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In this paper, a diffusion-based molecular communication channel between two nano-machines is considered. The effect of the amount of memory on performance is characterized, and a simple memory-limited decoder is proposed; its performance is shown to be close to that of the best possible decoder (without any restrictions on the computational complexity or its functional form), using Genie-aided upper bounds. This effect is adapted to the case of Molecular Concentration Shift Keying; it is shown that a four-bits memory achieves nearly the same performance as infinite memory for all of the examples considered. A general class of threshold decoders is considered and shown to be suboptimal for a Poisson channel with memory, unless the SNR is higher than a value specified in the paper. During each symbol duration (symbol period), the probability that a released molecule hits the receiver, changes over the duration of the period; thus, we also consider a receiver that samples at a rate higher than the transmission rate (a multiread system). A multi-read system improves performance. The associated decision rule for this system is shown to be a weighted sum of the samples during each symbol interval. The performance of the system is analyzed using the saddle point approximation. The best performance gains are achieved for an oversampling factor of three for the examples considered.

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Molecular Communication (MC) is a communication strategy that uses molecules as carriers of information, and is widely used by biological cells. As an interdisciplinary topic, it has been studied by biologists, communication theorists and a growing number of information theorists. This paper aims to specifically bring MC to the attention of information theorists. To do this, we first highlight the unique mathematical challenges of studying the capacity of molecular channels. Addressing these problems require use of known, or development of new mathematical tools. Toward this goal, we review a subjective selection of the existing literature on information theoretic aspect of molecular communication. The emphasis here is on the mathematical techniques used, rather than on the setup or modeling of a specific paper. Finally, as an example, we propose a concrete information theoretic problem that was motivated by our study of molecular communication.

In this paper, a solution for simulating negative signals based on the diffusion-reaction channel model is proposed. While the proposed solution does not exploit the full degrees of freedom available for signaling in a diffusion-reaction process, but its end-to-end system is a linear channel and amenable to Fourier transform analysis. Based on our solution, a modulation scheme and a precoder are introduced and shown to have a significant reduction in error probability compared to previous modulation schemes such as CSK and MCSK. The effects of various imperfections (such as quantization error) on the communication system performance are studied.

In [Scholtz (1993)], an ultra-wide bandwidth time-hopping spread-spectrum code division multiple-access system employing a binary PPM signaling has been introduced, and its performance was obtained based on a Gaussian distribution assumption for the multiple-access interference. In this paper, we begin first by proposing to use a practical low-rate error correcting code in the system without any further required bandwidth expansion. We then present a more precise performance analysis of the system for both coded and uncoded schemes. Our analysis shows that the Gaussian assumption is not accurate for predicting bit error rates at high data transmission rates for the uncoded scheme. Furthermore, it indicates that the proposed coded scheme outperforms the uncoded scheme significantly, or more importantly, at a given bit error rate, the coding scheme increases the number of users by a factor which is logarithmic in the number of pulses used in time-hopping spread-spectrum systems. Index Terms-CDMA, low-rate convolutional codes, spreadspectrum techniques, super-orthogonal codes, time-hopping, ultra-wide bandwidth radio. I. INTRODUCTION I N [1], an ultra-wide bandwidth time-hopping spread-spectrum code-division multiple-access system (UWB-TH-CDMA) employing a binary pulse-position modulation (PPM) signaling have been introduced. In this system, data is transmitted using extremely short pulses with duration less than 1 ns. This technique is called impulse radio (IR) and since the transmitted pulses are extremely short, the bandwidth of this system is a few hundred times larger than the bandwidth of other systems for the same applications. This communication system does not use sinusoidal carriers to raise the signal to higher frequencies, and in fact its frequency band is from about dc to several gigahertz. The advantages of this spread-spectrum multiple-access system are briefly power consumption, cost and complexity reductions.

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