The optimum generalized partial response (GPR) target for barium ferrite (BaFe) tape systems was studied. The shift in perpendicular magnetic recording technology in HDDs to systems employing single-pole-type (SPT) recording heads and media with a soft under layer (SUL) has been accompanied by a change in the read channel design, whereas current magnetic tape recording systems utilize a combination of a ring-type recording head with a single magnetic layer structured medium. Therefore, the read channel performance of current oriented BaFe particulate tape systems needs to be studied to best exploit the potential of this medium. Toward this end, DC-free, DC-full, and DC-suppressed targets were compared. The results show that assuming a GPRML detector with 16 or more states, a traditional DC-free target exhibits the best bit error rate performance for both longitudinally and perpendicularly oriented BaFe media, suggesting that the current read channel designed for longitudinally oriented media can also be utilized for BaFe particulate tape systems.

A recursive construction of (k+1)-ary error-correcting signature code is proposed to identify users for MAAC, even in the presence of channel noise. The recursion is originally from a trivial signature code. In the (j-1)-th recursion, from a signature code with minimum distance of 2j-2, a longer and larger signature code with minimum distance of 2j-1 is obtained. The decoding procedure of signature code is given, which consists of error correction and user identification.

This paper studies channel sounding for selfish dynamic spectrum control (S-DSC) in which each link dynamically maps its spectral components onto a necessary amount of discrete frequencies having the highest channel gain of the common system band. In S-DSC, it is compulsory to conduct channel sounding for the entire system band by using a reference signal whose spectral components are sparsely allocated by S-DSC. Using nonuniform sampling theory, this paper exploits the finite impulse response characteristic of frequency selective fading channels to carry out the channel sounding. However, when the number of spectral components is relatively small compared to the number of discrete frequencies of the system band, reliability of the channel sounding deteriorates severely due to the ill-conditioned problem and degradation in channel capacity of the next frame occurs as a result. Aiming at balancing frequency selection diversity effect and reliability of channel sounding, this paper proposes an S-DSC which allocates an appropriate number of spectral components onto discrete frequencies with low predicted channel gain besides mapping the rest onto those with high predicted channel gain. A numerical analysis confirms that the proposed S-DSC gives significant enhancement in channel capacity performance.

As CMOS devices scaling down in nowadays integrated circuits, the impact of layout-dependent effects (LDEs) to circuit performances becomes to be significant. This paper mainly focuses on LDE-aware analog circuit synthesis. Our circuit synthesis follows an optimization framework of transistor sizing based on geometric programming (GP) in which analog circuit performances are formulated in terms of monomials and posynomials. Providing GP models for the LDEs such as the shallow trench isolation (STI) stress and the well proximity effect (WPE), we can generate layout constraints related to LDEs during the circuit synthesis. Applying our circuit synthesis to a typical two-stage op-amp, we showed that the resultant circuit, which generated by GP with circuit performance and layout constraints, satisfied all the specifications with the verification of HSPICE simulation based on the BSIM model with LDE options.

This paper proposes an improved discrete Fourier transform (DFT)-based channel estimation technique for time domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) communication systems. The proposed technique, based on the concept of significant channel tap detector (SCTD) scheme, can effectively improve the system performance of TDS-OFDM systems. The correlation of two successive preambles is employed to estimate the average noise power as the threshold for obtaining the SCTD threshold estimation error and loss path information in large delay spread channel environments. The proposed estimation scheme roughly predicts the noise power in order to choose the significant channel taps to estimate the channel impulse response. Some comparative simulations are given to show that the proposed technique has the potential to achieve bit error rate performance superior to that of the conventional least squares channel estimation.

This paper proposes a novel design method involving the stages from analog circuit design to layout synthesis in hope of suppressing the process-induced variations with a design style called transistor array. We manage to decompose the transistors into unified sub-transistors, and arrange the sub-transistors on a uniform placement grid so that a better post-CMP profile is expected to be achieved, and that the STI-stress is evened up to alleviate the process variations. However, since lack of direct theoretical support to the transistor decomposition, we analyze and evaluate the errors arising from the decomposition in both large and small signal analysis. A test chip with decomposed transistors on it confirmed our analysis and suggested that the errors are negligibly small and the design with transistor array is applicable. Based on this conclusion, a design flow with transistor array covering from circuit design to layout synthesis is proposed, and several design cases, including three common-source amplifiers, three two-stage OPAMPS and a nano-watt current reference, are implemented on a test chip with the proposed method, to demonstrate the feasibility of our idea. The measurement results from the chip confirmed that the designs with transistor array are successful, and the proposed method is applicable.

Weissman introduced a coding problem for channels with action-dependent states. In this coding problem, there are two encoders and a decoder. An encoder outputs an action that affects the state of the channel. Then, the other encoder outputs a codeword of the message into the channel by using the channel state. The decoder receives a noisy observation of the codeword, and reconstructs the message. In this paper, we show an exponential error bound for channels with action-dependent states based on the random coding argument.

When attackers compromise a client system, they can steal user input. We propose a distributed one-time keyboard system to prevent information leakage via keyboard typing. We define the problem of secure keyboard arrangement over distributed multi-devices and channels. An analytical model is proposed for the optimal keyboard layout.

Relay selection is a promising technique with which to achieve remarkable gains in multi-relay cooperative networks. Opportunistic relaying (OR) and selection cooperation (SC) are two major relay selection schemes for dual-hop decode-and-forward cooperative networks; they have been shown to be globally outage-optimal under an aggregate power constraint. However, due to channel fluctuations, the channel state information (CSI) used in the selection process may become outdated and differ from the CSI during the actual transmission of data. In this work, we study the effect of outdated CSI on OR and threshold-based SC (TSC) schemes under independent but not necessarily identically distributed Rayleigh fading channels. The source can possibly cooperate with the best relay for data transmission, with the destination performing maximal ratio combining of the signals from the source and the relay. In particular, we analyze the average symbol error probability (ASEP) of OR and TSC with outdated CSI by deriving approximate but tight closed-form expressions for the moment generating function of the end-to-end signal-to-noise ratio. We also investigate the asymptotic behavior of the ASEP. The results show that the diversity orders of OR and TSC reduce to one and two, respectively, due to the outdated CSI. However, TSC achieves full spatial diversity order when the relay-to-destination CSI is perfect. Finally, to verify the analytical results Monte Carlo simulations are performed, in which OR attains better ASEP than TSC in a perfect CSI scenario, while TSC is less susceptible to outdated CSI.

In the literature, many resource allocation schemes have been proposed for multi-hop networks. However, the analyses provided focus mainly on the single cell case. Inter-cell interference severely degrades the performance of a wireless mobile network. Therefore, incorporating the analysis of inter-cell interference into the study of a scheme is required to more fully understand the performance of that scheme. The authors of this paper have proposed a parallel relaying scheme for a 2-hop OFDMA virtual cellular network (VCN). The purpose of this paper is to study a new version of that scheme which considers a multi-cell environment and evaluate the performance of the VCN. The ergodic channel capacity and outage capacity of the VCN in the presence of inter-cell interference are evaluated, and the results are compared to those of the single hop network (SHN). Furthermore, the effect of the location and number of wireless ports in the VCN on the channel capacity of the VCN is investigated, and the degree of fairness of the VCN relative to that of the SHN is compared. Using computer simulations, it is found that in the presence of inter-cell interference, a) the VCN outperforms the SHN even in the interference dominant transmission power region (when a single cell is considered, the VCN is better than the SHN only in the noise dominant transmission power region), b) the channel capacity of the VCN remains greater than that of the SHN even if the VCN is fully loaded, c) an optimal distance ratio for the location of the wireless ports can be found in the interval 0.2∼0.4, d) increasing the number of wireless ports from 3 to 6 can increase the channel capacity of the VCN, and e) the VCN can achieve better outage capacity than the SHN.

Under random linear coding (RLC) scheme, we present a simple expression of the probability distribution p(D=K) for decoding delay D incurred by the lossy channel, where K is a positive integer. In contrast with the previous contribution, our focus is firstly on deriving the cumulative distribution function of the discrete random variable D over a perfect channel. One benefit of such dispose is that, from the overall viewpoint, computing the cumulative distribution function of delay D can be related with calculating the cardinalities of sets of some special matrices, so that the former can be obtained from the latter. Moreover, our expression of the probability distribution is an explicit form, and is valid for any number of packets M, freewill field size q and arbitrary channel loss rate ε.

Broadcasting is an essential function in almost all wireless networks. Because of the dynamic nature of environment, broadcasting in cognitive radio ad hoc networks is a great challenge. Cognitive radio network technology has been well studied for more than a decade as a new way to improve the spectral efficiency of wireless networks and numerous precious works have been proposed. However, very few existing works consider how to broadcast messages in cognitive radio networks that operate in multichannel environments and none of these provides a full broadcast mechanism. Therefore, in this paper, we propose a broadcasting mechanism for multichannel cognitive radio ad hoc networks. Then, we analyze the mechanism regarding the speed of message dissemination, number of transmissions, fraction of the users that receive the broadcast message and so forth.

A mobile hotspot is a moving vehicle that hosts an Access Point (AP) such as train, bus and subway where users in these vehicles connect to external cellular network through AP to access their internet services. To meet Quality of Service (QoS) requirements, typically throughput and/or delay, a Call Admission Control (CAC) is needed to restrict the number of users accepted by the AP. In this paper, we analyze a modified guard channel scheme as CAC for mobile hotspot as follows: During a mobile hotspot is in the stop-state, we adopt a guard channel scheme where the optimal number of resource units is reserved for vertical handoff users from cellular network to WLAN. During a mobile hotspot is in the move-state, there are no handoff calls and so no resources for handoff calls are reserved in order to maximize the utility of the WLAN capacity. We model call's arrival and departure processes by Markov Modulated Poisson Process (MMPP) and then we model our CAC by 2-dimensional continuous time Markov chain (CTMC) for single traffic and 3-dimensional CTMC for two types of traffic. We solve steady-state probabilities by the Quasi-Birth and Death (QBD) method and we get various performance measures such as the new call blocking probabilities, the handoff call dropping probabilities and the channel utilizations. We compare our CAC with the conventional guard channel scheme which the number of guard resources is fixed all the time regardless of states of the mobile hotspot. Finally, we find the optimal threshold value on the amount of resources to be reserved for the handoff call subject to a strict constraint on the handoff call dropping probability.

This paper proposes an opportunistic feedback and user selection method for a multiuser two-way relay channel (MU-TWRC) in a time-varying environments where a base station (BS) and a selected mobile station (MS), one of K moving MSs, exchange messages during two time slots via an amplify-and-forward relay station. Specifically, under the assumption of perfect channel reciprocity, we analyze the outage probabilities of several channel feedback scenarios, including the proposed scheme. Based on the analysis, the transmission rates are optimized and the optimal user selection method is proposed to maximize the expected sum throughput. The simulation results indicate that, with opportunistic feedback, the performance can be significantly improved compared to that without feedback. Moreover, the performance is nearly identical to that with full feedback, and close to the case of perfect channel state information at BS for low mobility MSs.

Spatial correlation is an index for evaluating performance of multi-antenna systems. Although various equations exist, the distinction remains evasive. This paper presents applicable condition of equations for spatial correlation coefficient considering propagation channels. We reveal that under Rayleigh fading environments, the spatial correlation is properly evaluated by the equation based on three-dimensional radiation patterns, however, under environments with strong direct waves, the equation based on the channel matrix should be used for the evaluation.

We evaluated the behavior of a multi-user multiple-input multiple-output (MIMO) system in time-varying channels using measured data. A base station for downlink or broadcast transmission requires downlink channel state information (CSI), which is outdated in time-varying environments and we encounter degraded performance due to interference. One of the countermeasures against time-variant environments is predicting channels with an autoregressive (AR) model-based method. We modified the AR prediction for a time division duplex system. We conducted measurement campaigns in indoor environments to verify the performance of the scheme of channel prediction in an actual environment and measured channel data. We obtained the bit-error rate (BER) using these data. The AR-model-based technique of prediction assuming the Jakes' model was found to reduce BER. Also, the optimum AR-model order was investigated by using the channel data we measured.

Quantum steganography is to send secret quantum information through a quantum channel, such that an unauthorized user will not be aware of the existence of secret data. The depolarizing channel can hide quantum information by disguising it as channel errors of a quantum error-correcting code. We improve the efficiency of quantum steganography with noisy depolarizing channels, by modifying the twirling procedure and adding quantum teleportation. The proposed scheme not only meets the requirements of quantum steganography but also has higher efficiency.

MIMO transmission technologies have become an essential component of cellular systems such as Long Term Evolution (LTE) and LTE-Advanced. Recently, evaluating the communication performance of mobile users in cellular MIMO systems has become an urgent requirement. In this paper, we propose dynamic MIMO channel modeling for the urban environment. Our proposal is based on Geometry-based Stochastic Channel Modeling (GSCM). The cluster parameters such as the local scatterer locations around the measurement course are estimated by applying the particle filtering to measured data. We carried out radio propagation measurements in an urban environment at 3.35GHz band, and generated the dynamic channel from the measured data. The experiments showed that both the spreads and auto-correlation of Time of Arrival (ToA), Angle of Arrival (AoA) and Angle of Departure (AoD) were reconstructed within the acceptable error range in our dynamic channel model.

Intruder detection method by utilizing a time variation of Multiple Input Multiple Output (MIMO) channel (MIMO Sensor) has been proposed. Although the channel capacity on the MIMO transmission is severely degraded in time variant channels, we can take advantage of this feature in MIMO Sensor applications. We have already demonstrated the effectiveness of 2×2 MIMO sensor using 2.4GHz band at a small room (Size is 50m2). In this paper, we compare the detection probability of SIMO/MIMO sensors when the number of channel responses are same between SIMO/MIMO sensors: The numbers of transmit and receive antennas are 1 and 4 (SIMO), it is clarified that 2 and 2 (MIMO). The measurement was carried out at the room with the size of 140m2. From the measured results, 2×2 MIMO sensor obtains the same or higher detection probability compared to 4×1 SIMO sensor regardless of the measured location.

The extensive study and design of Body Area Networks (BANs) and development of related applications have been an object of interest during the last few years. Indeed, the majority of applications have been developed to operate at frequencies up to X band. However nowadays, a new growing attention is being focused on moving the study of BANs to higher frequencies such as those in V andW bands. The characterization of the on-body propagation channel is therefore essential for the design of reliable mm-wave BAN systems. However the classical methods (FDTD, MoM, FEM) commonly used at lower frequencies are not computationally efficient at mm-wave due to the large amount of mesh elements needed to discretize an electrically large geometry such as the human body. To overcome this issue, a ray tracing technique, generally used for characterizing indoor propagation, has been used to analyze a specific channel: chest-to-belt link. The reliability of this high frequency method has been investigated in this paper considering three different test cases. Moreover, a comparison of simulations and measurements, both performed on a body centric scenario at 94GHz, is also presented as well.