Intersymbol Interference Suppression Research Articles

MODELING OF A DIGITAL COMMUNICATION SYSTEM WITH INTERFERENCE-RESISTANT CODING OVER DELAYED MULTIPATH CHANNELS FOR A FIXED WIRELESS ACCESS SYSTEM


 
 
 In this study, an analysis of the performance of a digital communication system was conducted to improve the efficiency of the communication channel. The system was de- signed and evaluated in the MatLab/Simulink environment, specifically for the transmission of binary data in a multipath channel with static fading. One of the main advantages of this system is its ability to provide high noise immunity, even in the presence of noise, interference, and signal delays. The performance of the system was investigated in terms of bit error rate (BER) over both an additive white Gaussian noise (AWGN) channel and a multipath Rayleigh fading channel. The study also considered the impact of inter-symbol interference (ISI) and explored different parameters for a static channel, resembling a wireless LAN system based on IEEE 802.11 (as defined by Rec ITU-R M.1225). This study uses a solution to suppress inter-symbol interference using cascading coding (convolutional turbo codes with Reed Solo- mon code), Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT), amplifiers at the transmitter side and normalizer at the receiver side, by regulating the amplification ratios of transmitter and receiver sides. Modeling of a digital communication system for a wide-band fixed wireless LAN system (for Indoor office and Outdoor to indoor systems) has been performed. The modeling outcomes show that the applied method provides a good per- formance improvement in channels with ISI with static fading.
 The application of cascading coding (turbo code together with RS code), amplifiers, and FFT on the transmitter side, and IFFT on the receiver side will eliminate the effects of inter-symbol interference on digital signals in a multipath channel with static fading (as defined by Rec. ITU-R M.1225 for internal and external transmission systems) for wireless fixed systems.
 
 

Anti-interference Algorithm for Broadband Wireless Communication based on Embedded Microcontroller

In order to improve the reliability of broadband wireless communication, the anti-interference design of broadband wireless communication in embedded environment is carried out, and an anti-interference algorithm of broadband wireless communication based on embedded microcontroller is proposed. The hardware of the anti-interference device is mainly composed of the communication modulating module, ARM main control system module and the single chip microcomputer main control module. The anti-interference algorithm is designed by using inter-symbol interference suppression algorithm, and the data transmission channel distribution model of broadband wireless communication is constructed. The interference filtering of broadband wireless communication is based on the decision feedback equalization method. The simulation results show that the anti-interference design of broadband wireless communication using this method has strong anti-interference ability, the output SNR is higher than that of the traditional method, and the communication quality is improved.

Joint Time-Reversal Space-Time Block Coding and Adaptive Equalization for Filtered Multitone Underwater Acoustic Communications.

Underwater acoustic (UWA) sensor networks demand high-rate communications with high reliability between sensor nodes for massive data transmission. Filtered multitone (FMT) is an attractive multicarrier technique used in high-rate UWA communications, and can obviously shorten the span of intersymbol interference (ISI) with high spectral efficiency and low frequency offset sensitivity by dividing the communication band into several separated wide sub-bands without guard bands. The joint receive diversity and adaptive equalization scheme is often used as a general ISI suppression technique in FMT-UWA communications, but large receive array for high diversity gain has an adverse effect on the miniaturization of UWA sensor nodes. A time-reversal space-time block coding (TR-STBC) technique specially designed for frequency-selective fading channels can replace receive diversity with transmit diversity for high diversity gain, and therefore is helpful for ISI suppression with simple receive configuration. Moreover, the spatio-temporal matched filtering (MF) in TR-STBC decoding can mitigate ISI obviously, and therefore is of benefit to lessen the complexion of adaptive equalization for post-processing. In this paper, joint TR-STBC and adaptive equalization FMT-UWA communication method is proposed based on the merit of TR-STBC. The proposed method is analyzed in theory, and its performance is assessed using simulation analysis and real experimental data collected from an indoor pool communication trial. The validity of the proposed method is proved through comparing the proposed method with the joint single-input–single-output (SISO) and adaptive equalization method and the joint single-input–multiple-output (SIMO) and adaptive equalization method. The results show that the proposed method can achieve better communication performance than the joint SISO and adaptive equalization method, and can achieve similar performance with more simpler receive configuration as the joint SIMO and adaptive equalization method.

Secure Wideband Beamforming Design for Two-Way MIMO Relaying Systems

In this paper, secure wideband beamforming design is investigated for two-way multiple-input multiple-output (MIMO) relaying systems with one eavesdropper. Due to the wideband signals exchanged by two sources via the relay, inter-symbol-interference (ISI) occurs inevitably and makes the beamforming design more challenging than the narrowband beamforming design. To sufficiently combat the ISI, the tapped delay lines are deployed at the relay. Besides, to reduce the computational complexity at the tapped delay lines based relay, the analog beamforming structure is also considered, and thus the MIMO relay beamforming can be distinctly partitioned into a transmit beamforming and a receive beamforming bridged by a single link. Joint optimization of the transmit and receive beamformings at both the relay and two sources is considered to maximize the secrecy sum rate (SSR) of the two-way MIMO relaying systems. Since the joint optimization is nonconvex and intractable, an iterative algorithm is proposed to decompose the original SSR maximization problem into four individual subproblems that can be reformulated as three types of convex problems, i.e., the generalized Rayleigh quotient problems, the polynomial time differential convex problem, and the semidefinite programming problem. A suboptimal solution for the secure transmit and receive beamformings at all nodes can then be obtained iteratively. Finally, numerical experiments are conducted to corroborate the effectiveness of our proposed iterative algorithm in terms of the achievable maximum SSR and ISI suppression.

Hybrid Precoding for Single Carrier Wideband Multi-Subarray Millimeter Wave Systems

This letter studies digital/analog hybrid precoding for wideband millimeter wave (mmWave) systems with multi-subarray architecture. By exploiting the mmWave propagation property that the dominate signal energy arrives at the receivers through some concentrated directions, we first present the single carrier transmission with time delay compensation technique performed at the base station, which can efficiently suppress inter-symbol interference. Then, in order to address the number of radio-frequency chains limitation, we propose a joint subarray selection and precoding design scheme by using the group sparse approach. Numerical results also demonstrate the effectiveness of the proposed scheme.

Rprop and improved Rprop+ based constant modulus type (RCMT) blind channel equalization algorithm for QAM signal

The aim of paper is to address the issues such as poor convergence, moderate BER, residual ISI associated with unsupervised (blind) weight adaptation technique employed for channel equalization. Two noble algorithms based on resilient back propagation framework have been proposed as solution for QAM signal. The widely accepted gradient descent based Constant Modulus algorithm suffers from poor convergence issues, high residual ISI and Moderate BER. Proposed solution assimilate Constant Modulus Algorithm (CMA) like error function into a general Rprop algorithm having two distinctive approaches of with/ without weight backtracking capability, taking into consideration of frequency selective nature of channels and additive gaussian noise. The algorithms exploit the advantage of Rprop mechanism, thus improving the convergence rate and have better ISI (inter symbol interference) suppression capability. Simulation of the proposed Rprop and improved Rprop+ based CM type (RCMT) algorithm proves their advantageously enhanced capabilities in terms of convergence, complexity, and residual ISI in comparison to the CMA and its variants. Proposed algorithm can also been used for M-PSK signal for which it shows similar performance.

Channel shortening equaliser through energy concentration for TH-UWB systems

Channel shortening equaliser (CSE) plays an important role in ultra wide band (UWB). This paper presents a method for updating the coefficients of CSE based on the adaptation of energy optimisation method using singular value decomposition (SVD) algorithm in UWB channel with time hopping (TH) and pulse position modulation (PPM). This is to suppress inter-symbol interference (ISI) and to simultaneously simplify the rake receiver architecture by significantly reducing the number of channel taps. This CSE can be concentrated the most amount of channel energy within just first taps and suppressed the most of this out the desired window. The presence of the proposed CSE before rake receiver enables the rake receiver implementation with less number of correlators. Computer simulation results are provided to compare the performance of the proposed method with a MSSNR CSE, lower bound, partial-rake, and selective-rake in terms of channel shortening and bit error rate (BER).

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.

A Space-Time RLS Algorithm for Adaptive Equalization: The Camera Communication Case

This paper presents a novel space-time recursive least-squares adaptive algorithm, which performs filter coefficients updates in space and postponed filtering in time. The algorithm is used for intersymbol interference suppression in optical camera communications, which is a subgroup of visible light communication systems. Optical camera communications uses image sensor receivers, as those available in smartphones, tablets, and laptops, to detect changes in light intensity in order to allow data transmission. The achievable data transmission rate of optical camera communication systems is nowadays constrained by the frame-per-second rate achieved by those devices, so that the spatial dimension, e.g., multiple-input multiple-output techniques, are typically exploited. Spatial intersymbol interference could arise and image blurring can be an issue especially when the link distance grows and/or when the receiver is in mobility. We present here a semiblind spatial fractionally spaced equalizer that uses a novel space-time recursive least-square adaptive algorithm to counteracts the blur introduced by the optical channel. Numerical results show how the bit error rate can be drastically reduced in both motion and out-of-focus blur scenarios.

Molecular communications: channel model and physical layer techniques

This article examines recent research in molecular communications from a telecommunications system design perspective. In particular, it focuses on channel models and state-of-the-art physical layer techniques. The goal is to provide a foundation for higher layer research and motivation for research and development of functional prototypes. In the first part of the article, we focus on the channel and noise model, comparing molecular and radio-wave pathloss formulae. In the second part, the article examines, equipped with the appropriate channel knowledge, the design of appropriate modulation and error correction coding schemes. The third reviews transmitter and receiver side signal processing methods that suppress inter-symbol interference. Taken together, the three parts present a series of physical layer techniques that are necessary to produce reliable and practical molecular communications.

Unified low-complexity decision feedback equalizer with adjustable double radius constraint

The maximum likelihood sequence estimation (MLSE) is an optimal equalization method to suppress Inter-Symbol Interference (ISI) in communication and storage systems. The Viterbi Algorithm (VA) provides an exact solution of MLSE. To reduce the complexity of VA, MLSE-DFE, which combines the VA within a decision feedback equalizer (DFE), is widely used in practical designs; however, the computing complexity is still too high. In this paper, we propose the SDVA-DFE, a unified DFE combining the concept of sphere detector (SD) and VA. The computing complexity of the SDVA-DFE can be reduced by proposed double radius constraints, upper radius (UR) and lower radius (LR). By adjusting the values of the two radiuses, the SDVA-DFE also provides a trade-off between performance and complexity. Simulation shows that this method is suitable for high-order modulation and long-length channel impulse response. When applied to a Lorentzian channel and channels of different eigenvalue spread, the SDVA-algorithm can reduce the complexity by over 90% at high SNR compared with MLSE-DFE.

Performance Evaluation of Variant Error Correction Schemes in Terms of Extended Coding Rates & BER for OFDM Based Wireless Systems

Modern OFDM systems provide effective spectral usage by allowing overlapping in the frequency domain. Moreover, it is highly resistant to multipath delay spread. The suppression of inter-symbol interference (ISI) is one of the top features of OFDM. It also facilitates mobile bandwidth allocation and may increase the capacity in terms of number of users. Even though the presence of OFDM’s built in error preventing mechanism; error tends to occur that averts delivery of proper signal. In this work we evaluated and adapted ways of fine-tuning for different error correction methods so that they may bring positive impact on communication systems who are developing and using OFDM. Here the performance of different known error correcting techniques for OFDM systems have been analyzed after extending and puncturing feature is applied on them. Simulations are performed in well-known simulator MATLAB to evaluate the modified techniques for different channel conditions. As the advantage of OFDM based systems are mainly the robustness to channel impairments and narrow-band interference; thus added error reduction models will improve significant efficiency of systems based on OFDM.

Two Novel Blind Equalization Algorithms for Rectangular Quadrature Amplitude Modulation Constellations

Two novel blind equalization techniques for odd bit rectangular quadrature amplitude modulation (RQAM) signaling are proposed in this paper, namely, rectangular contour algorithm (R RECT CA) and improved rectangular contour algorithm (IRCA). The proposed R RECT CA algorithm minimizes the dispersion of constant with respect to a rectangular-shaped zero error contour. The algorithm exploits the geometry of the RQAM to correct phase error within 180°, thus enhancing the convergence rate while minimizing the equalizer mis-adjustments. On the other hand, the proposed IRCA algorithm employs the estimated output from the decision device into the cost function, thus guiding the equalizer output to reside on multiple zero error rectangular shaped moduli. This method of feeding back the slicer output further reduces the mis-adjustment between the transmitted constellation and the new cost function in an efficient manner, which leads to faster convergence and better intersymbol interference suppression. The proposed algorithms can also work for the square QAM by mere change of only two constellation dependent constants, thus facilitating the implementation in hardware to enable transmission of both even and odd number of bits per symbol based constellations. Steady-state error analysis, MSE, and residual ISI comparison through the simulation results confirm the good performance of the proposed algorithms. Furthermore, the convergence characteristics of the proposed IRCA scheme establish the supremacy of IRCA over R RECT CA, which is its parent algorithm.

Multi-channel time frequency shift keying in underwater acoustic communication

Current long-range underwater acoustic communication (UWAC) faces many difficulties such as great propagation loss, high ambient noise and long multi-path delay. In order to design an excellent long-range UWAC system, it is necessary to increase signal-to-noise ratio (SNR), suppress inter-symbol interference (ISI) and alleviate frequency selective fading. In this paper, a novel time frequency shift keying scheme named as Multi-channel Hex Four Time Four Frequency Shift Keying (McH-4T4FSK) is presented. Both theoretical analysis and simulation over Bellhop multi-path channel model indicate that McH-4T4FSK exhibits lower bit error rate (BER) at the same SNR compared with traditional Frequency Shift Keying (FSK) regardless of diversity or not. Moreover, shallow water sea trial experiments at Xiamen Port with 15km distance and at Taiwan Strait with 30km distance confirm that McH-4T4FSK possesses lower BER and better robustness.

An Iterative DFE Receiver for MIMO SC-FDMA Uplink

Ever since the adoption of the single carrier frequency division multiple access (SC-FDMA) scheme for the uplink in the Long Term Evolution (LTE) standard, there has been much interest in improved receiver algorithms for the same. Successive interference cancelation (SIC) based turbo receivers (Turbo SIC) have been proposed to tackle the multi-stream interference (MSI) for transmission modes such as spatial multiplexing (SM) and multiuser (MU) multiple input multiple output (MIMO). In addition, decision feedback equalizers (DFE) have been discussed as an alternative to the simple linear minimum mean square error (LMMSE) based receivers to suppress intersymbol interference (ISI) caused by the frequency selective multi-path channel. This paper proposes a DFE receiver variant based on parallel interference cancelation (PIC) with maximum likelihood detection (MLD) and ordered SIC (OSIC) principles to suppress ISI and MSI. Simulations show that the proposed receiver performs better than the existing SIC and DFE based receivers and achieves the matched filter bound (MFB) for both coded and uncoded systems.

Filter-and-forward beamforming with adaptive decoding delays in asynchronous multi-user relay networks

We consider distributed relay beamforming in frequency selective fading channels where the relays employ the filter-and-forward (FF) protocol to mitigate inter-symbol interference (ISI). Recently, the FF scheme has been expanded by incorporating an adaptive decoding delay at the destination to facilitate ISI suppression in single-user (SU) relay networks. In this paper, we propose a non-trivial generalization of the FF approach with adaptive decoding delays for multi-user peer-to-peer (MUP2P) systems in which flexible decoding delays are of crucial importance: Unlike in SU relay networks, perfect timing synchronization is generally impossible in realistic MUP2P relay networks. The problem of jointly optimizing the filter coefficients at the relays and the individual decoding delays at the destinations is a nonconvex mixed integer (MI) programming problem which is generally hard to solve optimally. We propose an efficient deflation algorithm providing an approximate solution and a branch-and-cut (BnC) method yielding a lower bound as a benchmark. Our simulation results demonstrate that the approximate solution obtained using the proposed scheme is close to optimal and outperforms the solutions obtained by state-of-the-art schemes which do not make use of adaptive decoding delays.

A 25-to-28 Gb/s High-Sensitivity (<formula formulatype="inline"> <tex Notation="TeX">$-$</tex></formula>9.7 dBm) 65 nm CMOS Optical Receiver for Board-to-Board Interconnects

To address the two main challenges concerning the design of a transimpedance amplifier (TIA), namely, improving the sensitivity of the TIA without sacrificing bandwidth and suppressing inter-symbol interference (ISI) due to insertion loss, a 25 Gb/s optical receiver (RX) based on 65 nm CMOS technology, including a TIA and a PD operating at 1.3 μm wavelength, was developed. The key components of the TIA are a two-stage offset-cancelation scheme and a low-voltage output driver with peaking gain of 7.7 dB at 12.5 GHz. This driver performance is achieved by separating the equalizer function and output buffer of the driver. The TIA attains a sensitivity of -9.7 dBm (86- μApp) OMA and an eye opening of 65% at data rate of 25 Gb/s. The optical RX operates at 28 Gb/s with sensitivity of -8.2 dBm (121- μApp) OMA. Utilizing the CMOS TIA, an implemented VCSEL-based optical link operating at 850 nm wavelength achieves sensitivity of -7.3 dBm (98- μApp) OMA. Power consumption and power efficiency of the optical RX at data rate of 28 Gb/s are respectively 137.5 mW and 4.9 mW/Gb/s.

Iterative Frequency Domain Equalization for Single-Carrier Space Time Diversity Systems

Single carrier frequency domain equalization (SC-FDE) has been receiving much attention for its advantage of suppressing inter-symbol interference (ISI). We proposed a frequency domain iterative decision feedback equalization (FD-IDFE) algorithm for single carrier space time block coding (STBC) systems. The paper use the multi-antenna transmit and Alamouti signaling scheme to achieve the significant diversity gain. We design the feedback equalization structure by Mean Square Error (MSE) criterion and Lagrange optimization method, and we also consider the parameters estimation. At last, we compare the proposed algorithm with the conventional equalization schemes, the simulation results illustrate that our method has excellent performance.

Single-Carrier Space Time Transmission Diversity with Decision Feedback Equalization

In order to suppress inter-symbol interference (ISI), the Frequency domain decision feedback equalization (FD-DFE) algorithm is proposed in this paper for single carrier frequency domain equalization (SC-FDE) combined with Alamouti space time block coding (STBC) systems over frequency-selective channels. We use the cyclic prefix (CP) and two transmit antennas to achieve the significant diversity gain. The feedback equalization part is designed by Mean Square Error (MSE) criterion and the coefficients of filters are all in the frequency domain for the given channel frequency response. The outage and diversity analysis of system is also made to measure the equalization performance. Finally, the simulation results show that the proposed algorithm has better performance than the conventional liner equalization (LE) and hybrid structure decision feedback equalization (HDFE) schemes, and the computational complexity of our method is acceptable.

A 20-Mb/s Pulse Harmonic Modulation Transceiver for Wideband Near-Field Data Transmission

This brief presents a fully integrated low-power transceiver for wideband near-field data transmission across inductive telemetry links based on pulse harmonic modulation (PHM). This PHM transceiver uses two narrow pulses with specific amplitudes and timing at the transmitter (Tx) to suppress intersymbol interference (ISI) at the receiver (Rx) high-Q LC tank to achieve high data rates (DRs) without reducing the inductive link quality factor to extend its bandwidth. This method significantly improves the range and selectivity of the link. The PHM Rx architecture is based on noncoherent energy detection utilizing a novel pulse-based automatic gain control circuit, which significantly reduces the power consumption (46%) and ISI at short coupling distances. The PHM transceiver was fabricated in a 0.35- μm standard CMOS process and achieved a measured DR of 20 Mb/s with a bit error rate of 8.7×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> at a 10-mm distance using planar figure-8 coils. The PHM Tx and Rx power consumptions were 180 and 12.15 pJ/bit, respectively, at a 1.8-V supply voltage.