This letter investigates the effects of using multiple transmit antennas on code acquisition for preamble search in the CDMA uplink when MIMO is used for signal transmission and reception. The performance of a ML code acquisition technique in the presence of MIMO channel is analyzed by considering the detection and miss probabilities. The acquisition performance is numerically evaluated on a frequency selective fading channel. It is found that the performance of code acquisition scheme for a SIMO system is better than that for the case of MIMO on the low thresholds in terms of detection performance and MAT.

This paper presents a method to improve field uniformity using two TX antennas in a reverberation chamber with less steps of a stirrer. A mode-stirred reverberation chamber (MSRC) is considered as an alternative to the semi-anechoic chamber for an electromagnetic compatibility test because it provides a large test volume, a statistically uniform field, and a high maximum electric field. To improve field uniformity, we introduce two transmitting antennas for excitation in an MSRC, and predict statistical distribution of the complex reflection coefficients (scattering parameters). To prove the validation of our theory and the reliability of measurement results, three kinds of stirrers with different shape and sizes were fabricated and their efficiencies were measured in an MSRC, and then field uniformities have been investigated for 1–3 GHz frequency within the maximum number of independent samples that stirrers can provide. The measurement results show that the average received power is about 1.5 times as high as when using one transmitting antenna, and field uniformity is improved. Use of two transmitting antennas in an MSRC is regarded as a useful method to improve field uniformity at less stirrer steps, for radiated immunity tests.

In large-scale collaborative computing, users and resource providers organize various Virtual Organizations (VOs) to share resources and services. A VO organizes other sub-VOs for the purpose of achieving the VO goal, which forms hierarchical VO environments. VO participants agree upon a certain policies, such as resource sharing amount or user accesses. In this letter, we provide an optimal resource sharing mechanism in hierarchical VO environments under resource sharing agreements. The proposed algorithm enhances resource utilization and reduces mean response time of each user.

The problem of estimating code timings in DS-CDMA systems with multiple antennas is considered in the presence of multipath time-varying fading channels and near-far environments. We present an efficient algorithm for an approximate maximum likelihood approach of jointly estimating the multipath timings of a desired user for DS-CDMA systems that consist of multiple antennas either uncorrelated or fully correlated in space. The procedures of the algorithm to estimate code-timings are developed in order to better exploit the time-varying characteristics of the fading process. In the multipath fading channels, the solution of the proposed algorithms is based on successively optimizing the criterion for increasing numbers of multipath delays. It is shown via simulation results that the modified approaches of the approximate maximum likelihood algorithm much more improve its acquisition performance in the time-varying fading channels. It is seen that the acquisition performance of multiple antennas based acquisition scheme is much better than that of a single antenna based timing estimator in the presence of multipath fading channels and the near-far problem. Furthermore, it is observed that the proposed algorithms outperform the correlator and MUSIC estimator in the multiuser environments with near-far situation on time-varying Rayleigh fading channels.

Sensor deployment to achieve better system performance is one of the critical issues in wireless sensor networks (WSN). This letter proposes an effective sensor deployment scheme for large area sensor networks, where the event occurrence rate varies over the sensor-deployed region. Based on local event occurrence rate, the proposed scheme determines the number of sensors that should be deployed in each local region to maximize the overall detection probability. Simulation results show that the sensor deployment by the proposed scheme improves detection capability by 21% in comparison to the Incidence algorithm.

This paper presents a two-tier coordinated checkpointing algorithm which can reduce the number of messages by being composed of two levels in mobile computing. Thus mobile devices have a high mobility and are lack of resources (e.g., storage, bandwidth, and battery power), traditional distributed algorithms like coordinated checkpointing algorithms could not be applied properly in mobile environment. In our proposed two-tier coordinated checkpointing algorithm, the messages to be transferred are requested by the mobile hosts and are handled by the appropriate MSS's (Mobile Support Stations). And the broadcast messages are handled by MSS instead of relaying the messages to all the mobile hosts directly as with the previous algorithms. This can reduce the communication cost and maintain the overall system consistency. In wireless cellular network, mobile computing based on a two-tier coordinated checkpointing algorithm reduces the number of synchronization messages. We perform performance comparisons by parametric analysis to show that a two-tier coordinated checkpointing algorithm can reduce communication cost compared to the previous algorithms in which the messages are directly sent to the mobile hosts.

A simple low power low phase noise LC QVCO (Quadrature Voltage Controlled Oscillator) topology is proposed. The topology minimizes phase noise by eliminating the contributions from the tail current source and coupling transistors. With no more than 3.36 mW power consumption from a 1.2 V power supply, the VCO achieves -124 dBc/Hz phase noise performance at 1 MHz offset from the 2.85 GHz carrier frequency.

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is a novel scheme where the information bits are conveyed through the subcarrier activation pattern (SAP) and the symbols on the active subcarriers. Specifically, the subcarriers are partitioned into many subblocks and the subcarriers in each subblock can have two states, active or idle. Unfortunately, OFDM-IM inherits the high peak-to-average power ratio (PAPR) problem from the classical OFDM. The OFDM-IM signal with high PAPR induces in-band distortion and out-of-band radiation when it passes through high power amplifier (HPA). Recently, there are attempts to reduce PAPR by exploiting the unique structure of OFDM-IM, which is adding dither signals in the idle subcarriers. The most recent work dealing with the dither signals is using dithers signals with various amplitude constraints according to the characteristic of the corresponding OFDM-IM subblock. This is reasonable because OFDM subblocks have distinct levels of robustness against noise. However, the amplitude constraint in the recent work is efficient for only additive white Gaussian noise (AWGN) channels and cannot be used for maximum likelihood (ML) detection. Therefore, in this paper, based on pairwise error probability (PEP) analysis, a specific constraint for the dither signals is derived over a Rayleigh fading channel.

By exploiting the inherent sparsity of wireless channels, the channel estimation in an orthogonal frequency division multiplexing (OFDM) system can be cast as a compressed sensing (CS) problem to estimate the channel more accurately. Practically, matching pursuit algorithms such as orthogonal matching pursuit (OMP) are used, where path delays of the channel is guessed based on correlation values for every quantized delay with residual. This full search approach requires a predefined grid of delays with high resolution, which induces the high computational complexity because correlation values with residual at a huge number of grid points should be calculated. Meanwhile, the correlation values with high resolution can be obtained by interpolation between the correlation values at a low resolution grid. Also, the interpolation can be implemented with a low pass filter (LPF). By using this fact, in this paper we substantially reduce the computational complexity to calculate the correlation values in channel estimation using CS.

Multi-hop Wireless LAN-based mesh network (WMN) provides high capacity and self-configuring capabilities. Due to data forwarding and path selection based on MAC address, WMN requires additional operations to achieve global connectivity using IPv6 address. The neighbor discovery operation over WLAN mesh networks requires repeated all-node broadcasting and this gives rise to a big burden in the entire mesh networks. In this letter, we propose the proxy neighbor discovery scheme for optimized IPv6 communication over WMN to reduce network overhead and communication latency. Using simulation experiments, we show that the control overhead and communication setup latency can be significantly reduced using the proxy-based neighbor discovery mechanism.

Cooperative communication enables single antenna to realize a virtual multiple antenna by sharing their antennas. Therefore, it offers transmit diversity. In this letter, we apply pre-coding scheme to the transmit symbols. Although pre-coding has shortcomings, it is possible to employ Space-Time Block Codes (STBC) with single antenna and achieve high gain.

In this letter, a prerake combining scheme for signal detection in ultra-wideband (UWB) multiple input single output (MISO) systems with a hybrid pulse amplitude and position modulation (PAPM) is analytically examined. For a UWB MISO system, the analytical BER performance of a prerake combining scheme with PAPM is presented in a log-normal multipath fading channel. The analytical BERs are observed to match well the simulated results for the set of parameters chosen. The prerake diversity combining UWB systems, which can significantly reduce the complexity of the receiver side compared to the rake diversity systems, improve the error performance as the number of transmit antennas increases.

In this paper, we propose an algorithm that automatically generates the intermediate scenes using the bidirectional disparity morphing (BDM) from the parallel stereo images. The two-step search strategy is used for speeding up the computation of the bidirectional disparity map and three occluding patterns are used for smoothing the computed disparities more elaborately. Using the bidirectional disparity map, we interpolate the left and the right image to their intermediate scenes. Then we dissolve two interpolated images into the desired intermediate scene which the holes are removed and the effect of the disparity estimation errors is minimized. We implemented the proposed algorithm on TM1300 supported by TriMedia using pSOSytem which enables to do multiprocessing. As a result, we can interpolate the high-quality intermediate scenes with real-time process.

In this paper, we propose an adaptive compensation algorithm to compensate cell delay variation (CDV) occurring during ATM/TDMA transition in a satellite ATM network. The proposed CDV compensation algorithm uses two types of additional information: cell position information (Cp)--indicating the number of cells (N) arriving within a control unit time (Tc) and positions of cells at a given time--and the number of cells in bursts--to take into account the characteristics of localized bursts. To evaluate the performance of the proposed algorithm, we performed a computer simulation based on an OPNET environment, using the Markov modulated Poisson process (MMPP) traffic model and assessed its effectiveness from varied standpoints. The results of the performance testing indicate that the proposed algorithm, while requiring significantly less additional information than previous CDV compensation algorithms, is able to more efficiently compensate CDV in localized burst traffic than the previous ones.

Many selected mapping (SLM) schemes have been proposed to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signal sequences. In this paper, an efficient selection (ES) method of the OFDM signal sequence with minimum PAPR among many alternative OFDM signal sequences is proposed; it supports various SLM schemes. Utilizing the fact that OFDM signal components can be sequentially generated in many SLM schemes, the generation and PAPR observation of the OFDM signal sequence are processed concurrently. While the u-th alternative OFDM signal components are being generated, by applying the proposed ES method, the generation of that alternative OFDM signal components can be interrupted (or stopped) according to the selection criteria of the best OFDM signal sequence in the considered SLM scheme. Such interruption substantially reduces the average computational complexity of SLM schemes without degradation of PAPR reduction performance, which is confirmed by analytical and numerical results. Note that the proposed method is not an isolated SLM scheme but a subsidiary method which can be easily adopted in many SLM schemes in order to further reduce the computational complexity of considered SLM schemes.

Recently, a new diversity scheme called spatial phase coding (SPC) have been introduced. In conventional SPC, it was assumed that the channel phases between the transmit antennas and the receive antenna independently vary. However, practical channel phase dependently vary between neighboring subcarriers. In this letter, a feedback design method which is more efficient than conventional SPC is proposed. Furthermore, the scheme to improve the BER performance of conventional SPC using 1-bit feedback is suggested.

In this paper, we propose a novel algorithm for all-digital high speed symbol synchronization to be called the MBECM (Modified-Band Edge Component Maximization). The proposed algorithm has a structure based on the spectral line method. It simplifies and modifies the existing BECM algorithm to compensate for the timing offset caused by different phase characteristics of the BPF (band pass filter) at 1/2T and -1/2T. The algorithm is also independent of the carrier recovery and requires only two samples per symbol for its operation. Until now the timing detector's characteristics of the spectral line method including the M-BECM was not analyzed, particularly effect of the timing offset at convergence point. We analyze the timing detector's characteristics of the M-BECM and derive expressions for the timing detector's mean value (often called the S-curve) as a function of the normalized symbol-clock phase, the rolloff parameterand the bandwidth of the BPF. By using these expressions, the PDbias for eliminating the timing offset at an optimal convergence point are calculated. We also analyze and evaluate performance of the proposed algorithm in various ways such as jitter, timing detector output characteristics, etc. and suggest improvements. The proposed M-BECM is compared to the popular Gardner algorithm for high speed modem applications. The proposed algorithm has simpler structure than the Gardner algorithm and simulation results reveal that the proposed algorithm has better overall performance than the Gardner algorithm in narrow band.

Recently, a graph labeling technique based on prime numbers has been suggested for reducing the costly transitive closure computations in RDF query languages. The suggested prime number graph labeling provides the benefit of fast query processing by a simple divisibility test of labels. However, it has an inherent problem that originates with the nature of prime numbers. Since each prime number must be used exclusively, labels can become significantly large. Therefore, in this paper, we introduce a novel optimization technique to effectively reduce the problem of label overflow. The suggested idea is based on graph decomposition. When label overflow occurs, the full graph is divided into several sub-graphs, and nodes in each sub-graph are separately labeled. Through experiments, we also analyze the effectiveness of the graph decomposition optimization, which is evaluated by the number of divisions.

In various studies of attacks on autonomous vehicles (AVs), a phantom attack in which advanced driver assistance system (ADAS) misclassifies a fake object created by an adversary as a real object has been proposed. In this paper, we propose F-GhostBusters, which is an improved version of GhostBusters that detects phantom attacks. The proposed model uses a new feature, i.e, frequency of images. Experimental results show that F-GhostBusters not only improves the detection performance of GhostBusters but also can complement the accuracy against adversarial examples.

We present a carrier and sampling frequency offset estimation and compensation scheme for a multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) modem. We first perform initial carrier frequency offset (CFO) estimation and compensation during the preamble period, and then conduct the estimation and compensation of the residual CFO and sampling frequency offset (SFO) during the payload period. The proposed design scheme reduces the logic gate count of the frequency offset compensation block by about 10%, while it gives almost the same performance at the packet error rate (PER) of 10-4 in the CM1 channel. The frequency offset estimation and compensation block is implemented using 90 nm CMOS technology and tested.