffusion-based modulation studies did not clearly suggest practical messenger-molecule structures, while insulin-based concepts remained unclear for practical use.
Method
The paper uses isomers as messenger molecules, proposes concentration-, molecular-type-, and molecular-ratio-based modulation, and evaluates achievable rates under modeled practical scenarios.
Results
About 7 dB and 7.5 dB SNR gains are obtained for the proposed hexose-based systems over corresponding insulin-based systems.
Takeaways & Limitations
Trioses suit low-data-rate systems requiring higher transmission reliability, whereas hexoses suit high-data-rate systems.
Abstract
from arXiv · showhide
In this paper, we propose three novel modulation techniques, i.e., concentration-based, molecular-type-based, and molecular-ratio-based, using isomers as messenger molecules for nano communication networks via diffusion. To evaluate achievable rate performance, we compare the proposed tech- niques with conventional insulin based concepts under practical scenarios. Analytical and numerical results confirm that the proposed modulation techniques using isomers achieve higher data transmission rate performance (max 7.5 dB signal-to-noise ratio gain) than the insulin based concepts. We also investigate the tradeoff between messenger sizes and modulation orders and provide guidelines for selecting from among several possible candidates.
I. INTRODUCTION
Nano communication networks connect nanomachines, and diffusion-based molecular communication offers a short-range, biocompatible, energy-efficient approach. This paper addresses practical messenger-molecule design and channel modeling using isomers.
- I. INTRODUCTION: Diffusion-based molecular communication is introduced as a short-range approach for nano communication networks that avoids some RF device barriers.
- I. INTRODUCTION: Biocompatibility and energy efficiency motivate the paper’s focus on molecular communication for intra-body applications.
- I. INTRODUCTION: Prior studies analyzed diffusion fundamentals and modulation techniques but did not clearly specify practical messenger-molecule structures, particularly for insulin-based networks.
- I. INTRODUCTION: The paper proposes isomers as messenger molecules, adds ratio-based modulation, and modifies the prior energy model to account for isomer properties.
- I. INTRODUCTION: The analyzed system uses one transmitter and one receiver, with messenger molecules propagating through a liquid medium by Brownian-motion-driven diffusion.
- I. INTRODUCTION: The channel models received molecules with hitting probability, previous-symbol overflow, and additive white Gaussian noise.
B. Energy Model
The energy model represents messenger-molecule transmission through intracellular synthesis, vesicle handling, transport, and membrane release. It estimates costs using molecular formation energy and vesicle-related parameters.
- B. Energy Model: Messenger molecules are synthesized inside a nucleus, encapsulated in vesicles, transported to the transmitter boundary, and released through vesicle membrane fusion.
- B. Energy Model: The synthesis cost of messenger molecules is calculated from the enthalpy of formation, while vesicle synthesis, intracellular transport, and membrane fusion contribute additional energy costs.
- B. Energy Model: The modeled transmission process has four steps: generating messenger molecules, synthesizing vesicles, carrying them, and extracting them into the medium.
- B. Energy Model: The total transmission energy depends on molecule count, synthesis cost, vesicle cost, transport cost, membrane-fusion cost, and vesicle capacity.
III. MODULATION TECHNIQUES
Messenger-molecule properties determine modulation techniques in diffusion-based molecular communication. The paper proposes practical isomer messengers, introduces ratio-based modulation, and compares achievable rates across techniques.
- III. MODULATION TECHNIQUES: The paper proposes practical messenger molecules and a new ratio-based modulation technique, alongside concentration- and type-based modulation.
- III. MODULATION TECHNIQUES: The proposed techniques are evaluated by analyzing and comparing their achievable rates.
A. Isomers for Messenger Molecules
The paper selects isomers as practical messenger molecules and develops concentration-based modulation using their concentrations. The section describes aldohexose structures and the threshold-based decoding framework.
- Isomers are considered because the previously suggested hydrofluorocarbon messenger is highly flammable and may be unsuitable for practical applications.
- For numerical analysis, the paper uses aldohexoses and selects isomer families such as hexoses, pentoses, tetroses, or trioses according to the required modulation order.
- Aldohexoses have 16 stereoisomers, comprising eight D-form diastereomers and their eight L-form enantiomers.
- D-glucose predominantly forms α- and β-pyranose anomers in aqueous solution, at 36% and 64%, respectively.
- ICSK encodes symbols with different concentrations separated by thresholds, theoretically allowing unlimited modulation order but increasing error probability as thresholds become closer.
- Q-ICSK uses three thresholds to represent four symbols, with error probabilities obtained similarly to binary ICSK.
2) Q-ICSK:
The section directs readers to the appendix for the remaining Q-ICSK expressions.
- 2) Q-ICSK:: The remaining Q-ICSK expressions are provided in Appendix A.
- 2) Q-ICSK:: Appendix A contains expressions not included in the main text.
- 2) Q-ICSK:: The main section does not reproduce the other Q-ICSK formulas.
C. Molecular-Type-Based
The paper introduces isomer-based MoSK, using different isomer types to represent symbols. It also analyzes decoding errors under mutarotation and supports modulation-order choices through isomer-set selection.
- C. Molecular-Type-Based: Isomer-based MoSK uses different isomer types to represent different symbols and requires only one detection threshold.
- C. Molecular-Type-Based: The modulation order depends on the selected isomer set, reaching up to 32 for hexoses and 4 for trioses.
- C. Molecular-Type-Based: Mutarotation can cause α- and β-D-glucopyranose symbols to be decoded incorrectly, so the paper derives error probabilities that account for the process.
- C. Molecular-Type-Based: The error model uses nα and nβ for the transmitted numbers of α- and β-form molecules, with n denoting the total transmitted molecules.
3) 32-IMoSK:
IRSK encodes information through messenger-molecule ratios, offering high modulation order with simpler detection than concentration-based schemes. Practical design choices include molecule selection and binary or quadrature configurations.
- IRSK encodes information using ratios of messenger molecules rather than their absolute concentrations.
- Theoretically, IRSK can provide an infinite modulation order while requiring only two molecule types in its simplest form.
- Ratio detection can simplify the receiver and is more robust than ICSK when channel distortion occurs.
- A binary IRSK system represents two symbols with ratios 1:0 and 0:1, paralleling binary MoSK.
- Because α and β forms can interconvert during propagation, other molecule pairs are preferable for IRSK deployment.
E. Comparisons
The modulation techniques involve tradeoffs among achievable rate, transmitter and receiver complexity, and sensitivity to channel distortion. Technique selection therefore depends on the operating conditions.
- IMoSK generally offers better achievable rates than ICSK and IRSK except in the binary case.
- IMoSK requires generating and detecting multiple molecule types, whereas ICSK and IRSK require only one or two.
- Additional channel materials can affect molecule counts differently, producing distinct extra error probabilities for IMoSK, ICSK, and IRSK.
- The most appropriate modulation technique depends on the channel conditions and the desired balance among each system’s advantages and disadvantages.
IV. NUMERICAL RESULTS
The numerical analysis evaluates achievable rates using mutual information under diffusion-based assumptions and compares isomer-based techniques with insulin-based systems. Results favor smaller isomers for signal-to-noise performance and larger isomer sets for higher modulation order.
- Achievable rate is evaluated by maximizing mutual information under assumed equal physical properties for hexoses.
- SNR is calculated from received signal power and noise energy, with signal power depending on transmitted molecules, hitting probability, and the energy model.
- 32-IMoSK reaches 5 bits per symbol, whereas B-IMoSK reaches 1 bit per symbol using hexoses.
- Trioses provide higher SNR gain than hexoses because of their smaller size, but their data transmission limit is 1 bit per symbol.
- At increasing modulation orders, IMoSK maintains a higher rate and its performance gap slightly increases.
V. CONCLUSIONS
The work proposes isomer-based modulation techniques for practical nano communication and supports up to five bits per symbol. It compares achievable rates across modulation order at 10 dB SNR and provides candidate-selection guidance.
- V. CONCLUSIONS: The paper proposes practical modulation techniques using isomers as messenger molecules for nano communication networks.The approach includes concentration-based, molecular-type-based, and molecular-ratio-based techniques.
- V. CONCLUSIONS: The proposed modulation methods support up to five bits per symbol.
- V. CONCLUSIONS: Achievable rate is evaluated against modulation order for IMoSK and ICSK systems at an SNR of 10 dB.
- V. CONCLUSIONS: The work provides guidelines for selecting among possible messenger-molecule candidates.Future extensions include multiple messenger-molecule sets, collision modeling, and velocity alongside diffusion.
APPENDIX
The appendix specifies probability expressions for Q-ICSK and Q-IRSK systems using threshold intervals and symbol-dependent coefficients. The Q-IRSK formulation represents four distinct symbols and adjusts molecule contributions according to transmitted symbols.
- APPENDIX: Q-ICSK probabilities are expressed over successive threshold intervals involving molecule-count variables.The listed cases partition outcomes below τ1, between τ1 and τ2, and between τ2 and τ3.
- APPENDIX: Q-IRSK uses four different symbols, defined as S = {s1, s2, s3, s4}.
- APPENDIX: The Q-IRSK probability is evaluated within threshold interval [τY−1, τY) using weighted molecule counts and noise.
- APPENDIX: The coefficients α and β encode molecule contributions according to the selected symbols, with τ0 and τ4 representing −∞ and ∞.