Iterative soft-minimum mean-square error equalization for digital nonlinear page-oriented memories

Digital page-oriented volume holographic memory (POVHM) is a promising candidate for next-generation ultrahigh capacity optical data storage technology. As the capacity of the POVHMs increases, the bit error rate performance of the system is degraded due to increased interpixel interference (IPI) and noise. To improve the system performance under these adverse effects and to increase the capacity, joint iterative soft equalization-detection and error correction decoding might be attractive. To address that, by considering the nonlinearity inherent in the channel, an iterative soft equalization method that is optimized in the minimum mean-square error (MMSE) sense, called the iterative soft-MMSE (ISMMSE) equalization, is devised. The performance of the ISMMSE is evaluated by use of numerical experiments under different amounts of IPI and optical noise. Simulation results suggest that the ISMMSE is a good candidate for an ultrahigh capacity POVHM, which employs joint iterative equalization-detection and decoding.     

Rate-optimal fair power allocation in complex field network coded relay communications

In this paper, we consider the complex field network coded relay assisted communication (CFNC-RAC) channel. Although CFNC-RAC is spectrally efficient, its bit error rate performance is degraded by multi-access interference, which can be improved by appropriately allocating the user and relay powers. Since the fairness is an important factor for a practical multi-user communication system, we have proposed a rate-optimal fair power adaptation (ROFPA) technique in this work. The proposed ROFPA policy not only aims to maximize the average achievable sum-rate of CFNC-RAC under the use of the decode and forward relaying but also intends to satisfy the average rate-fairness restriction while taking the total power constraint and the network topology into account. We formulate the ROFPA as a non-convex optimization program and then derive an analytical solution for it. Extensive performance evaluation and numerical simulations validate that ROFPA method can provide significant sum-rate with considerable user fairness when compared to symbol-error-rate optimized (SER-OPT) policy proposed by Eritmen et al. (Wirel Netw, 2015. doi:10.1007/s11276-015-0924-1).     

Two-Dimensional Equalization/Detection for Patterned Media Storage

Although patterned media storage (PMS) is a promising candidate for ultrahigh-capacity magnetic data storage, as the capacity of PMS increases, the bit error rate (BER) performance of the system is degraded by increased two-dimensional intersymbol interference (2D-ISI), which results from intertrack interference (ITI), intersymbol interference (ISI), and noise. To improve the system performance under these adverse effects and to increase the capacity, in this paper, we propose to use and/or devise two-dimensional equalization/detection techniques: iterative decision feedback detection (IDFD) and two-dimensional generalized partial response equalization, which is optimized in minimum mean square error (MMSE), followed by one-dimensional Viterbi algorithm (2D-GPR/1D-VA). We evaluate the performance of the proposed methods by using numerical experiments under different amounts of 2D-ISI and noise. Simulation results suggest that under high storage density, the performance of the IDFD is improved by using more iterations and that under the same computational load, 2D-GPR/1D-VA performs better than IDFD. 2D-GPR/1D-VA, therefore, is a good candidate for ultrahigh-capacity PMS.     

Advances in signal processing for wireless and wired communications [Guest Editorial]

The six articles in this feature topic cover advances in signal processing for wireless and wired communications.     

Application of linear minimum mean-squared-error equalization for volume holographic data storage

When target densities of volume holographic data storage systems are increased, the systems experience increased interference from adjacent pixels and noise. Here we present a method for designing and applying linear minimum mean-squared-error (LMMSE) equalization to improve the bit error rates (BER's) and hence the storage densities achievable. Numerical results with five defocused data pages indicate that a significant improvement in the BER is possible with LMMSE equalization.     

Cross-layer enhanced time scheduling for multi-band OFDM UWB networks

Multi-band Orthogonal Frequency Division multiplexing based Ultra Wide-band (MB-OFDM UWB) technology is one of the strong alternatives for high data rate wireless personal area networks (WPANs) with low power consumption. The capacity of such systems is degraded by multi-path fading, shadowing, multi-user interference and noise. To improve system capacity under these adverse effects, in this paper, we devise cross-layer time scheduling methods, Proportional Time Scheduling with Modiano Algorithm (PTS-MA) and Proportional Time Scheduling with Channel State Information (PTS-CSI), in which scheduling and link adaptation are performed using instantaneous bit error probability (IBEP) estimates obtained through Modiano’s algorithm and our novel estimation technique, respectively. We evaluate the performance of the PTS schemes by using numerical experiments. Simulation results suggest PTS-CSI scheduler as the most promising candidate for practical MB-OFDM UWB WPANs with high capacity and fair throughput distribution.     

Distributed decision fusion over fading channels in hierarchical wireless sensor networks

In this work, we investigate distributed decision fusion in hierarchical wireless sensor networks that are degraded by fading and noise. With the use of the complete fading channel state information (CSI), we first derive the likelihood ratio test (LRT) based optimum fusion rule, which we call LRT–CSI. Then, we relax the use of the complete CSI and only the exact phase information is employed together with channel envelope statistics (CS), and we develop another LRT based fusion rule named LRT–CS, which is computationally simpler to implement compared to LRT–CSI. Finally, we analyze the detection performance of all the proposed fusion rules through extensive numerical results.     

Discrete magnitude-squared channel modeling, equalization, and detection for volume holographic storage channels

As storage density increases, the performance of volume holographic storage channels is degraded, because intersymbol interference and noise also increase. Equalization and detection methods must be employed to mitigate the effects of intersignal interference and noise. However, the output detector array in a holographic storage system detects the intensity of the incident light's wave front, leading to loss of sign information. This sign loss precludes the applicability of conventional equalization and detection schemes. We first address channel modeling under quadratic nonlinearity and develop an efficient model named the discrete magnitude-squared channel model. We next introduce an advanced equalization method called the iterative magnitude-squared decision feedback equalization (IMSDFE), which takes the channel nonlinearity into account. The performance of IMSDFE is quantified for optical-noise-dominated channels as well as for electronic-noise-dominated channels. Results indicate that IMSDFE is a good candidate for a high-density, high-intersignal-interference volume holographic storage channel.     

Pressure drop across micro-pin heat sinks under unstable boiling conditions

Flow boiling was investigated under unstable boiling conditions in three different micro-pin fin heat sinks using water and R-123 as working fluids. Once boiling was initiated severe temperature fluctuations were recorded for all the tested (three) micro-pin fin heat sinks.Flow images and fast-Fourier transform (FFT) of pressure signals during flow boiling were used to explain experimental results. The boiling instability mechanisms behind unstable boiling were discussed for both water and R-123. Accordingly, no significant pressure fluctuations with respect to time averaged pressure drop were evident for the tested micro-pin fin heat sinks before and after flow boiling instability initiates. However, a step change in the pressure signals were recorded with the inception of unstable boiling, and a sharp increase in the magnitude peaks of the FFT profiles was observed in the device operated with R-123, while there was no significant change in the FFT profiles in the devices operated with water. According to complementary flow visualization studies, the oscillation frequency of the periodic flow patterns for the device operated with R-123 was higher (f～80 Hz) than that of the devices operated with water (f～20 Hz).