Frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can increase the downlink bit error rate (BER) performance of DS-CDMA beyond that possible with conventional rake combining in a frequency-selective fading channel. FDE requires accurate channel estimation. Recently, we proposed a pilot-assisted channel estimation (CE) based on the MMSE criterion. Using MMSE-CE, the channel estimation accuracy is almost insensitive to the pilot chip sequence, and a good BER performance is achieved. In this paper, we propose a channel estimation scheme using one-tap recursive least square (RLS) algorithm, where the forgetting factor is adapted to the changing channel condition by the least mean square (LMS) algorithm, for DS-CDMA with FDE. We evaluate the BER performance using RLS-CE with adaptive forgetting factor in a frequency-selective fast Rayleigh fading channel by computer simulation.

Fair allocation of bandwidth and maximization of channel utilization are two important issues when designing a contention-based wireless medium access control (MAC) protocol. However, fulfilling both design goals at the same time is very difficult. Considering the problem in the IEEE 802.11 wireless local area networks (WLANs), in this work we propose a method using a p-persistent enhanced DCF, called P-IEEE 802.11 DCF, to achieve weighted fairness and efficient channel utilization among multiple priority classes in a WLAN. Its key idea is that when the back-off timer of a node reaches zero, the transmission probability is properly controlled to reflect the relative weights among data traffic flows so as to maximize the aggregate throughput and to minimize the frame delay at the same time. In particular, we obtain the optimal transmission probability based on a theoretical analysis, and also provide an approximation to this probability. The derived optimal and approximation are all evaluated numerically and simulated with different scenarios. The results show that the proposed method can fulfill our design goals under different numbers of priority classes and different numbers of nodes.

A Recessed-Channel Dual-Gate Single Electron Transistor (RCDG-SET) which has the possibility of room temperature operation is proposed. Side gates of a RCDG-SET form electrical tunneling barriers around a recessed channel, which is newly introduced. Not only gate but also a recessed channel is self aligned to source and drain. Characteristics of a RCDG-SET are compared with those of previous DG-SETs through device simulation (SILVACO). Due to a recessed channel and a self aligned structure, MOSFET current which causes low Peak-to-Valley Current Ratio (PVCR) is suppressed. This property of a RCDG-SET is expected to contribute for room temperature operation.

In this paper, a compact channel thermal noise model for short-channel MOSFETs is presented and applied to the radio frequency integrated circuit (RFIC) design. Based on the analysis of the relationship among different short-channel effects such as velocity saturation effect (VSE), channel-length modulation (CLM), and carrier heating effect (CHE), the compact model for the channel thermal noise was analytically derived as a simple form. In order to simulate MOSFET's noise characteristics in circuit simulators, an appropriate methodology is proposed. The used compact noise model is verified by comparing simulated results to the measured data at device and circuit level by using 65 nm and 130 nm CMOS technologies, respectively.

The use of frequency-domain interleaving on a frame-by-frame basis for orthogonal frequency division multiplexing (OFDM) combined with time division multiplexing (OFDM/TDM) is presented. In conventional OFDM, FDE is not designed to exploit the channel frequency-selectivity and consequently, the frequency diversity gain cannot be obtained. To further improve the bit error rate (BER) performance of conventional OFDM an interleaving technique may be applied, but FDE cannot be fully exploited. In this letter, the OFDM/TDM signal (i.e., several concatenated OFDM signals) frequency components are interleaved at the transmitter and then, minimum mean square error frequency-domain equalization (MMSE-FDE) is applied at the receiver to obtain a larger frequency diversity gain. It is shown that frequency-domain interleaving on a frame-by-frame basis for OFDM/TDM using MMSE-FDE achieves improved BER performance in comparison with conventional OFDM due to enhanced frequency diversity gain.

This paper proposes a MIMO-OFDM precoder that can minimize a BER upper bound of the maximum likelihood detector (MLD) under a non-cooperative downlink multicell co-channel interference (CCI) environment. Since there is no cooperation among base stations (BSs), it is assumed that information on the interference can be estimated at a mobile station (MS) and then fed back to the desired BS for the precoder. The proposed scheme controls its precoding parameters under a transmit power constraint so as to minimize the BER upper bound, which is derived from the pairwise error probability (PEP) averaged with respect to CCI plus noise. Computer simulations demonstrate that the proposed precoder can effectively improve BER performance of cell edge users and is superior in terms of BER to the eigenmode and the minimum mean squared error (MMSE) precoded transmissions which aim to maximize the channel capacity and to minimize MSE, respectively.

This paper investigates the influence of channel estimation error on the precoding matrix selection and signal detection for MIMO multiplexing using precoding in the downlink OFDM radio access. In a simulation, we assume codebook-based unitary precoding and signal detection that employs a minimum mean squared error (MMSE) based interference suppression filter. The simulation results clarify the effect of the channel estimation error with respect to the precoding matrix selection and signal detection from the viewpoints of the number of streams, i.e., rank order, the number of transmit antennas, the modulation scheme and channel coding rate, and codebook size, i.e., quantization for precoding matrix feedback information.

This paper applies iterative multiuser detection employing a new channel estimation scheme to multicarrier interleave-division multiple access (MC-IDMA), called OFDM-IDMA, which is expected to offer improved spectral efficiency in mobile communications. The MC-IDMA transmitter uses both a low-rate channel code and an individual chip interleaver for each user. The MC-IDMA receiver, which this paper focuses upon, repeats the iterative multiuser detection and soft decision-directed channel estimation (SDCE) by exploiting log-likelihood ratios (LLRs) of the coded bits which the maximum a posteriori (MAP)-based channel decoders for all users provide. SDCE estimates channel impulse responses of all users by the least-mean-square (LMS) algorithm, which aims to minimize the mean squared error between the received signal and its replica. This paper investigates the performance of MC-IDMA employing SDCE and compares it with those of three MC-CDMA techniques. Computer simulations demonstrate that MC-IDMA employing SDCE outperforms time-spread MC-CDMA and frequency-spread MC-CDMA, and that it can achieve almost the same bit error rate performance as chip-interleaved MC-CDMA while requiring lower complexity.

Recently, various types of 3-D nonvolatile memory (NVM) devices have been researched to improve the integration density [1]-[3]. The NVM device of pillar structure can be considered as one of the candidates [4],[5]. When this is applied to a NAND flash memory array, bottom end of the device channel is connected to the bulk silicon. In this case, the current in vertical direction varies depending on the thickness of silicon channel. When the channel is thick, the difference of saturation current levels between on/off states of individual device is more obvious. On the other hand, when the channel is thin, the on/off current increases simultaneously whereas the saturation currents do not differ very much. The reason is that the channel potential barrier seen by drain electrons is lowered by read voltage on the opposite sidewall control gate. This phenomenon that can occur in 3-D structure devices due to proximity can be called gate-induced barrier lowering (GIBL). In this work, the dependence of GIBL on silicon channel thickness is investigated, which will be the criteria in the implementation of reliable ultra-small NVM devices.

This paper presents a comparison of hierarchical and non-hierarchical synchronization channel (SCH) structures in terms of the initial cell search time and neighboring cell search time in order to establish the optimum SCH structure in the Evolved UTRA downlink. Computer simulation results show that in a 19-cell configuration, the cell search time at 90% in the cumulative distribution function (CDF) using the hierarchical SCH structure is less than half that using the non-hierarchical SCH structure in a neighboring cell search under low signal-to-interference plus noise power ratio (SINR) conditions, although both structures achieve almost the same cell search time in the initial cell search. This is due to the cross-correlation based SCH symbol timing detection in the hierarchical SCH structure, which is affected less by noise than the auto-correlation based detection in the non-hierarchical SCH structure. Thus, we conclude that the hierarchical SCH structure is superior to the non-hierarchical SCH structure based on the cell search time performance especially in the neighboring cell search.

We propose a 3-dimensional terraced NAND flash memory. It has a vertical channel so it is possible to make a long enough channel in 1F2 size. And it has 3-dimensional structure whose channel is connected vertically along with two stairs. So we can obtain high density as in the stacked array structure, without silicon stacking process. We can make NAND flash memory with 3F2 cell size. Using SILVACO ATLAS simulation, we study terraced NAND flash memory characteristics such as program, erase, and read. Also, its fabrication method is proposed.

A novel transmit diversity scheme with space-time-frequency coded training sequence is proposed to perform channel estimation flexibly over doubly selective channel, which offers a trade-off between maximum delay spread and maximum Doppler spread. Simulation results are presented to verify the effectiveness of the proposed flexible channel estimation method under different propagation conditions.

Vector coding (VC) is a kind of eigen mode transmission scheme which is typically considered in MIMO systems. In VC systems, several code channels corresponding to the eigenvalues of the channel matrix are created. However, any code channels with low eigenvalues will cause a degradation in performance. In this paper, adaptive modulation and coding (AMC) for a VC system is proposed. In addition to AMC, the number of code channels is adaptively changed by code channel elimination. We show that the BER performance of VC is better than that of MMSE. Secondly, we also show the throughput performance of the proposed scheme is improved compared with the maximum throughput of each individual MCS.

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.

Time variations of wireless multipath channels can lead to severe intercarrier interference (ICI) in orthogonal frequency division multiplex (OFDM) systems, whereas large Doppler frequency spread can provide us with time diversity gain. In order to take advantage of the time diversity and to suppress the interference and noise enhancement at the same time, the receiver normally detects the data successively. In this letter, we propose an improved detection ordering based on the log-likelihood ratio (LLR) rather than the signal-to-noise ratio (SNR) for the successive detector. Using both theoretical analysis and computer simulation, it is shown that this scheme outperforms the traditional successive detection methods.

This paper proposes joint maximum a posteriori (MAP) detection and spatial filtering for MIMO-OFDM mobile communications; it offers excellent receiver performance even over interference-limited channels. The proposed joint processor consists of a log likelihood generator and a MAP equalizer. The log likelihood generator suppresses cochannel interference by spatially filtering received signals and provides branch metrics of transmitted signal candidates. Using the branch metrics, the MAP equalizer generates log likelihood ratios of coded bits and performs channel decoding based on the MAP criterion. In the first stage, the log likelihood generator performs spatio-temporal filtering (STF) of the received signals prior to the fast Fourier transform (FFT) and is referred to as preFFT-type STF. Estimation of parameters including tap coefficients of the spatio-temporal filters and equivalent channel impulse responses of desired signals is based on the eigenvalue decomposition of an autocorrelation matrix of both the received and transmitted signals. For further improvement, in the second stage, the generator performs spatial filtering (SF) of the FFT output and is referred to as postFFT-type SF. Estimation of both tap coefficients of the spatial filters and channel impulse responses employs the recursive least squares (RLS) with smoothing. The reason for switching from preFFT-type STF into postFFT-type SF is that preFFT-type STF outperforms postFFT-type SF with a limited number of preamble symbols while postFFT-type SF outperforms preFFT-type STF when data symbols can be reliably detected and used for the parameter estimation. Note that there are two major differences between the proposed and conventional schemes: one is that the proposed scheme performs the two-stage processing of preFFT-type STF and postFFT-type SF, while the other is that the smoothing algorithm is applied to the parameter estimation of the proposed scheme. Computer simulations demonstrate that the proposed scheme can achieve excellent PER performance under interference-limited channel conditions and that it can outperform the conventional joint processing of preFFT-type STF and the MAP equalizer.

This paper proposes a novel RBF training algorithm based on immune operations for dynamic problem solving. The algorithm takes inspiration from the dynamic nature of natural immune system and locally-tuned structure of RBF neural network. Through immune operations of vaccination and immune response, the RBF network can dynamically adapt to environments according to changes in the training set. Simulation results demonstrate that RBF equalizer based on the proposed algorithm obtains good performance in nonlinear time-varying channels.

Single-carrier (SC) multiple access is a promising uplink multiple access technique because of its low peak-to-average power ratio (PAPR) property and high frequency diversity gain that is achievable through simple one-tap frequency-domain equalization (FDE) in a strong frequency-selective channel. The multiple access capability can be obtained by combining either frequency division multiple access (FDMA) or code division multiple access (CDMA) with SC transmission. In this article, we review the recent research on the SC multiple access techniques with one-tap FDE. After introducing the principle of joint FDE/antenna diversity combining, we review various SC multiple access techniques with one-tap FDE, i.e., SC-FDMA, SC-CDMA, block spread CDMA, and delay-time/CDMA.

Time-variant channels degrade the performance of Orthogonal Frequency Division Multiplexing (OFDM) systems because they collapse the orthogonality between the sub-carriers, which necessitates estimating the resulting off-diagonals of the channel matrix in order to properly equalize the received signal. This letter presents a new method of estimating the channel matrix for OFDM systems in rapidly time-variant channels. The method approximates the time variation of the channel over a few successive OFDM symbols making use of Newton polynomial interpolation.

The capacity of multiuser OFDM systems can be maximized by allocating resources (subcarrier and power) to the user with the highest instantaneous channel gain. This assumes complete channel state information (CSI) at the transmitter, which is achieved by every user reporting its CSI for all subcarriers to the transmitter via feedback channel. In practice, due to the limited capacity of the feedback channel, the completeness of CSI may be severely restricted especially with a large number of users transmitting a large amount of feedback information. In order to reduce the amount of feedback information while preserving the maximal capacity, quality based CSI feedback (QCF) is proposed in this letter. The system capacity is derived with QCF and compared with that of full CSI feedback. The results show that QCF successfully reduces the amount of feedback information with little capacity loss.