Multi-hop cooperative communication has been investigated in order to overcome disadvantages such as fading, obstruction and low power. In addition, with the goal of increasing access capacity, the orthogonal frequency division multiplexing (OFDM) modulation is being advanced as a solution. In this paper, we propose the approach of relay ordering in a Decode-and-Forward OFDM scheme. Combining techniques such as maximal ratio combining and selection combining are employed at receivers and approximate outage capacity probabilities are derived for evaluating system performance over frequency selective Rayleigh fading channels. Final, the expressions are validated by Monte-Carlo simulations, and are used to compare with the same scheme based relay selection.

We propose a systematic method for improving the response time of forward collision warning (FCW) on vehicles. First, a performance metric, called the warning lag time, is introduced. We use the warning lag time because its measurement is practical in real driving situations. Next, we discuss two ideas to improve this warning lag time, vertical and horizontal methods. The vertical method gives an additional warning, derived from the cause of a car crash, to a normal FCW system. The experiment showed that it can improve the warning lag time by an average of 0.31sec. compared with a traditional FCW system. The horizontal method uses distributed sensing among vehicles, which helps the vehicle see farther. It can also improve the warning lag time by an average of 1.08sec. compared with a single vehicle FCW.

In this paper, an energy harvesting architecture in an Underlay Cooperative Cognitive Network (UCCN) is investigated, in which power constrained Decode-and-Forward relays harvest energy from radio-frequency signals received from a source, and then consume the harvested energy by forwarding the recoded signals to their destination. These recoded signals are launched by a transmitting power which is the harvested energy per a time interval. Based on the energy harvesting architectures that have been studied, two operation protocols are proposed: UCCN with Power Splitting architecture (UCCN-PS), and UCCN with Time Switching architecture (UCCN-TS). The best cooperative relay in both protocols is taken to be the one that satisfies the following conditions: maximum harvested energy, and maximum decoding capacity. As a result of the best relay selection, the signal quality of the selected link from the best relay to the destination is enhanced by the maximum harvested energy. The system performance of the secondary network in the UCCN-PS and UCCN-TS protocols is analyzed and evaluated by the exact closed-form outage probabilities and throughput analyses over Rayleigh fading channels. The Monte Carlo simulation method is performed to verify the theoretical expressions. Evaluations based on outage probability and throughput show that the system performance of the secondary network in the UCCN-PS and UCCN-TS protocols improves when the number of cooperative relays and the interference constraint increase as well as when the primary receiver is farther from the transmitting nodes such as the source and relays of the secondary network. In addition, the throughput performance of the UCCN-PS protocol outperforms that of the UCCN-TS protocol. Finally, the effects of the power splitting ratio, energy harvesting time, energy conversion efficiency, target Signal-to-Noise Ratio (SNR), and location of cooperative relays on the system performance of the secondary network are presented and discussed.

Many wireless communication systems use a relay station for cooperative diversity or cell coverage extension. In this letter, an efficient partial single relay selection scheme is proposed for wireless communications. The conventional schemes such as the best harmonic mean and the threshold-based relay selection should know channel state informaion (CSI), or noise variance at all stations in advance. But the proposed scheme does not require any priori information. It uses a characteristic of the repeated signal pattern at candidates of the relay station. Simulation results show that the performance of proposed scheme is very close to the best harmonic mean relay selection scheme as one of the optimal relay selection schemes.

The dynamic routing and wavelength assignment (RWA) problem in wavelength division multiplexing (WDM) optical networks with sparse wavelength conversion has been a hot research topic in recent years. An optimized algorithm based on a multiple-layered interconnected graphic model (MIG) for the dynamic RWA is presented in this paper. The MIG is constructed to reflect the actual WDM network topology. Based on the MIG, the link cost is given by the conditions of available lightpath to calculate an initial solution set of optimal paths, and by combination with path length, the optimized solution using objective function is determined. This approach simultaneously solves the route selection and wavelength assignment problem. Simulation results demonstrate the proposed MIG-based algorithm is effective in reducing blocking probability and boosting wavelength resource utilization compared with other RWA methods.

This paper describes a simple-yet-effective control method for a DC-DC buck converter with voltage mode control (VMC), with a triangular wave generator (TWG) which regulates the slope of triangular wave based on the input and output voltages of the converter. Using the proposed TWG, both the load and line transient responses are improved. Since the TWG provides a line feed-forward control for the line transient response, it increases the open-loop bandwidth, and then better dynamic performance is obtained. Additional required circuit components are only a voltage controlled linear resistor (VCR) and a voltage controlled current source (VCCS). Compared with the conventional voltage control, the proposed method significantly improves the line and load transient responses. Furthermore this triangular wave slope regulation scheme is simple compared to digital feed-forward control scheme that requires non-linear calculation. Simulation results shows the effectiveness of the proposed method.

We focus on forward-looking radar network systems for automotive usages. By using multiple radars, the radar network systems will achieve reliable detection and wide observation area. The forward-looking systems by cameras are famous. In order to realize more reliable safety, the cameras had better be used with other sensing devices such as the radar network. In the radar network, processing of the data, which is derived from the multiple receivers, is important because the processing decides the estimation performance. In this paper, we will introduce our estimation algorithm which focuses on target existence probability and virtual receivers. The performance will be evaluated by simulated targets which are both single point model and 3D target model.

An optimal design method of linear processors intended for a multi-input multi-output (MIMO) full-duplex (FD) amplify-and-forward (AF) relay network is presented under the condition of spatial-domain self-interference nulling. This method is designed to suit the availability of channel state information (CSI). If full CSI of source station (SS)-relay station (RS), RS-RS (self-interference channel), and RS-destination station (DS) links are available, the instantaneous end-to-end capacity is maximized. Otherwise, if CSI of the RS-DS link is either partially available (only covariance is known), or not available, while CSI of the other links is known, then the ergodic end-to-end capacity is maximized. Performance of the proposed FD-AF relay system is demonstrated through computer simulations, especially under various correlation conditions of the RS-DS link.

We consider a location-aware store-carry-forward routing scheme based on node density estimation (LA Routing in short), which adopts different message forwarding strategies depending on node density at contact locations where two nodes encounter. To do so, each node estimates a node density distribution based on information about contact locations. In this paper, we clarify how the estimation accuracy affects the performance of LA Routing. We also examine the performance of LA Routing when it applies to networks with homogeneous node density. Through simulation experiments, we show that LA Routing is fairly robust against the accuracy of node density estimation and its performance is comparable with Probabilistic Routing even in the case that that node density is homogeneous.

Most recent work on cooperative spectrum sensing using cognitive radios has focused on issues involving the sensing channels and seemed to ignore those involving the reporting channels. Furthermore, no research has treated the effect of correlated composite Rayleigh-lognormal fading, also known as Suzuki fading, in cognitive radio. This paper proposes a technique for reuse of shadowed CRs, discarded during the sensing phase, as amplified-and-forward (AF) diversity relays for other surviving CRs to mitigate the effects of such fading in reporting channels. A thorough analysis of and a closed-form expression for the outage probability of the resulting cooperative AF diversity network in correlated composite Rayleigh-lognormal fading channels are presented in this paper. In particular, an efficient solution to the “PDF of sum-of-powers” of correlated Suzuki-distributed random variables using moment generating function (MGF) is proposed.

Subcarrier pairing (SP) and power allocation (PA) can improve the channel capacity of the OFDM multi-hop relay system. Due to limitations of processing complexity and energy consumption, symbol-level relaying, which only regenerates the constellation symbols at relay nodes, is more practical than code-level relaying that requires full decoding and encoding. By modeling multi-hop symbol-level relaying as a multi-staged parallel binary symmetric channel, this paper introduces a jointly optimal SP and PA scheme which maximizes the end to end data rate. Analytical arguments are given to reveal the structures and properties of the optimal solution, and simulation results are presented to illustrate and justify the optimality.

This paper proposes an adaptive band activity ratio control (ABC) with cascaded energy allocation (CEA) scheme to improve end-to-end spectral efficiency for two-hop amplify-and-forward orthogonal frequency division multiplexing relay systems under transmit energy constraint. Subchannel pairing (SP) based spectrum mapping maps spectral components transmitted over high gain subchannels in the source-to-relay link onto high gain subchannels of the relay-to-destination link to improve the spectral efficiency. However, SP suffers from a frame efficiency reduction due to the notification of information of spectral component order. To compensate for the deficiency of SP, the proposed scheme employs dynamic spectrum control with ABC in which spectral components are mapped onto subchannels having high channel gain in each link, while band activity ratio (BAR) is controlled to an optimal value, which is smaller than 1, so that all spectral components are transmitted over relatively high gain subchannels of the two links. To further improve the performance, energy allocation at the source node and the relay node is serially conducted based on convex optimization, and BAR is controlled to improve discrete-input continuous-output memoryless channel capacity at the relay node. In the proposed scheme, since only information of BAR needs to be notified, the notification overhead is drastically reduced compared to that in SP based spectrum mapping. Numerical analysis confirms that the proposed ABC combined with CEA significantly reduces the required notification overhead while achieving almost the same frame error rate performance compared with the SP based scheme.

In this paper, we propose demodulators for the Golden and Alamouti codes in amplify-and-forward (AF) cooperative communication with one relay. The proposed demodulators output exact log likelihood ratios (LLRs) with recursion based on the Jacobian logarithm. The cooperative system with the proposed demodulator for the Golden code has the benefit of efficient data transmission, while the system for the Alamouti code has low demodulation complexity. Quantitative analyses of computational complexity of the proposed demodulators are conducted. The transmission performance for various relay location and power settings is evaluated on cooperative orthogonal frequency division multiplexing (OFDM)-based wireless local area network (LAN) systems. In evaluations, the optimal relay location and power settings are found. The cooperative system with the proposed demodulators for the Golden and Alamouti codes offers 1.5 and 1.9 times larger areas where 10.8 and 5.4Mbit/s can be obtained than a non-cooperative (direct) system in a typical office environment, respectively.

Stochastic decoding provides ultra-low-complexity hardware for high-throughput parallel low-density parity-check (LDPC) decoders. Asynchronous stochastic decoding was proposed to demonstrate the possibility of low power dissipation and high throughput in stochastic decoders, but decoding might stop before convergence due to “lock-up”, causing error floors that also occur in synchronous stochastic decoding. In this paper, we introduce a wire-delay dependent (WDD) scheduling algorithm for asynchronous stochastic decoding in order to reduce the error floors. Instead of assigning the same delay to all computation nodes in the previous work, different computation delay is assigned to each computation node depending on its wire length. The variation of update timing increases switching activities to decrease the possibility of the “lock-up”, lowering the error floors. In addition, the WDD scheduling algorithm is simplified for the hardware implementation in order to eliminate time-averaging and multiplication functions used in the original WDD scheduling algorithm. BER performance using a regular (1024, 512) (3,6) LDPC code is simulated based on our timing model that has computation and wire delay estimated under ASPLA 90nm CMOS technology. It is demonstrated that the proposed asynchronous decoder achieves a 6.4-9.8× smaller latency than that of the synchronous decoder with a 0.25-0.3 dB coding gain.

Nonlinearity compensation algorithm and soft-decision forward error correction (FEC) are considered as key technologies for future high-capacity and long-haul optical transmission system. In this report, we experimentally demonstrate the following three benefits brought by low complexity perturbation back-propagation nonlinear compensation algorithm in 224Gb/s DP-16QAM transmission over large-Aeff pure silica core fiber; (1) improvement of pre-FEC bit error ratio, (2) reshaping noise distribution to more Gaussian, and (3) reduction of cycle slip probability.

Luby Transform (LT) codes are the first practical implementation of digital fountain codes. In LT codes, encoding symbols are independently generated so as to realize the universal property which means that performance is independent of channel parameters. The universal property makes LT codes able to provide reliable delivery simultaneously via channels of different quality while it may also limit the flexibility of LT codes. In certain application scenarios, such as real-time multimedia transmission, most receivers have tolerable channels whose erasure rates are not fixed, and channels of high erasure rate are outside the design box. In this paper, Connection Choice (CC) codes are proposed to trade the universal property for better performance. The key to CC codes is replacement of random selection with tournament selection. Tournament selection can equalize the frequency of input symbols to join encoding and change the degree distribution of input symbols. Our study indicates that CC codes with appropriate degree distributions provide better performance than the best known LT code when channels of high erasure rate can be ignored. CC codes enable system designers to customize digital fountain codes by taking into account the distribution of the erasure rate and create a new possibility for setting trade-offs between performance and erasure rate.

In this paper, we consider decouple-and-forward (DCF) relaying, where the relay encodes and amplifies decoupled data using orthogonal space-time block codes (OSTBCs), to achieve the maximum diversity gain of multiple-input multiple-output (MIMO) amplify-and-forward (AF) relaying. Since the channel status of all antennas is generally unknown and time-varying for cooperation in multi-antenna multiple-relay systems, we investigate an opportunistic relaying scheme for DCF relaying to harness distributed antennas and minimize the cooperation overheads by not using the global channel state information (CSI). In addition, for realistic wireless channels which have spatial fading correlation due to closely-spaced antenna configurations and poor scattering environments, we analyze the exact and lower bound on the symbol error probability (SEP) of the opportunistic DCF relaying over spatially correlated MIMO Rayleigh fading channels. Numerical results show that, even in the presence of spatial fading correlation, the proposed opportunistic relaying scheme is efficient and achieves additional performance gain with low overhead.

This paper describes a simple packet combining scheme with maximum likelihood detection (MLD) for multiple-input multiple-output with orthogonal frequency division multiplexing (MIMO-OFDM) in relay channels to construct reliable wireless links in wireless local area networks (LANs). Our MLD-based approach employs the multiplexed sub-stream signals in different transmit slots. The proposed scheme uses an additional combining process before MLD processing. Moreover, the proposed scheme sets the cyclic shift delay (CSD) operation in the relay terminal. We evaluate the performance of the proposed scheme by the packet error rate (PER) and throughput performance in the decode-and-forward (DF) strategy. First, we show that the proposed scheme offers approximately 4.5dB improvement over the conventional scheme in the received power ratio of the relay terminal to the destination terminal at PER =0.1. Second, the proposed scheme achieves about 1.6 times the throughput of the conventional scheme when the received power ratio of the relay terminal to the destination terminal is 3dB.

In vehicular ad hoc networks, the efficient and reliable dissemination of emergency messages in a highly mobile environment under dense or sparse network is a significant challenge. This paper proposes a new vehicular broadcast protocol, called ACK-CAST, that can operate effectively in both dense and sparse network scenarios. ACK-CAST relies on acknowledgment messages from one-hop neighbors to select the next rebroadcasting vehicle. Simulation results show that ACK-CAST outperforms the SERVUS protocol in terms of the end-to-end delay, message delivery ratio and network overhead.

Toward the actualization of an automatic navigation system for fetoscopic tracheal occlusion (FETO) surgery, this paper proposes a 3D ultrasound (US) calibration-based approach that can locate the fetal facial surface, oral cavity, and airways by a registration between a 3D fetal model and 3D US images. The proposed approach consists of an offline process and online process. The offline process first reconstructs the 3D fetal model with the anatomies of the oral cavity and airways. Then, a point-based 3D US calibration system based on real-time 3D US images, an electromagnetic (EM) tracking device, and a novel cones' phantom, computes the matrix that transforms the 3D US image space into the world coordinate system. In the online process, by scanning the mother's body with a 3D US probe, 3D US images containing the fetus are obtained. The fetal facial surface extracted from the 3D US images is registered to the 3D fetal model using an ICP-based (iterative closest point) algorithm and the calibration matrices, so that the fetal facial surface as well as the oral cavity and airways are located. The results indicate that the 3D US calibration system achieves an FRE (fiducial registration error) of 1.49±0.44mm and a TRE (target registration error) of 1.81±0.56mm by using 24 fiducial points from two US volumes. A mean TRE of 1.55±0.46 mm is also achieved for measuring location accuracy of the 3D fetal facial surface extracted from 3D US images by 14 target markers, and mean location errors of 2.51±0.47 mm and 3.04±0.59 mm are achieved for indirectly measuring location accuracy of the pharynx and the entrance of the trachea, respectively, which satisfy the requirement of the FETO surgery.