A smart community can be considered an essential component to realize a sustainable, low-carbon, and disaster-tolerant society, thereby providing a base for community inhabitants to lead a simple, healthy, and energy-saving way of life as well as ensuring safety, security, and a high quality-of-life in the community. In particular, a smart community can be essential for senior citizens in an aging society. Smart community enablers such as information and communication technology (ICT) and electric vehicles (EVs) can perform essential roles to realize a smart community. With regard to ICT, the necessity of a dedicated wireless sensor backbone has been identified. With regard to EV, a small-sized EV with one or two seats (Mini-EV) has been identified as an emerging player to support personal daily mobility in an aged society. The Mini-EV may be powered by a solar battery, thereby mitigating vehicular maintenance burden for the elderly. It is essential to realize a dependable ICT network and communication service for a smart community. In the study, we present the concept of trans-locatable design to achieve this goal. The two possible roles of EVs in contributing to a dependable ICT network are highlighted; these include EV charging of the batteries of the base stations in the network, and the creation of a Mini-EV based ad-hoc network that can enable applications such as safe driving assistance and secure neighborhoods.

This letter summarizes three talks in the tutorial session of the 13th Asia-Pacific Network Operations and Management Symposium (APNOMS2011), which focused on the disaster recovery and further emergency management regarding the Great East Japan Earthquake of 2011. We present the damage and restoration of communication networks and points to a future disaster-resilient society.

Internet threats caused by botnets/worms are one of the most important security issues to be addressed. Darknet, also called a dark IP address space, is one of the best solutions for monitoring anomalous packets sent by malicious software. However, since darknet is deployed only on an inactive IP address space, it is an inefficient way for monitoring a working network that has a considerable number of active IP addresses. The present paper addresses this problem. We propose a scalable, light-weight malicious packet monitoring system based on a multi-dimensional IP/port analysis. Our system significantly extends the monitoring scope of darknet. In order to extend the capacity of darknet, our approach leverages the active IP address space without affecting legitimate traffic. Multi-dimensional monitoring enables the monitoring of TCP ports with firewalls enabled on each of the IP addresses. We focus on delays of TCP syn/ack responses in the traffic. We locate syn/ack delayed packets and forward them to sensors or honeypots for further analysis. We also propose a policy-based flow classification and forwarding mechanism and develop a prototype of a monitoring system that implements our proposed architecture. We deploy our system on a campus network and perform several experiments for the evaluation of our system. We verify that our system can cover 89% of the IP addresses while darknet-based monitoring only covers 46%. On our campus network, our system monitors twice as many IP addresses as darknet.

Virtualization technologies are widely deployed in data centers to improve system utilization. However, they increase the workload for operators, who have to manage the structure of virtual networks in data centers. A virtual-network management system which automates the integration of the configurations of the virtual networks is provided. The proposed system collects the configurations from server virtualization platforms and VLAN-supported switches, and integrates these configurations according to a newly developed XML-based management information model for virtual-network configurations. Preliminary evaluations show that the proposed system helps operators by reducing the time to acquire the configurations from devices and correct the inconsistency of operators' configuration management database by about 40 percent. Further, they also show that the proposed system has excellent scalability; the system takes less than 20 minutes to acquire the virtual-network configurations from a large scale network that includes 300 virtual machines. These results imply that the proposed system is effective for improving the configuration management process for virtual networks in data centers.

Nowadays portable devices with multiple wireless interfaces and using multimedia services are becoming more popular on the Internet. This paper describes a family of multipath binomial congestion control algorithms for audio/video streaming, where a low variant of transmission rate is important. We extend the fluid model of binomial algorithms for single-path transmission to support the concurrent transmission of packets across multiple paths. We focus on the extension of two particular algorithms, SQRT and IIAD, for multiple paths, called MPSQRT and MPIIAD, respectively. Additionally, we apply the design technique (using the multipath fluid model) for multipath TCP (MPTCP) into the extension of SQRT and IIAD, called fbMPSQRT and fbMPIIAD, respectively. Both two approaches ensure that multipath binomial congestion control algorithms achieve load-balancing, throughput improvement, and fairness to single-path binomial algorithms at shared bottlenecks. Through the simulations and comparison with the uncoordinated protocols MPSQRT/MPIIAD, fbMPSQRT/fbMPIIAD and MPTCP, we find that our extended multipath transport protocols can preserve lower latency and transmission rate variance than MPTCP, fairly share with single-path SQRT/IIAD, MPTCP and TCP, and also can achieve throughput improvements and load-balancing equivalent to those of MPTCP under various scenarios and network conditions.

Conventional mechanisms proposed for enhancing quality of service (QoS) in 802.11 networks suffer from a lack of backward compatibility and fairness with and to legacy devices. In this paper, we present a cooperative mechanism, called TXOP (transmission opportunity) Exchange, that provides a legacy-neutral solution in which only stations (STAs) participating in TXOP Exchange cooperatively use their available bandwidth to satisfy their required throughputs, while other legacy devices continue to get the same throughput performance as before. Specifically, we discuss the implementation of TXOP Exchange in legacy 802.11 networks. We show that this mechanism can be realized with minor modifications to the RTS (request-to-send) frames of only the STAs participating in TXOP Exchange and without any replacement of legacy access points or STAs. We show an example of a proportional fair algorithm for fair and efficient MAC cooperation using a Nash bargaining solution (NBS). A simulation study using a realistic simulator verifies that the TXOP Exchange mechanism ensures legacy neutrality and fair and efficient cooperation even when a large number of legacy STAs coexist.

We propose an optimal access-point (AP) selection algorithm for maximizing the aggregated throughput of each AP (system throughput) while preserving newly arrived-user throughput in multi rate WLAN system. In our algorithm, newly arrived users cooperate with a wireless local area network (WLAN) system they are trying to use, i.e., they are willing to move toward an appropriate AP before the newly arrived user connects to AP. To select the AP by using our AP selection algorithm, the newly arriving users request two novel parameter values, “the minimum acceptable throughput” with which newly arrived users can be satisfied and “the minimum movable distance” in which a user can move to an appropriate AP. While preserving these conditions, we maximize system throughput. When users cannot obtain a throughput greater than “the minimum acceptable throughput” with our proposed AP selection algorithm, they are rejected. Because, if users use streaming applications, which have strict bandwidth demands, with a very low bit-rate connection, they will not be satisfied. Thus, the newly arrived users having low bit-rate connection may be allowed to be rejected before the newly arrived user connects. In this paper, we show the optimal AP by using theoretical proof. We discuss the effectiveness of our proposed AP selection algorithm by using numerical analysis. We also clarify and analyze the characteristics of system throughput. Moreover, we show that a newly arrived user can select the movable distance and acceptable throughput by using examples from graphs depicting every position of newly arrived users. By using the graphs, we also show the relationship between the two parameters (the movable distance and the acceptable throughput) and the optimal AP, and the relationship between the two parameters and optimal system throughput when the movable distance and acceptable throughput are variable.

The market growths of smart-phones and thin clients have been significantly increasing communication traffic in mobile networks. To handle the increased traffic, network operators should consider how to leverage distributed wireless resources such as distributed spots of wireless local access networks. In this paper, we consider the system where multiple moving users share distributed wireless access points on their traveling routes between their start and goal points and formulate as an optimization problem. Then, we come up with three algorithms as a solution for the problem. The key idea here is 'longcut route instruction', in which users are instructed to choose a traveling route where less congested access points are available; even if the moving distance increases, the throughput for users in the system would improve. In this paper, we define the gain function. Moreover, we analyze the basic characteristics of the system using as a simple model as possible.

In this letter, we address the issue of estimating the temporal dependence characteristic of link loss by using network tomography. We use a k-th order Markov chain (k > 1) to model the packet loss process, and estimate the state transition probabilities of the link loss model using a constrained optimization-based method. Analytical and simulation results indicate that our method yields more accurate packet loss probability estimates than existing loss inference methods.

In this paper, a hybrid overlay/underlay cognitive radio system is modeled as an M/M/1 queue where the rate of arrival and the service capacity are subject to Poisson alternations. Each packet as a customer arriving at the queue makes a decision to join the queue or not. Upon arrival, the individual decision of each packet is optimized based on his observation about the queue length and the state of system. It is shown that the individually optimal strategy for joining the queue is characterized by a threshold of queue length. Thus, the individual optimal threshold of queue length is analyzed in detail in this work.

The impact of non-ideal delay line (DL) along with group delay ripple (GDR) on the performance of ultra wide bandwidth (UWB) system has not yet been studied in previous literatures. In this paper, according to the currently designed DLs, we propose a statistical GDR model to achieve a practical UWB DL, and investigate the degradation in average bit error rate (BER) caused by the GDR for the transmitted-reference (TR) UWB communication systems. According to the analysis results, an improved autocorrelation receiver (AcR) is proposed. Through Monte Carlo simulations, the great performance improvement of the proposed AcR is verified by comparing it with the conventional TR AcR under non-ideal DL conditions. The proposed receiver framework is simple enough to enable a tractable analysis, and provides valuable insights for designing a practical TR UWB AcR that experiences GDR.

400 V DC power distribution systems for data centers require a fast response DC circuit breaker is required. The semiconductor DC circuit breaker is an important key technology in DC power distribution systems. This paper considers the malfunction of Silicon Carbide- Static Induction Transistor (SiC-SIT) based DC circuit breakers in 400 V DC power distribution systems for data centers. The malfunction mechanism is explained, and a solution is proposed. Investigations are achieved by MATLAB/Simulink and experimental verification.

As ROADMs (Reconfigurable Optical Add/Drop Multiplexers) are becoming widely used in metro/core networks, distributed control of wavelength paths by extended GMPLS (Generalized MultiProtocol Label Switching) protocols has attracted much attention. For the automatic establishment of an arbitrary wavelength path satisfying dynamic traffic demands over a ROADM or WXC (Wavelength Cross Connect)-based network, precise determination of chromatic dispersion over the path and optimized assignment of dispersion compensation capabilities at related nodes are essential. This paper reports an experiment over in-field fibers where GMPLS-based control was applied for the automatic discovery of chromatic dispersion, path computation, and wavelength path establishment with dynamic adjustment of variable dispersion compensation. The GMPLS-based control scheme, which the authors called GMPLS-Plus, extended GMPLS's distributed control architecture with attributes for automatic discovery, advertisement, and signaling of chromatic dispersion. In this experiment, wavelength paths with distances of 24 km and 360 km were successfully established and error-free data transmission was verified. The experiment also confirmed path restoration with dynamic compensation adjustment upon fiber failure.

Multicast routing with Quality-of-Service (QoS) guarantees is the key to efficient content distribution and sharing. Developing QoS-aware multicast routing algorithm is an important open topic. This paper investigates QoS-aware multicast routing problem with K constraints where K > 2. The contributions made in this paper include a heuristic that employs the concept of nonlinear combination to extend the existing well-known algorithm for fast computation of a QoS multicast tree, and a Fully Polynomial Time Approximation Scheme (FPTAS) to approximate a multicast routing tree with QoS guarantees. The theoretical analyses and simulations conducted on both algorithms show that the algorithms developed in this paper are general and flexible, thus are applicable to the various networking systems.

As the Internet represents a key social infrastructure, its reliability is essential if we are to survive failures. Physical connectivity of networks is also essential as it characterizes reliability. There are collaboration structures, which are topological structures where two or more nodes are connected to a node, and collaboration structures are observed in transcriptional regulatory networks and the router-level topologies of ISPs. These collaboration structures are related to the reliability of networks. The main objective of this research is to find whether an increase in collaboration structures would improve reliability or not. We first categorize the topology into a three-level hierarchy for this purpose, i.e., top-level, middle-level, and bottom-level layers. We then calculate the reliability of networks. The results indicate that the reliability of most transcriptional regulatory networks is higher than that of one of router-level topologies. We then investigate the number of collaboration structures. It is apparent that there are much fewer collaboration structures between top-level nodes and middle-level nodes in router-level topologies. Finally, we confirm that the reliability of router-level topologies can be improved by rewiring to increase the collaboration structures between top-level and middle-level nodes.

Most large-scale Peer-to-Peer (P2P) live streaming systems are constructed as a mesh structure, which can provide robustness in the dynamic P2P environment. The pull scheduling algorithm is widely used in this mesh structure, which degrades the performance of the entire system. Recently, network coding was introduced in mesh P2P streaming systems to improve the performance, which makes the push strategy feasible. One of the most famous scheduling algorithms based on network coding is R², with a random push strategy. Although R² has achieved some success, the push scheduling strategy still lacks a theoretical model and optimal solution. In this paper, we propose a novel optimal pull-push scheduling algorithm based on network coding, which consists of two stages: the initial pull stage and the push stage. The main contributions of this paper are: 1) we put forward a theoretical analysis model that considers the scarcity and timeliness of segments; 2) we formulate the push scheduling problem to be a global optimization problem and decompose it into local optimization problems on individual peers; 3) we introduce some rules to transform the local optimization problem into a classical min-cost optimization problem for solving it; 4) We combine the pull strategy with the push strategy and systematically realize our scheduling algorithm. Simulation results demonstrate that decode delay, decode ratio and redundant fraction of the P2P streaming system with our algorithm can be significantly improved, without losing throughput and increasing overhead.

With the consideration of real-time stream processing technology, it's important to develop high availability mechanism to guarantee stream-based application not interfered by faults caused by potential anomalies. In this paper, we present a novel online prediction technique for predicting some anomalies which may occur in the near future. Concretely, we first present a value prediction which combines the Hidden Markov Model and the Mixture of Expert Model to predict the values of feature metrics in the near future. Then we employ the Support Vector Machine to do anomaly identification, which is a procedure to identify the kind of anomaly that we are about to alarm. The purpose of our approach is to achieve a tradeoff between fault penalty and resource cost. The experiment results show that our approach is of high accuracy for common anomaly prediction and low runtime overhead.

We propose a novel method for measuring the matched total radiated power (TRP) and matched total radiated sensitivity (TRS) of small radio terminals, called over-the-air (OTA) measurement, using a spheroidal coupler (SC). To measure these parameters accurately in a multiple-reflection environment, such as in an SC, we developed two key techniques, i.e. displacement method and reflection compensation method, and verified their effectiveness by several simulations and fundamental experiments on a test transmitter. We also describe an absolute method for measuring antenna radiation efficiency using the displacement method. Furthermore, we describe TRP and TRS measurements for actual UMTS (Universal Mobile Telecommunications System) terminals, and verify that the proposed method achieves quick measurements with good accuracy. The SC provides a compact, low-cost OTA measurement system with high sensitivity and high speed.

This report focuses on a design method for gradient index (GRIN) lens antennas with controllable aperture field distributions. First, we derive differential equations representing optical paths in a gradient index medium with two optical surfaces by using geometrical optics, and then we formulate a novel design method for GRIN lens antennas based on these equations. The Levenberg-Marquardt algorithm is applied as a nonlinear least squares method to satisfy two conditions-focusing and shaping the aperture field distribution-thus realizing a prescribed radiation pattern. The conditions can be fulfilled by optimizing only the index (or permittivity) distribution, whereas the shapes of the optical surfaces remain as free parameters that can be utilized for other purposes, such as reducing reflection losses that occur on the surfaces, as illustrated in this report. A plano-concave GRIN lens is designed as an example, applying the proposed method, to realize a sidelobe level of -30 dB pseudo Taylor distribution, and a maximum sidelobe level of -29.1 dB was observed, indicating it is sufficiently accurate for practical use. In addition, we discuss the convergence of this method considering the relationship between the number of the initial conditions and the differential order of the design equations, factoring in scale invariance of the design equations.

In this paper, to reduce the memory size requirements of IFFT for OFDM-based applications, we propose a new IFFT design technique based on a combined integer mapping of three IFFT input signals: modulated data, pilot and null signals. The proposed method focuses on reducing the size of memory cells in the first two stages of the single-path delay feedback (SDF) IFFT architectures since the first two stages require 75% of the total memory cells. By simulations of 2048-point IFFT design for cognitive radio systems, it is shown that the proposed IFFT design method achieves more than 13% reduction in gate count and 11% reduction in power consumption compared with conventional IFFT design.

In this paper, a low-complexity symbol-spaced turbo frequency domain equalization (FDE) algorithm based on Laurent decomposition is proposed for precoded binary continuous phase modulation (CPM) with modulation index h=1/2. At the transmitter, a precoder is utilized to eliminate the inherent memory of the CPM signal. At the receiver, a matched filter based on Laurent decomposition is utilized to make the detection symbol-spaced. As a result, the symbol-spaced iteration can be taken between the equalizer and the decoder directly without a CPM demodulator, and we derive a symbol-spaced soft interference cancellation frequency domain equalization (SSIC-FDE) algorithm for binary CPM with h=1/2. A new data block structure for FDE of partial response CPM is also presented. The computational complexity analysis and simulations show that this approach provides a complexity reduction and an impressive performance improvement over previously proposed turbo FDE algorithm for binary CPM with h=1/2 in multi-path fading channels.

Ultra-wideband (UWB) technology is an excellent candidate for supporting wireless personal area networks (WPANs) because of its wide bandwidth, low transmission power, low complexity and multipath immunity. We study density-aware exclusive region (ER)-based scheduling for a nonuniform UWB-WPAN. Using a generalized radius for the ER based on statistical topology, we propose a scheduling scheme that uses a radius for the ER that varies according to the density information around the destination in the nonuniform network. Computer simulations show that (i) our approach to the radius of the generalized ER provides better scheduling performance than the radius solution of the conventional work [3] and (ii) scheduling that is based on an adaptive ER radius can always outperform both the fixed ER-based scheme and the TDMA scheme with respect to network throughput.

This paper investigates the non-data-aided (NDA) carrier frequency estimation of amplitude and phase shift keying (APSK) signals. The true Cramer-Rao bound (CRB) for NDA frequency estimation of APSK signals are derived and evaluated numerically. Characteristic and jitter variance of NDA Luise and Reggiannini (L&R) frequency estimator are analyzed. Verified by Monte Carlo simulations, the analytical results are shown to be accurate for medium-to-high signal-to-noise ratio (SNR) values. Using the proposed closed-form expression, parameters of the algorithm are optimized efficiently to minimize the jitter variance.

In this paper, we consider the problem of waveform optimization for multi-input multi-output (MIMO) radar in the presence of signal-dependent noise. A novel diagonal loading (DL) based method is proposed to optimize the waveform covariance matrix (WCM) for minimizing the Cramer-Rao bound (CRB) which improves the performance of parameter estimation. The resulting nonlinear optimization problem is solved by resorting to a convex relaxation that belongs to the semidefinite programming (SDP) class. An optimal solution to the initial problem is then constructed through a suitable approximation to an optimal solution of the relaxed one (in a least squares (LS) sense). Numerical results show that the performance of parameter estimation can be improved considerably by the proposed method compared to uncorrelated waveforms.

In the work we introduce novel approach to remote sensing from space for the estimation of sea wave heights with a spaceborne high precision two-frequency radar altimeter with nadir synthesis antenna aperture. Experiments show considerable reduction of the decorrelation factor of the correlation coefficient and so significant enhancement of the sensitivity of the altimeter for the estimation for the sea wave status.

A direct inter-mode selection algorithm for P-frames in fast homogeneous H.264/AVC bit-rate reduction transcoding is proposed in this paper. To achieve the direct inter-mode selection, we firstly develop a low-complexity distortion estimation method for fast transcoding, in which the distortion is directly calculated from the decoded residual together with the reference frames. We also present a linear estimation method to approximate the coding rate. With the estimated distortion and rate, the rate-distortion cost can be easily computed in the transcoder. In our algorithm, a method based on the normalized rate difference of P-frames (RP) is used to detect the high motion scene. To achieve fast transcoding, only for the P-frames with RP larger than a threshold, the rate-distortion optimized (RDO) mode decision is performed; meanwhile, the average cost of each inter-mode (ACM) is calculated. Then for the subsequent frames transcoding, the optimal coding mode can be directly selected using the estimated cost and the ACM threshold. Experiments show that the proposed method can significantly simplify the complex RDO mode decision, and achieve transcoding time reductions of up to 62% with small loss of rate-distortion performance.

A new high-throughput turbo decoding scheme adopting double flow, sliding window and shuffled decoding is proposed. Analytical and numerical results show that the proposed scheme requires low number of clock cycles and small memory size to achieve a BER performance equivalent to those of existing schemes.

Classical jamming attack models in the time domain have been proposed, such as constant jammer, random jammer, and reactive jammer. In this letter, we consider a new problem: given k jammers, how does the attacker minimize the pair-wise connectivity among the nodes in a Wireless Sensor Network (WSN)? We call this problem k-Jammer Deployment Problem (k-JDP). To the best of our knowledge, this is the first attempt at considering the position-critical jamming attack against wireless sensor network. We mainly make three contributions. First, we prove that the decision version of k-JDP is NP-complete even in the ideal situation where the attacker has full knowledge of the topology information of sensor network. Second, we propose a mathematical formulation based on Integer Programming (IP) model which yields an optimal solution. Third, we present a heuristic algorithm HAJDP, and compare it with the IP model. Numerical results show that our heuristic algorithm is computationally efficient.

The current version of IEEE 802.15.4 MAC protocol does not support energy-efficient mobility for the low-power device. In this paper, we propose an energy-efficient sleep mode as part of the IEEE 802.15.4 that can conserve energy by considering mobility of mobile sensor devices. The proposed energy-efficient sleep mode dynamically extends the sleep interval if there is no data to transmit from the device or receive from corresponding nodes.

Topology control is one of the key issues in wireless networks. In this letter, we propose a simple topology control algorithm based on Connected Dominant Set (CDS) theory. The proposed algorithm uses less memory and less overhead cost than other existing schemes, and is therefore appropriate for implementation in wireless sensor networks. We will prove that the algorithm can form a CDS and guarantee network connectivity. The performance of our algorithm is demonstrated by simulation results.

In the channel measurement and characterization, selecting a suitable excitation signal for a specified scenario is the primary task. This letter describes several selecting criteria of the excitation signal for channel sounding. And then the popular types of probing signals are addressed and through simulations their accuracy performances are compared in time-varying channels. The conclusion is the Constant Amplitude Zero Auto-Correlation (CAZAC) sequence yields better results in time-varying scenarios.

Although the effect of electromagnetic interference on an implanted cardiac pacemaker due to a nearby mobile phone has been investigated, there have been few studies on the enhancement of the specific absorption rate (SAR) around an implanted cardiac pacemaker due to a nearby mobile phone. In this study, the SAR distribution around a pacemaker model embedded in a parallelepiped torso phantom when a mobile phone was nearby was numerically calculated and experimentally measured. The results of both investigations showed a characteristic SAR distribution. The system presented can be used to estimate the effects of electromagnetic interference on implanted electric circuits and thus could lead to the development of guidelines for the safe use of mobile radio terminals near people with medical implants.

Cooperative relaying, while effective in mitigating fading effects, might reduce the overall network throughput since its overhead such as additional time slot and frequency band can be significant. In order to overcome this problem, this paper proposes a superposition coding based cooperative relay scheme to provide reliable transmission with little or no overhead. This scheme exploits the superimposed messages for users in the network to achieve the simultaneous transmission of two or more independent data streams. This scheme reduces the number of transmission phases to the same as that of conventional cooperative relay schemes. The symbol error performance of the proposed scheme is analyzed and simulated.

We formulate the resource allocation problem to maximize the sum rate, subject to constraints on total power, bit error rate, and rate proportionality among the users for proportional resource allocation in orthogonal frequency division multiple access (OFDMA) systems. For this we propose a novel scheduling scheme based on weighted normalized user's channel state information (CSI). We then adopt the linear power distribution method and waterfilling technique to allocate power among the users and across the subcarriers respectively.

Joint transmit and receive antenna selection (JTRAS) is proposed for the multiple-input multiple-output (MIMO) two-way relaying channel. A simple and closed-form lower bound on the outage probability of JTRAS is derived. Furthermore, asymptotic analysis reveals that JTRAS can attain the maximum achievable diversity order of the MIMO dual-hop relaying channel.

Power consumption due to transmissions in base stations (BSs) has been a major contributor to communication-related CO₂ emissions. A power optimization model is developed in this study with respect to radio resource allocation and activation in a multiple Component Carrier (CC) environment. We formulate and solve the power-minimization problem of the BS transceivers for multiple-CC networks with carrier aggregation, while maintaining the overall system and respective users' utilities above minimum levels. The optimized power consumption based on this model can be viewed as a lower bound of that of other algorithms employed in practice. A suboptimal scheme with low computation complexity is proposed. Numerical results show that the power consumption of our scheme is much better than that of the conventional one in which all CCs are always active, if both schemes maintain the same required utilities.

We study threshold-based relaying in an amplify-and-forward (AF) cooperative diversity network. For the network, the relay helps the communication from the source to the destination only if the signal-to-noise ratio (SNR) of the link from the source to the relay is greater than or equal to a pre-determined threshold value; otherwise, the relay remains silent. We derive the exact bit-error rate (BER) of the threshold-based relaying for M-pulse amplitude modulation (PAM) and M-quadrature amplitude modulation (QAM). The obtained BER expression can help the design of the threshold-based relaying in determining the system parameters such as the transmission power, the amplifying coefficient at the relay, and the pre-determined threshold value.

In this letter, we propose a computationally efficient maximum likelihood log-likelihood ratio (LLR) calculation method for multiple input multiple output (MIMO) systems with two spatial streams.

A simple DFT-based noise variance estimator for orthogonal frequency division multiplexing access (OFDMA) systems is proposed. The conventional DFT-based estimator differentiates the channel impulse response and noise in the time domain. However, for partial frequency response, its time domain signal will leak to all taps due to the windowing effect. The noise and channel leakage power become mixed. In order to accurately derive the noise power, we propose a novel symmetric extension method to reduce the channel leakage power. This method is based on the improved signal continuity at the boundaries introduced by symmetric extension. Numerical results show that the normalized mean square error (NMSE) of our proposed method is significantly lower than that of the conventional DFT method.

We propose a 2N_r MIMO ARQ scheme that uses multi-strata space-time codes composed of two layers. The phase and transmit power of each layer are assigned adaptively at each transmission round to mitigate the inter-layer interference and improve the block error rate by retransmission. Simulation results show that the proposed scheme achieves better performance than the conventional schemes in terms of the throughput and the block error rate.

This paper proposes applying our inter-cell interference (ICI) cancellation method to fractional frequency reuse (FFR) and evaluates the resulting spectral efficiency improvement. With our ICI cancellation method based on base station cooperation, the control station generates ICI replica signals by simple linear processing. Moreover, FFR effectively utilizes frequency resources by both allowing users in the cell-center region to access all available sub-channels and increasing the transmission power to users in the cell-edge region. FFR provides the conditions under which the ICI cancellation method works effectively. Computer simulations show that the average spectral efficiency of the proposed method is comparable to that of cooperative MU-MIMO, which can completely remove ICI.

In this letter, we address the performance analysis of underlay selective decode-and-forward (DF) relay networks in Rayleigh fading channels with non-necessarily identical fading parameters. In particular, a novel result on the outage probability of the considered system is presented. Monte Carlo simulations are performed to verify the correctness of our exact closed-form expression. Our proposed analysis can be adopted for various underlay spectrum sharing applications of cognitive DF relay networks.

The lateral velocity is of importance in cases like target identification and traffic management. Conventional Doppler methods are not capable of measuring lateral velocities since they quantify only the radial component. Based on the spectrogram characteristic of laterally moving targets, an algorithm based on fractional Fourier transform has been studied in the signal processing literature. The algorithm searches the peak position of the transformation, and calculates the lateral velocity from the peak position. The performance analysis of this algorithm is carried out in this paper, which shows that this algorithm approaches Cramer-Rao bound with reasonable computational complexity. Simulations are conducted at last to compare the analytical performance and the experimental result.