The paper presents a carrier frequency offset(CFO) estimation algorithm with synchronization for digital communication receivers. The algorithm utilizes fractional time periods to arrive at a coarse CFO estimate. The reliability of the coarse CFO estimate is improved using information from the phase difference across the preamble period. The proposed algorithm is not specific to any standard and can estimate CFO of large magnitudes. This aspect is particularly useful in scenario wherein the preamble period falls short in capturing the phase information corresponding to CFO range specified by the standard. Simulation studies have been carried out to demonstrate the performance of the proposed algorithm.

We consider joint radio frequency and baseband physical (PHY) layer algorithms for ultra low power (ULP) wireless communications. Our focus is on the design of automatic gain control (AGC) and direct current offset compensation (DCOC) algorithms for non-coherent reception based on processing analog to digital converter output samples only. Specifically, we jointly design and evaluate AGC and DCOC algorithms for sliding intermediate frequency non-coherent wireless receiver with IEEE 802.15.4q ULP PHY packet format.

This paper presents a low complexity algorithm for compensating the sampling-clock frequency offset encountered in short-range WPAN receivers. The proposed algorithm leverages on the pulse shaping information in the transmitted signal to identify erroneous samples resulting from the sampling-clock frequency offset and then compensates for the same. Simulation results demonstrate that the proposed algorithm almost completely compensates for offsets of magnitudes specified by WPAN standards.

Two methods to estimate the direct current offset (DCO) of non-coherent receivers for on-off keying (OOK) systems are proposed. These estimate I-arm and Q-arm DCO solely from the digitized samples of the envelope detector. This ameliorates power consuming individual I-arm and Q-arm processing for DCO estimation and makes it more suitable for adoption in next generation wireless ultra-low power (ULP) receivers. Furthermore, the efficacy of the proposed methods is demonstrated for an IEEE 802.15.4q compliant ULP sliding intermediate frequency receiver.

We consider a non-coherent receiver architecture with low IF frequency down-conversion, complex band pass filtering and envelope detection for ultra low power (ULP) wireless communications. We model and evaluate the performance of ULP transceiver with IEEE 802.15.4q PHY packet format. Moreover, we provide a theoretical analysis of the image rejection properties of low IF receiver. We evaluate the performance of the low IF receiver via PER sweeps and ACI tests. Finally, we compare its performance with that of Weaver receiver.

In addressing user experience issues, users’ perceptions and emotions need to be considered important. This study examines the relationships between perceived usability/aesthetics and emotional valence/arousal/engagement through an experiment using 15 existing websites from various domains and questionnaire items developed to measure users’ responses. According to the experimental results, both perceived usability and perceived aesthetics were positively correlated with emotional valence and negatively correlated with emotional engagement. No specific relationship was found between perceived usability/aesthetics and emotional arousal. Perceived aesthetics potentially had a greater impact on valence than perceived usability. Unlike valence, engagement could be more influenced by perceived usability than by perceived aesthetics. These findings can be utilized as bases for applying users’ emotional responses in each dimension to the product-use situations in the chain of perceptions, emotions, and behaviors.

In this paper, we explore a method for simultaneous tranmission to coherent and non-coherent receivers, based on ternary sequences. In many communication scenarios, the transmitters are required to support both coherent and non-coherent forms of reception thereby requiring the transmission protocols to be designed such that the transmitted data is decoded reliably at both coherent and non-coherent receivers. Further, in such scenarios, for practical purposes, the transmitter is assumed to be agnostic to the type of the intended receiver, making the design more challenging. Thus motivated, we propose a transmission mechanism for simultaneous reception by coherent and noncoherent receivers. This transmission is enabled by ternary codes, i.e., codes over the ternary alphabet: {−1, 0, +1}. The design of these ternary codes, which exhibit good correlation properties for both coherent and non-coherent reception is a major contribution of this paper. Simulation results show that the proposed codes provide almost similar performance as the optimal codes meant for the respective receiver types.

This letter proposes a statistical cooperative scheme for transmit antenna subset selection in multiple-input multiple-output (MIMO) multicell systems. The proposed scheme is practical in that it only utilizes the statistical information for the adjacent links. However, it provides almost 90 percent of the average mutual information of the full cooperative scheme which requires a large amount of the instantaneous information and joint cooperation between base stations. Furthermore, the proposed scheme shows substantial performance enhancements over the competitive scheme in which the effects of intercell interference generated by the antenna selection are not considered.

Efficient channel feedback methods are becoming more important in limited-feedback multi-user multiple input multiple output (MU-MIMO) systems. We propose a new dynamic channel feedback control (DEFCON) scheme, which efficiently allocates the limited system resources for channel feedback to appropriate users. The main features of the proposed DEFCON scheme are as follows. Firstly, the channel feedback procedure is composed of two stages: rough channel feedback of all users and additional precise channel feedback of the selected users only. Secondly, each selected user is allocated with different amount of resources for additional channel feedback according to its channel status. We mathematically solve the resource allocation problem by proposing a suboptimal method, which utilizes convex optimization technique combined with iterative steepest decent direction search algorithm. Numerical results show that zero-forcing beamforming (ZFBF) with the proposed DEFCON scheme considerably outperforms previous limited-feedback MU-MIMO schemes such as ZFBF with conventional static feedback method and per user unitary beamforming rate control (PU2RC).

MOTIVATION: Importance of accurate automatic protein function prediction is ever increasing in the face of a large number of newly sequenced genomes and proteomics data that are awaiting biological interpretation. Conventional methods have focused on high sequence similarity-based annotation transfer which relies on the concept of homology. However, many cases have been reported that simple transfer of function from top hits of a homology search causes erroneous annotation. New methods are required to handle the sequence similarity in a more robust way to combine together signals from strongly and weakly similar proteins for effectively predicting function for unknown proteins with high reliability. RESULTS: We present the extended similarity group (ESG) method, which performs iterative sequence database searches and annotates a query sequence with Gene Ontology terms. Each annotation is assigned with probability based on its relative similarity score with the multiple-level neighbors in the protein similarity graph. We will depict how the statistical framework of ESG improves the prediction accuracy by iteratively taking into account the neighborhood of query protein in the sequence similarity space. ESG outperforms conventional PSI-BLAST and the protein function prediction (PFP) algorithm. It is found that the iterative search is effective in capturing multiple-domains in a query protein, enabling accurately predicting several functions which originate from different domains. AVAILABILITY: ESG web server is available for automated protein function prediction at http://dragon.bio.purdue.edu/ESG/.

Multiple-input multiple-output (MIMO) system with multicode transmission can provide high speed data services by transmitting independent parallel substreams from multiple antennas and through multicode channelization. In this paper, we first introduce an iterative two-stage successive interference cancellation (SIC) detection scheme for a multicode MIMO system. The proposed technique cancels the interference signals successively in the space domain followed by the code domain. Next, we develop various transmit power allocation schemes over different data substreams for the proposed detection process to improve error rate performance. The joint transmit power allocation is derived to make the post-detection signal-to-interference-plus-noise ratio (SINR) become the same for all substreams in both the space and code domains. As a computationally efficient scheme, we propose a two-stage power allocation scheme, which allocates the total transmit power to the substreams in the code domain at the first stage, and allocates this code domain power to the substreams in the space domain at the second stage. Furthermore, variable and constant power ratio (PR) schemes are derived to reduce the feedback overhead. In particular, the constant PR scheme utilizes the transmit power ratio determined by the long-term statistical properties of the fading channel amplitudes, and achieves significantly reduced feedback rate. Numerical results show that the proposed transmit power allocation schemes for the two-stage SIC significantly outperform the equal power allocation scheme.

In a wireless multiple-input multiple-output (MIMO) system, transmit antenna selection is an effective means of achieving good performance with low complexity. We consider spatial multiplexing with linear receivers, and equal power and equal rate allocation over different selected transmit antennas in order to reduce feedback overhead. Under these constraints, we address the problem of statistical multimode transmit antenna subset selection to improve the capacity of spatially correlated MIMO fading channels. In particular, we first derive an analytical closed-form expression for the expectation of the lower bound on the capacity using the smallest eigenvalue distribution of a Wishart matrix. Then, we propose a transmit antenna subset selection criterion of maximizing this average lower-bound capacity.

Multiple-input multiple-output (MIMO) system with multicode transmission can provide high speed data services by transmitting independent parallel substreams from multiple antennas and through multicode channelization. In this paper, we first introduce an iterative two-stage successive interference cancellation (SIC) detection scheme for a multicode MIMO system. Next, we derive various transmit power allocation schemes over different data substreams for the proposed detection process to improve error rate performance. The power allocation is performed to make the signal-to-interference-plus-noise ratio (SINR) become balanced for all data substreams. Numerical results show that the proposed transmit power allocation schemes for the two-stage SIC significantly outperform the equal power allocation scheme.

Recently, multiple-input multiple-output (MIMO) systems have shown the potential to achieve high speed data transmissions by improving spectral efficiency over wireless fading channels. In multiuser MIMO environment, the radio base station (Node-B) supports mobile user equipments (UEs) with different quality-of-service (QoS) requirements, where the adopted scheduling scheme controls the selection of UEs for service provision and has an impact on the system performance. In this paper, two basic scheduling rules are described, which are combined with and without successive interference cancellation (SIC) receivers, respectively. We then propose the hybrid scheduler which outperforms those two rules in terms of system capacity. Simulation results show that the performances of conventional scheduling schemes heavily depend on the number of UEs, to which the proposed scheme is robust and achieves the improved capacity gain.

In a multicarrier system, transmit power allocation over different subchannels is an effective means of improving the performance. We develop the optimal transmit power allocation scheme to improve bit-error rate (BER) performance in a multicarrier system with diversity reception. A simple suboptimal scheme is also derived from the optimal one, and an asymptotic case referred to as the equal-signal-to-noise ratio scheme is discussed. Numerical results show that the optimal and suboptimal power allocation schemes significantly outperform the equal power allocation scheme. The effects of the modulation level, the number of receiving antennas, and the number of subchannels on the BER performance are also investigated.

In a multicarrier system, transmit power allocation over different subchannels is an effective means of improving the performance. In this paper, the optimal transmit power allocation scheme is developed to improve bit error rate (BER) performance in a multicarrier system with diversity reception. A simple suboptimal scheme is also derived from the optimal one, and an asymptotic case referred to as the equal SNR scheme is discussed. Numerical results show that the optimal and suboptimal power allocation schemes significantly outperform the equal power allocation scheme. The effects of the modulation level, the number of receiving antennas, and the number of subchannels on the BER performance are also investigated.

There have been various receiver-based techniques for performance improvement of wireless communications systems. However, receiver-based techniques have a restricted application in the down-link because they increase computational complexity of the mobile station (MS). In this paper, a transmitter-based processing scheme for the down-link direct-sequence code division multiple access (DS/CDMA) systems with multiple transmit antennas is proposed. The proposed scheme uses a pre-RAKE method to exploit diversity gain and pre-decorrelating method to suppress multiple access interference (MAI) and multiple path interference (MPI). To make the total transmit power the same as that without pre-decorrelating processing, we present three power normalization methods and compare the performance of those with one another.

Checkpointing is a fault-tolerant technique for restoring faults and restarting jobs quickly. The algorithms for checkpointing on distributed systems have been under study for years. These algorithms can be classified into three types: coordinated, uncoordinated and communication-induced algorithms. In this paper we propose a new communication-induced checkpointing algorithm that has a minimum checkpointing count equivalent to the periodic checkpointing algorithm, and relatively short rollback distance at fault situations. The proposed algorithm is compared with the previously proposed communication-induced checkpointing algorithms with simulation results. In the simulation, the proposed algorithm produces better performance than other algorithms in terms of task completion time in both fault-free and fault situations.

Detecting global predicates in a distributed program is a useful tool for debugging and testing the program. Past research has considered several restricted forms of predicates, including conjunctive predicates and linked predicates, and their detection algorithms. The authors introduce an exclusive OR global predicates to describe exclusive usages of shared resources in distributed programs. An exclusive OR global predicate holds for a given run only when one or zero local predicate is true at every consistent global state during the run. One exclusive OR global predicate is enough to describe the mutual exclusion condition of n processes, while it takes O(n/sup 2/) conjunctive predicates. Moreover, the exclusive OR condition is easily detectable by sequentializing all true events in a given run. A centralized algorithm of detecting exclusive OR global predicates is presented.

CrownFS is a file system for continuous media server in the CROWN (Clustering Resources On Workstations' Network) system. Because of the high I/O bandwidth rate and strict real-time constraints, the design issues of CrownFS are that of efficiently balancing user load against limited disk: bandwidth, network and I/O channel bandwidth. CrownFS accomplishes this balancing by striping continuous data file across several workstations and computing at each workstation in the CROWN system. This paper describes the CROWN system architecture and the CrownFS design. CrownFS runs on a cluster of workstations consisted of Kawaiis, AlphaStations and PCs.