This paper proposes a Generalized Memory-Assisted Adaptive-Threshold (G-MAAT) detection scheme for diffusion-based Molecular Communication (MC) systems. The proposed scheme applies to MC systems in which a single-type of molecules is assumed to carry the information from the single transmitting nanomachine (Tx Bio-NM), through a fluid medium, to the single receiving nanomachine (Rx Bio-NM). Thus, the information is represented by the received concentration of the information molecules, where the communication takes place in a three-dimensional diffusion-based unbounded environment. We present the generalized model of adaptive-threshold detection algorithm with N-Memory depth suitable for binary On-OFF Keying (BOOK signaling), where the Rx Bio-NM adapts the 1/0 bit detection threshold based on past received bits. This adjustment of the 1/0 detection threshold based on past received bits helps to alleviate the inter-symbol interference resulting from residual (tail) diffusion molecules arriving at the receiver due to past bit transmissions and reception noise. Furthermore, the complexity of G-MAAT is calculated and the performance evaluation in various noisy channel sources shows a promising improvement in the un-coded Bit Error Rate (BER) performance of the proposed scheme compared with other threshold detection mechanisms, which considerably more complex approaches found in the literature.

In some communications systems, uncoded symbol error rate (SER) estimation is required to be performed "on-the-fly" at the receiver, in order to provide a measure of the quality of service or to aid in the power control process required for CDMA systems. An example is the 3GPP WCDMA UMTS standard, where transport channel and physical channel bit error rates have been required as metrics to be estimated by the receiver. In this paper, we analyze the performance of a number of uncoded SER estimation techniques, including a novel technique in which we use the soft information of the received symbols to obtain a fast and accurate estimate of the uncoded SER. The technique we introduce outperforms the commonly used decode/re-encode/compare technique, in terms of accuracy and required estimation interval. Our technique also outperforms the brute-force technique, which is to send a known test-pattern, demodulate it at the receiver, and count the observed discrepancies.

In this paper, we consider the estimation of Gallager's (1968) random coding exponent (RCE) for a peak power constraint at the transmitter for the two-dimensional fading channel with additive white Gaussian noise (AWGN) and with perfect channel estimation at the receiver. Despite the fact that many wireless channels are peak-power-limited, the RCE for such channels has not been considered previously in the literature. Such a problem has only been partially solved for the AWGN case due to the difficulty in finding an input signal distribution that yields the RCE. In this paper, we adopt a different approach in which we develop upper and lower bounds to the RCE with the hope of trapping it in a narrow region. Our quest is successful as we can estimate the RCE to an error of only 0.72 bit per modulation symbol. Furthermore, we find that the RCE for the peak-power-limited channel does not represent a severe degradation relative to that attained for the average-power-limited channel. Thus, good modulation and coding schemes at reasonable complexity should exist for a peak-power-constrained fading channel.

In some communications systems, it is required to estimate the size of the received frame, or block, blindly, that is, using only the received frame. An example where such a problem arises is third generation WCDMA UMTS systems, where it is sometimes required to perform a blind transport format detection. We propose and evaluate a novel method for block-size detection for MPSK signalling based on the maximum-likelihood principle. The method we propose can either be used to estimate the block-size directly when the operating SNR yields a satisfactory "one-shot" detection error probability, or it can be used as a good "coarse" estimate of the block-size. That is, it is used to obtain a good guess of only a few potential block-size candidates, instead of scanning all possible candidates, and then a more accurate detection technique, however more complex, is used to narrow down the number of potential candidates to one successful candidate.

We compute the random coding error exponent for memoryless flat fading channels with ideal channel state information (CSI) and inputs drawn from a discrete alphabet. The signal sets we consider here are standard signal constellations commonly used in digital coded modulation. In addition, estimates of the code lengths required to achieve a certain error probability are determined and compared to those required for the AWGN channel. Finally, the effect of receiver diversity combining on improving communications reliability over the fading channel is considered. The results we obtain here shed light on the achievable performance over the fading channel with coded modulation.

There has been a considerable interest in determining the limits to communications over multipath fading channels. However, most studies have assumed that the channel is perfectly known at the receiver. In this paper, the random coding error exponent for flat fading channels with realistic channel state information (CSI) is studied. It is assumed that the CSI is obtained via some practical technique which utilizes a linear estimation scheme. Two commonly used techniques for channel estimation are considered in this paper, namely pilot tone extraction and pilot symbol transmission. The degradation in the achievable performance due to partial CSI is assessed and comparison of the different channel estimation methods is made. The focus of this paper is on the Jake's mobile Rayleigh flat fading model. Although Jake's model does not have a Markov property, such as that found in the commonly used exponential correlation model, which is usually attractive from the mathematical tractability point of view, Jake's model has a physical basis. Also, this model is considered herein from the standpoint of the random coding exponent. The results in this paper shed light on the amount of degradation in the achievable performance that is expected when the receiver has partial CSI. Finally, the sensitivity of the loss in achievable performance for the various channel estimation techniques with respect to channel parameters, such as Doppler spread and signal-to-noise ratio (SNR), is studied.

We compute the random coding error exponent for coded modulation transmitted over a flat, memoryless, Rayleigh fading channel. In addition, estimates of code lengths required to achieve a certain error probability are determined and compared to those required for the additive white Gaussian noise channel. Finally, the effect of receiver antenna diversity is also considered as a method to compensate for fading and is shown to have a significant, positive impact on the error exponent. The results we obtain represent an information theoretic view that complements the existing literature on the performance of coded modulation over fading channels with receiver diversity.

There has been much interest in wireless communications and thus it is appropriate to determine the Shannon limit for such systems. There have been a number of papers that consider channel capacity and also the random coding error exponent for various scenarios, In this paper, we consider Gallager's random coding error exponent for flat fading channels with antenna (or space) diversity employed at the receiver. Receiver antenna diversity is well known to be a fundamental technique for combating fading in wireless communications. The random coding error exponent is also well known to be a key quantity in assessing the ultimate, or achievable, performance over communications channels. We derive the random coding error exponent for various fading scenarios for which diversity combining is used. The cases we consider include memoryless fading channels with complete channel state information (CSI) at the receiver as well as time-correlated fading channels with complete CSI at the receiver. We also present results for time-correlated channels with partial CSI at the receiver via some practical channel estimation technique. The results we present in this paper shed light on the achievable performance over fading channels with receiver diversity combining and provide insight regarding the amount of coding complexity required for reliable communications over such channels.

In this correspondence, we consider the random coding error exponent for nondispersive two-dimensional (2-D) (quadrature) fading channels for which the channel state information (CSI) is perfectly known at the receiver and the input to the transmitter is constrained in its average power. Also, the effect of space diversity on improving the performance is demonstrated. The results obtained in this correspondence shed light on the effect of fading on communications reliability as well as the amount of coding complexity required to achieve a certain decoding error rate. A treatment for the random coding error exponent for time-correlated flat fading channels with Rayleigh fading and Bessel function correlation (the Jake's model) is also provided.

In mobilesat communications, offsets in frequency are important to estimate before further processing and decoding of the received signal. We devise a straightforward technique for coarse frequency acquisition through FFT computation of a set of special preamble schemes suitable for any Nyquist pulse. We have considered the noise samples model when such samples are assumed to be uncorrelated, as in most of the literature. We also show how to approximate the analysis when the receiver's narrowband LPF is taken into account, which results in noise attenuation and correlation. The former is more important and results in relatively improved performance. The presented results are obtained through theory and verified by computer simulation.>