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Detection of the frequency-hopping (FH) signal is challenging when the hopping rate is unknown. Conventional spectrogram-based schemes can detect FH signals, but its performance is limited by the time-frequency resolution trade-off and spectral leakage. To alleviate this issue, we design convolutional neural network (CNN) and hybrid CNN/recurrent neural network (RNN)-based schemes. The CNN-based scheme alleviates spectral leakage by using feature maps. The hybrid CNN/RNN-based scheme mitigates the time-frequency resolution trade-off by using feature maps extracted from spectrograms of various window lengths. In simulations, the hybrid CNN/RNN-based scheme is shown to outperform the CNN-based and conventional detection schemes.

In this paper, we study the energy efficiency of small-cell on/off control schemes in which small-cells turn on when the number of active users reaches a certain threshold value called on-threshold. In particular, we derive analytical formulas for various performance metrics such as expected small-cell power consumption, average consumed energy per transmitted bit, expected energy saving, and energy saving probability. Moreover, we show that the expected small-cell power consumption strictly decreases with increased on-threshold value and derive a mathematical expression for the optimal on-threshold value that minimizes the average consumed energy per transmitted bit. With simulation results, we not only verify the validity of the analytical results but also discuss how the theoretical results can be used in system performance evaluation and optimization. We believe that many of the results in this paper can be used in practical small-cell network design and operation.

The frequency-hopping technique is widely used in commercial and military communications for its superiority in anti-jamming and low probability of interception and detection capabilities. To further lower its detection probability, a frequency-hopping signal randomly changes its carrier frequency within a transmission symbol. Conventional detection methods have poor performance in the presence of fast frequency-hopping signals. To solve this problem, we propose a dirty-template-based detection scheme. Dirty Template was originally proposed to blindly estimate the time delay in an ultra-wide-band system. We propose that it can be employed in the frequency domain to detect fast frequency-hopping signal. The decision statistic derived from the cross-correlation between the template and received signals in the frequency domain is analyzed. Using this cross-correlation, a detection scheme, based on the Neyman–Pearson test is proposed. The simulation results show that the dirty-template-based scheme outperforms the autocorrelation-based scheme when the hopping period is short.

In practical wireless relay communication systems, nondestination nodes are assumed to be idle not receiving signals while the relay sends messages to a particular destination node, which results in reduced bandwidth efficiency. To improve the bandwidth efficiency, we relax the idle assumption of non-destination nodes and assume that non-destination nodes may receive signals from sources. We note that the message relayed to a particular node in such a system gives rise to interference to other nodes. To study such a more general relay system, we consider, in this paper, a relay system in which the relay first listens to the source, then routes the source message to the destination, and finally produces interference to the destination in sending messages for other systems. We obtain capacity upper and lower bounds and study the optimal method to deal with the interference as well as the optimal routing schemes. From analytic results obtained, we find the conditions on which the direct transmission provides higher transmission rate. Next, we find the conditions, by numerical evaluation of the theoretical results, on which it is better for the destination to cancel and decode the interference. Also we find the optimal source power allocation scheme that achieves the lower bound depending on various channel conditions. We believe that the results provided in this paper will provide useful insights to system designers in strategically choosing the optimal routing algorithms depending on the channel conditions.

Notable changes in the next-generation wireless communication system include the fact that the nominal height of base-station antennas becomes lower than the height of typical rooftops. In this scenario, reflection and scattering of waves become more dominant than diffraction in short-range propagation. We first analyze the reflection and scattering loss of propagation by using ray-tracing simulation, and on the basis of the analysis, we propose a propagation prediction model based on geometric optics in the urban street canyon scenario. The proposed model is defined by geometrical parameters such as the street width and the distance to a corner, such that the model can be applied to various environmental scenarios. It can also simultaneously predict propagation losses in many corners. The proposed model is justified with measurement data.

In this paper, we propose a method of mixing modulation schemes to make it very difficult to intercept information from frequency hopping signals and assess analytically the difficulty of information interception using the interceptor computational complexity as a metric. In particular, we consider, to illustrate the effectiveness of mixing modulation schemes for secure communications, a method of randomly mixing BPSK and QPSK modulations in frequency hopping systems and compare it with conventional frequency hopping systems using BPSK only or QPSK only modulation scheme by deriving simple to evaluate upper and lower bounds on the interceptor complexity.

We address secure vehicle communication using secrecy capacity. In particular, we research the relationship between secrecy capacity and various types of parameters that determine secrecy capacity in the vehicular wireless network. For example, we examine the relationship between vehicle speed and secrecy capacity, the relationship between the response time and secrecy capacity of an autonomous vehicle, and the relationship between transmission power and secrecy capacity. In particular, the autonomous vehicle has set the system modeling on the assumption that the speed of the vehicle is related to the safety distance. We propose new vehicle communication to maintain a certain level of secrecy capacity according to various parameters. As a result, we can expect safer communication security of autonomous vehicles in 5G communications.

ITU-R has defined IMT-2020 as a new standard name for fifth generation mobile systems and has set the minimum performance requirements and evaluation methodologies of IMT-2020. IMT-2020 systems will be the mobile systems that include new radio interface which support the new capabilities of systems beyond IMT-Advanced. In particular, the data rate of IMT-2020 is expected to be 10 times to 20 times larger compared to IMT-Advanced for enhanced Mobile Broadband. In order to achieve the IMT-2020 data rate requirements, the use of mmWave band and micro-cell deployment is essential. In this paper, we evaluate the theoretically expected data rate of urban micro channel model by downlink 2×2 MIMO system level simulation. When the micro-cells are deployed over the macro-cells layout, the expected data rate is about 3.9Gbits/s, which is 5 times larger than only macro-cell scenario.

Frequency hopping (FH) is widely used in commercial and military communications. The purposes of FH in military communications are anti-jamming and low probability of interception. To implement low probability of detection or interception, FH signals randomly change carrier frequency. There are several kinds of FH detectors for example autocorrelation detector, maximum-likelihood detector and optimum detection. We focused on FFT-based detector kinds of maximum-likelihood detector. The FFT-based detector can monitor several MHz and more. However, the FFT-based detector suffers from frequency offset problem due to a lack of information of targeted FH signals. To improve the drawback, we propose interpolation estimation of frequency offset. The proposed approach mitigates the effect of frequency offset and increases probability of detection. Furthermore, the proposed approach has low complexity and does not require additional hardware. In this paper, we show the linear interpolation estimation of frequency offset and compare it with conventional detector in probability of detection.

In this paper, we describe a method of frequency-hopping signal detection, which is one of the methods of spread spectrum, by time-frequency analysis. Since the frequency hopping signal is a non-stationary signal, the signal changes very quickly. Therefore, time-frequency resolution is very important for detecting such non-stationary signals. The method considered in this paper is a spectrogram and has the form of a squared expression of STFT. Although the resolution of the simulation results was not good, We could get ideas on methodology to improve the resolution by applying various window functions. In addition to Spectrogram, better time-frequency resolution can be expected if various Window functions are applied to methods such as Scalogram, WVD, PWVD, SPWVD, S-transform.

The millimeter wave is in an extremely high frequency band whose frequency and wavelength ranges are 30–300 GHz and 10–1 mm, respectively. Owing to the large distance loss and weak diffraction, a channel in the millimeter wave band experiences a propagation loss that is much worse than that of a low frequency band. When the path loss in the millimeter wave band is measured, it is observed that the data is confined within a certain range owing to limitations. If the original least square is applied to the measurement data without considering the limitations of certain values, the path loss exponent can be underestimated. Therefore, both censoring and truncation environments should be taken into account in the regression model. In this paper, the performance of the Tobit maximum likelihood estimation, Heckman two-stage model and truncation regression model are compared with the ray-tracing simulation.

To evaluate 4G cellular systems, a system-level simulation (SLS) with the ITU-R channel model is often used. For the evaluation of the next generation communication systems, a SLS including a device-to-device (D2D) system is needed. However, as the number of multi-paths in a D2D link is squared compared to the link between a base station and a mobile station, the simulation run-time has to increase greatly. In this paper, we propose the ITU-R channel model extension to the D2D channel and the Doppler response-based fast fading channel generation as a realization method for the D2D channel. The proposed method can significantly reduce the simulation run-time.

Recently, a cooperative cognitive radio network (CCRN) and multiple-input multiple-output (MIMO) cognitive radio (CR) network have been proposed and investigated individually as promising paradigms for CR networks. Herein, we consider applying the MIMO techniques to a CCRN in order to achieve increased spectral efficiency. Assuming that the system comprises a single-input single-output (SISO) primary user (PU) pair and a multi-input single-output (MISO) secondary user (SU) pair, we propose jointly optimizing the beamforming vector and power allocation for the SU transmitter in order to maximize the rate for the SU while meeting the rate requirement for the PU. As the problem is nontrivial, we circumvent it using the uplink and downlink duality and equality of the left and right eigenvalues. Further, we introduce an iterative algorithm with a proof of convergence. From the numerical results, the proposed algorithm converges in a small number of iterations and outperforms the zero-forcing (ZF) beamforming algorithm while providing an upper bound for the CCRN-MIMO performance. Furthermore, the application of the proposed algorithm is not limited to CCRN-MIMO; it can also be extended to the conventional relay MIMO and/or MU-MIMO with a quality-of-service (QoS) requirement.

Scope Long-term feeding of a high-fat diet (HFD) causes gastrointestinal inflammation and gut microbiota disturbance, leading to the increased occurrence of obesity and anxiety. In the present study, the effects of heat-labile Lactobacillus sakei OK67, tyndallized OK67 (tOK67), and heat-stable Lactobacillus sakei PK16 on HFD-induced obesity and anxiety in mice are examined. Methods and results Obesity is induced in mice by feeding with HFD. Oral administration of live OK67, tOK67, or PK16 reduces HFD-induced body and liver weights and blood triglyceride, total cholesterol, corticosterone, and lipopolysaccharide levels. These treatments also suppress HFD-induced NF-κB activation and increased HFD-suppressed AMP-activated protein kinase (AMPK) activation and SIRT-1 expression in the liver. OK67 or PK16 treatment alleviates HFD-induced anxiety-like behaviors and increases BDNF expression and NF-κB activation in the hippocampus. Moreover, OK67 or PK16 treatment suppresses HFD-induced colitis and suppresses the Proteobacteria population and fecal lipopolysaccharide levels in mice. OK67 or PK16 treatment inhibits NF-κB activation and induced AMPK activation and SIRT-1 expression in lipopolysaccharide-stimulated Caco-2 cells. Overall, the antiobesity and anxiolytic effects of live OK67 are more potent than those of tOK67. Conclusion Lactobacillus sakei can alleviate HFD-induced obesity, colitis, and anxiety by regulating gut microbiota-mediated AMPK and NF-κB activation and SIRT-1 expression.

In this paper, we analyze a 28 GHz suburban channel using a hybrid ray-tracing simulation. Hybrid ray-tracing technique is a combination of image method and shooting-and-bouncing rays (SBR) method. The SBR method finds a rough propagation path and the image method predicts the exact propagation path. The hybrid ray-tracing simulation is compared with a measurement campaign conducted in Wolpyeong-dong, Daejeon, Korea, and its performance is verified. The transmitter is placed on a 29m building; the heights of the other buildings are between 10m and 12m. Based on a reasonable agreement between the results of ray-tracing and the measurement results, five streets of Wolpyeong-dong were analyzed using ray-tracing simulation. The path loss, power delay profile, root mean square delay spread, angle of arrival and angular spread were obtained.

This paper proposes an admission control algorithm for cellular networks based on the direct and dynamic monitoring of quality of services (QoS) performance metrics--both system delay tail and residual throughput. The main purpose of directly monitoring these QoS performance metrics is to more precisely meet the QoS requirements. The delay tail is efficiently estimated by the proposed algorithm and the total residual throughput is determined based on the total achieved throughput and total required throughput. With the estimated delay tails and measured residual throughput, the admission or rejection of a new user is determined at each base station. By doing so, the admission control algorithm improves resource utilization by guaranteeing the QoS. Additionally, the cellular system becomes more robust against the time-varying fading channel environment. The simulation results of the long term evolution downlink system show that the proposed algorithm can achieve a significant improvement in results compared to those of reference schemes. A general Neyman---Pearson-like framework is also used in evaluating the various admission control mechanisms.

In order to reflect a realistic wireless channel as closely as possible, the channel model becomes very complicated and is thus prone to error when implemented as a channel simulator. However, there is no rigorous way of verifying the implementation of the channel simulator. We propose a novel verification methodology that aims at implementing a verified channel simulator for the IMT-Advanced channel model. We first derive a systematic description of the channel model, where a random waveform is generated through various deterministic functional blocks and independent random number generators. We then verify the deterministic functional blocks by adopting the vector-based software verification methodology.

IEEE 802.16m technology is expected to provide high speed packet data service over wireless. Due to the large amount of data to be processed over a short period of time, an efficient MAC processing in the modem is crucial. Since the MAC processing algorithm has optimization limitations, we focus on a data flow optimization in the system level design, so that the number of external memory accesses is minimized. Experimental results show that our approach results in an up to sixteen times faster IEEE 802.16m modem system.

We consider a queuing model with applications to electric vehicle (EV) charging systems in smart grids. We adopt a scheme where an Electric Service Company (ESCo) broadcasts a one bit signal to EVs, possibly indicating ‘on-peak’ periods during which electricity cost is high. EVs randomly suspend/resume charging based on the signal. To model the dynamics of EVs we propose an M/M/∞ queue with random interruptions, and analyze the dynamics using time-scale decomposition. There exists a trade-off: one may postpone charging activity to ‘off-peak’ periods during which electricity cost is cheaper, however this incurs extra delay in completion of charging. Using our model we characterize achievable trade-offs between the mean cost and delay perceived by users. Next we consider a scenario where EVs respond to the signal based on the individual loads. Simulation results show that peak electricity demand can be reduced if EVs carrying higher loads are less sensitive to the signal.

We study the tradeoff between energy and bandwidth efficiency for short packet-transmission systems for wireless sensor networks. Using random coding bound (RCB) analysis, we show that 16-ary and 32-ary orthogonal modulation schemes provide reasonable balance between energy and bandwidth efficiency. In addition, we compare various channel-coding schemes and conclude that convolutional codes are well suited for wireless sensor network applications having excellent performance and reasonable robustness to imperfections, such as estimation errors.

Automatic Repeat reQuest (ARQ) is a very effective technique against transmission error at the medium access control (MAC) layer. An erroneous MAC protocol data unit can be typically retransmitted within a given limit. In order to improve the IP-level performance, which directly affects the user-perceived quality-of-service (QoS), we propose a new truncated ARQ strategy, called MAC service data unit-based ARQ (S-ARQ), where the finite number of opportunities for retransmissions are shared by multiple fragments out of an IP datagram. We describe how S-ARQ can be implemented in a practical system, and then propose another variant of S-ARQ employing a functionality called early detection of failure. Basically, we evaluate the performance of S-ARQ in two different manners. First, assuming i.i.d. error process, we analyze both the probability of the delivery failure and the average delay of IP datagram. Then, we assess the performance of S-ARQ via simulation over a 2-state Markov channel.

This letter deals with coding and multiplexing strategies for DL/UL MAP transmission in IEEE 802.16m. Separate coding gives a better choice against the joint coding due to the individual users' link adaptation gain. As a multiplexing option, frequency-domain multiplexing outperforms time-domain one in the system-level performance thanks to its flexible power sharing capability between overhead channels and user traffic channels. Overall system-wide performance results are presented with the system level simulation for the various options.

IEEE802.16m standard is based on the MIMO-OFDM technology to provide high speed packet data service both in downlink and uplink. For the downlink broadcasting of control information, in order to extend the coverage of a cell, the nominal operating point should be set for the user at the edge of a cell, and no feedback should be used. For broadcasting that information, the MIMO technology should take a transmit diversity form targeted for low SNR. Several transmit diversity schemes are presented and preferable modes of operations for the broadcasting channel are proposed with numerical analysis.

The information-theoretic sum capacity of reverse link CDMA systems is investigated in this paper. As the reverse link CDMA systems are interference-limited, for given channel and noise conditions, the information-theoretic system capacity can be achieved by optimally allocating the transmit powers of the mobile stations. The maximum capacity is often achieved by unfair resource allocation. To avoid such a case, QoS constraints are imposed to individual mobile stations. The exhaustive search of the optimal power allocation solution that maximizes the aggregate capacity, requires O(N/sup M/) computations, where M is the number of the mobile station in the system and N is the granularity of the transmit power of a mobile station. The paper shows that for a single cell, the optimal power allocation solution can be found by polynomial times of computations, without sacrificing the optimality. Numerical results are presented to show the multi-user diversity gain and the impact of QoS constraints.

This article describes enhancements to the physical layer design of single-carrier (1/spl times/) cdma2000/sup /spl reg// wireless networks introduced by Revision C of the IS-2000 standard (commonly referred to as 1/spl times/EV-DV). These improvements are mainly for the support of high-speed wireless packet data service on the forward (base station to mobile station) link. A new shared channel, the forward packet data channel, F-PDCH, is introduced to significantly increase spectral efficiency. This is accomplished through smart, channel-dependent scheduling of base station, BS, resources by taking advantage of the delay-tolerant nature of data traffic. This shared channel utilizes fast link adaptation through adaptive modulation and coding supported by the feedback of channel quality information. A form of hybrid ARQ type II technique commonly referred to as asynchronous adaptive incremental redundancy compensates for frame error events due to imperfect link adaptation. The impact of the new channel on voice capacity of the system is designed to be minimal because the F-PDCH utilizes resources that are not consumed by real-time users.

This paper addresses the problem of dynamic resource allocation in a multiservice direct-sequence code-division multiple-access (DS-CDMA) wireless network supporting real-time (RT) and nonreal-time (NRT) communication services. For RT users, a simple transmission power allocation strategy is assumed that maximizes the amount of capacity available to NRT users without violating quality of service requirements of RT users. For NRT users, a joint transmission power and spreading gain (transmission rate) allocation strategy, obtained via the solution of a constrained optimization problem, is provided. The solution maximizes the aggregate NRT throughput, subject to peak transmission power constraints and the capacity constraint imposed by RT users. The optimization problem is solved in a closed form, and the resulting resource allocation strategy is simple to implement as a hybrid CDMA/time-division multiple-access strategy. Numerical results are presented showing that the optimal resource allocation strategy can offer substantial performance gains over other conventional resource allocation strategies for DS-CDMA networks.

We propose a novel simulation method for modeling the game of golf using SystemC, a system description language that allows modeling of a concurrent system's behavior. Utilizing the proposed simulator, we compare different outing formats of golf, namely, regular and shotgun, in terms of playing time. Our simulation results reveal that the shotgun format can take longer than the regular format if the number of groups in a golf course exceeds 33 for the scenario we tested, confirming the belief that the shotgun format can take longer than the regular format. We also justify our simulation by comparing the simulation and analytical results.

In this paper, we consider a direct-sequence code division multiple access (DS-CDMA) network consisting of a single radio access point and a collection of wireless terminals. The network offers two classes of service: class-1 (real-time) and class-2 (reliable). We are interested in studying the effect of dynamic spreading gain control (SGC) on the dynamics of multiple access interference (MAI), spectral efficiency, and the quality of service (QoS) experienced by each service class. We first consider a time-slotted system in which class-2 terminals operate in a random access fashion. We show that under optimal (throughput maximizing) dynamic SGC: (1) the optimal retransmission probability is equal to one, and (2) the optimal spreading gain increases linearly, or equivalently, the transmission rate decreases inverse linearly, as the MAI level increases. We then model the system as a continuous-time finite-source queueing system with processor sharing, and obtain an explicit (closed-form) expression for the stationary distribution of the number of active class-1 and class-2 terminals, that is, the MAI level. This distribution is used to derive expressions for various QoS measures and define a capacity or admissible region. The results obtained by simulation and analysis are in extremely close agreement. This work contributes to a better understanding of the relationships between QoS, multiple access interference, and allocation of radio resources in DS-CDMA networks.

With the purpose of reducing energy consumption and increasing network connectivity, the cooperative communication (CC) technique has been adopted for topology control. In previous studies, the concept of transmit diversity, which adds partial signals using a maximum ratio combiner, had only been considered and never fully exploited for receiver diversity. In this paper, we introduce a novel topology control algorithm that uses a receiver diversity. Compared with existing topology control algorithms, proposed scheme shows significant improvements in connectivity, computational complexity, and average power consumption per communication link.

In this paper, we analyze the coexistence between the International Mobile Telecommunications (IMT) system and the digital television (DTV) system in the 700MHz band. The 700MHz band is now called the “digital dividend” and is expected to be allocated to IMT services. This plan could cause mutual interference between existing broadcasting and the IMT services. The members in the Asia-Pacific Telecommunity Wireless Group are currently discussing the coexistence issues associated with the 700MHz band. In order to allocate this band to the IMT services without harming the DTV system, coexistence problems should be solved. This paper presents the simulation methodology for analyzing the mutual interference between the IMT and DTV system and provides the results of the performance degradation of the two systems.

In this paper, we consider the discrete memoryless user relaying channel (DMURC) in which a user-relay switches its operational mode symbol-by-symbol. In particular, we obtain upper and lower bounds on the channel capacity for the general DMURC and then show that these the upper and lower bounds coincide for degraded DMURC. It is also shown that the capacity of the degraded DMURC can be achieved using two separate codebooks corresponding to the two UR states. While the UR is assumed to switch states symbol-by-symbol, the results in this paper is the same as when the UR switches states packet-by-packet.