Robust Precoder Adaptation for MIMO Links With Noisy Limited Feedback

In this paper, we propose two robust limited feedback designs for multiple-input multiple-output (MIMO) adaptation. The first scheme, namely, the combined design jointly optimizes the adaptation, CSIT (channel state information at the transmitter) feedback as well as index assignment strategies. The second scheme, namely, the decoupled design, focuses on the index assignment problem given an error-free limited feedback design. Simulation results show that the proposed framework has significant capacity gain compared to the naive design (designed assuming there is no feedback error). Furthermore, for large number of feedback bits $C_{rm fb}$, we show that under two-nearest constellation feedback channel assumption, the MIMO capacity loss (due to noisy feedback) of the proposed robust design scales like ${cal O}(P_e2^{-{{C_{rm fb}}over{t+1}}})$ for some positive integer $t$. Hence, the penalty due to noisy limited feedback in the proposed robust design approaches zero as $C_{rm fb}$ increases.      

Noncoherent Synchronization of UWB-IR Multiple-Antenna Multipath Channels

This paper deals with the maximum-likelihood (ML) noncoherent data-aided (e.g., no blind) synchronization of multiple-antenna ultrawideband impulse-radio (UWB-IR) terminals that operate over broadband channels and are affected by multipath fading with a priori unknown number of paths and path-gain statistics. The synchronizer that we developed achieves the ML data-aided joint estimate of the number of paths and their arrival times (e.g., time delays), without requiring any a priori knowledge and/or a posteriori estimate of the amplitude (e.g., module and sign) of the channel gains. The ultimate performance of the proposed synchronizer is evaluated (in closed form) by developing the corresponding CramÉr–Rao bound (CRB), and the analytical conditions for achieving this bound are provided. The performance gain for the synchronization accuracy of multipath-affected UWB-IR signals arising from the exploitation of the multiple-antenna paradigm is (analytically) evaluated. Furthermore, a low-cost sequential implementation of the proposed synchronizer is detailed. It requires an all-analog front-end circuitry composed of a bank of sliding-window correlators, whose number is fully independent from the number of paths comprising the underlying multiple-antenna channel. Finally, the actual performance of the proposed synchronizer is numerically tested under both the signal acquisition and tracking operating conditions.      

Design and Analysis of Isolated Noise-Tolerant (INT) Technique in Dynamic CMOS Circuits

Along with the progress of advanced VLSI technology, noise issues in dynamic circuits have become an imperative design challenge. The twin-transistor design is the current state-of-the-art design to enhance the noise immunity in dynamic CMOS circuits. To achieve the high noise-tolerant capability, in this paper, we propose a new isolated noise-tolerant (INT) technique which is a mechanism to isolate noise tolerant circuits from noise interference. Simulation results show that the proposed 8-bit INT Manchester adder can achieve 1.66$times$ average noise threshold energy (ANTE) improvement. In addition, it can save 34% power delay product (PDP) in low signal-to-noise ratio (SNR) environments as compared with the 8-bit twin-transistor Manchester adder under TSMC 0.18-$mu$ m process.      

Novel Scheme for Joint Estimation of SNR, Doppler, and Carrier Frequency Offset in Double-Selective Wireless Channels

As receiver performance will be degraded by carrier frequency offset (CFO), Doppler shift, and low signal-to-noise ratio (SNR), a novel estimator that jointly considers CFO, Doppler shift, and SNR is proposed in this paper. The proposed algorithm uses the Fourier transform (FT) to calculate the power spectral density of time-varying channels through channel estimates. Then, a new periodogram technique is utilized to estimate CFO, Doppler shift, and SNR together. Unlike conventional methods in sinusoid estimation, which rely on the peak-value search of a periodogram, this paper exploits the hypothesis test to address the random frequency modulation of time-varying channels. Furthermore, to optimize estimation performance, a theoretical analysis is also provided on the influences of some key parameters, e.g., the length of the signal processed with fast FT , the amplitude threshold value, the SNR dynamic range, and the velocity dynamic range. Correspondingly, the appropriate key parameters are chosen according to this analysis and are validated by simulations. The results are consistent with our analysis and present high accuracy over a wide range of velocities and SNRs.      

Single-Exclusion Number and the Stopping Redundancy of MDS Codes

For a linear block code ${cal C}$, its stopping redundancy is defined as the smallest number of check nodes in a Tanner graph for ${cal C}$, such that there exist no stopping sets of size smaller than the minimum distance of ${cal C}{bf .},$ Schwartz and Vardy conjectured that the stopping redundancy of a maximum-distance separable (MDS) code should only depend on its length and minimum distance.      

Buffered Cross-Bar Switches, Revisited: Design Steps, Proofs and Simulations Towards Optimal Rate and Minimum Buffer Memory

Regarding the packet-switching problem, we prove that the weighed max-min fair service rates comprise the unique Nash equilibrium point of a strategic game, specifically a throughput auction based on a “least-demanding first-served” principle. We prove that a buffered crossbar switch can converge to this equilibrium with no pre-computation or internal acceleration, with either randomized or deterministic schedulers, (the latter with a minimum buffering of a single-packet per crosspoint). Finally, we present various simulation results that corroborate and extend our analysis.      

A Control Strategy for Four-Switch Three-Phase Brushless DC Motor Using Single Current Sensor

A control strategy based on single current sensor is proposed for a four-switch three-phase brushless dc (BLDC) motor system to lower cost and improve performance. The system's whole working process is divided into two groups. In modes 2, 3, 5, and 6, where phase c works, phase- c current is sensed to control phases a and b, and phase-c current is consequently regulated. In modes 1 and 4, the combination of four suboperating modes for controlling phase-c current is proposed based on detailed analysis on the different rules that these operating modes have on phase-c current. Phase-c current is maintained at nearly zero level first, and phase- a and phase-b currents are regulated by speed circle. To improve control performance, a single-neuron adaptive proportional–integral (PI) algorithm is adopted to realize the speed regulator. Simulation and experimental systems are set up to verify the proposed strategy. According to simulation and experimental results, the proposed strategy shows good self-adapted track ability with low current ripple and strong robustness to the given speed reference model. Also, the structure of the drive is simplified.      

Message Scheduling for the FlexRay Protocol: The Static Segment

In recent years, time-triggered communication protocols have been developed to support time-critical applications for in-vehicle communication. In this respect, the FlexRay protocol is likely to become the de facto standard. In this paper, we investigate the scheduling problem of periodic signals in the static segment of FlexRay. We identify and solve two subproblems and introduce associated performance metrics: 1) The signals have to be packed into equal-size messages to obey the restrictions of the FlexRay protocol, while using as little bandwidth as possible. To this end, we formulate a nonlinear integer programming (NIP) problem to maximize bandwidth utilization. Furthermore, we employ the restrictions of the FlexRay protocol to decompose the NIP and compute the optimal message set efficiently. 2) A message schedule has to be determined such that the periodic messages are transmitted with minimum jitter. For this purpose, we propose an appropriate software architecture and derive an integer linear programming (ILP) problem that both minimizes the jitter and the bandwidth allocation. A case study based on a benchmark signal set illustrates our results.      

Perceptual Color Image Coding With JPEG2000

A perceptual color image coder (PCIC) is presented for the $YC_{b}C_{r}$ color space within the framework of JPEG2000. This coder employs a vision model based perceptual distortion metric (PDM) to approximate perceived error for rate-distortion (R-D) optimization in order to maximize the visual quality of coded images. The vision model employed in the PCIC is structurally based on an existing monochromatic multichannel vision model, which is extended for color image coding. Subjective tests with 30 viewers show that the PCIC provides superior picture quality at low to intermediate bitrates in comparison with a JPEG2000 compliant coder employing the mean squared error (MSE) and the visual distortion metric (Cvis) as distortion measures, respectively.      

Dynamically Configurable Bus Topologies for High-Performance On-Chip Communication

The on-chip communication architecture is a primary determinant of overall performance in complex system-on-chip (SoC) designs. Since the communication requirements of SoC components can vary significantly over time, communication architectures that dynamically detect and adapt to such variations can substantially improve system performance. In this paper, we propose Flexbus, a new architecture that can efficiently adapt the logical connectivity of the communication architecture and the components connected to it. Flexbus achieves this by dynamically controlling both the communication architecture topology, as well as the mapping of SoC components to the communication architecture. This is achieved through new dynamic bridge by-pass, and component remapping techniques. In this paper, we introduce these techniques, describe how they can be realized within modern on-chip buses, and discuss policies for run-time reconfiguration of Flexbus-based architectures.      

RLS-Based Joint Estimation and Tracking of Channel Response, Sampling, and Carrier Frequency Offsets for OFDM

This paper proposes a pilot-aided joint channel estimation and synchronization scheme for burst-mode orthogonal frequency division multiplexing (OFDM) systems. Based on the received signal samples containing pilot tones in the frequency domain, a cost function that includes the carrier frequency offset (CFO), sampling clock frequency offset (SFO) and channel impulse response (CIR) coefficients is formulated and used to develop an accompanying recursive least-squares (RLS) estimation and tracking algorithm. By estimating the channel CIR coefficients instead of the channel frequency response in the frequency domain, the proposed scheme eliminates the need for an IFFT block while reducing the number of parameters to be estimated, leading to lower complexity without sacrificing performance and convergence speed. Furthermore, a simple maximum-likelihood (ML) scheme based on the use of two long training symbols (in the preamble) is developed for the coarse estimation of the initial CFO and SFO to suppress dominant ICI effects introduced by CFO and SFO and to enhance the performance and convergence of the fine RLS estimation and tracking. Simulation results demonstrate that, over large ranges of CFO and SFO values, the proposed pilot-aided joint channel estimation and synchronization scheme provides a receiver performance that is remarkably close to the ideal case of perfect channel estimation and synchronization in both AWGN and Rayleigh multipath fading channels.      

Interconnect Exploration for Energy Versus Performance Tradeoffs for Coarse Grained Reconfigurable Architectures

Modern portable embedded devices require processors that can provide sufficient performance for demanding multimedia and wireless applications. At the same time they have to be flexible to support a wide range of products and extremely energy efficient to provide a long battery life. Coarse Grained Reconfigurable Architectures (CGRAs) potentially meet these constraints by providing a mix of flexible computational resources and large amounts of programmable interconnect. The vast design space of CGRAs complicates the development of optimized processors. Most effort has been spent on improving the performance. However, the energy cost of the programmable interconnect is becoming more expensive and this cost can no longer be neglected. In this work we present an energy- and performance-aware exploration for the interconnect of a CGRA and show that important tradeoffs can be made for those metrics. This will enable designers to develop more efficient architectures, tuned to a targeted application domain.      

Doubly-Generalized LDPC Codes: Stability Bound Over the BEC

The iterative decoding threshold of low-density parity-check (LDPC) codes over the binary erasure channel (BEC) fulfills an upper bound depending only on the variable and check nodes with minimum distance $2$. This bound is a consequence of the stability condition, and is here referred to as stability bound. In this paper, a stability bound over the BEC is developed for doubly-generalized LDPC codes, where variable and check nodes can be generic linear block codes, assuming maximum a posteriori erasure correction at each node. It is proved that also in this generalized context the bound depends only on the variable and check component codes with minimum distance $2$. A condition is also developed, namely, the derivative matching condition, under which the bound is achieved with equality. The stability bound leads to consider single parity-check codes used as variable nodes as an appealing option to overcome common problems created by generalized check nodes.      

Modeling of Distributed RLC Interconnect and Transmission Line via Closed Forms and Recursive Algorithms

This paper presents the closed forms of the state-space models and the recursive algorithms of the transfer function models for fast and accurate modeling of the distributed RLC interconnect and transmission lines, which may be evenly or unevenly distributed. Considered models include the distributed RLC interconnect lines with or without external source and load connection. The effective closed forms and recursive algorithms do not involve any matrix inverse, LU matrix factorization, or matrix multiplication, thus reducing the computation complexity dramatically. Especially, the computation complexity of the closed forms for any evenly or unevenly distributed RLC interconnect line circuits is only O(1) or $ { O}(m)$, respectively, in sense of the scalar multiplication times, where $ { m}ll{ N}$ of the system order. The features of new recursive algorithms are two recursive s-polynomials and the low computation complexity. Examples illustrate the new methods in both time and frequency domains. Comparing with the PSpice, the new methods can dramatically reduce the runtime of the time responses and the Bode plots by 25% – 98.5% in the examples. The results can be applied to the RLC interconnect analysis and model reduction as a key to new approach.      

Universal FIR MMSE Filtering

We consider the problem of causal estimation, i.e., filtering, of a real-valued signal corrupted by zero mean, time-independent, real-valued additive noise, under the mean-squared error (MSE) criterion. We build a universal filter whose per-symbol squared error, for every bounded underlying signal, is essentially as small as that of the best finite-duration impulse response (FIR) filter of a given order. We do not assume a stochastic mechanism generating the underlying signal, and assume only that the variance of the noise is known to the filter. The regret of the expected MSE of our scheme is shown to decay as $O(log n/n)$, where $n$ is the length of the signal. Moreover, we present a stronger concentration result which guarantees the performance of our scheme not only in expectation, but also with high probability. Our result implies a conventional stochastic setting result, i.e., when the underlying signal is a stationary process, our filter achieves the performance of the optimal FIR filter. We back our theoretical findings with several experiments showcasing the potential merits of our universal filter in practice. Our analysis combines tools from the problems of universal filtering and competitive on-line regression.      

Distributed Throughput Maximization in Wireless Mesh Networks via Pre-Partitioning

This paper considers the interaction between channel assignment and distributed scheduling in multi-channel multi-radio Wireless Mesh Networks (WMNs). Recently, a number of distributed scheduling algorithms for wireless networks have emerged. Due to their distributed operation, these algorithms can achieve only a fraction of the maximum possible throughput. As an alternative to increasing the throughput fraction by designing new algorithms, we present a novel approach that takes advantage of the inherent multi-radio capability of WMNs. We show that this capability can enable partitioning of the network into subnetworks in which simple distributed scheduling algorithms can achieve 100% throughput. The partitioning is based on the notion of Local Pooling. Using this notion, we characterize topologies in which 100% throughput can be achieved distributedly. These topologies are used in order to develop a number of centralized channel assignment algorithms that are based on a matroid intersection algorithm. These algorithms pre-partition a network in a manner that not only expands the capacity regions of the subnetworks but also allows distributed algorithms to achieve these capacity regions. We evaluate the performance of the algorithms via simulation and show that they significantly increase the distributedly achievable capacity region. We note that while the identified topologies are of general interference graphs, the partitioning algorithms are designed for networks with primary interference constraints.      

Analysis of Two Alternative ADI-FDTD Formulations for Transverse-Electric Waves in Lossy Materials

A numerical dispersion analysis of the alternating-direction implicit finite-difference time-domain method for transverse-electric waves in lossy materials is presented. Two different finite-difference approximations for the conduction terms are considered: the double-average and the synchronized schemes. The numerical dispersion relation is derived in a closed form and validated through numerical simulations. This study shows that, despite its popularity, the accuracy of the double-average scheme is sensitive to how well the relaxation-time constant of the material is resolved by the time step. Poor resolutions lead to unacceptably large numerical errors. On the other hand, for good conductors, the synchronized scheme allows stability factors as large as 100 to be used without deteriorating the accuracy significantly.      

Channel Estimation in OFDM Systems With Unknown Power Delay Profile Using Transdimensional MCMC

This paper considers the problem of channel estimation for orthogonal-frequency-division multiplexing (OFDM) systems, where the number of channel taps and their power delay profile are unknown. Using a Bayesian approach, we construct a model in which we estimate jointly the coefficients of the channel taps, the channel order and decay rate of the power delay profile (PDP). In order to sample from the resulting posterior distribution we develop three novel Trans-dimensional Markov chain Monte Carlo (TDMCMC) algorithms and compare their performance. The first is the basic birth and death TDMCMC algorithm. The second utilizes Stochastic Approximation to develop an adaptively learning algorithm to improve mixing rates of the Markov chain between model subspaces. The third approximates the optimal TDMCMC proposal distribution for between-model moves using conditional path sampling proposals. We assess several aspects of the model in terms of sensitivities to different prior choices. Next we perform a detailed analysis of the performance of each of the TDMCMC algorithms. This allows us to contrast the resulting computational effort required under each approach versus the estimation performance. Finally, using the TDMCMC algorithm which produces the best performance in terms of exploration of the model subspaces, we assess its performance in terms of channel estimation mean-square error (MSE) and bit error rate (BER). It is shown that the proposed algorithm can achieve results very close to the case where both the channel length and the PDP decay rate are known.      

Fault Tolerance Analysis for Switched Systems Via Global Passivity

In this brief, we introduce the passivity theory into the fault tolerance analysis for switched systems. We propose a “global passivity” concept which means that the total energy stored by the switched system is less than the total energy supplied from the outside. The individual passivity of each mode is not required, and the stability of the system can be achieved via the global energy dissipativity in the presence of faults. We further provide a “periodic fault tolerant passivity” to check the fault tolerance easily. The obtained results are extended to feedback interconnected systems. A switched RLC circuit example is taken to illustrate the efficiency of the proposed results.