Is Intersymbol Interference Research Articles

Detection Interval of Aerosol Propagation From the Perspective of Molecular Communication: How Long is Enough?

In this paper, we propose a two-layer heterogeneous network to realize the remote monitoring and advanced warning for infectious diseases spread by airborne pathogens, whose detection can be considered as a binary detection problem. To intuitively study the detection process, we abstract it as a molecular communication via diffusion (MCvD) model and uncover that one of the key factors to impact the detection performance is inter-symbol interference (ISI), i.e., the viral aerosol from other biological entities. Therefore, overcoming ISI is imperative to ensure reliable detection. In the abstracted MCvD model, the detection performance can be described by the bit error rate (BER) performance. Following this assumption, we propose to optimize the detection interval to minimize the impact of ISI while ensuring the accurate detection of the transmitted information symbol, which is suitable for both the absorbing and passive receivers. For tractability, based on the signal-to-interference difference (SID) and signal-to-interference-and-noise amplitude ratio (SINAR), we design a modified-SINAR (mSINAR) to measure BER performance for the MCvD system with a variable detection interval. Besides, we derive the optimal detection interval in closed-form. Using simulation results, we show that in terms of BER, our proposed mSINAR scheme is superior to the competitive schemes, and performs similarly to the scheme with optimal intervals determined by the exhaustive search.

Low Complex Receiver Design for Modified Inverse Source Coded Diffusion-Based Molecular Communication Systems

Diffusion Based Molecular Communication (DBMC) uses messenger molecules to transfer information between nanomachines. A major challenge for DBMC is Inter Symbol Interference (ISI), which is due to the diffusive nature of the molecular channel. By computing lower and upper bounds for the number of received molecules, in this letter we prove that ISI and Bit Error Rate (BER) of a DBMC system depend on a-priori probability of transmitted data. We derive the optimal value of the a-priori probability for which ISI and BER are minimized. A coding technique, called Modified Inverse Source Coding (MISC), is proposed to control the a-priori probability of the transmitted data. We also propose two low complexity receivers for MISC-DBMC. The first is a low complexity Reduced State Sequence Detector (RSSD) based on the Viterbi algorithm. The second is a computationally less intensive Decision Feedback based Maximum A-Posteriori (DF-MAP) threshold detector. Simulation results demonstrate that the DF-MAP receiver has a similar BER performance as that of the RSSD receiver in the ideal scenario, but practically it is limited by error propagation. Also, we show that the MISC-DBMC system using RSSD or DF-MAP receiver has better BER performance, increased range, and lower complexity compared to uncoded DBMC system.

Application of Diversity Combining with RLS Adaptive Filtering in Data Transmission in a Hydroacoustic Channel.

When transmitting data in a hydroacoustic channel under difficult propagation conditions, one of the problems is intersymbol interference (ISI) caused mainly by the effect of multipath propagation. This phenomenon leads to a decrease in transmission parameters, and sometimes completely prevents it. Therefore, we have made an attempt to use diversity combining with Recursive Least Squares (RLS) adaptive filtering to improve the quality of data transmission in a hydroacoustic channel with strong reflections. The method was tested in simulation and during measurements in a real environment. The influence of the method on data transmission in the hydroacoustic channel was examined in detail. The obtained results allow us to draw conclusions regarding the purposefulness of use of diversity combining and RLS adaptive filtering in order to improve the quality of data transmission by reducing the effect of ISI.

Position-based modulation in molecular communications

Molecular communications via diffusion (MCvD) is a new paradigm that aims establishing communications among nanomachines in a fluidic diffusive channel using messenger molecules. In general, encoding and decoding of messages are done by the number and/or type of the molecules. Concentration Shift Keying (CSK) is the earliest and simplest communication scheme that encodes and decodes information. However, due to the dynamics of diffusion, one of the major challenges in MCvD channels is Inter Symbol Interference (ISI), which degrades the communication quality in CSK and leads to an error floor. In order to cope with this problem, various solutions have been proposed in the literature. Many of them require the use of multiple types of molecules, which results in an additional cost and computational complexity. This paper proposes a novel modulation scheme in molecular communications using the Pulse Position Modulation (PPM) concept that utilizes a single type of molecule and a corresponding simple receiver structure. Conventional PPM scheme is modified for the molecular communications channel and is shown to be better than CSK and other modulations in the literature, due to its robustness to ISI. Another advantage of PPM is not requiring knowledge about the channel as in other modulation schemes.

Adaptive Equalizer Using Selective Partial Update Algorithm and Selective Regressor Affine Projection Algorithm over Shallow Water Acoustic Channels

One of the most important problems of reliable communications in shallow water channels is intersymbol interference (ISI) which is due to scattering from surface and reflecting from bottom. Using adaptive equalizers in receiver is one of the best suggested ways for overcoming this problem. In this paper, we apply the family of selective regressor affine projection algorithms (SR-APA) and the family of selective partial update APA (SPU-APA) which have low computational complexity that is one of the important factors that influences adaptive equalizer performance. We apply experimental data from Strait of Hormuz for examining the efficiency of the proposed methods over shallow water channel. We observe that the values of the steady-state mean square error (MSE) of SR-APA and SPU-APA decrease by 5.8 (dB) and 5.5 (dB), respectively, in comparison with least mean square (LMS) algorithm. Also the families of SPU-APA and SR-APA have better convergence speed than LMS type algorithm.

A SIMO one-bit time reversal for UWB communication systems

With the one-bit time reversal ultra wideband (OTR-UWB) transceiver, the data symbols are encoded using the reversed order of the channel phase. The major factor limiting SISO OTR capacity and performance is intersymbol interference (ISI). As the data rate goes up, the ISI becomes more severe and it degrades system performance and capacity. In this article, a new single input multiple output (SIMO) system is proposed for an OTR-UWB system. The proposed transceiver structure is based on spatial focusing property of OTR. The performance of the proposed SIMO OTR-UWB system is analyzed in terms of the signal-to-interference-plus-noise-ratio (SINR). It is shown that using a SIMO OTR transceiver, ISI is reduced and the system capacity is increased almost linearly with the number of received antenna. Transmitted signal power at SIMO OTR decreases therefore in low data rates, SISO performance is better than SIMO, but in high rate scenario, SIMO OTR suppresses ISI better than SISO OTR and its performance is better. It is possible to compensate the reduced power using a receiver with more sensitivity, but to compensate the ISI effects, an MMSE receiver or equalizer techniques should be used, since the computational complexity of MMSE receiver grows exponentially with channel length and equalizers reduce the efficient bit rate. It is shown that the proposed SIMO-OTR capacity linearly increases with the number of antennas and decreases logarithmic (almost linearly).

Frequency-Domain Turbo Equalization and Multiuser Detection for DS-UWB Systems

One of the major challenges in direct sequence-ultra wideband (DS-UWB) receiver design is intersymbol interference (ISI). Several equalization schemes to eliminate ISI in DS-UWB systems have been proposed in the literature. It was shown that frequency-domain (FD) equalization techniques can offer better trade off between performance and complexity compared to time- domain equalization schemes for DS-UWB systems on highly dispersive channels. In this paper, we derive low-complexity FD minimum mean square error turbo equalization schemes for single-user binary phase shift keying (BPSK) and quaternary bi-orthogonal keying (4BOK) DS-UWB systems. For multiuser DS-UWB systems, we combine FD turbo equalization schemes with soft interference cancelation to obtain multiuser FD turbo detectors. The bit error rate performance gain due to turbo detection is shown to be significant, particularly for multiuser DS-UWB systems.

Review and analytical comparison of recursive and nonrecursive equalization techniques for PAM transmission systems

After near-end crosstalk (NEXT), the principal problem with pulse amplitude modulation (PAM) is intersymbol interference (ISI). The author presents an analytical comparison of various recursive and nonrecursive subtractive equalization techniques which may be used to remove ISI. Properties of subscriber loop responses which may be used in the design of simple and efficient equalizers are also explored. Simulation results are presented comparing the performances of many of the described equalizer structures for an 800 kb/s 2B1Q PAM transmission system operating over 12 kft of 24 AWG cable. >