Reduce Intersymbol Interference Research Articles

A New Method to Enhance SC-FDMA Communication with Channel Estimation Errors

The single-carrier frequency division multiple access (SC-FDMA) system is a popular system in mobile communication because of its advantage of low peak-to-average-power-ratio (PAPR), and the use of frequency-domain equalizers to reduce inter-symbol interference (ISI) and inter-carrier interference (ICI). This paper presents a comprehensive study of the SC-FDMA system with PAPR reduction using clipping and filtering in the presence of channel estimation errors for two different versions of SC-FDMA adopting the FFT and the DCT. The effect of peak power reduction and the channel estimation error on the system bit error rate (BER) is investigated. Simulation results prove that the BER performance is not much affected by the PAPR reduction.

Diffusive Molecular Communications With Reactive Molecules: Channel Modeling and Signal Design

This paper focuses on molecular communication (MC) systems using two types of signaling molecules which may participate in a reversible bimolecular reaction in the channel. The motivation for studying these MC systems is that they can realize the concept of constructive and destructive signal superposition, which leads to favorable properties, such as inter-symbol interference (ISI) reduction and avoiding environmental contamination due to continuous release of signaling molecules into the channel. This paper first presents a general formulation for binary modulation schemes that employ two types of signaling molecules and proposes several modulation schemes as special cases. Moreover, two types of receivers are considered: 1) a receiver that is able to observe both types of signaling molecules (2TM) and 2) a simpler receiver that can observe only one type of signaling molecules (1TM). For both of these receivers, the maximum likelihood (ML) detector for general binary modulation is derived under the assumption that the detector has perfect knowledge of the ISI-causing sequence. The performance of this genie-aided ML detector yields an upper bound on the performance of any practical detector. In addition, two suboptimal detectors of different complexity are proposed, namely, an ML-based detector that employs an estimate of the ISI-causing sequence and a detector that neglects the effect of ISI. The proposed detectors, except for the detector that neglects ISI for the 2TM receiver, require knowledge of the channel response (CR) of the considered MC system. Moreover, the CR is needed for performance evaluation of all proposed detectors. However, deriving the CR of MC systems with reactive signaling molecules is challenging since the underlying partial differential equations that describe the reaction–diffusion mechanism are coupled and non-linear. Therefore, we develop an algorithm for efficient computation of the CR and validate its accuracy via particle-based simulation. Simulation results obtained using this CR computation algorithm confirm the effectiveness of the proposed modulation and detection schemes. Moreover, these results show that MC systems with reactive signaling have superior performance relative to those with non-reactive signaling due to the reduction of ISI enabled by the chemical reactions.

ANALISIS UNJUK KERJA ZERO FORCING EQUALIZER PADA SISTEM OFDM MIMO

Wireless network is one of the most important things in the development of telecommunication. However, the existing wireless technology has not been able to efficiently create a very high data rate because it was very sensitive to fading. Therefore, Orthogonal Frequency Division Multiplexing (OFDM) technology combined with MIMO (Multiple Input Multiple Output) transceiver system was used to gain more diversity and bandwidth efficiency. The propagation performed on the OFDM MIMO system was multipath propagation. To reduce Intersymbol Interference (ISI) was used Zero Forcing (ZF) equalizer which works by combining channel response and equalizer response itself to eliminate ISI. This study aims to determine the effect of Zero Forcing Equalizer on OFDM MIMO system using rayleigh fading channel and compared the result with OFDM MIMO STBC system. The research method used was simulation using MatLab R2015a. The simulation results showed that the performance of OFDM MIMO ZF system was worse than OFDM MIMO STBC system i.e BER vs EbNo simulation, eye diagram simulation, and constellation diagram simulation. The OFDM MIMO ZF system was required an Eb / No value more than 25 dB to achieve BER 10-4 while the OFDM MIMO STBC system only required an Eb / No value of 10.5 dB to achieve BER 10-4. The eye pattern generated by the OFDM MIMO ZF system was more closed and the dispersion of constellation signals away from the ideal point while OFDM MIMO STBC system displayed a more open eye pattern and the dispersion of its constellation signal closer to the ideal point. It indicated more ISI occurs in the OFDM MIMO ZF system than that in OFDM MIMO STBC system.

LMS-RLS JOINT ADAPTIVE EQUALIZATION IN WIRELESS COMMUNICATION

Equalization is a most widely used optimization scheme to reduce inter-symbol interference (ISI). Inter symbol interfering environment is a case of misrepresentation of the sent signal at the receiver. Different symbols can hinder with one another which results in noise and less relevant, reliable signal. Multipath propagation means a wireless signal from a spreader reaches the receiver through numerous paths. If inter symbol interfering occurs within an arrangement, it must be reduced to the most minimal quantity conceivable. The inter symbol interference is reduced through the use of adaptive algorithms; LMS (Least Mean Square Error) and RLS (Recursive Least Square) equalization procedures being the most prominent ones. In this work, a joint adaptive algorithm is proposed and simulated. A novel method involving both LMS and RLS is used for suppression of Inter symbol interference. The LMS has the benefit of a fast convergence rate but has a significant value of mean square error (MSE).However, the RLS complements it with low value of MSE and a slow convergence rate . Thus, a joint RLS and LMS is proposed The proposed method results in improved BER performance, lesser mean square error and a faster convergence.

Performance investigation of 110-Gbps optical MSK system using a Quad Mach-Zehnder IQ modulator

In this paper, numerical simulation is conducted to investigate the generation, transmission and detection of a 110 Gbps optical Minimum Shift Keying (MSK) signal. The transmitter has been designed using a Quad Mach-Zehnder IQ Modulator. At the transmitter, a 110 Gbps optical MSK signal with constant envelope and a continuous phase is generated by combining signals of I-arm and $$90^\circ$$ phase shifted of Q-arm. Error-free transmission of 110 Gbps optical MSK signal is achieved after traversing a distance of 240 km, also a comparison is made with respect to Differential Phase Shift Keying (DPSK) to show its effectiveness. At the receiver side, the original signal is recovered through a balanced detection method, with a power penalty of around 3.34 dB. Also, BER curves of different bit rates for MSK are studied ranging from 40 to 120 Gbps and found that maximum 110 Gbps can be achieved error-free. The optical spectrum of both MSK and DPSK signals are observed and found that MSK is having narrower main lobes with smaller side lobes compared with that of DPSK, which in turn results in an increase in spectral efficiency and reduction in intersymbol interference.

Environmental Model-Based Time-Reversal Underwater Communications

This paper addresses channel compensation in underwater acoustic communications by proposing a method for inserting physical propagation modeling into a passive time-reversal (PTR) receiver. PTR is known as a low complexity channel equalizer that uses multichannel probing for time signal refocusing, reducing inter-symbol interference caused by multipath propagation. The proposed method aims to improve PTR communications performance by replacing the conventional noisy channel estimates with optimized and noiseless channel replicas computed by a numerical ray trace model. The optimization consists of environmental focalization in an “ a priori ” physical parameter search space to obtain “ a posteriori ” channel impulse response replicas that best match the observed data. The results obtained on two data sets acquired during the UAN’11 experiment in a shallow water fjord near Trondheim, in May 2011, show that the proposed method clearly outperformed the traditional PTR by a mean square error gain from 1 up to 4 dB. Channel tracking was effective despite a reduced physical parameter search space that could be exhaustively covered with a minimal computational effort. To the best of our knowledge, this is the first successful report on the usage of a physical parameter fed numerical model for underwater acoustic communications channel equalization with real transmitted data in a useful underwater modem frequency band.

Estimate of Passive Time Reversal Communication Performance in Shallow Water

Time reversal processes have been used to improve communication performance in the severe underwater communication environment characterized by significant multipath channels by reducing inter-symbol interference and increasing signal-to-noise ratio. In general, the performance of the time reversal is strongly related to the behavior of the q -function, which is estimated by a sum of the autocorrelation of the channel impulse response for each channel in the receiver array. The q -function depends on the complexity of the communication channel, the number of channel elements and their spacing. A q -function with a high side-lobe level and a main-lobe width wider than the symbol duration creates a residual ISI (inter-symbol interference), which makes communication difficult even after time reversal is applied. In this paper, we propose a new parameter, E q , to describe the performance of time reversal communication. E q is an estimate of how much of the q -function lies within one symbol duration. The values of E q were estimated using communication data acquired at two different sites: one in which the sound speed ratio of sediment to water was less than unity and one where the ratio was higher than unity. Finally, the parameter E q was compared to the bit error rate and the output signal-to-noise ratio obtained after the time reversal operation. The results show that these parameters are strongly correlated to the parameter E q .

A Time-Division Multiplexing Signaling Scheme for Inter-Symbol/Channel Interference Reduction in Low-Power Multi-Drop Memory Links

A time-division multiplexing digital channel coding scheme with inter-channel interference reduction property for multi-drop memory interfaces has been proposed. Shaping the transmitter output spectrum to avoid channel frequency notches, the proposed digital time-domain multiplexing signaling reduces inter-symbol interference and far-end crosstalk in multi-drop bus interfaces. Thanks to a proper guard interval insertion, the transmitted signal exhibits reduced inter-channel interference among time-domain sub-channels, as compared to the previously proposed digital spectrum shaping signaling. Applying the proposed coding scheme, the data rate can be four times as high as the first channel notch frequency, without employing decision-feedback equalizer, feed-forward equalizer, and continuous-time linear equalizer. On the other hand, non-return-to-zero signaling necessitates decision-feedback equalizer with at least 12 taps on the receiver side for receiving data at the same rate for the same multi-drop bus interface.

CGH for Indoor Visible Light Communication System

In this paper, we propose, design, and evaluate two indoor visible light communication (VLC) systems based on computer generated holograms (CGHs); a simple static CGH-VLC system and an adaptive CGH-VLC system. Each transmitter is followed by the CGH, and this CGH is utilized to direct part of the total power from the best transmitter and focus it to a specific area on the communication floor. This leads to reduction in inter-symbol interference and increasing in the received optical power, which leads to higher data rates with a reliable connection. In the static CG11H-VLC system, the CGH generates 100 beams (all these beams carry same data) from the best transmitter and directs these beams to an area of 2 m $\times2$ m on the communication floor. In the adaptive CGH-VLC system, the CGH is used to generate eight beams from the best transmitter and steer these beams to the receiver’s location. In addition, each one of these eight beams carries a different data stream. Whereas in the first system, a single photodetector is used (added simplicity), an imaging receiver is used in the second one to obtain spatial multiplexing. We consider the lighting constraints where illumination should be at acceptable level and consider diffusing reflections (up to second order) to find the maximum data rate that can be offered by each system. Moreover, due to the fact that each beam in the adaptive CGH-VLC system conveys a different data stream, co-channel interference between beams is taken into account. We evaluate our proposed systems in two different indoor environments: an empty room and a realistic room using simple on–off-keying modulation. The results show that the static CGH-VLC system offers a data rate of 8 Gb/s while the adaptive CGH-VLC system can achieve a data rate of 40 Gb/s.

An efficient radon mapped discrete wavelet transform-based algorithm for MC-CDMA system

The proposed work is aimed at improving bit error rate (BER) performance and spectral efficiency, increasing data rate, reducing inter-symbol interference (ISI) and inter-channel interference (ICI). Implementation of a conventional MC-CDMA system normally involves the use of QAM techniques for mapping. In the proposed work a mapping technique based on finite radon transform is used. The use of finite radon transform (FRT) improves orthogonality between the subcarriers. It also reduces ISI and ICI, which is due to the loss of orthogonality between carriers. Since discrete wavelet transform (DWT) is used instead of fast Fourier transform (FFT), which is employed in conventional multi-carrier CDMA techniques, the insertion of guard interval is not required and it offers better spectral efficiency. The result shows that the bit error rate performance of the proposed algorithm is far better than conventional techniques in AWGN channel.

Design and Simulation of a Linear Prolate Filter for a Baseband Receiver

Digital signals transmitted over a communication channel are mostly affected by noise. To reduce the detrimental effects of noise, a band-limited filter is used at the receiver, which results a phenomenon known as Inter-Symbol Interference. To avoid Inter-Symbol Interference, filters with greater bandwidth can be used. However, this causes high frequency noise to interfere with the transmitted information signal. This paper illustrates an innovative way to reduce Inter-Symbol Interference in the received baseband signal. This is achieved by making use of the processing bandwidth of a special filter designed by using Linear Prolate Functions. The result of the signal reconstruction capabilities of a prolate filter are compared with those of an ideal low pass filter in this paper.

Multiple-input multiple-output passive time reversal acoustic communication using filtered multitone modulation

Passive time reversal (PTR) technique can be exploited to reduce inter-symbol interference (ISI) span and co-channel interference (CCI) span to some extent in the multiple-input multiple-output (MIMO) PTR underwater acoustic communication using single-carrier (SC) modulation. However, there are still large ISI and CCI in the signals processed by PTR if the communication frequency band is relatively wide. The residual ISI and CCI in wideband MIMO PTR communication using SC modulation add to the complexity of the follow-up interference suppression approach. In order to further reduce the span of the residual ISI and CCI, an efficient wideband MIMO-PTR underwater acoustic communication using filtered multitone (FMT) modulation is proposed in this paper. The proposed method is analyzed in theory and verified using the experiment carried out in an experimental pool. The experimental results of the proposed method are compared with that of the MIMO-PTR acoustic communication using SC modulation. The results show that the symbol interval is expanded and the span of residual ISI and CCI is reduced using FMT approach. Compared with the MIMO-PTR acoustic communication using SC modulation, the proposed method possesses higher communication performance and lower computational complexity in channel estimation, PTR, and residual interference suppression.

A Digital Spectrum Shaping Signaling Serial-Data Transceiver With Crosstalk and ISI Reduction Property in Multidrop Interfaces

A transceiver (TRX) architecture employing a spectrum shaping signaling scheme is proposed, which can significantly reduce intersymbol interference and crosstalk in multidrop interfaces. The proposed TRX architecture relies on digital implementation rather than an analog/multitone approach, which can offer a power-efficient and versatile silicon implementation. Moreover, the crosstalk-induced noise can be reduced by applying the spectrum shaping signaling, and the whole TRX can be customized to the communication link by digital calibration while the aggregate data rate is kept fixed.

Novel network coding approaches for diffusion‐based molecular nanonetworks

AbstractThis paper proposes 2 novel network coding approaches for diffusion‐based nanonetworks. In these 2 methods, messages from nanomachines are jointly decoded at the receiver, and in one of the methods multiple molecule types are simultaneously employed to provide simultaneous communications over both nanomachine‐to‐relay and relay‐to‐nanomachine channels. As a result of the simultaneous use of the channel, each communication channel is allowed to use longer symbol intervals. This, in turn, results in a drastically reduced intersymbol interference component in all channels and enables communicating over longer ranges with higher data rates. The performance of the proposed communication system is investigated both analytically and via computer simulations.

Two‐stage frequency‐domain oversampling receivers for cyclic prefix orthogonal frequency‐division multiplexing systems

Orthogonal frequency-division multiplexing (OFDM) is a widely adopted technique in most wireless applications. It has been shown that zero padded OFDM (ZP-OFDM) with frequency-domain oversampling (FDO) can exhibit better performance than cyclic prefix OFDM (CP-OFDM) if the whole OFDM symbol is oversampled in the frequency domain. In this study, the authors propose a novel FDO-based scheme for CP-OFDM, which consists of two stages. First, the conventional CP-OFDM receiver is adopted to estimate the transmitted data and channel information. Second, the received symbol is reconstructed to reduce inter-symbol interference and oversampled in the frequency domain. The proposed scheme combines FDO and symbol reconstruction together, which enables the minimum mean square error (MMSE) and zero forcing (ZF) equalisers to exploit the channel information in high-dimensional non-orthogonal subcarrier domain and thus significantly suppress the interference on multipath channels. Simulation results show that the proposed FDO-MMSE CP-OFDM receiver can achieve much better bit error rate performance than the traditional CP-OFDM receiver and is comparable to the ZP-OFDM receiver with FDO.

A Hybrid NRZ/Multi-Tone I/O With Crosstalk and ISI Reduction for Dense Interconnects

A low-power four-channel hybrid NRZ/multi-tone transceiver for multi-drop bus (MDB) memory interfaces is designed and fabricated in 40 nm CMOS technology. The proposed system achieves 1 pJ/bit power efficiency, while communicating over an MDB channel with 45 dB loss at 3 GHz. The multi-tone (MT) nature of the proposed transceiver helps to control the intersymbol interference (ISI) and reduce the far-end crosstalk (FEXT), which results in a very energy-efficient implementation. The core size area is ${{80\times60\; {\upmu}\text{m}^2}}$ and ${130\times60\; {\upmu}\text{m}^2}$ for the TX and RX blocks (including the clock unit), respectively.

Stub Effect Mitigations Using Absorbing Materials

A new technology is developed for the mitigation of stub effects in high-speed interconnects. This technology substantially reduces the stub effects for high-speed signaling. It dampens reflected signals on stubs, thus reducing intersymbol interference and harmful coupling, and correcting timing jitter, all typically induced by the stub’s reflected signals. This paper shows two applications for high-speed digital system designs, the mitigation of via stub effects and that of empty connector effects, respectively. However, it is notable that the present method is suitable for reflection suppression for arbitrary types of stubs to improve the signal integrity.

Technique for Reduction of Intersymbol Interference in Ultra- Wideband System

In Ultra-wideband system as the pulse period is decreased; Inter Symbol Interference will be present in multipath fading channel. To reduce ISI, CH-DSSS with Code Hopping search algorithm is used. Performance of the algorithm is evaluated based on BER using a rake receiver. Computational speed is also increased by using the Beaulieu Series Method (BSM). Code Hopping search algorithm is being compared for two channel models S-V Model and Intel Based Model.

Dynamic Element Matching Techniques for Static and Dynamic Errors in Continuous-Time Multi-Bit <formula formulatype="inline"><tex Notation="TeX">$\Delta\Sigma$</tex></formula> Modulators

This paper presents techniques to address static and dynamic errors in high performance continuous-time (CT), $\Delta\Sigma$ modulators. The inter-symbol interference (ISI) model is presented and existing ISI reduction techniques are reviewed. A novel technique has been presented which can high-pass shape both static mismatch and ISI error of each element of a multi-bit DAC while decorrelating the instantaneous number of transitions from the input signal. The proposed technique can easily be extended to higher order shaping for both static mismatch and ISI errors. Simulation results show that the proposed technique can improve DAC linearity significantly in presence of both static mismatch and ISI error.

Error Probabilities for Optical Receivers That Employ Dynamically Biased Avalanche Photodiodes

A novel theory was recently reported for the avalanche multiplication process in avalanche photodiodes (APDs) under dynamic reverse-biasing conditions. It has been shown theoretically that the bit-synchronized, periodic modulation of the electric field in the multiplication region can offer improvements in the gain-bandwidth product by reducing intersymbol interference in optical receivers. This paper reports a rigorous formulation of the sensitivity of optical receivers that employ dynamically biased APDs. To enable the sensitivity analysis, a recurrence theory is developed to calculate the joint probability distribution function (PDF) of the stochastic gain and avalanche buildup time in APDs that are operated under dynamic biasing. It is shown that in an ideal buildup-time limited scenario, a minimum receiver sensitivity of −20 dBm is predicted at an optimal gain of approximately 47 for a 60 Gb/s communication system, compared to a minimum of 0 dBm in the static-bias case. The receiver sensitivity analysis also reveals that, as the peak-to-peak voltage of the dynamic reverse bias increases, the device optimal gain increases while maintaining a short avalanche buildup time and reduced ISI. Of course, a point of diminishing return exists in practice when the tunneling current in the multiplication region becomes dominant.