Combining scheduled channel polling with channel diversity is a promising way for a MAC protocol to achieve high energy efficiency and performance under both light and heavy traffic conditions. However, the deafness problem may cancel out the benefit of channel diversity. In this paper, we first investigate the deafness problem of scheduled multi-channel polling MACs with experiments. Then we propose and evaluate two schemes to handle the deafness problem. Our experiment shows that deafness is a significant reason for performance degradation in scheduled multi-channel polling MACs. A proper scheme should be chosen depending on the traffic pattern and the design objective.

This paper presents a single-cycle shared output buffered router for Networks-on-Chip. In output ports, each input port always has an output virtual-channel (VC) which can be exchanged by VC swapper. Its critical path is only 24 logic gates, and it reduces 9.4% area overhead compared with the classical router.

This work presents a real-time human detection system for VGA (Video Graphics Array, 640480) video, which well suits visual surveillance applications. To achieve high running speed and accuracy, firstly we design multiple fast scalar feature types on the gradient channels, and experimentally identify that NOGCF (Normalized Oriented Gradient Channel Feature) has better performance with Gentle AdaBoost in cascaded classifiers. A confidence measure for cascaded classifiers is developed and utilized in the subsequent tracking stage. Secondly, we propose to use speedup techniques including a detector pyramid for multi-scale detection and channel compression for integral channel calculation respectively. Thirdly, by integrating the detector's discrete detected humans and continuous detection confidence map, we employ a two-layer tracking by detection algorithm for further speedup and accuracy improvement. Compared with other methods, experiments show the system is significantly faster with 20 fps running speed in VGA video and has better accuracy as well.

The authors have proposed Multi-Input Multi-Output (MIMO)-Constant Envelope Modulation, (MIMO-CEM), as a power and complexity efficient alternative to MIMO-OFDM, suitable for wireless backhaul networks in which relay nodes are fixed in their positions. One of the major problems hindering the real application of MIMO-CEM is to estimate MIMO channel characteristics. MIMO-CEM is based upon two contrary schemes; one is nonlinear equalization such as maximum likelihood sequence estimator, which needs accurate channel information to replicate the received signal passing through it. The other is a low resolution analog-to-digital converter (ADC), e.g., 1-bit in the default operation that removes the received signal amplitude fluctuation. In this paper, as a solution to the channel estimation problem in MIMO-CEM with low resolution ADC receiver, we propose an adaptive MIMO-CEM channel estimation scheme where iterative adaptive channel estimation is carried out to minimize the error between the received preamble signal and the replicated one. We also prove that Code Division Multiplexing (CDM) preamble transmission is effective in estimating MIMO channel parameters in the presence of large quantization noise. Computer simulation results show that MIMO-CEM with the proposed channel estimator using CDM preambles achieves identical BER performance to that with the ideal channel estimation even in presence of severe quantization noise caused by a low resolution ADC.

This letter considers a two-way relaying network where two nodes exchange their information based on the principle of physical layer network coding (PNC). We study the amplify-and-forward (AF) relay filter design with multiple-input multiple-output (MIMO) system. In order to maximize the sum-rate for information exchange, we propose a relay filter for two-way relaying network. Simulation results show that the proposed scheme performs better than the conventional schemes for two-way relay channel.

In our previous research, to achieve unequal error protection (UEP), we proposed a scheme which encodes the data by randomly switching between several codes which use different signal constellations and showed the effectiveness in AWGN channels. In this letter, we propose our UEP system using MMSE-FDE for fast and selective fading by using the fact that importance levels are changed every few symbols, i.e., every block, in the proposed system. We confirmed the improvement in BER performance and the effectiveness of adaptive equalization for the proposed system in fading channels. Moreover, in fading channels we confirmed the validity of the theoretical tradeoff shown in static conditions.

In this letter, we first present a new construction method for uncorrelated binary periodic Complementary sequence sets (CSS). Next, the uncorrelated periodic CSSs are used as pilot sequences for multiple-input multiple-output (MIMO) channel estimation. Later on, we propose a low-complexity periodic correlator. Finally, simulation results verify the optimality of pilot sequences for MIMO channel estimation.

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.

A power analysis attack is a well-known side-channel attack but the efficiency of the attack is frequently degraded by the existence of power components, irrelative to the encryption included in signals used for the attack. To enhance the performance of the power analysis attack, we propose a preprocessing method based on extracting encryption-related parts from the measured power signals. Experimental results show that the attacks with the preprocessed signals detect correct keys with much fewer signals, compared to the conventional power analysis attacks.

This paper presents a possibility of Electromagnetic (EM) analysis against cryptographic modules outside their security boundaries. The mechanism behind the information leakage is explained from the view point of Electromagnetic Compatibility: electric fluctuation released from cryptographic modules can conduct to peripheral circuits based on ground bounce, resulting in radiation. We demonstrate the consequence of the mechanism through experiments where the ISO/IEC standard block cipher AES (Advanced Encryption Standard) is implemented on an FPGA board and EM radiations from power and communication cables are measured. Correlation Electromagnetic Analysis (CEMA) is conducted in order to evaluate the information leakage. The experimental results show that secret keys are revealed even though there are various disturbing factors such as voltage regulators and AC/DC converters between the target module and the measurement points. We also discuss information-suppression techniques as electrical-level countermeasures against such CEMAs.

Underlay cognitive systems allow secondary users (SUs) to access the licensed band allocated to primary users (PUs) for better spectrum utilization with the power constraint imposed on SUs such that their operation does not harm the normal communication of PUs. This constraint, which limits the coverage range of SUs, can be offset by relaying techniques that take advantage of shorter range communication for lower path loss. Symbol error rate (SER) analysis of underlay cognitive relay systems over fading channel has not been reported in the literature. This paper fills this gap. The derived SER expressions are validated by simulations and show that underlay cognitive relay systems suffer a high error floor for any modulation level.

As an add-on device option for the ultra-low power CMOS technology, the double-gated vertical-channel Tunnel Field-Effect Transistors (TFETs) of different source configurations are comparatively studied from the perspectives of fabrication and current drivability. While the top-source design where the source of the device is placed on the top of the fin makes the fabrication and source engineering much easier, it is more susceptible to parasitic resistance issue. The bottom-source design is difficult to engineer the tunneling barrier and may require a special replacement technique. Examples of the schemes to engineer the tunneling barrier for the bottom-source TFET are suggested. A TCAD simulation study on the bottom-source devices shows that both the parasitic resistance of source region and the current enhancement mechanism by field coupling need be carefully considered in designing the source.

This letter presents a method for obtaining an exact average symbol error rate (ASER) of M-phase shift keying (M-PSK) transmission for the Nth best opportunistic amplify-and-forward (OAF) relay systems over Rayleigh fading channels. This approach begins with deriving the relay selection probability when a relay is selected as the Nth best one with respect to the received signal-to-noise ratio. We then derive the modified moment generating function (MGF) for the Nth best OAF relay systems by taking the given Nth best-relay selection probability into consideration. Based on the modified MGF, we derive the exact ASER which accurately explicates the Nth best OAF relay system characteristics. Simulation results confirm the exactness of the analysis results for M-PSK transmission with respect to the number of relays, the Nth best relay selection, and the relay position.

OFDM/offset-QAM (OFDM/OQAM) has been proven to be a promising multi-carrier transmission technique. However, carrier frequency offset (CFO) can lead to severe inter-carrier interference (ICI) and performance degradation. Meanwhile, channel estimation is also an important issue because of the intrinsic characteristics of OFDM/OQAM. In this paper, a novel pilot structure and a frequency-domain cross-correlation algorithm are proposed for the joint CFO and channel estimation. Analysis and simulation results validate the effectiveness of the proposed pilot structure and estimation algorithm.

In the current study, stress-induced capacitance determined by direct measurement on MOSFETs was compared with that determined by indirect simulation through the delay of CMOS ring oscillators (ROs) fabricated side by side with MOSFETs. External compressive stresses were applied on <110> silicon-on-insulator (SOI) n-/p-MOSFETs with the ROs in a longitudinal configuration. The measured gate capacitance decreased as the compressive stress on SOI increased, which agrees with the result of the capacitance difference between measured and simulated delay of the ROs. The oscillation frequency shift of the ROs should mainly be attributed to oxide capacitance, aside from the change in mobility of the n-/p-MOSFETs. The result suggests that the stress-induced gate capacitance of partially depleted MOSFETs is an important factor for the capacitance shift in a circuit and that ROs can be used in a vehicle to determine mechanical stress-induced gate capacitance in MOSFETs.

We propose a control-channel-hopping scheme to mitigate scrambling attacks in orthogonal frequency division multiple access (OFDMA) systems. A scrambling attack can be realized by jamming specific frames after monitoring the control channel or by jamming the control channel itself. This letter details a situation in which the control channel is scattered among OFDMA subcarriers. The scattered control channel has a two-dimensional hopping sequence with a mixed order. Simulation results show that our scheme can prevent a jammer from monitoring the control channel and from attacking the channel itself.

This paper proposes an iterative maximum a posteriori (MAP) receiver for orthogonal frequency division multiplexing (OFDM) mobile communications under fast-fading conditions. The previous work in [21] developed a MAP receiver based on the expectation-maximization (EM) algorithm employing the differential model, which can allow correlated time-variation of channel impulse responses. In order to make such a MAP receiver more robust against time-variant channels, this paper proposes two new message-passing algorithms derived from factor graphs; subcarrier removal and partial turbo processing. The subcarrier removal estimates the channel frequency response by using all subcarriers other than the targeted subcarrier. Such channel estimate can be efficiently calculated by removing information on the targeted subcarrier from the estimate of the original EM algorithm that uses all the subcarriers. This modification can avoid the repetitive use of incorrectly detected signals for the channel estimation. On the other hand, the partial turbo processing performs symbol-by-symbol channel decoding by using a symbol interleaver. Owing to this process, the current channel estimate, which is more accurate due to the decoding gain, can be used as the initial channel estimate for the next symbol. Computer simulations under fast multipath fading conditions demonstrate that the subcarrier removal and the partial turbo processing can improve the error floor and the convergence speed, respectively, compared to the conventional MAP receiver.

This paper proposed three channel aggregation schemes for cognitive radio networks, a constant channel aggregation scheme, a probability distribution-based variable channel aggregation scheme, and a residual channel-based variable channel aggregation scheme. A cognitive radio network can have a wide bandwidth if unused channels in the primary networks are aggregated. Channel aggregation schemes involve either constant channel aggregation or variable channel aggregation. In this paper, a Markov chain is used to develop an analytical model of channel aggregation schemes; and the performance of the model is evaluated in terms of the average sojourn time, the average throughput, the forced termination probability, and the blocking probability. Simulation results show that channel aggregation schemes can reduce the average sojourn time of cognitive users by increasing the channel occupation rate of unused channels in a primary network.

In this paper, Source/Drain (S/D) engineering for high performance (HP) Vertical MOSFET (V-MOSFET) in 3Xnm generation and its beyond is investigated, by using gradual S/D profile while degradation of driving current (ION) due to the parasitic series resistance (Rpara) is minimized through two-dimensional device simulation taking into account for gate-induced-drain-leakage (GIDL). In general, it is significant to reduce spreading resistance in the case of conventional Planar MOSFET. Therefore, in this study, we focused and analyzed the abruptness of diffusion layer that is still importance parameter in V-MOSFET. First, for improving the basic device performance such as subthreshold swing (SS), ION, and Rpara, S/D engineering is investigated. The dependency of device performance on S/D abruptness (σS/D) for various Lightly Doped Drain Extension (LDD) abruptness (σLDD) is analyzed. In this study, Spacer Length (LSP) is defined as a function of σS/D. As σS/D becomes smaller and S/D becomes more abrupt, LSP becomes shorter. SS depends on the σS/D rather than the σLDD. ION has the peak value of 1750 µA/µm at σS/D = 2 nm/dec. and σLDD=3 nm/dec. when the silicon pillar diameter (D) is 30 nm and the gate length (Lg) is 60 nm. As σS/D becomes small, higher ION is obtained due to reduction of Rpara while SS is degraded. However, when σS/D becomes too small in the short channel devices (Lg = 60 nm and Lg = 45 nm), ION is degraded because the leakage current due to GIDL is increased and reaches IOFF limit of 100 nA/µm. In addition, as σLDD becomes larger, larger ION is obtained in the case of Lg = 100 nm and Lg = 60 nm because channel length becomes shorter. On the other hand, in the case of Lg = 45 nm, as σLDD becomes larger, ION is degraded because short channel effect (SCE) becomes significant. Next, the dependency of the basic device performance on D is investigated. By slimming D from 30 nm to 10 nm, while SS is improved and approaches the ideal value of 60 mV/Decade, ION is degraded due to increase of on-resistance (Ron). From these results, it is necessary to reduce Rpara while IOFF meets limit of 100 nA/µm for designing S/D of HP V-MOSFET. Especially for the V-MOSFET in the 1Xnm generation and its beyond, the influence of the Rpara and GIDL on ION becomes more significant, and therefore, the trade-off between σS/D and ION has a much greater impact on S/D engineering of V-MOSFET.

Switch-and-stay combining (SSC) is a simple diversity technique where a single radio frequency (RF) chain is connected to one of several antenna branches and stays there if the channel quality is satisfied or otherwise switches to a new branch. Compared with Selection Combining (SC), SSC requires less overhead in channel estimation and antenna selection feedback. In this paper, we analyze the performance of SSC in a time-correlated flat fading channel and with causal channel state information. We derive the general expressions for the distribution of the output signal-to-noise ratio (SNR), outage rate and average bit error rate (ABER) and then the analytical results are compared with the simulation results under the Jakes Rayleigh fading channel. Our results show that (1) For slowly varying channels, L branch SSC can achieve the full diversity order and the same outage rate as SC; (2) Increasing the number of antenna branches can improve the performance of SSC, however, the gain from adding antennas diminishes quickly as the channel variation speed increases. Moreover, to avoid the complexity in optimizing the fixed threshold, we also propose a simple adaptive SSC scheme which has almost the same ABER as the SSC with optimized fixed threshold.