Intersymbol Interference Compensation Research Articles

A Design of Two Sub-Stage Square-Root Nyquist Matched Filter

A pair of matched filters whose cascade response satisfies the Nyquist criterion can guarantee the inter-symbol interference (ISI)-free transmission for band-limited communication systems. For a linear phase finite impulse response square root Nyquist filter, it is necessary to strike a balance between the stop-band attenuation (SBA) and ISI performance. This paper proposes a novel approach for obtaining the square root Nyquist filter by adopting two sub-stage cascade filters group, which is known as the compensated half-band (HB) filter group (CHFG). The first sub-stage of the CHFG is a HB filter which can guarantee the required SBA performance on low computational complexity; whereas, the second sub-stage is an ISI compensation filter to ensure that the cascaded response of two CHFGs satisfies the Nyquist criterion. Theoretical analysis and experimental results show that the proposed CHFG can either achieve better SBA/ISI performance or reduce the computational complexity.

비트 패턴드 미디어를 위한 2차원 인접 심볼 간 간섭 보상

비트 패턴드 미디어를 위한 2차원 인접 심볼 간 간섭 보상

Demonstration of 3×341-Gb/s PDM-OFDM-256 Iterative Polar Modulation Signals Over 495 km of a Field-Deployed WDM System

We report a field demonstration of transmission of 1.44 Tb/s over the Korean Advanced Research Network using three 341-Gb/s PDM-OFDM signals with 256-iterative-polar-modulation. The dispersion managed commercial wavelength-division multiplexed (WDM) transmission system, deployed on legacy fiber and supporting WDM transmission on a 100-GHz grid, covered the distance of 248 km between Daejeon and Seoul. Using a loop-back configuration, the three channels were transmitted over a total distance of 495 km. Successful transmission was achieved by adopting both a digital signal processing-based intersymbol-interference compensation technique and an enhanced soft-decision decoder for the coded modulation.

Compensation of Multiple Access Interference Effects in CDMA-Based Acoustic Positioning Systems

Recently developed acoustic positioning systems operate in a code division multiple access (CDMA) configuration, in which the ranging signals between the nodes are digitally modulated orthogonal codes with the same carrier frequency and overlapping in time. CDMA permits higher position update rate than the alternative time division multiple access, but suffers from multiple access interference (MAI) effects, leading to outliers in the estimated ranges, and potentially large errors in position estimation. In this communication, we present and demonstrate experimentally a subtractive parallel interference cancelation (PIC) method, which achieves a high degree of resistance to MAI effects, and also permits us to compensate the intersymbol interference (ISI) caused by the limited frequency range of acoustic transducers. When evaluated empirically in an acoustic positioning system, the PIC algorithm obtains nearly total outlier cancelation for four operating beacons, and 2/3 reduction of outliers for a seven beacon setup with 32 bits long codes. Outliers are further reduced (down to 2%) by the modified PIC algorithm with ISI compensation. The method outperforms alternative outlier reduction techniques like doubling or quadrupling the signal length, or using power control to adjust the relative amplitudes of the beacon signals, and permits that the system is available for positioning over 95% of the time.

Novel Blind Equalizer for Coherent DP-BPSK Transmission Systems: Theory and Experiment

Adaptive blind equalization based on modulus algorithm is very efficient to carry out polarization separation and inter-symbol interference compensation in a coherent dual-polarization quaternary-phase-shift-keying transmission system. Its performance is, however, very poor when coherent dual-polarization binary-phase-shift-keying (BPSK) modulation is considered. In this letter, we propose a new blind equalizer adapted to any PSK constellation and we theoretically show its convergence. Experimental BER measurements and convergence analysis are performed in a 40 Gbps coherent dual-polarization BPSK system under different physical impairments. We show that our equalizer outperforms existing blind algorithms.

A Network of Kalman Filters for MAI and ISI Compensation in a Non-Gaussian Environment

This paper develops a new multiuser detector based on a network of kalman filters (NKF) dealing with multiple access-interference (MAI), intersymbol Interference (ISI), and an impulsive observation noise. The two proposed schemes are based on the modeling of the DS-CDMA system by a discrete-time linear system that has non-Gaussian state and measurement noises. By approximating the non-Gaussian densities of the noises by a weighted sum of Gaussian terms and under the common MMSE estimation criterion, we first derive an NKF detector. This version is further optimized by introducing a feedback exploiting the ISI interference structure. The resulting scheme is an NKF detector based on a likelihood ratio test (LRT). Monte-Carlo simulations have shown that the NKF and the NKF based on LRT detectors significantly improve the efficiency and the performance of the classical Kalman algorithm.

Precision in situ flying height measurement during track seeking process with intersymbol interference compensation

In order to use the harmonic ratio to measure the flying height with wide usable bands and high signal to noise ratio for ultrahigh density magnetic recording systems, the harmonic selection channel should be made narrow. But intersymbol interference (ISI) could be, therefore, introduced when this setup is used in the track seeking process. As a result, the measurement accuracy deteriorates significantly. Due to the band-limited nature of the harmonic selection channel, a linear equalizer based on the minimum mean-square error algorithm can be adopted to compensate for ISI and the accuracy achievable is 99%.